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Astron. Astrophys. 315, L117-L120 (1996)

ISM parameters in the normal galaxy NGC5713*

S.D. Lord1, S. Malhotra1, T. Lim2, G. Helou1, R.H. Rubin3, G.J. Stacey4, D.J. Hollenbach3, M.W. Werner5, H.A. Thronson Jr.6, C.A. Beichman1, H. Dinerstein7, D.A. Hunter8, K.Y. Lo9, and N.Y. Lu1

1 IPAC, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
2 ESA Villafranca Satellite Tracking Station, Apartado 50727, E-28080 Madrid, Spain
3 NASA/Ames Research Center, MS 245-6, Moffett Field, CA 94035, USA
4 Cornell University, Astronomy Department, 220 Space Science Building, Ithaca, NY 14853, USA
5 Jet Propulsion Laboratory, MS 233-303, 4800 Oak Grove Rd., Pasadena, CA 91109, USA
6 University of Wyoming, Wyoming Infrared Observatory, Laramie, WY 82071, USA
7 University of Texas, Astronomy Department, RLM 15.308, Texas, Austin, TX 78712, USA
8 Lowell Observatory, 1400 Mars Hill Rd., Flagstaff, AZ 86001, USA
9 University of Illinois, Astronomy Department, 1002 W. Green St., Urbana, IL 61801, USA

Received 8 August 1996 / Accepted 1 October 1996

Abstract. We report ISO Long Wavelength Spectrometer (LWS) observations of the Sbc galaxy NGC5713. We have obtained strong detections of the fine-structure forbidden transitions img1.gif CII img2.gif 158  img3.gifm, img1.gif OI img2.gif 63  img3.gifm, and img1.gif OIII img2.gif 88  img3.gifm, and significant upper limits for img1.gif NII img2.gif 122  img3.gifm, img1.gif OIII img2.gif 52  img3.gifm, and img1.gif NIII img2.gif 57  img3.gifm, and have measured the galaxy's FIR dust continuum. These observations represent the first FIR line survey of a nearly normal galaxy and allow us to make comparisons with COBE results for the Milky Way, and with KAO observations of IR-bright starburst galaxies. We find that NGC5713 displays a fairly high img1.gif CII img2.gif /FIR ratio ( img4.gif %). Under the assumption that the disk emission is dominated by photodissociated molecular gas, we model the FIR continuum and the img1.gif CII img2.gif and img1.gif OI img2.gif line fluxes to derive the density of the warm atomic gas surrounding molecular clouds and the UV flux incident on the clouds. In this model, we find higher densities and lower UV fluxes in NGC5713 than are typical for starburst galaxies, but higher UV fluxes than suggested for the disks of NGC6946 and the Milky Way. We also discuss alternative origins for the strong img1.gif CII img2.gif emission, such as from a diffuse component of cold HI .

Key words: galaxies: individual - NGC5713; galaxies: ISM - galaxies: starburst - infrared: galaxies

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

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Last change: December 16, 1996
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