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

Abstract

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 (2 σ ) 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 Ly α 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 × 10 43 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 Ly α 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 Log 10 ( M h [ M ⊙ ] ) ≃ 12.2 − 1.2 + 0.7 . We compare these results to existing surveys at higher and lower redshift.