Thermal Formaldehyde Emission in NGC7538 IRS1
arXiv:2103.14492 · doi:10.1093/mnras/stab933
Abstract
Spectral lines from formaldehyde (H2CO) molecules at cm wavelengths are typically detected in absorption and trace a broad range of environments, from diffuse gas to giant molecular clouds. In contrast, thermal emission of formaldehyde lines at cm wavelengths is rare. In previous observations with the 100m Robert C. Byrd Green Bank Telescope (GBT), we detected 2 cm formaldehyde emission toward NGC7538 IRS1 - a high-mass protostellar object in a prominent star-forming region of our Galaxy. We present further GBT observations of the 2 cm and 1 cm H2CO lines to investigate the nature of the 2 cm H2CO emission. We conducted observations to constrain the angular size of the 2 cm emission region based on a East-West and North-South cross-scan map. Gaussian fits of the spatial distribution in the East-West direction show a deconvolved size (at half maximum) of the 2 cm emission of 50" +/- 8". The 1 cm H2CO observations revealed emission superimposed on a weak absorption feature. A non-LTE radiative transfer analysis shows that the H2CO emission is consistent with quasi-thermal radiation from dense gas (~10^5 to 10^6 cm^-3). We also report detection of 4 transitions of CH3OH (12.2, 26.8, 28.3, 28.9 GHz), the (8,8) transition of NH3 (26.5 GHz), and a cross-scan map of the 13 GHz SO line that shows extended emission (> 50").
16 pages, 14 figures. Accepted for publication in MNRAS
References in corpus (22)
- A computer program for fast non-LTE analysis of interstellar line spectra
- Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars
- Trigonometric Parallaxes of Massive Star Forming Regions: II. Cep A & NGC 7538
- Theoretical HDO emission from low-mass protostellar envelopes
- A near-infrared study of the NGC 7538 star forming region
- Formaldehyde Densitometry of Starburst Galaxies
- Toward gas exhaustion in the W51 high-mass protoclusters
- Outflows, Accretion, and Clustered Protostellar Cores around a Forming O Star
- The Formaldehyde Masers in NGC 7538 and G29.96-0.02: VLBA, MERLIN, and VLA Observations
- A multiple system of high-mass YSOs surrounded by disks in NGC7538 IRS1
- Galactic H2CO Densitometry I: Pilot survey of Ultracompact HII regions and methodology
- High-mass star-forming cloud G0.38+0.04 in the Galactic Center Dust Ridge contains H2CO and SiO masers
- KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds
- A multi-transition molecular line study of inward motions towards massive star-forming cores
- HII Region Ionization of the Interstellar Medium: A Case Study of NGC 7538
- A detailed study of the accretion disk surrounding the high-mass protostar NGC 7538S
- A New Galactic 6cm Formaldehyde Maser
- The Rare 23.1-GHz Methanol Masers in NGC 7538 IRS 1
- Formaldehyde Densitometry of Galactic Star-Forming Regions Using the H2CO 3(12)-3(13) and 4(13)-4(14) Transitions
- A Review of H2CO 6cm Masers in the Galaxy
- NGC 7538 IRS1: Interaction of a polarized dust spiral and a molecular outflow
- Long-term Variability of HCO Masers in Star-forming Regions