2016MNRAS.461.4192R

We present new maps of emission-line flux distributions and kinematics in both ionized (traced by H i and [Fe ii] lines) and molecular (H₂) gas of the inner 0.7 x 0.7 kpc² of the galaxy NGC 4303, with a spatial resolution 40-80 pc and velocity resolution 90-150 km/s obtained from near-IR integral field spectroscopy using the Very Large Telescope instrument SINFONI. The most prominent feature is a 200-250 pc ring of circumnuclear star-forming regions. The emission from ionized and molecular gas shows distinct flux distributions: while the strongest H i and [Fe ii] emission comes from regions in the west side of the ring (ages ∼ 4 Myr), the H₂ emission is strongest at the nucleus and in the east side of the ring (ages > 10 Myr). We find that regions of enhanced hot H₂ emission are anti-correlated with those of enhanced [Fe ii] and H i emission, which can be attributed to post-starburst regions that do not have ionizing photons anymore but still are hot enough (≃2000 K) to excite the H₂ molecule. The line ratios are consistent with the presence of an active galactic nucleus at the nucleus. The youngest regions have stellar masses in the range 0.3-1.5 x 10⁵ M_☉ and ionized and hot molecular gas masses of ∼0.25-1.2 x 10⁴ M_☉ and ∼2.5-5 M_☉, respectively. The stellar and gas velocity fields show a rotation pattern, with the gas presenting larger velocity amplitudes than the stars, with a deviation observed for the H₂ along the nuclear bar, where increased velocity dispersion is also observed, possibly associated with non-circular motions along the bar. The stars in the ring show smaller velocity dispersion than the surroundings, which can be attributed to a cooler dynamics due to their recent formation from cool gas.