1. Voids size distribution in the 2dFGRS
AIP
Volker Müller, Sander von Benda-Beckmann
Voids finder and void sizes
Analysis of 2dF: self-similar distribution
Faint galaxies in 2dF voids
Comparison with SAM of Millenium simulation
Amsterdam Workshop

2. Void definition 2dF voids Void galaxies
smoothed density field or galaxies
underdensity or empty volumes: spheres, ellipsoids, convex on grid
void size distribution provides void probability F(>r) -> P0(r)
void sizes depend on sample -> void hierarchy
2dF voids
count-in-cell study: Croton et al. -> P0(r) as function of N2
void finder of Hoyle, Vogeley -> wall and void galaxies - large voids
Patiri et al. -> abundance of large voids
here: void finder of Kauffmann & Fairall on grid -> fast & ‚complete‘
Void galaxies
much interest, but difficult (low number, wide fields)
Amsterdam Workshop

3. Void search yellow: void search including extensions, red: base voids
M., Arbabi, Einasto, Tucker, 00 & 02
LCRS & CDM-mock samples
M. & Maulbetsch 04
SDSS
yellow: void search including extensions, red: base voids
100 Mpc/h
M << M*
Void filling factor (VFF) or void size distribution, as function of diameter:
f(<D) is fraction of survey volume not contained in voids
Illustation void finder M*
D / Mpc/h
Amsterdam Workshop

4. Void statistics percentile sizes
form samples with mean separation , e.g. diffent random dilution or different magnitude cuts:
voids self-similar as function of relative size
dependence on M-cutoff and sampling fraction
Amsterdam Workshop

5. SDSS equatorial slices
Poisson SDSS
void hierarchy: broad differential size distribution
Amsterdam Workshop

6. 2dF volume limited samplesz
Blim
V / 106 Mpc3/h3 
Mpc/h
Nvoid D>20 1
.05-.1
-18.5
7 18 2
.1-.14
-19
55 51 3
.14-.2
-20
4.7 7
9.4 10
sample
area
galaxies
2x3 volume limited samples:
6000 to galaxies each
5.5 rsp. 7.5 deg thickness
( Mpc/h)
k+e-correction
uniform completeness threshold: c > % of galaxies % of sky surface undersampled
Amsterdam Workshop

7. 2dF versus Millenium SAM
Blim = Springel et al., Croton et al.
Amsterdam Workshop

8. Abundance of 2dF voids by number
yellow: void search including extensions,
red: base voids
voids up to radius of Mpc/h
Amsterdam Workshop

9. 2dF size distribution void size distribution without extensions
strong dependence on samples
compare Hoyle & Vogele 04
Amsterdam Workshop

10. Scaling of 2dF size distribution
 = 18 Mpc/h
 = 4 Mpc/h
Void size quartiles lie on tight linear relations:
 = 0.4, 0.8, 1.3 for 25-, med, & 75 percentile
Amsterdam Workshop

11. N/SGP vs. model
Voids in SAMs of Millenium simulation (Croton et al.) with survey masks:
excellent fit of cumulative void size distribution and scaling relation
Amsterdam Workshop

12. N/SGP2 versus 500 Mpc/h box
Sampples with B < -18, -19, -20, -21
60% dilutions
redshift
real
survey mask
Selection effects: sample size, real vs. redshift space, inhomogeous sampling:
voids in redshift space are 10% larger than in real space
voids in masked fields are 15% smaller than in complete box
Amsterdam Workshop

13. Mock size distribution (Millenium simulation)
void sizes depend on galaxy brightness, voids with max. size 40 Mpc/h
good statistics: For B>-20: 400 (20000) voids larger than 20 (10) Mpc/h
Amsterdam Workshop

14. Void scaling Voids among fainter galaxies have larger relative size
Amsterdam Workshop

15. Void size distribution for different objects
Self-similarity of voids among different objects: galaxies, groups and clusters
2dF/SDSS LCRS
groups
Amsterdam Workshop

16. Void size evolution
Size evolution of voids in small (left) and large halos (right)
Evolution of radial void profiles
Amsterdam Workshop
Arbabi, M. 03

17. Void statistics depends on galaxy sample
bright galaxies define large voids
large voids among faint galaxies have large D / 
faint galaxies define same structures as bright ones
void size distribution mainly parametized by galaxy separation 
parameter b describes cut off: f(r) flat from  to b, b = 3 - 4
selection effects due to finite volume
voids about 20% larger among red than blue galaxies
Void galaxies
special conditions for galaxy formation?
Amsterdam Workshop

18. Void galaxies (voids D > 8 Mpc/h by B < -20 galaxies)
Color distribution fit by sum of two Gaussian (cp. Baldry et al. 04)
similar results for void galaxies in SDSS by Royas et al. (04) and Patiri et al. (06)
here: shift of the blue maximum
Amsterdam Workshop

19. Void galaxies
2df
millenium
Amsterdam Workshop

20. Void galaxies
Weak influence of void environment on spectral parameter 
Similar results for 2dF by Croton et al. (05) for underdense regions on 8 Mpc/h
abundance of passive galaxies reduced especially among brighter magnitude bin
Amsterdam Workshop

21. Void galaxies Continuous transition from field to void galaxies:
central void galaxies
environment
Continuous transition from field to void galaxies:
higher star formation rates
galaxy fraction with low bulge fraction reduced
Amsterdam Workshop

22. void filling factor 2dF vs. simulation Void galaxies
self-similar distribution
median void size covering 50% of volume quite small: 5 Mpc/h + 
maximum voids depend on survey volume: exponential cut-off at 3-5 
void size distribution provides void probability: F(>r) <-> P0(r)
2dF vs. simulation
size distribution in excellent agreement with mock samples
Void galaxies
similar bimodality of blue and red galaxies as in the field
fraction of red galaxies reduced, blue increased
effect stronger for voids among bright galaxies
weak effect: blue shift of the colors of blue galaxies
Amsterdam Workshop