Astronomy Tea Talk

Identifying quasars at z > 5 is observationally challenging; they are rare (~10⁻⁹ Mpc⁻³ at z ~ 6) and require significant telescope time. While next-generation facilities like 4MOST and LSST will soon survey the southern hemisphere, can we identify these rare objects with limited photometric data? With a custom SED fitting methodology and selection pipeline, we created a catalog of 6,125 quasar candidates at z > 4.5 that will soon be observed with 4MOST. Spectroscopic follow-up at Palomar has already confirmed 2 candidates at z > 5.2. However, finding these distant quasars only raises more questions—what can they reveal about their environments? Do radio jets fundamentally alter their circumgalactic medium? Previous studies have shown conflicting results, and systematic investigations of radio-loud systems at the highest redshifts (z > 5) remain limited. We obtained MUSE integral field spectroscopy of 17 radio-loud quasars at 3.6 < z < 6.4 and detected extended Lyα halos in >70% of targets, significantly higher than the 38% rate for radio-quiet quasars at z>5. Our sample shows more extended morphologies, higher Lyα luminosities, and notably broader line widths than [CII] emission, indicating more turbulent gas kinematics. These results suggest radio jets may drive energetic feedback processes that actively reshape the circumgalactic medium during the epoch of reionization. Larger samples and multi-line observations will be necessary to confirm these findings and gain a deeper understanding of the physical mechanisms driving jet-CGM interactions.