Astrochemistry Focus and Research on Planck Cold Clumps

TL;DR

This paper reviews current gaps in astrochemistry understanding, especially regarding icy dust grain interactions and molecular chemistry, and presents observational results on Planck cold clumps, introducing the Chemical Evolution Factor to assess their star formation stages.

Contribution

It provides new observational data on Planck cold clumps and introduces the Chemical Evolution Factor for evaluating their chemical and star formation stages.

Findings

N2H+ distribution aligns with dust emission in observed clumps.

CCS emission is often clumpy and varies from N2H+ distribution.

Some starless clumps show signs of being on the verge of star formation.

Abstract

At the Astrochemistry Focus Group, we discussed what is still missing in our understanding even with new knowledge given at this conference, and what can be done for that within 10 years from now. Still missing in understanding are UV-photons and cosmic-rays interactions with icy dust grains, Sulphur and Phosphorus chemistry, Metallicity effect, Duration (time) effect, COM formation and destruction, phase transition, dust-gas interface, dust evolution, etc. What we should do are multi-scale high spectral resolution molecular observations, laboratory work, theory, radiative transfer, etc. We need careful modeling without simplifying things. Next, I introduce our research on Planck cold clumps. 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\%. 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.