New detections of (sub)millimeter hydrogen radio recombination lines towards high-mass star-forming clumps

Menten

et al. 2021

A&A

Self Cite

Context. The derived physical parameters for young H ii regions are normally determined assuming the emission region to be optically thin. However, this assumption is unlikely to hold for young H ii regions such as hyper-compact H ii (HC H ii) and ultra-compact H ii (UC H ii) regions and leads to underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies. Aims. The two primary goals of this study are (1) to determine the physical properties of young H ii regions from radio SEDs in the search for potential HC H ii regions, and (2) to use these physical properties to investigate their evolution. Methods. We used the Karl G. Jansky Very Large Array (VLA) to observe the X-band and K-band with angular resolutions of ∼ 1.7 and ∼ 0.7 , respectively, toward 114 H ii regions with rising-spectra (α 5 GHz 1.4 GHz > 0). We complement our observations with VLA archival data and construct SEDs in the range of 1−26 GHz and model them assuming an ionization-bounded H ii region with uniform density. Results. Our sample has a mean electron density of n e = 1.6 × 10 4 cm −3 , diameter diam = 0.14 pc, and emission measure EM = 1.9 × 10 7 pc cm −6. We identify 16 HC H ii region candidates and 8 intermediate objects between the classes of HC H ii and UC H ii regions. The n e , diam, and EM change, as expected, but the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman-continuum photons are absorbed by dust within these H ii regions and the dust absorption fraction tends to be more significant for more compact and younger H ii regions. Conclusions. Young H ii regions are commonly located in dusty clumps; HC H ii regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.

Section: G030mentioning

confidence: 90%

A population of hypercompact H II regions identified from young H II regions

Yang

Menten

et al. 2021

A&A

Self Cite

“…We have used Galactic plane surveys such as the Galactic Ring Survey (GRS; Jackson et al 2006), the Mopra CO Survey of the Southern Galactic Plane (Burton et al 2013;Braiding et al 2015), ThrUMMS, (Barnes et al 2015), COHRS (Dempsey et al 2013), and CHIMPS (Rigby et al 2016(Rigby et al , 2019 as well as large targeted observational programmes towards selected samples (e.g., MALT90 (Jackson et al 2013), RMS (Urquhart et al 2007(Urquhart et al , 2008(Urquhart et al , 2011(Urquhart et al , 2014a, and BGPS (Dunham et al 2011a;Schlingman et al 2011;Shirley et al 2013a). These have been augmented by dedicated ATLASGAL follow-up observations including NH 3 (Wienen et al 2012(Wienen et al , 2018, SiO (2-1) (Csengeri et al 2016b), radio recombination lines (Kim et al 2017(Kim et al , 2018 and an unbiased 3-mm chemical survey between 85.2-93.4 GHz (Urquhart et al 2019). Comparisons between the distances estimated by other survey teams and the ATLASGAL-determined distances finds agreement of ∼80 per cent (see Urquhart et al 2018 for more details).…”

Section: Survey Descriptionsmentioning

confidence: 99%

SEDIGISM-ATLASGAL: dense gas fraction and star formation efficiency across the Galactic disc

Monthly Notices of the Royal Astronomical Society

Figura

Cross

et al. 2020

By combining two surveys covering a large fraction of the molecular material in the Galactic disk we investigate the role the spiral arms play in the star formation process. We have matched clumps identified by ATLASGAL with their parental GMCs as identified by SEDIGISM, and use these giant molecular cloud (GMC) masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (DGFgmc = ∑Mclump/Mgmc) and the instantaneous star forming efficiencies (i.e., SFEgmc = ∑Lclump/Mgmc). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms (∼60 per cent found within ±10 km s−1 of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and H i to H2 conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of a any physical process.

“…The ATLASGAL CSC has therefore been the focus of an intensive campaign to characterise the properties and evolutionary state of the clumps. These have included dedicated molecular-line studies to produce the kinematics, temperatures, chemistry and determine kinematic distances (Wienen et al 2012;Giannetti et al 2014;Wienen et al 2015;Csengeri et al 2016;Kim et al 2017Kim et al , 2018Wienen et al 2018;Tang et al 2018;Navarete et al 2019;Urquhart et al 2019) and detailed analysis of clumps associated with star-formation tracers such as HII regions (Urquhart et al 2013b), methanol masers (Urquhart et al 2013a(Urquhart et al , 2015Billington et al 2019Billington et al , 2020, massive young stellar objects (MYSO; Urquhart et al 2014b;König et al 2017;Urquhart et al 2018) and filamentary structures (Li et al 2016;Mattern et al 2018;Lin et al 2019). This programme of follow-up observations and use of complementary multi-wavelength studies has resulted in the ATLASGAL sample being the most well characterised sample of high-mass star-forming clumps currently available.…”

Section: Introductionmentioning

confidence: 99%

ATLASGAL – evolutionary trends in high-mass star formation

Monthly Notices of the Royal Astronomical Society

Wells

Pillai

et al. 2021

ATLASGAL is a 870-μm dust survey of 420 square degrees of the inner Galactic plane and has been used to identify ∼10 000 dense molecular clumps. Dedicated follow-up observations and complementary surveys are used to characterise the physical properties of these clumps, map their Galactic distribution and investigate the evolutionary sequence for high-mass star formation. The analysis of the ATLASGAL data is ongoing: we present an up-to-date version of the catalogue. We have classified 5007 clumps into four evolutionary stages (quiescent, protostellar, young stellar objects and H ii regions) and find similar numbers of clumps in each stage, suggesting a similar lifetime. The luminosity-to-mass (Lbol/Mfwhm) ratio curve shows a smooth distribution with no significant kinks or discontinuities when compared to the mean values for evolutionary stages indicating that the star-formation process is continuous and that the observational stages do not represent fundamentally different stages or changes in the physical mechanisms involved. We compare the evolutionary sample with other star-formation tracers (methanol and water masers, extended green objects and molecular outflows) and find that the association rates with these increases as a function of evolutionary stage, confirming that our clasfication is reliable. This also reveals a high association rate between quiescent sources and molecular outflows, revealing that outflows are the earliest indication that star formation has begun and that star formation is already ongoing in many of the clumps that are dark even at 70 μm.