Damped Ly-alpha Research Articles

The Z = 0.8596 damped Ly-alpha absorbing galaxy toward PKS 0454+039

We present Hubble Space Telescope (HST) and ground-based data on the Z(sub abs) = 0.8596 metal-line absorption system along the line of sight to PKS 0454+0356. The system is a moderate-redshift damped Ly-alpha system, with N(H I) = (5.7 +/- 0.3) x 10(exp 20)/sq cm as measured from the Faint Object Spectrograph (FOS) spectrum. We also present ground-based images which we use to identify the galaxy which most probably gives rise to the damped system; the most likely candidate is relatively underluminous by QSO absorber standards M(sub B) approximately -19.0 for A(sub 0) = 0.5 and H(sub 0) = 50 km/s/Mpc) and lies approximately 8.5/h kpc in projection from the QSO sight line. Ground-based measurements of Zn II, Cr II, and Fe II absorption lines from this system allow us to infer abundances of (Zn/H) = -1.1, (Cr/H) = -1.2, and (Fe/H) = -1.2 indicating overall metallicity similar to damped systems at z is greater than 2, and that the depletion of Cr and Fe onto dust grains may be even less important than in many of the high-redshift systems of comparable metallicity. Limits previously placed on the 21 cm optical depth in the z = 0.8596 system, together with our new N(H I) measurement, suggest a very high spin temperature for the H I, T(sub s) is greater than 580 K.

A search for H I 21 CM emission from a damped Ly(alpha) absorption line system and possible cluster of galaxies at redshift Z approximately = 3.4 in the direction of Q0000-2619

A search for H I 21 CM emission from a damped Ly(alpha) absorption line system and possible cluster of galaxies at redshift Z approximately = 3.4 in the direction of Q0000-2619

EVOLUTION OF THE GASEOUS CONTENT OF THE UNIVERSE

ABSTRACT Results of a new spectroscopic survey for damped Ly-alpha absorption systems conducted at ultraviolet wavelengths are combined with those of previous surveys conducted at optical wavelengths in order to examine the evolution of the gaseous contnet of the universe at 0<~z<~3.5. Implicaitons for scenarios of galaxy formation and evolution are discussed.

Lick slit spectra of thirty-eight objective prism quasar candidates and low metallicity halo stars

Lick Observatory slit spectra of 38 objects which were claimed to have pronounced UV excess and emission lines are presented. Eleven QSOs, four galaxies at z of about 0.1, 22 stars, and one unidentified object with a low S/N spectrum were found. Of 11 objects which Zhan and Chen (1987, 1989) suggested were QSO with z(prism) not greater than 2.8; eight are QSOs. Six of the QSOs show absorption systems, including +027A with a relatively strong associated C IV absorption system, and Q0008+008 with a damped Ly-alpha system with an H I column density of 10 exp 21/sq cm. The equivalent widths of the Ca II K line, the G band, and the Balmer lines in 10 stars with the best spectra are measured, and metallicities are derived. Seven of them are in the range -2.5 to -1.7, while the others are less metal-poor.

The Hubble Space Telescope quasar absorption line key project. I - First observational results, including Lyman-alpha and Lyman-limit systems

Spectra are presented for 37 quasars with small and moderate redshifts; the quasars were observed with the Faint Object Spectrograph of the HST. New higher resolution measurements of the absorption lines in the UV spectra of 11 quasars with emission-line redshifts that lie between 0.3 and 1.0 are reported. Calibrated spectra and continuum fits are shown for each object. A total of 104 extragalactic Ly-alpha systems are identified, nine of which are found at the same redshifts as metal-line systems. The local number density of Ly-alpha systems with rest equivalent widths larger than 0.32 A and without detected metal lines is about 15.1 +/- 4.3 Ly-alpha systems per unit redshift with gamma = 0.30 +/- 0.62 and W* = 0.22 +/- 0.02 A. A total of 10 Lyman-limit systems with an optical depth greater than 0.4 are identified. The paucity of damped Ly-alpha lines at small and moderate redshifts shows that the number density of damped absorption systems decreases with decreasing redshift.

