Henrique Aita Fraquelli

The Frequency of Nuclear Star Formation in Seyfert 2 Galaxies

We investigate the detectability of starburst signatures in the nuclear spectrum of Seyfert 2 galaxies by constructing spectral models in the wavelength range λλ3500-4100, combining the spectrum of a bulge population (of age ≈10 Gyr) with that of younger stellar populations, spanning ages from ≈3 Myr to 1 Gyr. The major constraints in the analysis are (1) the continuum ratio λλ3660/4020, which efficiently discriminates between models combining a bulge spectrum with a stellar population younger than ≈50 Myr and those with older stellar populations; (2) the presence of the Balmer lines H8, H9, and H10 in absorption, which are unambiguous signatures of stellar populations with ages in the range 10 Myr-1 Gyr for the relevant metallicities. Their detectability depends both on the age of the young component and on its contribution to the total flux relative to that of the bulge. We also construct models combining the bulge template with a power-law (PL) continuum, which is observed in some Seyfert 2 galaxies in polarized light, contributing with typically 10%-40% of the flux at 4020 A. We conclude that such continuum cannot be distinguished from that of a very young stellar population (age ≤ 10 Myr), contributing with less than ≈0.02% of the mass of the bulge. The models are compared with nuclear spectra—corresponding to a radius of 200-300 pc at the galaxy—of 20 Seyfert 2 galaxies, in which we specifically look for the signatures above of young- to intermediate-aged stellar populations. We find them in 10 galaxies, thus 50% of the sample. But only in six cases (30% of the sample) can they be attributed to young stars (age < 500 Myr): Mrk 1210, ESO 362-G8, NGC 5135, NGC 5643, NGC 7130, and NGC 7582. In the remaining four cases, the signatures are caused by intermediate-aged stars (≈1 Gyr). We find a tendency for the young stars to be found more frequently among the late-type Seyfert galaxies, a well-known effect in the nuclei of normal galaxies. This tendency is supported by a comparison between the equivalent widths (W) of absorption lines of the nuclear spectra of the Seyfert 2 galaxies with those of normal galaxies of the same Hubble type. For the late-type galaxies, the W values of the Seyfert galaxies are within the observed range of the normal galaxies, suggesting a similar stellar population. On the other hand, the W values are lower than those of the normal galaxies for seven out of the 11 Seyferts in early-type galaxies.

The Extended Narrow-Line Region of the Seyfert 1 Galaxy ESO 362-G18 versus That of the Seyfert 2 Galaxy ESO 362-G8

