density evolution
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2022 ◽  
Vol 924 (2) ◽  
pp. 62
Author(s):  
Andrea Grazian ◽  
Emanuele Giallongo ◽  
Konstantina Boutsia ◽  
Giorgio Calderone ◽  
Stefano Cristiani ◽  
...  

Abstract Motivated by evidences favoring a rapid and late hydrogen reionization process completing at z ∼ 5.2–5.5 and mainly driven by rare and luminous sources, we have reassessed the estimate of the space density of ultra-luminous QSOs at z ∼ 5 in the framework of the QUBRICS survey. A ∼ 90% complete sample of 14 spectroscopically confirmed QSOs at M 1450 ≤ −28.3 and 4.5 ≤ z ≤ 5.0 has been derived in an area of 12,400 deg2, thanks to multiwavelength selection and Gaia astrometry. The space density of z ∼ 5 QSOs within −29.3 ≤ M 1450 ≤ −28.3 is three times higher than previous determinations. Our results suggest a steep bright-end slope for the QSO luminosity function at z ∼ 5 and a mild redshift evolution of the space density of ultrabright QSOs (M 1450 ∼ −28.5) at 3 < z < 5.5, in agreement with the redshift evolution of the much fainter active galactic nucleus (AGN) population at M 1450 ∼ −23. These findings are consistent with a pure density evolution for the AGN population at z > 3. Adopting our z ∼ 4 QSO luminosity function and applying a mild density evolution in redshift, a photoionization rate of Γ HI = 0.46 − 0.09 + 0.17 × 10 − 12 s − 1 has been obtained at z = 4.75, assuming an escape fraction of ∼70% and a steep faint-end slope of the AGN luminosity function. The derived photoionization rate is ∼50–100% of the ionizing background measured at the end of the reionization epoch, suggesting that AGNs could play an important role in the cosmological reionization process.


2022 ◽  
Vol 82 (1) ◽  
Author(s):  
Kamal Bora ◽  
R. F. L. Holanda ◽  
Shantanu Desai ◽  
S. H. Pereira

AbstractIn this paper, we implement a test of the standard law for the dark matter density evolution as a function of redshift. For this purpose, only a flat universe and the validity of the FRW metric are assumed. A deformed dark matter density evolution law is considered, given by $$\rho _c(z) \propto (1+z)^{3+\epsilon }$$ ρ c ( z ) ∝ ( 1 + z ) 3 + ϵ , and constraints on $$\epsilon $$ ϵ are obtained by combining the galaxy cluster gas mass fractions with cosmic chronometers measurements. We find that $$\epsilon =0$$ ϵ = 0 within 2$$\sigma $$ σ c.l., in full agreement with other recent analyses.


2021 ◽  
Author(s):  
John Fegyveresi ◽  
Richard Alley ◽  
Joan Fitzpatrick ◽  
Donald Voigt ◽  
Zoe Courville ◽  
...  

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