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Cited by 477Stellar, planetary, and galactic studiesGalaxies: Formation, Evolution, PhenomenaAstrophysical Phenomena and Observations

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

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Launhardt, R., Zylka, R., Mezger, P. G.·2002·Astronomy & Astrophysics
DOI 10.1051/0004-6361:20020017
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Abstract

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 pc and scale height pc, and the Nuclear Molecular Disk of same size. The total stellar mass and luminosity of the Nuclear Bulge are and , 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 , distributed in a warm inner disk with 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 of cold and dense material outside the Nuclear Bulge at positive longitudes and 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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  • The central parsec of the GC hosts a compact star cluster (M⋆≃10^6 M⊙) where the majority of stars are old (age≳1 Gyr) with an average rotation vector in the same direction as the Galaxy.

    “The central parsec of the GC is known to host a compact star cluster ( M ⋆ ≃ 10 6 M ⊙ ) where the majority of stars are old (age ≳ 1 Gyr) that have an average rotation vector in the same direction as the Galaxy itself (Becklin et al. 1978; Launhardt et al. 2002; Genzel et al. 1996; Trippe et al. 2008; Schödel et al. 2009; von Fellenberg et al. 2022).”

    From The Fermi/eROSITA bubbles: a look into the nuclear outflow from the Milky Way (2024) · cites this paper as Launhardt et al. 2002

    Section 5.2 identifies a nuclear stellar cluster in the central few parsecs, and §5.4 estimates about 7 × 10^5 solar masses of stars in the central cubic parsec, consistent with the approximate mass claimed. The cited passages do not establish that most stars in the central parsec are at least 1 Gyr old or that the cluster rotates in the same direction as the Galaxy; searches for stellar ages and rotation did not locate those findings. (LLM, conf=0.87)

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Research works printed but not linked: 3

  1. Eckart, A., & Genzel, R. 1998, in Black Holes: Theory and Observation, ed. F. W. Hehl, C. Kiefer, & R. J. K. Metzler (Springer), 60
  2. Hauser, M. G., Kelsall, T., Moseley, S. H. Jr., et al. 1991, in After the First Three Minutes, ed. S. S. Holt, C. L. Bennett, & V. Trimble, AIP Conf. Proc., 222, 161
  3. Lebofsky, M. J., & Rieke, G. H. 1987, in The Galactic Center, ed. D. C. Backer, AIP Conf. Proc., 155, 79

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Authors
Launhardt, R., Zylka, R., & Mezger, P. G.
Affiliations
  • California Institute of Technology (US)
  • University of Cologne (DE)
  • Max Planck Society (DE)
Corresponding author
Mezger, P. G.
ORCID
Launhardt, R.
Venue
Astronomy & Astrophysics
Publisher
EDP Sciences
Published
2002-03
Volume
384
Issue
1
Pages
112-139
ISSN
  • 0004-6361 (ISSN-L)
  • 1432-0746
DOI
10.1051/0004-6361:20020017
OpenAlex
W4293237181
Cited by
477
References
59
Citations by year
2026: 17 · 2025: 20 · 2024: 26 · 2023: 25 · 2022: 27 · 2021: 34 · 2020: 32 · 2019: 19 · 2018: 31 · 2017: 29 · 2016: 23 · 2015: 14 · 2014: 20 · 2013: 27 · 2012: 19
FWCI
6.13
Type
journal article
Language
en
Open access
Locations
  • Astronomy and Astrophysics (publishedVersion)
  • Springer Link (Chiba Institute of Technology) (submittedVersion)
Funders
  • National Science Foundation
  • National Aeronautics and Space Administration
  • Deutsche Forschungsgemeinschaft
  • Max-Planck-Gesellschaft
  • Goddard Space Flight Center
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
Keywords
Galactic Center, nuclear star clusters, nuclear stellar disk, molecular clouds, interstellar radiation field, extinction, Central Molecular Zone, star formation, Galactic bulge, Galactic disk

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