Recently some pessimism has been expressed about our lack of progress in understanding quasars over the 50+ year since their discovery. It is worthwhile to look back at some of the progress that has been made - but still lies under the radar - perhap
s because few people are working on optical/UV spectroscopy in this field. Great advances in understanding quasar phenomenology have emerged using eigenvector techniques. The 4D eigenvector 1 context provides a surrogate H-R Diagram for quasars with a source main sequence driven by Eddington ratio convolved with line-of-sight orientation. Appreciating the striking differences between quasars at opposite ends of the main sequence (so-called population A and B sources) opens the door towards a unified model of quasar physics, geometry and kinematics. We present a review of some of the progress that has been made over the past 15 years, and point out unsolved issues.
Highly accreting quasars are characterized by distinguishing properties in the 4D eigenvector 1 parameter space that make them easily recognizable over a broad range range of redshift and luminosity. The 4D eigenvector 1 approach allows us to define
selection criteria that go beyond the restriction to Narrow Line Seyfert 1s identified at low redshift. These criteria are probably able to isolate sources with a defined physical structure i.e., a geometrically thick, optically thick advection-dominated accretion disk (a slim disk). We stress that the importance of highly accreting quasars goes beyond the understanding of the details of their physics: their Eddington ratio is expected to saturate toward values of order unity, making them possible cosmological probes.
[Abridged] Context: The advent of 8-10m class telescopes makes possible for the first time detailed comparison of quasars with similar luminosity and very different redshifts. Aims: 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 [ergss]), 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. Method: Spectra for 22 high z sources were obtained with the 10.4m Gran Telescopio Canarias (GTC) while the HST (largely FOS) archive provides a low redshift control sample. Comparison is made in the context of the 4D Eigenvector 1 formalism meaning that we divide both source samples into high accreting Population A and low accreting Population B sources. Results: CIV 1549 shows very similar properties at both redshifts confirming at high redshift the CIV profile differences between Pop. A and B that are well established in local quasars. The CIV blueshift that appears quasi- ubiquitous in higher L sources is found in only half (Pop. A) of quasars observed in both of our samples. A CIV 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 black hole mass or Eddington ratio is found. Conclusions: Spectroscopic differences established at low redshift are also present in much higher redshift quasars. 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 appear representative of a slow evolving quasar population likely present at all redshifts.
We propose a method to identify quasars radiating closest to the Eddington limit, defining primary and secondary selection criteria in the optical, UV and X-ray spectral range based on the 4D eigenvector 1 formalism. We then show that it is possible
to derive a redshift-independent estimate of luminosity for extreme Eddington ratio sources. Using preliminary samples of these sources in three redshift intervals (as well as two mock samples), we test a range of cosmological models. Results are consistent with concordance cosmology but the data are insufficient for deriving strong constraints. Mock samples indicate that application of the method proposed in this paper using dedicated observations would allow to set stringent limits on Omega_M and significant constraints on Omega_Lambda.
[Abridged] Broad MgII 2800 and Hbeta lines have emerged as the most reliable virial estimators of black hole mass in quasars. Which is more reliable? Comparison of MgII 2800 and Hbeta profile measures in the same sources and especially FWHM measures
that provide the virial broadening estimator. Identification of 680 bright Sloan Digital Sky Survey DataRelease 7 quasars with spectra showing both MgII 2800 and Hbeta lines, at redshift 0.4 < z < 0.75. The s/n of these spectra are high enough to allow binning in the four-dimensional (4D) eigenvector 1 optical plane and construction of high s/n composite spectra. We confirm that MgII 2800 shows a profile that is ~ 20% narrower as suggested in some previous studies. FWHM measures for Population B sources (i.e., with FWHM of Hbeta larger than 4000 km/s) are uncertain because they show complex profiles with at least two broad-line components involving a nearly unshifted broad and redshifted very-broad component. Only the broad component is likely to be a valid virial estimator. If Hbeta and MgII 2800 are not corrected for the very broad component then black hole mass values for Population B sources will be systematically overestimated by up to logM ~ 0.3-0.4 dex. We suggest a simple correction that can be applied to the majority of sources. MgII 2800 is the safer virial estimator for Population B sources because the centroid shifts with respect to rest frame are lower than for Hbeta. In the broad and very broad component profile interpretation this is a consequence of the lower very broad to broad component intensity ratio for MgII 2800. Effective discrimination of black hole mass and Eddington ratio at fixed redshift is not achieved via luminosity binning but rather by binning in a 4D eigenvector 1 context that reflects different broad line region geometry/kinematics likely driven by Eddington ratio.
