Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1

JWST observations have uncovered a new population of red, compact objects at high redshifts dubbed “little red dots” (LRDs), which typically show broad emission lines and are thought to be dusty active galactic nuclei (AGNs). Some of their other features, however, challenge the AGN explanation, such as prominent Balmer breaks and extremely faint or even missing metal high-ionization lines, X-ray, or radio emission, including in deep stacks. Time variability is another robust test of AGN activity. Here, we exploit the z = 7.045 multiply imaged LRD A2744-QSO1, which offers a particularly unique test of variability due to lensing-induced time delays between the three images spanning 22 yr (2.7 yr in the rest-frame), to investigate its photometric and spectroscopic variability. We find the equivalent widths (EWs) of the broad H α and H β lines, which are independent of magnification and other systematics, to exhibit significant variations, of up to 18 ± 3% for H α and up to 22 ± 8% in H β , on a timescale of 875 d (2.4 yr) in the rest-frame. This suggests that A2744-QSO1 is indeed an AGN. We find no significant photometric variability beyond the limiting systematic uncertainties, so it currently cannot be determined whether the EW variations are due to line-flux or continuum variability. These results are consistent with a typical damped random walk variability model for an AGN such as A2744-QSO1 ( M BH = 4 × 10 7 M ⊙ ) given the sparse sampling of the light curve with the available data. Our results therefore support the AGN interpretation of this LRD, and highlight the need for further photometric and spectroscopic monitoring in order to build a detailed and reliable light curve.

Authors

Publication Details

Journal
Astronomy and Astrophysics
Published
2025-05-15
DOI
https://doi.org/10.1051/0004-6361/202554110
Citations
21
Primary Topic
Photoacoustic and Ultrasonic Imaging
Type
article
Field-Weighted Citation Impact
14.16

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article

Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1

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21 citations
Astronomy and Astrophysics
Photoacoustic and Ultrasonic Imaging
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article

Investigating photometric and spectroscopic variability in the multiply imaged little red dot A2744-QSO1

Seiji Fujimoto, Jorryt Matthee, Lukas J. Furtak, Rachel Bezanson, Vasily Kokorev, Karl Glazebrook, Sam E. Cutler, Richard Pan, Rohan P. Naidu, Jenny E. Greene, John R. Weaver, Miriam Golubchik, Robert Feldmann, Joel Leja, Iryna Chemerynska, Katherine A. Suess, Hakim Atek, Amy Secunda, Erica J. Nelson, Pascal A. Oesch, Gabriel Brammer, Ivo Labbé, Katherine E. Whitaker, Adi Zitrin, Sedona H. Price, Yilun Ma, Bingjie Wang, Pratika Dayal
article en
21 citations

Abstract

JWST observations have uncovered a new population of red, compact objects at high redshifts dubbed “little red dots” (LRDs), which typically show broad emission lines and are thought to be dusty active galactic nuclei (AGNs). Some of their other features, however, challenge the AGN explanation, such as prominent Balmer breaks and extremely faint or even missing metal high-ionization lines, X-ray, or radio emission, including in deep stacks. Time variability is another robust test of AGN activity. Here, we exploit the z = 7.045 multiply imaged LRD A2744-QSO1, which offers a particularly unique test of variability due to lensing-induced time delays between the three images spanning 22 yr (2.7 yr in the rest-frame), to investigate its photometric and spectroscopic variability. We find the equivalent widths (EWs) of the broad H α and H β lines, which are independent of magnification and other systematics, to exhibit significant variations, of up to 18 ± 3% for H α and up to 22 ± 8% in H β , on a timescale of 875 d (2.4 yr) in the rest-frame. This suggests that A2744-QSO1 is indeed an AGN. We find no significant photometric variability beyond the limiting systematic uncertainties, so it currently cannot be determined whether the EW variations are due to line-flux or continuum variability. These results are consistent with a typical damped random walk variability model for an AGN such as A2744-QSO1 ( M BH = 4 × 10 7 M ⊙ ) given the sparse sampling of the light curve with the available data. Our results therefore support the AGN interpretation of this LRD, and highlight the need for further photometric and spectroscopic monitoring in order to build a detailed and reliable light curve.

Astronomy and AstrophysicsVol. 698
National Science Foundation, National Aeronautics and Space Administration, Space Telescope Science Institute, Flatiron Health, European Commission, National Research Foundation, Rijksuniversiteit Groningen, Danmarks Grundforskningsfond, United States-Israel Binational Science Foundation
Openalex Percentile: Top 1%
Photoacoustic and Ultrasonic Imaging
14.16
DOIOpen Access PDFOpenAlex
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