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Title: A NEW LOOK AT THE GALACTIC CIRCUMNUCLEAR DISK

Abstract

We report the results of millimeter and submillimeter molecular line mapping observations of the Galactic circumnuclear disk (CND). The CND appears as a large, asymmetric disk of warm molecular gas with a high CO J = 3-2/CO J = 1-0 intensity ratio exceeding 1.5. It has a mass of (2-5) x 10{sup 5} M{sub sun} and a diameter of about 10 pc, including a well-known 2-pc radius ring of dense molecular gas around the minispiral. The CND can be clearly traced by the J = 1-0 lines of HCN, H{sup 13}CN, HCO{sup +}, and HNC, but it is barely traced by N{sub 2}H{sup +}, SiO, CCS, and HC{sub 3}N lines. These data confirm the entity of the CND, and the 2-pc ring is just a part of it. Line ratios suggest that the CND is chemically immature, having higher density and higher temperature than the ambient gas. A one-zone large-velocity-gradient analysis finds that molecular gas in the CND has a typical kinetic temperature of T{sub k} {approx_equal} 63 K and H{sub 2} density of n(H{sub 2}) {approx_equal} 10{sup 4.1} cm{sup -3}. The bulk of the CND seems to have an overall, systematic infall motion, with a velocity of V{sub infall}more » {approx_equal} 50 km s{sup -1}. Our results are consistent with the scenario that the CND has been formed by tidal capture and disruption of a giant molecular cloud (GMC). The progenitor GMC may have been formed recently inside the 120-pc ring, possibly by the encounter with the small inner bar of the Galaxy. Toomre's Q parameter indicates that the CND is gravitationally stable now, but it will become unstable and fragment as gas accumulates at r {approx_equal} 2 pc. It would trigger a burst of star formation, and subsequent processes could enhance the mass accretion rate to Sgr A*.« less

Authors:
;  [1];  [2];  [3]
  1. Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522 (Japan)
  2. Research Center for the Early Universe and Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
  3. Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
Publication Date:
OSTI Identifier:
21576837
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 732; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/732/2/120; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON MONOXIDE; GALAXIES; HYDROCYANIC ACID; HYDROGEN; NITRILES; SILICON OXIDES; CARBON COMPOUNDS; CARBON OXIDES; CHALCOGENIDES; ELEMENTS; HYDROGEN COMPOUNDS; INORGANIC ACIDS; INORGANIC COMPOUNDS; NONMETALS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; SILICON COMPOUNDS

Citation Formats

Oka, Tomoharu, Tanaka, Kunihiko, Nagai, Makoto, and Kamegai, Kazuhisa. A NEW LOOK AT THE GALACTIC CIRCUMNUCLEAR DISK. United States: N. p., 2011. Web. doi:10.1088/0004-637X/732/2/120.
Oka, Tomoharu, Tanaka, Kunihiko, Nagai, Makoto, & Kamegai, Kazuhisa. A NEW LOOK AT THE GALACTIC CIRCUMNUCLEAR DISK. United States. https://doi.org/10.1088/0004-637X/732/2/120
Oka, Tomoharu, Tanaka, Kunihiko, Nagai, Makoto, and Kamegai, Kazuhisa. 2011. "A NEW LOOK AT THE GALACTIC CIRCUMNUCLEAR DISK". United States. https://doi.org/10.1088/0004-637X/732/2/120.
@article{osti_21576837,
title = {A NEW LOOK AT THE GALACTIC CIRCUMNUCLEAR DISK},
author = {Oka, Tomoharu and Tanaka, Kunihiko and Nagai, Makoto and Kamegai, Kazuhisa},
abstractNote = {We report the results of millimeter and submillimeter molecular line mapping observations of the Galactic circumnuclear disk (CND). The CND appears as a large, asymmetric disk of warm molecular gas with a high CO J = 3-2/CO J = 1-0 intensity ratio exceeding 1.5. It has a mass of (2-5) x 10{sup 5} M{sub sun} and a diameter of about 10 pc, including a well-known 2-pc radius ring of dense molecular gas around the minispiral. The CND can be clearly traced by the J = 1-0 lines of HCN, H{sup 13}CN, HCO{sup +}, and HNC, but it is barely traced by N{sub 2}H{sup +}, SiO, CCS, and HC{sub 3}N lines. These data confirm the entity of the CND, and the 2-pc ring is just a part of it. Line ratios suggest that the CND is chemically immature, having higher density and higher temperature than the ambient gas. A one-zone large-velocity-gradient analysis finds that molecular gas in the CND has a typical kinetic temperature of T{sub k} {approx_equal} 63 K and H{sub 2} density of n(H{sub 2}) {approx_equal} 10{sup 4.1} cm{sup -3}. The bulk of the CND seems to have an overall, systematic infall motion, with a velocity of V{sub infall} {approx_equal} 50 km s{sup -1}. Our results are consistent with the scenario that the CND has been formed by tidal capture and disruption of a giant molecular cloud (GMC). The progenitor GMC may have been formed recently inside the 120-pc ring, possibly by the encounter with the small inner bar of the Galaxy. Toomre's Q parameter indicates that the CND is gravitationally stable now, but it will become unstable and fragment as gas accumulates at r {approx_equal} 2 pc. It would trigger a burst of star formation, and subsequent processes could enhance the mass accretion rate to Sgr A*.},
doi = {10.1088/0004-637X/732/2/120},
url = {https://www.osti.gov/biblio/21576837}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 732,
place = {United States},
year = {Tue May 10 00:00:00 EDT 2011},
month = {Tue May 10 00:00:00 EDT 2011}
}