Master's Thesis

The Large Scale Distribution and Photometric Properties of Galaxies Centered on the Hubble Deep Field

by Jennifer E. Parker

Under the supervision of Professor Roberta M. Humphreys

ABSTRACT

A two-color study was performed on the galaxies detected on the POSS-I in a 96 square degree region centered on the Hubble Deep Field (HDF) to investigate manifestations in the morphology density relationship [Dressler 1980] on large spatial scales. Using adaptive kernel mapping techniques developed by Odewahn and Aldering [1995], morphological type dependent properties of color (O-E) and concentration index (C31) were used to study the spatial and morphological distribution of 45,099 galaxies O < 20.5 magnitude. According to the morphology-density relationship as described by Dressler, galaxies drawn from samples of higher concentration have redder colors and are located in higher den sity regions. The region surrounding the HDF is a low-density environment (~ 225 galaxies/square degree). This study indicates that the adaptive kernel technique of mapping (O-E) and C31 produces results that are in accord with the morphology-density relationship. The second focus of this research compares the morphological distribution of foreground galaxies with the morphological properties of galaxies in the HDF. Investigating different density environments over large spatial scales as a function of look-back time may restrict theories for whether galaxies are products of initial conditions or of their environment. Mapping diameter limited samples (D >6.125 arcsec) and magnitude limited samples (O < 20.5), 6246 "blue" galaxies (O-E < 1.38), 6212 low-concentration galaxies (C31 < 1.78), 6354 "red" galaxies (O-E > 1.42), and 6144 high-concentration galaxies (C31 > 1.82) are identified in the HDF region. The adaptive kernel map was positionally matched with cluster catalogs to recover 95% of the Abell clusters [1958] and 100% of the Shectman clusters [1985] in the region. Maps at magnitude intervals were compared to determine at what magnitude structure becomes noticeable. Only 7 galaxies between 13 < O < 15 were mapped, increasing to 72 galaxies over the magnitude range 15 < O < 17, it was not until O > 17 that filaments were detected. No filaments were found in the 2.7 square arcminute HDF region, however it borders what appears to be a long filament. The HDF region has blue galaxies with low-concentration indicies consistent with studies by van den Bergh et al. [1996]. However, a concentration of blue galaxies or a "blue clump" was found that does not appear to have the corresponding low-concentration signature, but is coincident with a region in the high-concentration map. This indicates that these galaxies may be early-type galaxies exhibiting signs of current or recent star formation.



PhD Thesis

The Asymmetric Thick Disk: A Star Count and Kinematic Analysis

by Jennifer E. Parker

Under the supervision of Professor Roberta M. Humphreys

ABSTRACT

We present both a star count and a kinematic analysis using data from 40 (x 2) Automated Plate Scanner POSS-I plate pairs matched in galactic latitude at complementary longitudes, and the spectra of nearly 1000 stars using the HYDRA multi-object spectrometer at both CTIO and KPNO. We have identified a region with a significant excess of stars in Quadrant I above (+Q1) and below (-Q1) the galactic plane. The asymmetric distributution of stars consists of 20 contiguous POSS-I fields extending from l = 20° to 55° and |b| = 20° degrees to 50° and is symmetric above and below the galactic plane. We are unable to discriminate between thick disk or inner halo stars, however there appear to be more blue stars in +Q1 with LSR velocities suggestive of a thick disk population. We compare the LSR radial velocity distributions for a total of 741 stars in Quadrant I to Quadrant IV (+Q4), above the plane. Stars in +Q1 appear to have a more negative distribution of LSR radial velocities than stars in +Q4; additionally we calculate the circular angular velocities and find that Ω+Q1 = 19.5 ± 0.3 km/s/kpc is rotating slower than Ω+Q4 = 32.4 ± 0.1 km/s/kpc. Preliminary N-body simulations by Sellwood and Debattista (2003) reproduce both our excess in star counts and the negative LSR velocity signatures only if the models include a stellar bar in the disk and an asymmetric thick disk. The star count excess we find in Q1 along with the significantly slower circular angular velocity suggests that the thick disk may be interacting with the stellar bar in the disk. This interaction is likely inducing a gravitational wake which is trapping and piling up stars behind the bar.