A high-resolution study of the absorption spectra of the QSOs Q0002-422 and Q0453-423

Sargent, W. L. W.; Young, Patrick; Boksenberg, A.; Carswell, R. F.; Whelan, J. A. J.

doi:10.1086/157061

Cited by 49 publications

(23 citation statements)

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“…REFERENCES.È(1) Sargent et al 1979. (2) must be damped (see°2.5.2 for further details), gives our survey a certain degree of completeness since, for all observed systems that were selected in an unbiased manner, we have been able to determine whether or not they are damped.…”

Section: Exclusion and Selection Of DL A Systems Based On 21 Cmmentioning

confidence: 99%

Discovery of Damped Lyα Systems at Redshifts Less than 1.65 and Results on Their Incidence and Cosmological Mass Density

Rao

Turnshek

2000

ASTROPHYS J SUPPL S

266

335

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We present results from an efficient, nontraditional survey to discover damped Lya (DLA) absorption systems with neutral hydrogen column densities atoms cm~2 and redshifts z \ 1.65. In N H I º 2 ] 1020 the past, identiÐcation of DLA systems at z \ 1.65 has been difficult because of their rare incidence and the need for UV spectroscopy to detect Lya absorption at these low redshifts. Our survey relies on the fact that all known DLA systems have corresponding Mg II absorption. In turn, Mg II absorption systems have been well studied, and their incidence at redshifts 0.1 \ z \ 2.2 as a function of the Mg II rest equivalent width, is known. Therefore, by observing the Lya line corresponding to identiÐed W 0 j2796, low-redshift Mg II systems and determining the fraction of these that are damped, we have been able to infer the statistical properties of the low-redshift DLA population. In an earlier (1995) paper we presented initial results from an archival study with data from the Hubble Space T elescope (HST ) and IUE. Now, with new data from our HST GO program, we have more than doubled the sample of Mg II systems with available ultraviolet spectroscopic data. In total we have uncovered 12 DLA lines in 87 Mg II systems with Two more DLA systems were discovered serendipitously in our W 0 j2796 º 0.3 A . HST spectra. At the present time the total number of conÐrmed DLA systems at redshifts z \ 1.65 is 23.The signiÐcant results of the survey are as follows. (1) The DLA absorbers are drawn almost exclusively from the population of Mg II absorbers that have Moreover, half of all absorp-W 0 j2796 º 0.6 A . tion systems with both Mg II and Fe II are DLA systems. (2) The incidence of W 0 j2796 W 0 j2600 [ 0.5 A DLA systems per unit redshift, decreases as a function of decreasing redshift. The low-redshift data n DLA , are consistent with the larger incidence of DLA systems seen at high redshift and the inferred low incidence for DLA at z \ 0 derived from 21 cm observations of gas-rich spirals. However, the errors in our determination are large enough that it is not clear if the decrease per comoving volume begins to be signiÐcant at z B 2 or possibly does not set in until z B 0.5. (3) On the other hand, the cosmological mass density of neutral gas in low-redshift DLA absorbers, is observed to be comparable to that ) DLA , observed at high redshift. In particular, there is no observed trend that would indicate that at low ) DLA redshift is approaching the value at z \ 0, which is a factor of B4È6.5 lower than (4) The low-) DLA . redshift DLA absorbers exhibit a larger fraction of very high column density systems in comparison to determinations both at high redshift and at z \ 0. In addition, at no redshift is the column density distribution of DLA absorbers observed to fall o † in proportion to with increasing column density, DN H Ĩ 3 a trend that is theoretically predicted for disklike systems. We discuss this and other mounting evidence that DLA absorption arises not solely in luminous disks but in a mixture of gal...

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Section: Exclusion and Selection Of DL A Systems Based On 21 Cmmentioning

confidence: 99%

Discovery of Damped Lyα Systems at Redshifts Less than 1.65 and Results on Their Incidence and Cosmological Mass Density

Rao

Turnshek

2000

ASTROPHYS J SUPPL S

266

335

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“…Later, in particular the combination of echelle spectrographs and charge-coupled device (CCD) detectors permitted QSO spectroscopy to be done with 4-m telescopes at resolutions as high as R ∼ 5 × 10 4 . QSO observers have been quick to make use of these advances, as is obvious from the semantic drift of "high resolution": In 1979, it meant 0.8Å (Sargent et al 1979); in 1984, 0.25Å (Carswell et al 1984); and in 1990, 0.08Å (Pettini et al 1990). Naturally, the average signal-to-noise ratio per resolution element did not benefit from the increase in spectral dispersion, and a single high resolution QSO spectrum required an embarassingly large number of nights on a 4-m telescope.…”

Section: Technical Possibilities Observational Constraintsmentioning

confidence: 99%

The Lyman Alpha Forest in the Spectra of Quasistellar Objects

Rauch

1998

Annu. Rev. Astron. Astrophys.

