C₂H N = 1 − 0 and N₂H⁺ J = 1 − 0 observations of Planck Galactic cold clumps

Abstract

A survey of C 2 H N = 1 − 0 and N 2 H + J = 1 − 0 toward Planck Galactic cold clumps (PGCCs) was performed using the Purple Mountain Observatory's 13.7 m telescope. C 2 H and N 2 H + were chosen to study the chemical evolutionary states of PGCCs. Among 121 observed molecular cores associated with PGCCs, 71 and 58 are detected with C 2 H N = 1 − 0 and N 2 H + J = 1 − 0, respectively. The detected lines of most sources can be fitted with a single component with compatible V LSR and line widths, which confirms that these PGCC cores are very cold (with gas temperatures 9-21 K) and quiescent while still dominanted by turbulence. The ratio between the column densities of C 2 H and N 2 H + (N(C 2 H)/N(N 2 H + )) is found to be a good tracer for the evolutionary states of PGCC cores. Gas-grain chemical model can reproduce the decreasing trend of N(C 2 H)/N(N 2 H + ) as a function of time. The cores with the lowest abundances of N 2 H + (X[N 2 H + ] < 10 −10 ) are the youngest, and have nearly constant abundances of C 2 H. In evolved cores with X[N 2 H + ] ∼ 10 −9 , abundances of C 2 H drop quickly as the exhaustion of carbon atoms. Although these PGCC cores are in different evolutionary states, they are all quite young (<5 × 10 5 yr) with N(C 2 H) > N(N 2 H + ). Mapping observations are carried out toward 20 PGCC cores. The PGCC cores in Cepheus have lower N(C 2 H)/N(N 2 H + ) and larger line widths compared with those in Taurus. This implies that PGCC cores in Taurus are less chemically evolved than those in Cepheus.

A search for cloud cores affected by shocked carbon chain chemistry in L1251

“…It is consistent with the fact that the northern part of L1251-A is denser (see Fig. 2) and may be more evolved, since N 2 H + tends to be enhanced in evolved regions (Caselli et al 2002;Liu et al 2019b), while CS J = 2-1 is usually characterized by more extended emission, which is getting closer to the size of the CO emission region (Wu 1993). Besides, the abundance of CS tends to be enhanced in turbulent regions, and CS emission is consistent with the chemical effects expected in shocked regions (Hartquist et al 1980;Zhou et al 1989;Suzuki et al 1992;Luo et al 2019).…”

“…) have a mean value of 8 with a standard deviation of 3. The abundance ratios of N[C 2 H]/N[N 2 H + ] in the L1251-A region are comparable with the values of typical dark clouds and star-forming regions, but tend to be lower than the typical value (>10) of Planck Galactic cold clumps (PGCCs) (Liu et al 2019b). In starless cores the abundance ratio between C 2 H and N 2 H + will decrease as the cores evolve, but it is not well constrained in star forming regions.…”

Chemical compositions of five Planck cold clumps

“…The 12 CO line in C4 does not have a double peak but shows a strong redshifted wing. The presence of wings or multiple peaks in the emission lines of Planck's cold clumps have been discussed by Meng et al (2013) and Liu et al (2019), where it is often interpreted as a signature of multi-components in the line of sight, which may then be the case for C4. Furthermore, 12 CO in C3 and C5 also present a small double peak profile but since none of the other species (including isotopic CO) have it, we assume that this is due to an optical depth effect.…”

Non-Energetic Formation of Ethanol via CCH Reaction with Interstellar H2O Ices. A Computational Chemistry Study

“…74,75 Similar abundances are found in prestellar cores, as probably CCH resides in the least depleted zone, similar to the molecular clouds. 76,78,79 In summary, CCH is abundant (∼ 10 −9 −10 −8 ) in cold (≤ 20 K) regions where the interstellar dust grains are enveloped by icy mantles. Thus, it is worth to investigate the possibility that it interacts with the water molecules of the ice to form ethanol, following the path described above (reactions 1 to 3).…”