Flashlights: More than A Dozen High-Significance Microlensing Events of Extremely Magnified Stars in Galaxies at Redshifts z=0.7-1.5

Kelly, Patrick L.; Chen, Wenlei; Amruth, Alfred; Broadhurst, T.; Diego, J. M.; Emami, Najmeh; Filippenko, A. V.; Keen, Allison; Li, Sung Kei; Lim, Jeremy; Meena, Ashish Kumar; Oguri, Masamune; Scarlata, Claudia; Treu, Tommaso; Williams, Hayley; Williams, Liliya L. R.; Zhou, Rui; Zitrin, Adi; Foley, R. J.; Kaiser, Nick; Mehta, Vihang; Rieck, Steven; Salo, Laura; Smith, Nathan; Weisz, Daniel R.

doi:10.48550/arxiv.2211.02670

Cited by 9 publications

(7 citation statements)

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“…The star (named "Icarus"; Kelly et al 2018) was detected in a strongly lensed spiral galaxy (z = 1.49) and was found to have an estimated magnification factor of ∼2000. Several other lensed stars were since detected in HST imaging in various galaxy clusters (Rodney et al 2018;Chen et al 2019;Kaurov et al 2019;Diego et al 2022a;Meena et al 2022b;Welch et al 2022a), with rapidly increasing numbers (Kelly et al 2022). Thanks to the larger photon collecting area compared to HST, and its sensitivity to infrared light, the James Webb Space Telescope (JWST; Gardner et al 2006) significantly enhances our ability to detect such lensed stars, especially at higher redshifts (Windhorst et al 2018;Meena et al 2022a).…”

Section: Introductionmentioning

confidence: 99%

Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015

Meena

Zitrin

Jiménez-Teja

et al. 2023

ApJL

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We report the discovery of two extremely magnified lensed star candidates behind the galaxy cluster MACS J0647.7+015 using recent multiband James Webb Space Telescope (JWST) NIRCam observations. The star candidates are seen in a previously known, z phot ≃ 4.8 dropout giant arc that straddles the critical curve. The candidates lie near the expected critical curve position, but lack clear counter-images on the other side of it, suggesting these are possibly stars undergoing caustic crossings. We present revised lensing models for the cluster, including multiply imaged galaxies newly identified in the JWST data, and use them to estimate background macro-magnifications of at least ≳90 and ≳50 at the positions of the two candidates, respectively. With these values, we expect effective, caustic-crossing magnifications of ∼[103–105] for the two star candidates. The spectral energy distributions of the two candidates match well the spectra of B-type stars with best-fit surface temperatures of ∼10,000 K, and ∼12,000 K, respectively, and we show that such stars with masses ≳20 M ⊙ and ≳50 M ⊙, respectively, can become sufficiently magnified to be observable. We briefly discuss other alternative explanations and conclude that these objects are likely lensed stars, but also acknowledge that the less-magnified candidate may alternatively reside in a star cluster. These star candidates constitute the second highest-redshift examples to date after Earendel at z phot ≃ 6.2, establishing further the potential of studying extremely magnified stars at high redshifts with JWST. Planned future observations, including with NIRSpec, will enable a more detailed view of these candidates in the near future.

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Section: Introductionmentioning

confidence: 99%

Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015

Meena

Zitrin

Jiménez-Teja

et al. 2023

ApJL

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“…Director's Discretionary program (DD-2767; PI: P. Kelly), whose primary goal is to measure the light curves and spectra of a strongly lensed supernova SN 2022riv at z = 1.52 49,50 discovered in the RXJ2129 field, by a HST SNAP program (GO-16729; PI P. Kelly). The exposure times are 4982 seconds for the F150W/F356W filters, and are 2061 seconds for the other four NIRCam filters (F115W, F200W, F277W, and F444W).…”

