11,551 research outputs found
Near-infrared spectroscopy of nearby Seyfert galaxies - II. Molecular content and coronal emission
We present sub-arcsec near-infrared 1.5 - 2.5 micron moderate resolution
long-slit spectra of eight nearby Seyfert galaxies (z<0.01), both parallel to
the ionization cone and perpendicular to it. These spectra complement similar
data on six Seyferts, presented in Reunanen, Kotilainen & Prieto (2002). Large
concentrations of molecular gas (H2) are present in the nucleus regardless of
the Seyfert type. The spatial extent of the H2 emission is larger perpendicular
to the cone than parallel to it in 6/8 (75 %) galaxies, in agreement with the
unified models of Active Galactic Nuclei. Broad BrGamma was detected in nearly
half of the optically classified Seyfert 2 galaxies, including two objects with
no evidence for hidden polarized Broad Line Region. Nuclear [FeII] emission is
generally blueshifted which together with high BrGamma/[FeII] ratios suggests
shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal
emission lines [SiVI] and [SiVII] are common in Seyferts, as they are detected
in ~60 % of the galaxies. In three galaxies the coronal lines are extended only
in the direction parallel to the cone. This could be explained by shock
excitation due to the jet or superwind interacting with the interstellar
medium.Comment: 19 pages, accepted for publication in MNRA
Low optical polarisation at the core of the optically-thin jet of M87
We study the optical linear and circular polarisation in the optically-thin
regime of the core and jet of M87. Observations were acquired two days before
the Event Horizon Telescope (EHT) campaign in early April 2017. A high degree
( per cent) of linear polarisation (P) is detected in the
bright jet knots resolved at to
(-) from the centre, whereas the nucleus and inner jet
show P per cent. The position angle of the linear
polarisation shifts by degrees from each knot to the adjacent ones,
with the core angle perpendicular to the first knot. The nucleus was in a low
level of activity (P- per cent), and no emission was
detected from HST-1. No circular polarisation was detected either in the
nucleus or the jet above a level of P per cent,
discarding the conversion of P into P. A disordered
magnetic field configuration or a mix of unresolved knots polarised along axes
with different orientations could explain the low P. The latter
implies a smaller size of the core knots, in line with current interferometric
observations. Polarimetry with EHT can probe this scenario in the future. A
steep increase of both P and P with increasing
frequency is expected for the optically-thin domain, above the turnover point.
This work describes the methodology to recover the four Stokes parameters using
a wave-plate polarimeter.Comment: Accepted for publication in MNRAS. 10 pages, 8 figure
The central parsecs of active galactic nuclei: challenges to the torus
Type 2 AGN are by definition nuclei in which the broad-line region and
continuum light are hidden at optical/UV wavelengths by dust. Via accurate
registration of infrared (IR) Very Large Telescope adaptive optics images with
optical \textit{Hubble Space Telescope} images we unambiguously identify the
precise location of the nucleus of a sample of nearby, type 2 AGN. Dust
extinction maps of the central few kpc of these galaxies are constructed from
optical-IR colour images, which allow tracing the dust morphology at scales of
few pc. In almost all cases, the IR nucleus is shifted by several tens of pc
from the optical peak and its location is behind a dust filament, prompting to
this being a major, if not the only, cause of the nucleus obscuration. These
nuclear dust lanes have extinctions mag, sufficient to at least
hide the low-luminosity AGN class, and in some cases are observed to connect
with kpc-scale dust structures, suggesting that these are the nuclear fueling
channels. A precise location of the ionised gas H and
[\textsc{Si\,vii}] 2.48 m coronal emission lines relative to those of the
IR nucleus and dust is determined. The H peak emission is often shifted
from the nucleus location and its sometimes conical morphology appears not to
be caused by a nuclear --torus-- collimation but to be strictly defined by the
morphology of the nuclear dust lanes. Conversely, [\textsc{Si\,vii}] 2.48
m emission, less subjected to dust extinction, reflects the truly, rather
isotropic, distribution of the ionised gas. All together, the precise location
of the dust, ionised gas and nucleus is found compelling enough to cast doubts
on the universality of the pc-scale torus and supports its vanishing in
low-luminosity AGN. Finally, we provide the most accurate position of the NGC
1068 nucleus, located at the South vertex of cloud B.Comment: 23 pages, 10 figures, accepted for publication in MNRA
Optical Surface Photometry of a Sample of Disk Galaxies. II Structural Components
This work presents the structural decomposition of a sample of 11 disk
galaxies, which span a range of different morphological types. The U, B, V, R,
and I photometric information given in Paper I (color and color-index images
and luminosity, ellipticity, and position-angle profiles) has been used to
decide what types of components form the galaxies before carrying out the
decomposition. We find and model such components as bulges, disks, bars, lenses
and rings.Comment: 14 figures. Accepted for publication in A&
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