Near-infrared dust and line emission from the central region of Mrk1066: constraints from Gemini NIFS

Abstract

We present integral field spectroscopy of the inner 700 × 700pc² of the Seyfert galaxy Mrk1066 obtained with Gemini's Near-Infrared Integral Field Spectrograph (NIFS) at a spatial resolution of ~35pc. This high spatial resolution allowed us to observe, for the first time in this galaxy, an unresolved dust concentration with mass ~1.4 × 10^-2M_solar. This unresolved concentration, with emission well reproduced by a blackbody with temperature ~830K, is possibly part of the nuclear dusty torus. We compared maps of emission-line flux distributions and ratios with a 3.6cm radio-continuum image and [OIII] image in order to investigate the origin of the near-infrared emission. The emission-line fluxes are elongated in PA = 135°/315° in agreement with the [OIII] and radio images and, except for the H lines, are brighter to the north-west than to the south-east. This close association with the radio hot spot implies that at least part of the emitting gas is co-spatial with the radio outflow. The H emission is stronger to the south-east, where we find a large region of star-formation. The strong correlation between the radio emission and the highest emission-line fluxes indicates that the radio jet plays a fundamental role at these intensity levels. At lower emission-line fluxes this correlation disappears suggesting a contribution from the plane of the galaxy to the observed emission. The H₂ flux is more uniformly distributed and has an excitation temperature of ~2100K. Its origin appears to be circum-nuclear gas heated by X-rays from the central active nucleus. The [FeII] emission also is consistent with X-ray heating, but its spatial correlation with the radio jet and [OIII] emission indicates additional emission due to excitation and/or abundance changes caused by shocks in the radio jet. The coronal-line emission of [CaVIII] and [SIX] is unresolved by our observations indicating a distribution within 18pc from the nucleus. The reddening map obtained via the Paβ/Brγ line ratio ranges from E(B - V) ~ 0 to 1.7 with the highest values defining a S-shaped structure along PA ~ 135°/315°. The emission-line ratios are Seyfert-like within the ionization cone indicating that the line emission is powered by the central active nucleus in these locations. Low ionization regions are observed away from the ionization cone, and may be powered by the diffuse radiation field which filters through the ionization cone walls. Two regions at 0.5arcsec south-east and at 1arcsec north-west of the nucleus show starburst-like line ratios, co-spatial with an enhancement in the emission of the H lines. We attribute this change to additional emission from star-forming regions. The mass of ionized gas is M_HII ~ 1.7 × 10⁷M_solar and that of hot molecular gas is .