arXiv:1604.01122v4 [astro-ph.GA] 24 Jul 2016 ACCEPTED BY THE ASTROPHYSICAL J OURNAL,J UNE 2, 2016 Preprint typeset using L A T E X style emulateapj v. 05/12/14 SHOCKED POSTSTARBURST GALAXY SURVEY II: THE MOLECULAR GAS CONTENT AND PROPERTIES OF A SUBSET OF SPOGS KATHERINE ALATALO, 1† UTE LISENFELD, 2 LAURANNE LANZ, 3 PHILIP N. APPLETON, 3 FELIPE ARDILA, 4 SABRINA L. CALES, 5 LISA J. KEWLEY, 6 MARK LACY, 7 ANNE M. MEDLING, 6 KRISTINA NYLAND, 7 J EFFREY A. RICH, 1,3 & C. MEG URRY 5 1 Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA 2 Departamento de F´ ısica Te´ orica y del Cosmos, Universidad de Granada, Granada, Spain 3 Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, California 91125, USA 4 Department of Astrophysical Sciences, Princeton University, Peyton Hall, 4 Ivy Lane, Princeton, NJ 08544, USA 5 Department of Astronomy, Yale University, New Haven, CT 06511 USA 6 Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd., Weston ACT 2611, Australia 7 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA Accepted by the Astrophysical Journal, June 2, 2016 ABSTRACT We present CO(1–0) observations of objects within the Shocked POststarburst Galaxy Survey taken with the Institut de Radioastronomie Millim´ etrique (IRAM) 30m single dish and the Combined Array for Research for Millimeter Astronomy (CARMA) interferometer. Shocked Poststarburst Galaxies (SPOGs) represent a transi- tioning population of galaxies, with deep Balmer absorption (EW Hδ > 5 ˚ A), consistent with an intermediate-age (A-star) stellar population, and ionized gas line ratios inconsistent with pure star formation. The CO(1–0) sub- sample was selected from SPOGs detected by the Wide-field Infrared Survey Explorer with 22µm flux detected at a signal-to-noise (S/N) >3. Of the 52 objects observed in CO(1–0), 47 are detected with S/N>3. A large fraction (37–46±7%) of our CO-SPOG sample were visually classified as morphologically disrupted. The H 2 masses detected were between 10 8.7−10.8 M ⊙ , consistent with the gas masses found in normal galaxies, though approximately an order of magnitude larger than the range seen in poststarburst galaxies. When comparing the 22µm and CO(1–0) fluxes, SPOGs diverge from the normal star-forming relation, having 22µm fluxes in excess of the relation by a factor of 〈ǫ MIR 〉 = 4.91 +0.42 −0.39 , suggestive of the presence of active galactic nuclei (AGN). The Na I D characteristics of CO-SPOGs show that it is likely that many of these objects host interstellar winds. Objects with the large Na I D enhancements also tend to emit in the radio, suggesting possible AGN-driving of neutral winds. Keywords: galaxies: active — galaxies: evolution — galaxies: ISM — galaxies: interactions — galaxies: star formation — radio lines: galaxies 1. INTRODUCTION The bimodality of morphological classifications of galax- ies has long been known (Hubble 1926). Typical galaxies are either classified as “late-type” galaxies, or “early-type” galax- ies. “Late-types” have thin disks and exhibit spiral structure and blue colors. “Early-types” tend to be more ellipsoidal, contain smoother isophotes, and exhibit redder colors. Galax- ies also bifurcate across colors with a red and blue population (Baade 1958; Holmberg 1958; Tinsley 1978; Strateva et al. 2001; Baldry et al. 2004; Faber et al. 2007) based primarily on their star formation properties, and few galaxies have in- termediate, “green valley” colors (Bell et al. 2003). The mor- phological and color bimodalities seem to indicate that galax- ies transform rapidly between the blue cloud and red sequence (Martin et al. 2007). Star-forming galaxies are blue in color and span a large range of magnitudes, known as the “blue cloud”. Red sequence galaxies, on the other hand, inhabit a well defined region with much smaller variation in both color and magnitude. As in the case of the morphological classifi- cation of galaxies, the color bimodality seen in galaxies can be explained simply by quenching star formation. Once a star- forming galaxy has had its star formation quenched, it quickly migrates from the blue cloud and becomes a red sequence galaxy (Harker et al. 2006). The morphological and color [email protected]† Hubble fellow properties of individual galaxies are usually well-matched, with early-types also being red sequence galaxies, and late- types also being star-forming galaxies. Many transformational paths have been proposed, in- cluding a merger between two late-type galaxies into an early-type in simulation (Toomre & Toomre 1972; Springel et al. 2005), ram pressure stripping due to falling into a galaxy cluster (Bekki et al. 2002; Park et al. 2007; Blanton & Moustakas 2009; Chung et al. 2009; Kenney et al. 2014), morphological quenching (Martig et al. 2009, 2013), tidal disruption and harassment through group interac- tions (Zabludoff & Mulchaey 1998; Hickson et al. 1992; Rasmussen et al. 2008; Bitsakis et al. 2010, 2014), and Ac- tive Galactic Nucleus (AGN) feedback (Fischer et al. 2010; Feruglio et al. 2010, 2015; Sturm et al. 2011; Alatalo et al. 2011; Aalto et al. 2012a,b; Cicone et al. 2012, 2014; Alatalo 2015). In the modern universe (z ∼ 0), this transformation ap- pears to be one-way (Appleton et al. 2014; Young et al. 2014). Thus, it is essential to understand all pathways that can lead a blue late-type galaxy to become a red early-type. Schawinski et al. (2014) showed that the majority of galax- ies with green colors were in fact normal spiral galaxies, with normal star formation rates that had built up a significant pop- ulation of intermediate and older stars. For this reason, opti- cal color selection alone is not able to definitively identify a transitioning galaxy. With the onset of the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) mission, evidence
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ACCEPTED BY THEASTROPHYSICALJOURNAL, JUNE 2, 2016Preprint typeset using LATEX style emulateapj v. 05/12/14
SHOCKED POSTSTARBURST GALAXY SURVEY II: THE MOLECULAR GAS CONTENT AND PROPERTIES OF ASUBSET OF SPOGS
KATHERINE ALATALO ,1† UTE L ISENFELD,2 LAURANNE LANZ ,3 PHILIP N. APPLETON,3 FELIPE ARDILA ,4 SABRINA L. CALES,5
L ISA J. KEWLEY,6 MARK LACY,7 ANNE M. M EDLING,6 KRISTINA NYLAND ,7 JEFFREYA. RICH,1,3 & C. M EG URRY5
1Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA2Departamento de Fısica Teorica y del Cosmos, Universidadde Granada, Granada, Spain
3Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, California 91125, USA4Department of Astrophysical Sciences, Princeton University, Peyton Hall, 4 Ivy Lane, Princeton, NJ 08544, USA
5Department of Astronomy, Yale University, New Haven, CT 06511 USA6Research School of Astronomy and Astrophysics, AustralianNational University, Cotter Rd., Weston ACT 2611, Australia
7National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USAAccepted by the Astrophysical Journal, June 2, 2016
ABSTRACTWe present CO(1–0) observations of objects within the Shocked POststarburst Galaxy Survey taken with theInstitut de Radioastronomie Millimetrique (IRAM) 30m single dish and the Combined Array for Research forMillimeter Astronomy (CARMA) interferometer. Shocked Poststarburst Galaxies (SPOGs) represent a transi-tioning population of galaxies, with deep Balmer absorption (EWHδ > 5A), consistent with an intermediate-age(A-star) stellar population, and ionized gas line ratios inconsistent with pure star formation. The CO(1–0) sub-sample was selected from SPOGs detected by theWide-field Infrared Survey Explorerwith 22µm flux detectedat a signal-to-noise (S/N)>3. Of the 52 objects observed in CO(1–0), 47 are detected withS/N>3. A largefraction (37–46±7%) of our CO-SPOG sample were visually classified as morphologically disrupted. The H2masses detected were between 108.7−10.8 M⊙, consistent with the gas masses found in normal galaxies, thoughapproximately an order of magnitude larger than the range seen in poststarburst galaxies. When comparing the22µm and CO(1–0) fluxes, SPOGs diverge from the normal star-forming relation, having 22µm fluxes in excessof the relation by a factor of〈ǫMIR〉 = 4.91+0.42
−0.39, suggestive of the presence of active galactic nuclei (AGN).The NaI D characteristics of CO-SPOGs show that it is likely that many of these objects host interstellar winds.Objects with the large NaI D enhancements also tend to emit in the radio, suggesting possible AGN-driving ofneutral winds.Keywords:galaxies: active — galaxies: evolution — galaxies: ISM — galaxies: interactions — galaxies: star
formation — radio lines: galaxies
1. INTRODUCTION
The bimodality of morphological classifications of galax-ies has long been known (Hubble 1926). Typical galaxies areeither classified as “late-type” galaxies, or “early-type”galax-ies. “Late-types” have thin disks and exhibit spiral structureand blue colors. “Early-types” tend to be more ellipsoidal,contain smoother isophotes, and exhibit redder colors. Galax-ies also bifurcate across colors with a red and blue population(Baade 1958; Holmberg 1958; Tinsley 1978; Strateva et al.2001; Baldry et al. 2004; Faber et al. 2007) based primarilyon their star formation properties, and few galaxies have in-termediate, “green valley” colors (Bell et al. 2003). The mor-phological and color bimodalities seem to indicate that galax-ies transform rapidly between the blue cloud and red sequence(Martin et al. 2007). Star-forming galaxies are blue in colorand span a large range of magnitudes, known as the “bluecloud”. Red sequence galaxies, on the other hand, inhabit awell defined region with much smaller variation in both colorand magnitude. As in the case of the morphological classifi-cation of galaxies, the color bimodality seen in galaxies canbe explained simply by quenching star formation. Once a star-forming galaxy has had its star formation quenched, it quicklymigrates from the blue cloud and becomes a red sequencegalaxy (Harker et al. 2006). The morphological and color
properties of individual galaxies are usually well-matched,with early-types also being red sequence galaxies, and late-types also being star-forming galaxies.
