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

Context. The Lockman-SpReSO project is an optical spectroscopic survey of 956 far-infrared (FIR) objects within the Lockman Hole field limited by magnitude R-C(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 less than or similar to z less than or similar to 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-circle dot) < 11.50 and an SFR range of 1.01 < log(SFR) < 2.70.
Methods. We performed measurements of the Mg II lambda lambda 2796, 2803, Mg I lambda 2852, Fe II lambda lambda 2374, 82, Fe II lambda lambda 2586, 2600, and Fe II lambda 2344 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 10(7) bootstrap simulations using the Spearman's rank correlation coefficient (rho(s)) 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-* (rho(s) = 0.43, 4.5 sigma) and SFR (rho(s) = 0.42, 4.4 sigma). For the Fe II lines, we observed strong correlations between the EW and SFR (rho(s) similar to 0.65, > 3.9 sigma), with a weaker correlation for M-* (rho(s) similar to 0.35, > 1.9 sigma). No notable correlations were found between velocity measurements of the Mg II line and M-*, SFR, or sSFR of the objects (rho(s) similar to 0.1). However, a strong negative correlation was found between the velocity of the Fe II lines and the SFR of the galaxies (rho(s) similar to -0.45, similar to 3 sigma). 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 C III] and low line velocities (|v|less than or similar to 200 km s(-1)).