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The project constraints on dark energy properties from observations of active galaxies with the aim to use a novel tool, i.e. active galaxies (mostly quasars), in order to obtain constraints for the expansion rate of the Universe, and thus on the properties of the dark energy, was launched in 2018 under the grant 2017/26/A/ST9/00756 funded by National Science Center (NCN) of Poland (PI: Prof. Bożena Czerny).
Quasars and
Quasars and
cosmic distances
cosmic distances
Quasars as
Quasars as
dark energy probes
dark energy probes
The aim of the project is to develop and to apply a totally new method to determine the expansion rate of the Universe, and thus to determine the properties of the dark energy. The method is based on galaxies with active nuclei (AGN), including the most luminous ones, i.e. quasars, as a new cosmological tool. These objects are numerous, and they cover very broad redshift range from nearby sources at a distance of 10 Mpc to quasars at redshift 6. We will consider several variants of this general method. There are actually several independent ways how they can be used for cosmology (see e.g. Czerny et al. 2017), and the accuracy of those methods has still to be determined or improved. The basic idea behind is that we have to measure a specific property of a given AGN which allows (indirectly) to determine its absolute luminosity. This is later combined with the measurement of the source redshift and the observed flux, which are relatively easy to measure. In this way we construct the Hubble diagram for our sources, and we can trace the expansion rate of the Universe as a function of redshift (or, equivalently, time). We expect that after refining the details and collecting the requested number of measurements some of the variants of the method to be considered in this project should give more accurate results than the estimate of the expansion rate of the Universe based on Supernovae type Ia. In this way we plan not just confirm the accelerated expansion of the Universe but to measure it accurately enough to see if this accelerated expansion will continue forever, with the Universe becoming more and more empty.
A brief description of the fundamental method
The main method is based on the determination of the delay between the quasar emission lines and the quasar continuum, which allows to measure directly the size of the emitting region as a light travel time. As showed in our innovative pioneering model of the formation mechanism of this region, i.e. FRADO model, this size (RBLR) depends almost exclusively on the absolute luminosity (L) of a quasar, as
Log (RBLR) = 𝞪 + 𝞫 log (L) -->> D2 = L / ( 4 𝞹 Fobs )
Knowing the absolute luminosity from this relation, so-called radius-luminosity relation, and measuring (which is simple) the observed luminosity (Flux) and the redshift we can locate every quasar in a Hubble diagram. Having the model of the region we will work out in detail small but necessary corrections to minimize the systematic errors. Next we will combine all available observational data in order to use the largest possible number of sources with a broad range of redshifts. This will allow us to see the history of the Universe expansion.
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