MALT90 Kinematic Distances to Dense Molecular Clumps

Abstract

Using molecular-line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90), we have estimated kinematic distances to 1905 molecular clumps identified in the ATLASGAL 870 μm continuum survey over the longitude range 295°<l<350°. The clump velocities were determined using a flux-weighted average of the velocities obtained from Gaussian fits to the HCO + , HNC, and N 2 H + (1-0) transitions. The near/far kinematic distance ambiguity was addressed by searching for the presence or absence of absorption or self-absorption features in 21 cm atomic hydrogen spectra from the Southern Galactic Plane Survey. Our algorithm provides an estimation of the reliability of the ambiguity resolution. The Galactic distribution of the clumps indicates positions where the clumps are bunched together, and these locations probably trace the locations of spiral arms. Several clumps fall at the predicted location of the far side of the Scutum-Centaurus arm. Moreover, a number of clumps with positive radial velocities are unambiguously located on the far side of the Milky Way at galactocentric radii beyond the solar circle. The measurement of these kinematic distances, in combination with continuum or molecular-line data, now enables the determination of fundamental parameters such as mass, size, and luminosity for each clump.

Infall Signatures in a Prestellar Core Embedded in the High-mass 70 μm Dark IRDC G331.372-00.116

“…2. IRDC G331.372-00.116 G331.372-00.116 is located in the Galactic plane, in the RCW 106 complex (Nguyễn et al 2015), at a distance of 5.4 kpc (Whitaker et al 2017). It was detected via its bright continuum emission at 870 µm in the AT-LASGAL survey (AGAL331.372-00.116, Contreras et al 2013).…”

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation

“…By combining Herschel and ATLASGAL dust continuum emission observations, Guzmán et al (2015) derived tem-peratures and column densities for the MALT90 survey targets. After determining clump kinematical distances (Whitaker et al 2017), masses and number densities were calculated by Contreras et al (2017). With all these vast ancillary multi-wavelength data sets, we made a careful selection of prestellar clumps candidates that will potentially form high-mass stars.…”

G337.342–0.119 (The “Pebble”): A Cold, Dense, High-mass Molecular Cloud with Unusually Large Line Widths and a Candidate High-mass Star Cluster Progenitor

“…Here "GC" and "Sun" mark the locations of the Galactic Center and the Sun, respectively, L is the length of the Long Bar, R0 the distance to the Galactic Center from the Sun, i the inclination angle with respect to the line connecting the Sun and the Galactic Center, l+ the Galactic longitude of the near end of the Long Bar, and l− the Galactic longitude of the far end of the Long Bar. "Near" and "Far" mark the near and far kinematic distances of G337.342−0.119 (Whitaker et al 2017). Figure 9.…”

“…To search for such precursors, we have analyzed 870 µm ATLASGAL and 70 to 500 µm HiGAL images to estimate dust temperatures and gas column densities (Guzmán et al 2015). Combined with kinematic distance estimates (Whitaker et al 2017) from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90; Foster et al 2011Foster et al , 2013Jackson et al 2013) molecular line velocity data (Rathborne et al 2016), the dust continuum data can also be used to estimate masses. A high-mass cluster progenitor will manifest as a dense (n > 10 4 cm −3 ), cold (T <∼ 15 K) molecular cloud with sufficiently high mass (>∼ 10, 000 M ) to form a high-mass star cluster.…”