kevin bundy

Kevin Bundy, Caltech

The Mass Assembly History of Field

Galaxies: Detection of an Evolving Mass Limit for Star-Forming Galaxies

Kevin BundyR. 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

Submitted to ApJ, astro-ph/0512465


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 ObservationsSurveys to z < 2: Cowie et al. 1996, Brinchmann & Ellis 2000, Bell et al. 2005 COMBO17, Bauer et al. 2005, Juneau et al. 2005, …

Juneau et al. 2005

Treu et al. 2005

Other methods: Treu et al. 2005, van der Wel et al. 2005, Heavens et al. 2005, Jimenez et al. 2005, …

HigherSFR


Downsizing in Theory


Galaxy Transformation:Mergers fuel AGN which expel gas and prevent further star formation.

But, merging is hierarchical, driven by DM assembly.

Redshift z

DownsizingThreshold

Springel et al. 2004

Simulated Disk Merger with AGN Feedback

age

Partial Solution: AGN feedback

(Croton et al 2005)

The fundamental problem…


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.


The DEEP2 Redshift + Palomar K-band Survey

• 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

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

GOAL: Chart galaxy evolution as a function of M* over a wide range of environments


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


Results:Galaxy

Stellar Mass Function

Partitioned by restframe (U-B) color into blue

(active) and red (quiescent) populations.

Mass

Nu

mb

er

Den

sity

• Little total evolution


Results:Galaxy




Mass


• Assembly of early-types without dry merging

Nu

mb

er

Den

sity


Results:Galaxy




Mass


• Assembly of early-types without dry merging

• Evolving transition mass

Nu

mb

er

Den

sity


Assembly of Red, Early-types

Mass

Increasing abundance


Assembly of Red, Early-types

de Lucia et al. 2005

Possible problems in models

Mass

>1010 M

>1011 M


Mass

Key Result: Quenching Threshold Mass

Decreasing abundance


Evolution of MQ

SF = Tot exp (M*/MQ)

Key Result: Quenching Threshold Mass

Mass

Provides key test for downsizing scenarios


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.



• 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

ExtremeLow Density

ExtremeHigh Density

Second CutIn

EnvironmentalDensity



Mass

Low Density



Mass

Low/High Density



Mass

• Moderate dependence on density

• Downsizing accelerated in dense regions

Low/High Density


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

• 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

Documents