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An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers

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van de Voort, F, Davis, TA, Matsushita, S, Rowlands, K, Shabala, SS ORCID: 0000-0001-5064-0493, Allison, JR, Ting, T-S, Sansom, AE and van der Werf, PP 2018 , 'An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers' , Monthly Notices Royal Astronomical Society, vol. 476 , pp. 122-132 , doi: 10.1093/mnras/sty228.

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Abstract

Gas-rich minor mergers contribute significantly to the gas reservoir ofearly-type galaxies (ETGs) at low redshift, yet the star formation efficiency(SFE; the star formation rate divided by the molecular gas mass) appears to bestrongly suppressed following some of these events, in contrast to the morewell-known merger-driven starbursts. We present observations with the AtacamaLarge Millimeter/submillimeter Array (ALMA) of six ETGs, which have eachrecently undergone a gas-rich minor merger, as evidenced by their disturbedstellar morphologies. These galaxies were selected because they exhibitextremely low SFEs. We use the resolving power of ALMA to study the morphologyand kinematics of the molecular gas. The majority of our galaxies exhibitspatial and kinematical irregularities, such as detached gas clouds, warps, andother asymmetries. These asymmetries support the interpretation that thesuppression of the SFE is caused by dynamical effects stabilizing the gasagainst gravitational collapse. Through kinematic modelling we derive highvelocity dispersions and Toomre Q stability parameters for the gas, but cautionthat such measurements in edge-on galaxies suffer from degeneracies. Weestimate merger ages to be about 100~Myr based on the observed disturbances inthe gas distribution. Furthermore, we determine that these galaxies lie, onaverage, two orders of magnitude below the Kennicutt-Schmidt relation forstar-forming galaxies as well as below the relation for relaxed ETGs. Wediscuss potential dynamical processes responsible for this strong suppressionof star formation surface density at fixed molecular gas surface density.

Item Type: Article
Authors/Creators:van de Voort, F and Davis, TA and Matsushita, S and Rowlands, K and Shabala, SS and Allison, JR and Ting, T-S and Sansom, AE and van der Werf, PP
Keywords: galaxy evolution, galaxy formation, star formation, ISM
Journal or Publication Title: Monthly Notices Royal Astronomical Society
Publisher: Blackwell Publishing Ltd
ISSN: 0035-8711
DOI / ID Number: 10.1093/mnras/sty228
Copyright Information:

Copyright 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

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