[Paper Review] The ESO UVES Advanced Data Products Quasar Sample - II. Cosmological Evolution of the Neutral Gas Mass Density

Tayyaba Zafar, Céline Péroux+4 more|UWA Profiles and Research Repository (University of Western Australia)|Jul 2, 2013

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy104 references103 citations

TL;DR

This study uses an unbiased sample of 122 quasars from the ESO UVES advanced data products to measure the redshift evolution of the H i column density distribution function, $f_{{ m H} m I}(N,z)$, down to log $N_{{ m H} m I} = 19.0$ cm$^{-2}$, revealing a flattening in the sub-DLA regime. It finds that sub-DLAs contribute 8–20% to the total neutral gas mass density $\Omega_{\rm g}$ over $1.5 < z < 5.0$, with no significant evolution in $\Omega_{\rm g}$, implying the need for gas replenishment beyond star formation alone.

ABSTRACT

Quasar foreground damped absorbers, associated with HI-rich galaxies allow to estimate the neutral gas mass over cosmic time, which is a possible indicator of gas consumption as star formation proceeds. The DLAs and sub-DLAs are believed to contain a large fraction of neutral gas mass in the Universe. In Paper I of the series, we present the results of a search for DLAs and sub-DLAs in the ESO-UVES Advanced Data Products dataset of 250 quasars. Here we use an unbiased sub-sample of sub-DLAs from this dataset. We build a subset of 122 quasars ranging from 1.5

Motivation & Objective

• To derive the redshift evolution of the H i column density distribution function, $f_{{ m H} m I}(N,z)$, down to the sub-DLA limit using high-resolution quasar spectra.
• To determine the statistical properties of sub-DLAs and their contribution to the total neutral gas mass density $\Omega_{\rm g}$ over $1.5 < z < 5.0$.
• To test whether the neutral gas mass density evolves with redshift, given that previous studies report conflicting results.
• To assess the role of sub-DLAs in the cosmic baryon budget and their implications for gas consumption and replenishment in galaxy evolution.
• To combine the ESO UVES sample with literature sub-DLA data to build a robust, unbiased sample of 89 sub-DLAs over $\Delta z = 193$.

Proposed method

• Constructed a statistical sample of 122 quasars with redshifts $1.5 < z_{\rm em} < 5.0$ from the ESO UVES advanced data products, ensuring unbiased selection for sub-DLA detection.
• Measured H i column densities $N_{{ m H} m I}$ with high precision using the high spectral resolution of UVES, enabling detection down to log $N_{{ m H} m I} = 19.0$ cm$^{-2}$.
• Combined the ESO UVES sub-DLA sample with 89 sub-DLAs from the literature to form a total sample of 89 absorbers over $\Delta z = 193$ for statistical analysis.
• Calculated the number density and line density of sub-DLAs, and compared them with LLSs and DLAs to assess redshift evolution.
• Used $f_{{ m H} m I}(N,z)$ to compute the neutral gas mass density $\Omega_{\rm g}$ at different redshifts, integrating down to the sub-DLA threshold.
• Assessed the redshift evolution of $f_{{ m H} m I}(N,z)$ and found a flattening in the sub-DLA regime, indicating an increasing number of sub-DLAs at higher redshifts.

Figure 1: Upper panel : Redshift sensitivity function, $g(z)$ , as a function of sub-DLA redshift for the statistical EUADP (gray), O’Meara et al. ( 2007 ) MIKE $+$ ESI (green), Péroux et al. ( 2005 ) (red), Péroux et al. ( 2003a ) (blue), and combined sub-DLA sample (black). Lower panel : The distr

Experimental results

Research questions

• RQ1 How does the H i column density distribution function $f_{{ m H} m I}(N,z)$ evolve with redshift in the sub-DLA regime?
• RQ2 What fraction of the total neutral gas mass density $\Omega_{\rm g}$ is contributed by sub-DLAs at $1.5 < z < 5.0$?
• RQ3 Is the total neutral gas mass density $\Omega_{\rm g}$ constant or evolving over the redshift range $1.5 < z < 5.0$?
• RQ4 How does the number density of sub-DLAs compare to that of LLSs and DLAs across the redshift interval $1.0 < z < 5.0$?
• RQ5 What does the lack of evolution in $\Omega_{\rm g}$ imply about the mechanisms responsible for gas supply in high-redshift galaxies?

Key findings

• The H i column density distribution function $f_{{ m H} m I}(N,z)$ shows a flattening in the sub-DLA regime, indicating a higher number density of sub-DLAs at high redshifts compared to low redshifts.
• The combined sample of 89 sub-DLAs over $\Delta z = 193$ provides robust statistical constraints on the redshift evolution of sub-DLA properties.
• Sub-DLAs contribute 8–20% to the total neutral gas mass density $\Omega_{\rm g}$ over the redshift range $1.5 < z < 5.0$.
• No significant evolution in the total neutral gas mass density $\Omega_{\rm g}$ is observed from $z \sim 1.5$ to $z \sim 5.0$, despite ongoing star formation.
• The non-evolution of $\Omega_{\rm g}$ implies that star formation alone cannot account for the observed gas reservoirs, necessitating additional mechanisms such as recombination of ionized gas or external gas accretion.
• The high-resolution UVES data enable precise $N_{{ m H} m I}$ measurements down to log $N_{{ m H} m I} = 19.0$ cm$^{-2}$, confirming the presence of a significant population of sub-DLAs at high redshift.

Figure 2: Flowchart describing the building of the combined sub-DLA sample. For quasars in common with previous sub-DLA samples and the work presented here, we used $N_{{\rm H}\,{\sc\rm I}}$ and the redshift path from this work.