210 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
Near-IR dust and line emission from the central region of Mrk1066: Constraints from Gemini NIFS
We present integral field spectroscopy of the inner 350 pc of the Mrk1066
obtained with Gemini NIFS at a spatial resolution of 35 pc. This high spatial
resolution allowed us to observe, for the first time in this galaxy, an
unresolved dust concentration with mass 0.014 M_Sun, which may be part of the
dusty torus. The emission-line fluxes are elongated in PA=135/315deg in
agreement with the [OIII] and radio images and, except for the H lines, are
brighter to the north-west than to the south-east. The H emission is stronger
to the south-east, where we find a large region of star-formation. The strong
correlation between the radio emission and the highest emission-line fluxes
indicates that the radio jet plays a fundamental role at these intensity
levels. The H2 flux is more uniformly distributed and has an excitation
temperature of 2100 K. Its origin appears to be circumnuclear gas heated by
X-rays from the AGN. The [FeII] emission also is consistent with X-ray heating,
but with additional emission due to excitation by shocks in the radio jet. The
coronal-line emission of [CaVIII] and [SIX] are unresolved by our observations
indicating a distribution within 18pc from the nucleus. The reddening ranges
from E(B-V) ~ 0 to E(B-V) ~ 1.7 with the highest values defining a S-shaped
structure along PA ~ 135/315deg. The emission-line ratios are Seyfert-like
within the ionization cone indicating that the line emission is powered by the
central active nucleus in these locations. Low ionization regions are observed
away from the ionization cone, and may be powered by the diffuse radiation
field which filters through the ionization cone walls. Two regions at 0.5
arcsec south-east and at 1 arcsec north-west of the nucleus show starburst-like
line ratios, attributed to additional emission from star forming regions.Comment: 14 pages, 10 figures, accepted for publication in MNRA
Molecular Hydrogen and [FeII] in Active Galactic Nuclei
(Abridge) Near-infrared spectroscopy is used to study the kinematics and
excitation mechanisms of the H2 and [FeII] gas in a sample of AGN. The H2 lines
are unresolved in all objects in which they were detected while the [FeII]
lines have widths implying gas velocities of up to 650 km/s. This suggests
that, very likely, the H2 and [FeII] emission does not originate from the same
parcel of gas. Molecular H2 were detected in 90% of the sample, including PG
objects, indicating detectavel amounts of molecular material even in objects
with low levels of circumnuclear starburst activity. The data favors thermal
excitation for the H2 lines. Indeed, in NGC3227, Mrk766, NGC4051 and NGC4151,
the molecular emission is found to be purely thermal. This result is also
confirmed by the rather similar vibrational and rotational temperatures in the
objects for which they were derived. [FeII] lines are detected in all of the
AGN. The [FeII] 1.254mu/Pa-beta ratio is compatible with excitation of the
[FeII] by the active nucleus, but in Mrk 766 it implies a stellar origin. A
correlation between H2/Br-gamma and [FeII]/Pa-beta is found. We confirm that it
is a useful diagnostic tool in the NIR to separate emitting line objects by
their level of nuclear activity. X-ray excitation models are able to explain
the observed H2 and part of the [FeII] emission. Most likely, a combination of
X-ray heating, shocks driven by the radio jet, and circumnuclear star formation
contributes, in different proportions, to the H2 and [FeII] emission. In most
of our spectra, the [FeII] 1.257mu/1.644mu ratio is found to be 30% lower than
the intrinsic value based on current atomic data. This implies either than the
extinction towards the [FeII] emitting clouds is very similar in most objects
or there are possible inaccuracies in the A-values in the [FeII] transitions.Comment: 18 pages, 6 figures, Accepted for publication in Astronomy &
Astrophysic
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
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