Population synthesis of HII galaxies

We study the stellar population of galaxies with active star formation, determining ages of the stellar components by means of spectral population synthesis of their absorption spectra. The data consist of optical spectra of 185 nearby ($z \leq 0.075$) emission line galaxies. They are mostly HII galaxies, but we also include some Starbursts and Seyfert 2s, for comparison purposes. They were grouped into 19 high signal-to-noise ratio template spectra, according to their continuum distribution, absorption and emission line characteristics. The templates were then synthesized with a star cluster spectral base. The synthesis results indicate that HII galaxies are typically age-composite stellar systems, presenting important contribution from generations up to as old as 500 Myr. We detect a significant contribution of populations with ages older than 1 Gyr in two groups of HII galaxies. The age distributions of stellar populations among Starbursts can vary considerably despite similarities in the emission line spectra. In the case of Seyfert 2 groups we obtain important contributions of old population, consistent with a bulge. From the diversity of star formation histories, we conclude that typical HII galaxies in the local universe are not systems presently forming their first stellar generation.Comment: 12 pages, 4 figures, MNRAS in pres

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 2's, 5 LINER's, 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, LINER's, Seyfert 2's, Starbursts of Low and High reddening, for which we create average spectral energy distributions (SED). The individual groups SED's are normalized to the $\lambda$7000\AA flux and compared, looking for similarities and differences among them.The bolometric fluxes of different types of galaxies were calculated integrating their SED's. 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 SED's.Comment: 29 pages, 13 postscript figures and 10 tables. To appear in The Astronomical Journa

Long-Term Profile Variability of Double-Peaked Emmission Lines in AGNs

An increasing number of AGNs exhibit broad, double-peaked Balmer emission lines, which arise from the outer regions of the accretion disk which fuels the AGN. The line profiles vary on timescales of 5--10 years. Our group has monitored a set of 20 double-peaked emitters for the past 8 years (longer for some objects). Here we describe a project to characterize the variability patterns of the double-peaked H alpha line profiles and compare with those of two simple models: a circular disk with a spiral arm and an elliptical disk.Comment: 2 pages, 1 figure, to appear in the proceedings of "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. T. Storchi Bergmann, L.C. Ho, and H.R. Schmit

Extended Gas in Seyfert Galaxies: Near Infrared Observations of NGC 2110 and Circinus

We present results of near--IR long-slit spectroscopy in the J and K bands of the Seyfert 2 galaxies NGC 2110 and Circinus, investigating the gaseous distribution, excitation, reddening and kinematics. In NGC 2110, the emission line ratio [FeII]/Pa beta increases towards the nucleus (to ~ 7). The nuclear [Fe II]1.257 (microns) and Pa beta lines are broader (FWHM ~ 500 km/s) than the H2 (2.121) line (FWHM ~ 300 km/s). Both these results suggest that shocks, driven by the radio jet, are an important source of excitation of [Fe II]. The H2 excitation appears to be dominated by X-rays from the nucleus. In Circinus, both [FeII]/Pa beta and H2/Br gamma decrease from ~ 2 at 4 arcsec from the nucleus to nuclear values of ~ 0.6 and ~ 1, respectively, suggesting that the starburst dominates the nuclear excitation, while the AGN dominates the excitation further out (r > 2 arcsec). For both galaxies, the gaseous kinematics are consistent with circular rotation in the plane of the disk. Our rotation curves suggest that the nucleus (identified with the peak of the IR continuum) is displaced from the kinematic centre of the galaxies. This effect has been observed previously in NGC 2110 based on the kinematics of optical emission lines, but the displacement is smaller in the infrared, suggesting the effect is related to obscuration. The continuum J-K colours of the nuclear region indicate a red stellar population in NGC 2110 and a reddened young stellar population in Circinus. Right at the nucleus of both galaxies, the colours are redder, apparently a result of hot dust emission from the inner edge of a circumnuclear torus.Comment: 11 pages, 14 figures, accepted for publication in MNRA

The Ionizing Source of the Nucleus of NGC1097

We present new observations in X-ray and optical/ultraviolet of the nucleus of NGC1097, known for the abrupt appearance of broad, double-peaked Balmer lines in its spectrum in 1991. These new observations are used to construct the spectral energy distribution (SED) of the central engine. From the SED we infer that this AGN is radio-loud and has a bolometric luminosity L_Bol ~ 10^42 erg/s, implying a low Eddington ratio of L_Bol/L_Edd ~ 10^{-4}. These results suggest that the central ionizing source is an advection-dominated accretion flow (ADAF) in the form of an ellevated structure which photoionizes an outer thin disk. We fit a simplified ADAF model to the SED and obtain limits on the values of the mass accretion rate Mdot and accretion efficiency \eta, namely Mdot/Mdot_Edd >= 10^{-3} and \eta <= 10^{-2}. We identify an energy budget problem: if the central photoionizing source is isotropic, the covering factor of the line-emitting portion of the thin accretion disk is ~ 6, i. e. the central source accounts for only 20% of the energy emitted in the double-peaked Balmer lines.Comment: 4 pages, 3 figures, to appear in the proceedings of "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. Th. Storchi Bergmann, L.C. Ho, and H.R. Schmit

A New Superwind Wolf-Rayet Galaxy Mrk 1259

We report the discovery of a starburst-driven wind (superwind) from the starburst nucleus galaxy Mrk 1259. The estimated number ratio of Wolf-Rayet (WR) to O stars amounts to ~0.09. While the nuclear emission-line region is due to usual photoionization by massive stars, the circumnuclear emission-line regions show anomalous line ratios that can be due to cooling shocks. Since the host galaxy seems to be a face-on disk galaxy and the excitation conditions of the circumnuclear emission-line regions show the spatial symmetry, we consider that we are seeing the superwind nearly from a pole-on view. Cooling shock models may explain the observed emission line ratios of the circumnuclear regions although a factor of 2 overabundance of nitrogen is necessary. All these suggest that the high-mass enhanced starburst occurred ~5X10^6 years ago in the nuclear region of Mrk 1259.Comment: To be published in the Astrophysical Journal Letters, 15 pages, 4 figure