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A Multi-Wavelength Census of Star Formation at Redshift z ~ 2


Reddy, Naveen Ananta (2006) A Multi-Wavelength Census of Star Formation at Redshift z ~ 2. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9FXD-QX54.


We examine the census of star-forming galaxies and their extinction properties at redshift z ~ 2, when a large fraction of the stellar mass in the universe formed. We find a good agreement between the X-ray, radio, and de-reddened UV estimates of the average star formation rate (SFR) for our sample of z ~ 2 galaxies of ~ 50 M yr⁻¹, indicating that the locally calibrated SFR relations appear to be statistically valid from redshifts 1.5 ≾ z ≾ 3.0. Spitzer MIPS data are used to assess the extinction properties of individual star-forming galaxies, and we find that the rest-frame UV slope of most galaxies at z ~ 2 can be used to infer their attenuation factors, Lbol/LUV. As in the local universe, the obscuration, LFIR/LUV is strongly dependent on bolometric luminosity, and ranges in value from < 1 to ~ 1000 within the sample considered. However, the obscuration is ~ 10 times smaller at a given Lbol (or, equivalently, a similar level of obscuration occurs at luminosities ~ 10 times larger) at z ~ 2 than at z ~ 0. This trend is expected as galaxies age and their gas becomes more dust-enriched. Specific SFRs indicate wide range in the evolutionary state of galaxies at z ~ 2, from galaxies that have just begun to form stars to those that have already accumulated most of their stellar mass and are about to become, or already are, passively evolving. Finally, we examine two techniques for assessing the census of galaxies at z ~ 2. In the first, we select galaxies using optical, near-IR, and sub-mm criteria, and find a large overlap between optical and near-IR selected samples of galaxies at z ~ 2. The second technique involves reconstructing the luminosity function of z ~ 2 galaxies as determined from Monte Carlo simulations. We find that the SFR density increases between z = 4 to 2 by a factor of ~ 1.2. However, this increase is mild compared to the much steeper increase from z ~ 6 to z ~ 4, suggesting that the processes responsible for the increase in SFR density at early epochs saturate around z ~ 2.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:High redshift galaxies
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astrophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Steidel, Charles C.
Group:Astronomy Department
Thesis Committee:
  • Scoville, Nicholas Zabriskie (chair)
  • Blain, Andrew W.
  • Kamionkowski, Marc P.
  • Sargent, Wallace L. W.
  • Steidel, Charles C.
Defense Date:15 May 2006
Non-Caltech Author Email:naveen.reddy (AT)
Additional Information:Title listed in 2006 commencement program -- A Multi-Wavelength Census of Star Formation at Redshifts z Equals 2 -- differs from title listed in thesis file (PDF).
Record Number:CaltechETD:etd-05172006-133633
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 2. adapted for Chapter 3. adapted for Chapter 4. adapted for Chapter 5.
Reddy, Naveen Ananta0000-0001-9687-4973
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1846
Deposited By: Imported from ETD-db
Deposited On:22 May 2006
Last Modified:19 Feb 2020 23:27

Thesis Files

PDF (nar_thesis.pdf) - Final Version
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