Transcript Palomar JK Imaging in the EGS

The Mass Assembly History of Field Galaxies:
Detection of an Evolving Mass Limit
for Star-Forming Galaxies
Submitted to ApJ, astro-ph/0512465
Kevin Bundy
R. S. Ellis, C. J. Conselice, J. Taylor,
M. Cooper, C. Willmer, B. Weiner, P.
Eisenhardt, K. Noeske, A. Coil,
DEEP2 Team
Galaxies and Structures through Cosmic Time,
Venice
March 2006
Kevin Bundy, Caltech
Downsizing In Words
The sites of active star formation shift from
high-mass galaxies at early epochs (z~1-2)
to low-mass galaxies as a function of
cosmic time.
Term coined by Cowie et al. 1996
Kevin Bundy, Caltech
Downsizing In Observations
Surveys to z < 2: Cowie et al. 1996, Brinchmann & Ellis 2000, Bell
et al. 2005 COMBO17, Bauer et al. 2005, Juneau et al. 2005, …
Higher
SFR
Treu et al. 2005
Other methods: Treu et al. 2005,
Juneau et al. 2005
van der Wel et al. 2005, Heavens et
al. 2005, Jimenez et al. 2005, …
Kevin Bundy, Caltech
Downsizing in Theory
Simulated Disk Merger with AGN Feedback
Galaxy Transformation:
Mergers fuel AGN which expel
gas and prevent further star
formation.
Springel et al. 2004
Partial Solution: AGN feedback
The fundamental problem…
Downsizing
Threshold
age
But, merging is
hierarchical,
driven by DM
assembly.
Redshift z
(Croton et al 2005)
Kevin Bundy, Caltech
Possible Explanations
1. Local Environment:
Massive galaxies live in dense environments that
mature more rapidly: ram pressure stripping,
encounters, harassment.
2. Internal Physics:
Physical processes (AGN, SF) within galaxies
depend on both mass and redshift.
Kevin Bundy, Caltech
QuickTime™and a
TIFF(Uncompressed) decompressor
are needed to see this pi cture.
The DEEP2 Redshift +
Palomar K-band Survey
GOAL: Chart galaxy evolution as a function of M* over a
wide range of environments
•
DEEP2: 40,000 spec-z’s from DEIMOS on Keck II
80 Keck nights, z<1.5 over 3 deg2, R < 24.1
Spread over 4 fields, including the EGS
•
Palomar K-band: 65 nights with WIRC on 200 inch
1.5 deg2 to K=20, 0.2 deg2 to K=21
•
Combined: 12,000 redshifts with K-band detections
Kevin Bundy, Caltech
Key Physical Properties
1. SFR Indicator
•
(U-B) Restframe Color, C. Willmer
•
[OII] Equivalent Width, B. Weiner
•
Morphology (from GOODS, Bundy et al. 2005)
2. Stellar Mass
•
Palomar K-band, multi-band SED fitting
3. Environmental Density
•
3rd nearest neighbor, M. Cooper
Spectroscopic Redshifts and IR are essential
Kevin Bundy, Caltech
Results:
Galaxy Stellar
Mass Function
Number Density
Partitioned by
restframe (U-B)
color into blue
(active) and red
(quiescent)
populations.
•
Mass
Little total evolution
Kevin Bundy, Caltech
Results:
Galaxy Stellar
Mass Function
Number Density
Partitioned by
restframe (U-B)
color into blue
(active) and red
(quiescent)
populations.
Mass
•
Little total evolution
•
Assembly of earlytypes without dry
merging
Kevin Bundy, Caltech
Results:
Galaxy Stellar
Mass Function
Number Density
Partitioned by
restframe (U-B)
color into blue
(active) and red
(quiescent)
populations.
Mass
•
Little total evolution
•
Assembly of earlytypes without dry
merging
•
Evolving transition
mass
Kevin Bundy, Caltech
Assembly of Red, Early-types
Increasing abundance
Mass
Kevin Bundy, Caltech
Assembly of Red, Early-types
Increasing abundance
Mass
Kevin Bundy, Caltech
Assembly of Red, Early-types
Increasing abundance
Mass
Kevin Bundy, Caltech
Assembly of Red, Early-types
Possible problems in models
>1011 M
>1010 M
de Lucia et al. 2005
Mass
Kevin Bundy, Caltech
Key Result: Quenching Threshold Mass
Decreasing abundance
Mass
Kevin Bundy, Caltech
Key Result: Quenching Threshold Mass
Decreasing abundance
Mass
Kevin Bundy, Caltech
Key Result: Quenching Threshold Mass
Decreasing abundance
Mass
Kevin Bundy, Caltech
Key Result: Quenching Threshold Mass
SF = Tot exp (M*/MQ)
Evolution of MQ
Provides key test for
downsizing scenarios
Mass
Kevin Bundy, Caltech
Other Indicators of Star Formation
Kevin Bundy, Caltech
Other Indicators of Star Formation
• SF cut is median of mid-z bin. More stringent so more early types,
fewer late. SF increases in high-z bin.
Kevin Bundy, Caltech
Other Indicators of Star Formation
• SF cut is median of mid-z bin. More stringent so more early types,
fewer late. SF increases in high-z bin.
• Morph from Bundy et al. 2005 GOODS study. Slower to respond.
Not equivalent to color or SFR.
Kevin Bundy, Caltech
Extreme Environments
Extreme
Low Density
Extreme
High Density
Second Cut
In
Environmental
Density
Kevin Bundy, Caltech
Extreme Environments
Low Density
Mass
Kevin Bundy, Caltech
Extreme Environments
Low Density
Mass
Kevin Bundy, Caltech
Extreme Environments
Low/High Density
Mass
Kevin Bundy, Caltech
Extreme Environments
Low/High Density
• Moderate dependence
on density
• Downsizing accelerated
in dense regions
Mass
Kevin Bundy, Caltech
Summary & Conclusions
•
Intermediate to high mass galaxies assembled by z~1, but
demographics of population changes
•
Early appearance of massive early-types: a continuing
problem for models; dry merging not needed
•
Quenching of SF seems to produce downsizing,
transformation follows, quantify with Mtr and MQ
•
No density dependence in average environments - weak
in the extremes
•
Quenching caused by internal mechanism, possibly AGN?
MQ provides constraints
Kevin Bundy, Caltech
Future Work
• Probe the mass function at lower
masses and higher redshift
• Study galaxies in the midst of transition:
test the merger/AGN scenario directly
Kevin Bundy, Caltech