H\(\alpha\) and H\(\beta\) lines in low and high redshift type 2 (obscured) quasars

Abstract

Quasars are a type of extremely luminous AGN's (active galactic nuclei), and they can be divided into type 1 and type 2 based on orientation and obscuration according to the unified model of AGN. However, the classification of type 2 quasars is not as straightforward as one might hope. Some have proposed that the distinction of the two types is not purely viewpoint-induced, but involves intrinsic evolutionary differences as well. In this context, we attempt to contribute to the study of type 2 quasars by measuring H\(\alpha\) and H\(\beta\) on two samples of quasars: 1) a small sample of type 2 (obscured) quasars at relatively high redshift of 0.5 to 0.8; and 2) a larger sample of both types of quasars at relatively low redshift (below 0.34). We find that the optically-selected type 2 quasars based on narrow H\(\beta\) often have a broad H\(\alpha\), and these targets exhibit high extinction ratio of about 1 or higher. We also find that the widths of the narrow H\(\alpha\) and narrow H\(\beta\) have a quasi-linear relationship, and the same is true for the broad widths when they are present. In addition, we find that the objects with only narrow H\(\beta\) tend to have lower total H\(\alpha\) luminosity as well, especially for the lower redshift sample. However, to arrive at more reliable conclusions, we would need to check these results with larger samples covering broader range of redshifts.