The origin of the X-ray emission from the non-starburst gas-rich luminous infrared galaxies Arp 302

Abstract

ABSTRACT We present an analysis of the XMM–Newton observation of luminous infrared merging galaxies Arp 302 and a joint re-analysis of its Chandra observation. In particular, we focus on the more significant X-ray emitter of the pair, Arp 302N. Chandra detects significant soft X-ray emission from the hot gas in the star-forming region of Arp 302N spreading up to 12 kpc. We estimate the star formation rate of Arp 302N to be around 1–2 M⊙ yr−1 based on the X-ray luminosity of the star-forming region, similar to previous measurements at longer wavelengths. Chandra and XMM–Newton observations show evidence of a Si xiii emission line with 86 per cent confidence. Our best-fitting model infers a super-solar silicon abundance in the star-forming region, likely related to the past core-collapse supernovae in this galaxy. Similar silicon overabundance was reported in the circumstellar medium of core-collapse supernova remnants in our Galaxy. We also detect narrow Fe Kα and Fe Kβ (98.6 per cent confidence) emission lines as part of the active galactic nucleus (AGN) emission. Our best-fitting spectral model using mytorus indicates the evidence of a heavily obscured power-law emission with NH > 3 × 1024 cm−2 in addition to a weak, unobscured power-law emission. The scattering fraction of the unobscured power-law emission from Compton-thin materials is 0.7 per cent. All these spectral features suggest evidence of a Seyfert 2-like AGN in Arp 302N. The X-ray measurement of its AGN activity is consistent with the previous Spitzer measurement of the same object.