Oral Presentation

Excitation or efficiency: a multi-line analysis of dense gas tracers across the Antennae

Author(s): Ashley Bemis (Waterloo Centre for Astrophysics)

Presenter: Ashley Bemis (Waterloo Centre for Astrophysics)

As extreme systems, galaxy mergers are important testbeds for constraining star formation models and the baryon cycle. The Antennae, the nearest gas-rich major merger, is of particular importance as it is well studied with interesting variations in the star formation efficiency of dense gas (SFEdense) at sub-kpc scales. LHCN/LCO appears to be enhanced in the nuclei relative to the overlap, indicating a higher dense gas fraction (fdense), while multiple SFR indicators are suppressed relative to LHCN in the nuclei indicating a lower SFEdense. Additionally, LHCN is enhanced relative to LHCO+ in NGC 4038, but not elsewhere in the Antennae. This indicates that the conversion of molecular line luminosities to dense gas masses may be different than typically assumed. We present the first multi-J radiative transfer modeling of dense gas tracers at sub-kpc scales across the Antennae to constrain the physical conditions of the gas exciting HCN and HCO+ using data from ALMA and the SMA. This includes the J=1-0, 3-2, and 4-3 lines of HCN and HCO+ in NGC4038 and SGMCs in the overlap region. We combine this with data of the CN and HNC J=1-0 transitions to explore potential chemical variations in dense gas tracers at these scales. Finally, these results are compared against radiative transfer modelling and the predictions of star formation models to assess if we are observing true variations in SFEdense and fdense, or if the emissivity of HCN is enhanced in the nuclei due to physical conditions of the gas.