353 research outputs found
Outflows, Inflows and Young Stars in the inner 200 pc of the Seyfert galaxy NGC 2110
We present a two-dimensional mapping of stellar population age components,
emission-line fluxes, gas excitation and kinematics within the inner
pc of the Seyfert 2 galaxy NGC 2110. We used the Gemini North Integral Field
Spectrograph (NIFS) in the J and K bands at a spatial resolution of
pc. The unresolved nuclear continuum is originated in combined contributions of
young stellar population (SP; age Myr), a featureless AGN continuum
and hot dust emission. The young-intermediate SP (age Myr) is
distributed in a ring-shaped structure at pc from the nucleus,
which is roughly coincident with the lowest values of the stellar velocity
dispersion. In the inner pc the old SP (age Gyr) is dominant.
The [FeII]1.25m emission-line flux distribution is correlated with the
radio emission and its kinematics comprise two components, one from gas
rotating in the galaxy plane and another from gas in outflow within a bicone
oriented along north-south. These outflows seem to originate in the interaction
of the radio jet with the ambient gas producing shocks that are the main
excitation mechanism of the [FeII] emission. We estimate: (1) an ionized gas
mass outflow rate of M/yr at 70 pc from the nucleus;
and (2) a kinetic power for the outflow of only 0.05% of the AGN bolometric
luminosity implying weak feedback effect on the galaxy.Comment: Accepted for publication in MNRA
Disentangling the near infrared continuum spectral components of the inner 500 pc of Mrk 573: two-dimensional maps
We present a near infrared study of the spectral components of the continuum
in the inner 500500 pc of the nearby Seyfert galaxy Mrk573 using
adaptive optics near-infrared integral field spectroscopy with the instrument
NIFS of the Gemini North Telescope at a spatial resolution of 50 pc. We
performed spectral synthesis using the {\sc starlight} code and constructed
maps for the contributions of different age components of the stellar
population: young ( Myr), young-intermediate (
Myr), intermediate-old ( Myr Gyr) to the
near-IR K-band continuum, as well as their contribution to the total stellar
mass. We found that the old stellar population is dominant within the inner 250
pc, while the intermediate age components dominate the continuum at larger
distances. A young stellar component contributes up to 20% within the
inner 70 pc, while hot dust emission and featureless continuum components
are also necessary to fit the nuclear spectrum, contributing up to 20% of the
K-band flux there. The radial distribution of the different age components in
the inner kiloparsec of Mrk573 is similar to those obtained by our group for
the Seyfert galaxies Mrk1066, Mrk1157 and NGC1068 in previous works using a
similar methodology. Young stellar populations (100 Myr) are seen in the
inner 200-300 pc for all galaxies contributing with 20% of the K-band
flux, while the near-IR continuum is dominated by the contribution of
intermediate-age stars (100 Myr-2 Gyr) at larger distances. Older stellar
populations dominate in the inner 250 pc
Polycyclic Aromatic Hydrocarbon in the Central Region of the Seyfert 2 Galaxy NGC1808
We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC
1808, obtained with the Gemini's Thermal-Region Camera Spectrograph (T-ReCS) at
a spatial resolution of 26 pc. The high spatial resolution allowed us to detect
bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and
11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the
nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2
S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar
to Peeters's A class, with the line peak shifted towards the blue. The
differences in the PAH line profiles also suggests that the molecules in the
region located 26 pc NE of the nucleus are more in the neutral than in the
ionised state, while at 26 pc SW of the nucleus, the molecules are mainly in
ionised state. After removal of the underlying galaxy contribution, the nuclear
spectrum can be represented by a Nenkova's clumpy torus model, indicating that
the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud
distribution of sigma = 70degree, observer's view angle i = 90degree, and an
outer radius of R0 = 0.55 pc. The derived column density along the line of
sight is NH = 1.5 x 10^24 cm-2, which is sufficient to block the hard radiation
from the active nucleus, and would explain the presence of PAH molecules near
to the NGC 1808's active nucleus.Comment: Accepted by MNRAS 2012 December
2D mapping of young stars in the inner 180 pc of NGC 1068: correlation with molecular gas ring and stellar kinematics
We report the first two-dimensional mapping of the stellar population and
non-stellar continua within the inner 180 pc (radius) of NGC 1068 at a spatial
resolution of 8 pc, using integral field spectroscopy in the near-infrared. We
have applied the technique of spectral synthesis to data obtained with the
instrument NIFS and the adaptive optics module ALTAIR at the Gemini North
Telescope. Two episodes of recent star formation are found to dominate the
