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 report the detection of surprisingly strong HCN, HNC, and HCO+(J=6-5)emission in the host galaxy of the z=3.91 quasar APM08279+5255 throughobservations with CARMA. HCN, HNC, and HCO+ are typically used as starformation indicators, tracing dense molecular hydrogen gas [n(H2) > 10^5,cm^-3]within star-forming molecular clouds. However, the strength of their respectiveline emission in the J=6-5 transitions in APM08279+5255 is extremely high,suggesting that they are excited by another mechanism besides collisions in thedense molecular gas phase alone. We derive J=6-5 line luminosities ofL'(HCN)=(4.9+/-0.6), L'(HNC)=(2.4+/-0.7), and L'(HCO+)=(3.0+/-0.6)x10^10(mu_L)^-1 K km/s pc^2 (where mu_L is the lensing magnification factor),corresponding to L' ratios of ~0.23-0.46 relative to CO(J=1-0). Such high lineratios would be unusual even in the respective ground-state (J=1-0)transitions, and indicate exceptional, collisionally and radiatively drivenexcitation conditions in the dense, star-forming molecular gas inAPM08279+5255. Through an expansion of our previous modeling of the HCN lineexcitation in this source, we show that the high rotational line fluxes arecaused by substantial infrared pumping at moderate opacities in a ~220K warmgas and dust component. This implies that standard M_dense/L' conversionfactors would substantially overpredict the dense molecular gas mass M_dense.We also find a HCN J=6-5/5-4 L' ratio greater than 1 (1.36+/-0.31) - however,our models show that the excitation is likely not `super-thermal', but that thehigh line ratio is due to a rising optical depth between both transitions.These findings are consistent with the picture that the bulk of the gas anddust in this source is situated in a compact, nuclear starburst, where both thehighly active galactic nucleus and star formation contribute to the heating.

Dense Molecular Gas Excitation in Nuclear Starbursts at High Redshift: HCN, HNC, and HCO+(J=6-5) Emission in the z=3.91 Quasar Host of APM08279+5255