Study of the molecular and ionized gas in a possible precursor of an ultra-compact H II region

ORTEGA, M. E.; PARON, S.; GIACANI, E.; CELIS PEÑA, M.; RUBIO, M.; PETRIELLA, A.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2017 vol. 606

0004-6361

Aims: We aim to study the molecular and the ionized gas in apossible precursor of an ultra-compact H II region to contribute to the understanding of how high-mass stars build-up their masses once theyhave reached the zero-age main sequence. Methods: We carried outmolecular observations toward the position of the Red MSX sourceG052.9221-00.4892, using the Atacama Submillimeter Telescope Experiment(ASTE; Chile) in the 12CO J = 3-2, 13CO J = 3-2,C18O J = 3-2, and HCO+J = 4-3 lines with anangular resolution of about 22´´. We also present radio continuumobservations at 6 GHz carried out with the Jansky Very Large Array(JVLA; USA) interferometer with a synthesized beam of 4.8 arcsec ×4.1 arcsec. The molecular data were used to study the distribution andkinematics of the molecular gas, while the radio continuum data wereused to characterize the ionized gas in the region. Combining theseobservations with public infrared data allowed us to inquire about thenature of the source. Results: The analysis of the molecularobservations reveals the presence of a kinetic temperature andH2 column density gradients across the molecular clump inwhich the Red MSX source G052.9221-00.4892 is embedded, with the hotterand less dense gas in the inner region. The 12CO J = 3-2emission shows evidence of misaligned massive molecular outflows, withthe blue lobe in positional coincidence with a jet-like feature seen at8 μm. The radio continuum emission shows a slightly elongated compactradio source, with a flux density of about 0.9 mJy, in positionalcoincidence with the Red MSX source. The polar-like morphology of thiscompact radio source perfectly matches the hourglass-like morphologyexhibited by the source in the Ks band. Moreover, the axes ofsymmetry of the radio source and the near-infrared nebula are perfectlyaligned. Thus, based on the presence of molecular outflows, the slightlyelongated morphology of the compact radio source matching thehourglass-like morphology of the source at the Ks band, andthe lack of evidence of collimated jets in the near-infrared spectrum,one interpretation for the nature of the source, is that the Red MSXsource G052.9221-00.4892 could be transiting a hyper-compact H II regionphase, in which the young central star emits winds and ionizingradiation through the poles. On the other hand, according to acomparison between the Brγ intensity and the radio flux density at6 GHz, the source would be in a more evolved evolutionary stage of anoptically thin UC H II region in photoionization equilibrium. If this isthe case, from the radio continuum emission, we can conjecture upon thespectral type of its exciting star which would be a B0.5V.