The Mass Assembly History of Field Galaxies:
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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.

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Kevin bundy

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


Downsizing in words

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


Downsizing in observations

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, van der Wel et al. 2005, Heavens et al. 2005, Jimenez et al. 2005, …

Juneau et al. 2005


Downsizing in theory

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

Possible Explanations

Local Environment:

Massive galaxies live in dense environments that mature more rapidly: ram pressure stripping, encounters, harassment.

Internal Physics:

Physical processes (AGN, SF) within galaxies depend on both mass and redshift.


The deep2 redshift palomar k band survey

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


Key physical properties

Key Physical Properties

  • SFR Indicator

    • (U-B) Restframe Color, C. Willmer

    • [OII] Equivalent Width, B. Weiner

    • Morphology (from GOODS, Bundy et al. 2005)

  • Stellar Mass

    • Palomar K-band, multi-band SED fitting

  • Environmental Density

    • 3rd nearest neighbor, M. Cooper

Spectroscopic Redshifts and IR are essential


Results galaxy stellar mass function

Results:Galaxy Stellar Mass Function

Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations.

Number Density

  • Little total evolution

Mass


Results galaxy stellar mass function1

Results:Galaxy Stellar Mass Function

Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations.

Number Density

  • Little total evolution

  • Assembly of early-types without dry merging

Mass


Results galaxy stellar mass function2

Results:Galaxy Stellar Mass Function

Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations.

Number Density

  • Little total evolution

  • Assembly of early-types without dry merging

  • Evolving transition mass

Mass


Assembly of red early types

Assembly of Red, Early-types

Increasing abundance

Mass


Assembly of red early types1

Assembly of Red, Early-types

Increasing abundance

Mass


Assembly of red early types2

Assembly of Red, Early-types

Increasing abundance

Mass


Assembly of red early types3

Assembly of Red, Early-types

Possible problems in models

>1011 M

>1010 M

de Lucia et al. 2005

Mass


Key result quenching threshold mass

Key Result: Quenching Threshold Mass

Decreasing abundance

Mass


Key result quenching threshold mass1

Key Result: Quenching Threshold Mass

Decreasing abundance

Mass


Key result quenching threshold mass2

Key Result: Quenching Threshold Mass

Decreasing abundance

Mass


Evolution of m q

Key Result: Quenching Threshold Mass

Evolution of MQ

SF = Tot exp (M*/MQ)

Provides key test for

downsizing scenarios

Mass


Other indicators of star formation

Other Indicators of Star Formation


Other indicators of star formation1

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.


Other indicators of star formation2

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.


Extreme environments

Extreme Environments

Extreme

Low Density

Extreme

High Density

Second Cut

In

Environmental

Density


Extreme environments1

Extreme Environments

Low Density

Mass


Extreme environments2

Extreme Environments

Low Density

Mass


Extreme environments3

Extreme Environments

Low/High Density

Mass


Extreme environments4

Extreme Environments

Low/High Density

  • Moderate dependence on density

  • Downsizing accelerated in dense regions

Mass


Summary conclusions

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


Future work

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


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