Speaker
Description
Despite decades of research, cosmology still lacks reliable probes to study the Universe in the intermediate redshift regime (from z = 1 up to z = 1100). Very few astronomical objects observed at such high distances can be standardized. We present the case of two such sources: Gamma-Ray Bursts (GRBs, $z<9.4$) and Quasars (QSOs, $z<7.4$). For GRBs, the observational luminosity distance can be derived using an empirical log-linear relation between the luminosity at the end of the plateau phase ($L_{a}$), rest-frame time at the end of the plateau ($T^{*}_{a}$), and luminosity during the peak phase ($L_{peak}$). This relation was first formulated by Dainotti et al. (2016) as $\log_{10}L_{a} = a\times \log_{10}T^{*}_{a} + b\times \log_{10}L_{peak} +c$.
QSOs, on the other hand, follow a power-law correlation between the luminosity observed in the X-ray band ($L_{X}$) and the optical luminosity ($L_{UV}$). This correlation was presented by Risaliti & Lusso (2015) as $L_{X}=\beta \times L^{\gamma}_{UV}$. Although these correlations have been shown to result from the intrinsic physics of the sources rather than observational effects, applying them to cosmological computations remains challenging. A reliable fitting method must properly take into account selection bias and redshift evolution. We demonstrate that samples of GRBs and QSOs are significantly affected by these effects. Additionally, we present a circularity-free method for fitting the cosmological model based on a de-evolving procedure developed by Efron & Petrosian (1992). Lastly, we present our results of fitting cosmological parameters.
