Astrophysics Seminar

The circumgalactic medium (CGM) is the vast reservoir of gas that surrounds galaxies and plays a fundamental role in regulating galaxy growth through gas accretion, feedback, and interactions with the cosmic web. Among the most powerful tracers of the CGM is Lyman alpha (Lyα) emission, which reveals enormous gaseous nebulae extending far beyond galaxy disks.  These Lyα nebulae provide a unique probe of the exchange of matter and energy between galaxies and their environments, yet their origin remains an open question. Proposed powering mechanisms include resonant scattering, galactic outflows, cold gas accretion, or photoionization from active galactic nuclei (AGN) or star formation (SF).

In this talk, I will present the discovery of RaJav, a potentially largest circumgalactic Lyα nebula at cosmic noon, discovered in the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS). J-PAS is an optical survey in the  northern sky conducted with the 2.5 meter telescope at the Javalambre Astrophysical Observatory, Teruel, Spain. Exploiting J-PAS's unique combination of 56 contiguous narrow-band filters, a wide field of view, which together provide low-resolution integral field spectroscopy-like capabilities, We detect an enormous Lyα emission surrounding a pair of quasars at z=2.25 : a luminous SDSS quasar and a newly discovered fainter quasar separated by ~60 kpc. The nebula's luminosity, and morphology suggest that quasar photoionization is the dominant power source, with possible contributions from star formation and feedback-driven outflows. This discovery demonstrates the power of wide-field surveys like J-PAS to uncover extreme Lyα nebulae, offering new insights into the interplay between quasars, CGM gas, and the large-scale cosmic web during the peak epoch of galaxy formation.