The Quasar Continuum (original) (raw)
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The far-infrared continuum of quasars
Arxiv preprint astro-ph/ …, 1999
ISO provides a key new far-infrared window through which to observe the multi-wavelength spectral energy distributions (SEDs) of quasars and active galactic nuclei (AGN). It allows us, for the first time, to observe a substantial fraction of the quasar population in the far-IR, and to obtain simultaneous, multiwavelength observations from 5-200 µm. With these data we can study the behavior of the IR continuum in comparison with expectations from competing thermal and non-thermal models. A key to determining which mechanism dominates, is the measurement of the peak wavelength of the emission and the shape of the far-IR-mm turnover. Turnovers which are steeper than ν 2.5 indicate thermal dust emission in the far-IR.
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.
Emission Lines and the Spectral Energy Distributions of Quasars
1996
Many years of study have failed to conclusively establish relations between a quasar's spectral energy distribution (SED) and the emission lines it is thought to produce. This is at least partially due to the lack of well-observed SEDs. We present initial results from a line--SED study for a sample of 43 quasars and active galaxies for which we have optical and ultra-violet spectra and far-infrared--X-ray SEDs. We present the results of tests for correlations between line equivalent widths and SED luminosity and slope parameters and compare these results to those from earlier studies. We find that the Baldwin effect is weaker when the luminosity is defined close to the ionising continuum of that line and conclude that the detailed SED is likely to be important in making further progress.
The spectral index of the ionizing continuum of quasars
Arxiv preprint astro-ph/ …, 2002
El resumen será traducido al español por los editores. The ionizing spectral energy distribution of quasars exhibits a steepening of the distribution short-ward of 1200Å. The change of the power-law index from approximately −1 to −2 so far has been interpreted as being intrinsic to quasars. We study an alternative interpretation, in which a tenuous absorption screen is responsible for the change of index. We find that the most successful function of Hi with z requires that the ionization fraction be independent of the metagalactic background radiation, that is frozen in. This implies that the putative component should be of sufficiently low density that it could not recombine (while the background is subsiding) and/or cool from a high temperature state.
Astrophys J, 1996
Photoionization models dictate that many prominent quasar emission lines are sensitive to both the luminosity and shape of the quasars high- energy continuum-primarily the extreme ultraviolet (EUV) and soft X-ray continuum. Unfortunately, the EUV band is severely obscured by Galactic absorption. Using data from the adjacent UV and soft X-ray bandpasses, we initiate the first large-scale, multiline investigation of correlations between the QSO soft X-ray continuum and line emission in a sample of QSOs observed by Einstein and IUE. We present a new error analysis for objective, automated line measurements, which enables us to include the information contained in weak or undetected lines. We tabulate more than 300 UV emission-line equivalent widths from IUE spectra of 85 QSOs in the atlas of Lanzetta, Turnshek, & Sandoval, then characterize the distributions of line equivalent and velocity widths (Wlambda_ and FWHM). We then compare these line parameters to the QSO continuum spectral energy distributions from optical through soft X-ray wavelengths, using survival analysis to incorporate any nondetections for X-ray flux and/or UV emission lines. Several correlations noted in previous studies are not reproduced here. However, we illustrate that the exclusion of undetected lines from such studies may spuriously enhance apparent correlations. We find significant correlations between Wlambda_ and UV luminosity (e.g., the well-studied Baldwin effect) for Lyα, C IV, He II, and C III]. Wlambda_(C III]) and Wlambda_(He II) also show previously unreported correlations with X-ray luminosity that, for C III], appears to be primary. The line ratios C III]/Lyα and He II/Lyα both show strongest dependence on l_x_. Wlambda_(Lyα) correlates strongly with spectral slopes α_UV_ and α_OX_ (between 2500 A and 2 keV), but not with X-ray luminosity. Using these results, we argue that one simple geometrical interpretation of the Baldwin effect (BEff) as a result of a distribution of disk inclinations is not plausible. We also provide evidence that the BEff weakens or disappears when the line emission is correctly compared to the luminosity in the continuum bandpass relevant to its production. We thus support the interpretation of the BEff as a change in spectral energy distribution with luminosity, and we predict that no BEff relative to X-ray luminosity should be found for Fe II or Mg II emission lines. Extensions of our method to samples of a wider redshift/ luminosity range will be presented in a later paper, which will test these predictions.
