STAR FORMATION IN NGC 7538: MULTI-WAVELENGTH OBSERVATIONS AND ISSUES.

Abstract

New observations of the star formation region NGC 7538 are presented. Energetic outflows are commonly associated with regions of active star formation, despite the fact that the star formation process itself must be predominantly one of infall. This work shows how multi-wavelength observations can be used to study such phenomena on a variety of scales, in an attempt to infer their connection with star formation processes. Included are near-infrared spectroscopy of IRS 2; carbon monoxide J = 1-0 emission line mapping of the central regions of the NGC 7538 molecular cloud; and high spatial resolution maps of IRS 1 at 5 and 15 GHz. Other recent observational data are also considered, including far-infrared continua mapping, maser sources, and spectroscopy of numerous atomic and molecular species. A very large (r ≥ 1.5 pc) and massive (m ≥ 100 solar masses) distribution of high velocity (ΔV(FWHM) ≃ 35 - 40 km s⁻¹) molecular gas is identified in NGC 7538. The correspondence of far-infrared emission with the extent of the high velocity gas, along with the near-equality between the observed momentum flux of the gas and that which is available for radiation pressure L(*) /c (IRS 1-3) leads to the proposal of an in situ mechanism for radiative acceleration of the gas. This mechanism for radiative acceleration of the gas. This mechanism operates in cases where the optical depth of dust is insufficient to permit the "snowplow" outflow effect from strong radiation pressure. On the 1/2 - 1 pc minimum scale of these molecular observations, no obvious bipolarity or collimation is detected, consistent with the in situ mechanism. The highly luminous infrared source IRS 1 is identified as the probable source of this high velocity phenomenon. It is the most luminous source of the three (IRS 1-3) upon which the high velocity gas distribution is centered. The presence on a scale of 100 - 100 AU of a high density ridge perpendicular to a collimated distribution of ionized gas is strongly indicated in both mid-infrared and radio emission, and by anomalous optical and infrared extinctions. There is thus a startling discontinuity between collimation of gas on this scale and the lack of it observed at the arcminute scale of the molecular observations.