THE CHANDRA VIEW OF NGC 4178: THE LOWEST MASS BLACK HOLE IN A BULGELESS DISK GALAXY?

Using high-resolution Chandra data, we report the presence of a weak X-ray point source coincident with the nucleus of NGC 4178, a late-type bulgeless disk galaxy known to have high-ionization mid-infrared (mid-IR) lines typically associated with active galactic nuclei (AGNs). Although the faintness of this source precludes a direct spectral analysis, we are able to infer its basic spectral properties using hardness ratios. X-ray modeling, combined with the nuclear mid-IR characteristics, suggests thatNGC4178 may host a highly absorbed-AGN-accreting at a high rate with a bolometric luminosity on order of 10[sup 43] erg s[sup -1]. Its spectrum is well fit with an absorbed PL model, suggesting that it is a ULX. We also fit its spectrum with the Bulk Motion Comptonization model and suggest that this source is consistent with an intermediate-mass black hole of mass (6 [+ or -] 2) x 10[sup 3] M.