A study of the Baldwin effect in the IUE data set

Kinney, A. L.; Rivolo, A. R.; Koratkar, Anuradha

doi:10.1086/168924

Cited by 99 publications

(147 citation statements)

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“…When the GTC measurements are compared with the data of Kinney et al (1990), the GTC values are found to be similar to typical values for low-z quasars with the same luminosity, arguing against an evolutionary Baldwin effect. Overlaying the GTC equivalent width values onto the more recent data of Bian et al (2012) shows that our sample is consistent with the weak anticorrelation detected in large samples.…”

Section: Is There a CIV λ1549 Evolutionary Baldwin Effect?supporting

confidence: 55%

GTC spectra ofz≈ 2.3 quasars: comparison with local luminosity analogs

Sulentic¹,

Marziani²,

Olmo³

et al. 2014

A&A

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Context. The advent of 8−10 m class telescopes for the first time makes it possible to compare in detail quasars with similar luminosity and very different redshifts. Aims. We conducted a search for z-dependent gradients in line-emission diagnostics and derived physical properties by comparing, in a narrow bolometric luminosity range (log L ∼ 46.1± 0.4 [erg s −1 ]), some of the most luminous local z < 0.6 quasars with some of the lowest luminosity sources yet found at redshift z = 2.1−2.5. Methods. Moderate signal-to-noise ratio spectra for 22 high-redshift sources were obtained with the 10.4 m Gran Telescopio Canarias (GTC), for which the HST (largely the Faint Object Spectrograph) archive provides a low-redshift control sample. We compared the spectra in the context of the 4D Eigenvector 1 formalism, meaning that we divided both source samples into highly accreting population A and population B sources accreting at a lower rate. Results. Civλ1549, the strongest and most reliable diagnostic line, shows very similar properties at both redshifts, which confirms the Civλ1549 profile differences at high redshift between populations A and B, which are well established in local quasars. The Civλ1549 blueshift that appears quasi-ubiquitous in higher L sources is found in only half (population A) of the quasars observed in the two samples. A Civλ1549 evolutionary Baldwin effect is certainly disfavored. We find evidence for lower metallicity in the GTC sample that may point toward a gradient with z. No evidence for a gradient in M BH or L/L Edd is found. Conclusions. Spectroscopic differences established at low z are also present in much higher redshift quasars. Our results on the Civλ1549 blueshift suggest that it depends both on source luminosity and L/L Edd . Given that our samples involve sources with very similar luminosity, the evidence for a systematic metallicity decrease, if real, points toward an evolutionary effect. Our samples are not large enough to effectively constrain possible changes of M BH or L/L Edd with redshift. The two samples appear representative of a slowly evolving quasar population that is most likely present at all redshifts.

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Section: Is There a CIV λ1549 Evolutionary Baldwin Effect?supporting

confidence: 55%

GTC spectra ofz≈ 2.3 quasars: comparison with local luminosity analogs

Sulentic¹,

Marziani²,

Olmo³

et al. 2014

A&A

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“…The character of the emission-line variability is the subject of future work (Wilhite et al 2005). For now, we simply note that the broad lines are clearly less variable than the underlying continuum, a relationship known as the intrinsic Baldwin effect (IBE; Kinney et al 1990). More discussion on the IBE's effect on color variability can be found in x 4.…”

Section: Emission-line Variabilitymentioning

confidence: 99%

Spectral Variability of Quasars in the Sloan Digital Sky Survey. I. Wavelength Dependence

Wilhite

Berk

Krön

et al. 2005

ApJ

137

219

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SDSS repeat spectroscopic observations have resulted in multiepoch spectroscopy for $2500 quasars observed more than 50 days apart. From this sample, calibrating against stars observed simultaneously, we identify 315 quasars that have varied significantly between observations (with respect to assumed nonvariable stars observed concurrently). These variable quasars range in redshift from 0.5 to 4.72. This is the first large quasar sample studied spectroscopically for variability and represents a potentially useful sample for future high-redshift reverberation mapping studies. This also marks the first time the precise wavelength dependence of quasar variability has been determined, allowing both the continuum and emission-line variability to be studied. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 8. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index k ¼ À2:00, compared to an index of k ¼ À1:35 for the single-epoch spectrum. This confirms that quasar continua are bluer when brighter. The difference spectrum also exhibits very weak or absent emission-line features; the strongest emission lines vary only 30% as much as the continuum. This small emission-line variability with respect to the continuum is consistent with the intrinsic Baldwin effect. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for k rest < 2500 8, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.

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“…The results confirm that the continua are bluer when brighter and clearly show that variability is weak in the emission lines. They provide a natural explanation of the intrinsic Baldwin effect behaviour of individual AGNs (Kinney et al 1990; Wilhite et al 2006). Pereyra et al (2006) demonstrated that the composite flux differences in the rest-frame wavelength range 1300-6000 Å can be fit by a standard thermal accretion disk model in which the accretion rate has changed from epoch to epoch.…”

Section: Introductionmentioning

confidence: 99%

Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82

Meusinger

Hinze

Hoon

2010

A&A

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Aims. The study of the ensemble properties of the UV/optical broadband variability of quasars is hampered by the combined effects of the dependence of variability on timescale, rest-frame wavelength, and luminosity. Here, we present a new approach to analysing the dependence of quasar variability on rest-frame wavelengths. Methods. We exploited the spectral archive of the Sloan Digital Sky Survey (SDSS) to create a sample of over 9000 quasars in the Stripe 82. The quasar catalogue was matched with the Light Motion Curve Catalogue for SDSS Stripe 82 and first-order structure functions were computed from the lightcurves. The structure functions are used to create a variability indicator that is related to the same intrinsic timescales for all quasars (about 1 to 2 yr in the rest-frame). We study the variability ratios for adjacent SDSS filter bands as a function of redshift. A quantitative interpretation of these relations is provided by comparing with the results of simple Monte Carlo simulations of variable quasar spectra. Results. We confirm the well-known dependence of variability on time-lag; the best power-law fit of the sample-averaged structure function has a slope β = 0.31 ± 0.03. We also confirm that anti-correlations exist with luminosity, wavelength, and redshift, where the latter can be fully explained as a consequence of the former two dependencies. The variability ratios as a function of redshift resemble the corresponding colour index-redshift relations. While variability is almost always stronger in the bluer passband than in the redder, the variability ratio depends on whether strong emission lines contribute to either one band or the other. We find that the observed variability ratio-redshift relations are described well assuming that (a) the r.m.s. fluctuation of the quasar continuum flux follows a power law σ( f λ ) ∝ λ −2 (i.e., is bluer when brighter) and (b) the variability of the emission line flux is only ∼10% of that of the underlying continuum. These results, based upon the photometry of more than 8000 quasars, confirm the previous findings by Wilhite and collaborators for 315 quasars with repeated SDSS spectroscopy. Finally, we find that quasars with unusual spectra and weak emission lines tend to have less variability than conventional quasars. This trend is the opposite of that expected from the dilution effect of variability due to line emission and may be indicative of high Eddington ratios in these unusual quasars.

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A study of the Baldwin effect in the IUE data set

Cited by 99 publications

References 0 publications

GTC spectra ofz≈ 2.3 quasars: comparison with local luminosity analogs

GTC spectra ofz≈ 2.3 quasars: comparison with local luminosity analogs

Spectral Variability of Quasars in the Sloan Digital Sky Survey. I. Wavelength Dependence

Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82

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