In Search for Infall Gas in Molecular Clouds: A Catalogue of CO Blue-Profiles

Abstract

We started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation. Our first step is to utilize the data products by MWISP to make an unbiased survey for blue asymmetric line profiles of CO isotopical molecules. Within a total area of $\sim$ 2400 square degrees nearby the Galactic plane, we have found 3534 candidates showing blue-profiles, in which 3330 are selected from the \co\&\co[13]{} pair and 204 are from the \co[13]\&\CO{} pair. Exploration of the parametric spaces suggests our samples are in the cold phase with relatively high column densities ready for star formation. Analysis of the spatial distribution of our samples suggests that they exist virtually in all major components of the Galaxy. The vertical distribution suggest that the sources are located mainly in the thick disk of $\sim$ 85 parsec, but still a small part are located far beyond Galactic midplane. Our follow-up observation indicates that these candidates are a good sample to start a search for infall motions, and to study the condition of very early phase of star formation.

In Search of Infall Motion in Molecular Clumps. V. HCO+ (1–0) and HCN (1–0) Observations toward 210 Infall Candidates

“…We conducted an observational study of 210 infall candidates selected from those by Jiang et al (2023), using Note. The first four columns of values refer to the median values of each physical property, with their standard deviations in parentheses.…”

“…They follow the power-law distribution, T ∝ r −0.4 (Hogerheijde & van der Tak 2000). The kinetic temperature and column density of each source are adopted from Jiang et al (2023). We assume the filling factor of 1.0 and roughly take a beam size as the outer radius of each source.…”

“…Therefore, we started an unbiased survey of infall objects in the Milky Way. In the first step, we selected a sample of candidates with a 12 CO or 13 CO blue profile (Jiang et al 2023), with a total number of ∼3500. The CO data are from the Milky Way Imaging Scroll Painting project, which is an unbiased survey for more than 2600 deg 2 around the Galactic plane using three isotopic lines of CO.…”

In Search of Infall Motion in Molecular Clumps. IV. Mapping of the Global Infall Sources

“…In cases where the spectral line profile shows a peak-shoulder profile or a single-peaked profile with the peak skewed to the blue, it is difficult to identify the red peak and the dip. In such situations, two local maximum points and the saddle point between them are used to determine the blue peak, red peak, and dip (Jiang et al 2023). The uncertainty of these parameters is mainly caused by the noise of the spectral line and fitting error.…”

“…First, we carried out a blind search in all available MWISP CO data to find sources with a blue profile in the optically thick lines. About 3500 sources were initially identified and checked (Jiang et al 2023, hereafter referred to as Paper I). Subsequently, we selected 133 of them with a significant blue profile in the 12 CO line and the intensity of the C 18 O line >1 K for further confirmation.…”