J/A+A/625/A100 NGC 1068 SPHERE-VLT images (Rouan+, 2019)
Stellar cusp and warm dust at the heart of NGC 1068.
Rouan D., Grosset L., Gratadour D.
<Astron. Astrophys. 625, A100 (2019)>
=2019A&A...625A.100R 2019A&A...625A.100R (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, IR
Keywords: instrumentation: adaptive optics - galaxies: active - dust -
extinction - galaxies: Seyfert
Abstract:
Establishing precisely how stars and interstellar medium distribute
within the central 100 pc area around an AGN, down to the pc scale, is
key to understanding the late stages of transfer of matter onto the
accretion disc.
Using adaptive optics-assisted (SPHERE-VLT) near-IR images in the H
band, Ks band, and several narrow bands of the Seyfert 2 galaxy
NGC 1068, we analysed the radial distribution of brightness in the
central r<100pc area down to the pc scale. The median-averaged radial
profiles are fitted by a cusp (power law) plus a central point source.
A simple radiative transfer model is also used to interpret the data.
We find that the fit of radial brightness profiles beyond 10pc is done
quite precisely at Ks band by a cusp of exponent -2.0 plus a central
point source and by a cusp of exponent -1.2 at H. The difference of
exponents between H band and Ks band can be explained by differential
extinction, provided that the distribution of dust is itself cuspy,
with an exponent -1.0. However, the derived stellar density is found
to follow a r-4 cusp, which is much steeper than any other cusp,
either theoretically predicted around a massive black hole, or
observed in the centre of early- and late-type galaxies or in mergers.
Introducing a segregation in the stellar population with a central
excess of giant stars leads to a somewhat less steep exponent;
however, the de-reddened luminosity of the stellar cusp, as well as
the mass of dust and gas all appear much too high to be realistic. An
alternative scenario, where the Ks-band profile is well fitted by a
combination of radiation from a stellar cusp identical to the H-band
profile and thermal emission ofwarm/hot dust heated by the central
engine appears much more satisfactory. NGC 1068 is shown to satisfy a
relationship between half-light radius, cusp luminosity, and exponent
that we established using a sample of luminous infrared galaxies
(LIRGs) and ultraluminous infrared galaxies ULIRGs. This suggests that
the cusp is the remnant of a recent starburst. We identify the central
point-like source with the very hot dust at the internal wall of the
putative torus and derive an intrinsic luminosity that requires a
central extinction AK∼8, a value consistent with predictions by
several torus models.
The overall picture revealed by this study is closely consistent with
the scheme of a central rather steep stellar cusp, embedded in a
diluted medium of warm dust, while a compact and dense structure
identified with the putative torus is required to interpret a highly
reddened point-like central source of very hot dust.
Description:
Adaptive optics-assisted near-IR images in the H band, Ks band,
obtained with SPHERE-VLT. They are presented after application of
standard reduction.
Objects:
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RA (2000) DE Designation(s)
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02 42 40.77 -00 00 47.8 NGC 1068 = M 77
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 80 2 List of fits images
fits/* . 2 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 25 F6.4 arcsec/pix scale Scale of the image
27- 29 I3 --- Nx Number of pixels along X-axis
31- 33 I3 --- Ny Number of pixels along Y-axis
35- 38 I4 Kibyte size Size of FITS file
40- 55 A16 --- FileName Name of FITS file, in subdirectory fits
57- 80 A24 --- Title Title of the FITS file
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Acknowledgements:
Daniel Rouan, daniel.rouan(at)obspm.fr
(End) Daniel Rouan [Obs. de Paris, France], Patricia Vannier [CDS] 24-Apr-2019