The DIVING$^\mathrm{3D}$ Survey -- Deep IFS View of Nuclei of Galaxies -- II. First results: nuclear emission-line properties of the mini-DIVING$^\mathrm{3D}$ sample

TL;DR

This study presents initial findings from the DIVING$^ ext{3D}$ survey, revealing nuclear emission-line properties of galaxies, including the prevalence of LINERs and AGNs, and highlighting the importance of high-resolution spectroscopy in understanding galaxy nuclei.

Contribution

First results from the DIVING$^ ext{3D}$ survey demonstrate the effectiveness of deep integral field spectroscopy in distinguishing nuclear emission types and identifying AGNs in galaxy nuclei.

Findings

23% of galaxies show LINER-like nuclear emission

High spatial resolution reduces transition object classification

69% of LINERs exhibit active galactic nuclei evidence

Abstract

This work presents the first results of the Deep IFS View of Nuclei of Galaxies (DIVING$^\mathrm{3D}$) survey. We analysed the nuclear emission-line spectra of a sub-sample we call mini-DIVING$^\mathrm{3D}$, which includes all Southern galaxies with B < 11.2 and |b| > 15 degrees. We verified that $23\% \pm 4\%$ of the galaxies show nuclear emission-line properties characteristic of Low Ionization Nuclear Emission-Line Regions (LINERs). Diagnostic diagram analysis reveals an apparent dichotomy, not detected in previous studies, between objects classified as H II regions and as LINERs or Seyferts, with very few galaxies classified as transition objects. A possible explanation for this result is that at least part of the transition objects are composite systems, with a central LINER contaminated by the emission from circumnuclear H II regions. The higher spatial resolution of the DIVING$^\mathrm{3D}$ survey, in comparison with previous studies, allowed us to isolate the nuclear emission from circumnuclear contaminations, reducing the number of transition objects. We also propose an alternative scenario, in which the emission-line spectra of some transition objects are the result of shock heating by central outflows, together with photoionization by young stars. Clear evidence of active galactic nuclei (AGNs), in the optical and X-ray spectral bands, were detected in 69$\%$ of the LINERs in the mini-DIVING$^\mathrm{3D}$ sample. Considering the entire mini-DIVING$^\mathrm{3D}$ sample, evidence of AGNs were detected in 65$\%$ of the objects.