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.
Highlights
The spiral galaxy NGC 1068 ((R)SA(rs)b) has frequently been observed 70 pc arcsec−1)because and high olfumitisnopsritoyxi(mseitvyera(Dl A10=111L4.4Mpc ⇔ according to Pier et al 1994)
This large contribution is in good agreement with previous findings such as reported by Origlia et al (1993), who concluded from absorption features that stellar light accounts for ∼70% of the flux in the H band in the 4.4 × 4.4 central region, by Storchi-Bergmann et al (2012), who concluded from spectral synthesis in H and K bands that the stellar population dominates the spectrum in the inner 180 pc – 2, or most recently, by Rouan et al (2019), who revealed a young stellar cusp in the most central region of NGC 1068 based on high angular resolution imaging with SPHERE
In order to understand the physical processes that occur in the central region of NGC 1068, we performed a long-slit spectroscopy analysis of the nucleus in Y JH bands (0.95−1.65 μm) at sub-arcsecond angular resolution (0.35 )
Summary
The spiral galaxy NGC 1068 ((R)SA(rs)b) has frequently been observed 70 pc arcsec−1). Even if these four components (CE, dust, NLR and stars) in the nucleus of NGC 1068 are clearly confirmed, many questions remain, for instance, about their spatial distribution, their relative contribution to the flux at different wavelengths, the physical characteristics of this region (dust temperature, gas kinematics, and ionisation mechanisms), and about the age of the stellar population. Changing the stellar population for a younger one can slightly improve the quality of the fit, but our best explanation (presented in Fig. 8) is that the background is largely dominated by very hot stars, with a little contribution from hot dust Such stars in Y JH can be modelled by a blackbody in a Rayleigh-Jeans regime (valid for T > 12 000 K) and provide a good fit to our data.
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