Young stars and reflection nebulae near the lower “edge” of the Galactic molecular disc

Abstract

<i>Aims. <i/>We investigate the star formation occurring in a region well below the Galactic plane towards the optical reflection nebula ESO 368-8 (IRAS 07383-3325). We confirm the presence of a small young stellar cluster (or aggregate of tens of YSOs) identified earlier, embedded in a molecular cloud located near the lower “edge” of the Galactic disc, and characterise the young stellar population. We report the discovery of a near-infrared nebula, and present a CO map revealing a new dense, dynamic cloud core.<i>Methods. <i/>We used near-infrared images obtained with VLT/ISAAC, millimetre CO spectra obtained with the SEST telescope, and optical <i>V<i/>-band images from the YALO telescope.<i>Results. <i/>This star formation region displays an optical reflection nebula (ESO 368-8) and a near-infrared nebula located about 46<i>''<i/> (1.1 pc) from each other. The two nebulae are likely to be coeval and to represent two manifestations of the same single star formation episode with about 1 Myr age. The near-IR nebula reveals an embedded, optically and near-IR invisible source whose light scatters off a cavity carved by previous stellar jets or molecular outflows and into our line-of-sight. The molecular cloud is fully covered by our CO(<i>J<i/> = 1-0) maps and, traced by this line, extends over a region of <i>7.8<i/> pc<sup>2<sup/>, exhibiting an angular size <i>5.4'<i/> and shape (close to circular) similar to spherical (or slightly cometary) globules. Towards the direction of the near-IR nebula, the molecular cloud contains a dense core where the molecular gas exhibits large line widths indicative of a very dynamical state, with stirred gas and supersonic motions. Our estimates of the mass of the molecular gas in this region range from 600 to 1600 . The extinction <i>A<sub>V<sub/><i/> towards the positions of the optical reflection nebula and of the near-IR nebula was found to be mag and mag, respectively.