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KNAW colloquium “Cosmic Voids” December 12-15, 2006
Cosmic Voids, Void Galaxies, and Void AGN
Michael S. VogeleyDepartment of Physics
Drexel University
I. Void Finding in Nearby Redshift Surveys
Fiona Hoyle, Danny Pan
II. Morphology-Luminosity-Local Density Relation and Residual Effects at Low Density
Changbom Park, Yun-Young Choi, J. R. Gott, Michael Blanton
III. Active Galactic Nuclei in Voids
Anca Constantin, Fiona Hoyle
Thanks to NSF, NASA, Korea Institute for Advanced Study, Aspen Center for Physics, and KNAW
The Void Finder Algorithm
Procedure:
• Initial classification of galaxies as wall/void galaxies
• Detection of empty cells
• Growth of maximal spheres
• Unification of overlapping voids
• Calculation of void underdensity, profile
Hoyle & Vogeley 2002, ApJ, 566, 641
Goal: identify large voids that are dynamically distinct elements of large-scale structure = “bucket-shaped” voids with flat density profiles and sharp edges, <-0.8
Initial Classification of Void vs. Wall Galaxies
7h -1 Mpc
7h -1 Mpc
Void Galaxy
Wall Galaxy
If d3>7h-1 Mpc, then /<-0.6
Then grow maximal spheres bounded by wall galaxies
Voids in the PSCz SurveyYellow – voidsRed – void centersBlue – wall galaxies
Largest void = 17.85 Mpc/h
Average (of rmin = 10 Mpc/h) = 12.4 +/- 1.7
Nearly identical results for UZC.
Same voids found in IR-selected PSCz and optically-selected UZC.
Hoyle & Vogeley 2002, ApJ, 566, 641
Voids in the 2dFGRS
Red – void centersBlack – wall galaxies
289 voids in total (zmax=0.1)
Largest void radius =19.85 Mpc
Average(r > 10) =12.4 +/- 1.9 Mpc
Similar to PSCz and UZC results
Hoyle & Vogeley 2004, ApJ, 607, 751
Void Size Distributions in 2dF
No detected variation of size distributions between N and S or with redshift.
WFMOS on Subaru 8m could detect evolution of voids and measure q0.
Voids in Simulations
VoidFinder applied to “galaxies” in simulations
Radii of voids match sharp boundaries of voids seen in both galaxies and dark matter
Density within voids nearly constant, reaches mean at nearly twice void radius
Benson, Hoyle, Torres, & Vogeley 2003, MNRAS 340, 160
SDSS DR5
• Spectroscopy of 675,000 galaxies
• Covers 5740 sq deg
• Imaging of 8000 sq deg (imaging of NGC region now complete)
Voids in SDSS DR5
Parent galaxy sample:
r<17.77, z<0.107, area = 5000 sq deg, 394,984 galaxies (after boundary cuts)
Volume-limited sample:
density field from 61,084 galaxies, M<-20.0
Results of voidfinder:
617 voids R>10 Mpc/h
40,635 void galaxies r<17.77 (10% of galaxies are in voids)
Hoyle, Pan, Vogeley et al. 2007
QuickTime™ and aGIF decompressor
are needed to see this picture.
Intersection of Voids with 10 h-1 Mpc Slices
Hoyle, Pan, Vogeley et al. 2007
Results on Void Finding
Void distributions of 2dFGRS, PSCz, UZC, and SDSS agree; void properties are robust
No detected evolution of void size with redshift in nearby universe Voids are on average ~12 h-1 Mpc in radius, but largest void larger in
larger surveys? Filling factor 40% at density contrast Density profiles plateau in center to = -0.95 Voidfinder appears to detect dynamically distinct elements of large-
scale structure (peaks in initial gravitational potential, outflows in velocity, sharp boundaries in density)
II. The Morphology-Luminosity-Local Density Relation
and Residual Environmental Effects
Park, Choi, Vogeley, Gott, & Blanton 2007, ApJ, accepted, astro-ph/0611610
REMINDER: Earlier papers on photometric and spectroscopic properties of SDSS void galaxies found that void galaxies are fainter, bluer, more disk-like, and have higher specific star formation rates. See
Rojas, Vogeley, & Hoyle 2004a, ApJ, 617, 50, and 2005, ApJ, 624, 571
Hoyle, Rojas, & Vogeley 2005, ApJ, 620, 618
Adaptive smoothing of volume-limited M* sample using spline kernel weighting of nearest Ns=20 galaxies.
Environmental Dependence Using Adaptive Smoothing and Morphological Classification
Volume-limited samplesVolume-limited samples
L*
Bright galaxies added
Extinction, K-correction, L-evolution corrected
NS=20 smoothing NS=200 smoothing
Morphology-LuminosityLuminosity-Local Density Relation
Relation continues down to lowest densities both at ~5 & 12 h-1Mpc scales
Steepening of Efrac() relation on larger scales for fainter galaxies
Morphology-LuminosityLuminosity-Local Density Relation
At fixed L, morphology is a strong function of density
At fixed density, morphology is a strong function of L
Color-magnitude relations
• Early type “red sequence” shifts blueward by 0.025 mag from high to low density
• Late type “blue sequence” shifts blueward by 0.14 mag at low density
Size and environment
Small monotonic dependence of size on local density for all galaxies except the brightest E’s.
