C M Harrison

We present a novel approach to inspecting galaxy spectra using sound, via their direct audio representation (‘spectral audification’). We discuss the potential of this as a complement to (or stand-in for) visual approaches. We surveyed 58 respondents who use the audio representation alone to rate 30 optical galaxy spectra with strong emission lines. Across three tests, each focusing on different quantities measured from the spectra (signal-to-noise ratio, emission-line width, and flux ratios), we find that user ratings are well correlated with measured quantities. This demonstrates that physical information can be independently gleaned from listening to spectral audifications. We note the importance of context when rating these sonifications, where the order examples are heard can influence responses. Finally, we adapt the method used in this promising pilot study to spectral datacubes. We suggest that audification allows efficient exploration of complex, spatially resolved spectral data.

We present polarization images of 9 radio-loud (RL) quasars from the VLA B-array at 6 GHz. These quasars belong to the Palomar-Green (PG) ‘blazar’ sample comprising 16 RL quasars and 8 BL Lac objects. Extensive polarization is detected in the cores, jets and lobes of all the quasars, with cores primarily displaying magnetic (B-) fields transverse to, and jets displaying fields aligned with the jet direction. Hotspots display either transverse B-fields signifying B-field compression at terminal shocks or more complex structures. The fractional polarization in the cores ranges from 1-10 per cent and jets/lobes from 10-40 per cent. Several of the quasars show distorted or hybrid FRI/FRII radio morphologies with indications of restarted AGN activity. We attribute this to the optical/UV selection criteria of the PG sample that remains unbiased at radio frequencies. The in-band spectral indices of the radio cores are relatively flat while they are steep in the hotspots. This is consistent with the polarization structures where the hotspots appear to be locations of jet bends or bow-shocks. We present global properties for the entire PG ‘blazar’ sample. We find that jet powers correlate with accretion rates for the quasars; higher accretion rates result in more powerful radio jets. A correlation between the radio core fractional polarization and the 150 MHz total radio luminosity for the 9 quasars studied here may imply that more organized B-fields at the jet bases lead to higher core fractional polarization and to more radio powerful radio jets.