Many transformational paths have been proposed, in-cluding a merger between two late-type galaxies intoan early-type in simulation (Toomre & Toomre 1972;Springel et al. 2005), ram pressure stripping due to fallinginto a galaxy cluster (Bekki et al. 2002; Park et al. 2007;Blanton & Moustakas 2009; Chung et al. 2009; Kenney et al.2014), morphological quenching (Martig et al. 2009, 2013),tidal disruption and harassment through group interac-tions (Zabludoff & Mulchaey 1998; Hickson et al. 1992;Rasmussen et al. 2008; Bitsakis et al. 2010, 2014), and Ac-tive Galactic Nucleus (AGN) feedback (Fischer et al. 2010;Feruglio et al. 2010, 2015; Sturm et al. 2011; Alatalo et al.2011; Aalto et al. 2012a,b; Cicone et al. 2012, 2014; Alatalo2015). In the modern universe (z∼0), this transformation ap-pears to be one-way (Appleton et al. 2014; Young et al. 2014).Thus, it is essential to understand all pathways that can lead ablue late-type galaxy to become a red early-type.
Schawinski et al.(2014) showed that the majority of galax-ies with green colors were in fact normal spiral galaxies, withnormal star formation rates that had built up a significant pop-ulation of intermediate and older stars. For this reason, opti-cal color selection alone is not able to definitively identify atransitioning galaxy. With the onset of theWide-field InfraredSurvey Explorer(WISE; Wright et al. 2010) mission, evidence
Figure 1. The ionized gas line ratios of the ELG (grayscale) and SPOG samples (green dotsAlatalo et al. 2016), including [NII ]/Hα vs. [OIII ]/Hβ (left;Baldwin et al. 1981), [S II ]/Hα vs. [OIII ]/Hβ (middle), and [OI ]/Hα vs. [OIII ]/Hβ (right; Veilleux & Osterbrock 1987), overlaid with the line diagnostic modelsof Kauffmann et al.(2003); Kewley et al.(2006). The purple line defines the boundaries of the shock models,SPOG criterion (Allen et al. 2008; Rich et al. 2011;Alatalo et al. 2016). WISE22µm-detected SPOGs are shown in dark green. CO-SPOGs (light blue stars), and 1.4 GHz radio-matched CO-SPOGs (dark bluestars) are also shown. CO-SPOGs span the ionized gas diagnostic space of the larger SPOG sample. There is also little difference between the radio matched andunmatched 22µm-detected SPOGs.
mounted that mid-IR colors could be used to identify transi-tioning galaxies.Alatalo et al.(2014a) presented existence ofa prominent bifurcation between star-forming spiral galaxiesand quiescent early-type galaxies in theWISE[4.6]–[12]µmbands, deeming this the “Infrared Transition Zone” (IRTZ).Early-type galaxies that were within this IRTZ were foundto have red optical colors (also described inKo et al. 2013;Yesuf et al. 2014), indicating that galaxies must traverse theoptical green valley before the IRTZ.
Searches aiming to identify recently quenched galax-ies have focused on objects with deep Balmer absorptionlines, consistent with the presence of intermediate A-stars
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Figure 2. Color-magnitude diagram from the parent emission line galaxysample (grayscale;Alatalo et al. 2016) with the distribution of SPOGs over-laid (green contours), withMi representing the (uncorrected) absolute i-bandmagnitude. The CO-SPOGs are overlaid and color-coded basedon their radiodetections, with FIRST-detected SPOGs shown as dark blue stars, and radionon-detected CO SPOGs as light blue stars. The CO-SPOGs tendto be moremassive than SPOGs in general, but not significantly, and their colors tracethose colors of the underlying SPOGs distribution fairly well.
(Cannon & Pickering 1918) stellar population (Vazdekis et al.2010), and a lack of ionized gas emission lines usually as-sociated with star formation (nebular lines such as Hα or[O II ]λ3727; Dressler & Gunn 1983; Zabludoff et al. 1996;Quintero et al. 2004; Goto 2005, 2007). While this se-lection is able to find recently quenched galaxies, it pro-vides an incomplete picture of transforming objects. Tra-ditional “E+A” or “K+A” searches miss objects that ex-hibit line emission, including AGNs (Wild et al. 2009;Kocevski et al. 2011; Cales et al. 2011, 2013), emission frompost-asymptotic branch (post-AGB) stars (Yan et al. 2006)and shocks (Allen et al. 2008; Rich et al. 2011; Alatalo et al.2016). Traditional poststarburst searches also miss galaxiesthat have quenched but still have some low-level Hα or [O II ]emission (Yesuf et al. 2014; Rowlands et al. 2015).
While the most common picture of galaxy evolution in-volves the exhaustion of the star-forming fuel prior to thecomplete cessation of star formation (Hopkins et al. 2006),observations of molecular gas in “red and dead” galaxiesseems to indicate that a molecular reservoir can remain intactafter galaxy transformation (Combes et al. 2007; Young et al.2011; Davis et al. 2011), even without re-accretion of newmolecular material, although in these cases the molecular gasmass is no more than 1% of the total stellar mass. More re-cently, French et al.(2015) andRowlands et al.(2015) havebeen able to show that significant reservoirs of molecular gasremain in post-transition objects (in these cases, poststarburstgalaxies), calling into question the need to completely de-plete (or significantly reduce) the molecular reservoir withina galaxy to cause star formation quenching and galaxy transi-tion.
This reservoir of gas could also be explained if poststar-burst galaxies originate when early-type galaxies accretema-terial from the environment and go through a brief starburstphase, which was suggested by recent observations of a largesample of galaxies byDressler et al.(2013). Recently, in-terferometric molecular gas observations have shown thatthe star formation within some quenched objects is sup-pressed, with inefficiencies of factors of 20–70 (Alatalo et al.2015a,c; Guillard et al. 2015; Aalto et al. 2016; Salome et al.2016; Lanz et al. 2015), leading to the possibility that star
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 3
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Figure 3. SDSSg r i 3-color thumbnails of the 52 CO-SPOGs. The field of view of allthumbnails is 30′′. Objects detected by CARMA are labeled in green, withthe CARMA beam shown as an ellipse in the bottom right. Objects observed with the IRAM 30m are labeled in pale blue. The SPOGindex fromAlatalo et al.(2016) are labeled in white (bottom left). Non-detections are demarcated with a smallX in the top right. Objects that have been morphologically classified asclearly disrupted have a small yellow symbol (∞) below the object name. Those that are classified as possiblydisrupted, a (∼). Many SPOGs show signs ofinteraction, including tidal tails, dust lanes, and morphological disruption. Most galaxies appear to be red in color,with many also showing signs of peaked,bright nuclei, possibly due to the presence of an AGN.
formation-suppressed molecular reservoirs are a common partof galaxy transformation. Although a larger sample of galax-ies must be studied to determine whether this occurs only inrare and energetic objects.
The Shocked POststarburst Galaxy Survey (SPOGS;Alatalo et al. 2016)1 was created to search for rapidly tran-sitioning galaxies that would be missed by poststarburstsearches, aiming to identify galaxies that are quenching(rather than simply fading;Schawinski et al. 2014). TheSPOG sample was drawn from the Oh-Sarzi-Schawinski-Yisample (OSSY;Oh et al. 2011), selecting only galaxies withbright emission in all diagnostic lines (Baldwin et al. 1981;Veilleux & Osterbrock 1987), to create the parent EmissionLine Galaxy sample (ELG;Alatalo et al. 2016). The SPOGScriteria was applied to the ELG sample to include strong
1 http://www.spogs.org
Balmer absorption (EW(Hδ)> 5A)2 and ionized gas emissionthat isinconsistentwith pure star formation. While SPOGS isby no means complete, these criteria have resulted in select-ing 1,067 candidate objects (deemed SPOGs). Further detailsof the SPOG Survey are available inAlatalo et al.(2016).
We present new Combined Array from Research in Mil-limeter Astronomy (CARMA) and Institut de RAdioas-tronomie Millimetrique (IRAM) 30m CO(1–0) observationsof 52 SPOGs. In§2, we describe the selection used to drawthe CO(1–0) sample. In§3, we describe the observations fromIRAM and CARMA, including reduction and analysis meth-ods. In§4, we present the molecular properties of the sam-ple. In §5, we discuss these results in the context of transi-
2 It is possible that the SPOGS selection has missed shocked galaxies with-out ongoing star formation based on the requirement for suchdeep absorp-tion, given the possibility of Balmer emission filling the stellar absorptionfeatures.
fov = 30 ′′Figure 3 (Cont). Continuation of the SDSSg r i 3-color images of CO-SPOGs. The last panel shows the 22.3′′ single dish primary beam atνobs = 110 GHz forthe SPOGs observed with the IRAM 30m (labeled in pale blue).
tioning galaxies. In§6, we summarize our results. The cos-mological parametersH0 = 70 km s−1,Ωm = 0.3 andΩΛ = 0.7(Spergel et al. 2007) are used throughout.
2. THE CO(1–0) SAMPLE
The objects chosen for CO(1–0) observations were se-lected based on the SPOG subsample cross-correlated withthe WISE All-sky Survey (Wright et al. 2010), detailed inAlatalo et al.(2014a), to have detectable (signal-to-noise ra-tio >3) 22µm fluxes. 22µm emission is usually associatedwith star formation (Calzetti et al. 2007), but it is also strongin AGNs (Ward et al. 1987; Sanders et al. 1989; Elvis et al.1994). 22µm emission can also arise in quiescent galax-ies, from dust that is heated by the aging stellar popula-tion (Draine et al. 2007; Crocker et al. 2011, 2013; Dale et al.2012). Because our SPOG selection criteria removes galaxieswhose ionized gas line ratios are dominated by star forma-tion, the 22µm emission in these sources is less likely to beassociated primarily with star formation. It is possible thatsome of our objects are in fact “skin effect contaminants,” inwhich the bulk of star formation is obscured from the opticalview (in a compact core), and in which the overlying materialis heated primarily by older stellar populations (Wild et al.2011). This cannot be ruled completely out until other starformation indicators have been measured. Despite this, it isunlikely that this is a dominant effect, as in the vast majorityof cases, the optical emission and ionized gas line ratios ofdusty, buried starbursts manifest as star-forming (Casey et al.2014; Rich et al. 2015). A caveat to this is that this scenario
cannot remove star-forming objects completely and thus doesnot remove objects in which the dominant star formation istaking place outside of the 3′′ SDSS fiber (although this ismost problematic at low redshifts, where the fiber only tracesthe nucleus;Rich et al. 2014; Alatalo et al. 2016).
