arXiv subjects

J. T. Lauroesch

Publications and source records attributed to J. T. Lauroesch.

26 records · Page 2Linked to original sources

arXiv2003

Absorption-Line Systems and Galaxies in Front of the Second Brightest Quasar, PHL 1811

The extraordinarily bright quasar PHL 1811 at a redshift z = 0.192 provides an attractive opportunity to use ultraviolet absorption-line spectroscopy to study the properties of gas systems in the local universe. An R = 20,000 far-UV spectrum recorded by FUSE revealed 7 extragalactic absorption systems, one of which is a Lyman limit system at z = 0.08093 accompanied by three systems having redshifts which differ from it by less than 0.008. The abundance of O with respect to Fe in the Lyman limit system is not much different from the solar abundance ratio. Supplementary low resolution spectra recorded by STIS (on HST) at longer wavelengths helped to substantiate our identifications of systems in the FUSE spectrum and suggested the presence of an additional 4 systems that could be detected only through their Ly-alpha features. Spectroscopy at visible wavelengths of 7 galaxies within approximately 2' of PHL 1811 indicated that 2 of them are near the redshift of the quasar and 4 have redshifts within 850 km/s of the extragalactic absorption systems. The Lyman limit system is likely associated with an L* galaxy lying 23" from the sightline. Finally, in addition to prominent features at very low velocities arising from the disk of our Galaxy, the strong resonance transitions of C II and Mg II show evidence for material at v = -200 km/s; the column densities of these two species suggest that 17.7 < log N(H I) < 18.1 if the material has a solar composition.

astro-ph↗

arXiv2001

Small-Scale Interstellar Na I Structure Toward M92

We have used integral field echelle spectroscopy with the DensePak fiber-optic array on the KPNO WIYN telescope to observe the central 27" x 43" of the globular cluster M92 in the Na I D wavelength region at a spatial resolution of 4". Two interstellar Na I absorption components are evident in the spectra at LSR velocities of 0 km/s (Cloud 1) and -19 km/s (Cloud 2). Substantial strength variations in both components are apparent down to scales limited by the fiber-to-fiber separations. The derived Na I column densities differ by a factor of 4 across the Cloud 1 absorption map and by a factor of 7 across the Cloud 2 map. Using distance upper limits of 400 and 800 pc for Cloud 1 and Cloud 2, respectively, the absorption maps indicate structure in the ISM down to scales of 1600 and 3200 AU. The fiber-to-fiber Na I column density differences toward M92 are comparable to those found in a similar study of the ISM toward the globular cluster M15. Overall, the structures in the interstellar components toward M92 have significantly lower column densities than those toward M15. We interpret these low column density structures as small-scale turbulent variations in the gas and compare them to the larger-scale, higher column density variations toward M15, which may be the hallmarks of actual H I structures.

astro-ph↗

arXiv1999

A Na I Absorption Map of the Small-Scale Structure in the Interstellar Gas Toward M15

Using the DensePak fiber optic array on the KPNO WIYN telescope, we have obtained high S/N echelle spectra of the Na I D wavelength region toward the central 27" x 43" of the globular cluster M15 at a spatial resolution of 4". The spectra exhibit significant interstellar Na I absorption at LSR velocities of +3 km/s (LISM component) and +68 km/s (IVC component). Both components vary appreciably in strength on these scales. The derived Na I column densities differ by a factor of 4 across the LISM absorption map and by a factor of 16 across the IVC map. Assuming distances of 500 pc and 1500 pc for the LISM and IVC clouds, these maps show evidence of significant ISM structure down to the minimum scales of 2000 AU and 6000 AU probed in these absorbers. The smallest-scale N(Na I) variations observed in the M15 LISM and IVC maps are typically comparable to or higher than the values found at similar scales in previous studies of interstellar Na I structure toward binary stars. The physical implications of the small and larger-scale Na I features observed in the M15 maps are discussed in terms of variations in the H I column density as well as in the Na ionization equilibrium.

