The Lockman-SpReSO project: galactic flows in a sample of far-infrared galaxies

Abstract

Context. The Lockman–SpReSO project is an optical spectroscopic survey of 956 far-infrared (FIR) objects within the Lockman Hole field limited by magnitude RC(AB) < 24.5. Fe ii and Mg ii absorption lines have been detected in 21 out of 456 objects with a determined spectroscopic redshift in the catalogue. The redshifts of these objects are in the range 0.5 ≾ z ≾ 1.44. Aims. The aim of this study is to investigate material ejection from star-forming regions and material infall into galaxies by analysing the Fe ii and Mg ii absorption lines. Additionally, we explore whether the correlations found in previous studies between these galactic wind velocities, line equivalent widths (EWs), and galaxy properties such as stellar mass (M∗), star formation rate (SFR), and specific star formation rate (sSFR) are valid for a sample with FIR-selected objects. The objects analysed span an M∗ range of 9.89 < log (M∗/M ) < 11.50 and an SFR range of 1.01 < log (SFR) < 2.70. Methods. We performed measurements of the Mg ii λλ2796, 2803, Mg i λ2852, Fe ii λλ2374, 82, Fe ii λλ2586, 2600, and Fe ii λ2344 spectral lines present in the spectra of the selected sample to determine the EW and velocity of the flows observed in the star-forming galaxies. Subsequently, we conducted 107 bootstrap simulations using the Spearman’s rank correlation coefficient (ρs) to explore correlations with galaxy properties. Furthermore, we calculated the covering factor, gas density, and optical depth for the measured Fe ii doublets. Results. Our analysis reveals strong correlations between the EW of Mg ii lines and both M∗ (ρs = 0.43, 4.5σ) and SFR (ρs = 0.42, 4.4σ). For the Fe ii lines, we observed strong correlations between the EW and SFR (ρs ∼ 0.65, >3.9σ), with a weaker correlation for M∗ (ρs ∼ 0.35, >1.9σ). No notable correlations were found between velocity measurements of the Mg ii line and M∗, SFR, or sSFR of the objects (ρs ∼ 0.1). However, a strong negative correlation was found between the velocity of the Fe ii lines and the SFR of the galaxies (ρs ∼ −0.45, ∼3σ). Our results align with those of previous studies, although only FIR-selected objects are investigated here. Finally, we detect a candidate ‘loitering outflow’, a recently discovered subtype of the iron low-ionisation broad absorption line (FeLoBAL) quasars, at a redshift of z = 1.4399, exhibiting emission in Ciii] and low line velocities (|v| ≾ 200 km s−¹).