Of the 1,067 SPOGs, 491 (46±2%) are detected witha signal-to-noise ratio of at least 3 in theWISE 22µmband. Radio identifications of theWISE22µm-detected sam-ple were made via a 1.5′′ radial match (Ivezic et al. 2002)with the Faint Images of the Radio Sky at Twenty Cen-timeters (FIRST) Survey (Becker et al. 1995), described inAlatalo et al. (2016). There are 83/1,067 concurrentWISE22µm and FIRST-detected objects (8±1%), which accountsfor over 50% of the (160/1,067) total radio matches amongstthe entire SPOG sample.
The IRAM 30m sample was selected from the 491WISE22µm-detected SPOGs. TheWISE 22µm-detected samplewas divided into bins based on radio detections and radionon-detections, as well as shock models within the [OI ]/Hαvs. [OIII ]/Hβ line diagnostic diagram (Allen et al. 2008;and Fig. 1c), selecting one radio detection and one non-detection per bin. Of the 40 IRAM 30m proposed objects, 35were observed and 30 were detected. The CARMA-observedSPOG sample focused on aWISE22µm flux-limited sam-ple within the RA range of9h–15h. There were 51 SPOGswith F22µm > 14 mJy within this RA range that were queuedfor observation, and 19 were successfully observed. Table1presents the general properties of the objects observed withthe IRAM 30m and CARMA.
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 5
Table 1CO-SPOG Sample Properties
# SPOG Telescope RA Dec z F22µm F1.4 log(M⋆) MorphologyName (J2000) (J2000) (mJy) (mJy) (M⊙)
1057 J2245+1232 I 22 45 32.76 +12 32 36.2 0.093 16.4±1.2 ... 10.70 X
1062 J2326-0114 I 23 26 37.22 -01 14 36.2 0.197 38.4±1.7 ... 10.83 X
Column (1): SPOG #. Column (2): SDSS name. Column (3): Telescope (I: IRAM 30m, C: CARMA). Columns (4-5): SDSSRA/declination. Column (6): SDSS redshift. Column (7): 22µm flux from WISE detections. Column (8): 1.4 GHz integratedflux density from FIRST. Column (9): Log of the stellar mass. Column (10): Morphological classification of each CO-SPOG asclearly disrupted (X), possibly disrupted (?), or not.
Our requirement for aWISE22µm detection used to con-struct our follow-up sample of CO observations may biasthis subset of SPOGs to favor those harboring AGNs, anaging stellar population, or dusty compact starbursts. Thisis supported by the high prevalence of FIRST radio de-tections, which trace emission from AGNs (although can
also trace star formation;Condon 1992). Figure1 displaysSPOGs (green circles) on the emission line ratio diagnosticdiagrams (Baldwin et al. 1981; Veilleux & Osterbrock 1987),with 22µm-detected sources (sky blue stars) identified, aswell as concurrently 22µm+1.4GHz-detected objects (darkblue stars). Figure1 shows that the emission line ratios of
6 ALATALO ET AL .
J0003+0048
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vsys = 14260
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-15
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vsys = 43000J0037+0024
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vsys = 24250
J0119+1334
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vsys = 57170
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20
vsys = 48670
Figure 4. The CO(1–0) spectra of the 52 observed SPOGs. The IRAM 30m spectra are shaded in turquoise and CARMA in green. A bar below the spectrumshows the velocity range used to sum over the CO(1–0) line. IRAM 30m objects with strong detections have 21 km s−1 bins and those with more tentativedetections with 42 km s−1. The optically-determined recession velocities are demarcated by a dotted gray line. The 5 non-detections (all from the IRAM 30m)were not shaded, but have velocity width bars to denote what velocity range is taken to calculate the upper limit. CARMA detections have velocity widths (whichvary from source to source) noted in Table2. The systemic velocities associated with each line are listed in the top corner of each panel.
our CO-observed SPOG sample (hereafter, CO-SPOGs) donot exclusively lie in the Seyfert ionized gas ratio space orstar-forming space (Kewley et al. 2006). A large set of objectsin this sample are consistent with the low ionization nuclearemission line region (LINER) portion of the diagram. Thisstrongly suggests that the 22µm selection has selected AGNsin the SPOG sample.
To improve accuracy, we calculate the total stellar massesof our CO-SPOGs by fitting the complete (FUV, NUV, u, g,r, i, z, J, H, Ks) photometry usingMAGPHYS (da Cunha et al.
2008), which takes into account extinction and k-corrections.SED fitting of the full SPOG sample will be presented in T.Bitsakis et al. (2016), in preparation.
The selection for the CO-SPOG sample also spans the en-tire u–r color-range of SPOGs (Fig.2), but appear to tracemore massive objects than the underlying SPOG population.
Between the IRAM 30m and CARMA samples, a total of52 objects were observed (2 objects overlapped between theCARMA and IRAM 30m samples, with CARMA detectionsfavored due to better signal-to-noise). Figure3 shows the
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 7
J1046+2804
-1000 -500 0 500 1000Velocity [km s-1]
-10
-5
0
5
10
15
Flu
x [m
Jy]
vsys = 38520
J1057+0554
-500 0 500Velocity [km s-1]
-20
0
20
40
vsys = 16430
J1126+1913
-200 0 200 400Velocity [km s-1]
0
20
40
vsys = 30880
J1127+1256
-500 0 500Velocity [km s-1]
-6-4-20246
vsys = 45690
J1136+2453
-300 -200 -100 0 100 200Velocity [km s-1]
0
20
40
60
Flu
x [m
Jy]
vsys = 9800
J1139+4631
-400 -200 0 200 400Velocity [km s-1]
-5
0
5
10
15
vsys = 52009
J1153+0930
-400 -200 0 200 400Velocity [km s-1]
0
5
10
15
vsys = 41640
J1211+2936
-500 0 500Velocity [km s-1]
-10
0
10
20
30
vsys = 32080
J1216+1904
-1000 -500 0 500 1000Velocity [km s-1]
-20
-10
0
10
20
Flu
x [m
Jy]
vsys = 22710
J1229+3224
-600 -400 -200 0 200 400 600Velocity [km s-1]
-10
0
10
20
vsys = 51860
J1248+5514
-1000 -500 0 500 1000Velocity [km s-1]
-10
0
10
20
vsys = 24860
J1313+0207
-500 0 500 1000Velocity [km s-1]
-20
0
20
40
vsys = 9140
J1314+2106
-400 -200 0 200 400Velocity [km s-1]
-10
0
10
20
30
Flu
x [m
Jy]
vsys = 13730
J1315+2437
-1000 -500 0 500Velocity [km s-1]
0
100
200
300
400
500
vsys = 3900
J1326+1922
-600 -400 -200 0 200 400 600Velocity [km s-1]
-5
0
5
10
vsys = 52190J1336+3008
-600 -400 -200 0 200 400Velocity [km s-1]
-10
0
10
20
30
vsys = 7760
J1339+4422
-400 -200 0 200 400Velocity [km s-1]
-20
0
20
40
60
Flu
x [m
Jy]
vsys = 18830
J1356+2816
-400 -200 0 200 400 600 800Velocity [km s-1]
0
10
20
30
vsys = 39720
J1409+1016
-1000 -500 0 500 1000Velocity [km s-1]
-10
0
10
20
30
vsys = 28610
J1505+5847
-1000 -500 0 500 1000Velocity [km s-1]
-10
-5
0
5
10
15
vsys = 43930
J1506+0806
-500 0 500Velocity [km s-1]
-20
-10
0
10
20
30
Flu
x [m
Jy]
vsys = 11890
J1529+0601
-500 0 500Velocity [km s-1]
-10
-5
0
5
10
15
vsys = 31900
J1529+0913
-500 0 500Velocity [km s-1]
-10
0
10
20
vsys = 38000
J1555+2955
-1000 -500 0 500 1000Velocity [km s-1]
-30
-20
-10
0
10
20
vsys = 20820
J1611+0840
-1000 -500 0 500 1000Velocity [km s-1]
-10
-5
0
5
10
15
Flu
x [m
Jy]
vsys = 49850
J1645+3048
-500 0 500Velocity [km s-1]
-30
-20
-10
0
10
20
vsys = 17760J2245+1232
-1000 -500 0 500 1000Velocity [km s-1]
-15-10
-5
0
5
10
15
vsys = 27519
J2326-0114
-1000 -500 0 500 1000Velocity [km s-1]
-10
-5
0
5
10
vsys = 58900
Figure 4 (Cont). Continuation of the IRAM 30m and CARMA CO(1–0) spectra
SDSSg r i 3-color thumbnails of all objects, and details ofthe observations are presented below.
3. OBSERVATIONS AND ANALYSIS
3.1. The IRAM 30m
We observed the CO(1–0) line at the central position ofour sample galaxies on September 9-14, October 15-18 andNovember 6-9, 2014 with the IRAM 30m telescope on PicoVeleta. We used the dual polarization Eight MIxer Receiver(EMIR; Carter et al. 2012) in combination with the autocor-relator Fourier Transform Spectrometers (FTS) at a frequency
8 ALATALO ET AL .
resolution of 0.195 MHz at CO(1–0) (providing a velocity res-olution of 0.57 km s−1). The observations were done in wob-bler switching mode with a wobbler throw of 240′′ in the az-imuthal direction.
