Emission-line Variable Active Galactic Nuclei at Cosmic Noon from HETDEX
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| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| author | Liu, Chenxu Kong, Fanchuan Cooper, Erin Mentuch Davis, Dustin Guo, Wei-Jian Schneider, Donald P. Xu, Liang Gebhardt, Karl Hill, Gary J. Kollatschny, Wolfram Krumpe, Mirko Mukae, Shiro Powell, M. C. Farrow, Daniel J. |
| author_facet | Liu, Chenxu Kong, Fanchuan Cooper, Erin Mentuch Davis, Dustin Guo, Wei-Jian Schneider, Donald P. Xu, Liang Gebhardt, Karl Hill, Gary J. Kollatschny, Wolfram Krumpe, Mirko Mukae, Shiro Powell, M. C. Farrow, Daniel J. |
| contents | We present the first statistical census of emission-line variable active galactic nuclei (EVA) at cosmic noon by combining untargeted and deep HETDEX spectroscopy with multi-epoch spectra from SDSS, DESI, and LAMOST. Anchoring all candidates to a HETDEX spectroscopic epoch and requiring AGN classification in either the HETDEX or the external epoch(s), we identify a homogeneous sample of 100 EVA at z~1.5, including 98 newly identified. Emission-line variability is selected primarily through statistically significant line-flux changes, supplemented by extensive visual inspections using contemporaneous photometric light curves. The resulting incidence fraction is $f_{\rm EVA} \approx 0.9\%$. The rest-frame intervals between spectroscopic epochs span $\sim$1--10 yr, with brightening and dimming events exhibiting statistically indistinguishable characteristic timescales ($ΔT\sim2.2$ and $\sim2.6$ yr, respectively). A key result is the characterization of the Baldwin effect in the time domain: while many EVA follow the ensemble Baldwin effect (eBeff) between two epochs, a substantial fraction exhibit apparent anti-eBeff responses. Time-resolved spectroscopy of an individual source reveals that the intrinsic EW--luminosity relation is non-stationary, with the line-to-continuum responsivity systematically evolving from stronger to weaker across successive variability cycles; sparse two-epoch sampling of this evolving intrinsic Baldwin evolution (iBeff) naturally produces both eBeff-like and anti-eBeff behaviors. Finally, EVA show no strong preference for extreme Eddington ratios but exhibit a mild tendency toward lower $λ_{\rm Edd}$ values relative to matched control samples, driven primarily by sources observed in their dim states. Together, these results establish a coherent framework for interpreting emission-line variability in AGN at the peak epoch of cosmic black hole growth. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_18519 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Emission-line Variable Active Galactic Nuclei at Cosmic Noon from HETDEX Liu, Chenxu Kong, Fanchuan Cooper, Erin Mentuch Davis, Dustin Guo, Wei-Jian Schneider, Donald P. Xu, Liang Gebhardt, Karl Hill, Gary J. Kollatschny, Wolfram Krumpe, Mirko Mukae, Shiro Powell, M. C. Farrow, Daniel J. Astrophysics of Galaxies We present the first statistical census of emission-line variable active galactic nuclei (EVA) at cosmic noon by combining untargeted and deep HETDEX spectroscopy with multi-epoch spectra from SDSS, DESI, and LAMOST. Anchoring all candidates to a HETDEX spectroscopic epoch and requiring AGN classification in either the HETDEX or the external epoch(s), we identify a homogeneous sample of 100 EVA at z~1.5, including 98 newly identified. Emission-line variability is selected primarily through statistically significant line-flux changes, supplemented by extensive visual inspections using contemporaneous photometric light curves. The resulting incidence fraction is $f_{\rm EVA} \approx 0.9\%$. The rest-frame intervals between spectroscopic epochs span $\sim$1--10 yr, with brightening and dimming events exhibiting statistically indistinguishable characteristic timescales ($ΔT\sim2.2$ and $\sim2.6$ yr, respectively). A key result is the characterization of the Baldwin effect in the time domain: while many EVA follow the ensemble Baldwin effect (eBeff) between two epochs, a substantial fraction exhibit apparent anti-eBeff responses. Time-resolved spectroscopy of an individual source reveals that the intrinsic EW--luminosity relation is non-stationary, with the line-to-continuum responsivity systematically evolving from stronger to weaker across successive variability cycles; sparse two-epoch sampling of this evolving intrinsic Baldwin evolution (iBeff) naturally produces both eBeff-like and anti-eBeff behaviors. Finally, EVA show no strong preference for extreme Eddington ratios but exhibit a mild tendency toward lower $λ_{\rm Edd}$ values relative to matched control samples, driven primarily by sources observed in their dim states. Together, these results establish a coherent framework for interpreting emission-line variability in AGN at the peak epoch of cosmic black hole growth. |
| title | Emission-line Variable Active Galactic Nuclei at Cosmic Noon from HETDEX |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2603.18519 |