An XMM-Newton hard X-ray survey of ultraluminous infrared galaxies

Abstract

XMM-Newton observations of 10 ultraluminous infrared galaxies (ULIRGs) from a 200-ks mini-survey programme are reported. The aim is to investigate in hard X-rays a complete ULIRG sample selected from the bright IRAS 60-µm catalogue. All sources are detected in Xrays, five of which for the first time. These observations confirm that ULIRGs are intrinsically faint X-ray sources, their observed X-ray luminosities being typically L 2-10 keV 10 42 -10 43 erg s −1 , whereas their bolometric (mostly infrared) luminosities are L bol > 10 45 erg s −1 . In all sources we find evidence for thermal emission from hot plasma with a rather constant temperature kT 0.7 keV, dominating the X-ray spectra below 1 keV, and probably associated with a nuclear or circumnuclear starburst. This thermal emission appears uncorrelated with the far-infrared luminosity, suggesting that, in addition to the ongoing rate of star formation, other parameters may also affect it. The soft X-ray emission appears to be extended on a scale of ∼30 kpc for Mrk 231 and IRAS 19254−7245, possible evidence of galactic superwinds. In these two sources, IRAS 20551−4250 and 23128−5919, we find evidence for the presence of hidden active galactic nuclei (AGNs), while a minor AGN contribution may be suspected also in IRAS 20100−4156. In particular, we have detected a strong (EW ∼ 2 keV) Fe K line at 6.4 keV in the spectrum of IRAS 19254−7245 and a weaker one in Mrk 231, suggestive of deeply buried AGNs. For the other sources, the X-ray luminosities and spectral shapes are consistent with hot thermal plasma and X-ray binary emissions of mainly starburst origin. We find that the 2-10 keV luminosities in these sources, most probably due to high-mass X-ray binaries, are correlated with L FIR : both luminosities are good indicators of the current global star formation rate in the Galaxy. The composite nature of ULIRGs is then confirmed, with hints for a predominance of the starburst over the AGN phenomenon in these objects even when observed in hard X-rays.

Spectral energy distribution of hyperluminous infrared galaxies

“…X-ray and IR data clearly suggest that these sources are powered by SB and, A&A 515, A99 (2010) in some cases (∼50%), by AGN (Farrah et al 2003;Franceschini et al 2003;Teng et al 2005;Nardini et al 2008). The fraction of ULIRG hosting an AGN increases with increasing IR luminosity (Veilleux et al 1995(Veilleux et al , 1999.…”

C-GOALS:Chandraobservations of a complete sample of luminous infrared galaxies from the IRAS Revised Bright Galaxy Survey

“…Data obtained by us in Cycles 7 + 8 have been combined with data from the Chandra Archive to produce the first complete X-ray survey of the most luminous sources in the GOALS sample. Previous X-ray investigations of LIRGs, either by Chandra, XMM-Newton or Suzaku, have been presented in Ptak et al (2003), Franceschini et al (2003), Teng et al (2005Teng et al ( , 2009, and Grimes et al (2005).…”

Shocked gas in IRAS F17207-0014: ISM collisions and outflows

“…tidal stream). This galaxy is classified as a star forming system based on observations in the optical (Veilleux et al 1995;Yuan et al 2010), mid-infrared (Lutz et al 1999;Risaliti et al 2006;Stierwalt et al 2013;Inami et al 2013), and X-ray (Franceschini et al 2003;Iwasawa et al 2011). This galaxy has been studied by several other authors to date, most finding evidence for outflows on a variety of scales.…”