Invited Presentation

Star formation law in dense molecular gas

Author(s): Yu Gao (Purple Mountain Observatory)

Presenter: Yu Gao (Purple Mountain Observatory)

One of the fundamental questions in modern astrophysics is to understand how star formation (SF)
works across all star-forming systems near and far. The relations between the gas and SF rate (SFR)
in galaxies, i.e., Kennicutt-Schmidt (K-S) laws are reexamined in a large sample of 181 local star-forming
galaxies with far-infrared (FIR~SFR) luminosities spanning almost five orders of magnitude. The ΣSFR
is a steeper function of the total gas Σgas (H2+HI) than that of molecular gas ΣH2, with uncertain power law slopes. The dense molecular gas tracers such as HCN and CS
linearly correlate with the FIR for essential all star-forming systems near and far. The locally resolved FIR-HCN correlation, a local SF law in terms of dense molecular gas across the disks is also established. Herschel SPIRE/FTS observations of high-J CO lines in ~170 galaxies reveal all linear correlations between the FIR and high-J CO.
Such tight linear FIR - dense molecular gas correlations suggest that the SFR depends linearly upon the mass
of dense molecular gas. This is drastically different from the traditionally established K-S laws that relate the
total gas and SFR in galaxies and there are no unique correlations in these K-S laws. Finally, we
introduce the MALATANG large program on the JCMT to map the HCN and HCO+ J = 4 - 3 line emission
in over 20 nearest IR-brightest galaxies. MALATANG will bridge the gap, in terms
of physical scale and luminosity, between extragalactic (i.e., galaxy-integrated) and Galactic (i.e., single giant
molecular clouds) observations. A primary goal of the survey is to delineate for the first time the distributed
dense gas star formation relations, as traced by the HCN and HCO+ J = 4-3, on ~kpc scales.