Detection of Iron K{\alpha} Emission from a Complete Sample of Submillimeter Galaxies

TL;DR

This study detects iron Kα emission from a complete sample of submillimeter galaxies at z~2.6, revealing insights into their X-ray properties and ionization states, using stacking analysis of deep X-ray observations.

Contribution

It provides the first robust X-ray detection of Fe Kα emission in a complete, flux-limited SMG sample, highlighting the presence of highly ionized iron and potential spatial extension.

Findings

5σ detection in soft X-ray band

~4σ detection of Fe Kα emission at 6.7 keV

Indication of highly ionized iron and extended emission

Abstract

We present an X-ray stacking analysis of a sample of 38 submillimeter galaxies with <z>=2.6 discovered at >4{\sigma} significance in the Lockman Hole North with the MAMBO array. We find a 5{\sigma} detection in the stacked soft band (0.5-2.0 keV) image, and no significant detection in the hard band (2.0-8 keV). We also perform rest-frame spectral stacking based on spectroscopic and photometric redshifts and find a ~4{\sigma} detection of Fe K{\alpha} emission with an equivalent width of EW>1 keV. The centroid of the Fe K{\alpha} emission lies near 6.7 keV, indicating a possible contribution from highly ionized Fe XXV or Fe XXVI; there is also a slight indication that the line emission is more spatially extended than the X-ray continuum. This is the first X-ray analysis of a complete, flux-limited sample of SMGs with statistically robust radio counterparts.