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        Molecular and atomic gas in dust lane early-type galaxies - I : Low star-formation efficiencies in minor merger remnants

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        1503.05162v2 (PDF, 688Kb)
        Author
        Davis, Timothy A.
        Rowlands, Kate
        Allison, James R.
        Shabala, Stanislav S.
        Ting, Yuan-Sen
        Lagos, Claudia del P.
        Kaviraj, Sugata
        Bourne, Nathan
        Dunne, Loretta
        Eales, Steve
        Ivison, Rob J.
        Maddox, Steve
        Smith, Daniel
        Smith, Matthew W. L.
        Temi, Pasquale
        Attention
        2299/16795
        Abstract
        In this work we present IRAM-30m telescope observations of a sample of bulge-dominated galaxies with large dust lanes, which have had a recent minor merger. We find these galaxies are very gas rich, with H2 masses between 4x10^8 and 2x10^10 Msun. We use these molecular gas masses, combined with atomic gas masses from an accompanying paper, to calculate gas-to-dust and gas-to-stellar mass ratios. The gas-to-dust ratios of our sample objects vary widely (between ~50 and 750), suggesting many objects have low gas-phase metallicities, and thus that the gas has been accreted through a recent merger with a lower mass companion. We calculate the implied minor companion masses and gas fractions, finding a median predicted stellar mass ratio of ~40:1. The minor companion likely had masses between ~10^7 - 10^10 Msun. The implied merger mass ratios are consistent with the expectation for low redshift gas-rich mergers from simulations. We then go on to present evidence that (no matter which star-formation rate indicator is used) our sample objects have very low star-formation efficiencies (star-formation rate per unit gas mass), lower even than the early-type galaxies from ATLAS3D which already show a suppression. This suggests that minor mergers can actually suppress star-formation activity. We discuss mechanisms that could cause such a suppression, include dynamical effects induced by the minor merger.
        Publication date
        2015-06-01
        Published in
        Monthly Notices of the Royal Astronomical Society
        Published version
        https://doi.org/10.1093/mnras/stv597
        Other links
        http://hdl.handle.net/2299/16795
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