The SEDIGISM survey: A search for molecular outflows

Abstract

Context. The formation processes of massive stars are still unclear but a picture is emerging involving accretion disks and molecular outflows in what appears to be a scaled-up version of low-mass star formation. A census of outflow activity towards high-mass star-forming clumps in various evolutionary stages has the potential to shed light on high-mass star formation. Aims. We conducted an outflow survey towards ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) clumps, using SEDIGISM (structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) data and aimed to obtain a large sample of clumps exhibiting outflow activity in different evolutionary stages. Methods. We identify the high-velocity wings of the 13 CO lines, indicating outflow activity, toward ATLASGAL clumps by (1) extracting the simultaneously observed 13 CO (2 -1) and C 18 O (2 -1) spectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C 18 O (core emission) from the 13 CO line after considering opacity broadening. Results. We have detected high-velocity gas towards 1192 clumps out of a total sample of 2052 corresponding to an overall detection rate of 58%. Outflow activity has been detected in the earliest (apparently) quiescent clumps (i.e., 70µm weak), to the most evolved H ii region stages i.e., 8µm bright with tracers of massive star formation. The detection rate increases as a function of evolution (quiescent=51%, protostellar=47%, YSO = 57%, UC H ii regions = 76%). Conclusions. Our sample is the largest outflow sample identified so far. The high-detection rate from this large sample is consistent with the results of similar studies reported in the literature and supports the scenario that outflows are a ubiquitous feature of highmass star formation. The lower detection rate in early evolutionary stages may be due to the fact that outflows in the early stages are weak and difficult to detect. We obtain a statistically significant sample of outflow clumps for every evolutionary stage, especially for outflow clumps in the earliest stage (i.e., 70 µm dark). The detections of outflows in the 70 µm-dark clumps suggest that the absence of 70 µm emission is not a robust indicator of starless/pre-stellar cores.

New evidences in IRDC G333.73+0.37: colliding filamentary clouds, hub-filament system, and embedded cores

“…They also suggested the possibility of the presence of small-scale outflows toward S1. Most recently, Yang et al (2022) examined the presence and absence of the 13 CO outflows toward the ATLASGAL clumps using the SEDIGISM 13 CO(J = 2-1) and C 18 O(J = 2-1) line data. One can find the detailed steps for identifying the outflows toward ATLASGAL clumps in Yang et al (2022).…”

“…Most recently, Yang et al (2022) examined the presence and absence of the 13 CO outflows toward the ATLASGAL clumps using the SEDIGISM 13 CO(J = 2-1) and C 18 O(J = 2-1) line data. One can find the detailed steps for identifying the outflows toward ATLASGAL clumps in Yang et al (2022). In our selected target area, six ATLASGAL clumps are traced (see Figure 1c), and the molecular outflow is reported toward only one ATLASGAL clump (i.e., AGAL333.724+00.364) hosting S1 (Yang et al 2022).…”

“…One can find the detailed steps for identifying the outflows toward ATLASGAL clumps in Yang et al (2022). In our selected target area, six ATLASGAL clumps are traced (see Figure 1c), and the molecular outflow is reported toward only one ATLASGAL clump (i.e., AGAL333.724+00.364) hosting S1 (Yang et al 2022). They only provided the velocity range of the 13 CO(J = 2-1) blue wing-like velocity component at [−37.2, −35] km s −1 , and did not report the velocity range of the 13 CO(J = 2-1) red wing-like velocity component.…”

ATLASGAL -- Evolutionary trends in high-mass star formation

“…We have cross-matched the ATLASGAL sample with four other star formation tracers to test the validity of the evolutionary sequence identified in this paper. We have used the catalogue of ∼300 extended green objects (EGOs; Cyganowski et al 2008), catalogues of molecular outflows produced by Maud et al (2015); de Villiers et al ( 2014); Yang et al (2018Yang et al ( , 2021, the methanol multibeam (MMB) survey (Green et al 2009) and water masers identified by HOPS (Walsh et al 2011(Walsh et al , 2014. EGOs are identified by their enhanced emission in the 4.5-µm band that contains the rotationally excited H 2 (v = 0 − 0, S(9, 10, 11)) and CO (v = 1 − 0) band-head lines, which are indicative of outflow activity and active accretion (Cyganowski et al 2008).…”

Dependence of Molecular Cloud Samples on Angular Resolution, Sensitivity, and Algorithms

“…Molecular clouds (see Heyer & Dame 2015 for a review) are usually observed in three-dimensional position-position-velocity (PPV) space or two-dimensional dust continuum emission (e.g., Bot et al 2007;Könyves et al 2015;Arzoumanian et al 2019). PPV data provide valuable information about properties of molecular clouds and activities in them, such as densities (e.g., Kauffmann et al 2017;Evans et al 2021), temperatures (e.g., Wang et al 2019;Mazumdar et al 2021), and molecular outflows (e.g., Snell et al 1980;Zhang et al 2001Zhang et al , 2020Yang et al 2018Yang et al , 2022, as well as large-scale structures of the Milky Way (e.g., Dame et al 2001;Sun et al 2015;Du et al 2017). Missing one dimension of position, PPV data are incomplete compared with position-position-position (PPP) data and are unable to distinguish molecular clouds in crowded regions, such as the first Galactic quadrant, and velocity degenerated directions, such as the Galactic anticenter.…”