Metal Lines Associated with the Lyman-alpha Forest from eBOSS Data

Abstract

We investigate the metal species associated with the Ly$\alpha$ forest in the eBOSS quasar spectra. Metal absorption lines are revealed in the stacked spectra from cross-correlating the selected Ly$\alpha$ absorbers in the forest and the flux fluctuation field. Up to 13 metal species are identified associated with relatively strong Ly$\alpha$ absorbers (those with flux fluctuation $-1.0<{\delta }_{\mathrm{Ly}\alpha }<-0.6$ and with neutral hydrogen column density of ~ $10^{15-16}$ $\mathrm{c}{\mathrm{m}}^{-2}$) over absorber redshift range of $2<z_{\mathrm{abs}}<4$. The column densities of these species decrease toward higher redshift and for weaker Ly$\alpha$ absorbers. From modelling the column densities of various species, we find that the column density pattern suggests contributions from multiple gas components both in the circumgalactic medium (CGM) and in the intergalactic medium (IGM). While the low-ionization species (e.g., C II, Si II, and Mg II) can be explained by high-density, cool gas ($T\sim 10^4$ K) from the CGM, the high-ionization species may reside in low-density or high-temperature gas in the IGM. The measurements provide inputs to model metal contamination in the Ly$\alpha$ forest baryon acoustic oscillations measurement. Comparison with metal absorptions in high-resolution quasar spectra and with hydrodynamic galaxy formation simulations can further elucidate the physical conditions of these Ly$\alpha$ absorbers.

Accepted for publication in ApJ, Jun 21, 2022. In press. 28 pages, 19 figures, 2 tables

References in corpus (8)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• The Sloan Digital Sky Survey Quasar Catalog: Sixteenth Data Release
• The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Baryon acoustic oscillations with Lyman-$\alpha$ forests
• Baryon acoustic oscillations from the complete SDSS-III Ly$\alpha$-quasar cross-correlation function at $z=2.4$
• The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit Systems
• Metals in the z~3 intergalactic medium: results from an ultra-high signal-to-noise ratio UVES quasar spectrum
• The extended Baryon Oscillation Spectroscopic Survey: measuring the cross-correlation between the MgII flux transmission field and quasars and galaxies at $z=0.59$
• Detecting neutral hydrogen at z > 3 in large spectroscopic surveys of quasars

Cited by in corpus (4)

• DESI 2024 IV: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• The Dark Energy Spectroscopic Instrument: One-dimensional power spectrum from first Lyman-$\alpha$ forest samples with Fast Fourier Transform
• A framework to measure the properties of intergalactic metal systems with two-point flux statistics
• 3D Correlations in the Lyman-$\alpha$ Forest from Early DESI Data