Our Search for an HR Diagram of Quasars (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.
Quasars with Anomalous H Profiles. I. Demographics
Publications of the Astronomical Society of Japan, 2013
The Hβ emission line in a typical Type I quasar is composed of a broad base and a narrow core, with the core velocity typical of narrow-line region emission, and line-fitting routines typically assume this picture. We test the effects of removing this constraint, and find a substantial group of Type I quasars in the Sloan Digital Sky Survey catalog with Hβ emission line cores broader than 1200 km/s, above the velocity believed possible for gas in the quasar narrow-line region. We identify this group of "anomalous Hβ quasars" (AHQs) as a distinct population because of a variety of spectral and photometric signatures common to these AHQs but atypical of other quasars. These features are similar to some aspects of narrow-line Seyfert 1s and correlations identified by Eigenvector 1, but also contain distinct features that make AHQs difficult to classify. We demonstrate that AHQs comprise at least 11% and most likely approximately one quarter of the SDSS Type I quasar population at 0.2 < z < 0.8. For AHQs, the [OIII]λ4959, 5007 profile is often better fit by de-linking it from the Hβ core, while a more standard linked fit produces a tight correlation between narrow-and broad-line velocities. We find that [OIII] in AHQs sometimes has a standard narrow-line profile and other times matches the Hβ core, but is rarely in between the two, implying that the broadened core emission arises from a distinct physical region. Another feature of AHQs is a diminished [OII] line, which might indicate a connection between AHQs and the interstellar mediums of their host galaxies, through reduced photoionization or star formation. We find that it is difficult to produce AHQs using the current quasar standard model.
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.
Broad-line region physical conditions along the quasar eigenvector 1 sequence
2010
We compare broad emission line profiles and estimate line ratios for all major emission lines between Lyα and Hβ in a sample of six quasars. The sources were chosen with two criteria in mind: the existence of high quality optical and UV spectra as well as the possibility to sample the spectroscopic diversity in the 4D Eigenvector 1 context (4DE1). In the latter sense each source occupies a region (bin) in the FWHM(Hβ) vs. Fe ii opt strength plane that is significantly different from the others. High S/N Hβ emission line profiles are used as templates for modeling the other lines (Lyα, Civλ1549, Heiiλ1640, Aliiiλ1860, Siiii]λ1892, and Mgiiλ2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids (indicated as blue, broad and very broad component respectively). The broad component (electron density n e ∼ 10 12 cm −3 ; ionization parameter U ∼ 10 −2 ; column density N c 10 23 cm −2 ) is present in almost all type-1 quasars and therefore corresponds most closely to the classical broad line emitting region (the reverberating component). The bulk of Mgiiλ2800 and Feii emission also arises in this region. The blue component emission (log n e ∼ 10; log U ∼ −1; log N c < 23) arises in less optically thick gas; it is often thought to arise in an accretion disk wind. The least understood component involves the very broad component (high ionization and large column density) which is found in no more than half (but almost all radio-loud) type-1 quasars and luminous Seyfert nuclei. It is perhaps the most distinguishing characteristic of quasars with FWHM Hβ 4000 km s −1 that belong to the so-called Population B of our 4DE1 space. Population A quasars (FWHM Hβ 4000 km s −1 ) are dominated by broad component emission in Hβ and blue component emission in Civλ1549 and other high ionization lines. 4DE1 appears to be the most useful current context for revealing and unifying spectral diversity in type-1 quasars.
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 NEXT GENERATION ATLAS OF QUASAR SPECTRAL ENERGY DISTRIBUTIONS FROM RADIO TO X-RAYS
The Astrophysical Journal Supplement Series, 2011
We have produced the next generation of quasar spectral energy distributions (SEDs), essentially updating the work of by using high-quality data obtained with several space and ground-based telescopes, including NASA's Great Observatories. We present an atlas of SEDs of 85 optically bright, non-blazar quasars over the electromagnetic spectrum from radio to X-rays. The heterogeneous sample includes 27 radio-quiet and 58 radio-loud quasars. Most objects have quasi-simultaneous ultraviolet-optical spectroscopic data, supplemented with some far-ultraviolet spectra, and more than half also have Spitzer mid-infrared IRS spectra. The X-ray spectral parameters are collected from the literature where available. The radio, far-infrared, and near-infrared photometric data are also obtained from either the literature or new observations. We construct composite spectral energy distributions for radio-loud and radio-quiet objects and compare these to those of Elvis et al., finding that ours have similar overall shapes, but our improved spectral resolution reveals more detailed features, especially in the mid and near-infrared.
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
Astrophysical Journal Supplement Series, 2000
We have used the Very Large Array (VLA) FIRST survey and the Automated Plate Measuring Facility (APM) catalog of the Palomar Observatory Sky Survey I (POSS-I) plates as the basis for constructing a new radio-selected sample of optically bright quasars. This is the first radio-selected sample that is competitive in size with current optically selected quasar surveys. Using only two basic criteria, radio-optical positional coincidence and optical morphology, quasars and BL Lac objects can be identified with 60% selection efficiency; the efficiency increases to 70% for objects fainter than 17 mag. We show that a more sophisticated selection scheme can predict with better than 85% reliability which candidates will turn out to be quasars. This paper presents the second installment of the FIRST Bright Quasar Survey (FBQS), with a catalog of 636 quasars distributed over 2682 deg2. The quasar sample is characterized and all spectra are displayed. The FBQS detects both radio-loud and radio-quiet quasars out to redshift z>3. We find a large population of objects of intermediate radio loudness; there is no evidence in our sample for a bimodal distribution of radio characteristics. The sample includes ~29 broad absorption line quasars, both high and low ionization, and a number of new objects with remarkable optical spectra.
Astrometric comparisons of quasar catalogues
Astronomy and Astrophysics, 2008
Context. Large surveys, such as the Sloan Digital Sky Survey (SDSS) and the 2-degree Field (2QZ) considerably increased the number of recorded quasars at optical wavelengths. At the same time, the densification of very long baseline interferometry observations of extragalactic radio sources enabled an increase in the accuracy of the the quasi-inertial radio reference frame that realizes the International Celestial Reference System (ICRS). Aims. In the perspective of the realization of an accurate optical counterpart to the ICRF, we investigate the astrometric properties of quasars recorded by several surveys, both at radio and optical wavelengths. Methods. Cross-identifications of quasars are made between catalogues, both at optical (SDSS vs. 2QZ) and radio wavelengths (VLBA Calibrator Survey vs. SDSS). Equatorial coordinates of the quasars are compared to evaluate the astrometric quality of the catalogues. Results. We find more than 2000 objects in common between SDSS and 2QZ. We show that differences in position never exceed 1 , with a root mean square of 0.2. The agreement in redshift determinations is good with a typical dispersion of 0.05 root mean square. Similar comparisons between the SDSS and the VLBA Calibrator Survey find 831 cross-correlated sources within a 0.23 search radius. Systematic errors, likely due to the partial sky coverage of the SDSS, are detected in the coordinate differences, which produces to a rotation of the optical frame, with respect to the radio counterpart, at the level of 13 mas. Thus both the SDSS and the 2QZ can provide invaluable information for the accurate determination of the ICRS at the fainter end of the optical domain. We finally point out that the highest probability of finding radio loud quasars involves searching in the redder regions of the color−color space.