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Title: Strong far-infrared cooling lines, peculiar CO kinematics, and possible star-formation suppression in Hickson compact group 57

We present [C II] and [O I] observations from Herschel and CO(1-0) maps from the Combined Array for Research in Millimeter Astronomy (CARMA) of the Hickson compact group HCG 57, focusing on the galaxies HCG 57a and HCG 57d. HCG 57a has been previously shown to contain enhanced quantities of warm molecular hydrogen consistent with shock or turbulent heating. Our observations show that HCG 57d has strong [C II] emission compared to L {sub FIR} and weak CO(1-0), while in HCG 57a, both the [C II] and CO(1-0) are strong. HCG 57a lies at the upper end of the normal distribution of the [C II]/CO and [C II]/FIR ratios, and its far-infrared (FIR) cooling supports a low-density, warm, diffuse gas that falls close to the boundary of acceptable models of a photon-dominated region. However, the power radiated in the [C II] and warm H{sub 2} emissions have similar magnitudes, as seen in other shock-dominated systems and predicted by recent models. We suggest that shock heating of the [C II] is a viable alternative to photoelectric heating in violently disturbed, diffuse gas. The existence of shocks is also consistent with the peculiar CO kinematics in the galaxy, indicating that highly noncircularmore » motions are present. These kinematically disturbed CO regions also show evidence of suppressed star formation, falling a factor of 10-30 below normal galaxies on the Kennicutt-Schmidt relation. We suggest that the peculiar properties of both galaxies are consistent with a highly dissipative, off-center collisional encounter between HCG 57d and 57a, creating ring-like morphologies in both systems. Highly dissipative gas-on-gas collisions may be more common in dense groups because of the likelihood of repeated multiple encounters. The possibility of shock-induced star-formation suppression may explain why a subset of these HCG galaxies has been found previously to fall in the mid-infrared green valley.« less
Authors:
; ; ; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ;  [6] ; ;  [7] ;  [8] ;  [9] ;  [10] ;  [11]
  1. Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)
  2. Departamento de Física Teórica y del Cosmos, Universidad de Granada, E-18071 Granada (Spain)
  3. NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125 (United States)
  4. Institut d'Astrophysique Spatiale, Université Paris-Sud XI, F-91405 Orsay Cedex (France)
  5. Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR-15236 Penteli (Greece)
  6. Astrophysics Cosmology and Gravity Centre, Dept of Astronomy, University of Cape Town, Private Bag X3, Rondebosch, 7701, Republic of South Africa (South Africa)
  7. Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia)
  8. The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden)
  9. Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)
  10. Departamento Astronomía Extragaláctica, Instituto Astrofísica Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain)
  11. University of Massachusetts, Astronomy Department, Amherst, MA 01003 (United States)
Publication Date:
OSTI Identifier:
22370000
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 795; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; CARBON MONOXIDE; COLLISIONS; COOLING; DENSITY; DISTRIBUTION; EMISSION; EVOLUTION; GALAXIES; HYDROGEN; PHOTONS; SHOCK HEATING; STARS; TURBULENT HEATING; VALLEYS