The broad bandwidth of the receiver (16 GHz) and backendallowed us to group the observations of galaxies with similarredshifts. The central sky frequencies, taking into accountthe redshift of the objects, ranged between 96 and 111 GHz.Each object was observed until it was detected with a S/Nratio of at least 5 or until a RMS of 1.5 mK (T∗A) was achievedfor a velocity resolution of 20 km s−1. The integration timesper object ranged between half an hour and 2 hours, with amean value of 80 minutes. Pointing was monitored on nearbyquasars every 60-90 minutes. During the observation period,the weather conditions were generally good, with a pointingaccuracy better than 4′′. The mean system temperature for theobservations was 116 K on theT ∗
A scale. At 115 GHz, theIRAM forward efficiency,Feff , was 0.95; the beam efficiency,Beff , was 0.79; and the half-power beam size ranges between22.3′′ (for 110 GHz) and 25.6′′ (for 97 GHz). All CO spectraand luminosities are presented on the Jansky scale, convertedfrom the main beam temperature scale (Tmb) which is definedasTmb = (Feff/Beff) × T ∗
A, using a conversion factor of 5Jy/K.
For the data reduction, we first discarded poor scans andthen subtracted a constant or linear baseline. A large num-ber of scans were affected by platforming, i.e. the baselinelevel changed abruptly at one or two positions along the band.This effect could be reliably corrected because the baselinesin between these (clearly visible) jumps were flat and allowedto determine the (order 0 or 1) baseline which had to be sub-tracted from the different parts in order to move the baselinesto a zero level along the entire band. After this correction wesummed the spectra of each source, smoothed them to resolu-tions between 20–40km s−1 in order to increase the S/N ra-tio per channel, and visually determined the zero-level widths(the boundaries beyond which the spectra drop to zero). CO-SPOGs with S/N ratios>3 are considered detected, and CO-SPOGs with S/N ratios>5 are considered strongly detected.Figure4 shows the integrated spectra of the 35 SPOGs ob-served with the IRAM 30m (shaded turquoise). The systemicvelocity of the line is set to zero, and the total linewidth isrepresented by a turquoise line and is shaded in the spectrum.The optically-defined systemic velocity is shown as a blackdotted line. The velocity integrated spectra were calculatedby summing the individual shaded channels and multiplyingby the velocity width of each channel (21 or 42 km s−1).
As an alternative approach, we fit the spectra with a Gaus-sian profile and integrated it over velocity (details of the Gaus-sian fitting can be found in§A). The velocity integrated inten-sity determined by the two methods are in good agreement,with a mean difference of 5%, confirming that our velocityintegration is reliable. The line flux RMS was then calculatedby multiplying the RMS per channel by the channel veloc-ity width and the square root of the total number of channelsdetermined to contain line emission (those that are shaded).
3.2. CARMA
The CARMA SPOG observations were taken between Juneand December 2014 using CARMA, an interferometer of 15radio dishes (6×10.4m and 9×6.1m) located in the EasternSierras in California (Bock et al. 2006)3. 19 SPOGs were ob-
3 http://www.mmarray.org
served (with a 100% detection rate), either in D- or E-array,with baselines between 11–150m and 8–66 m, respectively.Standard reduction and calibration techniques (as describedin detail inAlatalo et al. 2013) were used on all targets.
Our SPOGs were unresolved in all cases exceptJ1315+2437 (IC 860, which was also observed in CARMAC-array byMcBride et al. 2014). The observing parametersassociated with each of the CARMA SPOGs are listed inTable2. A moment0 map for each CARMA SPOG (usingthe MIRIAD task moment; Sault et al. 1995), in which asigma clip was applied to velocity channels determined tohave emission (seeAlatalo et al. 2013for details). We didnot apply a standard sigma clip to the channel maps, insteaditeratively determining the correct sigma value to maximizethe detection of real emission to the exclusion of noise ineach individual object. Figure4 shows the integrated spectraof the 19 SPOGs observed with CARMA (shaded green).The systemic velocity of the line is set to zero, with thetotal linewidth represented by a green line, as well as in theshaded region of the spectrum. The integrated spectrum ofeach SPOG is determined by integrating the flux within anaperture determined by the moment0 map created for eachCARMA SPOG.
The RMS per channel is calculated by (1) taking the stan-dard deviation of all pixels within the cube that were outsidethe moment0 aperture, (2) applying an additional noise up-correction of 30% to account for the oversampling of the maps(see:Alatalo et al. 2015bfor details), and (3) multiplying bythe square root of the total number of beams represented inthe moment0 aperture.
To calculate the integrated line flux for each galaxy, wesummed the channels shaded in green in Fig.4 and multipliedby the velocity width of each channel, listed in Table2. Theline flux RMS was then calculated by multiplying the RMSper channel by the channel velocity width and the square rootof the total number of channels determined to contain lineemission. In the case of the two SPOGs observed by both theIRAM 30m and CARMA, the CO fluxes agreed to within thestandard 20% errors.
4. RESULTS
4.1. The Morphologies of CO-SPOGs
Figure3 show the 3-colorg r i images from SDSS of all 52CO-SPOGs. The thumbnails show a large number of galaxiesthat include signs of interaction, though only a handful appearto be major mergers in the coalescence phase (Dopita et al.2002). A significant fraction of CO-SPOGs have tidal featuresprominent enough to be seen in SDSS images. The remainingsample of CO-SPOGs mainly consists of early-type spirals,lenticular galaxies with bars, and objects with peaked nucleiconsistent with AGN. Our selection did not include morphol-ogy, so it is interesting that the number of tidally disruptedobjects represented in CO-SPOGs is larger than that in thegeneral SPOG sample.
In order to quantify whether the CO-SPOG galaxies are dis-rupted, six team members (Alatalo, Appleton, Cales, Lanz,Lisenfeld, Nyland) independently visually inspected theg r ithumbnails of these galaxies (Fig.3). Based on the (poten-tial) presence of tidally features, they classified the galaxiesas (possibly) disrupted or not. There was complete consensusof the classification of 47 galaxies, indicated by the presenceor absence of a check mark in Table1, as well as a (∞) sym-bol on Figure3. The other 5 galaxies had at least two clas-
sifications differing from the others and are therefore markedas ambiguous, represented as a question mark in Table1 and(∼) in Figure3. Based on these classifications, 19–24 (37–46±7%4) of our CO-SPOGs are classified as disrupted. Adetailed analysis of the morphologies of SPOGs will be pre-sented in a future paper.
4.2. CO(1–0) Properties
Figure 4 shows the CO(1–0) spectra of all CO-SPOGs,color coded to identify which facility was used to makethe observation (turquoise for the IRAM 30m and green forCARMA). A few double-horned spectral profiles, consistentwith molecular gas rotating in a disk that extends out to theflat part of the rotation curve, are present but are the minorityof detections (although this could in part be due to sensitivity).In many of the strong molecular gas detections, multiple com-ponents and peaks are present in the molecular gas, consistentwith the morphological disruption present ing r i images ofthe galaxies.
Table2 lists the derived properties for CARMA-observedCO-SPOGs, including the RMS noise in the channel maps,the spatial extent of the molecular gas (determined by sum-ming the total number of unmasked pixels in the mo-ment map; seeAlatalo et al. 2013for details of momentmap construction), channel widths, and total on-sourcehours. Derived molecular gas properties are listed in Ta-ble 3. CO luminosities are derived using the equation inSolomon & Vanden Bout(2005):
LCO = 1.20× 10−1SCO∆v D2L
1 + vsys/cL⊙, (1)
whereSCO∆v is the CO(1–0) flux (in Jy km s−1), DL isthe luminosity distance (in Mpc),vsys is the optically-definedsystemic velocity (in km s−1), andc is the speed of light (in
4 Errors are those from assuming a binomial distribution
km s−1). Converting the CO(1–0) luminosity into moleculargas masses requires the assumption of aLCO–MH2
conver-sion factor (Bolatto et al. 2013), which is known to be depen-dent on the state of the molecular gas. Interacting galaxiesand ultra-luminous infrared galaxies (ULIRGs) are known tohaveLCO–MH2
conversions that are lower than normal, star-forming galaxies by a factor of about 5 (Downes & Solomon1998), thoughNarayanan et al.(2011) have shown that thereis a large scatter above and below the standard value, evenwithin merging systems.Sandstrom et al.(2013) showed thatthe nuclei of normal star-forming galaxies can exhibit CO–to–H2 conversion up to an order of magnitude below the MilkyWay value. Determining the properLCO–MH2
conversion istherefore essential to deriving the molecular mass of a galaxy.
We calculateMH2with the following equation:
MH2= 1.05× 104
SCO∆vD2L
1 + vsys/cM⊙ (2)
assumingXCO = 2 × 1020 cm−2 (K km s−1)−1, themean conversion factor presented inBolatto et al. (2013),the derived H2 masses for our CO-SPOGs range between108.4−10.6M⊙.
5. DISCUSSION
5.1. The molecular gas fraction of CO-SPOGs
Figure 5 shows the molecular gas fraction distributionfor different subsets of galaxies that contain molecular gas.Normal, star-forming galaxies from CO Legacy Databasefor the GALEX Arecibo SDSS Survey (COLD GASS; top;Saintonge et al. 2011), have an average molecular gas frac-tion 〈log(fmol,SF)〉 = −1.29. The classical poststarbursts(middle;French et al. 2015) have〈log(fmol,PSB)〉 = −1.19,and CO-SPOGs (bottom) have〈log(fmol,SPOG)〉 = −0.83.SPOGs tend to have higher gas fractions than both nor-mal galaxies and poststarbursts. The molecular gas frac-
Column (1): SPOG #. Column (2): SDSS name. Column (3): Velocity range (optically-defined, local standard of rest).Column (4): Spectral RMS. Column (5): CO(1–0) line flux. Column (6): The signal-to-noise ratio of the CO detections.Column (7): CO(1–0) luminosity. Column (8): Observed mass of H2 (using the conversion factor ofBolatto et al.
