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 2dFGRSRed – 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 DR5Parent 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

Morphological classification

Choi & Park, 2005, ApJ 635, L29

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 galaxiesSeyferts

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)

6-line AGN Classification

Constantin, Hoyle, & Vogeley 2007 “AGN in Void Regions”

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 Voids

Void 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 galaxies

N-body + Semi-Analytic Models (Benson et al. 2003)Specialized void simulations (Goldberg & Vogeley 2004)