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

Nitrogen hydrides such as NH$_3$ and N$_2$H$^+$ are widely used by Galacticobservers to trace the cold dense regions of the interstellar medium. Inexternal galaxies, because of limited sensitivity, HCN has become the mostcommon tracer of dense gas over large parts of galaxies. We provide the firstsystematic measurements of N$_2$H$^+$(1-0) across different environments of anexternal spiral galaxy, NGC6946. We find a strong correlation ($r>0.98,p<0.01$)between the HCN(1-0) and N$_2$H$^+$(1-0) intensities across the inner$\sim8\mathrm{kpc}$ of the galaxy, at kiloparsec scales. This correlation isequally strong between the ratios N$_2$H$^+$(1-0)/CO(1-0) and HCN(1-0)/CO(1-0),tracers of dense gas fractions ($f_\mathrm{dense}$). We measure an averageintensity ratio of N$_2$H$^+$(1-0)/HCN(1-0)$=0.15\pm0.02$ over our set of fiveIRAM-30m pointings. These trends are further supported by existing measurementsfor Galactic and extragalactic sources. This narrow distribution in the averageratio suggests that the observed systematic trends found in kiloparsec-scaleextragalactic studies of $f_\mathrm{dense}$ and the efficiency of dense gas(SFE$_\mathrm{dense}$) would not change if we employed N$_2$H$^+$(1-0) as amore direct tracer of dense gas. At kiloparsec scales our results indicate thatthe HCN(1-0) emission can be used to predict the expected N$_2$H$^+$(1-0) overthose regions. Our results suggest that, even if HCN(1-0) and N$_2$H$^+$(1-0)trace different density regimes within molecular clouds, subcloud differencesaverage out at kiloparsec scales, yielding the two tracers proportional to eachother.

A constant N$_2$H$^+$(1-0)-to-HCN(1-0) ratio on kiloparsec scales