2013). Column (9): Molecular gas fraction,Fgas =MH2
MH2+Mstar
tions in relation to the stellar masses range from 10−1.56 to10−0.34, with those SPOGs at the high end of the molecu-lar gas fraction range being comparable to interactions (inwhich log(MH2
/Mstar + MH2)∼ -0.3; Combes et al. 2013;
Kaneko et al. 2014). We ran a Mann Whitney U-test5 (whichis used in cases of small numbers), and were able to showthatfmol in SPOGs is distinct from both star-forming galax-ies (p≈ 0) as well as poststarbursts (p= 0.0019), wherep is
5 IDL routine:rs test
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 11
0
5
10
15
20
25
Ng
als
Star-forming <log(fmol)> = -1.29
0
1
2
3
4
5
6
Ng
als
Classical PostSBs <log(fmol)> = -1.19
0
2
4
6
8
10
12
Ng
als
HCGs <log(fmol)> = -1.21
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5log(fmol)
0
2
4
6
8
10
12
14
Ng
als
<log(fmol)> = -0.83SPOGs
Figure 5. The distribution of molecular gas to stellar mass ratio in the COLDGASS star-forming galaxies (top;Saintonge et al. 2011), the classical post-starburst galaxies (middle; yellow;French et al. 2015), HCG galaxies (mid-dle, blue; Leon et al. 1998; Martinez-Badenes et al. 2012; Lisenfeld et al.2014, 2016 in prep) and CO-SPOGs (bottom; light or dark green), assumingthe sameXCO. The molecular-to-stellar mass fractions of CO-SPOGs arehigher than those seen in both the star-forming galaxies andpoststarbursts.All stellar masses were calculated as described in§5.1. The distribution ofmorphologically disrupted SPOGs (dark green) is overlaid,and reflects theoverall SPOG distribution faithfully.
the probability of a null hypothesis.The fraction of our CO-SPOGs classified as having dis-
rupted morphologies is large (37–46±7%). This optical dis-ruption suggests that the molecular gas should also be dis-rupted to some extent.Downes & Solomon(1998) showedthat in many interacting systems, the molecular gas mass pre-dicted from the CO(1–0) flux was larger than the dynamicalmass of the system, usually by about a factor of 5, though thisis quite uncertain (Yao et al. 2003; Bolatto et al. 2013). Theyconclude that this is due to the nature of the molecular gas ininteracting systems being more diffuse and warm (Aalto et al.1995; Rangwala et al. 2011), creating a more continuous cov-erage of CO-emitting gas rather than distributed in discrete gi-ant molecular clouds (which would also span a smaller veloc-ity range). If the molecular gas in SPOGs is indeed disruptedand therefore not confined to a disk as in the Milky Way, wecould be overestimating the molecular gas mass by∼5. IfCO-SPOGs are found on the extreme end of the conversionsfound bySandstrom et al.(2013) for nuclear regions of star-forming galaxies, then the conversion could be off by as muchas a factor of 7. If all CO-SPOGs require one of these reducedconversion factors, then the molecular-to-stellar mass ratiowould shift significantly, to an average ratio of 10−1.68, con-sistent with the COLD GASS sample (Saintonge et al. 2011),and less than the poststarburst sample (French et al. 2015).
Figure 5 also overlays the molecular gas fraction ofa sample of Hickson Compact Group (HCG) galaxies,with stellar masses from U. Lisenfeld et al. 2016 inpreparation, and H2 masses calculated from CO obser-vations (Leon et al. 1998; Verdes-Montenegro et al. 1998;Martinez-Badenes et al. 2012; Lisenfeld et al. 2014), usingXCO = 2×1020 cm−2 (K km s−1)−1. HCG galaxies to spanthe range offmol values, suggestive of their large range ofproperties and environments (Bitsakis et al. 2010, 2011, 2014;Zucker et al. 2016). Many HCGs contain warm H2-luminousgalaxies, known to host shocks (Cluver et al. 2013), whichmay be a better comparison sample with CO-SPOGs than in-teractions. Given that the SPOG criteria aimed to select ob-jects that host shocks, the warm H2-bright galaxies serve as areasonable comparison.Alatalo et al.(2015a) used CARMAto study the molecular gas in turbulent HCG galaxies andfound that the molecular gas-to-dust ratios within these sys-tems were consistent with the Milky Way value, and predictedgas masses that were consistent with a normal CO-to-H2 con-version. Despite the fact that both types of systems hostshocks, the molecular-to-stellar mass ratio for warm H2 brightHCG galaxies tends to be lower than for SPOGs (10−1.21;Martinez-Badenes et al. 2012; Lisenfeld et al. 2014).
It is unclear whichLCO–MH2conversion factor is more rel-
evant to our population of CO-SPOGs.Alatalo et al.(2014a,2016) suggested that SPOGs were at an earlier stage ofquenching than other poststarburst galaxies, and thus couldstill contain larger reservoirs of molecular gas as they undergoquenching. Observations of denser gas tracers, such as CS andHCN will be necessary to better infer the mass of dense gasand better define theXCO factor.
5.2. Comparing the CO(1–0) and 22µm flux
The well-known connection between mid-IR emission andstar formation (Calzetti et al. 2007) is caused by hot dustre-radiating UV photons from the young stars. Therefore,it is likely that a relation exists between the 22µm andCO(1–0) fluxes, given that the 22µm emission traces thestar formation and the CO(1–0) traces the star-forming fuel
12 ALATALO ET AL .
1 10 100 1000F(22µm) [mJy]
1
10
100
SC
O ∆
v [J
y km
s−1
]
COLD GASSEGNoGAMIGAETGsAGNsPostSBsCO−SPOGsNGC1266
(a)
Na D>3σ
(b)
Radio detected
(c)
Morph. disrupted
Figure 6. (Left): The 22µm and CO(1–0) fluxes are compared for many samples, includingstar-forming galaxies such as COLD GASS (black dots;Saintonge et al. 2011), EGNoG (gray dots;Bauermeister et al. 2013) and AMIGA (dark gray squares;Lisenfeld et al. 2011), early-type galaxies (yellow dia-monds; ATLAS3D: Young et al. 2011; Alatalo et al. 2013; Davis et al. 2014), AGNs (red triangles;Evans et al. 2005), poststarburst galaxies (green crosses;French et al. 2015), NGC 1266 (outlined yellow star;Alatalo et al. 2011, 2014b, 2015c), and CO-SPOGs (blue stars). Light blue dots inside of the stars denoteCO-SPOGs that have detections with S/N between 3–5. The 22µm and CO(1–0) fluxes of star-forming galaxies are well correlated (shown as a black line), withAGNs showing the strongest divergence from the relation. CO-SPOGs sit below the relation as well, though not as extremely as the AGNs.(Right): The 22µmvs. CO(1–0) fluxes are shown, emphasizing the SPOGs with particular properties (symbols for other samples from lefthandplot have been changed to grayscale).This includes those galaxies with 3σ excess NaI D absorption (a; top right, red), galaxies that were detected with FIRST (b; middle right, green), and galaxiesthat were classified as clearly or possibly morphologicallydisrupted (c; bottom right, pink). Although radio-detected CO-SPOGs account for most of the objectsthat fall the farthest from theF22–FCO relation, they do not universally exhibit quasar-like 22µm excess relative to their CO fluxes.
(Rosenberg et al. 2015). The left-most panel of Figure6 putsthis relation to the test by comparing the 22µm and CO(1–0) fluxes of different samples of galaxies, including star-forming galaxies (Lisenfeld et al. 2011; Saintonge et al. 2011;Bauermeister et al. 2013), early-type galaxies (Young et al.2011; Alatalo et al. 2013; Davis et al. 2014), radio galaxies(Evans et al. 2005), and poststarburst galaxies (French et al.2015). The 22µm emission was obtained through a cross-matching with the ALLWISE catalog (Wright et al. 2010). Incases that objects were flagged as extended in the 2-MicronAll-Sky Survey (2MASS;Skrutskie et al. 2006), the extendedsource flux was used (w4gmag), otherwise the profile fit flux(w4mpro) was used.
The star-forming objects of the COLD GASS survey(Saintonge et al. 2011), Evolution of molecular Gas in Nor-mal Galaxies (EGNoG;Bauermeister et al. 2013), and Analy-sis of the interstellar Medium of Isolated GAlaxies (AMIGA;Lisenfeld et al. 2011) samples (black and gray dots) on Fig-
ure 6 do indeed trace a reliable relation, allowing us to pre-dict the CO(1–0) flux from the 22µm flux. We used thescaling ofCalzetti et al.(2007) of SFR∝L0.885
24µm, as well asCarilli & Walter (2013) of LFIR ∝L1.4
CO (as well asLFIR be-ing linearly related to the SFR;Kennicutt 1998) to derive theexpected slope of the relation between F(22µm) and SCO∆v,setting it to: SCO∆v∝F(22µm)0.632. Using a 4σ-clippedsubset of the star-forming objects, and the relation notedabove, we find the following relationship betweenSCO∆vandF22µm:
SCO∆v
(Jy km s−1)= 2.402+0.128
−0.122
(
F22µm
mJy
)0.623
(3)
which corresponds to the bisecting line shown in Figure6. Forregular star-forming galaxies, this relation can predict aroughCO(1–0) flux, though the non-star forming samples show thatthis breaks down with the presence of other dominant contrib-
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 13
utors to the 22µm emission.The early-type galaxies from the ATLAS3D sample show
a much larger scatter than the star-forming galaxies on thisrelation, also noted byDavis et al.(2014), with a slight mid-IR enhancement (ǫMIR; defined as the ratio of the 22µmemission in the source to the expected 22µm at a givenSCO∆v based on the star-forming objects defined line),〈ǫMIR,ETG〉= 4.22+0.90
−0.74. This scatter is likely due to the factthat there are other sources of 22µm emission in early-typegalaxies, including the aged stellar population and the hard ul-traviolet field created by post-AGB stars (responsible for theUV upturn phenomenon;O’Connell 1999; Davis et al. 2014).
