Direct HST Dust Lane Detection in Powerful Narrow-Line Radio Galaxies

Edgar A Ramírez,Enrique Lopez-Rodriguez,Chris Packham,Itziar Aretxaga,Clive N Tadhunter

doi:10.3389/fspas.2017.00052

Abstract

We present the analysis of near-infrared Hubble Space Telescope imaging of 10 Fanaroff Riley II powerful radio galaxies at low redshift (0.03<z<0.11) optically classified as narrow-line radio galaxies. The photometric properties of the host galaxy are measured using Galfit, and compered with those from the literature. Our high resolution near-infrared observations provide new and direct information on the central kpc-scale dust lanes in our sample that could be connected to the pc-scale torus structure. Moreover, analyzing the infrared spectrograph Spitzer spectra of our sample, we suggest properties of the dust size of the torus}.

Highlights

Under the context of the unified schemes for active galactic nuclei (AGN, Barthel, 1989; Urry and Padovani, 1995), the pc-scale torus structure is perpendicular to the radio jet axis
In this work we present the analysis of near-IR images to investigate the connection between the pc-scale torus structure and the kpc-scale dust lane
We used archived infrared spectrograph (IRS) Spitzer data of our sample, to shed light on the extinction imposed by the dust structures and on the dust characteristics of the torus

Summary

INTRODUCTION

Under the context of the unified schemes for active galactic nuclei (AGN, Barthel, 1989; Urry and Padovani, 1995), the pc-scale torus structure is perpendicular to the radio jet axis. Various studies suggest that AGN have a lower dust-to-gas ratio than the Galactic standard value: AV /NH = 5.3 × 10−22 mag cm−2 (Bohlin et al, 1978; Maccacaro et al, 1982; Reichert et al, 1985; Maiolino et al, 2001) This result is interpreted as the circumnuclear region of the AGN is composed of large grains, because the small grains, responsible for absorbing the most of the optical radiation, are depleted or become large grains by a coagulation process. In this work we present the analysis of near-IR images to investigate the connection between the pc-scale torus structure and the kpc-scale dust lane This can potentially help us to inquire into the unified schemes. We used archived infrared spectrograph (IRS) Spitzer data of our sample, to shed light on the extinction imposed by the dust structures and on the dust characteristics of the torus

SAMPLE AND OBSERVATIONS

MODELING THE NEAR-IR HST IMAGES

Residual after Modeling Subtraction

IRS Spectra

CONCLUSIONS