RESOLVING THE FAR-IR LINE DEFICIT: PHOTOELECTRIC HEATING AND FAR-IR LINE COOLING IN NGC 1097 AND NGC 4559
- Department of Physics and Astronomy, University of Toledo, 2801 W Bancroft St., Toledo, OH 43606 (United States)
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Institut d'Astrophysique de Paris, UMR7095 CNRS, Universite Pierre and Marie Curie, 98 bis Boulevard Arago, F-75014 Paris (France)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States)
- Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States)
- NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125 (United States)
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387 (China)
The physical state of interstellar gas and dust is dependent on the processes which heat and cool this medium. To probe heating and cooling of the interstellar medium over a large range of infrared surface brightness, on sub-kiloparsec scales, we employ line maps of [C II] 158 {mu}m, [O I] 63 {mu}m, and [N II] 122 {mu}m in NGC 1097 and NGC 4559, obtained with the Photodetector Array Camera and Spectrometer on board Herschel. We matched new observations to existing Spitzer Infrared Spectrograph data that trace the total emission of polycyclic aromatic hydrocarbons (PAHs). We confirm at small scales in these galaxies that the canonical measure of photoelectric heating efficiency, ([C II] + [O I])/TIR, decreases as the far-infrared (far-IR) color, {nu}f{sub {nu}}(70 {mu}m) {nu}f{sub {nu}}(100 {mu}m), increases. In contrast, the ratio of far-IR cooling to total PAH emission, ([C II] + [O I])/PAH, is a near constant {approx}6% over a wide range of far-IR color, 0.5 < {nu}f{sub {nu}}(70 {mu}m) {nu}f{sub {nu}}(100 {mu}m) {approx}< 0.95. In the warmest regions, where {nu}f{sub {nu}}(70 {mu}m) {nu}f{sub {nu}}(100 {mu}m) {approx}> 0.95, the ratio ([C II] + [O I])/PAH drops rapidly to 4%. We derived representative values of the local ultraviolet radiation density, G{sub 0}, and the gas density, n{sub H}, by comparing our observations to models of photodissociation regions. The ratio G{sub 0}/n{sub H}, derived from fine-structure lines, is found to correlate with the mean dust-weighted starlight intensity, (U), derived from models of the IR spectral energy distribution. Emission from regions that exhibit a line deficit is characterized by an intense radiation field, indicating that small grains are susceptible to ionization effects. We note that there is a shift in the 7.7/11.3 {mu}m PAH ratio in regions that exhibit a deficit in ([C II] + [O I])/PAH, suggesting that small grains are ionized in these environments.
- OSTI ID:
- 22016288
- Journal Information:
- Astrophysical Journal, Vol. 747, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
SPITZER-IRS STUDY OF THE ANTENNAE GALAXIES NGC 4038/39
FAR-INFRARED LINE DEFICITS IN GALAXIES WITH EXTREME L{sub FIR}/M{sub H{sub 2}} RATIOS