The Nature of an Unidentified X-ray Source in the 7 Ms Chandra Deep Field-South Catalog

TL;DR

This study investigates an enigmatic X-ray source in the Chandra Deep Field-South, using multiwavelength data and SED fitting to determine its nature as an off-nuclear ultraluminous X-ray source rather than a background AGN.

Contribution

It presents the first detailed multiwavelength analysis of a highly significant but previously unidentified X-ray source in this deep field.

Findings

The source is likely an off-nuclear ultraluminous X-ray source.

It is not consistent with a background active galactic nucleus.

Multiwavelength data helped identify its nature.

Abstract

In the 7 Ms Chandra Deep Field-South catalog, only one source, XID 912, was highly significantly detected in X-rays but had no formally reported counterparts in the UV, optical, infrared, or radio bands. We identified its potential JWST and VLT VIMOS counterparts and measured the corresponding aperture photometry to construct its spectral energy distribution (SED). We fitted this SED using CIGALE. The results indicate that the source is most likely an off-nuclear ultraluminous X-ray source, rather than a background active galactic nucleus.