The broad MgII doublet has been much studied in connection with its potentially important role as a virial estimator of black hole mass in high redshift quasars. An important task is therefore identification of any line components likely related to b
roadening by non-virial motions. High s/n median composite spectra (binned in the 4D eigenvector 1 context of Sulentic et al. 2007) were constructed for the brightest 680 SDSS DR7 quasars in the 0.4 < z < 0.75 range where both MgII 2800 and Hbeta are recorded in the same spectra. Composite spectra representing 90% of the quasars confirm previous findings that FWHM(MgII 2800) is about 20% narrower than FWHM(Hbeta). The situation is clearly different for the most extreme (Population A) sources which are the highest Eddington radiators in the sample. In the median spectra of these sources FWHM MgII 2800 is equal to or greater than FWHM(Hbeta) and shows a significant blueshift relative to Hbeta. We interpret the MgII 2800 blueshift as the signature of a radiation-driven wind or outflow in the highest accreting quasars. In this interpretation the MgII 2800 line width -- affected by blueshifted emission -- is unsuitable for virial mass estimation in ~ 10% of quasars.
Gas outflows appear to be a phenomenon shared by the vast majority of quasars. Observations indicate that there is wide range in outflow prominence. In this paper we review how the 4D eigenvector 1 scheme helps to organize observed properties and lea
d to meaningful constraints on the outflow physical and dynamical processes.
Environmental research aimed at monitoring and predicting O2 depletion is still lacking or in need of improvement, in spite of many attempts to find a relation between atmospheric gas content and climate variability. The aim of the present project is
to determine accurate historical sequences of the atmospheric O2 depletion by using the telluric lines present in stellar spectra. A better understanding of the role of oxygen in atmospheric thermal equilibrium may become possible if high-resolution spectroscopic observations are carried out for different airmasses, in different seasons, for different places, and if variations are monitored year by year. The astronomical spectroscopic technique involves mainly the investigation of the absorption features in high-resolution stellar spectra, but we are also considering whether accurate measures of the atmospheric O2 abundances can be obtained from medium and low resolution stellar spectra.
[Abridged] We have been exploring a spectroscopic unification for all known types of broad line emitting AGN. The 4D Eigenvector 1 (4DE1) parameter space shows promise as a unification capable of organizing quasar diversity on a sequence primarily go
verned by Eddington ratio. This paper considers the role of CIV 1549 measures with special emphasis on the CIV 1549 line shift as a principal 4DE1 diagnostic. We use HST archival spectra for 130 sources with S/N high enough to permit reliable CIV 1549 broad component (BC) measures. We find a CIV 1549 BC profile blueshift that is strongly concentrated among (largely radio-quiet: RQ) sources with FWHM(H beta BC) < 4000 km/s (which we call Population A). Narrow line Seyfert 1 (NLSy1, with FWHM H beta < 2000 km/s) sources belong to this population but do not emerge as a distinct class. The systematic blueshift, widely interpreted as arising in a disk wind/outflow, is not observed in broader lined AGN which we call Population B. We find new correlations between FWHM(CIV 1549 BC) and CIV 1549 line shift as well as the equivalent width of CIV 1549. They are seen only in Pop. A sources. CIV 1549 measures enhance the apparent dichotomy at FWHM(Hbeta BC) approx. 4000 kms (Sulentic et al. 2000) suggesting that it has more significance in the context of Broad Line Region structure than the more commonly discussed RL vs. RQ dichotomy. Black hole masses computed from FWHM CIV 1549 BC for about 80 AGN indicate that the CIV 1549 width is a poor virial estimator. Comparison of mass estimates derived from Hbeta BC and CIV 1549 reveals that the latter show different and nonlinear offsets for population A and B sources. A significant number of sources also show narrow line CIV 1549 emission. We present a recipe for CIV 1549 narrow component extraction.
