Constraint on the time variation of the fine-structure constant with the SDSS-III/BOSS DR12 quasar sample

From the Sloan Digital Sky Survey Data Release 12, which covers the full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate the possible variation of the fine-structure constant over cosmological time scales. We a nalyze the largest quasar sample considered so far in the literature, which contains 10,363 s pectra with z< 1. All the BOSS quasar spectra are selected from a visually inspected quasar catalog. We apply the emission line method on the [Oiii] doublet (λλ 4960, 5008 A) and obtain�α/α = (1.4± 2.3)× 10 −5 for the relative variation of the fine-structure constant. We al so investigate the possible sources of systematics: misidentification of the lines, sky OH lines , Hβ and broad line contamination, optimal wavelength range for the Gaussian fits, chosen polyn omial order for the continuum spectrum, signal-to-noise ratio and good quality of the fits . The uncertainty of the measurement is dominated by the sky subtraction. The results presented in this work, being systematics limited, have suffi cient statistics to constrain robustly the variation of the fine structure constant in redshift bins (�z≈ 0.06) over the last 7.9 Gyr. In addition, we study the [Neiii] doublet (λλ 3870, 3969 A) present in 462 quasar spectra; and discuss the systematic effects on using these emission lines to constrain the fine-structure c onstant variation. Better constraints on �α/α (< 10 −6 ) using the emission line method would be possible with high resolution spectroscopy.