VLA detection of OH absorption from the elliptical galaxy NGC 1052

Free access article

Issue		A&A Volume 381, Number 1, January I 2002


Page(s)		L29 - L32
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20011604

A&A 381, L29-L32 (2002)
DOI: 10.1051/0004-6361:20011604

Letter

VLA detection of OH absorption from the elliptical galaxy NGC 1052

A. Omar¹, K. R. Anantharamaiah¹, M. Rupen² and J. Rigby³

¹ Raman Research Institute, C.V. Raman Avenue, Bangalore, 560 080, India
² National Radio Astronomy Observatory, Socorro, NM, USA
e-mail: mrupen@aoc.nrao.edu
³ Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
e-mail: jrigby@as.arizona.edu

(Received 3 September 2001 / Accepted 12 November 2001 )

Abstract
VLA observations of OH absorption towards the elliptical galaxy NGC 1052 are presented. Both OH lines, at 1665 and 1667 MHz, were detected in absorption towards the center of NGC 1052. The hyperfine ratio of the two OH lines ( $\tau$ ₁₆₆₇/ $\tau$ ₁₆₆₅) is $2.6\pm0.8$ as compared to 1.8 expected for the excitation under LTE conditions for an optically thin cloud. The column density of OH is estimated to be $2.73\,(\pm0.26)\times10^{14}$ cm ^-2 assuming $T_{\rm ex} \sim10$ K. The centers of both the OH lines are redshifted from the systemic velocity of the galaxy by ~173 km s ^-1. The velocity of OH line coincides with the velocity corresponding to the strongest HI absorption. We suggest that OH absorption is arising from a molecular cloud falling towards the nucleus. The OH line, though narrower, is found to be within the much broader and smoother H ₂O megamaser emission. The possible link between OH/HI and H ₂O emission is discussed.

Key words: galaxies: active -- galaxies: individual: NGC 1052 -- galaxies: ISM -- radio lines: galaxies

Offprint request: A. Omar, aomar@rri.res.in

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