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What makes galaxies red & dead?
Frank van den BoschUniversity of Utah
In collaboration with:Anna Pasquali (MPIA), Simone Weinmann (MPA)
Houjun Mo (UMass), Xiaohu Yang (SHAO),Dan McIntosh (UMKC), Xi Kang (MPIA)
The Origin of Galaxy Bimodality
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Spheroidal MorphologyOld Stellar Populations
No or Little Cold Gas
Red Colors
Abundant Cold Gas
Young Stellar PopulationsDisk-Like Morphology
Blue colors
Frank van den Bosch University of Utah
Late-Type
The Bi-Modal Distribution of Galaxies
Early-Type
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Spheroidal MorphologyOld Stellar Populations
No or Little Cold Gas
Red Colors
Abundant Cold Gas
Young Stellar PopulationsDisk-Like Morphology
Blue colors
Frank van den Bosch University of Utah
Late-Type
The Bi-Modal Distribution of Galaxies
Early-Type
What is the origin of this bimodality?
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All Galaxies Originally form as Central Disk GalaxiesPARADIGM:
blue
red
Wolf et al. 2003; Bell et al. 2004; Borch et al. 2006
Frank van den Bosch University of Utah
The Standard Paradigm
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In LCDM cosmology dark matter haloes grow hierarchically
A major merger between disk galaxies results in an early-type remnant
There are also several satellite-specific transformation processes
accretion
merging
quenching
sub!halo
central
central
orbit
central
satellite
orbit
satellite
Frank van den Bosch University of Utah
Galaxy Transformations
Strangulation
Ram-pressure stripping
Galaxy harassment
(stripping of hot gas atmosphere)
(stripping of cold gas)
(impulsive encounters with other satellites)
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Frank van den Bosch University of Utah
Outstanding Questions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
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Frank van den Bosch University of Utah
Outstanding Questions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
In particular, we study impact of satellite specific transformationprocesses by comparing satellites to centrals of the same stellar mass.
To address these questions, we constructed a large galaxy group catalogue from the SDSS
This allows us to split galaxy population in centrals and satellites, and to study galaxy properties as function of halo mass
Yang et al. 2005, 2007
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Sats are marginally redder than centrals of same stellar mass
Frank van den Bosch University of Utah
Centrals vs. Satellites
van den Bosch et al. (2008)
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Frank van den Bosch University of Utah
Blue-to-Red Transition Fractions
van den Bosch et al. (2008)
Roughly 40% of sats that are blue at accretion undergo transition
Above 10 h Msun majority of sats were already red at accretion
The red fraction of sats is higher than that of centrals of same M_star
Satellite transformation processes are only important at low M_star
10 -2
f_tr|rs
f_tr|s,bc
f_tr|s
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Color Difference is independent of halo mass of satellite
Transformation efficiency is independent of halo mass of satellite
Strangulation is main satellite-specific transformation process
Frank van den Bosch University of Utah
Dependence on Halo Mass
van den Bosch et al. (2008)
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Satellites Only!!!
Frank van den Bosch University of Utah
Satellite Ecology
van den Bosch et al. (2009)
At fixed stellar mass the average satellite coloris independent of halo mass
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The Dearth of Environment Dependence
Satellite color distribution depends strongly on stellar mass,but only very weakly on halo mass (environment)
colors
Frank van den Bosch University of Utah
van den Bosch et al. (2009)
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Satellite concentration distribution depends strongly on stellar mass,but is virtually independent of halo mass (environment)
concentrations
Frank van den Bosch University of Utah
The Dearth of Environment Dependence
van den Bosch et al. (2009)
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low concentration systems:
high concentration systems:
Centrals are brighter and bluer,especially at larger radii.
Surface photometry of centralsand satellites indistinguishable.
Independent of concentration, centrals and satellites have the
same average stellar surfacedensity, consistent with satellites
being quenched centrals.
Frank van den Bosch University of Utah
Density distributions of centrals and satellites
Weinmann et al. 2009
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Frank van den Bosch University of Utah
Modeling Strangulation
In standard SAMs, hot halo is instantaneously removed;results in red satellite fraction that is too large...
see also Weinmann et al. (2006) and Baldy et al. (2006)
Kang & van den Bosch (2008)
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Frank van den Bosch University of Utah
Modeling Strangulation
Delaying hot gas removal reduces red satellite fraction,but increases blue fraction of massive centrals.....
