Spatially resolved star formation and metallicity profiles in post-merger galaxies from MaNGA

Abstract

Large galaxy surveys have demonstrated that galaxy-galaxy mergers can dramatically change the morphologies, star formation rates (SFRs) and metallicities of their constituents. However, most statistical studies have been limited to the measurement of global quantities, through large fibres or integrated colours. In this work, we present the first statistically significant study of spatially resolved star formation and metallicity profiles using integral field spectroscopy, using a sample of ∼20,000 spaxels in 36 visually selected post-merger galaxies from the Mapping Nearby Galaxies with Apache Point Observatory (MaNGA) survey. By measuring offsets from SFR and metallicity scaling relations on a spaxel-by-spaxel basis, we are able to quantify where in the galaxy these properties are most affected by the interaction. We find that the SFR enhancements are generally centrally peaked, by a factor of 2.5 on average, in agreement with predictions from simulations. However, there is considerable variation in the SFR behaviour in the galactic outskirts, where both enhancement and suppression are seen. The median SFR remains enhanced by 0.1 dex out to at least 1.9 Re. The metallicity is also affected out to these large radii, typically showing a suppression of ∼ −0.04 dex.

Interacting galaxies in the IllustrisTNG simulations – II: star formation in the post-merger stage

“…Following coalescence, the SFR enhancement decays to be consistent with the controls. the merger remnants together disregarding their evolution 5 (e.g., Ellison et al 2015;Thorp et al 2019). On the other hand, observational studies use the projected galaxy separation as a proxy for time evolution during the interaction/pair phase of galaxy mergers (e.g., Ellison et al 2013;Patton et al 2016).…”

“…However, the effects of galaxy mergers are not limited to the growth of galaxies. There exists a rich body of theoretical predictions and observational evidence linking mergers to triggering and accelerating gas evolution (i.e., depletion, ejection, enrichment, SFRs (e.g., Ellison et al 2008Ellison et al , 2013Patton et al 2013;Knapen et al 2015; Thorp et al 2019) when compared to their non-interacting counterparts. Coupled with enhanced star formation and AGN activity, feedback processes (e.g., stellar & AGN feedback) play a vital role in the evolution of mergers.…”

Deep learning predictions of galaxy merger stage and the importance of observational realism

“…For example, star-formation correlates strongly with colour. Since interactions between gas rich galaxies are proven triggers of central star formation (Bushouse 1987;Noguchi 1991;Carlberg et al 1994;Mihos & Hernquist 1994Barton et al 2000;Springel 2000;Smith et al 2007;Cox et al 2008;Ellison et al 2008;Patton et al 2011;Hopkins et al 2013;Patton et al 2013;Moreno et al 2015;Sparre & Springel 2016;Thorp et al 2019), a colour-sensitive network may learn to exploit central star-formation to characterize interaction stage through its correlation with colour. However, the negative consequence of identifying/characterizing interactions based on triggered star-formation is that any study which then examines the relationship between interaction stage and star-formation is automatically biased.…”

“…There is now a strong numerical and observational framework linking this rapid and central accumulation of gas to boosts in central star formation rates (e.g. Ellison et al 2008;Patton et al 2011;Hopkins et al 2013;Patton et al 2013;Moreno et al 2015;Sparre & Springel 2016; Thorp et al 2019), dilution of central gas phase metallicity (e.g. Kewley et al 2006;Ellison et al 2008;Rupke et al 2010a,b;Sol Alonso et al 2010;Perez et al 2011;Torrey et al 2012;Moreno et al 2015; Thorp et al 2019) and accretion onto central black holes and triggering of active galactic nuclei (AGN, e.g.…”

“…Ellison et al 2008;Patton et al 2011;Hopkins et al 2013;Patton et al 2013;Moreno et al 2015;Sparre & Springel 2016; Thorp et al 2019), dilution of central gas phase metallicity (e.g. Kewley et al 2006;Ellison et al 2008;Rupke et al 2010a,b;Sol Alonso et al 2010;Perez et al 2011;Torrey et al 2012;Moreno et al 2015; Thorp et al 2019) and accretion onto central black holes and triggering of active galactic nuclei (AGN, e.g. Keel et al 1985;Di Matteo et al 2005;Koss et al 2010;Ellison et al 2011;Satyapal et al 2014;Ellison et al 2015;Goulding et al 2018;Ellison et al 2019).…”