Broad-band spectral energy distribution of 3000 Angstroem break quasars from the Sloan Digital Sky Survey

TL;DR

This study identifies and analyzes a rare class of quasars with a 3000 Å spectral break, revealing they are likely extreme BAL quasars with higher intrinsic luminosity, based on broad-band spectral energy distributions from multiple surveys.

Contribution

It systematically searches for 3000 Å break quasars using self-organising maps and characterizes their spectral energy distributions, linking them to BAL quasars and revealing their intrinsic luminosity.

Findings

3000 Å break quasars are similar to BAL quasars after correction for dust reddening.

They are intrinsically more luminous than typical quasars.

The spectral energy distributions suggest they are extreme versions of BAL quasars.

Abstract

The Sloan Digital Sky Survey (SDSS) discovered a few unusual quasars with a characteristic break in the continuum around 3000 A that neither shows the typical structure of broad absorption line (BAL) troughs nor is explained by typical intrinsic dust reddening. We used the method of Kohonen self-organising maps for a systematical search for quasars with such properties in the SDSS spectra archive. We constructed a sample of 23 quasars classified as 3000 A break quasars and two comparison samples of quasars with similar properties, to some extent, but also showing typical BAL features. We computed ensemble-averaged broad-band SEDs based on archival data from SDSS, GALEX, 2MASS, UKIDSS, and WISE. The SEDs were corrected for intrinsic dust absorption by the comparison with the average SED of normal quasars. The de-reddened arithmetic median composite SED of the 3000 A break quasars is found to be indistinguishable from that of the unusual BAL quasars. We conclude that 3000 A break quasars are most likely extreme versions of BAL quasars. Assuming that the intrinsic SED of the continuum source is represented by the quasar composite SED, the 3000 A break quasars tend to be intrinsically more luminous than ordinary quasars. (Abstract modified to match the arXiv format.)