37 research outputs found
Probing the stellar population of seyfert galaxies: a near infrared perspective
We employ IRTF SpeX NIR (0.8--2.4mu m) spectra to investigate the stellar
population (SP), active galactic nuclei (AGN), featureless continuum (FC) and
hot dust properties in 9 Sy1 and 15 Sy2 galaxies. Both the {\sc starlight} code
and the hot dust as an additional base element were used for the first time in
this spectral range. Our synthesis shows significant differences between Sy1
and Sy2 galaxies: the hot dust component is required to fit the K-band spectra
of ~90% of the Sy1 galaxies, and only of ~25% of the Sy2; about 50% of the Sy2
galaxies require an FC component contribution >20%; this fraction increases to
about 60% in the Sy1. In about 50% of the Sy2, the combined FC and young
components contribute with more than 20%, while this occurs in 90% of the Sy1,
suggesting recent star formation in the central region. The central few hundred
parsecs of our galaxy sample contain a substantial fraction of intermediate-age
SPs with a mean metallicity near solar. Our SP synthesis confirms that the
1.1microns CN band can be used as a tracer of intermediate-age stellar
populations.Comment: To appear in IAU S262 proceedings, 4 pages, 4 figure
Integral Field Spectroscopy of the inner kpc of the elliptical galaxy NGC 5044
We used Gemini Multi-Object Spectrograph (GMOS) in the Integral Field Unit
mode to map the stellar population, emission line flux distributions and gas
kinematics in the inner kpc of NGC 5044. From the stellar populations synthesis
we found that the continuum emission is dominated by old high metallicity stars
(13 Gyr, 2.5Z). Also, its nuclear emission is diluted by a non
thermal emission, which we attribute to the presence of a weak active galactic
nuclei (AGN). In addition, we report for the first time a broad component
(FWHM 3000km) in the H emission line in the nuclear
region of NGC 5044. By using emission line ratio diagnostic diagrams we found
that two dominant ionization processes coexist, while the nuclear region (inner
200 pc) is ionized by a low luminosity AGN, the filamentary structures are
consistent with being excited by shocks. The H velocity field shows
evidence of a rotating disk, which has a velocity amplitude of
240kms at 136 pc from the nucleus. Assuming a Keplerian
approach we estimated that the mass inside this radius is
, which is in agreement with the value obtained through the
M- relation, . Modelling the
ionized gas velocity field by a rotating disk component plus inflows towards
the nucleus along filamentary structures, we obtain a mass inflow rate of
0.4 M. This inflow rate is enough to power the central AGN in NGC
5044.Comment: 16 pages, 12 figures, accepted by MNRA
A photometric and kinematic study of the stars and interstellar medium in the central two kpc of NGC 3379
HST images of NGC 3379 show that the V and I luminosity profiles in the inner
13 arcsec of this E1 galaxy are represented by two different components: a
stellar bulge following a Sersic Law with exponent n = 2.36, and a central core
(r < 0.7 arcsec) with a characteristic "cuspy" profile. Subtraction of the
underlying stellar component represented by the fitted Sersic profile revealed
the presence of a small (r ~ 105 pc) dust disk of about 150 solar masses,
oriented at PA = 125 degrees and inclined ~ 77 degrees with respect to the line
of sight. The same absorption structure is detected in the color-index (V-I)
image. The stellar rotation in the inner 20 arcsec is well represented by a
parametric planar disk model, inclined ~ 26 degrees relative to the plane of
the sky, and apparent major axis along PA ~ 67 degrees. The gas velocity curves
in the inner 5 arcsec show a steep gradient, indicating that the gas rotates
much faster than the stars, although in the same direction. The velocity field
of the gaseous system, however, is not consistent with the simple model of
Keplerian rotation sustained by the large (7 x 10E9 solar masses within a
radius of ~ 90 pc) central mass implied by the maximum velocity observed, but
the available data precludes a more detailed analysis.Comment: 23 pages, LaTeX(aaspp4.sty), 9 figures included. Figs. 1 and 5 are
colour plates. Accepted for publication in The Astrophysical Journal (part 1
Interaction effects on galaxy pairs with Gemini/GMOS- I: electron density
We present an observational study about the impacts of the interactions on the electron density of HII regions located in seven systems of interacting galaxies. The data consist of long-slit spectra in the range 4400-7300 A, obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). The electron density was determined using the ratio of emission-lines [S II] lambda 6716/ lambda 6731. Our results indicate that the electron density estimates obtained of HII regions from our sample of interacting galaxies are systematically higher than those derived for isolated galaxies. The mean electron density values of interacting galaxies are in the range of Ne = 24 - 532 cm^{-3}, while those obtained for isolated galaxies are in the range of Ne = 40 - 137 cm^{-3}. Comparing the observed emission lines with predictions of photoionization models, we verified that almost all the HII regions of the galaxies AM1054A, AM2058B, AM2306B have emission lines excited by shocks, such as in AM2322B (one point) and AM 2322A (four points). No correlation is obtained between the presence of shocks and electron densities. Indeed, the highest electron density values found in our sample do not belong to the objects with gas shock excitation. We emphasize the importance of considering theses quantities especially when the metallicity is derived for this type of systems.Fil: Krabbe, A.. Universidade Do Vale Do Paraiba; BrasilFil: Rosa, D. A.. Universidade Do Vale Do Paraiba; BrasilFil: Dors Jr., Oli L.. Universidade Do Vale Do Paraiba; BrasilFil: Pastoriza, Miriani G.. Universidade Federal Do Rio Grande Do Sul; BrasilFil: Winge, C.. Gemini Observatory; ChileFil: HĂ€gele, Guillermo Federico. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico la Plata. Instituto de AstrofĂsica de la Plata; Argentina; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Cardaci, Monica Viviana. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico La Plata. Instituto de AstrofĂsica de La Plata; Argentina; ArgentinaFil: Rodrigues, Irapuan. Universidade Do Vale Do Paraiba; Brasi
Intermediate age stars as origin of the low velocity dispersion nuclear ring in Mrk1066
We report the first two-dimensional stellar population synthesis in the
near-infrared of the nuclear region of an active galaxy, namely Mrk1066.
