Gemini, SOFIA, and ATCA Reveal Very Young, Massive Protostars in the Collapsing Molecular Cloud BYF 73

TL;DR

This study uses multi-wavelength observations to identify and characterize very young, massive protostars within the collapsing molecular cloud BYF 73, revealing early-stage star formation processes.

Contribution

It provides new multi-wavelength data and detailed analysis of the protostellar objects and gas environments in BYF 73, highlighting the earliest stages of massive star formation.

Findings

Identification of eight protostellar objects, six deeply embedded in the cloud

Detection of a massive core (~240 M_sun) with a very young dynamical age (~7000 years)

Evidence of complex gas environments with high densities and specific line ratios

Abstract

We present multi-wavelength data on the globally infalling molecular cloud/protostellar cluster BYF 73. These include new far-IR spectral line and continuum data from SOFIA's Far Infrared Field-Imaging Line Spectrometer (FIFI-LS), mid-infrared (MIR) observations with the Thermal-Region Camera Spectrograph (T-ReCS) on Gemini-South, and 3 mm continuum data from the Australia Telescope Compact Array (ATCA), plus archival data from Spitzer/IRAC, and Herschel/PACS and SPIRE. The FIFI-LS spectroscopy in [OI]$\lambda63 \mu$m, [OIII]$\lambda88 \mu$m, [OI]$\lambda145 \mu$m, and [CII]$\lambda158 \mu$m highlights different gas environments in and between the dense molecular cloud and HII region. The photo-dissociation region (PDR) between the cloud and HII region is best traced by [OI]$\lambda145 \mu$m and may have density $>$10$^{10}$ m$^{-3}$, but the observed $\lambda145\mu$m/$\lambda63\mu$m and $\lambda63\mu$m/$\lambda158\mu$m line ratios in the densest gas are well outside model values. The HII region is well-traced by [CII], with the $\lambda158\mu$m/$\lambda145\mu$m line ratio indicating a density of 10$^{8.5}$ m$^{-3}$ and a relatively weak ionizing radiation field, 1.5 $\lesssim$ log$(G/G_0)\lesssim$ 2. The T-ReCS data reveal eight protostellar objects in the cloud, of which six appear deeply embedded ($A_V$ $>$ 30$^m$ or more) near the cloud's center. MIR 2 has the most massive core at $\sim$240 M$_{\odot}$, more massive than all the others combined by up to tenfold, with no obvious gas outflow, negligible cooling line emission, and $\sim3-8$% of its 4.7$\times$10$^3$ L$_{\odot}$ luminosity originating from the release of gravitational potential energy. MIR 2's dynamical age may be as little as 7000 yr. This fact, and the cloud's total embedded stellar mass being far less than its gas mass, confirm BYF 73's relatively early stage of evolution.