The nucleus of M33
1993; Institute of Physics; Volume: 105; Linguagem: Inglês
10.1086/116555
ISSN1538-3881
Autores Tópico(s)Stellar, planetary, and galactic studies
Resumoview Abstract Citations (125) References (113) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nucleus of M33 Kormendy, John ; McClure, Robert D. Abstract We have obtained high-resolution surface photometry and velocity dispersion measurements of the semistellar nucleus of M33 to study its structure and to look for a central black hole. The images were obtained with the DAO/CFHT HR Camera; this uses a tip-tilt mirror to correct the motion component of seeing. Our best images have resolution σ_*_ = 0.186" in the B band and σ_*_ = 0.177" in R σ_*_ = Gaussian dispersion radius of the point spread function). The nucleus is unresolved. Its true core radius is r_c_ <~ 0.10" ~ 0.39 pc; this is as small as in core-collapsed globular clusters. The true central surface brightness is μ_0_ <~ 11.3 R mag arcsec^-2^, and the central density is ρ_0_ ~> 5 x 10^5^ M_sun_ pc^-3^. Except for M32 and the nucleus of our Galaxy, this is the most compact galactic core known. The velocity dispersion of the nucleus was measured using the Ca II infrared triplet; σ = 21+/-3 km s^-1^. The seeing-corrected mass-to-light ratio is small, M/L-V_ <~ 0.4. Also, there is a substantial color gradient inside 0.5" radius: the center is {DELTA}(B - R) = 0.44 mag bluer than the rest of the nucleus. These observations and the F-type integrated spectrum imply that the nucleus contains young stars concentrated to the center. It may have been built out of gas funneled to the center from the rest of the disk. The small mass-to-light ratio leaves little room to hide dark matter. We derive a strict limit on the mass of a central black hole, M <~ 5 X 10^4^ M_sun_. The central relaxation time T_r_<~ 2 X 10^7^ yr is so short that core collapse has probably occurred. We estimate how core properties changed during the collapse, and compare the M33 nucleus with M32 and a globular cluster. If a black hole formed in M33, it is likely to have M ~ 10^2^ to 10^3^ M_sun_. Evidently it did not grow monstrous by accretion. M33 is the first high-luminosity galaxy in which we can rule out the presence of a dead quasar. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116555 Bibcode: 1993AJ....105.1793K Keywords: Astronomical Photography; Astronomical Photometry; Black Holes (Astronomy); Galactic Nuclei; Galactic Structure; Globular Clusters; Data Reduction; Elliptical Galaxies; Local Group (Astronomy); Mass To Light Ratios; Astrophysics; GALAXIES: INDIVIDUAL: M33; GALAXIES: NUCLEI full text sources ADS | data products SIMBAD (4) NED (1)
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