Probing the Circumgalactic Medium at High-Redshift Using Composite BOSS Spectra of Strong Lyman-alpha Forest Absorbers

Understand

We present composite spectra constructed from a sample of 242,150 Lyman-alpha (Lya) forest absorbers at redshifts 2.4<z<3.1 identified in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) as part of Data Release 9 of the Sloan Digital Sky Survey III.

• We select forest absorbers by their flux in bins 138 km/s wide (approximately the size of the BOSS resolution element).
• We split these absorbers into five samples spanning the range of flux -0.05 < F<0.45.
• Tests on a smaller sample of high-resolution spectra show that our three strongest absorption bins would probe circumgalactic regions (projected separation < 300 proper kpc and |Delta v| < 300km/s) in about 60% of cases for very high signal-to-noise ratio.