stellar population contribution: the first occurred 300 Myr ago, extending over
most of the nuclear region; the second occurred just 30 Myr ago, in a ring-like
structure at ~100 pc from the nucleus, where it is coincident with an expanding
ring of H2 emission. Inside the ring, where a decrease in the stellar velocity
dispersion is observed, the stellar population is dominated by the 300 Myr age
component. In the inner 35 pc, the oldest age component (age > 2Gyr) dominates
the mass, while the flux is dominated by black-body components with
temperatures in the range 700 < T < 800 K which we attribute to the dusty
torus. We also find some contribution from black-body and power-law components
beyond the nucleus which we attribute to dust emission and scattered light.Comment: Accepted for publication in Ap
Gemini NIFS survey of feeding and feedback processes in nearby Active Galaxies: I - Stellar kinematics
We use the Gemini Near-Infrared Integral Field Spectrograph (NIFS) to map the
stellar kinematics of the inner few hundred parsecs of a sample of 16 nearby
Seyfert galaxies, at a spatial resolution of tens of parsecs and spectral
resolution of 40 km/s. We find that the line-of-sight (LOS) velocity fields for
most galaxies are well reproduced by rotating disk models. The kinematic
position angle (PA) derived for the LOS velocity field is consistent with the
large scale photometric PA. The residual velocities are correlated with the
hard X-ray luminosity, suggesting that more luminous AGN have a larger impact
in the surrounding stellar dynamics. The central velocity dispersion values are
usually higher than the rotation velocity amplitude, what we attribute to the
strong contribution of bulge kinematics in these inner regions. For 50% of the
galaxies, we find an inverse correlation between the velocities and the
Gauss-Hermitte moment, implying red wings in the blueshifted side and blue
wings in the redshifted side of the velocity field, attributed to the movement
of the bulge stars lagging the rotation. Two of the 16 galaxies (NGC 5899 and
Mrk 1066) show an S-shape zero velocity line, attributed to the gravitational
potential of a nuclear bar. Velocity dispersion maps show rings of low-
values (50-80 km/s) for 4 objects and "patches" of low-sigma for 6 galaxies at
150-250 pc from the nucleus, attributed to young/ intermediate age stellar
populations.Comment: To be published in MNRA
High Spatial Resolution of the Mid-Infrared Emission of Compton-Thick Seyfert 2 Galaxy Mrk3
Mid-infrared (MIR) spectra observed with Gemini/Michelle were used to study
the nuclear region of the Compton-thick Seyfert 2 (Sy 2) galaxy Mrk 3 at a
spatial resolution of 200 pc. No polycyclic aromatic hydrocarbons (PAHs)
emission bands were detected in the N-band spectrum of Mrk 3. However, intense
[Ar III] 8.99 m, [S IV] 10.5 m and [Ne II] 12.8 m ionic
emission-lines, as well as silicate absorption feature at 9.7m have been
found in the nuclear extraction (200 pc). We also present
subarcsecond-resolution Michelle N-band image of Mrk 3 which resolves its
circumnuclear region. This diffuse MIR emission shows up as a wings towards
East-West direction closely aligned with the S-shaped of the Narrow Line Region
(NLR) observed at optical [O III]5007\AA image with Hubble/FOC. The
nuclear continuum spectrum can be well represented by a theoretical torus
spectral energy distribution (SED), suggesting that the nucleus of Mrk 3 may
host a dusty toroidal structure predicted by the unified model of active
galactic nucleus (AGN). In addition, the hydrogen column density
(N cm) estimated with a torus
model for Mrk 3 is consistent with the value derived from X-ray spectroscopy.
The torus model geometry of Mrk 3 is similar to that of NGC 3281, both
Compton-thick galaxies, confirmed through fitting the 9.7m silicate band
profile. This results might provide further evidence that the silicate-rich
dust can be associated with the AGN torus and may also be responsible for the
absorption observed at X-ray wavelengths in those galaxies.Comment: 11 pages, 6 figure
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
What drives the velocity dispersion of ionized gas in star-forming galaxies?
We analyze the intrinsic velocity dispersion properties of 648 star-forming
galaxies observed by the Mapping Nearby Galaxies at Apache Point Observatory
(MaNGA) survey, to explore the relation of intrinsic gas velocity dispersions
with star formation rates (SFRs), SFR surface densities (),
stellar masses and stellar mass surface densities (). By
combining with high z galaxies, we found that there is a good correlation
between the velocity dispersion and the SFR as well as . But
the correlation between the velocity dispersion and the stellar mass as well as
is moderate. By comparing our results with predictions of
theoretical models, we found that the energy feedback from star formation
processes alone and the gravitational instability alone can not fully explain
simultaneously the observed velocity-dispersion/SFR and
velocity-dispersion/ relationships.Comment: 11 pages, 11 figures. Accepted for publication in MNRA
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