Exploring the radio loudness of SDSS quasars with spectral stacking

Arnaudova, M I; Smith, D J B; Hardcastle, M J; Das, S; Drake, A; Duncan, K; Gürkan, G; Magliocchetti, M; Morabito, L K; Petley, J W; Shenoy, S; Tasse, C

Abstract

We use new 144 MHz observations over 5634 deg2 from the LOFAR (Low Frequency Array) Two-metre Sky Survey (LoTSS) to compile the largest sample of uniformly selected, spectroscopically confirmed quasars from the 14th data release of the Sloan Digital Sky Survey (SDSS-DR14). Using the classical definition of radio loudness, R = log (L1.4GHz/Li), we identify 3697 radio-loud (RL) and 111 132 radio-quiet (RQ) sources at 0.6 < z < 3.4. To study their properties, we develop a new rest-frame spectral stacking algorithm, designed with forthcoming massively multiplexed spectroscopic surveys in mind, and use it to create high signal-to-noise composite spectra of each class, matched in redshift and absolute i-band magnitude. We show that RL quasars have redder continuum and enhanced [O II] emission than their RQ counterparts. These results persist when additionally matching in black hole mass, suggesting that this parameter is not the defining factor in making a quasi-stellar object (QSO) RL. We find that these features are not gradually varying as a function of radio loudness, but are maintained even when probing deeper into the RQ population, indicating that a clear-cut division in radio loudness is not apparent. Upon examining the star formation rates (SFRs) inferred from the [O II] emission line, with the contribution from active galactic nucleus removed using the [Ne V] line, we find that RL quasars have a significant excess of star formation relative to RQ quasars out to z = 1.9 at least. Given our findings, we suggest that RL sources either preferably reside in gas-rich systems with rapidly spinning black holes, or represent an earlier obscured phase of QSO evolution.

Citation

Arnaudova, M. I., Smith, D. J. B., Hardcastle, M. J., Das, S., Drake, A., Duncan, K., …Tasse, C. (2024). Exploring the radio loudness of SDSS quasars with spectral stacking. Monthly Notices of the Royal Astronomical Society, 528(3), 4547-4567. https://doi.org/10.1093/mnras/stae233

• Journal Article Type: Article
• Acceptance Date: Jan 16, 2024
• Online Publication Date: Jan 22, 2024
• Publication Date: 2024-03
• Deposit Date: Mar 13, 2024
• Publicly Available Date: Mar 13, 2024
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 528
• Issue: 3
• Pages: 4547-4567
• DOI: https://doi.org/10.1093/mnras/stae233
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://durham-repository.worktribe.com/output/2326881