Accurate Systemic Redshifts and Outflow Speeds for Extremely Red Quasars (ERQs)

Extremely Red Quasars (ERQs) are thought to represent a brief episode of young quasar and galactic evolution characterized by rapid outflows and obscured growth due to dusty environments. We use new redshift measurements from CO and Ly$\alpha$ emission-lines to better constrain outflow velocities from previous line measurements. We present sample of 82 ERQs, and the analysis confirms that ERQs have a higher incidence of large CIV blueshifts, accompanied by large Rest Equivalent Widths (REWs) and smaller line widths than blue quasars. We find that strong blueshifts (>2000 km s$^{-1}$) are present in 12/54 (22.22 per cent) of ERQs with the most robust redshift indicators. At least 4 out of 15 ERQs in the sample also have blueshifts in their H$\beta$ and low-ionization UV lines ranging from $-$500 to $-$1500 km s$^{-1}$. ERQs with strong CIV blueshifts are substantially offset in CIV REW and Full-Width at Half-Maximum (FWHM) from typical blue quasars in the same velocity range. ERQs have average values of REW = 124 A and FWHM = 5274 km s$^{-1}$, while blue quasars have REW = 24 A and FWHM = 6973 km s$^{-1}$. The extreme nature of the outflows in ERQs might explain some of their other spectral properties, such as the large CIV REWs and peculiar wingless profiles owing to more extended broad-line regions participating in outflows. The physical reasons for the extreme outflow properties of ERQs are unclear; however, larger Eddington ratios and/or softer ionizing spectra incident on the outflow gas cannot be ruled out.