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Using high resolution Chandra data, we report the presence of a weak X-raypoint source coincident with the nucleus of NGC 4178, a late-type bulgelessdisk galaxy known to have high ionization mid-infrared (mid-IR) lines typicallyassociated with active galactic nuclei (AGNs). Although the faintness of thissource precludes a direct spectral analysis, we are able to infer its basicspectral properties using hardness ratios. X-ray modeling, combined with thenuclear mid-IR characteristics, suggests that NGC 4178 may host a highlyabsorbed AGN accreting at a high rate with a bolometric luminosity on order of10^43 ergs/s. The black hole mass estimate, based on our Chandra data andarchival VLA data using the most recent fundamental plane relations is \sim10^4 - 10^5 M\odot, possibly the lowest mass nuclear black hole currentlyknown. There are also three off-nuclear sources, two with a similar brightnessto the nuclear source at 36" and 32" from the center. As with the nuclearsource, hardness ratios are used to estimate spectra for these two sources, andboth are consistent with a simple power- law model with absorption. These twosources have X-ray luminosities of the order of \sim 10^38 ergs/s, which placethem at the threshold between X-ray binaries and ultra-luminous X-ray sources(ULXs). The third off-nuclear source, located 49" from the center, is thebrightest source detected, with an X-ray luminosity of \sim 10^40 ergs/s. Itsspectrum is well-fit with an absorbed power law model, suggesting that it is aULX. We also fit its spectrum with the Bulk Motion Comptonization (BMC) modeland suggest that this source is consistent with an intermediate-mass black hole(IMBH) of mass (6\times2)\times10^3 M\odot.

The Chandra View of NGC 4178: The Lowest Mass Black Hole in a Bulgeless Disk Galaxy?