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Title: Molecular gas heating mechanisms, and star formation feedback in merger/starbursts: NGC 6240 and Arp 193 as case studies

We used the SPIRE/FTS instrument aboard the Herschel Space Observatory to obtain the Spectral Line Energy Distributions (SLEDs) of CO from J = 4-3 to J = 13-12 of Arp 193 and NGC 6240, two classical merger/starbursts selected from our molecular line survey of local Luminous Infrared Galaxies (L {sub IR} ≥ 10{sup 11} L {sub ☉}). The high-J CO SLEDs are then combined with ground-based low-J CO, {sup 13}CO, HCN, HCO{sup +}, CS line data and used to probe the thermal and dynamical states of their large molecular gas reservoirs. We find the two CO SLEDs strongly diverging from J = 4-3 onward, with NGC 6240 having a much higher CO line excitation than Arp 193, despite their similar low-J CO SLEDs and L {sub FIR}/L {sub CO,} {sub 1} {sub –0}, L {sub HCN}/L {sub CO} (J = 1-0) ratios (proxies of star formation efficiency and dense gas mass fraction). In Arp 193, one of the three most extreme starbursts in the local universe, the molecular SLEDs indicate a small amount (∼5%-15%) of dense gas (n ≥ 10{sup 4} cm{sup –3}) unlike NGC 6240 where most of the molecular gas (∼60%-70%) is dense (n ∼ (10{sup 4}-10{sup 5})more » cm{sup –3}). Strong star-formation feedback can drive this disparity in their dense gas mass fractions, and also induce extreme thermal and dynamical states for the molecular gas. In NGC 6240, and to a lesser degree in Arp 193, we find large molecular gas masses whose thermal states cannot be maintained by FUV photons from Photon-Dominated Regions. We argue that this may happen often in metal-rich merger/starbursts, strongly altering the initial conditions of star formation. ALMA can now directly probe these conditions across cosmic epoch, and even probe their deeply dust-enshrouded outcome, the stellar initial mass function averaged over galactic evolution.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ; ;  [5] ;  [6] ;  [7] ;  [8]
  1. School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff, CF24 3AA (United Kingdom)
  2. Purple Mountain Observatory/Key Lab for Radio Astronomy, 2 West Beijing Road, Nanjing 210008 (China)
  3. Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing, I. Metaxa and Vas. Pavlou str., GR-15236 Athens (Greece)
  4. Max Planck Institute für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
  5. Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)
  6. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
  7. Research and Scientific Support Department, European Space Agency, Keplerlaan 1, 2200 AG Noordwijk (Netherlands)
  8. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, Jiangsu 210008 (China)
Publication Date:
OSTI Identifier:
22356581
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 788; 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; ABUNDANCE; CARBON 13; CARBON MONOXIDE; DUSTS; EFFICIENCY; ENERGY SPECTRA; EXCITATION; FEEDBACK; GALACTIC EVOLUTION; GALAXIES; MASS; METALS; MOLECULES; PHOTONS; SPACE; STARS; UNIVERSE