2018/01/31 by Adam Onus, Mark R. Krumholz, Christoph Federrath · 1 citation
Physics and Astronomy · #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1093/mnras/sty1662
published as Adam Onus, Mark R Krumholz, Christoph Federrath; Numerical calibration of the HCN-star formation correlation, Monthly Notices of the Royal Astronomical Society, Volume 479, Issue 2, 11 September 2018, Pages 1702-1710
arxiv created 2018/09/11 · arxiv updated 2018/09/12
HCN(1-0) emission traces dense gas and correlates very strongly with star formation rates (SFRs) on scales from small Milky Way clouds to whole galaxies. The observed correlation offers strong constraints on the efficiency of star formation in dense gas, but quantitative interpretation of this constraint requires a mapping from HCN emission to gas mass and density. In this paper we provide the required calibration by postprocessing high-resolution simulations of dense, star-forming clouds to calculate their HCN emission (L\rm HCN) and to determine how that emission is related to the underlying gas density distribution and star formation efficiency. We find that HCN emission traces gas with a luminosity-weighted mean number density of 0.8-1.7 × 104 \rm cm-3 and that HCN luminosity is related to mass of dense gas of \gtrsim 104 \rm cm-3 with a conversion factor of α\rm HCN ≈ 14 \rm M\odot/(K km s-1 pc2). We also measure a new empirical relationship between the SFR per global mean freefall time (ε\rm ff) and the SFR-HCN relationship, \rm SFR/L\rm HCN = 2.0 × 10-7 (ε\rm ff/0.01)1.1 \rm M\odot yr-1/(K km s-1 pc2). The observed SFR-HCN correlation strongly constrains ε\rm ff ≈ 1% with a factor of ∼ 3 systematic uncertainty. The scatter in ε\rm ff from cloud to cloud within the Milky Way is a factor of a few. We conclude that L\rm HCN is an effective tracer of dense gas and that the IR-HCN correlation is a significant diagnostic of the microphysics of star formation in dense gas.