The corals survey I: new estimates of the number density and gas content of damped lyman alpha systems free from dust bias

By Sara L. Ellison, Lin Yan, I. Hook, M. Pettini, J. Wall, P. Shaver. 2001

172 citations recorded by the source corpus.

We present the first results from the Complete Optical and Radio Absorption Line System (CORALS) survey. We have compiled a homogeneous sample of radio-selected QSOs from the Parkes Catalogue and searched for damped Lyman alpha systems (DLAs) towards every target, irrespective of its optical magnitude. This approach circumvents selection effects -particularly from intervening dust -which have long been suspected to affect DLA surveys in optically-selected, magnitude-limited QSO samples. The CORALS data set consists of 66 Z_(em) ≥ 2.2 QSOs in which 22 DLAs with absorption redshifts 1.8 ≤ Z-(abs) ≤ Z_(em) have been identified over a total redshift interval Δz = 55.46. Three of the DLAs are classified as "associated" systems with Z_(abs) ~ Z_(em); of the 19 intervening DLAs, 17 are new discoveries. In this first paper of the CORALS series we describe the sample, present intermediate resolution spectroscopy and determine the population statistics of DLAs. We deduce a value of the neutral gas mass density traced by DLAs (expressed as a fraction of the closure density) logΩ_(DLA)h = -2.59^(+0.17)_(-0.24), and a number density of DLAs per unit redshift n(z) = 0.31^(+0.09)_(-0.08), both at a mean redshift (z). Both values are only marginally higher than those measured in optically selected samples of QSOs. Taking into account the errors, we conclude that dust-induced bias in previous surveys may have led to an underestimate of these quantities by at most a factor of two. While n(z) is greater in fainter (B 〉20) QSOs, the effect is only at the ~1σ level and we have not uncovered a previously unrecognised population of high column density (N(HI) 〉10^(21) (cm^(-2)) DLAs in front of faint QSOs. These conclusions are tentative because of the limited size of our data set; in particular the distribution of column densities is poorly sampled at the high end where a much larger survey of radio-selected QSOs is required the improve the statistics.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/abfbecc4c58bd458ef06d41e1a471dc5459a24ac

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Citations in the corpus

The Age-Metallicity Relation of the Universe in Neutral Gas: The First 100 Damped Lyα Systems (2003, background): “This population could only exist if the current sample is significantly biased by selection effects (e.g. dust obscuration), an assertion unsupported by any recent observational test (e.g. Ellison et al. 2001; PW02).”
The Neutral Hydrogen Cosmological Mass Density at z = 5 (2015, result): “…are not associated with significant amounts of dust (e.g. Murphy & Liske 2004, Vladilo et al. 2008), and DLAs towards radio-selected QSOs, which are insensitive to the presence of dust, have a similar NHI distribution to those in optically-selected QSOs (Ellison et al. 2001; Jorgenson et al. 2006).”
Reconciling the local galaxy population with damped Lyman α cross-sections and metal abundances (2005, background): “…HI column densities and highest metallicities could be missed in magnitude-limited surveys as a consequence of their own extinction (see e.g. Fall & Pei 1989, 1993; Ellison et al. 2001; Murphy & Liske 2004; Vladilo & Péroux 2005; Wild & Hewett 2005, for a continued discussion on this issue).”
The Dust Opacity of Star‐forming Galaxies (2001, background): “…biases against the dustiest, and most metal-rich DLAs and problems with dust depletion corrections have been advocated as possible reasons for the observed weak metallicity evolution (Fall & Pei 1993; Boissé et al. 1998; Savaglio, Panagia & Stiavelli 2000, see, however, Ellison et al. (2001)).”
The evolution of ΩHI and the epoch of formation of damped Lyman α absorbers (2001, background): “But a recent work by Ellison et al. (2001) has shown that measurements of ΩDLA based on optically selected quasars survey are not significantly affected by dust at z∼2.”
Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7 (2009, background): “Finally, it has long been discussed whether the optically selected quasar samples are affected by extinction due to the presence of dust on the line of sight (Boissé et al. 1998; Ellison et al. 2001; Smette et al. 2005).”
The Very Large Telescope Ultraviolet and Visible Echelle Spectrograph survey for molecular hydrogen in high‐redshift damped Lyman α systems (2003, unknown): “If this dust-induced bias exists, however, it probably cannot lead to underestimate the H i mass in DLA systems by more than a factor of two (Ellison et al. 2001).”
LOW-RESOLUTION SPECTROSCOPY OF GAMMA-RAY BURST OPTICAL AFTERGLOWS: BIASES IN THE SWIFT SAMPLE AND CHARACTERIZATION OF THE ABSORBERS (2009, background): “Whereas there is eviden e that the QSO-DLAs drawn from samples of opti ally sele ted QSOsare fairly representative for the full underlying population (Ellison et al. 2001; Akerman et al.2005; Ellison et al. 2008) this may well not be the ase for the sample of GRB absorbers withOA spe tros opy.”
The UCSD HIRES/Keck I Damped Lyα Abundance Database. II. The Implications (2001, methodology): “Ellison et al. (2001b) have been pursuing such a program, and the Ðrst results are forthcoming.”
METALLICITY EVOLUTION OF DAMPED Lyα SYSTEMS OUT TO z ∼ 5 (2012, background): “The following analysis presents the results under the assumption and expectation that dust obscuration has a modest effect on the majority of DLA sightlines (Ellison et al. 2001b; Herbert-Fort et al. 2006; Jorgenson et al. 2006; Meiring et al. 2006; Khare et al. 2007).”
Damped Lyα Systems at z < 1.65: The Expanded Sloan Digital Sky Survey Hubble Space Telescope Sample (2006, background): “Second, dust obscuration does not cause DLA surveys to miss a large fraction of the neutral gas (Ellison et al. 2001, 2004).”
The physics of the intergalactic medium (2007, unknown): “…Lanzetta et al. (1991), Lu et al. (1993), Lu and Wolfe (1994), Lanzetta et al. (1995b), Wolfe et al. (1995), Storrie-Lombardi and Wolfe (2000), Ellison et al. (2001), Ellison et al. (2002), Colbert and Malkan (2002), Akerman et al. (2005), Srianand et al. (2005), Rao et al. (2006) and…”
Damped Lyman α systems in galaxy formation simulations (2008, result): “However, this is hard to reconcile with the most recent observations; in particular, radio-selected samples (which are unlikely to be biased by dust considerations) show little if any evidence for increased highNHI absorbers (Ellison et al. 2001; Jorgenson et al. 2006; Ellison et al. 2008).”