Mhot(t) = Mhot(tacc)e!(t!tacc)/!
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If significant fraction of low mass satellites is tidally disrupted before being accreted by central, data can be fit satisfactory
Half of orphans with M! < 1010h"1M#tidally disrupted
Frank van den Bosch University of Utah
Modeling Strangulation
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Frank van den Bosch University of Utah
The Fate of Satellite Galaxies
Symbols: group catalogueLines: model predictions
Use unevolved subhalo mass function to predict CLF of satellites, under the assumption that CLF of centrals does not evolve with redshift
Yang, Mo & vdB (2009)
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Frank van den Bosch University of Utah
The Fate of Satellite Galaxies
Symbols: group catalogueLines: model predictions
Use unevolved subhalo mass function to predict CLF of satellites, under the assumption that CLF of centrals does not evolve with redshift
Yang, Mo & vdB (2009)
Model overpredicts number of satellites, especially in low mass haloes.Satellites have to be (tidally) destroyed, or be accreted by centrals.
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Frank van den Bosch University of Utah
The Fate of Satellite GalaxiesWe fit CLF of satellites assuming a survival fraction that only depends
on ratio of subhalo mass (at time of accretion) and halo mass.
Yang, Mo & vdB (2009)
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Frank van den Bosch University of Utah
The Fate of Satellite GalaxiesWe fit CLF of satellites assuming a survival fraction that only depends
on ratio of subhalo mass (at time of accretion) and halo mass.
More massive subhaloes (and their satellites) are less likely to survive.Consistent with dynamical friction efficiency increasing with subhalo mass.
Yang, Mo & vdB (2009)
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Frank van den Bosch University of Utah
The Fate of Disrupted Satellite Galaxies
In massive haloes, the stellar mass in non-surviving satellites is several times larger than stellar mass of central galaxy.
Consequently, most of the non-surviving satellites have to be disrupted, giving rise to a significant stellar halo.
centrals
non-survivorssurviving satellitesun-evolved
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Frank van den Bosch University of Utah
The Fate of Disrupted Satellite Galaxies
In massive haloes, the stellar mass in non-surviving satellites is several times larger than stellar mass of central galaxy.
Consequently, most of the non-surviving satellites have to be disrupted, giving rise to a significant stellar halo.
centrals
non-survivorssurviving satellitesun-evolved
Satellite disruption is important ingredient for galaxy formation.(see also Monaco et al. 2006 & Conroy et al. 2007)
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The Amount of Intra-Cluster Light
Predicted amount of ICL consistent with observationsYang, Mo & vdB (2009)
Gonzales et al. (2007)data taken from
Frank van den Bosch University of Utah
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Frank van den Bosch University of Utah
Conclusions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
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Frank van den Bosch University of Utah
Conclusions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
From 70% for satellites with M_star = 10 Msun, to 0% for the most massive satellites
9
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Frank van den Bosch University of Utah
Conclusions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
From 70% for satellites with M_star = 10 Msun, to 0% for the most massive satellites
9
Strangulation...but needs to be better understood.Also, tidal disruption seems to be important...
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Frank van den Bosch University of Utah
Conclusions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
From 70% for satellites with M_star = 10 Msun, to 0% for the most massive satellites
9
Strangulation...but needs to be better understood.Also, tidal disruption seems to be important...
In all halos of all masses...
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Frank van den Bosch University of Utah
Conclusions
Which transformation process is most important?
What fraction of the red-sequence satellites underwent theirtransformation as a satellite?
In what environment (dark matter halo) do galaxies undergotheir transformation?
To what extent are satellite-specific transformation processesresponsible for environment dependence of galaxy population?
From 70% for satellites with M_star = 10 Msun, to 0% for the most massive satellites
9
Strangulation...but needs to be better understood.Also, tidal disruption seems to be important...
In all halos of all masses...
There is no environment dependence....
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Frank’s hot advice:
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Stop fiddling around with environment dependence; try to understand the stellar mass dependence
of galaxy properties instead
Frank’s hot advice: