HC$_3$N, H$^{13}$CN, and HN$^{13}$C in molecular cores evolving towards star-forming regions

Abstract

As a work in progress, results from a chemical and physical analysis of molecular cores in early evolutionary stages concerning star formation are presented. Using archival data from the Atacama Large Millimeter Array (ALMA), a sample of 37 sources was investigated, from which spectra in the frequency range 330--350 GHz were extracted towards the central positions of the molecular cores. Transitions of HC$_3$N, H$^{13}$CN, and HN$^{13}$C were analysed using Gaussian fits, obtaining peak intensities, fluxes, and line widths. The column densities of each molecule and their abundances were estimated. The behaviour of these abundances with the temperature of the region was studied, observing positive correlations for H$^{13}$CN and HN$^{13}$C, and none for HC$_3$N. This study contributes to the characterisation of the initial conditions of the interstellar medium in early phases of stellar evolution.

Figures (3)

• Figure 1: As an example, we show the ALMA continuum emission at 0.8 mm from the core embedded in the ATLASGAL source G359.6158$-$0.2429. The contour levels are 0.7, 1.2, and 1.7 Jy beam$^{-1}$. From a beam area centred at the peak of the core, the spectra presented in Fig. \ref{['fig:espectros']} were extracted. The rms noise level is 0.02 Jy beam$^{-1}$.
• Figure 2: Spectra obtained from the core presented in Fig. \ref{['core']} in which the transitions of HC$_3$N (detected in two lines), H$^{13}$CN, and HN$^{13}$C are identified. Gaussian fittings to the selected lines are displayed in colours. These spectra are shown as an example of the spectral analysis performed in the whole sample of 37 cores. All identified lines have signal to noice (S/N) ratios above 100.
• Figure 3: Molecular abundances X (in logarithmic scale) vs. kinetic temperature. The lines are the result of linear fits whose results are included in the top left corner of each panel.