Bringing the Norma Dark Cloud to Light in X-rays

TL;DR

This study presents the first X-ray observations of the Norma dark cloud, revealing numerous X-ray sources associated with young stellar objects, and provides a catalog to aid in understanding star formation in this region.

Contribution

It offers the first detailed X-ray source catalog of the Norma dark cloud, identifying potential young stars and their properties, advancing star formation studies in this cloud complex.

Findings

Detected 121 unique X-ray sources in the Norma dark cloud.

Identified several X-ray sources with properties typical of young stars with disks.

Provided a catalog to facilitate future studies of star formation in the region.

Abstract

The filamentary dark cloud complex in Norma reveals signs of active low-mass star formation including protostars, H-alpha emission line stars, Herbig Haro objects, and the eruptive FU Orionis-like star V346 Nor. We present results of the first pointed X-ray observations of the Norma dark cloud, focusing on the westernmost Sandqvist 187 region. Chandra detected 75 X-ray sources and a complementary XMM-Newton observation detected 92 sources within the Chandra field-of-view, of which 46 are cross-matched to Chandra, yielding 121 unique X-ray sources. We present a catalog of X-ray sources along with basic X-ray properties and candidate IR and optical counterparts. Existing near-IR photometry reveals several X-ray sources with color excesses as typical of young stars with disks. Gaia parallaxes single out foreground stars and X-ray sources with distances of 500 - 1000 pc that are probable cloud members. The known emission line stars Sz 136 and Sz 137 were detected but V346 Nor was not. Interestingly, the optical and IR counterparts of the brightest Chandra source are not known with certainty but the prime suspects are very faint. Thus, the nature of the object responsible for the bright X-ray emission remains speculative. The X-ray observations presented here will serve as a pathfinder for identifying and characterizing the young stellar population in the Norma dark cloud.