Eric Martin Monier

Low-Redshift Damped Lyα Galaxies toward the Quasars B2 0827+243, PKS 0952+179, PKS 1127–145, and PKS 1629+120

We present optical and near-infrared ground-based imaging results on four low-redshift damped Ly? (DLA) galaxies. The corresponding DLA systems were discovered in our Hubble Space Telescope spectroscopic surveys for DLA lines in known strong Mg II absorption-line systems toward the quasars B2 0827+243 (zDLA = 0.525), PKS 0952+179 (zDLA = 0.239), PKS 1127-145 (zDLA = 0.313), and PKS 1629+120 (zDLA = 0.532). Two of the four DLA galaxies have confirmed slit redshifts, one has a photometric redshift consistent with the absorption-line redshift, and the fourth identification is based on the galaxys proximity to the quasar sight line. The DLA galaxies span a mixture of morphological types from patchy, irregular, and low surface brightness to spiral galaxies. The luminosities range from 0.02L to 1.2L. We also discovered several extremely red objects (EROs) in two of these fields and discuss the possibility that they are associated with the DLA galaxies. These observations add to the small but growing list of DLA galaxies at low redshift. At the present time, 14 DLA galaxies in the redshift range 0.05 z 1 have been studied. The distributions of DLA galaxy properties for these 14 cases are discussed, and some important trends emerge. Low-luminosity dwarf galaxies with small impact parameters dominate this small sample. Also, four of the five highest column density systems, which dominate in the determination of the cosmological neutral gas mass density, arise in low surface brightness dwarf galaxies. Zwaan et al. have shown that only 15% of the neutral gas at the present epoch is contained in low surface brightness galaxies. Thus, if the low-redshift DLA galaxy trends hold up with larger samples, it would indicate that a different population of objects is responsible for the bulk of the neutral hydrogen gas in the universe at z ? 0.5.

Chandra ACIS-S Observations of Three Quasars with Low-Redshift Damped Lyα Absorption: Constraints on the Cosmic Neutral Gas-Phase Metallicity at Redshift z ≈ 0.4*

Chandra X-Ray Observatory ACIS-S spectra of three quasars that lie behind three foreground damped Lyα (DLA) absorbers are analyzed in order to attempt to determine the amount of photoelectric absorption due to metals present in their X-ray spectra. These absorbers are the three largest neutral hydrogen column density absorption-line systems known at low redshift (0.313 ≤ zabs ≤ 0.524). They have H I column densities that lie in the range 3 × 1021 NH I 5 × 1021 atoms cm-2. At these redshifts the amount of photoelectric absorption at X-ray energies is primarily an indicator of the oxygen abundance. Since the column densities of these systems are so high, one would expect accurate metallicity measurements of them to yield a robust estimate of the column density-weighted cosmic neutral gas-phase metallicity at z ≈ 0.4. We consider cases in which the DLA gas has solar element abundance ratios and ones with the α group element abundance ratios enhanced. For the adopted assumptions, the column density-weighted cosmic neutral gas-phase metallicity of the nonenhanced elements (e.g., Zn) at z ≈ 0.4 likely lies in the range ≈0.04-0.38 Z☉.

The BTC40 Survey for Quasars at 4.8 < z < 6*

The BTC40 Survey for high-redshift quasars is a multicolor search using images obtained with the Big Throughput Camera (BTC) on the Cerro Tololo Inter-American Observatory (CTIO) 4 m telescope in V, I, and z filters to search for quasars at redshifts of 4.8 < z < 6. The survey covers 40 deg2 in B, V, and I, and 36 deg2 in z. Limiting magnitudes (3 σ) reach to V = 24.6, I = 22.9, and z = 22.9. We used the V-I versus I-z two-color diagram to select high-redshift quasar candidates from the objects classified as point sources in the imaging data. Follow-up spectroscopy with the Anglo-Australian Telescope and CTIO 4 m telescopes of candidates having I ≤ 21.5 has yielded two quasars with redshifts of z = 4.6 and z = 4.8, as well as four emission-line galaxies with z ≈ 0.6. Fainter candidates have been identified down to I = 22 for future spectroscopy on 8 m class telescopes.