New insights on the central stellar population and gas outflow in NGC 1068 from YJH spectroscopy with SPHERE/VLT

LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 Place Jules Janssen, 92195 Meudon, France
e-mail: pierre.vermot@obspm.fr

Received: 17 April 2019
Accepted: 14 July 2019

Abstract

Aims. We characterise the properties of stars, dust, and gas and their spatial distribution in the central region of the Seyfert 2 galaxy NGC 1068.

Method. Our study is based on near-infrared (YJH, 0.95−1.650 μm, R = 350) long-slit spectroscopy observations of the central region of NGC 1068 with a 0.4″ spatial resolution. We decomposed the observed continuum emission into three components: hot dust, stars, and scattered light from the central engine. We measured their contributions at various distances from the nucleus. We also measured fluxes and Doppler shifts for the emission lines in our spectrum to probe the physical conditions of the narrow line region.

Results. Dust and stars are the main sources of continuum emission, but scattered light from the central engine has also been detected in the very central region. Together, these three components reproduce the observed continuum well. The dust emission is compatible with a 830 K blackbody. It has only been detected in the very central region and is not spatially resolved. The stellar content is ubiquitous. It harbours a 250 pc cusp centred around the nucleus, over-imposed on a young stellar background. The spectrum of the cusp is consistent with a 120 Myr old single stellar population. Finally, the emission lines exhibit a significant Doppler shift that is consistent with a radial outflow from the nucleus in a biconical structure. The [Fe II] behaviour strongly differs from other lines, indicating that it arises from a different structure.