A subset of the radio galaxies and quasars (Evans et al.2005) tend to diverge the most from this relation, astheir 22µm emission over-predicts the CO(1–0) flux with〈ǫMIR,AGN〉= 5.58+2.53
−1.75. Many of the galaxies that sit nearthe relation are known starbursting AGN hosts (Lanz et al.2015). The enhancement therefore is unsurprising, giventhat AGNs contribute substantially to the hot dust componentof a galaxy’s spectral energy distribution (SED) in the mid-infrared (Ward et al. 1987; Sanders et al. 1989; Elvis et al.1994). Thus, a quasar’s divergence from this relation is dueto the fact that star formation is not the primary contributor tothe 22µm emission.
The poststarburst galaxies fromFrench et al.(2015) appearto be strongly MIR-enhanced, sitting below theSCO∆v–F22µm relation by a factor of〈ǫMIR,PSB〉= 10.51+1.89
−1.60. Anadditional heating mechanism (that would only heat the dust,but not increase the CO flux by injecting turbulence) must bepresent in poststarburst galaxies to cause this enhancement,such as the radiation from the intermediate-aged stellar popu-lation or deeply buried AGNs.
CO-SPOGs are also a divergent population, albeit not tothe extent of the poststarbursts, with all objects lying belowtheSCO∆v–F22µm relation set by the star-forming galaxieswith 〈ǫMIR,SPOG〉= 4.91+0.42
−0.39. In fact, if we limit ourselvesonly to strong (S/N≥5) detections,〈ǫMIR,SPOG〉 increases to9.75+1.91
−1.60. This suggests that there could be AGNs in our CO-SPOGs, but that the bolometric luminosities of these AGNsare not as strong as the extreme objects in theEvans et al.(2005) sample. The selection criteria we applied to create theCO-SPOG sample (intermediate aged stars, a lack of star for-mation from the line diagnostic diagram, and detectable 22µmemission) favor AGNs; thus, theSCO∆v–F22µm relation in-dicating the presence of AGNs is expected. How CO-SPOGsand poststarbursts compare will be presented in detail in§5.4.
Their positions in Figure6 predict that SPOGs have AGNluminosities that are intermediate between the star-formingpopulation and the quasar/radio galaxy population. Giventhe prevalence of intermediate-aged stars found in quasars(Canalizo & Stockton 2013), it is possible that some SPOGsin our sample may migrate to more luminous AGN phases asthe galaxy transition proceeds.
The right panels of Figure6 have taken the relation andbroken CO-SPOGs down into sub-populations based on theirNa I D properties (top), radio detections (middle), and mor-phological properties (bottom) to determine whether anyof these properties influenceǫMIR. Our CO-SPOGs have〈ǫMIR,SPOG〉= 4.91+0.42
−0.39, falling off the star forming relationby a factor of≈5. Objects with either radio emission or aNa I D enhancement (detailed in§5.5) appear to fall slightlyfarther from the relation with〈ǫMIR,radio〉= 4.95+0.62
−0.55 and
〈ǫMIR,Na ID〉= 5.40+0.85−0.73, respectively, but agree within the
uncertainty. CO-SPOGs that were classified as morpholog-ically disrupted were found to have smaller deviations fromthe relation,〈ǫMIR,disrupted〉= 4.37+0.47
−0.43. In all of these cases,the overallǫMIR was not sufficiently deviant from the overallCO-SPOG population to be distinct, and thus we cannot con-clude whether the presence of any of these properties enhanceor suppress the mid-IR emission as compared to the CO flux(relative to star forming galaxies).
5.3. Ambiguity of star formation tracers in CO-SPOGs
In CO-SPOGs, shocks can dominate the ionized gas emis-sion (Allen et al. 2008; Rich et al. 2011), including [OII ] andHα. UV emission suffers from large uncertainties due to ex-tinction and contamination due to non-star formation domi-nated phenomena, such as heating by intermediate-age stars.Finally, as Figure6 laid out, the 22µm emission can besignificantly contaminated by the presence of an AGN. InNGC 1266, the 22µm emission overestimates the SFR by afactor of 10 (Alatalo et al. 2011), despite star formation beingsuppressed by a factor of> 50 (Alatalo et al. 2015c). Whilecentimeter-wave radio emission is a sensitive tracer of re-cent star formation (Condon 1992) the continuum emission at1.4 GHz can also be contaminated by the synchrotron emis-sion from an AGN (Zensus 1997; Laor & Behar 2008).
Constructing a SED that includes far-infrared emission isby far the most reliable tracer of star formation in all systemsexcept those with the most deeply buried AGNs, because thecold dust nearly unambiguously traces star formation origi-nating in imbedded clouds. It is possible that a single datapoint on the Rayleigh-Jeans tail of the dust continuum black-body could reduce the uncertainty of SFRs in ambiguous sys-tems, such as SPOGs. For instance, an observation at 850µmwould be able to anchor the blackbody. If we assume thatthe dust temperatures do not vary much away fromTd≈ 25K(Scoville et al. 2014), we should be able to use the 22µm and850µm points to interpolate the modified blackbody for thedust continuum across, inferring a star formation rate. Whilethis method is not as precise as fitting a full SED and dustcontinuum (with far-IR data near the peak of the blackbody),it could significantly improve SFR estimates for SPOGs.
5.4. CO-SPOGs and CO-detected poststarbursts
Alatalo et al.(2016) argue that the SPOGs criterion mightidentify objects at an earlier stage of transition than the clas-sical poststarburst criterion.French et al.(2015) showed that53% of poststarburst galaxies contain non-negligible reser-voirs of molecular gas, modifying the standard picture ofgalaxy evolution in which a galaxy expels its interstellarmedium before transitioning (Hopkins et al. 2006). We havealso shown that compared to their molecular gas content, thepoststarbursts ofFrench et al.(2015) are significantly 22µm-enhanced.
TheFrench et al.(2015) poststarburst sample has reservoirsof molecular gas ranging from 108.6–109.8M⊙ in mass, andmolecular-to-stellar mass fractions between 10−2–10−0.5. Inthat sample, the majority of the poststarburst galaxies containionized gas line ratios that are consistent with LINERs, anda substantial fraction show disrupted optical morphologies.Of the 17 CO-detected poststarbursts from theFrench et al.(2015) sample, 15 were detected in the 22µm WISE band witha S/N ratio>3, thus all but 2French et al.(2015) poststar-bursts would have surpassed the 22µm criterion of the CO-
14 ALATALO ET AL .
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Figure 7. The distribution of molecular gas in the classical poststarburstgalaxies (top;French et al. 2015) and CO-SPOGs (bottom, light green). Thedistribution for the morphologically disrupted SPOGs is overlaid in darkgreen, and reflects the overall SPOG distribution faithfully. SPOGs have sig-nificantly more molecular mass than poststarbursts.
SPOGs. There is no difference in averagefmol in the post-starburst sample when we remove the two 22µm non-detectedpostsarbursts from consideration.
CO-SPOGs compare well to theFrench et al.(2015) post-starbursts in ionized gas ratios and 22µm properties, and mor-phologies, including both sets presenting substantial LINER-like ionized gas line diagnostics, similar detection ratesinWISE22µm emission, and a similar fraction of objects presentmorphological disruptions. Due to a selection against strong[O III ] emission, theFrench et al.(2015) CO-detected post-starbursts have an average EW[OIII ] that is an order of mag-nitude smaller (〈EW[O III ]PSB〉= 0.60) than what is found forCO-SPOGs (〈EW[O III ]COSPOG〉= 5.74). The poststarburstsof French et al.(2015) show low CO fluxes compared to their22µm fluxes, and CO-SPOGs seem to contain larger reser-voirs of molecular gas (Fig.7; assuming equivalent values forXCO). We also see discrepancies between SPOGs and post-starbursts in the molecular-to-stellar mass ratio (Figure5),where SPOGs exhibit much higher gas fractions.6
The fact that SPOGs contain more molecular gas than
6 A standardXCO was used both for poststarbursts and for CO-SPOGs,since the time differentiation between the SPOG phase and poststarburstphase is sufficiently short that we do not expect a dramatic change inthe conversion outside of the scatter seen in different merger simulations(Narayanan et al. 2011).
French et al.(2015) poststarbursts could suggest one of thefollowing. Either (1) the SPOG criteria allowed for galaxiesthat contained more substantial reservoirs of molecular gasin the first place, due to not strictly excluding Hα or [O II ]emission, or (2) SPOGs are in an earlier phase of their tran-sition; possibly both of these effects are at play. It is alsopossible that in some CO-SPOGs, the bulk of star formationis taking place behind an optically thick screen, although IFUstudies of objects at different merger stages have shown thatsuch “skin effect” phenomena are rare (Rich et al. 2015) anddo not explain the excess 22µm enhancement present in thepoststarbursts. Optical IFU studies of CO-SPOGs would helpelucidate whether this effect is present in any of our objects.
Figure9 in Alatalo et al.(2016) indicates that SPOGs arebluer than poststarburst galaxies (Goto 2007; Yesuf et al.2014; Rowlands et al. 2015) and lie on the blueward side ofthe green valley, and Figure2 confirms that CO-SPOGs fol-low the colors of the general SPOG population. SPOG opti-cal colors may be bluer than poststarbursts because they havetruncated their star formation more recently, and thus havea larger population of blue stars (to contribute to the galaxycolors). A large-scale stellar population analysis of these twopopulations would be able to better pinpoint how SPOGs andpoststarbursts are related, but the larger reservoir of moleculargas in SPOGs could suggest that they are at an earlier phaseof evolution, if depletion of the molecular reservoir is relatedto the time since the start of a galaxy’s transition.
