Ammonia Observations of Planck Cold Cores
arxiv(2024)
摘要
Single-pointing observations of NH_3 (1,1) and (2,2) were conducted towards
672 Planck Early Release Cold Cores (ECCs) using the Nanshan 26-m radio
telescope. Out of these sources, a detection rate of 37
achieved, with NH_3(1,1) hyperfine structure detected in 187 and NH_3(2,2)
emission lines detected in 76 cores. The detection rate of NH3 is positively
correlated with the continuum emission fluxes at a frequency of 857 GHz. Among
the observed 672 cores, 22
beam size ( 2). This suggests that most of the cores in our sample may
be starless. The kinetic temperatures of the cores range from 8.9 to 20.7 K,
with an average of 12.3 K, indicating a coupling between gas and dust
temperatures. The ammonia column densities range from 0.36 to
6.07×10^15 cm^-2, with a median value of 2.04×10^15
cm^-2. The fractional abundances of ammonia range from 0.3 to
9.7×10^-7, with an average of 2.7 ×10^-7, which is one order
of magnitude larger than that of Massive Star-Forming (MSF) regions and
Infrared Dark Clouds (IRDCs). The correlation between thermal and non-thermal
velocity dispersion of the NH_3(1,1) inversion transition indicates the
dominance of supersonic non-thermal motions in the dense gas traced by NH_3,
and the relationship between these two parameters in Planck cold cores is
weaker, with lower values observed for both parameters relative to other
samples under our examination. The cumulative distribution shapes of line
widths in the Planck cold cores closely resemble those of the dense cores found
in regions of Cepheus, and Orion L1630 and L1641, with higher values compared
to Ophiuchus. A comparison of NH3 line-center velocities with those of
^13CO and C^18O shows small differences (0.13 and 0.12 km s^-1 ),
suggesting quiescence on small scales.
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