Damped Lyman-alpha absorption in Q0957+561A, B

A series of archival IUE low-dispersion spectral observations of the double quasar Q0957+561A, B are analyzed. The components of this gravitationally lensed quasar are separated by about 6 arcsec. Damped Ly-alpha absorption at redshift z(abs) = 1.3911 with neutral hydrogen column density N(H I) about 7 x 10 exp 19/sq cm is present in the spectra of both the A and B components. Using an accepted model by Young et al. for the gravitational lens, the damped Ly-alpha absorber is inferred to have a minimum size of about 0.5/h50 kpc. The standard interpretation is that a damped Ly-alpha absorber represents a galactic or protogalactic H I disk. In the context of this standard model, the absorption-line properties and evidence for Faraday rotation are discussed.

Clustering of galaxies near damped Lyman-alpha systems with (z) = 2.6

The galaxy two-point correlation function, xi, at (z) = 2.6 is determined by comparing the number of Ly-alpha-emitting galaxies in narrowband CCD fields selected for the presence of damped L-alpha absorption to their number in randomly selected control fields. Comparisons between the presented determination of (xi), a density-weighted volume average of xi, and model predictions for (xi) at large redshifts show that models in which the clustering pattern is fixed in proper coordinates are highly unlikely, while better agreement is obtained if the clustering pattern is fixed in comoving coordinates. Therefore, clustering of Ly-alpha-emitting galaxies around damped Ly-alpha systems at large redshifts is strong. It is concluded that the faint blue galaxies are drawn from a parent population different from normal galaxies, the presumed offspring of damped Ly-alpha systems.

LINE EMISSION FROM GALAXIES AT HIGH REDSHIFT

ABSTRACT The results of a multifaceted search for spectral-line emission from galaxies at high redshift are presented. Deep two-dimensional spectra of four blank sky fields were taken at the Muliple Mirror Telescope (MMT) at wavelengths corresponding to redshifted Lyman alpha emission in the range 2.7 < z < 4.7, and the resulting nondetections are used to place upper limits on the space density of randomly distributed Ly-alpha emitters. Although the predictions of a conservative model of galaxy formation incorporating cold dark matter are not excluded in a statistical sense, the search would have detected star-forming dwarf galaxies comparable to the Magellanic Clouds at z = 3, given minimal extinction by dust. The Goddard Fabry-Perot Imager, a piezoelectrically controlled tuneable narrow-band filter system with a stand-alone CCD, was developed and tested, and used a the Kitt Peak National Observatory (KPNO) 4-m telescope to image the damped Ly-alpha absorbing clouds toward three high-redshift QSOs in the light of redshifted Ly-alpha. A companion galaxy to one of the damped systems was discovered, confirmed with follow-up spectroscopy, and its properties are presented and discussed. The companion exhibits strong Ly-alpha and weak C IV lambda-1550 and He II lambda-1640 emission lines, and is apparently producing stars at a rate of 5-10 solar mass yr-1. The implications of the companion's proximity to the damped cloud are analyzed in view of the previous nondetections, and a lower limit to the spatial correlation function of the damped Ly-alpha systems with galaxies is given. Spectroscopic limits on Ly-alpha emission from seven damped systems, including some known to have low chemical and dust abundances, imply levels of star formation lt 1 solar mass yr-1, but extinction by dust in some cases may cause an underestimation of these rates. With near-infrared spectrographs at the MMT and the KPNO 4-m telescope, eight damped Ly-alpha systems were searched for spectral lines characteristic of star-formation regions but redshifted from the optical into the near infrared. A possible detection of [O III] lambda-3727 and H-beta from one system implies a star-formation rate on the order of 100 solar mass yr-1, though the remainder of the observations produced nondetections. The implications for galaxy formation and evolution at high redshift are discussed.

