Abstract

Contributed Talk - Splinter 4MOST   (MW-0337)

First Light on the Baryon Cycle: Initial 4MOST Survey Programme Validation Results from the ByCycle Survey

Rajesh Potlia
ESO Garching

The circumgalactic medium (CGM) is thought to hold a major share of the Universe's baryons and metals, yet it remains difficult to characterise directly. The ByCycle survey (S17) on ESO's 4MOST instrument addresses this by combining high-resolution quasar absorption spectroscopy with low-resolution emission spectroscopy of foreground galaxies, groups, and clusters in the same fields, ultimately aiming to probe the CGM of 1.5 million objects and build a legacy sample of Lyman-α and metal absorbers three orders of magnitude larger than currently available. Here, I present the first Survey Programme Validation (SPV) results from ByCycle, showing initial data quality, spectral performance, and early detections of quasar absorbers matched to foreground galaxies — an early validation of the survey's target selection and observing strategy ahead of full operations. Together, these results are intended to support validation of HRS performance for S17 and to help inform survey-wide best practices for robust high-resolution spectroscopy with 4MOST.