Stefano Ciroi

Exploring Narrow-Line Seyfert 1 Galaxies through the Physical Properties of Their Hosts*

In this work we address the still open question of the nature of narrow-line Seyfert 1 galaxies (NLS1s): are they really active nuclei with lower mass black holes (BHs) than Seyfert 1 galaxies (S1s) and quasars? Our approach is based on the recently discovered physical connections between nuclear supermassive BHs and their hosting spheroids (spiral bulges or elliptical galaxies). In particular, we compare BH masses of NLS1s and S1s, analyzing the properties of their hosts by means of spectroscopic and photometric data in the optical wavelength domain. We find that NLS1s fill the low BH mass and bulge luminosity values of the MBH-MB relation, a result strongly suggesting that NLS1s are active nuclei in which less massive BHs are hosted by less massive bulges. The correlation is good, with a relatively small scatter fitting simultaneously NLS1s, S1s, and quasars. On the other hand, NLS1s seem to share the same stellar velocity dispersion range as S1s in the MBH-σ* relation, indicating that NLS1s have a smaller BH/bulge mass ratio than S1s. These two conflicting results support in any case the idea that NLS1s could be young S1s. Finally, we do not confirm the significantly nonlinear BH-bulge relation claimed by some authors.

The carbon-rich type Ic SN 2007gr: the photospheric phase

The first 2 months of spectroscopic and photometric monitoring of the nearby Type Ic SN 2007gr are presented. The very early discovery (less than 5 days after the explosion) and the relatively short distance of the host galaxy motivated an extensive observational campaign. SN 2007gr shows an average peak luminosity but unusually narrow spectral lines and an almost flat photospheric velocity profile. The detection of prominent carbon features in the spectra is shown and suggests a wide range in carbon abundance in stripped-envelope supernovae. SN 2007gr may be an important piece in the puzzle of the observed diversity of CC SNe.

Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad-Line Active Galactic Nuclei

In order to contribute to the general effort aiming at the improvement of our knowledge about the physical conditions within the broad-line regions (BLRs) of active galactic nuclei (AGNs), here we present the results achieved by our analysis of the spectral properties of a sample of 90 broad-line-emitting sources, collected from the Sloan Digital Sky Survey database. By focusing our attention mainly on the Balmer series of hydrogen emission lines, which is the dominant feature in the optical wavelength range of many BLR spectra, we extracted several flux and profile measurements, which we related to other source properties, such as optical continuum luminosity, inferred black hole mass, and accretion rate. Using the Boltzmann plot method to investigate the Balmer-line flux ratios as a function of the line profiles, we found that AGNs that emit broader lines typically have larger Hα/Hβ and smaller Hγ/Hβ and Hδ/Hβ line ratios. With the help of some recent investigations, we model the structure of the BLR, and we study the influence of the accretion process on the properties of BLR plasma.

Parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

Flat-spectrum radio-loud Narrow-Line Seyfert 1 galaxies (NLS1s) are a recently discovered class of

Balmer Emission Line Profiles and Complex Properties of Broad-Line Regions in Active Galactic Nuclei

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X-RAY GRATING OBSERVATIONS OF RECURRENT NOVA T PYXIDIS DURING THE 2011 OUTBURST

-ray emitting Active Galactic Nuclei (AGN), that exhibit some blazar-like properties which are explained with the presence of a relativistic jet viewed at small angles. When blazars are observed at larger angles they appear as radio-galaxies, and we expect to observe an analogue parent population for beamed NLS1s. However, the number of known NLS1s with the jet viewed at large angles is not enough. Therefore, we tried to understand the origin of this deficit. Current hypotheses about the nature of parent sources are steep-spectrum radio-loud NLS1s, radio-quiet NLS1s and disk-hosted radio-galaxies. To test these hypotheses we built three samples of candidate sources plus a control sample, and calculated their black hole mass and Eddington ratio using their optical spectra. We then performed a Kolmogorov-Smirnov statistical test to investigate the compatibility of our different samples with a beamed population. Our results indicate that, when the inclination angle increases, a beamed source appears as a steep-spectrum radio-loud NLS1, or possibly even as a disk-hosted radio-galaxy with low black hole mass and high Eddington ratio. Further investigations, involving larger complete samples and observations at radio frequency, are needed to understand the incidence of disk-hosted radio-galaxies in the parent population, and to assess whether radio-quiet NLS1s can play a role, as well.

Spectral properties of the narrow-line region in Seyfert galaxies selected from the SDSS-DR7

