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Transcript 
Galaxies within
Dark Matter Halos
Michael Brown
(Monash University)
Image stolen from Millennium Run Collaboration
Why?
• How does HI vary with halo mass?
• Virial shocking heating
• AGN feedback (this can be detected by EMU)
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Does HI vary with location within halos?
When is gas removed from satellite galaxies?
When is gas heated in central galaxies?
What is the role of mergers in galaxy growth?
How are populations connected?
Similar questions for AGNs and stellar mass.
SF/HI varies with DM mass
Rapid galaxy merging
SF/HI varies with stellar mass
Long lived satellite galaxies
SF/HI varies with DM mass
Rapid galaxy merging
SF/HI varies with stellar mass
Long lived satellite galaxies
Simulations performed at the National Center for Supercomputer Applications
by Andrey Kravtsov (The University of Chicago) and Anatoly Klypin (New Mexico State University).
Visualizations by Andrey Kravtsov.
How?
• Clustering of DM halos is known.
• Space density of DM halos is known.
• The clustering and space density of galaxies
constrains models of how galaxies populate halos.
• Halo Occupation Distribution (HOD) modelling.
• Conditional Luminosity Function (CLF) modelling.
• Large-scale clustering constrains halo mass.
• Small-scale clustering constrains galaxies per halo.
• More constraints and tests from cross-correlations.
HIPASS
• Wyithe, Brown, Zwaan & Meyer (2009).
• Small fingers-of-god imply high halo mass cutoff.
• Small fraction of satellite galaxies.
Redshift
Excess galaxy pairs
c/w random distribution
Redshift space clustering
Projected Distance (Mpc/h)
Projected Distance (Mpc/h)
Light from galaxies
Brown et al. (2008)
The Bootes Field
Real z~0.9 galaxies
& 3 CDM simulations
populated using the
HOD
Brown et al. (2008)
Summary
• We can determine how galaxies populate DM
halos using galaxy clustering.
• Determining how galaxies populate halos
provides insights into galaxy formation:
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Mode of growth (mergers, star formation).
Regulation star formation (AGN, starvation)
Stripping and heating of cold gas.
Connections between galaxy populations.
Angular correlation function
Red Galaxy Clustering
Angular Scale
Number of galaxies per halo
MB<-18 red galaxies
at 0.4<z<0.6
Brown et al. (2008)
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