168 research outputs found
The Narrow Line Region of Ark 564
The continuum and emission-line spectrum of the narrow-line Seyfert 1 galaxy
Ark 564 is used to investigate, for the first time, the physical conditions and
structure of its narrow line region (NLR). For this purpose, composite models,
accounting for the coupled effect of photoionization and shocks, are employed.
The emission-line spectrum of Ark 564, which ranges from the ultraviolet to the
near-infrared, shows a rich forbidden line spectrum. Strong emphasis is given
to the study of the coronal line region. The diversity of physical conditions
deduced from the observations requires multi-cloud models to reproduce the
observed lines and continuum. We find that a combination of high velocity (Vs =
1500 km/s) shock-dominated clouds as well as low velocity (Vs = 150 km/s)
radiation-dominated clouds explains the coronal lines, while the optical
low-ionization lines are mainly explained by shock-dominated clouds. The
results for Ark 564 are compared with those obtained for other Seyfert galaxies
previously analyzed such as NGC 5252, Circinus, NGC 4051 and NGC 4151. The
model results for the ultraviolet and optical permitted lines suggest that the
broad line region may contribute up to 80%, depending on the emission-line,
being of about 30% for Hbeta. The consistency of the multi-cloud model is
checked by comparing the predicted and observed continuum, from radio to X-ray,
and indicate that the dust-to-gas ratio in the clouds varies from 10^{-15} to
10^{-12}.Comment: 18 pages, 1 figure. Accepted in A&
Probing the Circumnuclear Stellar Populations of Starburst Galaxies in the Near-infrared
We employ the NASA Infrared Telescope Facility's near-infrared spectrograph
SpeX at 0.8-2.4m to investigate the spatial distribution of the stellar
populations (SPs) in four well known Starburst galaxies: NGC34, NGC1614,
NGC3310 and NGC7714. We use the STARLIGHT code updated with the synthetic
simple stellar populations models computed by Maraston (2005, M05). Our main
results are that the NIR light in the nuclear surroundings of the galaxies is
dominated by young/intermediate age SPs (yr), summing from
40\% up to 100\% of the light contribution. In the nuclear aperture of
two sources (NGC1614 and NGC3310) we detected a predominant old SP component
(yr), while for NGC34 and NGC7714 the younger component
prevails. Furthermore, we found evidence of a circumnuclear star formation
ring-like structure and a secondary nucleus in NGC1614, in agreement with
previous studies. We also suggest that the merger/interaction experienced by
three of the galaxies studied, NGC1614, NGC3310 and NGC7714 can explain the
lower metallicity values derived for the young SP component of these sources.
In this scenario the fresh unprocessed metal poorer gas from the
destroyed/interacting companion galaxy is driven to the centre of the galaxies
and mixed with the central region gas, before star formation takes place. In
order to deepen our analysis, we performed the same procedure of SP synthesis
using Maraston (2011, M11) EPS models. Our results show that the newer and
higher resolution M11 models tend to enhance the old/intermediate age SP
contribution over the younger ages
A Near-Infrared Template Derived from I Zw 1 for the FeII Emission in Active Galaxies
In AGN spectra, a series of FeII multiplets form a pseudo-continuum that
extends from the ultraviolet to the near-infrared (NIR). This emission is
believed to originate in the Broad Line Region (BLR), and it has been known for
a long time that pure photoionization fails to reproduce it in the most extreme
cases, as does the collisional-excitation alone. The most recent models by
Sigut & Pradhan (2003) include details of the FeII ion microphysics and cover a
wide range in ionization parameter log U_ion= (-3.0 -> -1.3) and density log
n_H = (9.6 -> 12.6). With the aid of such models and a spectral synthesis
approach, we study for the first time in detail the NIR emission of I Zw 1. The
main goals are to confirm the role played by Ly\alpha-fluorescence mechanisms
in the production of the FeII spectrum and to construct the first
semi-empirical NIR FeII template that best represents this emission and can be
used to subtract it in other sources. A good overall match between the observed
FeII+MgII features with those predicted by the best fitted model is obtained,
corroborating the Ly\alpha-fluorescence as a key process to understand the FeII
spectrum. The best model is then adjusted by applying a deconvolution method on
the observed FeII+MgII spectrum. The derived semi-empirical template is then
fitted to the spectrum of Ark 564, suitably reproducing its observed FeII+MgII
emission. Our approach extends the current set of available FeII templates into
the NIR region.Comment: 47 pages, 5 tables, 12 figures. Accepted for publication in The
Astrophysical Journa
A 0.8-2.4 microns spectral atlas of Active Galactic Nuclei
Aims: We present a near-infrared spectral atlas of 47 active galactic nuclei
(AGN), of all degrees of activity, in the wavelength interval of 0.8-2.4
microns, including the fluxes of the observed emission lines. We analyze the
spectroscopic properties of the continuum and emission line spectra of the
sources Methods: In order to exclude aperture and seeing effects we use
near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8-2.4