astro-ph↗

arXiv1999

The Diffuse Interstellar Clouds toward 23 Orionis

Spectra obtained with the Hubble Space Telescope GHRS are combined with high-resolution optical spectra and UV spectra from Copernicus to study the abundances and physical conditions in the diffuse interstellar clouds seen along the line of sight to the star 23 Ori. Strong low-velocity (SLV) absorption, due to cool, moderately dense neutral gas and representing about 92% of the total N(H I), is seen for various neutral and singly ionized species at +20 km/s < v < +26 km/s. Weaker low-velocity absorption, probably largely due to warmer neutral gas, is seen primarily for various singly ionized species at 0 km/s < v < +30 km/s. Absorption from a number of singly and doubly ionized species, perhaps due to a radiative shock, is seen at -108 km/s < v < -83 km/s. Weak absorption components from ionized gas are seen at intermediate velocities (-43 km/s < v < -4 km/s). The large range in n_e (from 0.04 cm^{-3} to 0.95 cm^{-3}) derived independently from nine pairs of neutral and singly ionized species in the SLV gas suggests that additional processes besides simple photoionization and radiative recombination affect the ionization balance. The adopted average SLV electron density, n_e = 0.15+/-0.05 cm^{-3}, implies a relatively large n_e/n_H ~ 0.01, and thus some ionization of hydrogen in these predominantly neutral components. Comparisons of the SLV depletions and n_H with those found for the strong ``component B'' (v ~ -14 km/s) blend toward zeta Oph hint at a possible relationship between depletion and local density for relatively cold interstellar clouds. Calcium appears to be more severely depleted in warm, low density gas than has generally been assumed. An appendix summarizes the most reliable oscillator strengths currently available for a number of the interstellar absorption lines analyzed in this work.

astro-ph↗

arXiv1999

Observations of Small Scale ISM Structure in Dense Atomic Gas

We present high resolution (R~170,000) Kitt Peak National Observatory Co'ude Feed telescope observations of the interstellar KI 7698 angstrom line towards 5 multiple star systems with saturated NaI components. We compare the KI absorption line profiles in each of the two (or three) lines of sight in these systems, and find significant differences between the sight-lines in 3 out of the 5 cases. We infer that the small scale structure traced by previous NaI observations is also present in at least some of the components with saturated NaI absorption lines, and thus the small scale structures traced by the neutral species are occurring at some level in clouds of all column densities. We discuss the implications of that conclusion and a potential explanation by density inhomogeneities.

astro-ph↗

arXiv1998

The Physical Characteristics of the Small-Scale Interstellar Structure towards Mu Crucis

We present HST/GHRS echelle observations of multiple interstellar lines of CI, MgI, CrII, and ZnII towards both stars in the mu Cru binary system. Despite large differences in the profiles of the neutral species, no significant variations between the stars are seen in the CrII and ZnII line profiles. In particular, the ZnII absorption observed at -8.6 km/sec towards mu Cru is constant despite greatly enhanced columns of the neutral species at this velocity towards mu^1 Cru. An analysis of the fine-structure excitation of CI in this cloud implies that the density is n_H < 250 cm^{-3}. From the lack of variation in the (optical) NaI D2 line profiles towards mu^1 and mu^2 Cru in spectra taken 21 months apart, we can place a lower limit to the size of the structures of ~10 AU. These results are discussed in the context of recent radio and optical studies of apparently pervasive high density small-scale interstellar structure.

astro-ph↗

arXiv1997

Light Element Abundances From z=0 To z=5

Plausible ratios of deuterium to hydrogen D/H as a function of metallicity, time, and redshift are investigated. Guided by the heavy element abundance patterns observed locally in Galactic dwarf stars and at large redshift in quasi-stellar object absorption line systems, empirical evolution of the relative abundance ratios Li/D, B/D, N/D, O/D, and F/D for QSO absorption line systems are given for the possible evolutionary patterns in D/H. Shortened abstract.

astro-ph↗

arXiv1995

Abundance Histories for QSO Absorption Line Systems

Abundance histories for QSO absorption line systems as a function of redshift are presented for all metals lighter than gallium. Coupling various conventional cosmological models with a simple, first--order model for the chemical evolution of the QSO absorption line systems allows transformation of the observed abundance trends in the Galaxy to abundance histories for the gas in QSO absorption line systems. Comparison of the transformed abundance patterns with the zinc to hydrogen [Zn/H] and silicon to hydrogen [Si/H] ratios observed in damped Lyman-$α$ systems finds agreement over more than two orders of magnitude in abundance with a $Λ$=0, \ $Ω$=0.2 -- 1.0, \ and $τ_{\rm {delay}}$=3 Gyr cosmology, where $τ_{\rm {delay}}$ is the time between the start of the Big Bang and the beginning of galaxy formation. Alternative meanings for the required time delay are explored, along with extensions to the simple first--order model. Predictions are made for the abundance histories of elements not yet observed in QSO absorption line systems.

astro-ph↗