The FLASHES Survey. I. Integral Field Spectroscopy of the CGM around 48 z ≃ 2.3-3.1 QSOs

We present the pilot study of the Fluorescent Lyman-Alpha Structures in High-z Environments Survey; the largest integral field spectroscopy survey to date of the circumgalactic medium at z = 2.3-3.1. We observed 48 quasar fields with the Palomar Cosmic Web Imager to an average (2σ) limiting surface brightness of 6 10^-18 erg s^-1 cm^-2 arcsec^-2 (in a 1″ aperture and ∼20 Å bandwidth). Extended H i Lyα emission is discovered around 37/48 of the observed quasars, ranging in projected radius from 14 to 55 proper kiloparsecs (pkpc), with one nebula exceeding 100 pkpc in effective diameter. The dimming-adjusted circularly averaged surface brightness profile peaks at 1 10^-15 erg s^-1 cm^-2 arcsec^-2 at R _⊥ ∼ 20 pkpc and integrated luminosities range from 0.4 to 9.4 10⁴³ erg s^-1. The emission appears to have an eccentric morphology and an average covering factor of ∼30%-40% at small radii. On average, the nebular spectra are redshifted 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 profiles with global dispersions ranging from 143 to 708 km s^-1, though the individual Gaussian components of lines with complex shapes mostly 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 QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with those expected from gravitational motions in dark matter halos of mass Log₁₀(M_h[M])≃ 12.2_-1.2}^+0.7. We compare these results to existing surveys at higher and lower redshift.