A striking excess of red quasars with steep radio spectral slopes: a dusty blow-out phase revealed through AGN-driven shocks?
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| Format: | Preprint |
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2026
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| _version_ | 1866908913937416192 |
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| author | Sargent, Ciera L. Alexander, David M. Greenwell, Claire L. Fawcett, Victoria A. Morabito, Leah K. Harrison, Chris M. Meenakshi, Moun Hickox, Ryan C. |
| author_facet | Sargent, Ciera L. Alexander, David M. Greenwell, Claire L. Fawcett, Victoria A. Morabito, Leah K. Harrison, Chris M. Meenakshi, Moun Hickox, Ryan C. |
| contents | Red quasars exhibit a higher incidence of compact (galaxy-scale or smaller) radio emission than blue quasars, arising from systems near the radio-loud/radio-quiet threshold. In this paper we select quasars from SDSS ($0.2 <z <2.4$), and use archival radio data (FIRST, VLASS, LoTSS) to visually determine the radio morphologies of 573 red quasars compared to a control sample of 1278 typical blue quasars. We find an excess of steep-slope radio emission ($α_{1.4-3\text{ GHz}}\sim-1$, where $S_ν\propto ν^α$) from red quasars with compact ($<6''$) radio morphologies over 144 MHz, 1.4 GHz, and 3 GHz. This excess steep radio emission signature is not seen in normal blue quasars (radio compact or extended) or red quasars with extended low-frequency radio emission, which instead show a broad range of radio spectral slopes consistent with a range of different physical processes. We show that the strength of the excess steep spectral slope component increases with dust extinction, along with an overall increase in the radio-detection fraction. We argue that this excess steep-slope radio emission is due to shocks between quasar-driven winds/jets and the dusty nuclear-host galaxy environment. The majority ($86^{+5}_{-21}\%$) of the dustiest quasars ($E(B-V)>0.4$ mag) with steep slopes have radio luminosities consistent with the prediction from a wind-shock model with wind efficiencies of up to 7%. This agrees with the scenario where these compact red quasars are undergoing a "dusty blow-out" phase, where compact jets and/or AGN-driven winds interact with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_24739 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A striking excess of red quasars with steep radio spectral slopes: a dusty blow-out phase revealed through AGN-driven shocks? Sargent, Ciera L. Alexander, David M. Greenwell, Claire L. Fawcett, Victoria A. Morabito, Leah K. Harrison, Chris M. Meenakshi, Moun Hickox, Ryan C. Astrophysics of Galaxies Red quasars exhibit a higher incidence of compact (galaxy-scale or smaller) radio emission than blue quasars, arising from systems near the radio-loud/radio-quiet threshold. In this paper we select quasars from SDSS ($0.2 <z <2.4$), and use archival radio data (FIRST, VLASS, LoTSS) to visually determine the radio morphologies of 573 red quasars compared to a control sample of 1278 typical blue quasars. We find an excess of steep-slope radio emission ($α_{1.4-3\text{ GHz}}\sim-1$, where $S_ν\propto ν^α$) from red quasars with compact ($<6''$) radio morphologies over 144 MHz, 1.4 GHz, and 3 GHz. This excess steep radio emission signature is not seen in normal blue quasars (radio compact or extended) or red quasars with extended low-frequency radio emission, which instead show a broad range of radio spectral slopes consistent with a range of different physical processes. We show that the strength of the excess steep spectral slope component increases with dust extinction, along with an overall increase in the radio-detection fraction. We argue that this excess steep-slope radio emission is due to shocks between quasar-driven winds/jets and the dusty nuclear-host galaxy environment. The majority ($86^{+5}_{-21}\%$) of the dustiest quasars ($E(B-V)>0.4$ mag) with steep slopes have radio luminosities consistent with the prediction from a wind-shock model with wind efficiencies of up to 7%. This agrees with the scenario where these compact red quasars are undergoing a "dusty blow-out" phase, where compact jets and/or AGN-driven winds interact with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates. |
| title | A striking excess of red quasars with steep radio spectral slopes: a dusty blow-out phase revealed through AGN-driven shocks? |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2603.24739 |