X-ray detection of the most extreme star-forming galaxiesãt the cosmic noon via strong lensing

Abstract

Hyperluminous infrared galaxies (HyLIRGs)ãre the most extreme star-forming systems observed in the early Universe,ãnd their properties still elude comprehensive understanding. We have undertakenã large XMM -Newton observing programme to probe the totalãccreting black hole population in three HyLIRGsãt z = 2.12, 3.25,ãnd 3.55, gravitationally lensed by foreground galaxies. Selected from the Planck All-Sky Survey to Analyse Gravitationally lensed Extreme Starbursts (PASSAGES), these HyLIRGs haveãpparent infrared luminosities > 10 14 L⊙. Our observãtions re vealed X-ray emission in each of them. PJ1336 + 49ãppears to be dominated by high-mass X-ray binaries (HMXBs). Remarkably, the luminosity of this non-AGN X-ray emission exceeds byã factor ofãbout 3 the value obtained by calibration with local galaxies with much lower star formation rates. This enhanced X-ray emission most likely highlights the efficacy of dynamical HMXB production within compact clusters, which isãn important mode of star formation in HyLIRGs. The remaining two (PJ0116 -24ãnd PJ1053 + 60) morphologicallyãnd spectrally exhibitã compact X-ray component inãddition to the extended non-AGN X-ray emission, indicating the presence of Active Galactic Nuclei (AGNs). The AGNãppears to be centrally located in the reconstructed source plane images of PJ0116 -24, which manifests its star-formingãctivity predominantly withinãn extended galactic disc. In contrast, the AGN in the field of PJ1053 + 60 is projected 60 kpcãway from the extreme star-forming galaxyãnd could be ejected from it. These results underline the synergistic potential of deep X-ray observations with strong lensing for the study of high-energyãstrophysical phenomena in HyLIRGs.