A Chandra view of NGC 3621: a bulgeless galaxy hosting an AGN in its
  early phase?
  We report the detection of a weak X-ray point source coincident with the
nucleus of the bulgeless disk galaxy NGC 3621, recently discovered by Spitzer
to display high ionization mid-infrared lines typically associated with AGN.
These Chandra observations provide confirmation for the presence of an AGN in
this galaxy, adding to the growing evidence that black holes do form and grow
in isolated bulgeless disk galaxies. Although the low signal-to-noise ratio of
the X-ray spectrum prevents us from carrying out a detailed spectral analysis
of the nuclear source, the X-ray results, combined with the IR and optical
spectroscopic results, suggests that NGC 3621 harbors a heavily absorbed AGN,
with a supermassive black hole of relatively small mass accreting at a high
rate. Chandra also reveals the presence of two bright sources straddling the
nucleus located almost symmetrically at 20" from the center. Both sources have
X-ray spectra that are well-fitted by an absorbed power-law model. Assuming
they are at the distance of NGC 3621, these two sources have luminosities of
the order of 1.e39 erg/s, which make them ULXs and suggest that they are black
hole systems. Estimates of the black hole mass based on the X-ray spectral
analysis and scaling laws of black hole systems suggest that the 2 bright
sources might be intermediate mass black holes with M_BH of the order of a few
thousand solar masses. However, higher quality X-ray data combined with
multi-wavelength observations are necessary to confirm these conclusions.