Galaxies in voids are slightly smaller: M=-19.7 galaxies are 8% smaller at the lowest density, for both early and late types (but possible sky subtraction error?).
Star formation rates (H)
At fixed morphology (early vs. late) and luminosity, very small dependence of SFR on local density: log[W(H)]=1.466-0.046 log(1+) for M=-18.9 galaxies, weaker for brighter galaxies
Early Late
Results on Environmental Dependence Strong local density-morphology-luminosity
relation. Environment matters down to very low density!
At fixed luminosity and morphology, other galaxy properties show only weak dependence on density
Residual effects at low density Color-magnitude shifts blueward, particularly for late
typesSizes of galaxies are smaller Star formation in late types is higher
Morphology-density relation steepens for faint galaxies (for smoothing ~12 h-1 Mpc
III. Active Galactic Nuclei in Voids
Constantin & Vogeley 2006, ApJ 650, 727
Constantin, Hoyle, & Vogeley 2007
Finding AGN among SDSS galaxies
Seyferts
H II
nuclei
LINERs
Transition objects
emission-line
20% of all galaxies are strong line-emitters
52% H II20% (pure) LINERs7% Transition obj’s
5% Seyferts
(Constantin & Vogeley 2006)
AGN Clustering
H IIs: s0= 5.7 0.2 h-1
Mpc less clustered than galaxies
Seyferts: s0= 6.0 0.6
less clustered than galaxies
LINERs: s0= 7.3 0.6 clustered like galaxiesall galaxies: s0= 7.8
0.5
higher peaks in the density field are more clustered
Seyferts & H II’s: - less massive Dark Matter halos
LINERs: - more massive Dark Matter halos
Absolute Magnitude limited samples, -21.6 <M < -20.2
MBH Seyferts < MBHLINERs
MDM halo ~ MBH
(Ferraresse 2002, Baes et al. 2003)
(Constantin & Vogeley 2006)
AGNAGN in Voids: Populations
AGN of all types exist in voids:
(Constantin, Hoyle, & Vogeley 2007)
Fraction in voids
Fraction in walls
Seyferts 1.5% 1.5%
LINERs 2.0% 4.1%
Transition Objects
5.3% 6.4%
H IIs 32.8% 20.8%
• No AGN in bright (L>>L*) void galaxies• Seyferts more frequent among Mr ~ -20 mag void galaxies• otherwise very similar AGN occurrence rate for S’s, L’s, and T’s (but not HII’s!)
fractions
in voidsin walls
Compare at fixed brightness
AGNAGN in voids: accretion activity
•Accretion rates may be lower in void AGN…lower fueling rate?
Log L[O I]/4 Log L[O III]/4
in wallsin voids
• Void galaxies have higher SFR per unit mass (Rojas, Vogeley, Hoyle 2005)
Gas available for forming stars but not driven efficiently to nucleus?
(Constantin, Hoyle, & Vogeley 2007)
Seyferts
LINERs
AGNAGN in voids: local environment
In voids: HII’s have the closest nn, thenTransition, Seyferts, whileLINERs have the farthest nn LINERs most isolated
In walls: LINERs have closest nnHI’s have the farthest nn HII’s most isolated
as measured by nearest neighbor distance
(Constantin, Hoyle, & Vogeley 2007)
NN distance
voids
NN distance
walls
LINERs 5.9 0.6 1.3 0.05
Seyferts 5.8 0.9 1.6 0.1
Transition Objects
4.8 0.4 1.8 0.05
H IIs 4.4 0.2 1.9 0.03
HII’s in poor groups?
LINERs not driven by close interactions
Stellar massBH mass
Accretion rate, [O I] Accretion rate, [O III]
Stellar ages Obscuration
Dist to 3rd neighbor Dist to 1st neighbor
An AGN evolutionary sequence?
I. HII’s - circumnuclear starburst, high accretion but obscured
II. Seyferts - waning SF, brief breakout of accretion emission
III. Transition obj’s - aging stellar pop, accretion weaker
IV. LINERs - older stellar pop, minimal accretion, fuel exhausted
Results on Void AGN
• All types of AGN are found in voids, though 50% fewer LINERs and 50% more HII’s
• No AGN in the brightest void galaxies• Excess of Seyferts in ~L* void galaxies• Possible lower accretion rate in void AGN• Local environments (nearest neighbor) of AGN
types are opposite in voids/walls• Are void AGN (and their hosts) at an earlier stage
in an evolutionary sequence?
Publications about nothingMethods for void finding
VoidFinder (Hoyle & Vogeley 2002, 2004)
Statistics of VoidsVoid Probability Function (Hoyle & Vogeley 2004)
Properties of observed void galaxies Photometry (Rojas, Vogeley, Hoyle 2004)Spectroscopy (Rojas, Vogeley, Hoyle 2005)Luminosity Function (Hoyle, Rojas, Vogeley 2005)Mass function (Goldberg et al. 2005)Metallicity (Hao et al. 2007, in prep)AGN in voids (Constantin, Hoyle, & Vogeley 2007)Environmental dependence (Park, Choi, Vogeley, Gott, & Blanton
2007)
Simulations of void galaxiesN-body + Semi-Analytic Models (Benson et al. 2003)Specialized void simulations (Goldberg & Vogeley 2004)