English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We have mapped HCN and HCO$^{+}$ (J = 1 $\to$ 0) line emission toward asample of seven star-forming regions (with 12 + log[O/H] range from 8.34 to8.69) in the outer Milky Way (Galactocentric distance > 9.5 kpc), using the14-meter radio telescope of the Taeduk Radio Astronomy Observatory (TRAO). Wecompare these two molecular lines with other conventional tracers of dense gas,millimeter-wave continuum emission from dust and extinction thresholds ($A_{V}\geq 8$ mag), inferred from the $^{13}$CO line data. HCN and HCO$^{+}$correlate better with the millimeter emission than with the extinctioncriterion. A significant amount of luminosity comes from regions below theextinction criterion and outside the millimeter clump for all the clouds. Theaverage fraction of HCN luminosity from within the regions with $A_{V} \geq 8$mag is $0.343\pm0.225$; for the regions of millimeter emission, it is$0.478\pm0.149$. Based on a comparison with column density maps from Herschel,HCN and HCO$^{+}$ trace dense gas in high column density regions better thandoes $^{13}$CO. HCO$^{+}$ is less concentrated than HCN for outer Galaxytargets, in contrast with the inner Galaxy sample, suggesting that metallicitymay affect the interpretation of tracers of dense gas. The conversion factorbetween the dense gas mass ($M_{dense}$) and line luminosities of HCN andHCO$^{+}$, when integrated over the whole cloud, is comparable with factorsused in extragalactic studies.

Tracers of Dense Gas in the Outer Galaxy