X‐Ray–Luminous Galaxies. I.ChandraObservations of IRAS 00317−2142

I. Georgantopoulos, A. Zezas, M. J. Ward
2003 Astrophysical Journal  
We present Chandra observations of the enigmatic galaxy IRAS00317-2142, which is classified as a star-forming galaxy on the basis of the ionization level of its emission lines. However, a weak broad Hα wing and a high X-ray luminosity give away the presence of an active nucleus. The Chandra image reveals a nuclear point source (L_(2-10 keV) 6x10^41 erg s-1), contributing over 80 This is surrounded by some fainter nebulosity extending up to 6 kpc. The nucleus does not show evidence for
more » ... dence for short-term variability. However, we detect long term variations between the ROSAT, ASCA and Chandra epoch. Indeed,the source has decreased its flux by over a factor of 25 in a period of about 10 years. The nuclear X-ray spectrum is well represented by a power-law with a photon index of 1.91^+0.17_-0.15 while the extended emission by a Raymond-Smith component with a temperature of 0.6 keV. We find no evidence for the presence of an Fe line. The nucleus is absorbed by an intrinsic column density of N_H 8x10^20 cm-2. Thus the Chandra observations suggest that at least the X-ray emission is dominated by a type-1 AGN. Then the observed optical spectrum can be explained due to the masking of the nucleus by the powerful star-forming component. These together with previous X-ray observations of galaxies with no clear signs of AGN activity in the optical, (eg NGC6240) cast doubt on the optical classification scheme and have implications for the nature of the 'normal' galaxies detected in deep Chandra X-ray surveys.
doi:10.1086/345598 fatcat:epndggyjhvcx7lbysygkdvwefy