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Warm Molecular Gas in Luminous Infrared Galaxies

Lu, N. and Zhao, Y. and Xu, C. K. and Gao, Y. and Armus, L. and Mazzarella, J. M. and Isaak, K. G. and Petric, A. O. and Charmandaris, V. and Díaz-Santos, T. and Evans, A. S. and Howell, J. and Appleton, P. and Inami, H. and Iwasawa, K. and Leech, J. and Lord, S. and Sanders, D. B. and Schulz, B. and Surace, J. and van der Werf, P. P. (2014) Warm Molecular Gas in Luminous Infrared Galaxies. Astrophysical Journal Letters, 787 (2). Art. No. L23. ISSN 2041-8205.

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We present our initial results on the CO rotational spectral line energy distribution (SLED) of the J to J−1 transitions from J = 4 up to 13 from Herschel SPIRE spectroscopic observations of 65 luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey (GOALS). The observed SLEDs change on average from one peaking at J ≤ 4 to a broad distribution peaking around J ~6−7 as the IRAS 60-to-100μm color, C(60/100), increases. However, the ratios of a CO line luminosity to the total infrared luminosity, L_(IR), show the smallest variation for J around 6 or 7. This suggests that, for most LIRGs, ongoing star formation (SF) is also responsible for a warm gas component that emits CO lines primarily in the mid-J regime (5 ≾ J ≾ 10). As a result, the logarithmic ratios of the CO line luminosity summed over CO(5−4), (6−5), (7−6), (8−7) and (10−9) transitions to L_(IR), log R_(midCO), remain largely independent of C(60/100), and show a mean value of −4.13 (≡ log R^(SF)_(midCO)) and a sample standard deviation of only 0.10 for the SF-dominated galaxies. Including additional galaxies from the literature, we show, albeit with small number of cases, the possibility that galaxies, which bear powerful interstellar shocks unrelated to the current SF, and galaxies, in which an energetic active galactic nucleus contributes significantly to the bolometric luminosity, have their R_(midCO) higher and lower than R^(SF)_(midCO), respectively.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lu, N.0000-0002-8948-1044
Zhao, Y.0000-0002-9128-818X
Xu, C. K.0000-0002-1588-6700
Gao, Y.0000-0003-0007-2197
Armus, L.0000-0003-3498-2973
Mazzarella, J. M.0000-0002-8204-8619
Petric, A. O.0000-0003-4030-3455
Charmandaris, V.0000-0002-2688-1956
Díaz-Santos, T.0000-0003-0699-6083
Evans, A. S.0000-0003-2638-1334
Appleton, P.0000-0002-7607-8766
Inami, H.0000-0003-4268-0393
Iwasawa, K.0000-0002-4923-3281
Sanders, D. B.0000-0002-1233-9998
Surace, J.0000-0001-7291-0087
van der Werf, P. P.0000-0001-5434-5942
Additional Information:© 2014 American Astronomical Society. Received 2014 March 25; accepted 2014 May 1; published 2014 May 13. Based on Herschel observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. This Letter benefited from a number of useful comments made by an anonymous referee. This work is based in part on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. Support for this work was provided in part by NASA through an award issued by JPL/Caltech. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies: active, galaxies: ISM, galaxies: star formation, infrared: galaxies, ISM: molecules, submillimeter: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20140520-090210121
Persistent URL:
Official Citation:Warm Molecular Gas in Luminous Infrared Galaxies N. Lu et al. 2014 ApJ 787 L23
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45833
Deposited By: Ruth Sustaita
Deposited On:28 May 2014 19:01
Last Modified:05 Nov 2019 05:58

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