"The Mean Metal-line Absorption Spectrum of Damped Lyman Alpha Systems in BOSS", ApJ, 846, 4. - L. Mas-Ribas, J. Miralda-Escudé, I. Pérez-Ràfols, et al. 2017.

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 This paper studies an average spectrum of absorption of intergalactic Damped Lyman Alpha systems (dense clouds of gas associated with galaxies
that are forming), carefully observing their metal lines, which are absorption lines by ions of the heavy elements that are present in the gas. This is obtained from the quasar spectra of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III, and allows a careful observation of the average spectrum of many of these systems. Interesting physical properties of the entire sample can be derived from this average, low-quality spectrum, even though individual systems can be studied in much greater detail from individual spectra of much better quality obtained in large telescopes with high-resolution spectroscopy.