APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Sofia Gallego (ETH Zurich)
Title: A new method to constrain the UVB via fluorescent Lyman-alpha emission
Date (JST): Thu, Apr 08, 2021, 16:00 - 17:00
Place: Zoom
Related File: 2652.pdf
Abstract: The cosmic UV background (UVB) shapes the ionization state and thermal evolution of the Intergalactic Medium (IGM) and it is, therefore, a crucial ingredient of cosmic structure formation models.
Most UVB studies focused primarily on characterizing the properties of the Lyα forest which assume parameters that are very difficult to estimate, such as the redshift evolution of the escape fraction of ionizing photons from faint galaxies. I will present an independent method to constrain the UVB and in particular, the photoionization rate of hydrogen ΓHI, based on the detection of fluorescent Lyα emission produced by Lyman Limit Systems (LLS) illuminated by the UVB. Our method provides direct observational constraints on the product of the ionizing radiation field intensity (ΓHI) and the covering factor of LLSs around our galaxies.
We apply this methodology to deep MUSE observations. In order to achieve the required sensitivity limits, we performed a three-dimensional stacking of the IGM around Lyman-α emitting galaxies (LAEs) between 2.9<z<6.6. Combining our results with covering fractions of LLSs obtained from mock cubes extracted from the EAGLE simulation, we obtain new and independent constraints on the UVB at z>3 that are consistent with previous measurements, with a preference for relatively low UVB intensities at z=3, and which suggest a non-monotonic decrease of ΓHI with increasing redshift between 3<z<5. This could suggest a possible tension between some UVB models and current observations which however require deeper and wider observations in Lyman-α emission and absorption to be confirmed. Assuming instead a value of UVB from current models, our results constrain the covering fraction of LLSs at 3<z<4.5 to be less than 25% within 150kpc from LAEs.