High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel/PACS

Journal Article · Wed Apr 01 00:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/802/2/81· OSTI ID:22882597

Mashian, N. ^[1]; Sturm, E.; Janssen, A.; Contursi, A.; Graciá-Carpio, J.; Poglitsch, A.; Davies, R.; Genzel, R.; Lutz, D.; Tacconi, L. ^[2]; Sternberg, A. ^[3]; Hailey-Dunsheath, S. ^[4]; Fischer, J.; Polisensky, E. ^[5]; González-Alfonso, E. ^[6]; Veilleux, S. ^[7]; Verma, A. ^[8]; Weiß, A. ^[9]

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2. Max-Planck-Institute for Extraterrestrial Physics (MPE), Giessenbachstraße 1, D-85748 Garching (Germany)
3. The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel)
4. California Institute of Technology, 1200 E California Blvd, Pasadena CA 91125 (United States)
5. Naval Research Laboratory, Remote Sensing Division, 4555 Overlook Ave SW, Washington, DC 20375 (United States)
6. Universidad de Alcalá de Henares, 28871 Alcalá de Henares, Madrid (Spain)
7. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
8. Sub-dept. of Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford, OX1 3RH (United Kingdom)
9. Max-Planck-Institute for Radioastronomy (MPIfR), Auf dem Hügel 69, D-53121 Bonn (Germany)

We report the detection of far-infrared (FIR) CO rotational emission from nearby active galactic nuclei (AGNs) and starburst galaxies, as well as several merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs). Using the Herschel Photodetector Array Camera and Spectrometer (PACS), we have detected transitions in the J{sub upp} = 14–30 range. The PACS CO data obtained here provide the first reference of well-sampled FIR extragalactic CO spectral line energy distributions (SLEDs) for this range. We find a large range in the overall SLED shape, even among galaxies of similar type, demonstrating the uncertainties in relying solely on high-J CO diagnostics to characterize the excitation source of a galaxy. Combining our data with low-J line intensities taken from the literature, we present a CO ratio–ratio diagram and discuss its value in distinguishing excitation sources and physical properties of the molecular gas. The position of a galaxy on such a diagram is less a signature of its excitation mechanism, than an indicator of the presence of warm, dense molecular gas. We then quantitatively analyze the CO emission from a subset of the detected sources with single-component and two-component large velocity gradient (LVG) radiative transfer models to fit the CO SLEDs. From these fits we derive the molecular gas mass and the corresponding CO-to-H{sub 2} conversion factor, α{sub CO}, for each respective source. For the ULIRGs we find α values in the canonical range 0.4– 5M{sub ⊙} (K km s{sup −1} pc{sup 2}){sup −1}, while for the other objects, α varies between 0.2 and 14. Finally, we compare our best-fit LVG model results with previous studies of the same galaxies and comment on any differences.

• OSTI ID: 22882597
• Journal Information: Astrophysical Journal, Vol. 802, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CARBON MONOXIDE
COMPARATIVE EVALUATIONS
DETECTION
EMISSION
ENERGY SPECTRA
EXCITATION
GALAXIES
GALAXY NUCLEI
MASS
RADIANT HEAT TRANSFER
VELOCITY