C2H N = 1 - 0 and N2H+ J = 1 - 0 observations of Planck Galactic cold clumps
Abstract
A survey of C2H N = 1 - 0 and N2H+ J = 1 - 0 toward Planck Galactic cold clumps (PGCCs) was performed using the Purple Mountain Observatory's 13.7 m telescope. C2H and N2H+ were chosen to study the chemical evolutionary states of PGCCs. Among 121 observed molecular cores associated with PGCCs, 71 and 58 are detected with C2H N = 1 - 0 and N2H+ J = 1 - 0, respectively. The detected lines of most sources can be fitted with a single component with compatible VLSR 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 C2H and N2H+ (N(C2H)/N(N2H+)) 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(C2H)/N(N2H+) as a function of time. The cores with the lowest abundances of N2H+ (X[N2H+] < 10-10) are the youngest, and have nearly constant abundances of C2H. In evolved cores with X[N2H+] 10-9, abundances of C2H drop quickly as the exhaustion of carbon atoms. Although these PGCC cores are in different evolutionary states, they are all quite young (< 5 × 105 yr) with N(C2H) > N(N2H+). Mapping observations are carried out toward 20 PGCC cores. The PGCC cores in Cepheus have lower N(C2H)/N(N2H+) and larger line widths compared with those in Taurus. This implies that PGCC cores in Taurus are less chemically evolved than those in Cepheus.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 2019
- DOI:
- 10.1051/0004-6361/201834411
- arXiv:
- arXiv:1901.01124
- Bibcode:
- 2019A&A...622A..32L
- Keywords:
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- ISM: molecules;
- ISM: abundances;
- ISM: kinematics and dynamics;
- stars: formation;
- ISM: clouds;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 23 pages, 6 figures, 5 tables