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          Institute: MPI für Radioastronomie     Collection: Publikationen des MPI für Radioastronomie     Display Documents

ID: 125371.0, MPI für Radioastronomie / Publikationen des MPI für Radioastronomie
Dense gas in nearby galaxies - XV. Hot ammonia in NGC 253, Maffei 2 and IC 342
Authors:Mauersberger, R.; Henkel, C.; Weiss, A.; Peck, A. B.; Hagiwara, Y.
Date of Publication (YYYY-MM-DD):2003-05
Title of Journal:Astronomy & Astrophysics
Journal Abbrev.:Astron. Astrophys.
Issue / Number:2
Start Page:561
End Page:571
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:The detection of NH3 inversion lines up to the (J,K) = (6,6) level is reported toward the central regions of the nearby galaxies NGC 253, Maffei 2, and IC 342. The observed lines are up to 406 K (for (J,K) = (6,6)) and 848 K (for the (9,9) transition) above the ground state and reveal a warm (T-kin = 100...140 K) molecular component toward all galaxies studied. The tentatively detected (J,K) = (9,9) line is evidence for an even warmer (>400 K) component toward IC 342. Toward NGC 253, IC 342 and Maffei 2 the global beam averaged NH3 abundances are 1-2 x 10(-8), while the abundance relative to warm H-2 is around 10(-7). The temperatures and NH3 abundances are similar to values found for the Galactic central region. C-shocks produced in cloud-cloud collisions can explain kinetic temperatures and chemical abundances. In the central region of M 82, however, the NH3 emitting gas component is comparatively cool (similar to30 K). It must be dense (to provide sufficient NH3 excitation) and well shielded from dissociating photons and comprises only a small fraction of the molecular gas mass in M 82. An important molecular component, which is warm and tenuous and characterized by a low ammonia abundance, can be seen mainly in CO. Photon dominated regions (PDRs) can explain both the high fraction of warm H-2 in M 82 and the observed chemical abundances.
Free Keywords:galaxies : individual : NGC 253, Maffei 2, IC 342, M 82, galaxies : ISM, galaxies : starburst, galaxies : abundances, radio lines : galaxies
Comment of the Author/Creator:Date: 2003, MAY
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Radioastronomie
External Affiliations:IRAM, E-18012 Granada, Spain.; Max Planck Inst Radioastron, D-53121 Bonn, Germany.; Univ Bonn, Inst Radioastron, D-53121 Bonn, Germany.; SMA, Hilo, HI 96721 USA.; Westerbork Observ, ASTRON, NL-7990 AA Dwingeloo, Netherlands.
Identifiers:ISI:000182678800022 [ID No:1]
ISSN:0004-6361 [ID No:2]
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