Broad-line region physical conditions along the quasar eigenvector 1 sequence (original) (raw)
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Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
The Astrophysical …, 2006
We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ∼ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGN) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA and ROSAT data where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to -2errors as large as a factor of 2 for individual quasars. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.
New Constraints on the Quasar Broad Emission Line Region
The Astrophysical Journal, 2012
We demonstrate a new technique for determining the physical conditions of the broad-line-emitting gas in quasars, using near-infrared hydrogen emission lines. Unlike higher ionization species, hydrogen is an efficient line emitter for a very wide range of photoionization conditions, and the observed line ratios depend strongly on the density and photoionization state of the gas present. A locally optimally emitting cloud model of the broad emission line region was compared to measured emission lines of four nearby (z ≈ 0.2) quasars that have optical and NIR spectra of sufficient signal to noise to measure their Paschen lines. The model provides a good fit to three of the objects, and a fair fit to the fourth object, an ultraluminous infrared galaxy. We find that low-incident-ionizing fluxes (Φ H < 10 18 cm −2 s −1 ) and high gas densities (n H > 10 12 cm −3 ) are required to reproduce the observed hydrogen emission line ratios. This analysis demonstrates that the use of composite spectra in photoionization modeling is inappropriate; models must be fitted to the individual spectra of quasars.
Detailed characterization of Hβ emission line profile in low- z SDSS quasars
Monthly Notices of the Royal Astronomical Society, 2010
ABSTRACT We explore the properties of the Hbeta emission line profile in a large, homogeneous and bright sample of N ~ 470 low-redshift quasars extracted from Sloan Digital Sky Survey (Data Release 5). We approach the investigation from two complementary directions: composite/median spectra and a set of line diagnostic measures (asymmetry index, centroid shift and kurtosis) in individual quasars. The project is developed and presented in the framework of the so-called 4D Eigenvector 1 (4DE1) parameter space, with a focus on its optical dimensions, full width at half-maximum of broad Hbeta [FWHM(Hbeta)] and the relative strength of optical FeII [RFeII ≡ W(FeII4434-4684 Å)/W(Hbeta)]. We reenforce the conclusion that not all quasars are alike and spectroscopically they do not distribute randomly about an average typical optical spectrum. Our results give further support to the concept of two populations A and B [narrower and broader than 4000kms-1 FWHM(Hbeta), respectively] that emerged in the context of 4DE1 space. The broad Hbeta profiles in composite spectra of Population A sources are best described by a Lorentzian and in Population B by a double Gaussian model. Moreover, high- and low-accretion sources (an alternative view of the Population A/B concept) not only show significant differences in terms of black hole (BH) and Eddington ratio Lbol/LEdd, but they also show distinct properties in terms of line asymmetry, shift and shapes. We finally suggest that a potential refinement of the 4DE1 space can be provided by separating two populations of quasars at RFeII ~ 0.50 rather than at FWHM(Hbeta) = 4000kms-1. Concomitantly, the asymmetry and centroid shift profile measures at 1/4 fractional intensity can be reasonable surrogates for the FWHM(Hbeta) dimension of the current 4DE1.
Our Search for an HR Diagram of Quasars
Revista Mexicana de …, 2008
El espacio de parámetros conocido como 4DE1 (Eigenvector 1 en cuatro dimenciones) fue introducido hace siete años en un intento de representar las propiedades espectroscópicas en multifrecuencias de los cuasares. Este espacio de diagnóstico ha demoastrado ser el más adecuado para intentar unificar la diversidad de AGNs con líneas anchas. Aqui reportamos que el poder de diagnóstico del espacio de parámetros 4DE1 se confirma usando espectrosópticos tomados del SDSS, espectros UV del HST y datos de rayos X del satelite XMM. La introducción del concepto de Poblaciónes A y B, continua brindandonos una maneraútil de entender la diversidad de los cuasares. La gran mayoria de los objetos radio callados son de población A (FWHM Hβ≤ 4000 km s −1 ) y tienen altas tasas de acrecion y relativamente bajas masas del Hoyo Negro nuclear. Son potentes emisores de FeII, del llamado exceso en rayos X suaves, y muestran corrimientos al azul en los perfiles de las lineas de CIV. Los objetos de población B (FWHM Hβ> 4000 km s −1 ) incluyen a la mayoria de los objetos radio fuertes, con mayores masas del Hoyo Negro y bajas tasas de acrecion. Estos muestran debil (o nula) emisión de FeII, del exceso en rayos X suaves y de corrimientos al azul de las lineas de CIV.
