6 research outputs found
A search for spectral features in the XMM-Newton observation of UGC11763
This is an electronic version of an article published in Revista Mexicana de AstronomĂa y AstrofĂsica. Cardaci, M.V. et al. A search for spectral features in the XMM-Newton observation of UGC11763. Revista Mexicana de AstronomĂa y AstrofĂsica 32 (2008): 13
Long-term IR Photometry of Seyferts
Long-term (up to 10000d) monitoring has been undertaken for 41 Seyferts in
the near-IR (JHKL). All but 2 showed variability, with K ampl in the range <0.1
to > 1.1 mags. The timescale for detectable change is from about one week to a
few years. A simple cross-correlation study shows evidence for delays of up to
several hundred days between the variations seen at the shortest wavelengths
and the longest in many galaxies. In particular, the data for F9 now extend to
twice the interval covered earlier and the delay between its UV and IR outputs
persists. An analysis of the fluxes shows that, for any given galaxy, the
colours of the variable component are usually independent of the level of
activity. The state of activity can be parameterized. Taken over the whole
sample, the colours of the variable components fall within moderately narrowly
defined ranges. In particular, the H-K colour is appropriate to a black body of
temperature 1600K. The H-K excess for a heavily reddened nucleus can be
determined and used to find E_{B-V}, which can be compared to the values found
from the visible region broad line fluxes. Using flux-flux diagrams, the flux
within the aperture from the underlying galaxy can often be determined without
the need for model surface brightness profiles. In many galaxies it is apparent
that here must be an additional constant contribution from warm dust.Comment: Better quality available from ftp://ftp.saao.ac.za/pub/isg/seyf.pd
The Dusty Nuclear Torus in NGC 4151: Constraints from Gemini Near-Infrared Integral Field Spectrograph Observations
We have used a near-infrared nuclear spectrum (covering the Z, J, H and K
bands) of the nucleus of NGC 4151 obtained with the Gemini Near-infrared
Integral Field Spectrograph (NIFS) and adaptive optics, to isolate and
constrain the properties of a near-IR unresolved nuclear source whose spectral
signature is clearly present in our data. The near-IR spectrum was combined
with an optical spectrum obtained with the Space Telescope Imaging Spectrograph
which was used to constrain the contribution of a power-law component. After
subtraction of the power-law component, the near-IR continuum is well fitted by
a blackbody function, with K, which dominates the nuclear
spectrum -- within an aperture of radius 0\farcs3 -- in the near-IR. We
attribute the blackbody component to emission by a dusty structure, with hot
dust mass , not resolved
by our observations, which provide only an upper limit for its distance from
the nucleus of 4 pc. If the reddening derived for the narrow-line region also
applies to the near-IR source, we obtain a temperature K and a
mass for the hot dust.
This structure may be the inner wall of the dusty torus postulated by the
Unified Model or the inner part of a dusty wind originating in the accretion
disk.Comment: 5 pages, 1 figure; ApJ, 698, 176
The continuum and narrow line region of the NLS1 galaxy Mrk 766
We present the first spectroscopic observations in the interval 0.8-4.0
microns, complemented with HST/UV and optical spectroscopy, of the narrow line
Seyfert 1 galaxy Mrk766. The NIR spectrum is characterized by permitted lines
of HI, HeI, HeII and FeII, and forbidden lines of [SII], [SIII] and [FeII]
among others. High ionized species such as [SiIX], [SiX], [SIX] and [MgVII] are
also observed. The continuum has a complex shape, with contribution of the
central engine, circumnuclear stellar population and dust. This last component
is evidenced by the presence of an excess of emission peaking at 2.25 microns,
fitted by blackbody function with T_bb=1200K. That temperature is close to the
evaporation temperature of graphite grains. As such, it provides strong
evidence of hot dust, probably very close to the nucleus. Consistent modeling
of the line and broad band continuum spectrum by composite models, which
account for the photoionizing flux of the central engine and shocks, shows that
the shock velocities are between 100 and 500 km/s, the preshock densities
between 100 and 1000 cm^-3 and the radiation fluxes from the active centre
between 10^9 and 5x10^12 photons cm^-2 s^-1 eV^-1 at 1 Ryd with spectral
indices =-1.5 and =-0.4. Adopting silicon grains,
dust-to-gas ratios are between 10^-{6} and 4x10 by mass. The emitting
clouds are at an average distance of 160 pc from the centre, with high velocity
clouds closer and low velocity clouds farther from the centre. The N/H relative
abundance could be twice solar. In constrast, Fe is depleted from the gaseous
phase by a factor >2. Ratios of calculated to observed line ratios to Hbeta
indicate an average contribution of the broad line region to the observed Hbeta
of about 40%.Comment: 15 pages, 6 figures. Accepted to MNRA
AGN-Starburst connection in NGC7582: Gemini near-infrared spectrograph integral field unit observations
We analyse two-dimensional near-IR K-band spectra from the inner 660x315 pc^2
of the Seyfert galaxy NGC7582 obtained with the Gemini GNIRS IFU. The nucleus
harbors an unresolved source well reproduced by a blackbody of temperature T
1050 K, which we attribute to emission by circumnuclear dust located closer
than 25 pc from the nucleus, with total mass of ~3x10^{-3}M_Sun. Surrounding
the nucleus, we observe a ring of active star formation with radius of ~190 pc,
an age of ~5 Myr. The radiation of the young stars in the ring accounts for at
least 80 % of the ionization observed in the Brgamma emitting gas, the
remaining being due to radiation emitted by the active nucleus. The stellar
kinematics reveals: (1) a distorted rotation pattern in the radial velocity
field with kinematic center apparently displaced from the nuclear source by a
few tens of parsecs; (2) a high velocity dispersion in the bulge of sigma=170
km/s; (3) a partial ring of sigma=50 km/s interpreted as due to stars formed
from cold gas in a previous burst of star formation. The kinematics of the
ionized gas shows an additional blueshifted component with velocities > 100
km/s interpreted as due to an outflow along the ionization cone. The mass
outflow rate in the ionized gas was estimated as ~0.05 M_Sun/yr, which is one
order of magnitude larger than the accretion rate to the AGN. The flux
distribution and kinematics of the hot molecular gas, traced by the H2l2.22um
emission line, suggests that most of this gas is in the galactic plane. An
excess blueshift along PA~-70 can be interpreted as an inflow towards the
nucleus. An AGN-Starburst connection in the nucleus of NGC7582 is supported by
the ratio between the mass accretion rate and the star formation rate in the
circumnuclear region of ~0.26%, which is close to the Magorrian relation.Comment: 16 pages, 11 figures, accepted for publication in MNRA