Abstract
ABSTRACT The majority of star-forming galaxies follow a simple empirical correlation in the star formation rate (SFR) versus stellar mass (M *) plane, of the form SFR ∝ M * &agr; ?> , usually referred to as the star formation main sequence (MS). The physics that sets the properties of the MS is currently a subject of debate, and no consensus has been reached regarding the fundamental difference between members of the sequence and its outliers. Here we combine a set of hydro-dynamical simulations of interacting galactic disks with state-of-the-art radiative transfer codes to analyze how the evolution of mergers is reflected upon the properties of the MS. We present Chiburst, a Markov Chain Monte Carlo spectral energy distribution (SED) code that fits the multi-wavelength, broad-band photometry of galaxies and derives stellar masses, SFRs, and geometrical properties of the dust distribution. We apply this tool to the SEDs of simulated mergers and compare the derived results with the reference output from the simulations. Our results indicate that changes in the SEDs of mergers as they approach coalescence and depart from the MS are related to an evolution of dust geometry in scales larger than a few hundred parsecs. This is reflected in a correlation between the specific star formation rate, and the compactness parameter  ?> , that parametrizes this geometry and hence the evolution of dust temperature ( T dust ?> ) with time. As mergers approach coalescence, they depart from the MS and increase their compactness, which implies that moderate outliers of the MS are consistent with late-type mergers. By further applying our method to real observations of luminous infrared galaxies (LIRGs), we show that the merger scenario is unable to explain these extreme outliers of the MS. Only by significantly increasing the gas fraction in the simulations are we able to reproduce the SEDs of LIRGs.
Highlights
Over the last decade, deep optical and infrared surveys have established that the majority of star-forming galaxies up to z = 2.5 follow a simple scaling correlation linking their stellar mass with 0.5 < a
The simulations cover a broad range of galactic masses, interactions stages, luminosities, and morphologies; we expect them to be a fair sample of the conditions found in real galaxies
In this paper we limit our study of the mock spectral energy distribution (SED) to a single viewing angle, but further down we briefly explore the effect of viewing angle on the derived parameters
Summary
The existence of a MS has been interpreted as evidence that the majority of galaxies throughout cosmic history form stars in a steady, secular mode, in time scales that are longer than their dynamical timescales (Genzel et al 2010; Wuyts et al 2011), a mode that requires a continuous replenishment of gas from the intergalactic medium. In this picture, the outliers above the MS would be explained by starburst events, probably triggered by mergers, with shorter depletion timescales yielding larger specific star formation rates (sSFRs) for systems off the MS. A possible interpretation of this behavior is given in terms of a larger gas fraction ( fgas) in galaxies earlier in cosmic history (e.g., Scoville et al 2015)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