Magnetic fields in damped Ly-alpha systems

The incidence of Faraday rotation in a sample of radio-selected QSOs is combined with the incidence of foreground metal-line absorption to compute the probability for Faraday rotation in various types of metal- line absorbers. We divide the sample into subsets with and without damped Ly α absorption. The probability for Faraday rotation is significantly higher in the damped subset. Moreover, the probability is higher in the damped subset than in nondamped subsets selected on the basis of Mg II or C IV absorption. Owing to evidence linking damped systems to the progenitors of galactic disks and the Mg II systems to the progenitors of galactic halos, we conclude that magnetic fields were significantly higher in protogalactic disks than in proto-galactic halos. We estimate that the B fields in two damped Ly α systems with z ~ 2 are a few microgauss. The existence of microgauss magnetic fields in rotating galactic disks at these redshifts is extremely difficult to understand if magnetic field amplification is due to a global galactic dynamo. This is because there is not enough time available for amplification of an infinitesimal seed field of B ~ 10^-21^ G to B ~ 10^-6^ G by z ~ 2 in any standard Friedmann cosmology. The observations thus indicate either a more rapid amplification mechanism, possibly by a rapid local dynamo, or the presence of a finite primordial B field.

Lyman-alpha emission from the damped Lyman-alpha system toward H0836 + 113

This study presents results of a comprehensive search for Ly-alpha emission from the 2.466-redshift damped Ly-alpha system toward the QSO H0836 + 113. Deep CCD images of the field surrounding the QSO were acquired with a narrow-band filter tuned to the wavelength centroid of the 2.466-redshift damped Ly-alpha line. Two superposed objects, one extended and the other compact, were detected within 4 arcsec of the QSO. Evidence is presented indicating that the extended object, seen only in the narrow-band frames, was detected in the light of Ly-alpha line radiation emitted by the damped system, while the compact object, seen with the broadband filters and in the narrow-band frames acquired with superior seeing, was detected in the light of the continuum radiation emitted by a foreground Mg II galaxy with a redshift of 0.79. Accurate spectra of the QSO were also obtained in order to observe the spatially unresolved Ly-alpha emission feature reported to exist at the bottom of the damped Ly-alpha absorption trough.

A new spectroscopic survey for damped Ly-alpha absorption lines from high-redshift galaxies

The results of a new survey for distant galaxies identified on the basis of the damped Lyα absorption lines they produce in the spectra of high-redshift background QSOs are presented. These results are based on new, low-resolution spectroscopy of a sample of 57 QSOs, which are combined with similar low-resolution spectroscopy of 53 QSOs, to yield a total of 101 spectra of high-redshift QSOs which are suitable for identifying damped Lyα absorption lines. The spectra are analyzed to generate a complete sample of absorption features which, if the features are assumed to be Lyα lines, have rest-frame equivalent widths satisfying W ≥ 5 A. A total of 84 such damped Lyα absorption-line candidates are detected.

Discovery of a Ly-alpha galaxy near a damped Ly-alpha absorber at Z = 2.3

The detection of a galaxy associated with the damped Ly-alpha absorbing cloud seen at z = 2.309 toward the QSO PHL 957 is reported. In addition to a strong but narrow Ly-alpha emission line and weaker C IV and He II lines, the object shows continuum at V about 24, with a slope rising slightly toward the red. This is similar to what is seen in high-redshift radio galaxies, but this galaxy does not correspond to any known radio source. The detected emission lines and continuum are most easily interpreted as light from hot, recently formed stars, implying a sizable star formation rate and a scarcity of dust. The spatial correlation of the absorbing cloud and the companion galaxy supports the interpretation of damped Ly-alpha clouds as objects fundamentally different from the lower column density Ly-alpha forest clouds, which show weak or no clustering.

A search for molecular hydrogen and dust in the Z = 2.796 damped Ly-alpha absorber toward Q1337+113