We have used integral field spectroscopy with adaptive optics at the Gemini
North Telescope to map the to map the age distribution of the stellar
population in the inner 300 pc at a spatial resolution of 35 pc. An old stellar
population component (age >5Gyr) is dominant within the inner ~160pc, which we
attribute to the galaxy bulge. Beyond this region, up to the borders of the
observation field (~300 pc), intermediate age components (0.3-0.7Gyr) dominate.
We find a spatial correlation between this intermediate age component and a
partial ring of low stellar velocity dispersions (sigma). Low-sigma nuclear
rings have been observed in other active galaxies and our result for Mrk1066
suggests that they are formed by intermediate age stars. This age is consistent
with an origin for the low-sigma rings in a past event which triggered an
inflow of gas and formed stars which still keep the colder kinematics (as
compared to that of the bulge) of the gas from which they have formed. At the
nucleus proper we detect, in addition, two unresolved components: a compact
infrared source, consistent with an origin in hot dust with mass ~1.9x10^{-2}
M_Sun, and a blue featureless power-law continuum, which contributes with only
~15% of the flux at 2.12 microns.Comment: 6 pages, 2 figs, accepted by Ap
Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs
The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are
observed in a variety of astrophysical objects, including the circumnuclear
medium of active galactic nuclei (AGNs). These are sources of highly energetic
photons (0.2 to 10 keV), exposing the PAHs to a harsh environment. In this
work, we examined experimentally the photoionization and photostability of
naphthalene (CH), anthracene (CH),
2-methyl-anthracene (CHCH) and pyrene (CH)
upon interaction with photons of 275, 310 and 2500 eV. The measurements were
performed at the Brazilian Synchrotron Light Laboratory using time-of-flight
mass-spectrometry (TOF-MS). We determined the absolute photoionization and
photodissociation cross sections as a function of the incident photon energy;
the production rates of singly, doubly and triply charged ions; and the
molecular half-lives in regions surrounding AGNs. Even considering moderate
X-ray optical depth values () due to attenuation by the dusty
torus, the half-lives are not long enough to account for PAH detection. Our
results suggest that a more sophisticated interplay between PAHs and dust
grains should be present in order to circumvent molecular destruction. We could
not see any significant difference in the half-life values by increasing the
size of the PAH carbon backbone, N, from 10 to 16. However, we show that
the multiple photoionization rates are significantly greater than the single
ones, irrespective of the AGN source. We suggest that an enrichment of multiply
charged ions caused by X-rays can occur in AGNs.Comment: 20 pages (appendix: 3 pages), 10 figures, 4 tables. Accepted for
publication in the Montly Notices of the Royal Astronomical Society (MNRAS).
Accepted 2019 April
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
Erratum:Optical/NIR stellar absorption and emission-line indices from luminous infrared galaxies
Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. 5: Variability of the ultraviolet continuum and emission lines of NGC 3783
We report on the results of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variability was observed in both continuum and emission-line fluxes. The light curves for the continuum fluxes exhibited two well-defined local minima or 'dips,' the first lasting is less than or approximately 20 days and the second is less than or approximately 4 days, with additional episodes of relatively rapid flickering of approximately the same amplitude. As in the case of NGC 5548 (the only other Seyfert galaxy that has been the subject of such an intensive, sustained monitoring effort), the largest continuum variations were seen at the shortest wavelengths, so that the continuum became 'harder' when brighter. The variations in the continuum occurred simultaneously at all wavelengths (delta(t) is less than 2 days). Generally, the amplitude of variability of the emission lines was lower than (or comparable to) that of the continuum. Apart from Mg II (which varied little) and N V (which is relatively weak and badly blended with Ly(alpha), the light curves of the emission lines are very similar to the continuum light curves, in each case with a small systematic delay or 'lag.' As for NGC 5548, the highest ionization lines seem to respond with shorter lags than the lower ionization lines. The lags found for NGC 3783 are considerably shorter than those obtained for NGC 5548, with values of (formally) approximately 0 days for He II + O III), and approximately 4 days for Ly(alpha) and C IV. The data further suggest lags of approximately 4 days for Si IV + O IV) and 8-30 days for Si III + C III). Mg II lagged the 1460 A continuum by approximately 9 days, although this result depends on the method of measuring the line flux and may in fact be due to variability of the underlying Fe II lines. Correlation analysis further shows that the power density spectrum contains substantial unresolved power over timescales of is less than or approximately 2 days, and that the character of the continuum variability may change with time