Dense Molecular Gas and Dusty Torus in NGC 4303

Abstract

Spectrum analysis at 3 mm of the central region (r≈800 pc) of NGC 4303 showed molecular gas lines of both dense gas tracers (HCN, HNC, HCO⁺, and C₂H) and diffuse gases (¹³CO and C¹⁸O). Molecular gas parameters: H₂ mass M_H2=(1.75±0.32)×10⁸M_☉; radial velocity V_dense=178±60 km s^‑1, and V_CO=151±29 km s^‑1; HCN luminosity L_HCN=(7.38±1.40)×10⁶ K km s^‑1 pc²; dense gas mass M_dense=(4.7±0.3)×10⁷ M_☉, indicating a significant contribution of dense to total molecular gas mass. To explore the AGN nature and central dusty torus of the galaxy, CIGALE was used to fit the integrated spectral energy distribution. Large torus properties are estimated: luminosity L_TORUS=(7.1±2.8)×10⁴³ erg s^‑1 and line of sight inclination of 67±16°, which is consistent with a Type 2 AGN; total infrared luminosity L_IR=(3.51± 0.30)×10⁴⁴ erg s^‑1; star formation rate SFR=6.0±0.3 M_☉ yr^‑1. A marginal AGN contribution of ≈20% was found.