70 research outputs found
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
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
Astronomia como ferramenta lúdica para o ensino de física: equação de estado e as estrelas anãs brancas
This interdisciplinary work proposes the use of astronomy as a ludic tool to teach Physics, hence, to arouse the curiosity of undergraduate and graduate students from the program of Exact Sciences and the Earth courses, providing enhance on the teaching-learning process in Statistical Mechanics classes. The main goal of the present study is to discuss white dwarf stars (WDS), which are the final stage of the evolution of a star like the Sun and up to 8 M⊙ , since those are an interesting object of study because of their compact nature, high density, and, also, because they are eliminated as a degenerated fermi gas. Having as motivation and interest in the improvement of the knowledge regarding these objects, we aim to obtain the relationship between the mass and the radius of the white dwarf stars, as well as to classify a sample of 5 white dwarfs required by the Sloan Digital Sky Survey (SDSS), according to the chemical element that is destined for the surface. At the end of this work, we conclude throughthe mass and radius ratio of white dwarf stars that the greater the mass of the star, the smaller its size, and that in equilibrium it must have a mass less than 1.44 M⊙. In addition, we show a experiment reports of this teaching innovative that used astronomy as ludic tool to teach Physics in the subject of statistical mechanics at undergraduate and master’s level.Este trabalho propõe utilizar a interdisciplinaridade e a astronomia como ferramenta lúdica para o ensino de física, assimdespertando maior interesse nos discentes de graduação e pós-graduação das ciências exatas e da Terra, assim, potencializandoo processo ensino-aprendizagem nas aulas da disciplina de Mecânica Estatística. O objetivo foi discutir sobre as estrelasanãs brancas (WDS), que são o estágio final da evolução de uma estrela com até 8M⊙, como o Sol, e são objetos de estudointeressantes por serem compactos, de alta densidade, e descritas como um gás de fermi degenerado. Como motivação o interesseem aperfeiçoar o conhecimento temos como objetivo obter a relação entre amassa e o raio das estrelas anãs brancas, assimcomo classificar uma amosta de 7 anãs brancas obtidas pelo Sloan Digital Sky Survey (SDSS), de acordo com o elemento químicoque se dispõem em sua superfície. Ao final deste trabalho, foi possível concluir através da relação massa e raio das WDS quequanto maior a massa da estrela menor o seu tamanho, e que em equilíbrio,deve possuir uma massa menor que 1,44 M⊙. Alémdisso, foi adicionado um relato de experiência da abordagem didática inovadora que usou a astronomia como ferramenta lúdicapara o ensino de Física
Star formation and gas inflows in the OH Megamaser galaxy IRAS03056+2034
We have obtained observations of the OH Megamaser galaxy IRAS03056+0234 using
Gemini Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU), Very Large
Array (VLA) and Hubble Space Telescope (HST). The HST data reveals spiral arms
containing knots of emission associated to star forming regions. The GMOS-IFU
data cover the spectral range of 4500 to 7500 \AA\ at a velocity resolution of
90 km s and spatial resolution of 506 pc. The emission-line flux
distributions reveal a ring of star forming regions with radius of 786 pc
centred at the nucleus of the galaxy, with an ionized gas mass of 1.2
10M, an ionizing photon luminosity of log Q[H]=53.8 and a
star formation rate of 4.9 M yr. The emission-line ratios and
radio emission suggest that the gas at the nuclear region is excited by both
starburst activity and an active galactic nucleus. The gas velocity fields are
partially reproduced by rotation in the galactic plane, but show, in addition,
excess redshifts to the east of the nucleus, consistent with gas inflows
towards the nucleus, with velocity of 45 km s and a mass inflow
rate of 7.710 M yr.Comment: To be published in MNRA
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&
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 (5.2–38 μm range) under the active galactic nucleus (AGN) unified model. We compare the observed spectra with ∼106 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, σ, 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 ∼6 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 ∼ 104−107M . The main difference appears to be related to the clouds’ intrinsic properties: type 2 sources present higher optical depths τ 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
Optical and mid-infrared neon abundance determinations in star-forming regions
We employed observational spectroscopic data of star-forming regions compiled
from the literature and photoionization models to analyse the neon ionic
abundances obtained using both optical and mid-infrared emission-lines.
Comparing Ne++/H+ ionic abundances from distinct methods, we found that, in
average, the abundances obtained via IR emission-lines are higher than those
obtained via optical lines by a factor of 4. Photoionization models with
abundance variations along the radius of the hypothetical nebula provide a
possible explanation for a large part of the difference between ionic
abundances via optical and infrared emission-lines. Ionization Correction
Factor (ICF) for the neon is obtained from direct determinations of ionic
fractions using infrared emission-lines. A constant Ne/O ratio (logNe/O \approx
-0.70) for a large range of metallicity, independently of the ICF used to
compute the neon total abundance is derived.Comment: 17 pages, 14 figures, accepted by MNRA
The OH Megamaser galaxy IRAS11506-3851: an AGN and starformation revealed by multiwavelength observations
We present Gemini Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU),
Hubble Space Telescope (HST) and Very Large Array (VLA) observations of the OH
Megamaser (OHM) galaxy IRAS 11506-3851. The HST images reveal an isolated
spiral galaxy and the combination with the GMOS-IFU flux distributions and VLA
data allow us to identify a partial ring of star-forming regions surrounding
the nucleus with a radius of ~ 500 pc. While this ring shows starburst
excitation and low velocity dispersion, the region internal to the ring shows
higher excitation and velocity dispersion values, with values increasing
towards its borders at ~ 240 pc from the nucleus, resembling a projected
bubble. The enhanced excitation and velocity dispersion of this bubble
surrounds a 8.5 GHz radio emission structure, supporting its origin in a faint
AGN that is mostly shocking the surrounding gas via a plasma ejection seen in
radio at the present stage. This is the fourth of the 5 OHM galaxies we have
studied so far (from our sample of 15 OHM) for which GMOS-IFU data indicate the
presence of a previously unknown faint AGN at the nucleus, consistent with the
hypothesis that OHM galaxies harbor recently triggered AGN
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