Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...429..602m&link_type=abstract
The Astrophysical Journal, vol. 429, no. 2, pt. 1, p. 602-611
Astronomy and Astrophysics
Astrophysics
62
Infrared Imagery, Infrared Spectra, Light (Visible Radiation), Luminosity, Mapping, Seyfert Galaxies, Star Formation, Starburst Galaxies, Arrays, Calibrating, Cameras, Contours, Detectors, Infrared Spectrometers, Infrared Telescopes
Scientific paper
We present visible and infrared images, 1.5 to 2.3 micrometer infrared spectra and (Fe II) 1.64 micrometer, H2 (1 - 0) S(1) 2.121 micrometer, and Brgamma 2.165 micrometer infrared line contour maps obtained to investigate the nature of the activity and the origin of the infrared line emission in two relatively nearby infrared luminous galaxies. NGC 3256 is a merging system exhibiting starburst activity over a region several kpc across and a high infrared luminosity of approximately 3 x 1011 solar luminosity. A specific search for (Si VI) 1.96 micrometer coronal line emission from a possibly visually obscured Seyfert nucleus proved negative. Extremely high star-formation and SN rates of approximately 20 solar mass/year and approximately 1.5/year, respectively, however, are estimated using the observed integrated Brgamma line luminosites and He I 2.06 micrometer/Brgamma ratios together with an existing starburst model. At this rate, the injection energy associated with SN explosions alone could account for the observed (Fe II) 1.64 micrometer and H2(1 - 0)S(1) line luminosities. NGC 4945 is an almost edge-on spiral with an order of magnitude lower infrared luminosity which is powered by both a approximately 400 pc size starburst and a visually obscured Seyfert nucleus which is a variable source of hard X-ray emission and could substantially contribute to the total luminosity. Its star formation efficiency is higher than in NGC 3256 whereas its luminosity and star formation and SN rates of (approximately 0.4 solar mass/year and approximately 0.05/year are much lower although still adequate to account for the excitation of the observed (Fe II) 1.64 micrometer and H2(1 - 0)S(1) lines. Based on previous survey work, however, the large integrated H2(1 - 0)S(1)/Brgamma ratio observed in this galaxy is also indicative of the presence of a Seyfert nucleus. Maps of the Brgamma, (Fe II), and H2 (1 - 0)S(1) line emission reveal significantly different spatial distributions in the two galaxies. In NGC 3256 the emission extends over a region approximately 4 kpc across and shows similar (Fe II) and Brgamma morphologies, whereas the H2 (1 - 0)S(1) emission does not correlate in detail with either. In particular, it is less peaked on the nucleus and traces a spiral arm and embedded source to the south of the nucleus. This source is also prominent in our K' (2.1 micrometer) image but totally obscured by dust in the visible and is probably the nucleus of the merging companion. Additional evidence that the merger is not yet complete is also provided by the fact that the light distribution in the K' image does not correspond to that expected of a relaxed system. In NGC 4945 the Brgamma emission is largely confined to a approximately 380 pc diameter and less than or equal to 190 pc thick disk in the plane of the galaxy whereas both the (Fe II) 1.64 micrometer and H2 (1 - 0)S(1) line emission extends over the full extent of the molecular complex which is a factor of 2 larger perpendicular to the plane. This morphology is consistent with additional excitation by an embedded active galactic nucleus and/or a starburst driven superwind. The similarity of the observed (Fe II) and H2 intensity profiles perpendicular to the plane suggests a common excitation mechanism for the 'excess' emission which we propose can be attributed to partial ionization and heating of molecular gas respectively by X-rays from the nuclear source. The overall conclusion of this study is that NGC 4945 is probably at an advanced stage of its evolution from a starburst to a Seyfert galaxy whereas there is no evidence that such an evolution is occurring yet in the considerably more luminous, merging system, NGC 3256.
Moorwood Alan F. M.
Oliva Ernesto
No associations
LandOfFree
Extended infrared line emission excited by starburst and Seyfert activity in NGC 3256 and NGC 4945 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Extended infrared line emission excited by starburst and Seyfert activity in NGC 3256 and NGC 4945, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Extended infrared line emission excited by starburst and Seyfert activity in NGC 3256 and NGC 4945 will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1253012