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