The first detection of SiC$_2$ in the interstellar medium

TL;DR

This paper reports the first detection of the SiC$_2$ molecule in the interstellar medium, specifically in a molecular cloud near the Galactic center, using multiple radio telescopes and spectral analysis.

Contribution

It provides the first observational evidence of SiC$_2$ in space and explores its formation mechanisms in shocked interstellar gas.

Findings

Detected SiC$_2$ through six rotational transitions in G+0.693-0.027

Derived a column density of 1.02×10^{13} cm^{-2} and an excitation temperature of 5.9 K

Compared fractional abundances of SiC$_2$, SiS, and Si$^{18}$O with those in evolved stars

Abstract

We report the first detection of SiC$_2$ in the interstellar medium. The molecule was identified through six rotational transitions toward G\,+0.693$-$0.027, a molecular cloud located in the Galactic center. The detection is based on a line survey carried out with the GBT, the Yebes 40m, and the IRAM 30m telescopes covering a range of frequencies from 12 to 276 GHz. We fit the observed spectra assuming local thermodynamic equilibrium and derive a column density of ($1.02\pm0.04)\times10^{13}$ cm$^{-2}$, which gives a fractional abundance of $7.5\times10^{-11}$ with respect to H$_2$, and an excitation temperature of $5.9\pm0.2$ K. We conclude that SiC$_2$ can be formed in the shocked gas by a reaction between the sputtered atomic silicon and C$_2$H$_2$, or it can be released directly from the dust grains due to disruption. We also search for other Si-bearing molecules and detect eight rotational transitions of SiS and four transitions of Si$^{18}$O. The derived fractional abundances are $3.9\times10^{-10}$ and $2.1\times10^{-11}$, respectively. All Si-bearing species toward G\,+0.693$-$0.027 show fractional abundances well below what is typically found in late-type evolved stars.