Young massive stars in the ISOGAL survey II. The catalogue of bright YSO candidates

TL;DR

This paper refines criteria for identifying young stellar object candidates in the Galactic Plane using ISOGAL survey data, resulting in a catalog of 715 bright YSO candidates with improved selection accuracy.

Contribution

The study updates YSO selection criteria based on radio and IR data comparison, producing a new catalog of bright YSO candidates from ISOGAL observations.

Findings

Identified 715 YSO candidates, about 2% of sources with good IR detections.

Revised selection criteria to reduce contamination from Post-MS stars.

Provided a catalog with small diameter, high-resolution YSO candidates.

Abstract

The 7 and 15 um observations of selected fields in the Galactic Plane obtained with ISOCAM during the ISOGAL program offer an unique possibility to search for previously unknown YSOs, undetected by IRAS because of lower sensitivity or confusion problems. In a previous paper (Felli et al. 2000) we established criteria of general validity to select YSOs from the much larger population of Post Main Sequence (Post-MS) stars present in the ISOGAL fields by comparing radio and IR observations of five fields located at l +45 deg. The selection was based primarily on the position of the point sources in the [15] - [7]--[15] diagram, which involves only ISOGAL data and allows to find possible YSOs using the survey data alone. In the present work we revise the adopted criteria by comparing radio-identified UC HII regions and ISOGAL observations over a much larger region. The main indications of the previous analysis are confirmed, but the criteria for selecting YSO candidates had to be revised to select only bright objects, in order to limit the contamination of the sample by Post-MS stars. The revised criteria ([15]<=4.5, [7]--[15]>=1.8) are then used to extract YSO candidates from the ISOGAL Point Source Catalogue in preparation. We select a total of 715 YSO candidates, corresponding to ~2% of the sources with good detections at 7 and 15 um. The results are presented in a table form that provides an unique input list of small diameter, <=6", Galactic YSO candidates. The global properties of the sample of YSO candidates are briefly discussed.