Section: Methodsmentioning

confidence: 99%

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

Wang

Cheng

Ge³

et al. 2022

Preprint

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Cosmic hydrogen reionization and cosmic production of first metals are major phase transitions of the Universe occurring during the first billion years after the Big Bang, but still poorly explored observationally. Using the JWST NIRSpec prism spectroscopy, we report the discovery of a sub-L* galaxy at zspec = 8.1623-0.0008+0.0007, dubbed RXJ2129-z8HeII, via the detection of a series of strong rest-frame UV/optical nebular emission lines and the clear Lyman break. A strong He II λ1640 emission is present, the highest redshift He II line currently known. Its high rest-frame equivalent width (EW=19.38 ± 3.24 Å) and extreme flux ratios with respect to UV metal lines and Balmer lines raise the possibility that part of RXJ2129-z8HeII's stellar populations could be Pop III-like5,6. RXJ2129-z8HeII also shows a pronounced UV continuum with an extremely steep (i.e. blue) spectral slope of β =-2.50±0.08, the steepest amongst all spectroscopically confirmed galaxies at z ≳ 7, in support of its very hard ionizing spectrum that could lead to a significant leakage of its ionizing flux7. Therefore, RXJ2129-z8HeII is representative of the key galaxy population driving the cosmic reionization. To date, this is also the most compelling case where trace Pop III stars might coexist with more metal-enriched stars.

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“…These results highlight the need for some form of mass substructure in the lens. However, the effect of wave dark matter is expected to be smaller on cluster compared to galaxy scales, and remains to be explored in detail, with preliminary results presented by Kelly et al (2022). CDM subhalos, on the other hand, lead to an asymmetry between +ve and −ve sides of clusters.…”

Section: Subhalos Versus Nonstandard Forms Of Dark Mattermentioning

confidence: 97%

“…Recent work has shown that high magnification near galaxy cluster critical curves makes it possible to detect individual stars in background, strongly lensed galaxies at intermediate and high redshifts (Kelly et al 2018;Chen et al 2019;Kaurov et al 2019;Chen et al 2022;Kelly et al 2022;Welch et al 2022;Meena et al 2023aMeena et al , 2023b, realizing a prediction made three decades ago (Miralda-Escude 1991). The recent 192-orbit Hubble Space Telescope (HST) Flashlights project (PI: P. Kelly, GO-15936; Kelly et al 2022) was specifically designed to look for such high-magnification events in the six Hubble Frontier Field galaxy clusters (Lotz et al 2017). Lensing theory has evolved rapidly in the last several years to explain and take advantage of these new exciting events (Venumadhav et al 2017;Dai & Pascale 2021;Diego 2022;Meena et al 2022).…”

Section: Introductionmentioning

confidence: 99%

Flashlights: Properties of Highly Magnified Images Near Cluster Critical Curves in the Presence of Dark Matter Subhalos

Williams,

Kelly,

Treu

et al. 2024

ApJ

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Dark matter subhalos with extended profiles and density cores, and globular star clusters of mass 106–108 M ⊙ that live near the critical curves in galaxy cluster lenses can potentially be detected through their lensing magnification of stars in background galaxies. In this work, we study the effect such subhalos have on lensed images, and compare to the case of more well-studied microlensing by stars and black holes near critical curves. We find that the cluster density gradient and the extended mass distribution of subhalos are important in determining image properties. Both lead to an asymmetry between the image properties on the positive- and negative-parity sides of the cluster that is more pronounced than in the case of microlensing. For example, on the negative-parity side, subhalos with cores larger than about 50 pc do not generate any images with magnification above ∼100 outside of the immediate vicinity of the cluster critical curve. We discuss these factors using analytical and numerical analysis, and exploit them to identify observable signatures of subhalos: Subhalos create pixel-to-pixel flux variations of ≳0.1 mag on the positive-parity side of clusters. These pixels tend to cluster around (otherwise invisible) subhalos. Unlike in the case of microlensing, signatures of subhalo lensing can be found up to 1″ away from the critical curves of massive clusters.

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Flashlights: More than A Dozen High-Significance Microlensing Events of Extremely Magnified Stars in Galaxies at Redshifts z=0.7-1.5

Cited by 9 publications

References 0 publications

Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015

Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

Flashlights: Properties of Highly Magnified Images Near Cluster Critical Curves in the Presence of Dark Matter Subhalos

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