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Physical conditions of molecular gas in the Circinus galaxy Multi-J CO and Ci ^3P_1 →^3P_0 observations

Zhang, Zhi-Yu and Henkel, Christian and Gao, Yu and Güsten, Rolf and Menten, Karl M. and Papadopoulos, Padelis P. and Zhao, Yinghe and Ao, Yiping and Kaminski, Tomasz (2014) Physical conditions of molecular gas in the Circinus galaxy Multi-J CO and Ci ^3P_1 →^3P_0 observations. Astronomy and Astrophysics, 568 . Art. No. A122. ISSN 0004-6361.

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We report mapping observations of the ^(12)CO J = 3 → 2, 4 → 3, 6 → 5, and 7 → 6 transitions and the Ci ^3P→^3P_0 (Ci) 492GHz transition toward the central 40" × 40" region of the Circinus galaxy, using the Atacama Pathfinder EXperiment (APEX) telescope. We also detected ^(13)COJ = 3 → 2 at the central position of Circinus. These observations are to date the highest CO transitions reported in Circinus. With large velocity gradient (LVG) modeling and likelihood analysis we try to obtain density, temperature, and column density of the molecular gas in three regions: the nuclear region (D < 18" ~ 360 pc), the entire central 45" (D < 45" ~ 900 pc) region, and the star-forming (S-F) ring (18" < D < 45"). In the nuclear region, we can fit the CO excitation with a single excitation component, yielding an average condition of n_H_2~10^(3.2) cm^(-3), T_(kin)~ 200 K, and dν/dr~3 km s^(-1) pc^(-1). In the entire 45" region, which covers both the nucleus and the S-F ring, two excitation components are needed with n_H_2~ 10^(4.2) cm^(-3) and 10^(3.0) cm^(-3), T_(kin)~ 60 K and 30 K, and M_H_2~2.3 × 10^7 M_⊙ and 6.6 × 10^7 M_⊙, respectively. The gas excitation in the S-F ring can also be fitted with two LVG components, after subtracting the CO fluxes in the 18" nuclear region. The S-F ring region contributes 80% of the molecular mass in the 45" region. For the entire 45" region, we find a standard conversion factor of N(H_2) /I_(CO 1 → 0) = 0.37 × 10^(20)cm^(-2)(K km s^(-1))^(-1), about 1/5 of the Galactic disk value. The luminosity ratios of Ci and ^(12)COJ = 3 → 2 (R_(CI/CO 3 → 2)) in Circinus basically follow a linear trend, similar to that obtained in high-redshift galaxies. The average R_(CI/CO J = 3 → 2) in Circinus is found to be ~0.2, lying at an intermediate value between non-AGN nuclear regions and high-redshift galaxies.

Item Type:Article
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URLURL TypeDescription
Zhang, Zhi-Yu0000-0002-7299-2876
Gao, Yu0000-0003-0007-2197
Menten, Karl M.0000-0001-6459-0669
Zhao, Yinghe0000-0002-9128-818X
Ao, Yiping0000-0003-3139-2724
Additional Information:© 2014 ESO. Received: 10 September 2013. Accepted: 4 June 2014. Published online 04 September 2014. We thank the anonymous referee for his/her very thorough reading of the draft, and the very detailed comments that have significantly improved the quality of the paper. We are grateful to the staff at the APEX Station of MPIfR for their assistance during the observations. Z.Z. thanks J. Z.Wang, L. J. Shao and K. J. Li for their constructive discussions. Z.Z. acknowledges support from the European Research Council (ERC) in the form of Advanced Grant, cosmicism. This work was partly supported by NSF China grants #11173059 and #11390373, and CAS No. XDB09000000. Y.A. acknowledges support from the grant 11003044/11373007 from the National Natural Science Foundation of China.
Funding AgencyGrant Number
European Research Council (ERC) Advanced GrantUNSPECIFIED
NSFC (China)11173059
NSFC (China)11390373
National Natural Science Foundation of China11003044
National Natural Science Foundation of China11373007
Subject Keywords:galaxies: abundances, galaxies: ISM, galaxies: individual: Circinus, galaxies: evolution, radio lines: galaxies
Record Number:CaltechAUTHORS:20141017-101840124
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Official Citation:Physical conditions of molecular gas in the Circinus galaxy Multi-J CO and Ci 3PP0 observations Zhi-Yu Zhang, Christian Henkel, Yu Gao, Rolf Güsten, Karl M. Menten, Padelis P. Papadopoulos, Yinghe Zhao, Yiping Ao and Tomasz Kaminski A&A 568 A122 (2014) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50488
Deposited By: Ruth Sustaita
Deposited On:17 Oct 2014 17:55
Last Modified:03 Oct 2019 07:24

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