In search of infall motion in molecular clumps III: HCO+ (1-0) and H13CO+ (1-0) mapping observations toward the confirmed infall sources

TL;DR

This study uses HCO+ and H13CO+ line observations to identify and analyze infall motions in 24 molecular clumps, revealing infall signatures, clumpy structures, and star-forming activities consistent with intermediate or massive star formation.

Contribution

First detailed mapping of infall motions in 24 molecular clumps using HCO+ and H13CO+ lines, with modeling to estimate infall parameters and star formation activity.

Findings

19 sources show blue asymmetric profiles indicating infall.

Infall velocities range from 0.3 to 1.3 km/s.

Star formation indicators like outflows and masers are present.

Abstract

The study of infall motion helps us to understand the initial stages of star formation. In this paper, we use the IRAM 30-m telescope to make mapping observations of 24 infall sources confirmed in previous work. The lines we use to track gas infall motions are HCO+ (1-0) and H13CO+ (1-0). All 24 sources show HCO+ emissions, while 18 sources show H13CO+ emissions. The HCO+ integrated intensity maps of 17 sources show clear clumpy structures; for the H13CO+ line, 15 sources show clumpy structures. We estimated the column density of HCO+ and H13CO+ using the RADEX radiation transfer code, and the obtained [HCO+]/[H2] and [H13CO+]/[HCO+] of these sources are about 10^-11 ~ 10^-7 and 10^-3~1, respectively. Based on the asymmetry of the line profile of the HCO+, we distinguish these sources: 19 sources show blue asymmetric profiles, and the other sources show red profiles or symmetric peak profiles. For eight sources that have double-peaked blue line profiles and signal-to-noise ratios greater than 10, the RATRAN model is used to fit their HCO^+ (1-0) lines, and to estimate their infall parameters. The mean Vin of these sources are 0.3 ~ 1.3 km/s, and the Min are about 10^-3 ~ 10^-4 Msun/yr , which are consistent with the results of intermediate or massive star formation in previous studies. The Vin estimated from the Myers model are 0.1 ~ 1.6 km/s, and the Min are within 10^-3 ~ 10^-5 Msun/yr. In addition, some identified infall sources show other star-forming activities, such as outflows and maser emissions. Especially for those sources with a double-peaked blue asymmetric profile, most of them have both infall and outflow evidence.