24 research outputs found
Short timescale variations of the H{\alpha} double-peaked profile of the nucleus of NGC 1097
The broad (FWHM ~ 10,000 km/s) double-peaked H{\alpha} profile from the
LINER/Seyfert 1 nucleus of NGC 1097 was discovered in 1991, and monitored for
the following 11 years. The profile showed variations attributed to the
rotation of gas in a non-axisymmetric Keplerian accretion disk, ionized by a
varying radiatively inefficient accretion flow (RIAF) located in the inner
parts of the disk. We present and model 11 new spectroscopic observations of
the double-peaked profile taken between 2010 March and 2011 March. This series
of observations was motivated by the finding that in 2010 March the flux in the
double-peaked line was again strong, becoming, in 2010 December, even stronger
than in the observations of a decade ago. We also discovered shorter timescale
variations than in the previous observations: (1) the first, of ~7 days, is
interpreted as due to "reverberation" of the variation of the ionizing source
luminosity, and the timescale of 7 days as the light crossing time between the
source and the accretion disk; this new timescale and its interpretation
provides a distance between the emitting gas and the supermassive black hole
and as such introduces a new constraint on its mass; (2) the second, of
approximately 5 months, was attributed to the rotation of a spiral arm in the
disk, which was found to occur on the dynamical timescale. We use two accretion
disk models to fit theoretical profiles to the new data, both having
non-axisymmetric emissivities produced by the presence of an one-armed spiral.
Our modeling constrains the rotation period for the spiral to be approximately
18 months. This work supports our previous conclusion that the broad
double-peaked Balmer emission lines in NGC 1097, and probably also in other
low-luminosity active nuclei, originate from an accretion disk ionized by a
central RIAF.Comment: Published in ApJ (2012 March). 13 pages, 11 figure
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
Photometry and dynamics of the minor mergers AM\,1228-260 and AM\,2058-381
We investigate interaction effects on the dynamics and morphology of the
galaxy pairs AM\,2058-381 and AM\,1228-260. This work is based on images
and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the
Gemini South Telescope. The luminosity ratio between the main (AM\,2058A) and
secondary (AM\,2058B) components of the first pair is a factor of 5,
while for the other pair, the main (AM\,1228A) component is 20 times more
luminous than the secondary (AM\,1228B). The four galaxies have pseudo-bulges,
with a S\'ersic index . Their observed radial velocities profiles (RVPs)
present several irregularities. The receding side of the RVP of AM\,2058A is
displaced with respect to the velocity field model, while there is a strong
evidence that AM\,2058B is a tumbling body, rotating along its major axis. The
RVPs for AM\,1228A indicate a misalignment between the kinematic and
photometric major axes. The RVP for AM\,1228B is quite perturbed, very likely
due to the interaction with AM\,1228A. NFW halo parameters for AM\,2058A are
similar to those of the Milky Way and M\,31. The halo mass of AM\,1228A is
roughly 10\% that of AM\,2058A. The mass-to-light (M/L) of AM\,2058 agrees with
the mean value derived for late-type spirals, while the low M/L for AM\,1228A
may be due to the intense star formation ongoing in this galaxy.Comment: 20 pages, 10 figures, accepted for publication in MNRA
The Gemini spectral library of near-IR late type stellar templates and its application for velocity dispersion measurements
We present a spectroscopic library of late spectral type stellar templates in
the near-IR range 2.15-2.42microns, at R=5300-5900 resolution, oriented to
support stellar kinematics studies in external galaxies, such as the direct
determination of the masses of supermassive black-holes in nearby active (or
non-active) galaxies. The combination of high spectral resolution and
state-of-the-art instrumentation available in 8-m class telescopes has made the
analysis of circumnuclear stellar kinematics using the near-IR CO band heads
one of the most used techniques for such studies, and this library aims to
provide the supporting datasets required by the higher spectral resolution and
larger spectral coverage currently achieved with modern near-IR spectrographs.
Examples of the application for kinematical analysis are given for data
obtained with two Gemini instruments, but the templates can be easily adjusted
for use with other near-IR spectrographs at similar or lower resolution. The
example datasets are also used to revisit the "template mismatch" effect and
the dependence of the velocity dispersion values obtained from the fitting
process with the characteristics of the stellar templates. The library is
available in electronic form from the Gemini web pages (link above).Comment: To appear in the ApJ Supplement Series, December 2009. AASTex, 25
pages, 17 figures. The library spectra are available in standard FITS format
from the Gemini Observatory webpage at
http://www.gemini.edu/sciops/instruments/nearir-resources/?q=node/1016
Short-Timescale monitoring of the X-ray, UV and broad double-peak emission line of the nucleus of NGC 1097
Recent studies have suggested that the short-timescale ( days)
variability of the broad (10,000 km s) double-peaked H
profile of the LINER nucleus of NGC1097 could be driven by a variable X-ray
emission from a central radiatively inefficient accretion flow (RIAF). To test
this scenario, we have monitored the NGC1097 nucleus in X-ray and UV continuum
with Swift and the H flux and profile in the optical spectrum using
SOAR and Gemini-South from 2012 August to 2013 February. During the monitoring
campaign, the H flux remained at a very low level --- 3 times lower
than the maximum flux observed in previous campaigns and showing only limited
() variability. The X-ray variations were small, only
throughout the campaign, while the UV did not show significant variations. We
concluded that the timescale of the H profile variation is close to the
sampling interval of the optical observations, which results in only marginal
correlation between the X-ray and H fluxes. We have caught the AGN in
NGC1097 in a very low activity state, in which the ionizing source was very
weak and capable of ionizing just the innermost part of the gas in the disk.