If galaxy transition does correlate with the depletion ofmolecular material, then the larger gas reservoirs and gas frac-tions are suggestive of a timescale effect, which correlateswith the phase of transition.Alatalo et al.(2015a) used in-terferometric CO measurements to show that in some warmH2-bright HCG galaxies, the expulsion of the molecular reser-voir was not required for a galaxy to transform. Instead,these authors argue that the inhibition of the molecular gasto form stars was a more important factor in predicting agalaxy’s color. Whether CO-SPOGs or the poststarbursts ofFrench et al.(2015) show this impact too will require suffi-ciently resolved molecular gas and accurate star formationrates to study whether a star formation suppression phaseglobally manifests in transforming galaxies or whether it is aspecial phenomenon seen in the compact group environment.
5.5. Na I D in CO-SPOGs: do they contain neutral winds?
Alatalo et al.(2016) showed that, as a population, SPOGshave a higher fraction of sources with NaI D propertiesthat require an interstellar component compared to the (starformation-dominated) ELG sample. Figure8 shows the un-derlying distribution from the ELG sample (in grayscale),along with the SPOG distribution (green contours), where wesee that there is a NaI D-enhanced wing. Overplotted areCO-SPOGs (stars), labeled based on whether they were de-tected at 1.4 GHz by FIRST (dark blue) or not (light blue),and whether they are disrupted (magenta outline). We cansee that the CO-SPOGs are even more NaI D-enhanced thanthe underlying SPOG population. We ran the Mann Whit-ney U-test to test whether the NaI D properties of CO-SPOGscould be randomly drawn from the SPOG sample, and foundthat the null hypothesis was ruled out (p≈0). 19 (37±7%) ofthe CO-SPOGs contain NaI D emission above the 3σ bound-ary defined by the NaI D-Mg b relation of the ELG sample(Equation 10 inAlatalo et al. 2016). This excess suggeststhe possibility that many CO-SPOGs host interstellar winds(Rupke et al. 2005; Veilleux et al. 2005; Murray et al. 2007;
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 15
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Figure 8. The equivalent widths EW(Mg b) vs. EW(NaI D) of the ELGsample (grayscale;Alatalo et al. 2016) compared with the entire SPOGSsample (green contours). The dashed line represents the empirical relationfound inAlatalo et al.(2016). The dotted line represents a 3σ departure fromthe empirical relation. The CO-SPOG sample is shown (stars), includingFIRST radio detections (dark blue) and non-detections (light blue), as well asNGC 1266 (gold;Davis et al. 2012). CO-SPOGs with a light blue dot in theircenters are detected with S/N between 3–5. SPOGs have NaI D comparedto Mg b that is enhanced beyond what is seen in normal star-forming galax-ies in the ELG sample. The CO(1–0) detected objects show evenmore en-hanced NaI D characteristics compared to non-CO observed SPOGs, with 19(37%) objects beyond the 3σ boundary defined by the normal (ELG-defined)relation. There does not appear to be a difference between the objects ob-served by CARMA and those observed by the IRAM 30m. Clearly and pos-sibly morphologically disrupted SPOGs are outlined in pink. Radio-detectedSPOGs tend to have the largest NaI D excess, and radio non-detected, non-disrupted SPOGs have the least excess. Most radio non-detected SPOGs thatdo show NaI D excess at the>3σ level also show morphological disruptions.
Park et al. 2015).Figure8 indicates that a fraction of CO-SPOGs host NaI D
properties as extreme as what is seen in AGN-driven outflowhosts (Rupke & Veilleux 2011, 2015), including NGC 1266(Alatalo et al. 2011; Davis et al. 2012; Nyland et al. 2013).The extreme NaI D widths of these sources suggests that theymay host an AGN-driven molecular outflow like NGC 1266.If so, it would indeed shed light on how such outflows relate togalaxy transformation. However, it is also possible that NaI Denhancements are due to unsettled neutral gas along the lineof sight instead.
We have investigated how NaI D absorption changes acrossthe ELG sample. Table4 shows the median values, and10th and 90th percentile values of the ELG, SPOG, and CO-SPOG subsamples.7 Overall, objects that have been detectedin the 22µm band ofWISEappear to show more enhancedNa I D in the both ELG and the SPOG samples. In the caseof galaxies within the ELG (and thus star formation domi-nant) sample, this NaI D enhancement might be able to beexplained by neutral winds being launched by the starburst(Murray et al. 2007; Park et al. 2015; Sarzi et al. 2016), whichwould correlate with the 22µm hot dust emission (and there-
7 It is of note that there is very little difference in the NaI D properties ofstrong (S/N≥5) detections and tentative (3≤S/N<5) detections.
Column (1): Total number of objects in each class. Column (2): MedianNa I D enhancement of each sample. Column (3): The 10th percentile NaI Denhancement. Column (4): The 90th percentile NaI D enhancement.
fore, the star formation rate). The SPOG selection criteriaeliminated strong star-formers (based on ionized gas emissionline ratios;Baldwin et al. 1981; Veilleux & Osterbrock 1987;Kewley et al. 2006), so the NaI D excess and 22µm emissionare possibly from an alternative source.
As discussed in§2, the ramifications of this selectionare that our CO-SPOGs likely favor the presence of AGNs.SPOGs also follow the trend that objects hosting radio emis-sion and 22µm emission show a significant NaI D enhance-ment when compared to other samples, including radio or22µm non-detected SPOGs. Radio-detected SPOGs exhibita median NaI D-enhancement (defined as the deviation fromthe mean relation of the ELG of NaI D = (0.685Mg b+0.8)from Alatalo et al. 2016) of 〈ǫNaD,radio〉 = 1.421, and 13/19(68±11%) objects found with 3σ Na I D enhancementswere radio-detected (although 57±7% of the CO-SPOGshave been detected in radio). Objects that were not de-tected in FIRST have a median NaI D enhancement of〈ǫNaD,non−radio〉 = 0.547. CO-SPOGs with radio emissionhave higher NaI D enhancements than objects that do not.This is further supported by the results of the Mann-WhitneyU-test, which was able to rule out that the NaI D propertiesof radio non-detected CO-SPOGs were drawn from the samedistribution of radio-detected CO-SPOGs with the probabil-ity of a null hypothesis ofp<0.04. Given that AGN activityis a probable origin of the radio emission, we suggest thatAGN-hosting SPOGs are the most likely to contain enhancedNa I D.
We also tested whether the morphologies of the SPOGshad a strong influence on the NaI D enhancement, given thatmany objects that host strong neutral winds are starburstsin ULIRGs, which are mostly major mergers (Veilleux et al.2005). The overall effect of morphological disruption seemsto have a slight impact on the NaI D enhancement, with me-dian 〈ǫNaD,disrupted〉= 1.495, slightly larger than the medianfor galaxies that were not classified as being disrupted of〈ǫNaD,undisturbed〉= 1.206. Therefore, morphological disrup-tion appears to have a smaller influence on the NaI D en-hancement of CO-SPOGs than the presence of radio emission.
Sarzi et al.(2016) showed that in a sample of 456 nearbygalaxies, sources with NaI D enhancements attributable to in-terstellar winds (as opposed to [Na/Fe] overabundances as isseen in the most massive galaxies;Jeong et al. 2013) were notobserved in objects detected with Very Long Baseline Inter-ferometry (Deller & Middelberg 2014). These authors con-cluded that the majority of NaI D-enhanced objects were pro-lifically star-forming galaxies with neutral winds that were
16 ALATALO ET AL .
star formation driven, and that NaI D winds originate mostcommonly in star-forming galaxies due to star formation driv-ing. In CO-SPOGs, it appears that there are (radio-detected)AGNs and NaI D enhancements in the same objects, consis-tent with the results ofLehnert et al.(2011) that 33% of radiogalaxies within SDSS also contain NaI D enhancements. Thelack of this type of object within theSarzi et al.(2016) samplesuggests that they could be quite rare or are possibly a shortand violent phase in galaxy evolution, in which the star forma-tion has quenched and an AGN is driving a neutral wind thatis stirring up the remaining interstellar medium. The SPOGcriterion selected against star-forming objects (which isableto rule out strong starbursts that are needed to drive winds;Alatalo et al. 2016), and thus include many more galaxieswith LINER emission, as opposed to theSarzi et al.(2016)sample.
Further studies are needed, including observations withhigher spectral resolution to investigate the shape and struc-ture of the NaI D line, to look for outflows (Veilleux et al.2005; Rupke et al. 2005; Rupke & Veilleux 2011). Integralfield spectrographs will be able to determine the extent of theNa I D absorption, provide high resolution kinematics to de-termine the neutral mass flux and compare the NaI D kinemat-ics to the stellar kinematics. Deeper CO observations mightdetect broad molecular wings, resulting in the measurementof a range of the mass outflow (and mass escape) rates ob-served in transitioning objects. In-depth studies of theseob-jects’ star formation rates and molecular gas distributions willshed light on how often star formation is suppressed, leadingto the conserving and extending the lifetime of the molecu-lar gas as galaxies undergo transformations from late-typesto early-types. Deep X-ray observations will put limits onthe AGN luminosity, helping to determine the range in en-ergy budgets these systems might exhibit, and 2-dimensionalstellar population studies might be able to provide a range oftimescales over which triggering mechanisms started the pro-cess of star formation quenching in these systems.
6. SUMMARY
We have followed up 52 of theWISE22µm-detected ob-jects from the Shocked POststarburst Galaxy Survey usingthe IRAM 30m and CARMA to search for CO(1–0). We wereable to detect 47 of these 52 SPOGs to at least 3σ significance.
• The requirement of detected 22µm emission, combinedwith ionized gas emission line ratiosinconsistentwithstar formation, likely biases our CO-SPOG sample to-ward the detection of AGNs. Despite this, a large subsetof our objects do not have line ratios consistent with apure Seyfert nucleus.
• The CO-SPOG sample appears to span the color phasespace of the SPOG parent sample, though with a biastoward the more massive SPOGs. A morphological in-vestigation was undertaken to visually classify whetheran object was disrupted, finding that 37–46±7% of ourCO-SPOG sample show signs of morphological disrup-tions.
