A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59−0.05 high-mass star-forming region

Abstract

Aims. We wish to investigate the structure, velocity field, and stellar content of the G16.59−0.05 high-mass star-forming region, where previous studies have established the presence of two almost perpendicular (NE-SW and SE-NW), massive outflows, and a rotating disk traced by methanol maser emission. Methods. We performed Very Large Array observations of the radio continuum and ammonia line emission, complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid-and far-infrared. Results. Our centimeter continuum maps reveal a collimated radio jet that is oriented E-W and centered on the methanol maser disk, placed at the SE border of a compact molecular core. The spectral index of the jet is negative, indicating non-thermal emission over most of the jet, except the peak close to the maser disk, where thermal free-free emission is observed. We find that the ammonia emission presents a bipolar structure consistent (on a smaller scale) in direction and velocity with that of the NE-SW bipolar outflow detected in previous CO observations. After analyzing our previous N 2 H + (1-0) observations again, we conclude that two scenarios are possible. In one case both the radio jet and the ammonia emission would trace the root of the large-scale CO bipolar outflow. The different orientation of the jet and the ammonia flow could be explained by precession and/or a non-isotropic density distribution around the star. In the other case, the N 2 H + (1-0) and ammonia bipolarity is interpreted as two overlapping clumps moving with different velocities along the line of sight. The ammonia gas also seems to undergo rotation consistent with the maser disk. Our infrared images complemented by archival data allow us to derive a bolometric luminosity of ∼10 4 L and to conclude that most of the luminosity is due to the young stellar object associated with the maser disk. Conclusions. The new data suggest a scenario where the luminosity and the outflow activity of the whole region could be dominated by two massive young stellar objects: 1) a B-type star of ∼12 M at the center of the maser/ammonia disk; 2) a massive young stellar object (so far undetected), very likely in an earlier stage of evolution than the B-type star, which might be embedded inside the compact molecular core and power the massive, SE-NW outflow.

VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers

“…G16.59−0.05-This EGO is adjacent to IRAS 18182−1433 (nominal separation ∼19″; Cyganowski et al 2008); unusually among our sample, its cm-λ continuum emission has been well studied, primarily by authors targeting the IRAS source (e.g., Zapata et al 2006;Sanna et al 2010;Hofner et al 2011;Moscadelli et al 2013Moscadelli et al , 2016Rosero et al 2016). We detect a single compact 1.3 cm continuum source (CM1), which is coincident with the EGO and with a local peak in the 24 μm emission (Figure 1).…”

“…CM1 corresponds to the brightest of the five components (18182-1433 C) detected at both 1.3 cm and 6 cm in deep VLA observations of this field by Rosero et al (2016), who measure a spectral index of +0.8±0.1 for this object. The compact 1.3 cm source is coincident with the 6.7 GHz CH 3 OH maser emission (e.g., Green et al 2010;Sanna et al 2010;Moscadelli et al 2013). At longer wavelengths, the continuum emission is elongated E-W, with a size scale of ∼4″ at 6 cm (Moscadelli et al 2013(Moscadelli et al , 2016.…”

“…The compact 1.3 cm source is coincident with the 6.7 GHz CH 3 OH maser emission (e.g., Green et al 2010;Sanna et al 2010;Moscadelli et al 2013). At longer wavelengths, the continuum emission is elongated E-W, with a size scale of ∼4″ at 6 cm (Moscadelli et al 2013(Moscadelli et al , 2016. The orientation of this elongation, which is interpreted as an ionized jet (e.g., Moscadelli et al 2013Moscadelli et al , 2016, is notably similar to that of the extended 4.5 μm emission of the EGO, which is elongated E-W on larger scales (∼10″-15″).…”

Accretion disks in luminous young stellar objects

“…However, only for the O-type (proto)star W51e2-E the methanol maser features appear located at <1000 au from the central star (Surcis et al, 2012). What is more, in most cases the proper motions of the methanol maser spots do not indicate rotation but expansion (e.g., Li et al, 2012;Moscadelli et al, 2013).…”

On the accretion process in a high-mass star forming region

“…Some observations of the ground state rotational transition of ortho-NH 3 at 572 GHz were performed by the Kuiper Airborne Observatory (Keene et al 1983) and the Odin satellite (e.g., Larsson et al 2003;Persson et al 2009;Wirström et al 2010). The launch of ESA's 3.5 m Cassegrain telescope, the Herschel Space Observatory 1 (Pilbratt et al 2010) opened up unique opportunities to observe rotational 1 http://herschel.esac.esa.int/ Kuchar & Bania (1994); (b) from C 17 O (3-2) line observations with the APEX telescope (Wyrowski et al 2012). transitions in the sub-mm and far-infrared, with high sensitivity and spectral resolution using the Heterodyne Instrument for the Far-Infrared (HIFI;de Graauw et al 2010), e.g., Hily-Blant et al (2010), Persson et al (2012), Biver et al (2012), Moscadelli et al (2013). From 2010 and onwards, observations of THz transitions have also been possible using the Stratospheric Observatory For Infrared Astronomy 2 (SOFIA).…”