Nonetheless, the data presented here still support the picture in which the gas
that emits the broad double-peaked Balmer lines is illuminated/ionized by a
source of high-energy photons which is located interior to the inner radius of
the line-emitting part of the disk.Comment: The paper contains 14 pages, 7 figures and is accepted for
publication at the Astrophysical Journa
The effects of the interaction on the kinematics, stellar population and metallicity of AM2322-821 with Gemini/GMOS
We present an observational study about the impacts of the interactions in
the kinematics, stellar populations, and oxygen abundances of the components of
the galaxy pair AM\,2322-821. A fairly symmetric rotation curve for the
companion (AM\,2322B) galaxy with a deprojected velocity amplitude of 110 km
s was obtained, and a dynamical mass of 1.1 - 1.3 \times 10^{10}
M_{\sun} within a radius of 4 kpc was estimated using this deprojected
velocity. Asymmetries in the radial velocity field were detected for the
companion, very likely due the interaction between the galaxies. The
interaction between the main and companion galaxies was modelled using
numerical N-body/hydrodynamical simulations, with the result indicating that
the current stage of the system would be about 90 Myr after perigalacticum. The
spatial variation in the distribution of the stellar-population components in
both galaxies was analysed using the stellar population synthesis code {\sc
STARLIGHT}. The companion galaxy is dominated by a very young (t yr) population, with the fraction of this population to the
total flux at , increasing outwards in the galaxy disc.
On the other hand, the stellar population of AM\,2322A is heterogeneous along
the slit positions observed. Spatial profiles of oxygen abundance in the
gaseous phase were obtained using the diagnostic diagram R23 vs. [OIII]/[OII],
where we compared the observed values with the ones obtained from
photoionization models.
Such gradients of oxygen abundance are significantly flatter for this pair of
galaxies than in typical isolated spiral galaxies. This metallicity
distribution is interpreted as the gradients having been destroyed by
interaction-induced gas flows from the outer parts to the centre of the galaxyComment: accepted by MNRA
Kinematics and physical properties of Southern interacting galaxies: the minor merger AM 2306-721
We present an observational study about the effects of the interactions in
the kinematics, stellar population and abundances of the components of the
galaxy pair AM2306-721. Rotation curves for the main and companion galaxies
were obtained, showing a deprojected velocity amplitude of 175 km/s and 185
km/s, respectively. The interaction between the main and companion galaxies was
modeled using numerical N-body/hydrodynamical simulations, with the result
indicating that the current stage of the merger would be about 250 Myr after
perigalacticum. The spatial variation in the distribution of the stellar
population components in both galaxies was analysed by fitting combinations of
stellar population models of different age groups. The central region of main
galaxy is dominated by an old (5-10 Gyr) population, while significant
contributions from a young (200 Myr) and intermediate (1 Gyr) components are
found in the disk, being enhanced in the direction of the tidal features. The
stellar population of the companion galaxy is overall much younger, being
dominated by components with 1 Gyr or less, quite widely spread over the whole
disk. Spatial profiles of the oxygen abundance were obtained from the a grid of
photoionization models using the R23 line ratio. The disk of the main galaxy
shows a clear radial gradient, while the companion galaxy presents an oxygen
abundance relatively homogeneous across the disk. The absence of an abundance
gradient in the secondary galaxy is interpreted in terms of mixing by gas flows
from the outer parts to the center of the galaxy due to the gravitational
interaction with the more massive primary.Comment: 13 pages, 12 figures, accepted for publication on MNRA
Gemini/GMOS IFU stellar kinematics of the nuclear region of six nearby active galaxies
We present two-dimensional (2D) mapping of the stellar velocity field within
the inner 5 arcsec of six nearby active galaxies, using spectra obtained with
the Integral Field Unit of the GMOS instrument at the Gemini North telescope.
The spatial resolution range from 20 to about 180 pc, and the observed field of
view covers a few hundred parsecs around the nuclei. The Calcium II triplet
absorption features at ~ 8500 A were used to measure the stellar radial
velocities and velocity dispersions (sigma). A simple kinematical model
assuming a purely rotating system with circular orbits in a plane was fitted to
the radial velocity data. The turnover of the rotation curve is at only ~ 50 pc
for NGC 4051 and between 200 and 700 pc for the other 5 galaxies. The sigma
maps show the largest values at the centre. In the cases of NGC 2273 and NGC
3227, there is a decrease to sigma ~ 70-80 km/s at ~ 200-300 pc from the
nucleus, delineating partial rings of low sigma values. A similar broken ring
seems to be present at ~ 400 pc from the nucleus also in NGC 4593. We interpret
these low sigma rings as traces of recently formed stars that partially keep
the cold kinematics of the original gas from which they have formed.
The main novelty of the present work is the unprecedented spatial resolution
reached by a 2D study of stellar kinematics of Seyfert galaxies using an IFU.
The few similar IFU studies available in the literature for Seyfert galaxies
have a much poorer spatial resolution and/or are restricted to the study of
emission line kinematics.Comment: 18 pages, 11 figure
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