Henrique R. Schmitt

A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. II. The Large Magellanic Cloud

A survey of extended objects in the Large Magellanic Cloud was carried out on the ESO/SERC R and J Sky Survey Atlases, checking entries in previous catalogs and searching for new objects. The census provided 6659 objects including star clusters, emission-free associations, and objects related to emission nebulae. Each of these classes contains three subclasses with intermediate properties, which are used to infer total populations. The survey includes cross identifications among catalogs, and we present 3246 new objects. We provide accurate positions, classification, and homogeneous measurements of sizes and position angles, as well as information on cluster pairs and hierarchical relation for superimposed objects. This unification and enlargement of catalogs is important for future searches of fainter and smaller new objects. We discuss the angular and size distributions of the objects of the different classes. The angular distributions show two off-centered systems with different inclinations, suggesting that the LMC disk is warped. The present catalog together with its previous counterpart for the SMC and the inter-Cloud region provide a total population of 7847 extended objects in the Magellanic System. The angular distribution of the ensemble reveals important clues on the interaction between the LMC and SMC.

The spectral energy distribution of normal, starburst, and active galaxies

We present the results of an extensive literature search of multiwavelength data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2s, 5 LINERs, 6 normal spirals and 7 normal elliptical galaxies. The data include soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared photometry and radio measurements, selected to match as closely as possible the IUE aperture (10 X 20). The galaxies are separated into 6 groups with similar characteristics, namely, Ellipticals, Spirals, LINERs, Seyfert 2s, Starbursts of Low and High reddening, for which we create average spectral energy distributions (SED). The individual groups SEDs are normalized to the

Spectral synthesis of the nuclear regions of Seyfert 2 and radio galaxies

lambda

The Stellar Content of Active Galaxies

7000AA flux and compared, looking for similarities and differences among them.The bolometric fluxes of different types of galaxies were calculated integrating their SEDs. These values are compared with individual waveband flux densities, in order to determine the wavebands which contribute most to the bolometric flux. Linear regressions were performed between the bolometric and individual band fluxes for each kind of galaxy. These fits can be used in the calculation of the bolometric flux for other objects of similar activity type, but with reduced waveband information. We have also collected multiwavelength data for 4 HII regions, a thermal supernova remnant, and a non-thermal supernova remnant (SNR), which are compared with the Starburst SEDs.

CHEMICAL ABUNDANCE CALIBRATIONS FOR THE NARROW-LINE REGION OF ACTIVE GALAXIES

We present the results of an optical spectral synthesis analysis for the nuclei of 20 Seyfert 2 and four radio galaxies, using a base of stellar population templates of different ages and metallicities and a power-law continuum. Compared with the stellar population of elliptical galaxies, we find that Seyfert 2s usually have a smaller contribution from old metal-rich stars (age 10 Gyr, Z ≥ Z⊙), and a larger contribution from stars with ages of 100 Myr. We also find that the contributions from stars with ages ≤ 10 Myr and from a power-law continuum are small, rarely exceeding 5 per cent. These results show that the general assumption of elliptical galaxies as stellar population templates for these objects is incorrect, also implying that the excess blue continuum frequently found in their nuclear spectra is probably due to this template mismatch. We find a considerable contribution from 100-Myr-old stars (≈ 5 per cent), which can be interpreted from the point of view of models where the fuelling of the AGN is carried out by interactions/mergers.

A comparison of radio axis with host galaxy plane axis in Seyfert galaxies

We present the results of a long-slit spectroscopic study of 38 active and four normal galaxies. Stellar absorption features, continuum colours and their radial variations are analysed in an effort to characterize the stellar population in these galaxies and detect the presence of a featureless continuum underlying the starlight spectral component. Spatial variations of the equivalent widths of conspicuous absorption lines and continuum colours are detected in most galaxies. Star-forming rings, in particular, leave clear fingerprints in the equivalent widths and colour profiles. We find that the stellar populations in the inner regions of active galaxies present a variety of characteristics, and cannot be represented by a single starlight template. Dilution of the stellar lines by an underlying featureless continuum is detected in most broad-lined objects, but little or no dilution is found for most of the 20 type 2 Seyferts in the sample. Colour gradients are also ubiquitous. In particular, all but one of the observed Seyfert 2s are redder at the nucleus than in its immediate vicinity. Possible consequences of these findings are briefly outlined.

