206 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
The XDSPRES CL-based package for reducing OSIRIS cross-dispersed spectra
We present a description of the CL-based package XDSPRES, which aims at being
a complete reducing facility for cross-dispersed spectra taken with the Ohio
State Infrared Imager/Spectrometer, as installed at the SOAR telescope. This
instrument provides spectra in the range between 1.2um and 2.35um in a single
exposure, with resolving power of R ~ 1200. XDSPRES consists of two tasks,
namely xdflat and doosiris. The former is a completely automated code for
preparing normalized flat field images from raw flat field exposures. Doosiris
was designed to be a complete reduction pipeline, requiring a minimum of user
interaction. General steps towards a fully reduced spectrum are explained, as
well as the approach adopted by our code. The software is available to the
community through the web site http://www.if.ufrgs.br/~ruschel/software.Comment: 14 pages, 10 figure
Near-infrared surface photometry of early-type galaxies
CCD infrared (JHKs) photometry was performed on a sample of 10 elliptical and 2 lenticular galaxies. Isophotal parameters, brightness proïŹles, integrated colors and color gradients arepresented. Color gradients found arevery weak, showing bluer colors towards the outer regions. The colors of the sample galaxies are compatible with stellar populations like those found in metal-rich clusters of the Galaxy; objects NGC7192, NGC7562 and NGC7619 are compatible with less metal-rich populations. The brightness proïŹle of most galaxies is well described by the r1/4 law. The proïŹles of NGC1600 and NGC720 are described by SĂ©rsicâs law with n ⌠1.5 andn ⌠1.8 respectively. The infrared eïŹective radius of the objects studied is typically one half of its counterpart in the B band, which can be an indication that the stellar population that dominates the infrared emission is more concentrated in the central regions. Weshow that the sample satisïŹes the Fundamental Plane relation of elliptical galaxies in the infrared, with an rms scatter of 0.20 for J and H and 0.23 for Ks
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
Probing the active galactic nucleus unified model torus properties in Seyfert galaxies
We studied the physical parameters of a sample comprising of all Spitzer/Infrared Spectrograph public spectra of Seyfert galaxies in the mid-infrared (5.2â38 ÎŒm range) under the active galactic nucleus (AGN) unified model. We compare the observed spectra with âŒ106 CLUMPY model spectral energy distributions, which consider a torus composed of dusty clouds. We find a slight difference in the distribution of line-of-sight inclination angle, i, requiring larger angles for Seyfert 2 (Sy 2) and a broader distribution for Seyfert 1 (Sy 1). We found small differences in the torus angular width, Ï, indicating that Sy 1may host a slightly narrower torus than Sy 2. The torus thickness, together with the bolometric luminosities derived, suggests a very compact torus up to âŒ6 pc from the central AGN. The number of clouds along the equatorial plane, N, as well the index of the radial profile, q, is nearly the same for both types. These results imply that the torus cloud distribution is nearly the same for type 1 and type 2 objects. The torus mass is almost the same for both types of activity, with values in the range of Mtor ⌠104â107M . The main difference appears to be related to the cloudsâ intrinsic properties: type 2 sources present higher optical depths Ï V. The results presented here reinforce the suggestion that the classification of a galaxy may also depend on the intrinsic properties of the torus clouds rather than simply on their inclination. This is in contradiction with the simple geometric idea of the unification model
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
Understanding the two-dimensional ionization structure in luminous infrared galaxies. A near-IR integral field spectroscopy perspective
We investigate the 2D excitation structure of the ISM in a sample of LIRGs
and Seyferts using near-IR IFS. This study extends to the near-IR the
well-known optical and mid-IR emission line diagnostics used to classify
activity in galaxies. Based on the spatially resolved spectroscopy of
prototypes, we identify in the [FeII]1.64/Br - H_2 1-0S(1)/Br
plane regions dominated by the different heating sources, i.e. AGNs, young MS
massive stars, and evolved stars i.e. supernovae. The ISM in LIRGs occupy a
wide region in the near-IR diagnostic plane from -0.6 to +1.5 and from -1.2 to
+0.8 (in log units) for the [FeII]/Br and H_2/Br line ratios,
respectively. The corresponding median(mode) ratios are +0.18(0.16) and
+0.02(-0.04). Seyferts show on average larger values by factors ~2.5 and ~1.4
for the [FeII]/Br and H_2/Br ratios, respectively. New areas
and relations in the near-IR diagnostic plane are defined for the compact, high
surface brightness regions dominated by AGN, young ionizing stars, and SNe
explosions, respectively. In addition, the diffuse regions affected by the AGN
radiation field cover an area similar to that of Seyferts, but with high values
in [FeII]/Br that are not as extreme. The extended, non-AGN diffuse
regions cover a wide area in the diagnostic diagram that overlaps that of
individual excitation mechanisms (i.e. AGN, young stars, and SNe), but with its
mode value to that of the young SF clumps. This indicates that the excitation
conditions of the diffuse ISM are likely due to a mixture of the different
ionization sources. The integrated line ratios in LIRGs show higher excitation
conditions i.e. towards AGNs, than those measured by the spatially resolved
spectroscopy. If this behaviour is representative, it would have clear
consequences when classifying high-z, SF galaxies based on their near-IR
integrated spectra.Comment: 18 pages, 13 figures, accepted for publication in A&
Profile comparison of the 6â9 ÎŒm polycyclic aromatic hydrocarbon bands in starburst-dominated galaxies
Polycyclic aromatic hydrocarbons (PAHs) are of great astrochemical and astrobiological interest due to their potential to form prebiotic molecules. We analyse the 7.7 and 8.6 ÎŒm PAH bands in 126 pre-dominantly starburst-dominated galaxies extracted from the Spitzer/IRS ATLAS project. Based on the peak positions of these bands, we classify them into the different A, B, and C Peetersâ classes, which allows us to address the potential characteristics of the PAH-emitting population. We compare this analysis with previous work focused on the 6.2 ÎŒm PAH band for the same sample. For the first time in the literature, this statistical analysis is performed on a sample of galaxies. In our sample, the 7.7 ÎŒm complex is equally distributed in A and B objectâs class while the 8.6 ÎŒm band presents more class B sources. Moreover, 39 per cent of the galaxies were distributed into A class objects for both 6.2 and 7.7 ÎŒm bands and only 18 per cent received the same A classification for the three bands. The âA A Aâ galaxies presented higher temperatures and less dust in their interstellar medium. Considering the redshift range covered by our sample, the distribution of the three bands into the different Peetersâ classes reveals a potential cosmological evolution in the molecular nature of the PAHs that dominate the interstellar medium in these galaxies, where B class objects seem to be more frequent at higher redshifts and, therefore, further studies have to be addressed
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
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