Tracers of Dense Gas in the Outer Galaxy

• DOI: 10.48550/arxiv.2207.11613
• Publication Date: 2022-01-01
• Authors: Sudeshna Patra; Neal J. Evans; Kee‐Tae Kim; M. H. Heyer; Jens Kauffmann; Jessy Jose; M. R. Samal; Swagat R. Das
• Keywords: Extinction (optical mineralogy); Line (geometry); Green Bank Telescope

We have mapped HCN and HCO$^{+}$ (J = 1 $\to$ 0) line emission toward a sample of seven star-forming regions (with 12 + log[O/H] range from 8.34 to 8.69) in the outer Milky Way (Galactocentric distance > 9.5 kpc), using 14-meter radio telescope Taeduk Radio Astronomy Observatory (TRAO). compare these two molecular lines with other conventional tracers dense gas, millimeter-wave continuum dust extinction thresholds ($A_{V} \geq 8$ mag), inferred $^{13}$CO data. correlate better millimeter than criterion. A significant amount luminosity comes below criterion outside clump for all clouds. The average fraction within $A_{V} mag is $0.343\pm0.225$; emission, it $0.478\pm0.149$. Based on comparison column density maps Herschel, trace gas high does $^{13}$CO. less concentrated Galaxy targets, contrast inner sample, suggesting that metallicity may affect interpretation gas. conversion factor between mass ($M_{dense}$) luminosities HCO$^{+}$, when integrated over whole cloud, comparable factors used extragalactic studies.