Gas fractions and depletion times in galaxies with different degrees of interaction

• Published in: Astronomy and astrophysics (Berlin) 2020-03, Vol.635, p.A197
• Main Authors: Díaz-García, S., Knapen, J. H.
• Format: Article
• Language: English
• Subjects: Atomic properties; Depletion; Fluxes; Galactic evolution; Galactic rotation; Galaxy mergers & collisions; Interacting galaxies; Spiral galaxies; Star & galaxy formation; Star formation; Starburst galaxies; Starbursts; Stars & galaxies; Stellar mass
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201937384

Context . A moderate enhancement of the star formation rates (SFR) in local interacting galaxies has been reported, but the physical mechanisms leading to this increase are not clear. Aims . We study the atomic gas content and the central stellar mass concentration for a sample of almost 1500 nearby galaxies to further investigate the nature of starbursts and the influence of galaxy-galaxy interactions on star formation. Methods . We used a sample of catalogued interacting and non-interacting galaxies in the S 4 G survey – along with archival H  I gas masses, stellar masses ( M * ), and SFRs from IRAS far-infrared fluxes – and calculate depletion times ( τ ) and gas fractions. We traced the central stellar mass concentration from the inner slope of the stellar component of the rotation curves, d R v * (0). Starbursts are defined as galaxies with a factor > 4 enhanced SFR relative to a control sample of non-interacting galaxies which are ±0.2 dex in stellar mass and ±1 in T -type. Results . Starbursts are mainly early-type ( T  ≲ 5), massive spiral galaxies ( M *  ≳ 10 10   M ⊙ ) that are not necessarily interacting. For a given stellar mass bin, starbursts are characterised by lower gas depletion times, similar gas fractions, and larger central stellar mass concentrations than non-starburst galaxies. The global distributions of gas fraction and gas depletion time of interacting galaxies are not statistically different from those of their non-interacting counterparts. However, in the case of currently merging galaxies, the median gas depletion time is a factor of 0.4 ± 0.2 that of control sample galaxies, and their SFRs are a factor of 1.9 ± 0.5 enhanced, even though the median gas fraction is similar. Conclusions . Starbursts present long-lasting star formation in circumnuclear regions, which causes an enhancement of the central stellar density at z  ≈ 0 in both interacting and non-interacting systems. Starbursts have low gas depletion timescales, yet similar gas fractions as normal main-sequence galaxies. Galaxy mergers cause a moderate enhancement of the star formation efficiency.