Great Barriers in HMSF 2010: Gerhardt R. Meurer International Centre for Radio Astronomy Research...

Great Barriers in HMSF 2010:

Gerhardt R. MeurerInternational Centre for Radio Astronomy

ResearchUniversity of Western Australia

Great Barriers in HMSF 2010:Great Barriers in HMSF 2010:

Outline

High Mass Star formation tracersSINGG & SUNGG SurveysWhy study extragalactic HMSF?Results

The Star Formation LawThe Initial Mass FunctionModes of star formation

Take home points

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Great Barriers in HMSF 2010: 3

H traces O stars M* > ~20 Msun

t < ~7 Myr

Vacuum UV traces O and B stars M* > ~3 Msun

B stars dominate Dominates emitted

spectrum of star forming regions

t < ~ 300 MyrStarburst99 CSFR models

(Leitherer et al 1999, ApJS, 123, 3)

Mu = 100 Msun UV HMu = 30 Msun UV H


Dust reprocessingIRX-: dust absorption

correlates with UV colourRequires that much of

dust is in a foreground screen or shell near SF

Allows crude dust correction

Different relationships for starburst and normal galaxies

Meurer et al. (1999, ApJ, 521, 64)

Wong et al. (2010 in prep…)

Gil de Paz et al. (2007, ApJS, 173, 185)

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Other HMSF tracersMid-IR Radio continuum

24 8 3.6• 24m + H trace O stars• 8m (PAH) not as good HMSF tracer Calzetti et al. (2007, ApJ, 666, 870)

• Strong linear Radio – FIR correlation• neither trace HMSF well at low L • FIR + FUV should trace HMSF wellBell (2003, ApJ, 586, 794)

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HIPASS, SINGG, and SUNGG HI Parkes All Sky Survey

(HIPASS) HI 21cm Parkes 64m 4315 sources

Survey of Ionization in Neutral Gas Galaxies (SINGG) H & R band CTIO 1.5m 468 sources selected 331 observed

Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) FUV & NUV Galex 0.5m 139 selected ~200 observed


Some resultsAll HI galaxies are

forming starsMultiple emission line

galaxies commonDiverse morphologies

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Meurer et al. 2006, ApJS, 165, 307Hanish et al. 2006, ApJ, 649, 150


Why study extragalactic HMSF?Obvious reasons:

Avoid galactic planeKnown distanceSample large ranges of

Gas densities Abundance Radiation intensity

(extremes esp. important)

HMSF useful forHighlighting dynamicsFinding companions…the most luminous

galaxies..the most distant

galaxiesTracing cosmic

evolution

Probe Physics of HMSF!

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Highlighting dynamics with HMSF

NIR: stellar mass distribution

H: better defined usually

UV: often washed out, but outer disks light up

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Finding companion galaxiesHIPASS J2149-60

HIPASS J1059-09

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The most luminous galaxiesUltra-Luminous Infrared

Galaxies (ULIRGs)Lbol > 1012 Lsun

Highly dust extinctedUsually disturbed or

interacting

Hyper-Luminous Infrared GalaxiesLbol > 1013 Lsun

Mostly known at z > 1Often contain AGNDisturbed morphology

Arp220 HST/ACS

HST/NICMOS

Farrah et al. (2002, 329, 605)

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The most distant galaxiesLyman Break

Galaxiesz > ~1 Need a rest frame

UV spectrum dominated by HMSF

z ~ 8 is state of the art

Can also select in Rest frame FIRRadio

Dickinson (1998, astro-ph/9802064)Bouwens et al. (2010, ApJL, 709, L133)

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Tracing cosmic evolutionHMSF as shorthand

for galaxy evolutionOver 10x decline

since z~1.5 (~7 Gyr ago)Fuel running out?Less accretion?

SFRD from H and UV differ

Hopkins & Beacom (2006, ApJ, 651, 142)

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The Star Formation LawDefinition: the SFR (Msun/year)

given the properties of the ISM

Schmidt (1959, ApJ, 129, 243)

SFR ∝ gn; n ~ 2

Kennicutt (1989, ApJ, 344, 685; 1998, ApJ, 498, 541; Martin & Kennicutt 2001, ApJ, 555, 301)

SFR ∝ gN ; N ~ 1.4

when g > c =Q

Q = /(gG) disk stability

= epicyclic frequency

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Kennicutt (1998) global SFL15

GlobalAnd galaxy centers

SFR ~ 0.4 dex


THINGS SFL results

1. SFR ~ H2 (N = 1.0) Linear relation between molecular gas and SFR

2. Rmol = H2/HI ~ * molecular fraction set by hydrostatic pressure

3. Q(2 Fluids) ~ constant ISM disks maintained at constant stabilityLeroy et al. (2008, AJ, 136, 2782) , Bigiel et al. (2008, AJ, 136, 2846)

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Test with SINGG global fluxes

H/HISFR/HIH2/HIRmolP(!)

