Astrochemical Properties of Planck Cold Clumps

TL;DR

This study investigates the chemical properties of 13 Planck cold clumps using multiple telescopes, revealing diverse molecular distributions, cold temperatures, and potential early star formation stages, and introduces a new chemical evolution metric.

Contribution

It provides the first comprehensive chemical analysis of Planck cold clumps, including molecular distributions, temperature estimates, and a new chemical evolution factor for starless cores.

Findings

Most clumps are cold, with temperatures below 20 K.

CCS emission often surrounds N$_2$H$^+$ cores in some clumps.

Half of the observed clumps show N$_2$D$^+$ detection, indicating chemical maturity.

Abstract

We observed thirteen Planck cold clumps with the James Clerk Maxwell Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N$_2$H$^+$ distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2 dust distribution. The 82 GHz HC$_3$N, 82 GHz CCS, and 94 GHz CCS emission are often distributed differently with respect to the N$_2$H$^+$ emission. The CCS emission, which is known to be abundant in starless molecular cloud cores, is often very clumpy in the observed targets. We made deep single-pointing observations in DNC, HN$^{13}$C, N$_2$D$^+$, cyclic-C$_3$H$_2$ toward nine clumps. The detection rate of N$_2$D$^+$ is 50\%. Furthermore, we observed the NH$_3$ emission toward 15 Planck cold clumps to estimate the kinetic temperature, and confirmed that most of targets are cold ($\lesssim$ 20 K). In two of the starless clumps observe, the CCS emission is distributed as it surrounds the N$_2$H$^+$ core (chemically evolved gas), which resembles the case of L1544, a prestellar core showing collapse. In addition, we detected both DNC and N$_2$D$^+$. These two clumps are most likely on the verge of star formation. We introduce the Chemical Evolution Factor (CEF) for starless cores to describe the chemical evolutionary stage, and analyze the observed Planck cold clumps.