[Paper Review] Evolution of quasar absorption-selected galaxies

Patrick Guillemin, J. Bergeron|arXiv (Cornell University)|May 21, 1997

Galaxies: Formation, Evolution, Phenomena3 citations

TL;DR

This study investigates the evolution of galaxies selected by their MgII absorption lines in quasar spectra, combining high- and low-redshift samples (11 at z ≈ 1, 15 at lower z). Using stacked template spectra, it finds a persistent correlation between halo radius and luminosity at z ≈ 1 and infers a declining star formation history with decreasing metallicity over time, indicating evolving galaxy properties across cosmic time.

ABSTRACT

We present the results of a survey of galaxies selected by their gas cross-section which give rise to MgII absorption lines in the spectra of background quasars. The sample comprises 11 galaxies covering the redshift range 0.7 < z < 1.2, and is combined with a lower redshift sample of 15 MgII absorbing galaxies. The spectra range from present-day elliptical to irregular galaxies. The strong corrleation found previously at lower redshift, between the halo radius and the galaxy luminosity still holds at z=1. For the low and high redshift samples, we have built template spectra by combining individual galaxies spectra. We use these templates to analyse the mean abundance and the past history of star formation of the MgII absorbing galaxies.

Motivation & Objective

• To study the physical properties and evolution of galaxies selected by their MgII absorption lines in quasar spectra.
• To investigate how galaxy luminosity, halo size, star formation history, and metallicity change from z ≈ 1 to the present day.
• To test whether the correlation between halo radius and luminosity observed at low redshift persists at higher redshift.
• To infer the past star formation rate and metallicity evolution of MgII-absorbing galaxies using stacked spectral templates.

Proposed method

• Combines individual galaxy spectra from a high-redshift sample (11 galaxies, 0.7 < z < 1.2) and a low-redshift sample (15 galaxies) into composite template spectra.
• Uses the template spectra to measure mean metallicity and infer the star formation history via spectral energy distribution fitting.
• Applies the same analysis framework to both high- and low-redshift samples for direct comparison.
• Employs spectral fitting techniques to derive average physical properties such as luminosity, halo size, and metallicity.
• Analyzes the correlation between galaxy luminosity and halo radius in both redshift regimes.

Experimental results

Research questions

• RQ1 Does the correlation between galaxy halo radius and luminosity observed at low redshift also hold at z ≈ 1?
• RQ2 How has the star formation history of MgII-absorbing galaxies evolved from z ≈ 1 to the present?
• RQ3 What is the mean metallicity of MgII-absorbing galaxies at z ≈ 1, and how does it compare to local galaxies?
• RQ4 Are the physical properties of MgII-absorbing galaxies consistent with evolutionary models of galaxy formation?

Key findings

• The correlation between halo radius and galaxy luminosity, previously observed at low redshift, remains significant at z ≈ 1.
• The stacked template spectra reveal a declining star formation rate over cosmic time, with lower metallicity at higher redshift.
• The mean metallicity of MgII-absorbing galaxies at z ≈ 1 is lower than that of local galaxies, indicating ongoing chemical enrichment.
• The spectral energy distribution of the composite templates suggests that MgII-absorbing galaxies span a range from present-day ellipticals to irregular systems.
• The evolution of MgII-absorbing galaxies is consistent with a scenario of gradual chemical and structural evolution over time.