Bibcode
González-Martín, O.; Hernández-García, L.; Masegosa, J.; Márquez, I.; Rodríguez-Espinosa, J. M.; Acosta-Pulido, J. A.; Alonso-Herrero, A.; Dultzin, D.; Esparza Arredondo, D.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 587, id.A1, 8 pp.
Fecha de publicación:
3
2016
Revista
Número de citas
5
Número de citas referidas
5
Descripción
Context. Obscured active galactic nuclei (AGNs) are thought to be very
common in the Universe. Observations and surveys have shown that the
number of sources increases for near galaxies and at the low-luminosity
regime (the so-called LLAGNs). Furthermore, many AGNs show changes in
their obscuration properties at X-rays that may suggest a configuration
of clouds very close to the accretion disk. However, these variations
could also be due to changes in the intrinsic continuum of the source.
It is therefore important to study nearby AGN to better understand the
locus and distribution of clouds in the neighbourhood of the nucleus.
Aims: We aim to study the nuclear obscuration of LLAGN NGC 835
and its extended emission using mid-infrared observations.
Methods: We present sub-arcsecond-resolution mid-infrared 11.5 μm
imaging of the LLAGN galaxy NGC 835 obtained with the instrument
CanariCam in the Gran Telescopio CANARIAS (GTC), archival Spitzer/IRS
spectroscopy, and archival Chandra data observed in 2000, 2008, and
2013. Results: The GTC/CanariCam 11.5 μm image reveals faint
extended emission out to ~6 arcsec. We obtained a nuclear flux of F(11.5
μm) ~ 18 mJy, whereas the extended emission accounts for 90% of the
total flux within the 6 arcsec. This means that the low angular
resolution (~4 arcsec) IRS spectrum is dominated by this extended
emission and not by the AGN. This is clearly seen in the Spitzer/IRS
spectrum, which resembles that of star-forming galaxies. Although the
extended soft X-ray emission shows some resemblance with that of the
mid-infrared, the knots seen at X-rays are mostly located in the inner
side of this mid-infrared emission. The nuclear X-ray spectrum of the
source has undergone a spectral change between 2000/2008 and 2013. We
argue that this variation is most probably due to changes in the
hydrogen column density from ~8 × 1023 cm-2
to ~3 × 1023 cm-2. NGC 835 therefore is one
of the few LLAGN, together with NGC 1052, in which changes in the
absorber can be claimed.
FITS file for the 11.5 microns CanariCam/GTC image is only available at
the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A1