Deborah Dultzin-Hacyan

An Optical Spectroscopic Atlas of Low-Redshift Active Galactic Nuclei

We present a spectral atlas of the Hβ region for 215 type 1 AGNs (luminous Seyfert 1/radio galaxy nuclei and low-z quasars) up to z ≈ 0.8. Line profiles and measures were derived from the database of intermediate resolution spectra (R 1000) with average continuum level S/N ratio ≈30. Parameters including rest frame equivalent width and FWHM are provided for the Fe IIopt blend at λ4570, Hβ, He II λ4686, and the [O III] λλ4959, 5007 emission lines. We extract clean broad component Hβ profiles and provide wavelength measurements at 0, 1/4, 1/2, 3/4, and 0.9 peak intensity levels in order to permit a quantitative definition of the Hβ broad component for statistical studies. We also discuss sources of uncertainty, selection effects, and biases in our sample. The data are especially important for tests of the eigenvector 1 parameter space occupation and correlation. We show that the I Zw 1 template Fe IIopt spectrum reproduces well the observed Fe IIopt emission for a wide range of line width and strength. A detailed analysis of the data within the eigenvector 1 context is deferred to a companion paper.

X-ray nature of the LINER nuclear sources

We report the results from an homogeneous analysis of the X-ray (Chandra-ACIS) data available for a sample of 51 LINER galaxies selected from the catalogue by Carrillo et al. (1999) and representative of the population of bright LINER sources. The nuclear X-ray morphology has been classified attending to their nuclear compactness in the hard band (4.5-8.0 keV) into 2 categories: Active Galactic Nuclei (AGN) candidates (with a clearly identified unresolved nuclear source) and Starburst (SB) candidates (without a clear nuclear source). 60% of the total sample are classified as AGNs, with a median luminosity of LX(2-10 keV)=2.5 x 10^(40)erg/s, which is an order of magnitude higher than that for SB-like nuclei. The spectral fitting allows to conclude that most of the objects need a non-negligible power-law contribution. When no spectral fitting can be performed (data with low signal-to-noise ratio), the Color-Color diagrams allow us to roughly estimate physical parameters such as column density, temperature of the thermal model or spectral index for a power-law and therefore to better constrain the origin of the X-ray emission. All together the X-ray morphology, the spectra and the Color-Color diagrams allow us to conclude that a high percentage of LINER galaxies, at least ~60%, could host AGN nuclei, although contributions from High Mass X-ray Binaries or Ultra-luminous X-ray sources cannot be ruled out for some galaxies.

A Multiwavelength Study of Stephan's Quintet

Stephans Quintet (SQ) is a compact group that we find in an atypical moment when a high-velocity intruder is passing through it. The intrusion is particularly interesting because a previous intruder had stripped most of the gas from the group members. This debris field was shocked in the ongoing collision with the new intruder. This evolutionary history agrees well with observations and explains how a strongly interacting system can show low levels of star formation. We present new multiwavelength data including previously unpublished ROSAT X-ray, Hα interference filter/Fabry-Perot, ISO MIR/FIR, and radio line and continuum images. These observations and previously published data provide new insights, as well as support for some previous hypotheses. (1) Fabry-Perot and H I velocities allow us to unambiguously distinguish between gas associated with SQ and the new intruder. (2) Most detected emission regions are found in the remnant interstellar medium (ISM) of the new intruder, which allows us to infer its size and present physical state. (3) The few emission regions associated with the stripped ISM of SQ include the best candidate tidal dwarf galaxy. (4) Multiwavelength data suggest that strong MIR/FIR emission from the Seyfert 2 nucleus of NGC 7319 comes from dust heated directly by a power-law continuum rather than a starburst. (5) The correspondence between extended X-ray/radio continuum/forbidden optical emission confirms the existence of a large scale shock in SQ. (6) We confirm the presence of two stripped spiral members in the process of transformation into E/S0 morphology. Finally (7) observations are consistent with the idea that the collision in SQ is ongoing with possible detection of H II region ablation and Rayleigh-Taylor instabilities.

Radio-loud Active Galactic Nuclei in the Context of the Eigenvector 1 Parameter Space

We consider the properties of radio-loud (RL) active galactic nuclei in the context of the eigenvector 1 (E1) parameter space. RL sources show a restricted E1 parameter space occupation relative to the radio-quiet (RQ) majority. The Fanaroff-Riley II parent population of relatively unboosted RL sources (median radio/optical flux ratio ~490) shows the most restricted occupation. RL sources have different broad-line properties (and inferred black hole masses and Eddington ratios). FWHM H? for the broad-line component in RL sources are at least twice as large as in the RQ majority. The average broad Fe II ?4570 emission-line strength is also about half that for RQ sources. Our sample suggests that the RL cutoff occurs near RK ? 70 or log P6 cm ~ 32.0 ergs s-1 Hz-1. Sources below this cutoff are RQ, although we cannot rule out the existence of a distinct intermediate population. We show that the Doppler-boosted core-dominated RL sources (median flux ratio ~1000) lie toward smaller FWHM(H?BC) and stronger Fe IIopt in E1, as expected if the lines arise in an accretion disk. Our subsample of superluminal sources, with orientation inferred from the synchrotron self-Compton model, reinforce this general E1 trend and allow us to estimate the role of source orientation in driving E1 domain occupation.

