Peculiar emission line spectra of core extremely red BOSS quasars at z∼2–3: orientation and/or evolution?

M. V. M. acknowledges support from the Spanish Ministerio de Ciencia, Innovacion y Universidades through the grants AYA2015- 64346-C2-2-P and PGC2018-094671-B-I00 (MCIU/AEI/FEDER,UE). M. P. is supported by the Programa Atraccion de Talento de la Comunidad de Madrid via grant 2018-T2/TIC-11715. M. P. acknowledges support from the Spanish Ministerio de Economia y Competitividad through the grant ESP2017-83197-P. AH acknowledges FCT Fellowship SFRH/BPD/107919/2015; Support from European Community Programme (FP7/2007-2013) under grant agreement No. PIRSES-GA-2013-612701 (SELGIFS); Support from FCT through national funds (PTDC/FIS-AST/3214/2012 and UID/FIS/04434/2013), and by FEDER through COMPETE (FCOMP-01-0124-FEDER-029170) and COMPETE2020 (POCI-01-0145-FEDER-007672). S. M. acknowledges financial support through grant AYA2016-76730-P (MINECO/FEDER).