view Abstract Citations (31) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Search for Molecular Hydrogen and Dust in the Z = 2.796 Damped LY alpha Absorber toward Q1337+113 Lanzetta, Kenneth M. ; Wolfe, Arthur M. ; Turnshek, David A. Abstract Spectroscopic and spectrophotometric observations aimed at detecting molecular hydrogen and dust in the z = 2.796 damped Lyα absorber toward Q1337+ 113 are presented. No evidence for absorption from the Lyman- and Werner-band H_2_ lines is detected, and adopting an excitation temperature of T_ex_ = 1000 K (typical in regions of the Galaxy with low H_2_ abundances) and a Doppler parameter of b = 12 km s^-1^ (determined from a curve-of-growth analysis of metal-ion lines of the absorber), an upper limit to the fractional H_2_ abundance of <f> < 1.3 x 10^-4^ is established. This value is considerably lower than what is typically found for the high-column-density clouds of the Galaxy. No evidence for selective extinction due to dust is detected, and based on the absence of departures of the background QSO continuum from a power-law form an upper limit to the dust abundance of about half the Galactic value is set. The observations are not sensitive to dust abundances like those of the Magellanic Clouds. It is found that the abundance ratios of the metal elements are consistent with solar values and that the C^0^ column density is at least 200 times less than that for the H I region toward ζ Oph; these results are consistent with a lack of dust in the absorber. The overall metallicity of the absorber could range from 10^-2^ to 1 times solar values. A model of the equilibrium abundance of H_2_ is constructed, and it is found that the observed limit to the fractional H_2_ abundance can be used to place an independent upper limit to the dust content of the absorber of less than one-third the Galactic value. Tighter constraints will require a more sensitive limit to the fractional H_2_ abundance (or a positive detection) and an accurate determination of the radiation field longward of the Lyman limit. Publication: The Astrophysical Journal Pub Date: September 1989 DOI: 10.1086/167796 Bibcode: 1989ApJ...344..277L Keywords: Cosmic Dust; Hydrogen; Interstellar Matter; Lyman Alpha Radiation; Quasars; Absorption Spectra; Abundance; Astronomical Spectroscopy; Doppler Effect; H I Regions; Metal Ions; Milky Way Galaxy; Astrophysics; INTERSTELLAR: ABUNDANCES; INTERSTELLAR: MATTER; QUASARS full text sources ADS | data products NED (6) SIMBAD (5)

Observations of NI II absorption at Z = 2.811 toward the QSO PKS 0528-250

view Abstract Citations (43) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of NI II Absorption at Z = 2.811 toward the QSO PKS 0582-250 Meyer, David M. ; York, Donald G. Abstract Observations of strong Ni II absorption corresponding to the damped Ly-alpha absorption-line system at z = 2.811 toward the QSO PKS 0528-250 are presented. Cr II absorption corresponding to the damped Ly-alpha system at z = 2.142 has also been detected toward this QSO. These observations constitute the first confident identifications of Ni and Cr in a QSO absorption-line system. The abundances of Ni II and Cr II relative to H I indicate that much less Ni and Cr is depleted from the gas phase in these systems than in Galactic interstellar clouds. The 2sigma upper limit of 3.0 x 10 to the 13th/sq cm on the column density of C I in the z = 2.811 system is consistent with this implied lack of dust in that C I is much more likely to be photoionized when there are few dust grains to shield it from the surrounding radiation field. The implications of these observations with regard to the interpretation of damped Ly-alpha systems as galactic disks and the possibility of using them as probes of galactic evolution at early epochs is discussed. Publication: The Astrophysical Journal Pub Date: August 1987 DOI: 10.1086/184952 Bibcode: 1987ApJ...319L..45M Keywords: Absorption Spectra; Abundance; Chromium; Interstellar Matter; Lyman Alpha Radiation; Quasars; Disk Galaxies; Line Of Sight; Morphology; Signal To Noise Ratios; Astrophysics; QUASARS; ABUNDANCES full text sources ADS | data products SIMBAD (7) NED (5)

Discovery of a huge low-surface-brightness galaxy - A protodisk galaxy at low redshift?

The accidental discovery of an extremely large, extremely H I-rich low-surface-brightness galaxy located at a redshift of z = 0.083 is reported. Its nuclear spectrum exhibits broad, low-level emission lines. Surface photometry at V indicates the presence of a bulge component and a very extended disk, with scale length of about 45 arcsec and with central surface brightness of V(0) of about 25.5 mag/sq arcsec. The total amount of H I is at least 1.0 x 10 to the 11th solar masses. This amount of H I is at least 5 times more H I than any spiral galaxy previously observed. If disk formation is a quiescent process, then it is likely that a disk was caught in the process of formation. The properties of this disk are likely to be similar to the suspected sources that produce the observed damped Ly-alpha absorption profiles that are so conspicuous at z of about 2. 31 references.