Title: The star formation law: the dense cores and star-forming galaxies connection

Speaker: Yu Gao (Purple Mountain Observatory)

Time & Place: Thursday, 3.00pm, June 6th, Lecture Hall, 3rd floor

Abstract: We first show that the disk-averaged surface density of star formation rate (SFR) has the tightest linear correlation with that of dense molecular gas (traced by HCN), not the molecular gas (H2) or total gas (HI+H2), using a large sample of ~180 galaxies including over 60 (ultra)luminous IR galaxies [(U)LIRGs]. This is consistent with the tight FIR-HCN correlation established globally for both dense cores and star-forming galaxies near and far. The Kennicutt-Schmidt law that relates the total gas and SFR appears to have no unique power-law slope with larger scatters since the correlation slopes change from ~1 for normal spirals to ~1.5 when (U)LIRGs are included. New observations using other dense molecular gas tracers, such as multi-transition CS lines, as well as high-J CO lines from Herschel SPIRE/FTS observations, further reveal that the SFR and dense gas relationship is linear. Additionally, the locally resolved SFR-HCN correlation in M51 is also roughly consistent with the globally established linear SFR-HCN correlation. All of these suggest that dense cores are the basic units contributing to the SFR and SFR might depend linearly upon the mass of dense molecular gas (the star formation law).