Multiwavelength Study of Chandra X-Ray Sources in the Antennae

TL;DR

This study combines infrared, optical, and X-ray data to identify and analyze star clusters in the Antennae galaxy, revealing that X-ray sources are often associated with massive, young star clusters.

Contribution

It provides a comprehensive multiwavelength analysis of X-ray sources and their star cluster counterparts in the Antennae, nearly doubling known IR counterparts and characterizing their properties.

Findings

38 X-ray sources have IR counterparts, mostly bright star clusters.

Most clusters with X-ray sources are massive (~10^6 M_sun) and young (~10^6 yr).

Optical counterparts are identified for 27 IR star clusters.

Abstract

We use WIRC, IR images of the Antennae (NGC 4038/4039) together with the extensive catalogue of 120 X-ray point sources (Zezas et al. 2006) to search for counterpart candidates. Using our proven frame-tie technique, we find 38 X-ray sources with IR counterparts, almost doubling the number of IR counterparts to X-ray sources first identified in Clark et al. (2007). In our photometric analysis, we consider the 35 IR counterparts that are confirmed star clusters. We show that the clusters with X-ray sources tend to be brighter, K_s ~16 mag, with (J-K_s) = 1.1 mag. We then use archival HST images of the Antennae to search for optical counterparts to the X-ray point sources. We employ our previous IR-to-X-ray frame-tie as an intermediary to establish a precise optical-to-X-ray frame-tie with <0.6 arcsec rms positional uncertainty. Due to the high optical source density near the X-ray sources, we determine that we cannot reliably identify counterparts. Comparing the HST positions to the 35 identified IR star cluster counterparts, we find optical matches for 27 of these sources. Using Bruzual-Charlot spectral evolutionary models, we find that most clusters associated with an X-ray source are massive, ~10^6 M_sun, young, ~10^6 yr, with moderate metallicities, Z=0.05.