Abstract

We present HST/STIS spectra of the Sbc spiral galaxy NGC 4041 which were used to map the velocity field of the gas in its nuclear region. We detect the presence of a compact (r ≃ 0.′′4 ≃ 40 pc), high surface brightness, rotating nuclear disk co-spatial with a nuclear star cluster. The disk is characterized by a rotation curve with a peak to peak amplitude of ∼ 40 km s−1 and is systematically blueshifted by ∼ 10−20 km s−1 with respect to the galaxy systemic velocity. With the standard assumption of constant mass-to-light ratio and with the nuclear disk inclination taken from the outer disk, we find that a dark point mass of (1+0.6 −0.7) × 107 M⊙ is needed to reproduce the observed rotation curve. However the observed blueshift suggests the possibility that the nuclear disk could be dynamically decoupled. Following this line of reasoning we relax the standard assumptions and find that the kinematical data can be accounted for by the stellar mass provided that either the central mass-to-light ratio is increased by a factor of ∼ 2 or that the inclination is allowed to vary. This model results in a 3 upper limit of 6×106 M⊙ on the mass of any nuclear black hole. Overall, our analysis only allows us to set an upper limit of 2×107 M⊙ on the mass of the nuclear BH. If this upper limit is taken in conjunction with an estimated bulge B magnitude of −17.7 and with a central stellar velocity dispersion of ≃ 95 km s−1, then these results are not inconsistent with both the MBH-Lsph and the MBH- ⋆ correlations. Constraints on BH masses in spiral galaxies of types as late as Sbc are still very scarce and therefore the present result adds an important new datapoint to our understanding of BH demography. (Refer to PDF file for exact formulas).

Publication Date

4-1-2003

Comments

Also archived in: arXiv:astro-ph/0211650 v1 29 Nov 2002 Support for proposal GO-8228 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555 This work was partially supported by the Italian Space Agency (ASI) under grants I/R/35/00 and I/R/112/01. This work was partially supported by the Italian Ministry for Instruction, University and Research (MIUR) under grants Cofin00-02-35 and Cofin01-02-02.ISSN:1538-4357 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type

Article

Department, Program, or Center

School of Physics and Astronomy (COS)

Campus

RIT – Main Campus

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