On the Evolution of Field Galaxies

Citation

Hogg, David Wardell (1998) On the Evolution of Field Galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4s4s-gv41. https://resolver.caltech.edu/CaltechTHESIS:09222017-145437571

Abstract

This thesis presents the analysis of spectroscopic and photometric data on faint galaxies in an 8-arcmin diameter region centered on the Hubble Deep Field. Source detection and photometry is performed in the U_n, G, R and K_s-band images to create catalogs complete to U_n = 25, G = 26, R = 25.5 and K_s = 20 mag. Number counts and color distributions are consistent with those found in other, similar imaging surveys. Keck Telescope spectroscopy exists for 483 sources in the sample.

The rest-frame equivalent widths of the [O II] 3727 Å emission line are measured as a function of galaxy flux, color and redshift. The probability that a source of a given flux, color and redshift has its [O II] line detected is estimated. [O II] line luminosity functions and integrated [O II] line luminosity densities are computed; they show strong evolution, implying a much higher star formation rate density at redshifts z > 0.6 than locally.

The spectroscopic survey is incomplete; not all selected sources have been observed spectroscopically, and not all observed sources have redshifts. Four methods for estimating the luminosity function in an incomplete survey are developed, three based on the maximum-likelihood method. Simulated catalogs which accurately reproduce the redshift structure and redshift-incompleteness found in real redshift surveys are created and used to test the methods for bias. All methods are biased for "steep" (i.e., dwarf-rich) luminosity functions.

The B-band luminosity function for the R-selected sample is computed using an estimate of the probability that a source is assigned a redshift given that it has been observed spectroscopically, based on the [O II] detection probability. The luminosity function is flat (constant number per log luminosity) and consistent with local determinations except for a higher overall normalization. No evidence is found for dependence of the luminosity function on redshift or environment, but the blue galaxy luminosity function is more dwarf-rich than the red.

It is argued that, taken together, the observations support the existence of a dwarf-dominated, strongly star forming galaxy population in the past which merged into (or otherwise became physically associated with) the luminous galaxies observed locally.

Thesis Files