459

325

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Observations of redshifted Lyman α (Lyα) forest absorption in the spectra of quasistellar objects (QSOs) provide a highly sensitive probe of the distribution of gaseous matter in the universe. Over the past two decades, optical spectroscopy with large ground-based telescopes, and more recently ultraviolet (UV) spectroscopy from space, have yielded a wealth of information on what appears to be a gaseous, photoionized intergalactic medium (IGM), partly enriched by the products of stellar nucleosynthesis, residing in coherent structures over many hundreds of kiloparsecs.Recent progress with cosmological hydro-simulations based on hierarchical structure formation models has led to important insights into the physical structures giving rise to the forest. If these ideas are correct, a truly inter-and protogalactic medium [at high redshift (z ∼ 3), the main repository of baryons] collapses under the influence of dark matter gravity into flattened or filamentary structures, which are seen in absorption against background QSOs. With decreasing redshift, galaxies forming in the denser regions may contribute an increasing part of the Lyα absorption cross section. Comparisons between large data samples from the new generation of telescopes and artificial Lyα forest spectra from cosmological simulations promise to become a useful cosmological tool.

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“…Line parameters are consistent with a photoionized gas (Rauch et al 1996). The C iv absorbers appear to be highly clustered (Sargent, Boksenberg & Steidel 1988; Petitjean & Bergeron 1994; Loh, Quashnock & Stein 2001) and have been thought to originate in gas clouds orbiting in galactic haloes (Sargent et al 1979; Steidel 1993; Petitjean & Bergeron 1994; Mo & Miralda‐Escudé 1996). Hydrodynamical simulations also support a picture in which high‐redshift C iv arises in protogalactic clumps (PGCs), i.e.…”

Section: Introductionmentioning

confidence: 99%

Size estimates for intervening C IV absorbers from high-resolution spectroscopy of APM 0827+5255

Tzanavaris

Carswell

2003

Monthly Notices of the Royal Astronomical Society

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A new analysis of Keck/HIRES observations of the broad absorption line quasi‐stellar object (QSO) APM 0827+5255 indicates that a number of intervening C iv absorbers give rise to absorption lines for which the observed optical depths for the 1548, 1550 Å doublet components are not in the expected 2:1 ratio. To compensate for the effect, a local adjustment of the zero‐level is required. We model this effect as coverage of one line of sight to this gravitationally lensed QSO and perform a set of simulations to select a sample of lines for which our model provides an explanation for the effect. We use lines in this sample to obtain estimates for minimum C iv absorber sizes from total coverage and the separations of the lines of sight for a range of lens redshifts, zl, and two cosmologies. We also obtain best estimates for overall sizes from a statistical ‘hit and miss’ approach. For zl= 0.7 our results set a lower limit to sizes of C iv absorbers of ∼0.3 h −1 72 kpc (∼0.5 h −1 72 kpc) for ΩM= 1, ΩΛ= 0 (ΩM= 0.3, ΩΛ= 0.7), in agreement with other results from similar work but are limited by sample size and the uncertainty in zl. Our method can be used to detect lensed QSOs and to probe absorber sizes when separate spectra cannot be obtained for each line of sight.

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A high-resolution study of the absorption spectra of the QSOs Q0002-422 and Q0453-423

Cited by 49 publications

References 0 publications

Discovery of Damped Lyα Systems at Redshifts Less than 1.65 and Results on Their Incidence and Cosmological Mass Density

Discovery of Damped Lyα Systems at Redshifts Less than 1.65 and Results on Their Incidence and Cosmological Mass Density

The Lyman Alpha Forest in the Spectra of Quasistellar Objects

Size estimates for intervening C IV absorbers from high-resolution spectroscopy of APM 0827+5255

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