The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars

Abstract

We present Spitzer Space Telescope photometry of 18 Sloan Digital Sky Survey (SDSS) quasars at 2.7 z 5.9 which have weak or undetectable high-ionization emission lines in their rest-frame ultraviolet (UV) spectra (hereafter weak-lined quasars, or WLQs). The Spitzer data are combined with SDSS spectra and ground-based, near-infrared (IR) photometry of these sources to produce a large inventory of spectral energy distributions (SEDs) of WLQs across the rest-frame ∼0.1-5 μm spectral band. The SEDs of our sources are inconsistent with those of BL Lacertae objects which are dominated by synchrotron emission due to a jet aligned close to our line of sight, but are consistent with the SED of ordinary quasars with similar luminosities and redshifts that exhibit a near-to-mid-IR "bump," characteristic of hot dust emission. This indicates that broad emission lines in WLQs are intrinsically weak, rather than suffering continuum dilution from a jet, and that such sources cannot be selected efficiently from traditional photometric surveys.

Detection of Rest-Frame Optical Lines From X-Shooter Spectroscopy of Weak Emission-Line Quasars

“…Dilution of emission lines by a beamed relativistic jet (as is partly responsible for the weak BELR emission from BL Lac objects; Blandford & Rees 1978) is also extremely unlikely: WLQs are not radioloud 16 (Collinge et al 2005;DS09;P10), their optical emission is not polarized (Fan et al 1999;Smith et al 2007; DS09; Heidt & Nilsson 2011), their X-ray to optical luminosity ratios are smaller than for BL Lac objects (Shemmer et al 2009, P10, Plotkin et al 2010bWu et al 2011Wu et al , 2012 , and their infrared (IR) colors are also different from BL Lac objects (Plotkin et al 2012). Further arguing against a beamed synchrotron continuum, the UV through IR spectral energy distributions (SEDs) of WLQs are similar to other SDSS quasars, showing "big blue bump" emission in the UV and reprocessed dust radiation in the IR (Lane et al 2011;Wu et al 2012). WLQs are also far too luminous for their weak or absent BELRs to be explained by a radiatively inefficient accretion flow due to low Eddington ratios, as has been proposed for so-called "optically dull" active galactic nuclei (AGN; e.g., Nicastro et al 2003;Hawkins 2004;Tran et al 2011;Trump et al 2011).…”

RADIO-WEAK BL LAC OBJECTS IN THEFERMIERA

“…For the two RWBL selected we also built the SEDs to check if they are similar or not to those of WELQs (Lane et al 2011). Analysis of the SEDs is equivalent to comparing broad band spectral indices that could give an additional indication of the differences between BL Lacs and WELQs (see e.g Wu et al 2012).…”

OPTICAL SPECTROSCOPY OF SDSS J004054.65-0915268: THREE POSSIBLE SCENARIOS FOR THE CLASSIFICATION. A z ∼ 5 BL LACERTAE, A BLUE FSRQ, OR A WEAK EMISSION LINE QUASAR

“…For comparison, the SED of QSO is reported (orange dashed line, Richards et al 2006). Black dots are from Spitzer IR (Lane et al 2011). using typical values for the parameters (see, e.g Ghisellini et al 2010), to check the consistency of the different classifications. Figure 4 shows the spectrum produced by a disk around a black hole of mass M BH =1.9×10…”

“…Although in the literature there are a number of papers that discuss the existence of quasars with weak emission lines (see, e.g., Diamond-Stanic et al 2009;Plotkin et al 2010;Lane et al 2011;Meusinger et al 2014), no exhaustive broadband spectral energy distributions (SEDs) are interpreted adopting various models, ranging from normal QSO to BL Lacs. In particular, in this work, we present SEDs assembled with data from far-IR to X-Rays data and we apply physical models to possibly shed light on the nature of the source.…”