A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

Abstract

We have studied 14 southern infrared dark clouds (IRDCs) using the data taken from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey and the GLIMPSE and MIPSGAL mid-infrared survey of the inner Galaxy. The physical and chemical characteristics of the 14 IRDCs are investigated using N 2 H + (1-0), HNC(1-0), HCO + (1-0), and HCN(1-0) molecular lines. We find that the 14 IRDCs are in different evolutionary stages from the "starless" to the sources with an UCHII region. Three IRDCs are detected to have the star forming activities. The integrated intensity ratios I HCO + /HCN , I N2H + /HCN , and I HNC/HCN are all about 1.5, which is different from the previous measurements, suggesting that the integrated intensity ratios may be affected by the cloud environments. The integrated intensities of HNC, HCO + and HCN show a tight correlation for the 14 IRDCs, implying a close link to the chemical evolution of these three species in the IRDCs. The derived excitation temperature for each IRDC is less than 25 K. We estimate the abundances of the four molecules from 10 −11 to 10 −9 , and the average abundance ratios N HNC /N HCN = 1.47 ± 0.50, N HNC /N HCO + = 1.74 ± 0.22, N HCN /N HCO + = 1.21 ± 0.41.

ALMA INVESTIGATION OF VIBRATIONALLY EXCITED HCN/HCO+/HNC EMISSION LINES IN THE AGN-HOSTING ULTRALUMINOUS INFRARED GALAXY IRAS 20551−4250

“…With respect to HCN and HNC, in our Galaxy, the abundance of HCN and HNC are comparable in cold dark clouds (Hirota et al 1998;Liu et al 2013;Graninger et al 2014). However, in high-temperature clouds around active regions, the HNC abundance decreases by more than an order of magnitude relative to the HCN abundance (Schilke et al 1992;Hirota et al 1998;Graninger et al 2014).…”

“…In our Milky Way Galaxy, the HCN-to-HCO + abundance ratio is estimated to be 1.2 ± 0.4 in infrared dark clouds, based on molecular emission line studies (Liu et al 2013) and 1.9 ± 0.9 in diffuse interstellar medium, based on molecular Mrk 231 Imanishi et al (2011), analyzed in the same manner as described in our previously published Spitzer IRS papers (Imanishi et al 2007a(Imanishi et al , 2010aImanishi 2009). It is virtually identical to the spectrum shown by Sargsyan et al (2011), except for small gaps among different spectral modules in the latter.…”

The SEDIGISM survey: molecular clouds in the inner Galaxy

“…Using these criteria, we cross-matched our clouds with catalogued Dark Clouds with velocity information (Otrupcek et al 2000), as well as with IRDCs, some with and some without velocity information (Simon et al 2006, Jackson et al 2008, Du & Yang 2008, Peretto & Fuller 2009, Chira et al 2013, Liu et al 2013. Their extinction makes Dark Clouds and IRDCs appear in silhouette against a bright background (in the visible and in the IR, respectively).…”

Molecular Deuterations in Massive Starless Clump Candidates

“…Although the chemistry of HCN and HNC is not clear, the [HCN]/[HNC] ratio has been proposed as a potential tool to probe the temperature in massive star-forming regions (e.g., Graninger et al 2014;Hacar et al 2020), and the ratio decreases with increasing temperature. Observations found the [HCN]/[HNC] ratio 1 in starless cores (Tennekes et al 2006;Hily-Blant et al 2010) and infrared dark clouds (Liu et al 2013). The [HCN]/[HNC] ratios of our sources may also have values lower than 1 based on our estimated N (HN 13 C)/N(H 13 CN) ratios.…”