The Nature of the Optical Light in Seyfert 2 Galaxies with Polarized Continua

We investigate two chemical abundance calibrations for the narrow-line region (NLR) of active galaxies in terms of three easily observable optical emission-line ratios, namely, [O III] λλ4959, 5007/Hβ; [N II] λλ6548, 6584/Hα; and [O II] λ3727/[O III] λλ4959, 5007. The calibrations are obtained from a grid of models on the assumption that the main process responsible for the production of these lines is photoionization by a typical active galactic nucleus continuum. The elemental abundances vary with oxygen, except nitrogen, which is assumed to be a product of secondary nucleosynthesis. The calibrations are calculated for the range 8.4 ≤ 12 + log (O/H) ≤ 9.4 and tested using NLR data for a sample of Seyfert galaxies and LINERs that have H II regions in the vicinity of the nucleus. The gaseous abundances of these H II regions have been determined in previous works, and the NLR abundances are obtained on the assumption that they can be extrapolated from those of the H II regions. The calibrations work very well for the Seyfert galaxies, yielding abundance values that agree with those obtained from the H II regions, and can thus be used for quick estimates of the chemical abundances of the NLRs. For the LINERs, the calibrations yield lower values than those derived from the corresponding H II regions, suggesting that the assumptions of the models do not apply for them and that there are different physical processes at work in the NLR of the LINERs.

The Difference between the Narrow-Line Regions of Seyfert 1 and Seyfert 2 Galaxies

We use the radio axis as an indicator of the orientation of the obscuring torus in Seyfert galaxies and analyze the difference between the position angles of extended radio structures and host galaxy major axis of Seyfert 1 and Seyfert 2 galaxies. We find that Seyfert 1s are less likely to have extended radio structures along the host galaxy major axis while Seyfert 2s have these structures distributed in most directions. We also find a zone of avoidance in the distribution of position angles: both Seyfert 1s and Seyfert 2s seem to avoid close alignment between the radio axis and the host galaxy plane axis. These results are analyzed from the point of view of a model in which Seyfert 1s have their obscuring torus axis aligned preferentially along the host galaxy disk axis and Seyfert 2s have their torus axis lying at an intermediate angle between the galaxy disk and its axis.

A new Wolf-Rayet galaxy with a Seyfert nucleus

We investigate the nature of the optical continuum and stellar population in the central kiloparsec of the Seyfert 2 galaxies Mrk 348, Mrk 573, NGC 1358, and Mrk 1210 using high signal-to-noise-ratio, long-slit spectra obtained along the radio axis or along the extended high-excitation emission. These four galaxies are known to have polarized continua, including polarized broad lines in Mrk 348 and Mrk 1210, and previous studies indicate featureless continua contributions in the 20%-50% range at λ ≈ 5500 A. Nevertheless, our measurements of the equivalent widths of absorption lines and continuum ratios as a function of distance from the nuclei show no decrease of the equivalent widths (i.e., no dilution) nor blueing of the spectrum toward the nucleus, as expected if a blue, featureless continuum was present at the nucleus in the above proportions. We investigate one possibility to account for the lack of dilution: that the stellar population at the nucleus is the same as that from the surrounding bulge and dominates the nuclear light. By comparing the nuclear and the extranuclear spectra of each galaxy, we conclude that this hypothesis works for Mrk 348, NGC 1358, and Mrk 1210, for which we find stellar population contributions at the nucleus larger than 90% at all wavelengths. Our approach differs from that adopted in previous studies, where an elliptical galaxy template is used to represent the stellar population of the nucleus. Although the latter may be valid for some galaxies—as, for example, Mrk 573—in several cases the stellar population may be different from that of an elliptical galaxy. We find that a larger stellar population contribution to the nuclear spectra can play the role of the second featureless continuum source inferred from previous studies. In particular, stellar population synthesis shows that the nuclear regions of Mrk 348 and Mrk 1210 have important contributions of young to intermediate-age stars (0-108 yr) not present in templates of elliptical galaxies. In the case of Mrk 1210, this is further confirmed by the detection of a Wolf-Rayet feature in the nuclear emission-line spectrum.

Two-dimensional kinematics of the circumnuclear region of Seyfert galaxies using GMOS-IFU

This paper presents a comparative study of emission-line ratios of the narrow-line regions (NLRs) of Seyfert 1 and Seyfert 2 galaxies. It includes a literature compilation of the emission-line fluxes [O II] λ3727, [Ne III] λ3869, [O III] λ5007, and [Ne V] λ3426 as well as 60 μm continuum flux, for a sample of 52 Seyfert 1 and 68 Seyfert 2 galaxies. The distribution of the emission-line ratios [O II]/[Ne III] and [O II]/[Ne V] shows that Seyfert 1 and Seyfert 2 galaxies are statistically different: Seyfert 1 galaxies have smaller values than Seyfert 2 galaxies, indicating a higher excitation spectrum. These and other emission-line ratios are compared with sequences of models that combine different proportions of matter and ionization-bounded clouds and also with sequences of models that vary only the ionization parameter. This comparison shows that the former models better reproduce the overall distribution of emission-line ratios, indicating that Seyfert 1 galaxies have a smaller number of ionization-bounded clouds than Seyfert 2 galaxies. This difference, together with other results available in the literature, are interpreted from the point of view of four different scenarios. The most likely scenario assumes that Seyfert 1 galaxies have smaller NLRs than Seyfert 2 galaxies, possibly due to a preferential alignment of the torus axis close to the host galaxy plane axis in Seyfert 1 galaxies.