Giant Radio Quasars: Composite Optical Spectra (original) (raw)
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Composite Spectra from the FIRST Bright Quasar Survey
ApJ, 2001
We present a very high signal-to-noise ratio composite spectrum created using 657 radio-selected quasars from the FIRST Bright Quasar Survey. The spectrum spans rest-frame wavelengths 900 -7500Å. Additionally we present composite spectra formed from subsets of the total data set in order to investigate the spectral dependence on radio loudness and the presence of broad absorption. In particular, radio-loud quasars are red compared to radio-quiet quasars, and quasars showing low-ionization broad absorption lines are red compared to other quasars. We compare our composites with those from the Large Bright Quasar Survey. Composite quasar spectra have proven to be valuable tools for a host of applications, and in that spirit we make these publically available via the FIRST survey web page.
Composite Quasar Spectra from the Sloan Digital Sky Survey
Astronomical Journal, 2001
We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ¹ z ¹ 4.789 and an absolute r@ magnitude range of [18.0 to [26.5. The input spectra cover an observed wavelength range of 3800È9200 at a resolution of 1800. The median composite covers a rest-A wavelength range from 800 to 8555 and reaches a peak signal-to-noise ratio of over 300 per 1 A A resolution element in the rest frame. We have identiÐed over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we Ðnd that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is [100 km s~1, compared with shifts of up to 550 km s~1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lya emission, the continuum of the geometric mean composite is well Ðtted by two power laws, with a break at B5000
Optical and radio properties of giant radio quasars: central black hole characteristics
Monthly Notices of the Royal Astronomical Society, 2012
We analysed the optical and radio properties of lobe-dominated giant-sized (>0.72 Mpc) radio quasars and compared the results with those derived for a sample of smaller radio sources to determine whether the large size of some extragalactic radio sources is related to the properties of their nuclei. We compiled the largest (to date) sample of giant radio quasars, including 24 new and 21 previously known objects, and calculated a number of important parameters of their nuclei such as the black hole mass and the accretion rate. We conclude that giant radio quasars have properties similar to those of smaller size and that giant quasars do not have more powerful central engines than other radio quasars. The results obtained are consistent with evolutionary models of extragalactic radio sources, which predict that giant radio quasars could be more evolved (aged) sources compared with smaller radio quasars. In addition we found out that the environment may play only a minor role in the formation of large-scale radio structures.
On the radio properties of the highest redshift quasars
Monthly Notices of the Royal Astronomical Society, 2006
We present deep radio observations of the most distant complete quasar sample drawn from the Sloan Digital Sky Survey. Combining our new data with those from literature we obtain a sample which is ∼ 100 per cent complete down to S 1.4GHz = 60µJy over the redshift range 3.8 ≤ z ≤ 5. The fraction of radio detections is relatively high (∼ 43 per cent), similar to what observed locally in bright optical surveys. Even though the combined radio and optical properties of quasars remain overall unchanged from z ∼ 5 to the local Universe, there is some evidence for a slight overabundance of radio-loud sources at the highest redshifts when compared with the lower-z regime. Exploiting the deep radio VLA observations we present the first attempt to directly derive the radio luminosity function of bright quasars at z ∼ > 4. The unique depth-both in radio and optical-allows us to thoroughly explore the population of optically bright FR II quasars up to z ∼ 5 and opens a window on the behaviour of the brightest FR I sources. A close investigation of the space density of radio loud quasars also suggests a differential evolution, with the more luminous sources showing a less pronounced cutoff at high z when compared with the less luminous ones.
The radio-optical correlation in steep-spectrum quasars
Monthly Notices of the Royal Astronomical Society, 1998
Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation dependence (such as relativistic beaming), nor a byproduct of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion onto a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio luminous high-redshift galaxies.
Radio spectra and polarization properties of radio-loud broad absorption-line quasars
Monthly Notices of the Royal Astronomical Society, 2008
We present multifrequency observations of a sample of 15 radio-emitting broad absorption-line quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They mostly display convex radio spectra which typically peak at about 1-5 GHz (in the observer's rest frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e. ν 20 GHz. Very Large Array (VLA) 22-GHz maps (HPBW ∼80 mas) show unresolved or very compact sources, with linear projected sizes of ≤1 kpc. About two-thirds of the sample looks unpolarized or weakly polarized at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarized intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and in the rest frame, finding steeper spectra among non-BAL QSOs. However, constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarization properties shows that radio BAL QSOs share several properties common to young radio sources like compact steep spectrum or gigahertz peaked spectrum sources.
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.
Proceedings of the International Astronomical Union, 2009
The powerful compact continuum emission from quasars is understood only in outline. New surveys allow investigation of the quasar continuum over a wide range of parameters (z, L, L/LEdd) and wavelengths (radio to X-ray). I review the spectral energy distributions of quasars and how new scaling relations with physical parameters promise to take us to a deeper understanding of the quasar continuum.
A Comparison of the Optical Properties of Radio‐loud and Radio‐quiet Quasars
The Astrophysical Journal, 1999
We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity. The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3 ≤ z ≤ 1.5 and an optical absolute magnitude range of −26.5 ≤ M B ≤ −23.5 (h,q 0 =1/2). We have also matched up other existing surveys with the FIRST and NVSS radio catalogues and combined these data so that the optical luminosity-redshift plane is now far better sampled than previously. We have fitted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift and from this model infer the radio-loud and radio-quiet optical luminosity functions. The radio-loud optical luminosity function is featureless and flatter than the radio-quiet one. It evolves at a marginally slower rate if quasars evolve by density evolution, but the difference in the rate of evolutions of the two different classes is much less than was previously thought. We show, using Monte-Carlo simulations, that the observed difference in the shape of the optical luminosity functions can be partly accounted for by Doppler boosting of the optical continuum of the radio-loud quasars and explain how this can be tested in the future.
Publications of the Astronomical Society of Australia, 2001
We measure the spectral properties of a representative sub-sample of 187 quasars, drawn from the Parkes Half-Jansky, Flat-radio-spectrum Sample (PHFS). Quasars with a wide range of rest-frame optical/UV continuum slopes are included in the analysis: their colours range over 2 <B–K< 7. We present composite spectra of red and blue sub-samples of the PHFS quasars, and tabulate their emission line properties.The median Hβ and [O III] emission line equivalent widths of the red quasar sub-sample are a factor of ten weaker than those of the blue quasar sub-sample. No significant differences are seen between the equivalent width distributions of the C IV, C III] and Mg II lines. Both the colours and the emission line equivalent widths of the red quasars can be explained by the addition of a featureless red synchrotron continuum component to an otherwise normal blue quasar spectrum. The red synchrotron component must have a spectrum at least as red as a power-law of the formFυαυ−2.8. T...