| dc.description.abstract | Gaseous flows inside and outside galaxies are key to understanding galaxy evolution, as they regulate their star formation activity and chemical enrichment across cosmic time. We study the interstellar medium (ISM) kinematics of a sample of 330 galaxies with Ca ¯III] or Hea ¯II emission using far-ultraviolet (far-UV) ISM absorption lines detected in the ultra deep spectra of the VANDELS survey. These galaxies span a broad range of stellar masses from 108 to 1011 M, and star formation rates (SFRs) from 1 to 500 M yrin the redshift range between 2 and 5. We find that the bulk ISM velocity along the line of sight (vIS) is globally in outflow, with a vIS of a60a ±a10 km sfor low-ionisation gas traced by Sia ¯IIλ1260 A, Ca ¯IIλ1334 A , Sia ¯IIλ1526 A , and Ala ¯IIλ1670 A absorption lines, and a vIS of a160a±a30 and a170a±a30 km sfor higher ionisation gas traced respectively by Ala ¯IIIλλ1854-1862 A and Sia ¯IVλλ1393-1402 A . Interestingly, we notice that BPASS models are able to better reproduce the stellar continuum around the Sia ¯IV doublet than other stellar population templates. For individual galaxies, 34% of the sample has a positive ISM velocity shift, almost double the fraction reported at lower redshifts. We additionally derive a maximum outflow velocity vmax for the average population, which is of the order of a14;aaa500 and a 14;aaa600 km sfor the lower and higher ionisation lines, respectively. Comparing vIS to the host galaxies properties, we find no significant correlations with stellar mass Mor SFR, and only a marginally significant dependence (at a 14;2Ï) on morphology-related parameters, with slightly higher velocities found in galaxies of smaller size (probed by the equivalent radius rT50), higher concentration (CT), and higher SFR surface density ΣSFR. From the spectral stacks, vmax shows a similarly weak dependence on physical properties (at 2Ï). Moreover, we do not find evidence of enhanced outflow velocities in visually identified mergers compared to isolated galaxies. From a physical point of view, the outflow properties are consistent with accelerating momentum-driven winds, with densities decreasing towards the outskirts. Our moderately lower ISM velocities compared to those found in similar studies at lower redshifts suggest that inflows and internal turbulence might play an increased role at za > 2 and weaken the outflow signatures. Finally, we estimate mass-outflow rates á out that are comparable to the SFRs of the galaxies (hence a mass-loading factor η of the order of unity), and an average escape velocity of 625 km sa1, suggesting that most of the ISM will remain bound to the galaxy halo. © 2022 EDP Sciences. All rights reserved. | |
