Voids size distribution in the 2dFGRS Volker Müller, Benda-Beckmann Sander von AIP • Voids finder and void sizes • Analysis of 2dF: self-similar distribution • Faint galaxies in.
Download ReportTranscript Voids size distribution in the 2dFGRS Volker Müller, Benda-Beckmann Sander von AIP • Voids finder and void sizes • Analysis of 2dF: self-similar distribution • Faint galaxies in.
Voids size distribution in the 2dFGRS Volker Müller, Benda-Beckmann Sander von AIP • Voids finder and void sizes • Analysis of 2dF: self-similar distribution • Faint galaxies in 2dF voids • Comparison with SAM of Millenium simulation 06.11.2015 Amsterdam Workshop 1 Void definition • 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 N2 • 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) 06.11.2015 Amsterdam Workshop 2 Void search M., Arbabi, Einasto, Tucker, 00 & 02 LCRS & CDM-mock samples M. & Maulbetsch 04 SDSS 100 Mpc/h yellow: void search including extensions, red: base voids 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 M* D / Mpc/h 06.11.2015 Amsterdam Workshop 3 Void statistics percentile sizes D25 , Dmed , D75: Dp D0 form samples with mean separation , e.g. diffent random dilution or different magnitude cuts: 06.11.2015 Amsterdam Workshop 4 SDSS equatorial slices x D/ x f expx 2 /a2 , a 3 ax 1 Poisson 06.11.2015 SDSS void hierarchy: broad differential size distribution Amsterdam Workshop 5 2dF volume limited samples sample area z Blim V / 106 Mpc3/h3 Mpc/h 1 .05-.1 -18.5 .8 1.3 4.4 5.4 7 18 2 .1-.14 -19 1.1 2.4 5.8 6.3 55 51 3 .14-.2 -20 4.7 7 9.4 10 196 246 Nvoid D>20 Mpc/h galaxies 2x3 volume limited samples: k+e-correction 6000 to 10000 galaxies each uniform completeness threshold: c > 0.6 75% of galaxies 5% of sky surface undersampled 06.11.2015 5.5 rsp. 7.5 deg thickness Amsterdam Workshop (15 - 70 Mpc/h) 6 2dF versus Millenium SAM Blim = -20 06.11.2015 Springel et al., Croton et al. Amsterdam Workshop 7 Abundance of 2dF voids by number yellow: void search including extensions, red: base voids voids up to radius of 26 Mpc/h 06.11.2015 Amsterdam Workshop 8 2dF size distribution f expD/ (D/3)3 void size distribution without extensions strong dependence on samples compare Hoyle & Vogele 04 06.11.2015 Amsterdam Workshop 9 Scaling of 2dF size distribution = 18 Mpc/h = 4 Mpc/h Void size quartiles lie on tight linear relations: Dp D0 06.11.2015 = 0.4, 0.8, 1.3 for 25-, med, & 75 percentile Amsterdam Workshop 10 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 06.11.2015 Amsterdam Workshop 11 N/SGP2 versus 500 Mpc/h box Sampples with B < -18, 19, -20, -21 60% dilutions redshift survey mask real 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 06.11.2015 Amsterdam Workshop 12 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 06.11.2015 Amsterdam Workshop 13 Void scaling Voids among fainter galaxies have larger relative size P0 (R) 06.11.2015 F( D) expD/ (D/b)3 b3 4 2 3 f (D)(R D/2) /D dD Amsterdam Workshop 14 Void size distribution for different objects D D0 Self-similarity of voids among different objects: galaxies, groups and clusters 2dF/SDSS LCRS 06.11.2015 groups Amsterdam Workshop 15 Void size evolution Size evolution of voids in small (left) and large halos (right) Evolution of radial void profiles 06.11.2015 Amsterdam Workshop Arbabi, M. 03 16 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? 06.11.2015 Amsterdam Workshop 17 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 06.11.2015 Amsterdam Workshop 18 Void galaxies 06.11.2015 2df millenium Amsterdam Workshop 19 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 06.11.2015 Amsterdam Workshop 20 Void galaxies central void galaxies environment Continuous transition from field to void galaxies: higher star formation rates galaxy fraction with low bulge fraction reduced 06.11.2015 Amsterdam Workshop 21 void filling factor • 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 06.11.2015 Amsterdam Workshop 22