QSOs redshifts and photometry

For redshifts 0.8<z<=1.5, the red and blue quasars have a radio-detection fraction of 0.153^+0.037^_-0.032_ and 0.132^+0.034^_-0.030_, respectively. The red and blue quasars with redshifts 1.5<z<=2.4 have radio-detection fractions of 0.059+0.019_-0.016_ and 0.060^+0.019^_-0.016_, respectively, and the red and blue quasars with redshifts z>2.4 have radio-detection fractions of 0.029^+0.017^_-0.012_ and 0.058^+0.024^_-0.019_, respectively.

For the WISE color-selected red quasars, we find a radio-detection fraction of 0.160^+0.038^_-0.034_ for redshifts 0.8<z<=1.5, 0.063^+0.020^_-0.017_ for redshifts 1.5<z<=2.4, and 0.051^+0.030^_-0.022_ for redshifts z>2.4. In other words, we find similar radio-detection fractions for red and blue quasars within <1{sigma} uncertainty, independent of redshift. This disagrees with what has been found in the literature for red quasars in SDSS.

It should be noted that the fraction of broad absorption line (BAL) quasars in red SDSS quasars is about five times lower. BAL quasars have been observed to be more frequently radio quiet than other quasars, therefore the difference in BAL fractions could explain the difference in radio-detection fraction. The dusty torus of a quasar is transparent to radio emission.

When we do not observe a difference between red and blue quasars, it leads us to argue that orientation is the main cause of quasar redness. Moreover, the observed higher proportion of BAL quasars in our dataset relative to the SDSS sample, along with the higher rate of radio detections, indicates an association of the redness of quasars and the inherent BAL fraction within the overall quasar population. This correlation suggests that the redness of quasars is intertwined with the inherent occurrence of BAL quasars within the entire population of quasars.

In other words, the question why some quasars appear red or exhibit BAL characteristics might not be isolated; it could be directly related to the overall prevalence of BAL quasars in the quasar population. This finding highlights the need to explore the underlying factors contributing to both the redness and the frequency of BAL quasars, as they appear to be interconnected phenomena.