A study of the ionized gas in Stephan's Quintet from integral field spectroscopy observations

TL;DR

This study uses integral field spectroscopy to analyze the ionized gas in Stephan's Quintet, revealing complex excitation mechanisms, shock properties, and gas abundances in interacting galaxies.

Contribution

First detailed spatially-resolved spectroscopic analysis of ionized gas in Stephan's Quintet, combining shock and photoionization models to understand galaxy interactions.

Findings

Gas excitation in NGC 7319 is a mix of AGN photoionization and shocks.

Shock front in NGC 7318A/B shows multiple kinematic components consistent with shock models.

Gas oxygen abundance in NGC 7318B was determined using an updated calibration.

Abstract

The Stephan's Quintet (SQ) is a famous interacting compact group of galaxies in an important stage of dynamical evolution, but surprisingly very few spectroscopic studies are found in the literature. We present optical integral field spectroscopy (IFS) observations of the SQ from the PPAK IFS Nearby Galaxies Survey (PINGS), that provide a powerful way of studying with spatial resolution the physical characteristics of the ionized gas within the group. The nature of the gas emission is analysed using 2D maps of continuum-subtracted, pure emission-line intensities, stacked spectra, diagnostic diagrams, and photoionization model predictions. In the case of NGC 7319, we study the galaxy-wide high-velocity outflow emission by comparing the emission properties with theoretical shock and AGN models. We conclude that the excitation mechanism of the gas in this galaxy is a mixture of AGN photoionization and shocks with a photoionizing precursor. The emission spectra from the large scale shock front in the interacting pair NGC 7318A/B is analysed, confirming the presence of several kinematic components. Comparison with predictions from theoretical shock models suggests that the gas emission is consistent with shocks without a photoionizing precursor, low pre-shock density, and velocities in the range of 200 - 400 km s-1. The gas oxygen abundance for NGC 7318B is determined using an updated O3N2 calibration. Although NGC 7317 shows no significant gas emission, an ionizing cluster is found southwest of this galaxy, probably the result of tidal interaction. As a by-product, we analyse the gas emission of the foreground galaxy NGC 7320.