http://arxiv.org/abs/2002.09257

We study the atomic gas content and the central stellar mass concentration for a sample of almost 1500 nearby galaxies to investigate the nature of starbursts and the influence of galaxy-galaxy interactions on star formation. We use the catalogue on interacting and merging galaxies in the S$^4$G survey of Knapen et al. (2014) along with archival HI gas masses, stellar masses ($M_{\ast}$), and SFRs (from IRAS far-IR fluxes), and calculate depletion times ($\tau$) and gas fractions. We trace the central stellar mass concentration from the inner slope of the stellar component of the rotation curves, $d_{\rm R}v_{\ast}(0)$. Starbursts – defined as galaxies with a factor $>4$ enhanced SFR relative to a control sample ($\pm 0.2$ dex in stellar mass, $\pm 1$ in $T$-type, non-interacting) – are mainly early-type ($T\lesssim 5$) massive spiral galaxies ($M_{\ast}\gtrsim 10^{10}M_{\odot}$), 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 are not statistically different for interacting and non-interacting galaxies. However, in the case of currently merging galaxies, the median gas depletion time is a factor of $0.4 \pm 0.2$ that of control sample galaxies, and their star formation rates are a factor of $1.9 \pm 0.5$ enhanced, even though the median gas fraction is similar. Starbursts present long-lasting star formation in the circumnuclear regions that causes an enhancement of the central stellar density at $z\approx0$ 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 (Abridged).

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S. Díaz-García and J. Knapen
Mon, 24 Feb 20
36/49

Comments: Accepted for publication in A&A (February 21, 2020). 6 pages, 5 figures