ﻻ يوجد ملخص باللغة العربية
We investigate the implications of our measurement of the Lyman-alpha forest opacity at redshifts 2<z<4.2 from a sample of 86 high-resolution quasar spectra for the evolution of the cosmic ultraviolet luminosity density and its sources. The derived hydrogen photoionization rate is remarkably flat over this redshift range, implying an increasing comoving ionizing emissivity with redshift. Because the quasar luminosity function is strongly peaked near z~2, star-forming galaxies likely dominate the ionizing emissivity at z>~3. Our measurement argues against a star formation rate density declining beyond z~3, in contrast with existing state-of-the-art determinations of the cosmic star formation history from direct galaxy counts. Stellar emission from galaxies therefore likely reionized the Universe.
The combination of both contributions from the observed UV emission and the absorbed radiations reprocessed in the infrared represents the ideal approach to constrain the activity of massive star formation in galaxies. Using recent results from GALEX
We investigate the relation between star formation rates ($dot{M}_{s}$) and AGN properties in optically selected type 1 quasars at $2<z<3$ using data from Herschel and the SDSS. We find that $dot{rm{M}}_s$ remains approximately constant with redshift
We provide a systematic measurement of the rest-frame UV continuum slope beta over a wide range in redshift (z~2-6) and rest-frame UV luminosity (0.1-2L*) to improve estimates of the SFR density at high redshift. We utilize the deep optical and infra
The intensity of the Cosmic UV background (UVB), coming from all sources of ionising photons such as star-forming galaxies and quasars, determines the thermal evolution and ionization state of the intergalactic medium (IGM) and is, therefore, a criti
Recent studies of galaxies ~2-3 Gyr after the Big Bang have revealed large, turbulent rotating systems. The existence of well-ordered rotation in galaxies during this peak epoch of cosmic star formation may suggest that gas accretion through cold str