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

Abstract

Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100 Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, onmore » average, two orders of magnitude below the Kennicutt–Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density.« less

Authors:
 [1]; ORCiD logo [2];  [3]; ORCiD logo [4]; ORCiD logo [5]; ORCiD logo [6];  [7];  [8];  [9]
  1. Heidelberg Inst. for Theoretical Studies (Germany); Academia Sinica, Taipei (Taiwan); Yale Univ., New Haven, CT (United States); Univ. of California, Berkeley, CA (United States)
  2. Cardiff Univ. (United Kingdom)
  3. Academia Sinica, Taipei (Taiwan)
  4. Johns Hopkins Univ., Baltimore, MD (United States)
  5. Univ. of Tasmania, Hobart, TAS (Australia)
  6. ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Sydney, NSW (Australia); Univ. of Sydney, NSW (Australia). Sydney Inst. for Astronomy
  7. Inst. for Advanced Study, Princeton, NJ (United States); Princeton Univ., NJ (United States); Observatories of the Carnegie Inst. of Washington, Santa Barbara, CA (United States)
  8. Univ. of Central Lancashire, Preston (United Kingdom)
  9. Leiden Univ. (Netherlands)
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE
OSTI Identifier:
1543968
Resource Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 476; Journal Issue: 1; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; Astronomy & Astrophysics

Citation Formats

van de Voort, Freeke, Davis, Timothy A., Matsushita, Satoki, Rowlands, Kate, Shabala, Stanislav S., Allison, James R., Ting, Yuan-Sen, Sansom, Anne E., and van der Werf, Paul P. An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers. United States: N. p., 2018. Web. doi:10.1093/mnras/sty228.
van de Voort, Freeke, Davis, Timothy A., Matsushita, Satoki, Rowlands, Kate, Shabala, Stanislav S., Allison, James R., Ting, Yuan-Sen, Sansom, Anne E., & van der Werf, Paul P. An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers. United States. doi:10.1093/mnras/sty228.
van de Voort, Freeke, Davis, Timothy A., Matsushita, Satoki, Rowlands, Kate, Shabala, Stanislav S., Allison, James R., Ting, Yuan-Sen, Sansom, Anne E., and van der Werf, Paul P. Mon . "An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers". United States. doi:10.1093/mnras/sty228. https://www.osti.gov/servlets/purl/1543968.
@article{osti_1543968,
title = {An ALMA view of star formation efficiency suppression in early-type galaxies after gas-rich minor mergers},
author = {van de Voort, Freeke and Davis, Timothy A. and Matsushita, Satoki and Rowlands, Kate and Shabala, Stanislav S. and Allison, James R. and Ting, Yuan-Sen and Sansom, Anne E. and van der Werf, Paul P.},
abstractNote = {Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100 Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, on average, two orders of magnitude below the Kennicutt–Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density.},
doi = {10.1093/mnras/sty228},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 1,
volume = 476,
place = {United States},
year = {2018},
month = {1}
}

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