Mid-infrared spectra of optically-selected type 2 quasars
Type 2 quasars are luminous Active Galactic Nuclei whose central engines are seen through large amounts of gas and dust. We present Spitzer spectra of twelve type 2 quasars selected on the basis of their optical emission line properties. Within this sample, we find a surprising diversity of spectra, from those that are featureless to those showing strong PAH emission, deep silicate absorption at 10µm, hydrocarbon absorption, high-ionization emission lines and H 2 rotational emission lines. About half of the objects in the sample are likely Compton-thick, including the two with the deepest Si absorption. The median star-formation luminosity of the objects in our sample measured from the strength of the PAH features is 5 × 10 11 L ⊙ , much higher than for field galaxies or for any other AGN sample, but similar to other samples of type 2 quasars. This suggests an evolutionary link between obscured quasars and peak star formation activity in the host galaxy. Despite the high level of star formation, the bolometric output is dominated by the quasar in all cases. For a given strength of 10µm Si absorption, ULIRGs are significantly colder than are type 2 quasars (their F ν [14.5µm]/F ν [27.5µm] ratio is 0.5 dex lower), perhaps reflecting different obscuration geometries in these sources. We find that the appearance of the 10µm feature (i.e., whether it shows in emission or in absorption) is wellcorrelated with the optical classification in type 1 and type 2 quasars, contrary to some models of clumpy obscuration. Furthermore, this correlation is significantly stronger in quasars (L bol 10 45 erg/s) than it is in Seyfert galaxies (L bol ≪ 10 45 erg/s).
2017
The evidence is reviewed that the Broad Line Region (BLR) probably has two distinct components located at about the same distance from the central black hole. One component, BLR II, is optically-thick, low-ionization emission at least some of which arises from a disc and the other, BLR I, is probably optically-thin emission from a more spherically symmetric halo or atmosphere. The high Fe II/Hβ ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are not due to strong Fe II emission, as is commonly thought, but to unusually weak Balmer emission, probably caused by higher densities. NLS1s probably differ from non-NLS1s because of the higher density of gas near the black hole. This produces a higher accretion rate, a denser BLR, and a view of the central regions that is more face-on.
New Astronomy Reviews
The evidence is reviewed that the Broad Line Region (BLR) probably has two distinct components located at about the same distance from the central black hole. One component, BLR II, is optically-thick, low-ionization emission at least some of which arises from a disc and the other, BLR I, is probably optically-thin emission from a more spherically symmetric halo or atmosphere. The high Fe II/Hβ ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are not due to strong Fe II emission, as is commonly thought, but to unusually weak Balmer emission, probably caused by higher densities. NLS1s probably differ from non-NLS1s because of the higher density of gas near the black hole. This produces a higher accretion rate, a denser BLR, and a view of the central regions that is more face-on.
The Astrophysical Journal, 2012
We report on a spectral principal component analysis (SPCA) of a sample of 816 quasars, selected to have small Fe II velocity shifts with spectral coverage in the rest wavelength range 3500-5500 Å. The sample is explicitly designed to mitigate spurious effects on SPCA induced by Fe II velocity shifts. We improve the algorithm of SPCA in the literature and introduce a new quantity, the fractional-contribution spectrum, that effectively identifies the emission features encoded in each eigenspectrum. The first eigenspectrum clearly records the power-law continuum and very broad Balmer emission lines. Narrow emission lines dominate the second eigenspectrum. The third eigenspectrum represents the Fe II emission and a component of the Balmer lines with kinematically similar intermediate velocity widths. Correlations between the weights of the eigenspectra and parametric measurements of line strength and continuum slope confirm the above interpretation for the eigenspectra. Monte Carlo simulations demonstrate the validity of our method to recognize cross talk in SPCA and firmly rule out a single-component model for broad Hβ. We also present the results of SPCA for four other samples that contain quasars in bins of larger Fe II velocity shift; similar eigenspectra are obtained. We propose that the Hβ-emitting region has two kinematically distinct components: one with very large velocities whose strength correlates with the continuum shape, and another with more modest, intermediate velocities that is closely coupled to the gas that gives rise to Fe II emission.
The Nature of the Emission Components in the Quasar/NLS1 PG 1211+143
The Astrophysical Journal, 2001
We present the study of the emission properties of the quasar PG1211+143, which belongs to the class of Narrow Line Seyfert 1 galaxies. On the basis of observational data analyzed by us and collected from the literature, we study the temporal and spectral variability of the source in the optical/UV/X-ray bands and we propose a model that explains the spectrum emitted in this broad energy range. In this model, the intrinsic emission originating in the warm skin of the accretion disk is responsible for the spectral component that is dominant in the softest X-ray range. The shape of reflected spectrum as well as Fe K line detected in hard X-rays require the reflecting medium to be mildly ionized (ξ ∼ 500). We identify this reflector with the warm skin of the disk and we show that the heating of the skin is consistent with the classical αP tot prescription, while αP gas option is at least two orders of magnitude too low to provide the required heating. We find that the mass of the central black hole is relatively small (M BH ∼ 10 7 − 10 8 M ⊙ ), which is consistent with the Broad Line Region mapping results and characteristic for NLS1 class.
Hints on the Broad Line Region Structure of Quasars at High and Low Luminosities
Quasars show a considerable spectroscopic diversity. However, the variety of quasar spectra at low redshifts is non-random: a principal component analysis applied to large samples customarily identifies two main eigenvectors. In this contribution we show that the range of quasar optical spectral properties observed at low-z\ and associated with the first eigenvector is preserved up to z ≈ 2 in a sample of high luminosity quasars. We also describe two major luminosity effects.