ABSTRACTIn this work we analyze a sample of AGN spectra, selected from the 6 th Data Release of the SloanDigital Sky Survey, exploiting a generalized technique of line profile analysis, designed to take intoaccount the whole profiles of their broad emission lines. We find that the line profile broadeningfunctions result from a complex structure, but we may be able to infer some constraints about therole of the geometrical factor, thus improving our ability to estimate AGN properties and their relationwith the host galaxy. Our results suggest that flattening and inclination within the structure of theBroad Line Region (BLR) must be taken into account. We detect low inclinations of the BLR motionplane with respect to our line of sight, typically i ≤ 20 ◦ , with a geometrical effect which generallydecreases as the line profile becomes broader.Subject headings: galaxies: active — galaxies: nuclei — galaxies: Seyfert — line: profiles — quasars:emission lines 1. INTRODUCTION During the past decades, spectroscopic observationsprovided a fundamental starting point for our under-standing of the physical processes in Active GalacticNuclei (AGN). In particular, the study of broad emis-sion lines, characterizing the spectra of many objectsat different wavelengths, is a key feature to penetratetheir intrinsic properties (Osterbrock 1989). Unfortu-nately, a correct interpretation of the observations re-quires to collect information in various spectral rangesand for long monitoring times, a task which is cur-rently possible only in a fairly small number of cases.While much work has been devoted to calibrate empir-ical methods which should be able to deal with largersamples (see e. g. Kaspi et al. 2000, 2005; Bentz et al.2006), the fundamentally unknown structure in the coreof AGN influences the physical interpretation of spec-tra with a geometrical factor, whose value depends onthe structure and orientation of the source (see for in-stance Vestergaard et al. 2000; Niko lajuk et al. 2005;Marziani et al. 2006; Decarli et al. 2008a).The prominent broad emission lines, visible in the spec-tra of many AGN, originate close to the central powersource, in the so called Broad Line Region (BLR). Be-cause of its small distance from the power source, theBLR is in strong interaction with the radiation field pro-duced by the central engine and with its gravitationalforces. Many interesting details about the physics of pro-cesses that are taking place within AGN can be identi-fied in the signal of the BLR, but they suffer from a stillmissing complete picture of the complex kinematical andthermodynamical properties of the line emitting plasma.Since it is not yet possible to directly observe the spatial

Silicates in D-Type Symbiotic Stars: An Infrared Space Observatory Overview

The recurrent nova T Pyx was observed with the X-ray gratings of Chandra and XMM-Newton, 210 and 235?days, respectively, after the discovery of the 2011 April 14 outburst. The X-ray spectra show prominent emission lines of C, N, and O, with broadening corresponding to an FWHM of ~2000-3000?km s?1, and line ratios consistent with high-density plasma in collisional ionization equilibrium. On day 210 we also measured soft X-ray continuum emission that appears to be consistent with a white dwarf (WD) atmosphere at a temperature ~420,000?K, partially obscured by anisotropic, optically thick ejecta. The X-ray continuum emission is modulated with the photometric and spectroscopic period observed in quiescence. The continuum at day 235 indicated a WD atmosphere at a consistent effective temperature of 25?days earlier, but with a lower flux. The effective temperature indicates a mass of ~1 M ?. The conclusion of partial WD obscuration is supported by the complex geometry of non-spherically symmetric ejecta confirmed in recent optical spectra obtained with the Southern African Large Telescope in November and December of 2012. These spectra exhibited prominent [O III] nebular lines with velocity structures typical of bipolar ejecta.

Compact steep-spectrum sources as the parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

Although the properties of the narrow-line region (NLR) of active galactic nuclei (AGN) have been deeply studied by many authors in the past three decades, many questions are still open. The main goal of this work is to explore the NLR of Seyfert galaxies by collecting a large statistical spectroscopic sample of Seyfert 2 and Intermediate-type Seyfert galaxies having a high signal-to-noise ratio in order to take advantage of a high number of emission lines to be accurately measured. 2153 Seyfert 2 and 521 Intermediate-type Seyfert spectra were selected from Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) with a diagnostic diagram based on the oxygen emission-line ratios. All the emission lines, broad components included, were measured by means of a self-developed code, after the subtraction of the stellar component. Physical parameters, such as internal reddening, ionization parameter, temperature, density, gas and stellar velocity dispersion were determined for each object. Furthermore, we estimated mass and radius of the NLR, kinetic energy of the ionized gas and black hole accretion rate. From the emission-line analysis and the estimated physical properties, it appears that the NLR is similar in Seyfert 2 and Intermediate-Seyfert galaxies. The only differences, lower extinction, gas kinematics in general not dominated by the host galaxy gravitational potential and higher percentage of [O iii]λ5007 blue asymmetries in Intermediate-Seyfert, can be ascribed to an effect of inclination of our line of sight with respect to the torus axis.

The origin of gas in extended narrow-line regions of nearby Seyfert galaxies – I. NGC 7212

We investigate the IR spectral features of a sample of D-type symbiotic stars. Analyzing unexploited ISO-SWS data, deriving the basic observational parameters of dust bands and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physic. We find strong amorphous silicate emission bands at 10 micron and 18 micron in a large fraction of the sample. The analysis of the 10 micron band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelength of the 10 and 18 micron dust bands is found. By the modeling of IR spectral lines we investigate also dust grains conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO moleculae, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-infrared and mm observations.We investigate the IR spectral features of a sample of D-type symbiotic stars in order to constrain the emitting properties of coupled dust-gas particles across the whole system. In particular, by analyzing unexploited ISO Short Wavelength Spectrometer data, deriving the basic observational parameters of dust bands, and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physics. We find strong amorphous silicate emission bands at ~10 and ~18 ?m in a large fraction of the sample. The analysis of the ~10 ?m band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelengths of the ~10 and ~18 ?m dust bands is found. By modeling IR spectral lines we also investigate dust grain conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO molecules, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-IR and millimeter observations.