Ronaldo Eustaquio de Souza

Shape of the Galactic Orbits in Clusters

A kinematical analysis applied to a sample of galaxy clusters indicates that the differences between the velocity distributions of elliptical and spiral galaxies are associated with the shape of their orbit families. The orbital anisotropies present in each morphological population could be measured with a parameter that is the ratio of the radial and tangential velocity dispersions, which can be recovered through the observed line-of-sight velocity distribution. When a Gaussian velocity distribution is assumed, having different dispersions along the radial and tangential directions, we conclude that the orbits of elliptical galaxies in clusters are close to radial, while spirals have more circularly shaped or isotropic orbits. Lenticulars galaxies share an intermediate orbital parameter, between spirals and ellipticals.

A spectral atlas of H ii galaxies in the near-infrared

Recent models show that TP-AGB stars should dominate the NIR spectra of populations 0.3 to 2 Gyr old, leaving unique signatures that can be used to detect young/intermediate stellar population in galaxies. However, no homogeneous database of star-forming galaxies is available in the NIR to fully explore these results. With this in mind, we study the NIR spectra of a sample of 23 HII and starburst galaxies, aimed at characterizing the most prominent spectral features and continuum shape in the 0.8-2.4 micron region of these objects. Spectral indices are derived for the relevant absorption lines/bands and a comparison with optical indices of the same sample available in the literature is made. We found no correlation between the optical and the NIR indexes. This is probably due to the differences in aperture between these two sets of data. That result is further supported by the absence or weakness of emission lines in the NIR for a subsample galaxies, while in the optical the emission lines are strong and clear, which means that the ionisation source in many of these galaxies is not nuclear, but circumnuclear or located in hot spots. We detected important signatures predicted for a stellar population dominated by the TP-AGBs, like CN 1.1 micron and CO 2.3 micron. In at least one galaxy (NGC 4102) the CN band at 1.4 micron was detected for the first time. We also detect TiO and ZrO bands that have never been reported before in extragalactic sources. The shape of the continuum emission is found to be strongly correlated to the presence/lack of emission lines. An observational template for the star-forming galaxies is derived to be used as a benchmark of stellar population(s) in starburst galaxies against which to compare near-IR spectroscopy of different types of galaxies, especially those with AGN activity and/or those at high-redshift.

SPECTRAL SYNTHESIS OF STAR-FORMING GALAXIES IN THE NEAR-INFRARED

The near-infrared spectral region is becoming a very useful wavelength range to detect and quantify the stellar population of galaxies. Models are developing to predict the contribution of TP-AGB stars, that should dominate the NIR spectra of populations 0.3 to 2 Gyr old. When present in a given stellar population, these stars leave unique signatures that can be used to detect them unambiguously Maraston (2005). However, to identify and quantify tracers of star formation in the NIR, we need galaxies known to have a significant fraction of star formation. With this in mind, we used the NIR sample of star-forming galaxies of Martins et al. (2013), which are known to have star formation from their optical observations. In this work we performed stellar population on these galaxies to understand how the star-formation tracers in the near-infrared can be used in practice. Martins et al. (2013) compared emission line properties from the optical observations and from the NIR. They found that for a subsample of galaxies the emission lines in the NIR were much weaker than in the optical, sometimes even absent. They concluded that this was mainly due to the differences in aperture between these two sets of data - the aperture in the optical has 5 times the area than the aperture in the NIR. In many of these galaxies the star-formation is probably not nuclear, but circumnuclear, or located in hot spots outside the nucleus. Based on this comparisons, they classified the galaxy sample in four classes: • Weak emission lines in the optical, no emission lines in the NIR, either at the nucleus or in the extended region (class 1). • Strong emission lines in the optical, no emission lines in the NIR, either at the nucleus or in the

Nuclear and extended spectra of NGC 1068 – II. Near-infrared stellar population synthesis

