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

TL;DR

This study uses near-infrared integral field spectroscopy to map the gas and stellar dynamics and distributions in the nuclear region of NGC 4303, revealing a star-forming ring, distinct gas phases, and signs of an active galactic nucleus.

Contribution

First detailed near-IR integral field spectroscopic analysis of NGC 4303's nuclear region, mapping ionized and molecular gas, stellar populations, and kinematics at high spatial resolution.

Findings

Identified a 200-250pc star-forming ring with distinct gas emission regions.

Detected anti-correlation between hot H2 and ionized gas emissions, indicating post-starburst regions.

Observed gas and stellar rotation patterns with non-circular motions near the nuclear bar.

Abstract

We present new maps of emission-line flux distributions and kinematics in both ionized (traced by HI and [FeII] lines) and molecular (H2) gas of the inner 0.7x0.7kpc2 of the galaxy NGC4303, with a spatial resolution 40-80pc and velocity resolution 90-150 km/s obtained from near-IR integral field specroscopy using the VLT instrument SINFONI. The most promiment feature is a 200-250pc ring of circum-nuclear star-forming regions. The emission from ionized and molecular gas shows distinct flux distributions: while the strongest HI and [FeII] emission comes from regions in the west side of the ring (ages~4Myr), the H2 emission is strongest at the nucleus and in the east side of the ring (ages>10Myr). We find that regions of enhanced hot H2 emission are anti-correlated with those of enhanced [FeII] and HI emission, which can be attributed to post starburst regions that do not have ionizing photons anymore but still are hot enough (~2000K) to excite the H2 molecule. The line ratios are consistent with the presence of an AGN at the nucleus. The youngest regions have stellar masses in the range 0.3-1.5E5 MSun and ionized and hot molecular gas masses of ~0.25-1.2E4 Msun and 2.5-5 Msun, 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, that can be attributed to a cooler dynamics due to their recent formation from cool gas.