TY - JOUR
T1 - Mid-infrared and X-ray luminosity correlations of X-ray point sources in NGC 1399
AU - Shalima, P.
AU - Jithesh, V.
AU - Jeena, K.
AU - Misra, R.
AU - Ravindranath, S.
AU - Dewangan, G. C.
AU - Ravikumar, C. D.
AU - Babu, B. R.S.
PY - 2013/9
Y1 - 2013/9
N2 - It is known that the infrared (IR) and X-ray luminosities of active galactic nuclei (AGN) are correlated with LIR ̃ LX. Moreover, the IR flux ratio between the 5.8 and3.6 μm bands is a good distinguishing characteristic of AGN or AGN-like behaviour. On the other hand, Galactic X-ray binaries (GXB) are underluminous in the IR with LIR ≪ LX. Since ultraluminous Xray sources in nearby galaxies may be an intermediate class between AGN and GXB, it is interesting to study if their IR properties indicate which kind of objects they resemble. We use Spitzer InfraRed Array Camera (IRAC) images to identifymid-IR counterparts of bright X-ray sources, detected by Chandra in the elliptical galaxy NGC 1399.We find that for sources with AGN-like IR flux ratios, the IR luminosity strongly correlates with that in X-rays, LIR ̃ LX, while for the others, there is no correlation between the two. Some of the former objects may be background AGN. If they are not strongly contaminated by background AGN, this result extends the IR-X-ray luminosity correlation down to LX ̃ 1039 erg s-1. We calculate their g - z colours and find that the bright X-ray sources with IR counterparts are typically blue in optical colour. This is in contrast to typical X-ray sources, without IR counterparts which have predominantly red optical counterparts. We highlight the need for IR or optical spectra of these sources to distinguish background AGN and unveil the effect of the X-ray emission on the different environments of these systems.
AB - It is known that the infrared (IR) and X-ray luminosities of active galactic nuclei (AGN) are correlated with LIR ̃ LX. Moreover, the IR flux ratio between the 5.8 and3.6 μm bands is a good distinguishing characteristic of AGN or AGN-like behaviour. On the other hand, Galactic X-ray binaries (GXB) are underluminous in the IR with LIR ≪ LX. Since ultraluminous Xray sources in nearby galaxies may be an intermediate class between AGN and GXB, it is interesting to study if their IR properties indicate which kind of objects they resemble. We use Spitzer InfraRed Array Camera (IRAC) images to identifymid-IR counterparts of bright X-ray sources, detected by Chandra in the elliptical galaxy NGC 1399.We find that for sources with AGN-like IR flux ratios, the IR luminosity strongly correlates with that in X-rays, LIR ̃ LX, while for the others, there is no correlation between the two. Some of the former objects may be background AGN. If they are not strongly contaminated by background AGN, this result extends the IR-X-ray luminosity correlation down to LX ̃ 1039 erg s-1. We calculate their g - z colours and find that the bright X-ray sources with IR counterparts are typically blue in optical colour. This is in contrast to typical X-ray sources, without IR counterparts which have predominantly red optical counterparts. We highlight the need for IR or optical spectra of these sources to distinguish background AGN and unveil the effect of the X-ray emission on the different environments of these systems.
UR - https://www.scopus.com/pages/publications/84881579814
UR - https://www.scopus.com/pages/publications/84881579814#tab=citedBy
U2 - 10.1093/mnras/stt1052
DO - 10.1093/mnras/stt1052
M3 - Article
AN - SCOPUS:84881579814
SN - 0035-8711
VL - 434
SP - 639
EP - 651
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -