TY - JOUR
T1 - High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel/PACS
AU - Mashian, N.
AU - Sturm, E.
AU - Sternberg, A.
AU - Janssen, A.
AU - Hailey-Dunsheath, S.
AU - Fischer, J.
AU - Contursi, A.
AU - González-Alfonso, E.
AU - Graciá-Carpio, J.
AU - Poglitsch, A.
AU - Veilleux, S.
AU - Davies, R.
AU - Genzel, R.
AU - Lutz, D.
AU - Tacconi, L.
AU - Verma, A.
AU - Weiss, A.
AU - Polisensky, E.
AU - Nikola, T.
N1 - Publisher Copyright: © 2015. The American Astronomical Society. All rights reserved.
PY - 2015/4/1
Y1 - 2015/4/1
N2 - 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 Jupp = 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-H2 conversion factor, αCO, for each respective source. For the ULIRGs we find α values in the canonical range 0.4-5M⊙ (K km s-1 pc2)-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.
AB - 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 Jupp = 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-H2 conversion factor, αCO, for each respective source. For the ULIRGs we find α values in the canonical range 0.4-5M⊙ (K km s-1 pc2)-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.
KW - Galaxies: Active
KW - Galaxies: Ism
KW - Galaxies: Starburst
UR - http://www.scopus.com/inward/record.url?scp=84926472681&partnerID=8YFLogxK
U2 - https://doi.org/10.1088/0004-637X/802/2/81
DO - https://doi.org/10.1088/0004-637X/802/2/81
M3 - مقالة
SN - 0004-637X
VL - 802
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 81
ER -