Interstellar matter and star formation in W5-E - A Herschel view

摘要

Aims. We identify the young stellar objects (YSOs) present in the vicinity of the W5-E H?ii?region, and study the influence of this H?ii?region on the star formation process in its surrounding molecular material. Methods. W5-E has been observed with the Herschel-PACS and -SPIRE photometers, as part of the?HOBYS key program; maps have been obtained at?100?μm, 160?μm, 250?μm, 350?μm, and?500?μm. The dust temperature and column density have been obtained by fitting spectral energy distributions (SEDs). Point sources have been detected and measured using?PSF?photometry with?DAOPHOT. Results. The dust temperature map shows a rather uniform temperature, in the range 17.5?K?20?K in the dense condensations or filaments, in the range 21?K?22?K in the photodissociation regions (PDRs), and in the range 24?K?31?K in the direction of the ionized regions. The values in the column density map are rather low, everywhere lower than?1023?cm-2, and of the order of a few?1021?cm-2 in the?PDRs. About?8000?M⊙ of neutral material surrounds the ionized region, which is low with respect to the volume of this H?ii?region; we suggest that the exciting stars of the?W5-E, W5-W, Sh?201, A and?B?H?ii?regions formed along a dense filament or sheet rather than inside a more spherical cloud. Fifty point sources have been detected at?100?μm. Most of them are Class?0/I?YSOs. The?SEDs of their envelopes have been fitted using a modified blackbody model. These envelopes are cold, with a mean temperature of 15.7?±?1.8?K. Their masses are in the range 1.3?M⊙–47?M⊙. Eleven of these point sources are candidate Class?0?YSOs. Twelve of these point sources are possibly at the origin of bipolar outflows detected in this region. None of the?YSOs contain a massive central object, but a few may form a massive star as they have both a massive envelope and also a high envelope accretion rate. Most of the Class?0/I?YSOs are observed in the direction of high column density material, for example in the direction of the massive condensations present at the waist of the bipolar Sh?201 H?ii?region or enclosed by the bright-rimmed cloud?BRC14. The overdensity of Class?0/I?YSOs on the borders of the H?ii?regions present in the field strongly suggests that triggered star formation is at work in this region but, due to insufficient resolution, the exact processes at the origin of the triggering are difficult to determine.