A Three-dimensional Study of the Local Environment of Bright IRAS Galaxies: The Active Galactic Nucleus-Starburst Connection

We present a three-dimensional study of the local (≤100 h-1 kpc) and the large scale (≤1 h-1 Mpc) environment of bright IRAS balaxies (BIRGs). For this purpose we use 87 BIRGs located at high Galactic latitudes (with 0.008 ≤ z ≤ 0.018), as well as a control sample of nonactive galaxies having the same morphological, redshift, and diameter size distributions as the corresponding BIRG sample. Using the Center for Astrophysics and the Southern Sky Redshift Survey galaxy catalogs (mb 15.5), as well as our own spectroscopic observations (mb 19.0), for a subsample of the original BIRG sample, we find that the fraction of BIRGs with a close neighbor is significantly higher than that of their control sample. Comparing with a related analysis of Seyfert 1 and Seyfert 2 galaxies by Koulouridis and coworkers, we find that BIRGs have a similar environment to that of Seyfert 2 galaxies, although the fraction of BIRGs with a bright, close neighbor is even higher than that for Seyfert 2 galaxies. An additional analysis of the relation between FIR colors and the type of activity of each BIRG shows a significant difference between the colors of strongly interacting and noninteracting starbursts and a resemblance between the colors of noninteracting starbursts and Seyfert 2 galaxies. Our results support the view that close interactions can drive molecular clouds toward the galactic center, triggering starburst activity and obscuring the nuclear activity. When the close neighbor moves away, starburst activity is reduced with the simultaneous appearance of an obscured (type 2) active galactic nucleus (AGN). Finally, the complete disentanglement of the pair gives birth to an unobscured (type 1) AGN.

Nuclear obscuration and scattering in Seyfert 2 galaxies

We study the relation between gaseous ab- sorbing column density (NH), infrared colors and de- tectability of the broad lines in a large sample of Seyfert 2 galaxies(Sy2s). We confirm that Sy2s without polarized broad lines tend to have cooler 60µm/25µm colors; this correlation was previously ascribed to the effect of obscu- ration towards the nuclear region. We find some evidence that Sy2s without polarized broad lines have larger ab- sorbing column density (NH) and that a fraction of them are characterized by dust lanes crossing their nuclei. How- ever, we find that the IR colors do not correlate with NH, in disagreement with the obscuration scenario. Also, Sy2s without polarized broad lines follow the same radio-FIR relation as normal and starburst galaxies, at variance with Sy2s with polarized broad lines. These results indicate that the lack of broad lines in the polarized spectrum of Sy2s is mostly due to the contribution/dilution from the host galaxy or from a circumnuclear starburst, though at a lower extent the obscuration toward the nuclear region also plays a role.

SDSS J1130+0058 an X-shaped radio source with double-peaked low-ionization emission lines: a binary black hole system?

In this paper, we study the object SDSS J1130+0058 which is the only active galactic nuclei (AGN) known to have both double-peaked low-ionization broad emission lines and X-shaped radio structures. Emission from an accretion disc can reproduce the double-peaked line profile of broad Ha, but not the radio structure. Under the accretion disc model, the period of the inner emission-line region is about 230 yr. Using a new method to subtract the stellar component from the data of the Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4), we obtain an internal reddening factor which is less than previously found. The implied smaller amount of dust disfavours the backflow model for the X-shaped radio structure. The presence of a binary black hole (BBH) system is the most natural way to explain both the optical and radio properties of this AGN. Under the assumption of the BBH model, we can estimate the BBH system has a separation of less than 0.04 pc with a period less than 59 yr; this may pose some problem to the emission-line region (BLR) sizes, still we conclude that the BBH model is favoured on the basis of the present limited information.

The sizes of broad emission line regions and black hole masses of double-peaked broad low-ionization emission line objects

In this paper, the sizes of the broad emission line regions (BLRs) and black hole (BH) masses of double-peaked broad low-ionization emission line emitters (DBP emitters) are compared using different methods: virial BH masses versus BH masses from stellar velocity dispersions, the size of BLRs from the continuum luminosity versus the size of BLRs from the accretion disc model. First, the virial BH masses of DBP emitters estimated by the continuum luminosity and linewidth of broad Hβ are about six times (a much larger value, if including another DBP emitters, of which the stellar velocity dispersions are traced by the linewidths of narrow emission lines) larger than the BH masses estimated from the relation MBH‐σ which is a more accurate relation to estimate BH masses. Second, the sizes of the BLRs of DBP emitters estimated by the empirical relation of RBLR‐L 5100 A are about three times (a much larger value, if including another DBP emitters, of which the stellar velocity dispersions are traced by the linewidths of narrow emission lines) larger than the mean flux-weighted sizes of BLRs of DBP emitters estimated by the accretion disc model. The higher electron density of BLRs of DBP emitters would be the main reason which leads to smaller size of BLRs than the predicted value from the continuum luminosity.

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.

Supermassive Black Holes in Quasars

Computing the basic accretion parameters for the supermassive black holes expected to be present in quasars is still a major challenge. In this paper we stress how a systematization of observational properties through the so‐called “eigenvector 1” of quasars helps to develop a clearer view of the structure and dynamics of the Broad Line Region. “Eigenvector 1”‐based results also provide guidelines for more reliable estimates of the black hole mass and Eddington ratio over a wide redshift range, 0 ≲ z ≲ 2.5. We summarize the results of computations for a sample of ≈ 300 low and intermediate redshift quasars, and we suggest that black hole masses may not generally exceed ≈ 5 ⋅ 109 M⊙. We also found no convincing evidence of sources radiating above the Eddington limit.