- [*] Is there really a Supermassive Black Hole at the nucleus
of the Sbc spiral galaxy NGC 4041?
- Marconi A., Axon D., Capetti A., Maciejewski W., Atkinson, J.,
Batcheldor, D., Binney J., Carollo M., Dressel L.,
Ford H., Gerssen J., Hughes M., Macchetto D.,
Merrifield M., Scarlata C., Sparks B., Stiavelli M.,
Tsvetanov Z., van der Marel R.P.
- ApJ, 586, 868-890, 2003
this paper in the ADS
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 and is systematically blueshifted
by 10 - 20 km/s 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(-0.7;+0.6) 10^7 Msun 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 sigma upper limit of 6 10^6 Msun on the mass of
any nuclear black hole. Overall, our analysis only allows us to set an
upper limit of 2 10^7 Msun on the mass of the nuclear black hole. 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, then these results are not inconsistent with both the
MBH-Lsph and the MBH-sigma correlations. Constraints on black hole
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 black hole demography.
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Last modified March 30, 2003.
Roeland van der Marel,