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The nuclear bulge of the Galaxy. III. Large-scale physical characteristics of stars and interstellar matter

Launhardt, R. and Zylka, R. and Mezger, P. G. (2002) The nuclear bulge of the Galaxy. III. Large-scale physical characteristics of stars and interstellar matter. Astronomy and Astrophysics, 384 (1). pp. 112-139. ISSN 0004-6361.

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We analyse IRAS and COBE DIRBE data at wavelengths between 2.2 and 240 of the central 500 pc of the Galaxy and derive the large-scale distribution of stars and interstellar matter in the Nuclear Bulge. Models of the Galactic Disk and Bulge are developed in order to correctly decompose the total surface brightness maps of the inner Galaxy and to apply proper extinction corrections. The Nuclear Bulge appears as a distinct, massive disk-like complex of stars and molecular clouds which is, on a large scale, symmetric with respect to the Galactic Centre. It is distinguished from the Galactic Bulge by its flat disk-like morphology, very high density of stars and molecular gas, and ongoing star formation. The Nuclear Bulge consists of an R^(-2) Nuclear Stellar Cluster at the centre, a large Nuclear Stellar Disk with radius 230 ± 20 pc and scale height 45 ± 5 pc, and the Nuclear Molecular Disk of same size. The total stellar mass and luminosity of the Nuclear Bulge are 1.4 ± 0.6 x 10^9 and 2.5 ± 1 x 10^9, respectively. About 70% of the luminosity is due to optical and UV radiation from young massive Main-Sequence stars which are most abundant in the Nuclear Stellar Cluster. For the first time, we derive a photometric mass distribution for the central 500 pc of the Galaxy which is fully consistent with the kinematic mass distribution. We find that the often cited R^(-2) distribution holds only for the central ~30 pc and that at larger radii the mass distribution is dominated by the Nuclear Stellar Disk which has a flatter density profile. The total interstellar hydrogen mass in the Nuclear Bulge is M_H = 2 ± 0.3 x 10^7, distributed in a warm inner disk with R = 110 ± 20 pc and a massive, cold outer torus which contains more than 80% of this mass. Interstellar matter in the Nuclear Bulge is very clumpy with ~90% of the mass contained in dense and massive molecular clouds with a volume filling factor of only a few per cent. This extreme clumpiness, probably caused by the tidal stability limit in the gravitational potential of the Nuclear Bulge, enables the strong interstellar radiation field to penetrate the entire Nuclear Bulge and explains the relatively low average extinction towards the Galactic Centre. In addition, we find 3 x 10^7 of cold and dense material outside the Nuclear Bulge at positive longitudes and 1 x 10^7 at negative longitudes. This material is not heated by the stars in the Nuclear Bulge and gives rise to the observed asymmetry in the distribution of interstellar matter in the Central Molecular Zone.

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Additional Information:© 2002 ESO. Article published by EDP Sciences. Received 31 August 2001; Accepted 16 November 2001; Published online 15 March 2002. We wish to thank W. Reich for assisting with radio continuum data retrieval from the MPIfR archive. L. Bronfman kindly provided the ^(12)CO(1-0) map of the inner Milky Way and D. Lis provided the 800 µm continuum map of the inner NB. We wish to thank A. Schulz, S. Jogee, E. Schinnerer, S. Stolovy, and N. Scoville for helpful comments and stimulating discussions. Our special thanks go to W. Duschl who elucidated the results given here in terms of Active Galactic Nuclei and to the referee, Ian Glass, for useful suggestions. RL acknowledges financial support by a research grant of the Max Planck Society and by NSF grant AST 99-81546. RZ acknowledges finacial support by the Deutsche Forschungsgemeinschaft. The COBE datasets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group and were provided by the National Space Science Data Center. SkyView was developed and is maintained under NASA ADP Grant NAS 5-32068 with P. I. Thomas A. McGlynn under the auspices of the High Energy Astrophysics Science Archive Research Center (HEASARC) at the Goddard Space Flight Center Laboratory for High Energy Astrophysics.
Funding AgencyGrant Number
Max Planck SocietyUNSPECIFIED
NSFAST 99-81546
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
NASANAS 5-32068
Subject Keywords:dust, extinction - ISM: structure - Galaxy: centre - Galaxy: structure - infrared: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20180213-125653000
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Official Citation:The nuclear bulge of the Galaxy - III. Large-scale physical characteristics of stars and interstellar matter R. Launhardt, R. Zylka and P. G. Mezger A&A, 384 1 (2002) 112-139. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84814
Deposited By: Tony Diaz
Deposited On:13 Feb 2018 21:08
Last Modified:03 Oct 2019 19:23

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