A SINFONI view of the nuclear activity and circumnuclear star formation in NGC 4303

Abstract

We present new maps of emission-line flux distributions and kinematics in both ionized (traced by HI and [Fe II] lines) and molecular (H2) gas of the inner 0.7 × 0.7 kpc2 of the galaxy NGC 4303, with a spatial resolution 40–80 pc and velocity resolution 90–150 km s−1 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 HI 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 HI 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 × 105 M and ionized and hot molecular gas masses of ~0.25–1.2 × 104 M and ~2.5–5M , 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.