GTC spectra of z ≈ 2.3 quasars: Comparison with local luminosity analogs

DOI: 
10.1051/0004-6361/201423975
Publication date: 
01/10/2014
Main author: 
Sulentic J.W.
IAA authors: 
Sulentic J.W.;Del Olmo A.;Perea J.
Authors: 
Sulentic J.W., Marziani P., Del Olmo A., Dultzin D., Perea J., Alenka Negrete C.
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
570
Pages: 
Number: 
A96
Abstract: 
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 MBH or L/LEdd 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/LEdd. 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 MBH or L/LEdd with redshift. The two samples appear representative of a slowly evolving quasar population that is most likely present at all redshifts. © ESO, 2014.
Database: 
SCOPUS
WOK
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2014A&A...570A..96S/abstract
ADS Bibcode: 
2014A&A...570A..96S
Keywords: 
Cosmology: observations; ISM: abundances; Line: profiles; Quasars: emission lines; Quasars: supermassive black holes