CHANDRA OBSERVATIONS OF MRK 273: UNVEILING THE CENTRAL AGN AND THE EXTENDED HOT GAS HALO

X.-Y. Xia(Dept. of Physics, Tianjin Normal University, 300074 Tianjin, China) S.J. Xue (National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, 100012 Beijing, China), S. Mao (Univ. of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK),

Abstract

We report X-ray results of the ultraluminous IRAS galaxy Mrk 273 obtained using the ACIS-S3 instrument on board Chandra. The high resolution X-ray image, for the first time, reveals a compact hard X-ray nucleus. Its position is coincident with the northern nucleus identified in the optical, infrared, radio and in molecular CO maps. Its X-ray energy distribution is well described by a heavily obscured AGN spectra with an absorbed power-law plus a narrow FeK$\alpha$ emission line at 6.4 keV. The neutral hydrogen column density is about $4\times 10^{23} cm^{-2}$, implying an absorption-corrected X-ray luminosity (0.1-10 keV) for the nucleus of $L_x\approx 6.5\times 10^{43} ergs~s^{-1}$ for $H_0=50 km~s^{-1} {\rm Mpc}^{-1}$. The X-ray properties therefore firmly establishes the northern nucleus of Mrk 273 as a Seyfert 2 active galactic nucleus. There are also bright soft X-ray clumps and diffuse soft X-ray emissions surrounding the central hard X-ray nucleus within the 10'' of the nuclear region. Its spectrum can be fitted by a MEKAL thermal model with temperature of about 0.8 keV and high metallicity ( $Z\sim 1.5Z_\odot$) plus emission lines from $\alpha$ elements and ions. We find that a soft X-ray clump, about 4'' (projected separation of about 4 kpc) southwest of the northern hard X-ray nucleus, is coincident with a nebula with strong OIII emissions. Further outside the central region, the Chandra observations reveal a very extended hot halo in Mrk 273. The X-ray halo encompasses the entire optical tidal tail and plume, with a projected size of about $54 kpc\times 34 kpc$. The total soft X-ray luminosity (0.1-2.4 keV) of the hot halo is $L_x\approx 1.9\times 10^{41} ergs~s^{-1}$, in the range of the soft X-ray luminosity of bright elliptical galaxies. The temperature of the hot gas is about 0.62 keV with a low metallicity ( $Z \sim 0.1 Z_\odot$). We discuss the nature of AGN and the implications of our results on the origin of X-ray halos in elliptical galaxies.

CATEGORY: ACTIVE GALAXIES AND QUASARS