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Variation of Molecular Line Ratios and Cloud Properties in the Arp 299 Galaxy Merger

Aalto, S. and Radford, Simon J. E. and Scoville, N. Z. and Sargent, A. I. (1997) Variation of Molecular Line Ratios and Cloud Properties in the Arp 299 Galaxy Merger. Astrophysical Journal, 475 (2). L107-L110. ISSN 0004-637X. doi:10.1086/310475.

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High-resolution observations of ^(12)CO (2.”3),^(13)CO (3.”9), and HCN (5.”4) J = 1-0 in the galaxy merger Arp 299 (IC 694 and NGC 3690) show that the line ratios vary dramatically across the system. The ^(12)CO/^(13)CO ratio is unusually large, 60 ± 15, at the IC 694 nucleus, where ^(12)CO emission is very strong, and much smaller, 10 ± 3, in the southern extended disk of that galaxy. Elsewhere, the ^(12)CO/^(13)CO line ratio is 5-20, typical of spiral galaxies. The line ratio variation in the overlap between the two galaxies is smaller, ranging from 10 ± 3 in the east to 20 ± 4 in the west. The ^(12)CO/HCN line ratio also varies across Arp 299, although to a lesser degree. HCN emission is bright toward each galaxy nucleus and in the extranuclear region of active star formation; it was not detected in the IC 694 disk or the eastern part of the overlap region, leading to lower limits of 25 and 20, respectively. By contrast, at the nuclei of IC 694 and NGC 3690 the ratios are 9 ± 1 and 14 ± 3, respectively. In the western part of the overlap region it is 11 ± 3. The large ^(12)CO/^(13)CO 1-0 intensity ratio at the nucleus of IC 694 can primarily be attributed to a low-to-moderate optical depth (τ ≾ 1) in the ^(12)CO 1-0 line. These data support the hypothesis that unusually high ^(12)CO/^(13)CO line ratios (>20) are associated with extremely compact molecular distributions in the nuclei of merging galaxies. Relative to ^(12)CO,^(13)CO 1-0 is brightest in quiescent regions of low ^(12)CO surface brightness and weakest in starburst regions and the galactic nuclei. A medium consisting of dense (n = 10^4-10^5 cm^(-3)) and warm (T_k > 50 K) gas will reproduce the extreme line ratios observed in the nucleus of IC 694, where the area filling factor must be at least 20%.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Scoville, N. Z.0000-0002-0438-3323
Sargent, A. I.0000-0002-4633-5098
Additional Information:© 1997 The American Astronomical Society. Received 7 August 1996; accepted 1996 November 13. We thank Peter Bryant for helpful discussions and suggestions. The OVRO mm array is supported in part by NSF grant AST 9314079 and the K. T. and E. L. Norris Foundation. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
Funding AgencyGrant Number
Kenneth T. and Eileen L. Norris FoundationUNSPECIFIED
Associated Universities, Inc.UNSPECIFIED
Subject Keywords:galaxies: evolution—galaxies: individual (Arp 299) — galaxies: ISM — galaxies: starburst — radio lines: galaxies — radio lines: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20190507-103932839
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Official Citation:S. Aalto et al 1997 ApJ 475 L107
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95294
Deposited By: Tony Diaz
Deposited On:07 May 2019 18:32
Last Modified:16 Nov 2021 17:11

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