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The Mass Assembly History of Field Galaxies


Bundy, Kevin A. (2006) The Mass Assembly History of Field Galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3QVQ-FH17.


The work presented in this thesis utilizes the combination of near-IR photometry and spectroscopic redshifts to estimate the stellar masses of distant field galaxies in order to characterize their assembly history since z~1. The primary data set for this analysis comes from an extensive near-IR survey conducted at Palomar Observatory that includes over 12,000 galaxies detected in the Ks-band with DEEP2 spectroscopic redshifts in the range 0.2<z<1.5. Utilizing stellar masses estimated for this sample, little evolution is observed in the galaxy stellar mass function since z~1, indicating that the stellar content of intermediate to high-mass galaxies has largely assembled by this epoch. Significant evolution since z~1 in the characteristics of the galaxy population does take place, however. As a function of time, red early-types--already established at the highest masses at z~1--increase in abundance as star formation shifts to late-type galaxies with lower masses. This pattern is interpreted in the context of "downsizing," and a new mechanism is proposed that is capable of quenching star formation in massive galaxies and driving their morphological transformation into systems with spheroidal configurations.

New diagnostics are introduced to quantify this downsizing behavior including the quenching mass, M_Q, which traces the stellar mass scale above which star formation in galaxies is suppressed. M_Q decreases by a factor of ~5 after z~1, indicating that the quenching mechanism responsible for downsizing becomes more efficient in galaxies with lower masses as a function of time. This evolution is analyzed as a function of environmental density, and no environmental dependence is observed except in the most extreme environments, where downsizing appears to be slightly accelerated in high density regions. This weak environmental dependence suggests that the quenching mechanism for most galaxies is primarily driven by internal processes. The nature of the quenching mechanism is discussed in the context of CDM galaxy formation models, and additional motivation for this comparison is also presented in a direct study of the near-IR merger rate and an analysis of the relationship between stellar mass and dark matter in disk galaxies.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:downsizing; evolution; galaxy; star formation
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astrophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ellis, Richard S.
Group:Astronomy Department
Thesis Committee:
  • Sari, Re'em (chair)
  • Readhead, Anthony C. S.
  • Steidel, Charles C.
  • Scoville, Nicholas Zabriskie
  • Ellis, Richard S.
Defense Date:28 February 2006
Record Number:CaltechETD:etd-03092006-120454
Persistent URL:
Bundy, Kevin A.0000-0001-9742-3138
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:907
Deposited By: Imported from ETD-db
Deposited On:09 Mar 2006
Last Modified:05 Nov 2021 22:57

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