Intervening Mg II absorption systems from the SDSS DR12 quasar spectra

Intervening Mg II absorption systems from the SDSS DR12 quasar spectra
Monthly Notices of the Royal Astronomical Society (2016), 463, 2640.

Intervening Mg II absorption systems from the SDSS DR12 quasar spectra

Srinivasan Raghunathan1,2, Roger G. Clowes3, Luis E. Campusano1,
Ilona K. Söchting4, Matthew J. Graham5,6 and Gerard M. Williger3,7,8

1 Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Santiago, Chile
2 School of Physics, University of Melbourne, Parkville VIC 3010, Australia
3 Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
4 Astrophysics, Denys Wilkinson Building, Keble Road, University of Oxford, Oxford OX1 3RH, UK
5 California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
6 National Optical Astronomy Observatory, 950 N Cherry Avenue, Tucson, AZ 85719
7 Department of Physics and Astronomy, University of Louisville, KY 40292, USA
8 Institute for Astrophysics and Computational Sciences, The Catholic University of America, DC 20064, USA

We present the catalogue of the Mg II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the 12th data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars were searched for the presence of absorption systems in their spectra. The continuum modelling for the quasar spectra was performed using a mean filter. A pseudo-continuum derived using a median filter was used to trace the emission lines. The absorption system catalogue contains 39,694 Mg II systems detected at a 6.0, 3.0σ level respectively for the two lines of the doublet. The catalogue was constrained to an absorption line redshift of 0.35 ≤ z2796 ≤ 2.3. The rest-frame equivalent width of the λ2796 line ranges between 0.2 ≤ Wr ≤ 6.2 Å. Using Gaussian noise-only simulations, we estimate a false positive rate of 7.7 per cent in the catalogue. We measured the number density ∂N2796/∂z of Mg II absorbers and find evidence for steeper evolution of the systems with Wr ≥ 1.2 Å at low redshifts (z2796 ≤ 1.0), consistent with other earlier studies. A suite of null tests over the redshift range 0.5 ≤ z2796 ≤ 1.5 was used to study the presence of systematics and selection effects like the dependence of the number density evolution of the absorption systems on the properties of the background quasar spectra. The null tests do not indicate the presence of any selection effects in the absorption catalogue if the quasars with spectral signal-to-noise level less than 5.0 are removed. The resultant catalogue contains 36,981 absorption systems. The Mg II absorption catalogue is publicly available and can be downloaded from the link