The Astrophysical Journal, 1999
We investigate the relations between the observed emission-line strengths, widths, and continuum properties of a sample of 41 low-redshift (z \ 1) quasars for which contemporaneous IR/soft X-ray spectral energy distributions are available. This includes investigating correlations between optical and UV lines with both the luminosity and the shape of the quasarsÏ continuum, as well as correlations between the various lines. The sample is heterogeneous, primarily selected on the existence of good-quality Einstein X-ray data, and includes 18 radio-loud and 23 radio-quiet quasars. We Ðnd anticorrelations between the equivalent width and various UV luminosities (the Baldwin e †ect) for the Lya and Hb lines and a marginal anticorrelation for C III]. Exclusion of narrow-line, low-luminosity active galactic nuclei reveals a signiÐcant Baldwin e †ect for the C IV and C III] lines. A signiÐcant anticorrelation of EW(C IV) with is also present. We Ðnd no correlations between any lines and the X-ray luminosity or X-ray a ox slope. The Fe II optical multiplet shows no simple relationship with luminosity or continuum slope ; however, there is a tendency for objects with Ñat X-ray spectra and/or strong X-ray luminosities to have weak Fe II.
The Ultraviolet-To-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars
The Astrophysical Journal, 2011
We present Spitzer Space Telescope photometry of 18 Sloan Digital Sky Survey (SDSS) quasars at 2.7 ≤ z ≤ 5.9 which have weak or undetectable high-ionization emission lines in their rest-frame ultraviolet (UV) spectra (hereafter weak-lined quasars, or WLQs). The Spitzer data are combined with SDSS spectra and ground-based, near-infrared (IR) photometry of these sources to produce a large inventory of spectral energy distributions (SEDs) of WLQs across the rest-frame ∼ 0.1 − 5 µm spectral band. The SEDs of our sources are inconsistent with those of BL Lacertae objects which are dominated by synchrotron emission due to a jet aligned close to our line-of-sight, but are consistent with the SED of ordinary quasars with similar luminosities and redshifts that exhibit a near-to-mid-IR 'bump', characteristic of hot dust emission. This indicates that broad emission lines in WLQs are intrinsically weak, rather than suffering continuum dilution from a jet, and that such sources cannot be selected efficiently from traditional photometric surveys.
Atlas of quasar energy distributions
The Astrophysical Journal Supplement Series, 1994
We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, and 18 are radio loud. The SEDs are presented both in figures and in tabular form, with additional tabular material published on CD-ROM. Previously unpublished observational data for a second set of quasars excluded from the primary sample are also tabulated. The effects of host galaxy starlight contamination and foreground extinction on the UVSX sample are considered and the sample is used to investigate the range of SED properties. Of course, the properties we derive are influenced strongly by the selection effects induced by quasar discovery techniques. We derive the mean energy distribution (MED) for radio-loud and radio-quiet objects and present the bolometric corrections derived from it. We note, however, that the dispersion about this mean is large (-one decade for both the infrared and ultraviolet components when the MED is normalized at the near-infrared inflection). At least part of the dispersion in the ultraviolet may be due to time variability, but this is unhkely to be important in the infrared. The existence of such a large dispersion indicates that the MED reflects only some of the properties of quasars and so should be used only with caution. Subject headings: atlases-galaxies: photometry-quasars: general
Giant Radio Quasars: Composite Optical Spectra
The Astrophysical Journal
We present the composite optical spectrum for the largest sample of giant radio quasars (GRQs). They represent a rare subclass of radio quasars due to their large projected linear sizes of radio structures, which exceed 0.7 Mpc. To construct the composite spectrum, we combined the optical spectra of 216 GRQs from the Sloan Digital Sky Survey (SDSS). As a result, we obtained the composite spectrum covering the wavelength range from 1400 Å to 7000 Å. We calculated the power-law spectral slope for the GRQ’s composite, obtaining α λ = −1.25, and compared it with that of the smaller-sized radio quasars, as well as with the quasar composite spectrum obtained for a large sample of SDSS quasars. We obtained that the GRQ’s continuum is flatter (redder) than the continuum of comparison quasar samples. We also show that the continuum slope depends on core and total radio luminosity at 1.4 GHz, being steeper for higher radio luminosity bins. Moreover, we found that there is a flattening of the ...