CosmoStat Calendar

Comptonization Problem and Its solution in Application
to the Spectra of the Neutron Star and Black Hole Sources

Lev TITARCHUK

In 2017, the work on the Comptonization (Sunyaev-Titarchuk) seen in the X-ray spectra of astrophysical sources was a candidate for the Nobel Prize in Physics. In this talk I provide all the details of the exciting prehistory of this topic and precise details of this discovery. The solution of this problem and its subsequent development and application to the spectra of accreting neutron star (NS) and black hole (BH) binaries reveals a lot of information on these objects. In particular, now we can unambiguously distinguish between a NS and a BH (Galactic or extragalactic) using correlations of their spectral indices vs mass accretion rate (or QPO frequency). I further demonstrate how we can determine a BH mass using this correlation.

A decade of the main sequence of star-forming galaxies: new insights and perspectives on massive galaxy formation

Benjamin MAGNELLI (LCEG)

The observed tight correlation between the star formation rate (SFR) and the stellar mass of star-forming galaxies (SFGs) is now well constrained over the last 10 Gyr of look-back time. This so-called main sequence (MS), whose normalization declines from z~3 to 0, is commonly interpreted as evidence that SFGs are evolving primarily through a steady and long star-forming mode, likely sustained by the cold gas accretion along the cosmic web. Over the last decade, a plethora of studies have investigated within this framework the physical properties of SFGs along and across the MS, establishing key scaling relations between, e.g., the stellar mass, gas content, and/or morphology of SFGs in the SFR-stellar mass plane. In this talk I will review past and recent observational evidences of this new MS paradigm and how it has shaped our understanding of the evolution of massive galaxies. Then, I will present the limitations of this simple paradigm, and in particular how it fails to explain the more diverse than anticipated population of MS galaxies (e.g., starburst hidden within the MS), the importance of secondary parameters (e.g., environment) and the transition of SFGs to quiescence. I will conclude by presenting future observational opportunities that can be used to investigate this hidden complexity within the main sequence and to further unveil the physics involved in the evolution of massive galaxies over cosmic time.