arXiv subjects

D. Tytler

Publications and source records attributed to D. Tytler.

22 records · Page 2Linked to original sources

arXiv1994

The Origin of Intermediate-Redshift Lyman Alpha Absorption Systems

We present initial results of an imaging and spectroscopic survey of faint galaxies in fields of Hubble Space Telescope spectroscopic target QSOs. The primary objectives of the survey are (a) to determine the incidence, extent, and covering factor of extended gaseous envelopes of luminous galaxies and (b) to determine the fraction of Lyman alpha absorption systems that arise in luminous galaxies. The goal of the survey is to identify in each field under consideration all objects with apparent r-band magnitudes satisfying r< 21.5 within angular distances to the QSOs satisfying theta < 1.3 arcmin. We find that at z \apl 1 most luminous galaxies are surrounded by extended gaseous envelopes of approx 160 h^{-1} kpc radius and roughly unit covering factor and that at z \apl 1 the fraction of Ly alpha absorption systems that arise in luminous galaxies is at least 0.35 \pm 0.10 and is likely 0.65 \pm 0.18.

astro-ph↗

arXiv1994

Lick Optical Spectra of Quasar HS 1946+7658 at 10 km/sec Resolution: Lyman-Alpha Forest and Metal Absorption Systems

We present optical spectra of QSO HS~1946+7658 with either high resolution (FWHM=10 km/s) or high signal to noise ratio (SNR=40-100). We find 113 Lyman alpha and six metal line systems. The metal systems at Zabs=2.844 and 3.050 have complex velocity structures. We find that the system at 2.844 is a damped Ly-a absorption system, with neutral hydrogen column density of logN(HI)=20.2+/-0.4, and it is the cause of the Lyman limit break at 3520Å. The metal abundance in the gas phase of the system is [M/H]=-2.6+/-0.3, with a best estimate of [M/H]= -2.8, with ionization parameter Gamma=-2.75, from a photoionization model. We show that the abundance ratios rule out appreciable dust in this DLA system. We do not see the enhancement of O over C reported in Nature by Reimers last years. We see CII*(1335) offset by 15 km/s with respect to CII(1334), presumably because the gas density varies from 2 - 8 cm(-3) with changing velocity in the DLA system. These densities imply that the damped component is 6 - 25 pc thick, which is reasonable for a single cloud in a cold spiral disk. We see a 2.6sigma lack of Ly-a forest lines well away from the QSO redshift, which may be a chance fluctuation. We also see a correlation between column density N(HI) and Doppler parameter b for 96 unsaturated Ly-a forest absorption lines, and although this correlation persists in the 36 Ly-a lines which lie in regions where SNR=8-16, we agree with Rauch etal (1993) that it is probably a bogus effect of low SNR. We show that there are few low-b Ly-a forest lines in moderate SNR data.

astro-ph↗

arXiv1994

Upper Limits on Metals in Quasar Lyman-Alpha Forest Clouds: Absence of C IV Lines in Echelle Spectra

Recently Lu presented tentative evidence for C IV lines in QSO Lyman-alpha forest systems with strong lines. We have performed a similar search for C IV in our 10 km/sec echelle spectra of the bright QSO HS~1946+7658. We shifted the spectra to align the expected positions of the C IV lines in 65 Lyman-alpha systems, then added them. The resulting composite spectrum, equivalent to 390 hours of exposure time on the Lick 3-m telescope, has a signal-to-noise ratio of 80 per 0.025 Angstrom in the rest frame of the absorbers. We do not see any C IV lines down to a $2σ$ limit of W$(1548) \leq 1.4 $~mÅ, about one-fifth of the strength of the lines seen by Lu. The C IV lines which Lu saw must be restricted to rare Lyman-alpha systems with large H I column densities $\geq 10^{14}$~cm$^{-2}$, which are too rare to show C IV in our sample. More common Lyman-alpha systems with H I column densities of $10^{13}$ -- $10^{14}$~cm$^{-2}$ do not show C IV lines. If their ionization is H/H~I $= 10^4$ then they have [C/H] $\leq -2.0$.

astro-ph↗

arXiv1993

Lick Slit Spectra of Thirty-Eight Objective Prism QSO Candidates and Low Metallicity Halo Stars

We present Lick Observatory slit spectra of 38 objects which were claimed to have pronounced ultraviolet excess and emission lines by Zhan \& Chen. Most of our spectra have FWHM spectral resolutions of about 4~Å, and relatively high S/N of about 10 -- 50, although some have FWHM $\simeq 15$~Å~or lower S/N. We find eleven QSOs, four galaxies at $z \simeq 0.1$, twenty-two stars and one unidentified object with a low S/N spectrum. Six of the QSOs show absorption systems, including Q0000+027A with a relatively strong associated C~IV absorption system, and Q0008+008 (V$\simeq 18.9$) with a damped Ly$α$ system with an H~I column density of $10^{21}$ cm$^{-2}$. The stars include a wide variety of spectral types. There is one new DA4 white dwarf at 170~pc, one sdB at 14~kpc, and three M stars. The rest are of types F, G and K. We have measured the equivalent widths of the Ca~II~K line, the G-band and the Balmer lines in ten stars with the best spectra, and we derive metallicities. Seven of them are in the range $-2.5 \leq$~[Fe/H]~$\leq -1.7$, while the others are less metal poor. If the stars are dwarfs, then they are at distances of 1 to 7~kpc, but if they are giants, typical distances will be about 10~kpc.

astro-ph↗