| Abstract: | Quasars with extremely red infrared-to-optical colors are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called AGN unified model. To identify such a population we search the quasar catalogs of the Sloan Digital Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) and the Wide-Field Infrared Survey Explorer (WISE) for quasars with extremely high infrared-to-optical ratios. We identify 65 objects with r-W4>14 mag, i.e., F_nu(22um)/F_nu(r) >~1000. This sample spans a redshift range of 0.28 < z < 4.36 and has a bimodal distribution, with peaks at z~0.8 and $z~2.5. It includes three z>2.6 objects that are detected in the W4-band but not W1 or W2, i.e., ``W1W2-dropouts''. The SDSS/BOSS spectra show that the majority of the objects are reddened Type 1 quasars, Type 2 quasars (both at low and high redshift) or objects with deep low-ionization broad absorption lines (BALs) that suppress the observed $r$-band flux. In addition, we identify a class of Type 1 permitted broad-emission line objects at z~2-3 which are characterized by emission line rest-frame equivalent widths (REWs) of >150AA, much larger than those of typical quasars. These objects often also have unusual line ratios, and these large REWs might be caused by suppressed continuum emission analogous to Type 2 quasars; however, there is no obvious mechanism in the Unified Model to suppress the continuum without also obscuring the broad emission lines. |