Understanding the two-dimensional ionization structure in luminous infrared galaxies. A near-IR integral field spectroscopy perspective

Abstract

We investigate the 2D excitation structure of the ISM in a sample of LIRGs and Seyferts using near-IR IFS. This study extends to the near-IR the well-known optical and mid-IR emission line diagnostics used to classify activity in galaxies. Based on the spatially resolved spectroscopy of prototypes, we identify in the [FeII]1.64/Br$\gamma$ - H_2 1-0S(1)/Br$\gamma$ plane regions dominated by the different heating sources, i.e. AGNs, young MS massive stars, and evolved stars i.e. supernovae. The ISM in LIRGs occupy a wide region in the near-IR diagnostic plane from -0.6 to +1.5 and from -1.2 to +0.8 (in log units) for the [FeII]/Br$\gamma$ and H_2/Br$\gamma$ line ratios, respectively. The corresponding median(mode) ratios are +0.18(0.16) and +0.02(-0.04). Seyferts show on average larger values by factors ~2.5 and ~1.4 for the [FeII]/Br$\gamma$ and H_2/Br$\gamma$ ratios, respectively. New areas and relations in the near-IR diagnostic plane are defined for the compact, high surface brightness regions dominated by AGN, young ionizing stars, and SNe explosions, respectively. In addition, the diffuse regions affected by the AGN radiation field cover an area similar to that of Seyferts, but with high values in [FeII]/Br$\gamma$ that are not as extreme. The extended, non-AGN diffuse regions cover a wide area in the diagnostic diagram that overlaps that of individual excitation mechanisms (i.e. AGN, young stars, and SNe), but with its mode value to that of the young SF clumps. This indicates that the excitation conditions of the diffuse ISM are likely due to a mixture of the different ionization sources. The integrated line ratios in LIRGs show higher excitation conditions i.e. towards AGNs, than those measured by the spatially resolved spectroscopy. If this behaviour is representative, it would have clear consequences when classifying high-z, SF galaxies based on their near-IR integrated spectra.

18 pages, 13 figures, accepted for publication in A&A

References in corpus (10)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• A 0.8-2.4 microns spectral atlas of Active Galactic Nuclei
• Near-Infrared and Star-forming properties of Local Luminous Infrared Galaxies
• Feeding versus Feedback in NGC 4151 probed with Gemini NIFS. I. Excitation
• Starburst-AGN mixing: II. Optically-selected active galaxies
• VLT-SINFONI integral field spectroscopy of low-z luminous and ultraluminous infrared galaxies I. Atlas of the 2D gas structure
• Outflow of hot and cold molecular gas from the obscured secondary nucleus of NGC3256: closing in on feedback physics
• A mid-infrared view of the inner parsecs of the Seyfert galaxy Mrk 1066 using CanariCam/GTC
• The Mid-Infrared [SIV]/[NeII] versus [NeIII]/[NeII] Correlation

Cited by in corpus (6)

• Star formation in a galactic outflow
• Star formation and gas flows in the centre of the NUGA galaxy NGC 1808 observed with SINFONI
• A SINFONI view of the nuclear activity and circum-nuclear star formation in NGC 4303
• A close look at the dwarf AGN of NGC 4395: optical and near-IR integral field spectroscopy
• Gemini NIFS survey of feeding and feedback processes in nearby Active Galaxies: II -The sample and surface mass density profiles
• Outflows, Inflows and Young Stars in the inner 200 pc of the Seyfert galaxy NGC 2110