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

The 7 and 15 mum observations of selected fields in the Galactic Plane obtained with ISOCAM during the ISOGAL program offer a 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 similar to +45degrees. 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] less than or equal to 4.5, [7] [15] greater than or equal to 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 similar to 2% of the sources with good detections at 7 and 15 mum. The results are presented in a table form that provides an unique input list of small diameter, less than or equal to 6, Galactic YSO candidates. The global properties of the sample of YSO candidates are briefly discussed.