Paola Marziani

The Close Environment of Seyfert Galaxies and Its Implication for Unification Models

In this Letter, we present a statistical analysis of the circumgalactic environment of nearby Seyfert galaxies based on a computer-aided search of companion galaxies on the Digitized Sky Survey. We defined a sample of 72 nearby Seyfert 1 galaxies (redshift 0.007≤z≤0.034) and a sample of 60 Seyfert 2 galaxies (0.007≤z≤0.020), which include only high galactic latitude objects. In addition, we built two control samples of nonactive galaxies that match the number of sample members, the redshift, morphological type, and diameter distribution of the Seyfert 1 and Seyfert 2 galaxy samples separately. We stress how our sample selection introduces important methodological improvements that avoid several sources of strong bias. An intrinsic difference between the environment of Seyfert 1 galaxies and that of Seyfert 2 galaxies, suggested by previous work, is confirmed as statistically significant. For Seyfert 2 galaxies, we find a significant excess of large companions (D10 kpc) within a search radius 100 kpc of projected linear distance as well as within a search radius equal to 3 times the diameter DS of each Seyfert galaxy. For Seyfert 1 galaxies, there is no clear evidence of any excess of companion galaxies either within 100 kpc or within 3DS. For all samples, the number of companions that are actually counted within a search radius of 3DS is a factor of ≈2 above the expectation values derived from the number density of galaxies over the 1 deg2 fields that are centered on the sample galaxies, suggesting a markedly non-Poissonian distribution for galaxies on scales 100 kpc. This difference in environment is not compatible with the simplest formulation of the unification model for Seyfert galaxies: both type 1 and type 2 should be intrinsically alike, the only difference being the result of the orientation of an obscuring torus. We propose an alternative formulation.

On the Origin of Broad Fe Kα and H I Hα Lines in Active Galactic Nuclei

We examine the properties of the Fe emission lines that arise near 6.4 keV in the ASCA spectra of AGN. Our emphasis is on the Seyfert 1 galaxies where broad and apparently complex Fe K alpha emission is observed. We consider various origins for the line but focus on the pros and cons for line emitting accretion disk models. We develop a simple model of an illuminated disk capable of producing both X-ray and optical lines from a disk. The model is able to reproduce the observed Fe K alpha FWHM ratio as well as the radii of maximum emissivity implied by the profile redshifts. The overall profile shapes however do not fit well the predictions of our disk illumination model nor do we derive always consistent disk inclinations for the two lines. We conclude that the evidence for and against an accretion disk origin for the Fe K alpha emission is equal at best. The bulk of the data requires a very disparate set of line fits which shed little light on a coherent physical model. We briefly consider alternatives to disk emission models and show that a simple bicone model can reproduce the FE line profiles equally well.We examine the properties of the Fe emission lines that arise near 6.4 keV in the ASCA spectra of AGNs. Our emphasis is on the Seyfert 1 galaxies where broad and apparently complex Fe Kα emission is observed. We consider various origins for the line but focus on the pros and cons for line-emitting accretion disk models. We develop a simple model of an illuminated disk capable of producing both X-ray and optical lines. The model is able to reproduce the observed Fe Kα FWHM ratio as well as the radii of maximum emissivity implied by the profile redshifts. The overall profile shapes, however, do not fit well the predictions of our disk illumination model nor do we derive always consistent disk inclinations for the two lines. We conclude that the evidence for and against an accretion disk origin for the Fe Kα emission is equivocal. The bulk of the data requires a very disparate set of line fits, shedding little light on a coherent physical model. We briefly consider alternatives to disk-emission and show that a simple bicone model can reproduce the Fe line profiles equally well.

Fifty Years of Quasars: Current Impressions and Future Perspectives

Contributors to the previous chapters describe an impressive body of research carried out over the past 50 years. One can argue that there is now considerable evidence supporting the hypothesis that the quasar phenomenon is driven by accretion onto a supermassive object. Hard X-ray emission may be the most direct signature of that accretion process and perhaps the only universal property shared by all types of AGN. This possibility brings us closer to an operational definition of the quasar phenomenon and therefore may answer the question posed in the Introduction.

Asymmetry of the C IV λ 1549 Å and [O III] λλ 4959, 5007 Å Lines in a Sample of RQ and RL AGN

Here we investigate the asymmetry of the C IV λ 1549 A line in a sample of Radio Quiet (RQ) and Radio Loud (RL) Active Galactic Nuclei (AGN), in order to find signature of an outflow in C IV λ 1549 A emission region. We apply two‐component Gaussian analysis to fit the lines. We consider the parameters of the components (emission and absorption), separately in Radio Loud and Radio Quiet AGN, and we compared those parameters with parameters of the fits of [O III] λλ 4959, 5007 A lines, trying to see if there is any kinematical correlation between the emission regions (HIL BLR and NLR) where C IV λ 1549 A and [O III] λλ 4959, 5007 A lines are formed.

Quasar evolution: black hole mass and accretion rate determination

Accurate measurements of emission line properties are crucial to understand the physics of the broad line region in quasars. This region consists of warm gas that is closest to the quasar central engine and has not been spatially resolved for almost all sources. We present here an analysis of optical and IR data for a large sample of quasars, covering the Hi Hβ spectral region in the redshift range 0 z 2.5. Spectra were interpreted within the framework of the the so-called “eigenvector 1” parameter space, which can be viewed as a tentative H-R diagram for quasars. We stress the lack of spectral evolution in the low ionization lines of quasars, with prominent Feii emission also at z 2. We also show how selection effects influence the ability to find quasars radiating at low Eddington ratio in flux-limited surveys. The quasar similarity at different redshift is probably due to the absence of super-Eddington radiators (at least within the caveats of black hole mass and Eddington ratio determination discussed in this paper) as well as to the limited Eddington ratio range within which quasars seem to radiate.

An Introduction to 50 Years of Research on Quasars

We are approaching the 50th anniversary of the discovery of quasars. Those old enough to have been cognizant of astronomy in 1962–1963 can remember the sense of excitement connected with this finding. There was talk of a major new constituent of the universe. The excitement of the discovery was palpable even to one of us (the most senior of the editors) who was then a high school teenager.

The Circum-Galactic Environment of LINERs and Bright IRAS Galaxies

We compared the environment of LINERs and Bright IRAS galaxies with those of Seyfert 1, Seyfert 2, and non-active galaxies. Interacting and merging systems are more frequently found among LINERs and Bright IRAS galaxies than among Seyfert 1 and normal galaxies. The environment of LINERs and Bright IRAS galaxies resembles that of Seyfert 2 galaxies. A notable exception are LINERs showing a broad component in Hα, whose environment is apparently similar to that of Seyfert 1s.

Host Galaxies and Environment of Narrow Line Seyfert 1 Nuclei

We compared the environment and host galaxies of “Narrow Line” Seyfert 1 with those of Sy1, Sy2, and non-active galaxies. We found that NLSyls are hosted in smaller galaxies than Sy1s. This result supports the idea of NLSy1s as Sy1s with higher Eddington ratio. NLSy1 hosts may be more isolated and farther away from bright companions than Sy2s and normal galaxies.