Accretion disks, quasars and cosmology: meandering towards understanding

Abstract

As Setti and Woltjer noted back in 1973, one can use quasars to construct the Hubble diagram; however, the actual application of the idea was not that straightforward. It took years to implement the proposition successfully. Most ways to employ quasars for cosmology now require an advanced understanding of their structure, step by step. We briefly review this progress, with unavoidable personal biases, and concentrate on bright unobscured sources. We will mention the problem of the gas flow character close to the innermost stable circular orbit near the black hole, as discussed five decades ago. This problem later led to the development of the slim disk scenario and is recently revived in the context of Magnetically Arrested Disks (MAD) and Standard and Normal Evolution (SANE) models. We also discuss the hot or warm corona issue, which is still under debate and complicates the analysis of X-ray reflection. We present the scenario of the formation of the low ionization part of the Broad Line Region as a failed wind powered by radiation pressure acting on dust (Failed Radiatively Driven Dusty Outflow – FRADO). Next, we examine the cosmological constraints currently achievable with quasars, primarily concentrating on light echo methods (continuum time delays and spectral-line time delays to the continuum) that are (or should be) incorporating the progress mentioned above. Finally, we briefly discuss prospects in this lively subject area.

High Redshift $\Lambda$Cdm Cosmology: To Bin or Not to Bin?

“…Here, it is worth stressing that QSOs represent emerging cosmological probes [103] and considerable work remains to turn the proposal into standardisable candles on par with Type Ia SNe, where developments span 3 decades. See [104] for a historical account of the quest to construct a QSO Hubble diagram. Nevertheless, in defence of the Risaliti-Lusso methodology, it should be noted that the logarithms of X-ray and UV fluxes show an apparent correlation (see for example Figs.…”

Effect of Extinction on Quasar Luminosity Distances Determined from UV and X-Ray Flux Measurements

“…Active galactic nuclei (AGN), especially bright quasars (quasi-stellar objects (QSOs); Karas et al 2021;Zajaček et al 2023), appear to be promising alternative probes due to their broad redshift coverage, ranging from the nearby Universe (z = 0.00106 for NGC4395; Brum et al 2019) to z ≈ 7.642 (J0313-1806; Wang et al 2021). For cosmological applications, so far three types of QSO data have been more widely utilized: (i) QSO angular size observations (Cao et al 2017;Ryan et al 2019;Cao et al 2020Cao et al , 2021aCao et al , 2021bLian et al 2021;Cao et al 2022b); (ii) data based on the nonlinear relation between QSO X-ray and UV luminosities, the L X -L UV relation (Risaliti & Lusso 2015Khadka & Ratra 2020a, 2020bLusso et al 2020;Li et al 2021;Colgáin et al 2022;Dainotti et al 2022;Hu & Wang 2022;Khadka & Ratra 2022;Petrosian et al 2022;Rezaei et al 2022;Khadka et al 2023); and (iii) data based on the correlation between the rest-frame broad-line region (BLR) time delay and the monochromatic luminosity, the R-L relation (Panda et al 2019a(Panda et al , 2019bMartínez-Aldama et al 2019;Khadka et al 2021bKhadka et al , 2022aKhadka et al , 2022bCzerny et al 2021;Zajaček et al 2021;Cao et al 2022cCao et al , 2023Cao & Ratra 2022;Panda 2022;Cao & Ratra 2023a;…”

$H_0=69.8\pm1.3$ $\rm{km \ s^{-1} \ Mpc^{-1}}$, $Ω_{m0}=0.288\pm0.017$, and other constraints from lower-redshift, non-CMB and non-distance-ladder, expansion-rate data

“…Cosmological models have been compared and cosmological parameter constraints have been determined using various observations, including cosmic microwave background (CMB) anisotropy data, [7], that probe the highredshift Universe, and lower-redshift expansion-rate observations like those we use here. These lower-redshift data sets include better-established probes such as Hubble parameter [H(z)] data that reach to redshift z ∼ 2, and baryon acoustic oscillation (BAO) and type Ia supernova (SN Ia) measurements that reach to z ∼ 2.3, [8][9][10], as well as emerging probes such as H ii starburst galaxy (H iiG) apparent magnitude data that reach to z ∼ 2.5, [11][12][13][14][15][16], quasar angular size (QSO-AS) measurements that reach to z ∼ 2.7, [17][18][19][20][21], reverberationmeasured (RM) Mg ii and C iv quasar (QSO) measurements that reach to z ∼ 3.4, [22][23][24][25][26][27][28], and gamma-ray burst (GRB) data that reach to z ∼ 8.2, [29][30][31][32][33][34][35][36][37][38][39], of which only 118 Amati-correlated (A118) GRBs, with lower intrinsic dispersion, are suitable for cosmological purposes, [37,[40][41][42][43].…”