We performed stellar population synthesis on the nuclear and extended regions of NGC 1068 by means of near-infrared spectroscopy to disentangle their spectral energy distribution components. This is the first time that such a technique is applied to the whole 0.8-2.4 μm wavelength interval in this galaxy. NGC 1068 is one of the nearest and probably the most studied Seyfert 2 galaxy, becoming an excellent laboratory to study the interaction between black holes, the jets that they can produce and the medium in which they propagate. Our main result is that traces of young stellar population are found at ~ 100 pc south of the nucleus. The contribution of a power-law continuum in the centre is about 25 per cent, which is expected if the light is scattered from a Seyfert 1 nucleus. We find peaks in the contribution of the featureless continuum about 100-150 pc from the nucleus on both sides. They might be associated with regions where the jet encounters dense clouds. Further support to this scenario is given by the peaks of hot dust distribution found around these same regions and the H 2 emission-line profile, leading us to propose that the peaks might be associated to regions where stars are being formed. Hot dust also has an important contribution to the nuclear region, reinforcing the idea of the presence of a dense, circumnuclear torus in this galaxy. Cold dust appears mostly in the south direction, which supports the view that the south-west emission is behind the plane of the galaxy and is extinguished very likely by dust in the plane. Intermediate-age stellar population contributes significantly to the continuum, especially in the inner 200 pc.

Nuclear and extended spectra of NGC 1068 – I. Hints from near-infrared spectroscopy

We report the first simultaneous zJHK spectroscopy on the archetypical Seyfert 2 galaxy NGC 1068 covering the wavelength region 0.9-2.4 μm. The slit, aligned in the north-south direction and centred in the optical nucleus, maps a region 300 pc in radius at subarcsec resolution, with a spectral resolving power of 360 km s -1 . This configuration allows us to study the physical properties of the nuclear gas including that of the north side of the ionization cone, map the strong excess of continuum emission in the K band and attributed to dust and study the variations, both in flux and profile, in the emission lines. Our results show the following. (1) Mid- to low-ionization emission lines are split into two components, whose relative strengths vary with the position along the slit and seem to be correlated with the jet. (2) The coronal lines are single-peaked and are detected only in the central few hundred of pc from the nucleus. (3) The absorption lines indicate the presence of intermediate age stellar population, which might be a significant contributor to the continuum in the near-IR spectra. (4) Through some simple photoionization models we find photoionization as the main mechanism powering the emitting gas. (5) Calculations using stellar features point to a mass concentration inside the 100-200 pc of about 10 10 M ⊙ .

Optical Photometry and the Continuum of Active Galactic Nuclei

In this paper, the continuum emission of active galactic nuclei is studied using broadband B, V, R, and I photometry. The nuclear contribution is estimated from the observations using two different approaches. In the first one, the images are deconvolved by the seeing profile and the corrected images are used to derive the nuclear contribution. In the second method, in order to extract the stellar contribution, a de Vaucouleurs brightness profile is assumed for the bulge. After subtraction of this component, the total nuclear emission is obtained from the corrected image. Both methods indicate that the stellar contribution is dominant. The average contribution of the featureless continuum to the total observed continuum is 30% in the four bands. We show that over 2 orders of magnitude the Hα emission-line luminosity correlates with the continuum emission in all the observed bands. As a consequence, the galaxies in the sample must have similar color index. This result provides a method to estimate the reddening correction for the nuclear continuum, which we found to be lower than the emission-line extinction correction estimated from the observed Hα/Hβ observed line ratio.

On the lengths, colours and ages of bars

In an effort to obtain further observational evidences for secular evolution processes in galaxies, as well as observational constraints to current theoretical models of secular evolution, we have used BVRI and Ks images of a sample of 18 barred galaxies to measure the lengths and colours of bars, create colour maps and estimate global colour gradients. In addition, applying a method we developed in a previous article, we could distinguish for 7 galaxies in our sample those whose bars have been recently formed from the ones with already evolved bars. We estimated an average difference in the optical colours between young and evolved bars that may be translated to an age difference of the order of 10 Gyr, meaning that bars may be long standing structures. Moreover, our results show that, on average, evolved bars are longer than young bars. This seems to indicate that, during its evolution, a bar grows longer by capturing stars from the disk, in agreement with recent numerical and analytical results.

A new challenge: Bar formation and secular evolution in lenticular galaxies

Departamento de Astronomia, Instituto de Astronomia, Geof´isica e CiˆenciasAtmosf´ericas, Universidade de S˜ao Paulo — Rua do Mat˜ao, 1226 – Cid. Univers.CEP 05508-900, S˜ao Paulo – SP, BrasilAbstract. To further enhance our understanding on the formation and evolutionof bars in lenticular (S0) galaxies, we are undertaking a detailed photometric andspectroscopic study on a sample of 22 objects. Here we report the results of a 2Dstructural analysis on two barred face–on S0’s, which indicate that presently thesegalaxies do not possess disks. We discuss two possibilities to explain these surprisingresults, namely strong secular evolution and bar formation without disks.Keywords: galaxies: evolution, galaxies: structure, methods: N-body simulations