xiaohu yang shanghai astronomical observatory partner group of mpa collaborators: yu wang (shao),...
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Xiaohu Yang
Shanghai Astronomical Observatory
Partner group of MPA
Collaborators: Yu Wang (SHAO), H.J. Mo (UMass), F.C. van den Bosch (MPIA), Neal Katz (UMass), A. Pasquali (MPIA), D.H. McIntosh (UMK), S. Weinmann (MPA), etc.
The 4500 faintest galaxies
With M_r>-17.05, dwarf galaxies There are a significant fraction of red dwarf galaxies. Where are they? What makes them red?
Galaxy groups in the SDSS DR4 (Yang et al. 2007)Sky coverage: 4514 deg^2
Galaxies with redshifts: 369447 (408119)
Groups selected: 301237 (300049)
Galaxies are grouped according to their common halos Halo mass is assigned for each group The most massive galaxy is defined as the central galaxy
The environment of red dwarf galaxies
Satellite galaxies (45%) They are in massive halos
Central galaxies (55%) They are in small halos They are at r_p/r_200 to a nearest more massive halo.
(1) 20% red dwarfs are not randomly distributed
(2) Additional galaxies seem randomly distributed
The distribution of red dwarf galaxies
Wang et al. 2009
(1) 20% red w.r.t. the dwarfs of similar stellar masses
(2) 20% blue
(3) 20% random
(4) 20% high concentration
What about other population dwarfs?
Wang et al. 2009
Only the red dwarfs have the radial dependent distribution
Wang et al. 2009
The distribution of other population dwarfs
The nearest neighbor dependent
Wang et al. 2009
The red dwarfs near more massive halos have stronger radial dependence
Test against the N-body simulation
Wang et al. 2009
(1) Case 1: contamination
(2) Case 2: randomly distributed
(3) Case 3: depends the distance to the nearby more massive halo
Summary and discussion There are about 70% central dwarf galaxies
About ¼ of them are red according to bimodal color distribution
These red central dwarf galaxies are not randomly distributed They are preferentially distributed around massive halos There is also a background distribution.
The dependence does not exist for high concentration dwarf galaxies.
The formation of red dwarf galaxies Massive halo environment, quenches the star formation Other mechanism that quenches the star formation in small halos
(in low density regions)