Unseen Progenitors of Luminous High-z Quasars in the R_h = ct Universe

Abstract

Quasars at high redshift provide direct information on the mass growth of supermassive black holes (SMBHs) and, in turn, yield important clues about how the universe evolved since the first (Pop III) stars started forming. Yet even basic questions regarding the seeds of these objects and their growth mechanism remain unanswered. The anticipated launch of eROSITA and ATHENA is expected to facilitate observations of high-redshift quasars needed to resolve these issues. In this paper, we compare accretion-based SMBH growth in the concordance ΛCDM model with that in the alternative Friedmann-Robertson-Walker cosmology known as the R h =ct universe. Previous work has shown that the timeline predicted by the latter can account for the origin and growth of the 109 M e highest redshift quasars better than that of the standard model. Here, we significantly advance this comparison by determining the soft X-ray flux that would be observed for Eddington-limited accretion growth as a function of redshift in both cosmologies. Our results indicate that a clear difference emerges between the two in terms of the number of detectable quasars at redshift z7, raising the expectation that the next decade will provide the observational data needed to discriminate between these two models based on the number of detected high-redshift quasar progenitors. For example, while the upcoming ATHENA mission is expected to detect ∼0.16 (i.e., essentially zero) quasars at z∼7 in R h =ct, it should detect ∼160 in ΛCDM-a quantitatively compelling difference.

The maximum angular-diameter distance in cosmology

“…All of the comparative tests completed thus far (see, e.g., Table 1 in Melia 2017b for a summary and references) suggest that the zero active mass condition in general relativity is the influence guiding the Universe's expansion. Several exciting new tests are under development, including the measurement of redshift drift (Melia 2016b) and the detection of progenitors to high-z quasars (Fatuzzo & Melia 2017). Within a few years, we should know for certain whether or not R h = ct is the correct cosmology.…”

Cosmological test using the high-redshift detection rate of FSRQs with the Square Kilometre Array

“…The total spectral energy distribution (SED) across all wavebands for an AGN depends on a large number of physical phenomena. The more commonly included components of quasar emission are: a relativistic jet emitting in the radio (Urry & Padovani, 1995) and, sometimes, in X-rays and γrays via inverse Compton scattering (Melia & Königl 1989); a thermally-radiating accretion disk emitting predominantly at UV wavelengths (Shakura & Sunyaev 1973); a hot corona emitting primarily in X-rays (Lusso & Risalti 2016;Fatuzzo & Melia 2017), and an obscuring torus (Krolik & Begelman 1986); as well as any radiation from the stars in the rest of the galaxy. Roughly 8.1 +5.0 −3.2 % (Bañados et al 2015) of the AGNs at high redshift are known to emit strongly at radio frequencies.…”

“…Now that the blazar radio emission may be estimated as a function of black-hole mass, we use the distribution from Willott et al (2010) to establish (i.e., normalize) the mass function at a known redshift. Following Fatuzzo & Melia (2017), we begin with the observed black-hole mass function at z = 6, and devolve the entire population in lockstep towards higher redshifts, with the assumption that all quasars at z = 6 are undergoing Eddington-limited accretion, with a duty cycle very close to 1. This growth with a fiducial efficiency of 10% corresponds to an e-folding time of t Edd ≈ 45 Myr (known as the Salpeter time; see, e.g., Melia 2013).…”

“…The different timeline in R h = ct makes it especially attractive when considering the growth rates of black-hole seeds into supermassive black holes, a topic addressed in detail in Melia (2013) and Melia & McClintock (2015). In ΛCDM, the time elapsed between z = 7 and z = 6 is 167 Myr, compared with 249 Myr in R h = ct. With a ∼ 45 Myr e-folding time associated with Eddington-limited growth based on 10% efficiency (see, e.g., Fatuzzo & Melia 2017), R h = ct black holes could grow by a factor of ∼ 150 in that redshift range, while they would only have had time to grow by a factor of ∼ 28 in ΛCDM. This choice, that all of the blazars of interest are experiencing Eddington-Limited growth is motivated by the inferred Eddington ratio of highz quasars (such as those in the Wilott et al 2010 sample).…”

“…The SKA, with its unprecedented capabilities, is poised to probe the intermediate to high-redshift radio universe with greater sensitivity than any instrument before it. In our previous study of high-redshift active galaxies (Fatuzzo & Melia 2017), we analyzed the high-redshift quasar detection rate based on their X-ray emission in order to predict the various quasar counts to be compiled by the upcom-ing eROSITA and ATHENA observatories. While R h = ct and ΛCDM are very similar in describing the local universe, their predictions diverge towards higher redshifts.…”