The FLASHES survey I: Integral field spectroscopy of the CGM around 48 z ' 2.3 − 3.1 QSOs

We present the pilot study component of the Fluorescent Lyman-Alpha Structures in High-z Environments (FLASHES) Survey; the largest integral-field spectroscopy survey to date of the circumgalactic medium at z = 2.3 − 3.1. We observed 48 quasar fields between 2015 and 2018 with the Palomar Cosmic Web Imager (Matuszewski et al. (2010)). Extended HI Lyman-α emission is discovered around 42/48 of the observed quasars, ranging in projected, flux-weighted radius from 21−71 proper kiloparsecs (pkpc), with 26 nebulae exceeding 100 pkpc in effective diameter. The circularly averaged surface brightness radial profile peaks at a maximum of 1 × 10⁻¹⁷ erg s⁻¹ cm⁻² arcsec⁻² (2 × 10⁻¹⁵ erg s⁻¹ cm⁻² arcsec⁻² adjusted for cosmological dimming) and luminosities range from 1.9×10⁴³ erg s⁻¹ to −14.1×10⁴³ erg s⁻¹. The emission appears to have a highly eccentric morphology and a maximum covering factor of 50% (60% for giant nebulae). On average, the nebular spectra are red-shifted with respect to both the systemic redshift and Lyα peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single or double-peaked line shapes with global dispersions ranging from 167 km s⁻¹ to 690 km s⁻¹, though the individual (Gaussian) components of lines with complex shapes mostly appear to have dispersions ≤ 400 km s⁻¹, and the flux-weighted velocity centroids of the lines vary by thousands of km s⁻¹ with respect to the systemic QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with gravitational motions expected in dark matter halos of mass M_h ' 10^12.5M☉. We compare these results to existing surveys at both higher and lower redshift.