A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey

We revisited the spectroscopic characteristics of narrow-line Seyfert 1 galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7) public archive. We confirm that NLS1s are mostly characterized by Balmer lines with Lorentzian profiles, lower black hole masses and higher Eddington ratios than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common properties. Strong Fe II emission does not seem to be a distinctive property of NLS1s, as low values of Fe II/H$\beta$ are equally observed in these AGNs. Our data indicate that Fe II and Ca II kinematics are consistent with the one of H$\beta$. On the contrary, O I $\lambda$8446 seems to be systematically narrower and it is likely emitted by gas of the broad-line region more distant from the ionizing source and showing different physical properties. Finally, almost all NLS1s of our sample show radial motions of the narrow-line region highly-ionised gas. The mechanism responsible for this effect is not yet clear, but there are hints that very fast outflows require high continuum luminosities (> $10^{44}$ erg/s) or high Eddington ratios (log(L$_{\rm bol}$/L$_{\rm Edd}$) > -0.1).Comment: 27 pages, 31 figures, 4 tables, accepted for publication in MNRA

[O III] line properties in two samples of radio-emitting narrow-line Seyfert 1 galaxies

The [O III] $\lambda\lambda$ 4959,5007 lines are a useful proxy to test the kinematic of the narrow-line region (NLR) in active galactic nuclei (AGN). In AGN, and particularly in narrow-line Seyfert 1 galaxies (NLS1s) these lines often show few peculiar features, such as blue wings, often interpreted as outflowing component, and a shift $-$ typically toward lower wavelengths $-$ of the whole spectroscopic feature in some exceptional sources, the so-called blue outliers, which are often associated to strong winds. We investigated the incidence of these peculiarities in two samples of radio-emitting NLS1s, one radio-loud and one radio-quiet. We also studied a few correlations between the observational properties of the [O III] lines and those of the AGN. Our aim was to understand the difference between radio-quiet and radio-loud NLS1s, which may in turn provide useful information on the jet formation mechanism. We find that the NLR gas is much more perturbed in radio-loud than in radio-quiet NLS1s. In particular the NLR dynamics in $\gamma$-ray emitting NLS1s appears to be highly disturbed, and this might be a consequence of interaction with the relativistic jet. The less frequently perturbed NLR in radio-quiet NLS1s suggests instead that these sources likely do not harbor a fully developed relativistic jet. Nonetheless blue-outliers in radio-quiet NLS1s are observed, and we interpret them as a product of strong winds.Comment: 16 pages, 13 figures, 7 tables, accepted for publication on Astronomy & Astrophysic

Are Boltzmann Plots of Hydrogen Balmer lines a tool for identifying a subclass of S1 AGN?

It is becoming clear that we can define two different types of nearby AGN belonging to the Seyfert 1 class (S1), on the basis of the match of the intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP). These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are characterized, in first approximation, by Broad Line Regions (BLR) with different structural and physical properties. In this communication, we show that these features can be well pointed out by a multi-wavelength analysis of the continuum and of the broad recombination Hydrogen lines, that we carry out on a sample of objects detected at optical and X-ray frequencies. The investigation is addressed to verify whether BP-S1 are the ideal candidates for the study of the kinematical and structural properties of the BLR, in order to derive reliable estimates of the mass of their central engine and to constrain the properties of their nuclear continuum spectrum.Comment: 26 pages, 4 figures (1 multi-paged). Accepted for publication on Advances in Space Research. Contribution to the IX SCSLS

Exploring NLS1 through the physical properties of their hosts

In this work we aim at addressing the still open question about the nature of Narrow-Line Seyfert 1 (NLS1) galaxies: are they really active nuclei with lower mass Black-Holes (BHs) than Seyfert 1 (S1) and quasars? Our approach is based on the recently discovered physical connections between nuclear supermassive BHs and their hosting spheroids (spiral bulges or ellipticals). 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 BH mass - bulge magnitude relation, a result strongly suggesting that NLS1s are active nuclei where 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 of S1s in the BH mass - stellar velocity dispersion 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 non linear BH--bulge relation claimed by some authors

X-Ray Grating Observations of Recurrent Nova T Pyxidis During The 2011 Outburst

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 a full width at half maximum of ~2000-3000 km/s, 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 solar mass. 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 (SALT) in November and December of 2012. These spectra exhibited prominent [O III] nebular lines with velocity structures typical of bipolar ejecta.Comment: Accepted to ApJ 2013 October 23, 14 pages, 9 figures, 3 table

Nuclear activity and star formation properties of Seyfert 2 galaxies

In order to characterize the amount of recent or ongoing stellar formation in the circumnuclear region of active galaxies on a statistically sound basis, we have studied the stellar component of the nuclear spectra in three different samples of galaxies, namely Seyfert 2 galaxies (hereafter S2G), star-forming galaxies (SFG) and passive normal galaxies (NG), i.e., no emission lines observed, using Sloan Digital Sky Survey data (SDSS) (Adelman-McCarthy, 2008). The stellar component of the observed spectra has been extracted using STARLIGHT (Cid Fernandes et al., 2004), which fits an observed spectrum with a model (template) spectrum obtained by combining a library of pre-defined simple stellar populations spectra, with distinct ages and metallicities. The resulting template spectra for the different samples of galaxies have been compared to determine the features of the stellar emission component and to evaluate the presence and intensity of the star formation in the nuclear regions of different families of galaxies. From a first qualitative analysis it results that the shape of the Spectral Energy Distribution (SED) of S2G and NG is very similar, while that of SFG is characterized by a strong blue excess. The presence of the 4000 A break in the spectra of S2G and NG together with the lack of a strong blue continuum clearly indicate the absence of ongoing star formation in the circumnuclear regions of S2G and obviously of NG. Anyway traces of a recent star formation history are evident in the spectra of S2G galaxies, which show a 4000 A break systematically shallower than in NG.Comment: Proceeding of the VII Serbian Conference on Spectral Line Shapes in Astrophysic