Searching for intergalactic star forming regions in Stephan's Quintet with SITELLE: II. Physical properties and metallicity
Abstract
Based on SITELLE spectroscopy, we studied the ionised gas emission for the 175 Hα emission regions in the Stephan's Quintet (SQ). A detailed analysis is performed of the star formation rate (SFR), oxygen abundance (O/H), and nitrogen-to-oxygen abundance ratio (N/O) of the SQ regions, to explore the provenance and evolution of this complex structure. According to the BPT diagram, we found 91 HII, 17 composite, and 7 active galactic nucleus-like regions in SQ. Several regions are compatible with fast shocks models without a precursor for solar metallicity and low density (n=0.1 cm-3), with velocities between 175 - 300 km s-1. We derived the total SFR in SQ (log(SFR/M\,yr-1=0.496); starburst A and B provide 28% and 9% of the total SFR, and 45% comes from the regions with a radial velocity lower than 6160 km s-1. For this reason, we assume that the material prior to the collision with the new intruder (NI) does not show a high SFR, and therefore SQ was apparently quenched. When considering the integrated SFR for the whole SQ and the NI, we found that both zones have a SFR consistent with those obtained in the SDSS star-forming galaxies. At least two chemically different gas components cohabit in SQ where, on average, the regions with high radial velocities (v>6160 km s-1) have lower values of O/H and N/O than those with low radial velocities (v≤6160 km s-1). The values found for the line ratios, O/H, and N/O for the southern debris region and the northernmost tidal tail, are compatible with regions belonging to the outer part of the galaxies. We highlight the presence of inner-outer variation for O/H and some emission line ratios along the NI strands and the young tidal tail south strand. Finally, the SQ Hα regions are outside the galaxies because the interactions have dispersed the gas to the peripheral zones.