Quasars as Cosmological Standard Candles

Abstract

We propose the use of quasars with accretion rate near the Eddington ratio (extreme quasars) as standard candles. The selection criteria are based on the Eigenvector 1 (E1) formalism. Our first sample is a selection of 334 optical quasar spectra from the SDSS DR7 database with a S/N > 20. Using the E1, we define primary and secondary selection criteria in the optical spectral range. We show that it is possible to derive a redshift-independent estimate of luminosity for extreme Eddington ratio sources. Our results are consistent with concordance cosmology but we need to work with other spectral ranges to take into account the quasar orientation, among other constrains.

A Main Sequence for Quasars

“…The distance modulus computed from the virial equation, µ = 2.5[log L(δv) − BC] − 2.5 log(f λ λ) − const. + 5 · log(1 + z), where f λ λ is the flux at 5100 Å, and BC the bolometric correction, is in agreement with the expectation of the concordance CDM cosmology, providing a proof of the conceptual validity of the virial luminosity L ∝ (δv) 4 estimates (a plot of µ for several quasar samples is provided by Marziani et al, 2017b, andby Negrete et al 2017).…”

“…A and B in terms of Balmer line profile shapes Cracco et al, 2016), the transition between the profile types is apparently occurring at 4,000 km s −1 and not at 2,000 km s −1 , the canonical limit of NLSy1. This early result has been confirmed by several later analyses (e.g., Zamfir et al, 2010;Marziani et al, 2013b;Negrete et al, 2017). Figure 3 shows composite spectra in the FWHM range 2,000-4,000 and 0-2,000 km s −1 : the profile shape remains the same as the line gets broader (Negrete et al, 2017).…”

“…This early result has been confirmed by several later analyses (e.g., Zamfir et al, 2010;Marziani et al, 2013b;Negrete et al, 2017). Figure 3 shows composite spectra in the FWHM range 2,000-4,000 and 0-2,000 km s −1 : the profile shape remains the same as the line gets broader (Negrete et al, 2017). Mirroring Paolo Padovani's prescription as enunciated at the Padova meeting (Padovani 2017: no more RL, only jetted!…”

Extreme quasars at high redshift

“…Simultaneous observations of the Aliiiλ1860 and of the Hβ spectral ranges are needed to make an exhaustive assessment of Aliiiλ1860 as a virial broadening estimator. The conceptual validity of luminosity estimates based on the Hβ line width measurements has been confirmed by the Hubble diagrams shown by MS14 and Negrete et al (2017). The large scatter displayed by quasars with respect to supernovae demands that random and systematic sources of error should be understood and, if possible, corrected or reduced before the xA sources can be exploited as useful distance indicators for cosmology.…”

“…the rotational velocity of Hi disks in spiral galaxies Tully & Fisher 1977). Initial computations for samples of 100-200 low-z quasars ( 1) confirm the conceptual validity of the "virial luminosity" estimates (Negrete et al 2017;Negrete et al 2018, submitted), although scatter in the distance modulus is still too large to draw meaningful inferences for cosmology.…”