A new search for star forming regions in the southern outer Galaxy

Abstract

Context. Star formation in the outer Galaxy is thought to be different from that in the inner Galaxy, as it is subject to different environmental parameters such as metallicity, interstellar radiation field, or mass surface density, which all change with galactocentric radius. Extending our star formation knowledge, from the inner to the outer Galaxy, helps us to understand the influences of the change of the environment on star formation throughout the Milky Way. Aims. We aim to obtain a more detailed view on the structure of the outer Galaxy, determining physical properties for a large number of star forming clumps and understanding star formation outside the solar circle. As one of the largest expanding Galactic super-shells is present in the observed region, a unique opportunity is taken here to investigate the influence of such an expanding structure on star formation as well. Methods. We used pointed 12CO(2–1) observations conducted with the APEX telescope to determine the velocity components towards 830 dust clumps identified from 250 μm Herschel/Hi-GAL SPIRE emission maps in the outer Galaxy between 225° < ℓ < 260°. We determined kinematic distances from the velocity components, in order to analyze the structure of the outer Galaxy and to estimate physical properties such as dust temperatures, bolometric luminosities, clump masses, and H2 column densities for 611 clumps. For this, we determined the dust spectral energy density distributions from archival mid-infrared to submillimeter (submm) emission maps. Results. We find the identified CO clouds to be strongly correlated with the highest column density parts of the H I emission distribution, spanning a web of bridges, spurs, and blobs of star forming regions between the larger complexes, unveiling the complex three-dimensional structure of the outer Galaxy in unprecedented detail. Using the physical properties of the clumps, we find an upper limit of 6% (40 sources) capable of forming high-mass stars. This is supported by the fact that only two methanol Class II masers, or 34 known or candidate H II regions, are found in the whole survey area, indicating an even lower fraction that are able to form high-mass stars in the outer Galaxy. We fail to find any correlation of the physical parameters of the identified (potential) star forming regions with the expanding supershell, indicating that although the shell organizes the interstellar material into clumps, the properties of the latter are unaffected. Conclusions. Using the APEX telescope in combination with publicly available Hi-GAL, MSX, and Wise continuum emission maps, we were able to investigate the structure and properties of a region of the Milky Way in unprecedented detail.

A census of young stellar objects in two line-of-sight star forming regions toward IRAS 22147+5948 in the outer Galaxy

“…The distance of 7.8 kpc is clearly inconsistent with the distance of 5.6 kpc determined using CO 1-0 (Section 3), and suggest that the radio source is not related to IRAS 22147+5948. On the contrary, the distance of G104.699+02.781 roughly agrees with the CO measurements and the differences may be due to uncertainties in the adopted model of the Galaxy for the outer Galaxy (König et al 2021). The velocity of hydrogen radio recombination lines of -57.8 km s −1 corresponds to the distance of 5.17 ± 0.6 kpc according to the updated rotational curve from the Bar and Spiral Structure Legacy Survey (BeSSeL; Reid et al 2014).…”

“…In the Solar neighborhood, about 3000 YSOs has been identified in molecular clouds as part of the Spitzer Space Telescope Gould Belt survey, providing life-times of YSO evolutionary stages and star formation efficiencies in various clouds (Dunham et al 2015;Kristensen & Dunham 2018). Similar efforts in the outer Galaxy suffer from low angular resolution, sensitivity and distance uncertainties, and are often limited to high-mass objects (Urquhart et al 2008;König et al 2021). Yet, due to differences in environmental conditions and high fraction of atomicto-molecular gas, the star formation rate at the outer parts of the Galactic disk is expected to be lower (Kennicutt & Evans 2012).…”

OGHReS: Large-scale filaments in the outer Galaxy

“…where I CO(2 1) is the integrated intensity of the 12 CO(2-1) emission. We assumed X CO(1 0) = 2.3 ⇥ 10 20 cm 2 (K km s 1 ) 1 inferred by Brand & Wouterloot (1995) (see also Heyer et al 2001b;Bolatto et al 2013;König et al 2021) who showed that in the outer Galaxy, the CO-to-H 2 conversion factor, X CO(1 0) , is within the uncertainties consistent with the inner Galaxy value. As X CO(1 0) was calculated for the 12 CO(1-0) line, we used a ration between the 12 CO(2-1) to the 12 CO(1-0) intensity, R 21 = 0.7 (e.g.…”

A global view on star formation: the GLOSTAR Galactic plane survey

“…Using the same procedures as described in König et al (2021), we determined the flux densities from Herschel/Hi-GAL (Molinari et al 2010) and MSX (Price et al 2001) continuum maps in nine bands using an aperture-annulus approach. As the 160 µm PACS band and the D-configuration maps of methanol have similar beam widths (i.e., 13.…”