• The molecular gas fractions exhibited by the CO-SPOGs are larger than those in normal star-forminggalaxies and those in a sample of traditionally-identified poststarburst galaxies, most of which weredetected in 22µm emission. The molecular gas frac-tions identified in our sample are consistent with those
seen in interactions, supported by our identification ofa large fraction of morphologically disrupted objects,although it is possible that our 22µm selection has bi-ased the sample to select objects with buried ongoingstar formation, which will require further observationsto measure accurately.
• We used star-forming galaxies to derive a relation be-tween the 22µm flux from WISE and the CO(1–0)flux, finding that they were in agreement (support-ing the claim that the mid-IR in star-forming galax-ies is originating from the star formation itself) andthat quasars and radio galaxies fall off this relation.SPOGs in general sit between star-forming galaxiesand quasars/radio galaxies, with an average mid-IR en-hancement of〈ǫMIR〉= 4.91+0.42
−0.39. Presence of radioemission, NaI D enhancement, or morphological dis-ruption might influenceǫMIR, but not in a way that sig-nificantly deviates from the underlying CO-SPOG pop-ulation.
• The enhancement in the NaI D absorption relative tothe Mg b absorption is more significant in the CO-SPOGs than in the general SPOG population, with19/52 (37±7%) detected 3σ above the empirical rela-tion from the original ELG sample. This may be due tothe likely AGN over-population within the CO-SPOGsample, further supported by the larger NaI D enhance-ment present in the radio-detected objects.
KA thanks K. Decker French for useful discussions regard-ing the “E+A” sample. KA also thanks Jonathan McDow-ell & Michael J. I. Brown for Twitter dialogues regardingWISEand mid-infrared dust emission in AGNs, improvingthe manuscript. We also thank the anonymous referee for aninsightful report that has improved the manuscript.
Support for KA is provided by NASA through Hubble Fel-lowship grant #HST-HF2-51352.001 awarded by the SpaceTelescope Science Institute, which is operated by the Asso-ciation of Universities for Research in Astronomy, Inc., forNASA, under contract NAS5-26555. UL acknowledges sup-port by the research projects AYA2011- 24728 and AYA2014-53506-P financed by the Spanish Ministerio de Economıay Competividad and by FEDER (Fondo Europeo de Desar-rollo Regional) and the Junta de Andalucıa (Spain) grantsFQM108. PNA is partially supported by funding throughHerschel, a European Space Agency Cornerstone Missionwith significant participation by NASA, through an awardissued by JPL/Caltech. SLC was supported by ALMA-CONICYT program 31110020. KN acknowledges supportfrom NASA through theSpitzerSpace Telescope. AMMand LJK acknowledge the support of the Australian ResearchCouncil (ARC) through Discovery project DP130103925.
Based on observations carried out with the IRAM 30mTelescope. IRAM is supported by INSU/CNRS (France),MPG (Germany) and IGN (Spain). Support for CARMAconstruction was derived from the Gordon and Betty MooreFoundation, the Kenneth T. and Eileen L. Norris Foundation,the James S. McDonnell Foundation, the Associates of theCalifornia Institute of Technology, the University of Chicago,the states of California, Illinois, and Maryland, and the Na-tional Science Foundation. Ongoing CARMA development
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 17
and operations are supported by the National Science Foun-dation under a cooperative agreement, and by the CARMApartner universities. This publication makes use of dataproducts from theWide-field Infrared Survey Explorer, whichis a joint project of the University of California, Los Angeles,and the Jet Propulsion Laboratory/California Institute ofTechnology, funded by the National Aeronautics and SpaceAdministration. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the JetPropulsion Laboratory, California Institute of Technology,under contract with the National Aeronautics and SpaceAdministration. The National Radio Astronomy Observatoryis a facility of the National Science Foundation operatedunder cooperative agreement by Associated Universities, Inc.
Facilities: CARMA, IRAM, WISE
APPENDIX
A. GAUSSIAN FITTING THE IRAM 30M OBSERVATIONS
As a check of the accuracy of the fluxes measured by theIRAM 30m (especially those that with S/N ratios between 3–5), we fit each spectrum to a single Gaussian profile in orderto investigate the likelihood that our detections are real or spu-rious. We used theminimize procedure inGILDAS8 on thecontinuum-subtracted, calibrated IRAM SPOG datasets (ex-cluding non-detections).minimize was free to search forthe line in a 3000 km s−1 width centered on the recessionvelocity, but no initial velocity guess was provided for theCO(1–0) line. FigureA1 shows the results of the single Gaus-sian fits (pink) overlaid on the spectra of the IRAM SPOGs,with the chosen velocity widths shaded gray underlaid. Thecases with a disagreement between the optical and radio re-cession velocities are most likely due to uncertainties in theSDSS recession velocities (individual SDSS spectral channelshave widths of≈100km s−1; Bolton et al. 2012), although itis possible that the molecular gas in some of these systems issystemically offset from the stars and possibly part of a tidaltail or some disrupted gas structure, though consider the for-mer possibility more likely. Overall, we can see that for themajority of sources, the Gaussian fitting faithfully detectedand fit the profiles, although in some cases the SPOGs wouldhave been better fit with an additional Gaussian.
FigureA2 shows the direct comparison between the inten-sities derived from both methods for strong detections (>5σ,blue points) and tentative detections (3–5σ, red triangles)within the IRAM sample. In all but two cases, the flux de-terminations match within errors, with an average mismatchof 5%. In the cases where the Gaussian method has underes-timated the total intensities, often at least 2 Gaussian profileswere needed for the fit (e.g., J1505+5847 and J1529+0601).
Overall, the Gaussian fits fluxes agreed well with ourlinewidth-determined fluxes, both in confirming the presenceof the line at the optically-defined velocity, as well as in thetotal amount of flux that was detected.
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18 ALATALO ET AL .
J0003+0048
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
Tm
b [
mK
]
vsys = 41330
J0011−0054
−500 0 500Velocity [km s −1]
−2
0
2
4
6
vsys = 14260
J0029+1433
−1000 −500 0 500 1000Velocity [km s −1]
−3
−2
−1
0
1
vsys = 43000
J0037+0024
−500 0 500Velocity [km s −1]
−3
−2
−1
0
1
2
vsys = 24250
J0119+1334
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
vsys = 57170
J0803+2530
−500 0 500Velocity [km s −1]
−2
−1
0
1
2
Tm
b [
mK
]
vsys = 40430
J0807+2006
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
3
vsys = 19810
J0816+1936
−500 0 500Velocity [km s −1]
−1.5
−1.0
−0.5
0.0
0.5
1.0
1.5
vsys = 33850
J0845+2006
−1000 −500 0 500 1000Velocity [km s −1]
−4
−2
0
2
vsys = 37290
J0853+0310
−1000 −500 0 500 1000Velocity [km s −1]
−2
0
2
4
vsys = 38860
J0859+1006
−1000 −500 0 500 1000Velocity [km s −1]
−2
0
2
4
Tm
b [
mK
]
vsys = 16450
J0928+0741
−500 0 500Velocity [km s −1]
−2
0
2
vsys = 31530
J1008+1916
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
vsys = 54990
J1008+5123
−1000 −500 0 500 1000Velocity [km s −1]
−3
−2
−1
0
1
2
3
vsys = 46910
J1018+1536
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
3
vsys = 33120
J1028+5736
−1000 −500 0 500 1000Velocity [km s −1]
−4
−2
0
2
4
6
Tm
b [
mK
]
vsys = 21500
J1031+0540
−1000 −500 0 500 1000Velocity [km s −1]
−3
−2
−1
0
1
2
3
vsys = 48670
J1046+2804
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
vsys = 38520
J1057+0554
−500 0 500Velocity [km s −1]
−4
−2
0
2
4
6
vsys = 16430
J1211+2936
−500 0 500Velocity [km s −1]
−2
0
2
4
vsys = 32080
J1216+1904
−1000 −500 0 500 1000Velocity [km s −1]
−2
0
2
Tm
b [
mK
]
vsys = 22710
J1248+5514
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
3
4
vsys = 24860
J1313+0207
−500 0 500 1000Velocity [km s −1]
−4
−2
0
2
4
6
vsys = 9140
J1409+1016
−1000 −500 0 500 1000Velocity [km s −1]
−2
0
2
4
vsys = 28610
J1505+5847
−1000 −500 0 500 1000Velocity [km s −1]
−1
0
1
2
vsys = 43930
J1506+0806
−500 0 500Velocity [km s −1]
−2
0
2
4
6
Tm
b [
mK
]
vsys = 11890
J1529+0601
−500 0 500Velocity [km s −1]
−2
−1
0
1
2
vsys = 31900
J1529+0913
−500 0 500Velocity [km s −1]
−2
−1
0
1
2
3
vsys = 38000
J1555+2955
−1000 −500 0 500 1000Velocity [km s −1]
−6
−4
−2
0
2
4
vsys = 20820
J1611+0840
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
vsys = 49850
J1645+3048
−500 0 500Velocity [km s −1]
−4
−2
0
2
4
Tm
b [
mK
]
vsys = 17760
J2245+1232
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
vsys = 27519
J2326−0114
−1000 −500 0 500 1000Velocity [km s −1]
−2
−1
0
1
2
vsys = 58900
Figure A1. The 33 IRAM 30m spectra (as in Fig.4), with the chosen linewidths shaded gray, overlaid with thebest fit single Gaussian profile (pink), overlaidwith the optically-determined velocity (dotted maroon line).
SPOGS II: CO(1–0) OBSERVATIONS OFSPOGS 19
0.0 0.5 1.0 1.5ICO (Linewidth) [K km s−1]
0.0
0.5
1.0
1.5
I CO (
Gau
ssia
n)
[K k
m s
−1]
>5σ3−5σ
Figure A2. A comparison betweenICO determined in both of the methods:fitting a single Gaussian vs. integrating the total intensity of the line fordetected IRAM CO-SPOGs. Strong (S/N>5) detections are shown as bluecircles and tentative (S/N = 3–5) are shown as red triangles.The averagedisagreement between the two methods is 5%, and the vast majority of objectsagree within errors.
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