We use long-slit spectroscopic data to study in detail the extended narrow-line regions (ENLRs) of the Seyfert 1 galaxy ESO 362-G18 and Seyfert 2 galaxy ESO 362-G8. These two galaxies have similar emission-line luminosities and extents of the ENLR (D4 kpc), whose shapes in previous narrowband (O III) images suggest anisotropic escape of the nuclear ionizing radiation as expected for shadowing by a nuclear torus in the framework of the uni—ed model. In the Seyfert 1 galaxy the high-excitation gas shows an approximately cone-shaped morphology. From the observed kinematics, we conclude that the gas within the cone most probably belongs to the galaxy disk, which implies that the collimation axis is closer to the disk than half the opening angle of the cone of ionizing radiation. In the Seyfert 2 galaxy, the main structure in the high-excitation gas is an emission blob which apparently consists of a high- latitude cloud being blown away from the nuclear region and ionized by the nuclear source. We use the radial distribution of stellar population features in order to extrapolate this population to the nucleus and isolate the optical continuum of the nuclear source. We obtain a featureless power-law continuum for the Seyfert 1 galaxy, while for the Seyfert 2 galaxy we conclude that the F l P l~0.76 nuclear bluer color and smaller equivalent widths of the absorption lines are due to an aging burst of star formation (age B 300 Myr) and that the nuclear source is hidden from direct view. Using the photoionization code MAPPINGS Ic and a mixture of matter-bounded (MB) and ionization-bounded (IB) clouds, we model the ENLRs of the two galaxies. We use all the observables, mostly the emission-line —uxes as a function of distance from the nucleus and the optical nuclear contin- uum observed in the Seyfert 1 galaxy as well as its X-ray —ux, to constrain the parameters of a self- consistent model for the ENLR. For both galaxies, we conclude that a power-law ionizing continuum better reproduces the high-excitation lines near the nucleus than a multisegmented power law F l P l~1.2 used in previous works. For the Seyfert 1 galaxy ESO 362-G18, the inferred luminosity of the ionizing continuum can be reconciled with the —ux observed in the optical, while in the X-rays the observed —ux is D100 times weaker than that necessary to reproduce the line —uxes, suggesting that the X-ray contin- uum is absorbed toward Earth. For the Seyfert 2 galaxy ESO 362-G8, the inferred ionizing continuum when extrapolated to the optical implies a minimum obscuration toward the nuclear source of A V B 4.0 mag. In the hypothesis of an isotropic nuclear source, in order to better constrain the model parameters, we have adopted symmetrical physical conditions as a function of distance on both sides of the nucleus: namely, the ionizing —ux, the temperature, density, and ionization parameter of the MB gas, and the metallicity. The radial density behavior of the IB gas was observationally inferred from the (S II) doublet ratio. The only free parameter, which was allowed to vary independently, was the relative proportion of the MB and IB emission-line components along the ENLR. The high-excitation gas within the cone of ESO 362-G18 and within the blob of ESO 362-G8 have been modeled as regions of larger mass contri- bution from the MB component relative to other locations of the ENLR. We derive the —lling factors, covering factors, and gas masses along the ENLR as a function of dis- tance from the nucleus. A comparison between the model results for the two galaxies shows that, around the nucleus, the Seyfert 1 galaxy has a larger excitation due to a larger contribution of the MB com- ponent. However, in the cone, the excitation is lower than in the blob of the Seyfert 2 galaxy due to a combination of a lower ionizing —ux and larger gas density in the disk of the Seyfert 1 galaxy. The total ionized gas mass derived for the blob in the Seyfert 2 galaxy is 105.8 consistent with its proposed M _ , origin in a nuclear superwind which probably occurred D300 Myr ago, while the ionized gas mass in the disk of the Seyfert 1 galaxy is 1 order of magnitude smaller. Subject headings: galaxies: activegalaxies: ISMgalaxies: nucleigalaxies: Seyfert

Roteiro para a experiência de levitação de um imã repelido por um supercondutor no ensino de Física

The aim of this paper is to propose an outline to demonstrate the phenomenon of superconductivity by means of a levitation experiment of a magnet, repelled by a sample of YBa2Cu3O7. The experiment is based on the evidence of the Meissner effect, a characteristic property of a superconducting material under the action of magnetic fields. This demonstration of the levitation phenomenon does not imply large expenditures. It helps to introduce contents of the contemporary physics that leads to update curriculum. The main physical concepts involved in the levitation of a magnet and the phenomenon of superconductivity are both discussed here. Finally, the appendix describes the procedures involved in the preparation and thermal treatment of a sample of the ceramic high critical temperature superconducting material YBa2Cu3O7 (Tc ~ 92 K).

Extended emission in Seyfert galaxies

We use the photoionization code MAPPINGS Ic to model optical emission-line ratios of the extended emission-line regions of 24 Seyfert galaxies. Although most line ratios can be reproduced by varying the ionization parameter, gas density and/or the shape of the ionizing continuum, the ratio [NII]λλ6548,84/[OII]λ3727 can only be reproduced if we allow for a range of oxygen abundances of 0.5≤ (O/H)/(O/H)

Extended gas in Seyfert 2 galaxies : implications for the nuclear source

_{\odot} \leq

Roteiro para a experiência de levitação de um imã repelido por um supercondutor no Ensino de Física (An outline to the experiment of levitation on a superconductor in Physics teaching)

3 for the whole sample. We propose a calibration to obtain (O/H) in terms of [NII]/[OII]. Also, in order to reproduce the emission-line spectra beyond 2 kpc from the nucleus, we had to introduce the contribution from hot stars to the ionizing spectra. We conclude that this is due to an increasing contribution of HII regions with distance from the nucleus to the emission-line regions. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html