We present the results of a 100ks Chandra observation of the NGC404 nuclear region. The long exposure and excellent spatial resolution of Chandra have enabled us to critically examine the nuclear environment of NGC404, which is known to host a nuclear star cluster and potentially an intermediate-mass black hole (IMBH; on the order of a few times 105 M ·). We find two distinct X-ray sources: a hard, central point source coincident with the optical and radio centers of the galaxy, and a soft extended region that is coincident with areas of high Hα emission and likely recent star formation. When we fit the 0.3-8keV spectra of each region separately, we find the hard nuclear point source to be dominated by a power law (Γ = 1.88), while the soft off-nuclear region is best fit by a thermal plasma model (kT = 0.67keV). We therefore find evidence for both a power-law component and hot gas in the nuclear region of NGC404. We estimate the 2-10keV luminosity to be 1.3+0.8 -0.5 × 1037ergs-1. A low level of diffuse X-ray emission was detected out to ∼15″ (∼0.2kpc) from the nucleus. We compare our results to the observed relationships between power-law photon index and Eddington ratio for both X-ray binaries and low-luminosity active galaxies and find NGC404 to be consistent with other low-luminosity active galaxies. We therefore favor the conclusion that NGC404 harbors an IMBH accreting at a very low level.
Copyright 2015 Elsevier B.V., All rights reserved.
- X-rays: general
- galaxies: active
- galaxies: individual (NGC 404)
- galaxies: nuclei