Expect 1:1 correlation with R

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X-axis SFR R

rxy 0.76 -0.80 Slope 0.71 0.89 y 0.28 0.27 x 0.40 0.30


SFL Implications

Tighter than the Kennicut SFLFrom optical observations can estimate HI

content to better than a factor of 2Good physical understanding of the results

Star formation in the molecular phase of a pressure regulated disk near critical stability

Stellar disk important for setting the equilibrium pressure

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Some SFL complications from M83…

SF edges not always seen in UV (e.g. Thilker et al. 2005, ApJ, 619, L79)

SFR(UV) traces HI at very low g (Bigiel et al. 2010, ApJ, 720, L31)

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The Initial Mass FunctionDefinition: the mass

distribution of stars formed in a single event

The argument for a constant IMF: Same Salpeter IMF slope seen

where it can be measured well - populous star clusters(Kroupa 2001, MNRAS, 322, 231)

All stars form in star clusters (Lada & Lada, 2003, ARA&A, 41, 57)

(later they disperse…)

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-1)


The H/FUV ratio & the IMF

Ranges by a factor of 10Strongly correlates with optical surface brightnessMost galaxies below expectations for Salpeter (or Kroupa) IMFFrom FUV data: all galaxies should have multiple O stars (Meurer et al. 2009, ApJ, 695, 765)

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A. Low FH/fFUV

HIPASS J0249-02 log (FH/fFUV) = 0.51

log(SFR,H) = -3.28

log(R/R,sun) = 6.87

UGCA44 IB(s)m: log(MHI/Msun) = 8.85 log(LR/LR,sun) = 8.29

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B. High FH/fFUV

HIPASS J0419-54 log(FH/fFUV) = 1.33

log(SFR,H) = -1.21

log(R/R,sun) = 8.70

NGC1566 SAB(rs)bc log(MHI/Msun) = 10.19 log(LR/LR,sun) = 11.09

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Effect of Star Formation HistoryModels of effects of bursting and gasping SFHCSFR + Gaussian increase (burst) or decrease (gasp) in SFRMax/min SFR: 2,10, 100FWHM = 10, 100, 1000 Myr

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Escaping ionizing radiation?Perhaps low H/FUV points are due to escaping ionizing

radiationDirect measurements of escape fraction have only been

attempted in HSB starburstsHowever

LSB galaxies are gas rich Would require naked O stars O stars not seen or rare in CMDs of nearby LSB dwarfs

(e.g. Tolstoy 1996, ApJ, 462, 684; Young et al. 2007, ApJ, 659, 331) But are seen in CMDs of higher SB irregulars

(e.g. Annibali et al. 2008, AJ, 135, 1900)

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Phoenix dI (Young et al. 2007)

NGC4449 (Annibali et al. 2008)


Related resultsBuat et al. (1987, A&A, 185, 33)

use UV + H to suggest possibility of IMF variations in nearby galaxies.

Outer disks H edges not so apparent in UV (Thilker et al 2005, ApJ, 619, L79; Thilker et al. ApJS, 2007, 173, 578; Boissier et al. 2007, ApJS, 173, 524)

Hoversten & Glazebrook (2008, ApJ, 675, 163) use EW(H) versus g-r (SDSS) to infer variable IMF.

Lee et al. (Lee et al. 2009, ApJ,

706, 599) similar results for 11 HUGS

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Field versus clusterAbout 60% of H is

diffuse(Oey et al. 2007, AJ, 661, 801)

>~80% of UV is diffuse(Meurer et al. 1995, AJ, 110, 2665; Larsen 2004, A&A, 416, 537)

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Field: deficient in O starsSpectrum dominated by B stars

(Tremonti et al. 2001, ApJ, 555, 322)

Low H/FUV (Hoopes et al. 2001, ApJ 559, 878)

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Stars don’t form just in clustersTwo modes of star formation

(Meurer et al. 1995, AJ 110, 2665) Bound clusters - prominent Diffuse star formation - dominant

(groups, associations, star clouds)

Lada & Lada (2003) is misleading Based on expansive redefinition of

“cluster” to include unbound objects (groups, associations)

Recent results on Galactic YSOs:(Bresert et al. 2010, MNRAS, arXiv:1009.1150)

Stars form over a wide of densities No clear field vs. cluster distinction 26% of YSOs in dense clusters

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Our scenario Highest mass stars form in bound clusters (Bonnell et al. 2003, MNRAS,

343, 413; 2004, MNRAS, 349, 735; Bonnell & Bate, 2006, MNRAS, 370, 488)

Bound clusters form in dense mol ISM Hydrostatic pressure determines molecular fraction (McKee &

Ostriker 1977, ApJ, 218, 148; Wolfire et al. 2003, ApJ,, 587, 278; Blitz & Rosolowsky 2006, ApJ, 650, 933)

Pressure also determines how well bound star clusters are when formed (Elmegreen & Efremov 2007, ApJ, 280, 235; Elmegreen 2008, ApJ, 672, 1006)

Stars dominate disk plane potential and set hydrostatic pressure

Hence we have the surface brightness IMF correlation:

* P cluster/field O/B H/FUV

Consistent with cluster fraction versus surface brightness (Meurer et al. 1995, AJ, 110, 2665; Larsen 2004, A&A, 416, 537)

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Take Home MessagesHMSF useful for tracing galaxy evolution at all redshiftsResults depend on tracer:

H (P…, 24 m) traces the most massive (O) stars, formed in: Tightly bound clusters Starbursts Spiral density waves

UV (FIR, radio) sensitive to lower mass (O + B) stars: formed in: Clusters or field Outer disks

IMF varies within and between galaxies* is a key parameter for setting SF intensity and effective

IMF Probably by setting the hydrostatic P of the ISM

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Great Barriers in HMSF 2010:Great Barriers in HMSF 2010: 34


Wavelength [Angstroms]

FUV

Ultraviolet Optical

H

Spectrum of starburst galaxy NGC1705 (Meurer et al. 1992, AJ, 103, 60)


SINGG SFL results

X-axis pseudo HI R

rxy 0.59 0.75 slope 1.66 1.01 y 0.50 0.29 x 0.30 0.29Older populations also important for star formation regulation

(cf Dopita & Ryder 1994, ApJ, 430, 163)

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Correlations with tgas ~ 2.3MHI/SFR

X-axis SFR R

rxy -0.75 -0.77 slope -0.77 -0.87 y 0.26 0.28 x 0.33 0.32

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Great Barriers in HMSF 2010: Gerhardt R. Meurer International Centre for Radio Astronomy Research...

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