A Complete HCN Survey of the Perseus Molecular Cloud

Abstract

We present a survey of the Perseus molecular cloud in the J $=$ 1$\to$0 transition of HCN, a widely used tracer of dense molecular gas. The survey was conducted with the CfA 1.2 m telescope, which at 89 GHz has a beam width of 11' and a spectral resolution of 0.85 km s${}^{-1}$. A total of 8.1 deg${}^2$ was surveyed on a uniform 10' grid to a sensitivity of 14 mK per channel. The survey was compared with similar surveys of CO and dust in order to study and calibrate the HCN line as a dense gas tracer. We find the HCN emission to extend over a considerable fraction of the cloud. We show that the HCN intensity remains linear with H${}_2$ column density well into the regime where the CO line saturates. We use radiative transfer modeling to show that this likely results from subthermal excitation of HCN in a cloud where the column and volume densities of H${}_2$ are positively correlated. To match our HCN observations the model requires an exponential decrease in HCN abundance with increasing extinction, consistent with HCN depletion onto grains. The modeling also reveals that the mean volume density of H${}_2$ in the HCN emitting regions is $\sim$ 10${}^4$ cm${}^{-3}$, well below the HCN critical density. For the first time, we obtain a direct measurement of the ratio of dense gas mass to HCN luminosity for an entire nearby molecular cloud: $\alpha$(HCN) $=$ 92 M${}_{\odot }$/(K km s${}^{-1}$ pc${}^2$).

14 pages, 7 figures, Accepted for the Astrophysical Journal, Jan 16, 2023

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Cited by in corpus (10)

• Characterizing the line emission from molecular clouds. II. A comparative study of California, Perseus, and Orion A
• HCN emission from translucent gas and UV-illuminated cloud edges revealed by wide-field IRAM 30m maps of Orion B GMC: Revisiting its role as tracer of the dense gas reservoir for star formation
• A constant N${}_2$H${}^{+}$(1-0)-to-HCN(1-0) ratio on kiloparsec scales
• 3D structure of the Milky Way out to 10 kpc from the Sun. Catalogue of large molecular clouds in the Galactic Plane
• PRUSSIC III -- ALMA and NOEMA survey of dense gas in high-redshift star-forming galaxies
• Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula
• The factors that influence protostellar multiplicity I: Gas temperature, density, and mass in Perseus with Nobeyama
• Does the HCN/CO ratio trace the star-forming fraction of gas? II. Variations in CO and HCN Emissivity
• On volume density and star formation in nearby molecular clouds
• The factors that influence protostellar multiplicity II. Gas temperature and mass in Perseus with APEX