Near-infrared light and the morphology of ARP 220

Abstract

view Abstract Citations (8) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Light and the Morphology of ARP 220 Smith, J. ; Gehrz, R. D. ; Grasdalen, G. L. ; Hackwell, John A. ; Dietz, R. D. Abstract We present 2.2 micron imaging and a near-infrared energy distribution for the luminous galaxy Arp 220. The image reveals a 40" (20 kpc) diameter source of extended emission centered symmetrically on a single bright peak. This near-infrared peak coincides with the position of maximum radio continuum emission and probably the dynamical center of the galaxy. The near-infrared energy distribution was observed at the position of peak 2.2 micron emission; it confirms that Arp 220 is much redder than normal galaxies. Together, the image and energy distribution give νFnu_ = 8 x 10^-14^ W m^-2^ and a luminosity of 1 x 10^10^ L_sun_ at near-infrared wavelengths for the central 40" of Arp 220. The observed near-infrared values of size and luminosity are common to normal giant galaxies. No infrared evidence is found for interacting galaxies, the original explanation of Arp 220. The flux transmitted from 0.36 to 2.2 microns by the dust of Arp 220 is 1.5 x 10^-13^ W m^-2^. This value is approximately 50 times less than the flux observed from Arp 220 at far-infrared wavelengths, confirming that almost all (98%) of the galaxy's light is reradiated by dust. No single component morphology, spheroidal or disk, describes Arp 220 adequately. We explain it as a hybrid galaxy form, consisting of an active giant elliptical galaxy with an extensive disk of interstellar matter oriented edge-on to the observed line of sight and centered on the galaxy's nucleus. Starlight from the host elliptical galaxy gives the near-infrared morphology. Obscuration by diffuse dust of the disk gives the double-lobed morphology and band of red color exhibited by optical observations. Observed signs of energetic activity include compact sources of nonthermal radio continuum emission and dust reradiation, both proximate to the near-infrared nucleus. Some radio galaxies (e.g., Cygnus A and Centaurus A) have properties in common with Arp 220, including multiple-component morphologies and great amounts of dust reradiation. We compare Arp 220 with five familiar radio galaxies having dust emission bright enough to be detected by IRAS. The connection with radio galaxies led us to consider more than one type of heating source for the dust of Arp 220. Hot stars are probable sources of heating for the diffuse dust and perhaps some portion of a nuclear component. Heating by a nonstellar source of ultraviolet radiation is possible at the nucleus. If significant, the nonstellar source would have a luminosity of ~10^12^ L_sun_ and may be a luminous relative of the nuclear sources of excitation used to explain the optical spectra of Cygnus A and related active galaxies. Neither type of dust heating source should contribute much to the observed near-infrared flux. Publication: The Astrophysical Journal Pub Date: June 1988 DOI: 10.1086/166361 Bibcode: 1988ApJ...329..107S Keywords: Galactic Structure; Infrared Sources (Astronomy); Morphology; Near Infrared Radiation; Radio Emission; Star Formation; Cosmic Dust; Energy Distribution; Line Of Sight; Stellar Luminosity; Astrophysics; GALAXIES: INDIVIDUAL NAME: ARP 220; GALAXIES: STRUCTURE; INFRARED: SOURCES; INTERSTELLAR: GRAINS; STARS: FORMATION full text sources ADS | data products SIMBAD (6) NED (6)