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

Pierre Vermot, Yann Clénet, Damien Gratadour

Published 2019-05-22Version 1

Aims : In this paper we aim at characterizing the properties of stars, dust and gas and their spatial distribution in the central region of the Seyfert 2 galaxy NGC1068. Method : Our study is based on NIR (YJH, 0.95-1.650 um, R=350) long slit spectroscopy observations of NGC 1068's central region with 0.4" spatial resolution. On the one hand we decomposed the observed continuum emission into three components: hot dust, stars and scattered light from the central engine to measure their contributions at various distances from the nucleus. On the other hand, we measured fluxes and doppler shifts for the emission lines present in our spectrum to probe the physical conditions of the Narrow Line Region. Results : Dust and stars are the main contributors to the continuum, but scattered light from the central engine is also detected in the very central region. Together, those three components are well reproducing the observed continuum. The dust emission is well modeled by a 800K blackbody, is spatially unresolved and only located in the very central region. The stellar content is ubiquitous and harbours a 250 pc cusp centered around the nucleus, overimposed to a young stellar background. The spectrum of the cusp is consistent with a 120 Myr single stellar population. Finally, the emission lines exhibit a significant doppler shift, consistent with a radial outflow from the nucleus in a biconical structure. The $\left[Fe\ II\right]$ behaviour strongly differs from other lines, suggesting that it arises from a different structure.