microns), taking the JHK-bands spectra simultaneously. Results: We present the
most extensive NIR spectral atlas of AGN to date. This atlas offers a suitable
database for studying the continuum and line emission properties of these
objects in a region full of interesting features. The shape of the continuum of
QSOs and Seyfert 1's are similar, being essentially flat in H and K band, in
the J band, a strong variation is found. In Seyfert 2 galaxies, the continuum
in the F_lambda X lambda space smoothly decreases from 1.2 microns redwards in
almost all sources. In J, it smoothly rises bluewards in some sources while in
others a small decreased in flux is observed. The spectra are dominated by
strong emission features of H I, He I, He II, [S III] and conspicuous forbidden
lines of low and high ionization species. Molecular lines of H2 are common
features to most objects. The absence of O I and Fe II lines in Seyfert 2
galaxies give observational support to the fact that these lines are formated
in the outermost portion of the broad line region. [P II] and coronal lines are
detected in all degrees of activity. The [Fe II] 12570A/16436A line ratio
becomes a reliable reddening indicator for the narrow-line region of Seyfert
galaxies.Comment: 39 pages, 17 figures, accepted for publication in Astronomy and
Astrophysics (15/05/2006
The first detection of near-infrared CN bands in active galactic nuclei: signature of star formation
We present the first detection of the near-infrared CN absorption band in the
nuclear spectra of active galactic nuclei (AGN). This feature is a recent star
formation tracer, being particularly strong in carbon stars. The equivalent
width of the CN line correlates with that of the CO at 2.3 microns, as expected
in stellar populations (SP) with ages between ~ 0.2 and ~ 2 Gyr. The presence
of the 1.1 microns CN band in the spectra of the sources is taken as an
unambiguous evidence of the presence of young/intermediate SP close to the
central source of the AGN. Near-infrared bands can be powerful age indicators
for star formation connected to AGN, the understanding of which is crucial in
the context of galaxy formation and AGN feedback.Comment: Accepted for publication in The Astrophysical Journal Letters. 4
pages, 3 figure
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
Multi-wavelength properties of the high-energy bright Seyfert 1 galaxy IGR J18027-1455
A new sample of hard X-ray sources in the Galactic Plane is being revealed by
the regular observations performed by the INTEGRAL satellite. The full
characterization of these sources is mandatory to understand the hard X-ray
sky. Here we report new multifrequency radio, infrared and optical observations
of the source IGR J18027-1455, as well as a multi-wavelength study from radio
to hard X-rays. The radio counterpart of IGR J18027-1455 is not resolved at any
observing frequency. The radio flux density is well fitted by a simple power
law with a spectral index alpha=-0.75+/-0.02. This value is typical of
optically thin non-thermal synchrotron emission originated in a jet. The NIR
and optical spectra show redshifted emission lines with z=0.034, and a broad
Halpha line profile with FWHM ~3400 km/s. This suggests an Active Galactic
Nucleus (AGN) of type 1 as the optical counterpart of IGR J18027-1455. We
confirm the Seyfert 1 nature of the source, which is intrinsically bright at
high energies both in absolute terms and when scaled to a normalized 6 cm
luminosity. Finally, comparing its X-ray luminosity with isotropic indicators,
we find that the source is Compton thin and AGN dominated. This indicates that
INTEGRAL might have just seen the tip of the iceberg, and several tens of such
sources should be unveiled during the course of its lifetime.Comment: 6 pages, 6 figures. Accepted for publication in A&A. Minor changes
according to referee repor
Optical/NIR stellar absorption and emission-line indices from luminous infrared galaxies
We analyze a set of optical-to-near-infrared long-slit nuclear spectra of 16
infrared-luminous spiral galaxies. All of the studied sources present H
emission, which reflects the star-forming nature of our sample, and they
clearly display H I emission lines in the optical. Their continua contain many
strong stellar absorption lines, with the most common features due to Ca I, Ca
II, Fe I, Na I, Mg I, in addition to prominent absorption bands of TiO, VO,
ZrO, CN and CO. We report a homogeneous set of equivalent width (EW)
measurements for 45 indices, from optical to NIR species for the 16
star-forming galaxies as well as for 19 early type galaxies where we collected
the data from the literature. This selected set of emission and
absorption-feature measurements can be used to test predictions of the
forthcoming generations of stellar population models. We find correlations
among the different absorption features and propose here correlations between
optical and NIR indices, as well as among different NIR indices, and compare
them with model predictions. While for the optical absorption features the
models consistently agree with the observations,the NIR indices are much harder
to interpret. For early-type spirals the measurements agree roughly with the
models, while for star-forming objects they fail to predict the strengths of
these indices.Comment: accepted for publication in MNRA
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