Galaxy Growth: The role of environment

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Galaxy Growth The role of environment
Sept 17th, Galaxies in Real Life Simulations

• Simone Weinmann (MPA Garching)
• Collaborators Guinevere Kauffmann, Frank van den
  Bosch,
• Anna Pasquali, Dan McIntosh, Xiaohu Yang, Houjun
  Mo

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Environment affects galaxy evolution
Distinguish centrals and satellites centrals are
the most massive galaxy in their group.
Many environmental processes have been proposed.
Perhaps the most natural one is starvation (or
strangulation) Infalling gas is mainly accreted
by the central galaxy. Satellites galaxies
(slowly) starve. This is the only environmental
process currently included in semi-analytical
models. Is this good enough? What about the
morphology-density relation? What about stripping
of ISM, harassement... ?
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The SDSS DR4 group catalogue(Yang et al. 07)
Iterative group finder (Yang et al. 2005)
Method has been carefully tested using Mock
Galaxy Redshift Surveys constructed with the
Conditional Luminosity Function. Our sample
280,000 galaxies in 50,000 groups.
Group masses estimated using the summed stellar
mass for each group.
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Relation between morphology and environment
revisited
Environment quantified to first order by
distinguishing satellite and central galaxies in
the group catalogue. Morphological indicator
Concentration (R90/R50)
Satellites more concentrated than centrals _at_
fixed stellar mass.
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Relation between morphology and environment
revisited
Environment quantified to first order by
distinguishing satellite and central galaxies in
the group catalogue. Morphological indicator
Concentration (R90/R50)
Satellites more concentrated than centrals _at_
fixed stellar mass. However Fraction of galaxies
with Cgt3 is the same!

Ellipticals are not produced by environmental
processes acting on satellites
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Average radial profiles of SDSS galaxies
bright
The average surface brightness profiles of Clt3
galaxies (with log(M)10.9) show Satellites
are fainter, and more so towards
out- skirts. Explains increased C. What is the
origin of this difference?
faint
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Average radial profiles of SDSS galaxies
red
The average colour profile of the same galaxies
show Colours of satellite galaxies
redder across the disk. Central
bulge-dominated region is unchanged.
T
blue
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Average radial profiles of SDSS galaxies
Average stellar mass profiles show Mass
distribution in satellites and centrals is very
similar. No major rearrangement of mass
distribution by environmental process
-gt evidence against harassement, tidal
stripping, disk instabilities.
T
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Average radial profiles of SDSS galaxies
Average stellar mass profiles show Mass
distribution in satellites and centrals is very
similar. No major rearrangement of mass
distribution by environmental process
-gt evidence against harassement, tidal
stripping, disk instabilities.
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Process affecting star formation can explain
environmental dependencies of galaxy
concentration!
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Ram-pressure stripping of ISM vs. starvation
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Ram-pressure stripping of ISM vs. starvation
Starvation Affects fuel for future star
formation. Star formation decreases slowly ( 2
Gyr)
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Ram-pressure stripping of ISM vs. starvation
Ram pressure stripping of ISM Affects fuel for
current star formation. Leads to fast decline of
SF in affected regions.
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How fast does the star formation decline? We
model colour profiles using Bruzual Charlot 03
SPS and different SF histories.
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red
Slow (e-folding time 2.5 Gyr) decrease of SFR
reproduces satellite profile well! Colour
difference increases with radius due to stronger
reaction in young parts of galaxy.
data
model infall 9 Gyr ago infall 1 Gyr
ago
blue
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How fast does the star formation decline?
Alternative option Fast truncation of star
formation
Truncation only 1 Gyr ago still leads to colours
which are much too red.
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How fast does the star formation decline?
Alternative option Fast truncation of star
formation
Truncation only 1 Gyr ago still leads to colours
which are much too red.
Environmental processes do not lead to fast star
formation truncation.
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Summary

• Ellipticals not produced by environmental
  effects
• violent environmental processes not needed.
• Remaining concentration differences can be
  explained
• by slowly decreasing SF
• Starvation is dominant environmental process
• and is able to explain what remains of
  "morphology
• - density relation"

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But Starvation is clearly over-efficient in most
SAMs. (Adressed by Font et al. 2008, Guo et al.
in prep)
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