Recent star formation at low metallicities. The star-forming region NGC 346/N66 in the Small Magellanic Cloud from near-infrared VLT/ISAAC observations ^*,**

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: dgoulier@mpia-hd.mpg.de
² Armagh Observatory, College Hill, Armagh BT61 9DG, UK

Received: 29 March 2009
Accepted: 27 February 2010

Abstract

Context. The emission nebula N66 is the brightest H II region in the Small Magellanic Cloud (SMC), the stellar association NGC 346 being located at its center. The youthfulness of the region NGC 346/N66 is well documented by studies of the gas and dust emission, and the detection in the optical of a rich sample of pre-main sequence (PMS) stars, and in the mid- and far-IR of young stellar objects (YSOs). However, a comprehensive study of this region has not been performed in the near-IR that would bridge the gap between previous surveys.

Aims. We perform a photometric analysis on deep, seeing-limited near-IR VLT images of the region NGC 346/N66 and a nearby control field of the SMC to locate the centers of active high- and intermediate-mass star formation by identifying near-IR bright objects as candidate stellar sources under formation.

Methods. We use archival imaging data obtained with the high-resolution camera ISAAC at VLT of NGC 346/N66 to construct the near-IR color–magnitude (CMD) and color–color diagrams (C-CD) of all detected sources. We investigate the nature of all stellar populations in the observed CMDs, and we identify all stellar sources that show significant near-IR excess emission in the observed C-CD. We, thus, select the most likely young stellar sources.

Results. Based on their near-IR colors, we select 263 candidate young stellar sources. This sample comprises a variety of objects, such as intermediate-mass PMS and Herbig Ae/Be stars and possible massive YSOs, providing original near-IR colors for each of them. The spatial distribution of the selected candidate sources indicates that they are located along the dusty filamentary structures of N66 seen in mid- and far-IR dust emission and agrees very well with that of previously detected candidate YSOs and PMS stars.

Conclusions. Our study provides an original accurate set of near-IR colors for candidate young stellar sources. This provides significant information about the star formation process in NGC 346/N66, but does not establish the types of these objects, which requires the construction of complete spectral energy distributions for individual sources from multiwavelength data. This would be an important follow-up study to that presented here.