Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Ashish Kumar Meena
Adi Zitrin
Yolanda Jiménez-Teja
Erik Zackrisson
Wenlei Chen
Dan Coe
Jose M. Diego
Paola Dimauro
Lukas J. Furtak
Patrick L. Kelly
Masamune Oguri
Brian Welch
Abdurro'uf
Felipe Andrade-Santos
Angela Adamo
Rachana Bhatawdekar
Maruša Bradač
Larry D. Bradley
Pratika Dayal
Megan Donahue
Abstract： We report the discovery of two extremely magnified lensed star candidates behind the galaxy cluster MACS J0647.7+7015, in recent multi-band James Webb Space Telescope (JWST) NIRCam observations. The candidates are seen in a previously known, $z_{phot}\simeq4.8$ 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 a background macro-magnification of at least $\gtrsim90$ and $\gtrsim50$ at the positions of the two candidates, respectively. With these values, we expect effective, caustic-crossing magnifications of $10^4-10^5$ for the two star candidates. The Spectral Energy Distributions (SEDs) of the two candidates match well spectra of B-type stars with best-fit surface temperatures of $\sim10,000$ K, and $\sim12,000$ K, respectively, and we show that such stars with masses $\gtrsim20$ M$_{\odot}$ and $\gtrsim50$ M$_{\odot}$, respectively, can become sufficiently magnified to be observed. We briefly discuss other alternative explanations and conclude these are likely lensed stars, but also acknowledge that the less magnified candidate may instead be or reside in a star cluster. These star candidates constitute the second highest-redshift examples to date after Earendel at $z_{phot}\simeq6.2$, establishing further the potential of studying extremely magnified stars to high redshifts with the JWST. Planned visits including NIRSpec observations will enable a more detailed view of the candidates already in the near future.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Amy Etherington
James W. Nightingale
Richard Massey
Sut-Ieng Tam
XiaoYue Cao
Anna Niemiec
Qiuhan He
Andrew Robertson
Ran Li
Aristeidis Amvrosiadis
Shaun Cole
Jose M. Diego
Carlos S. Frenk
Brenda L. Frye
David Harvey
Mathilde Jauzac
Anton M. Koekemoer
David J. Lagattuta
Marceau Limousin
Guillaume Mahler
Abstract： The distribution of mass in galaxy-scale strong gravitational lenses is often modelled as an elliptical power law plus `external shear', which notionally accounts for neighbouring galaxies and cosmic shear. We show that it does not. Except in a handful of rare systems, the best-fit values of external shear do not correlate with independent measurements of shear: from weak lensing in 45 Hubble Space Telescope images, or in 50 mock images of lenses with complex distributions of mass. Instead, the best-fit shear is aligned with the major or minor axis of 88% of lens galaxies; and the amplitude of the external shear increases if that galaxy is disky. We conclude that `external shear' attached to a power law model is not physically meaningful, but a fudge to compensate for lack of model complexity. Since it biases other model parameters that are interpreted as physically meaningful in several science analyses (e.g. measuring galaxy evolution, dark matter physics or cosmological parameters), we recommend that future studies of galaxy-scale strong lensing should employ more flexible mass models.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Tiger Yu-Yang Hsiao
Dan Coe
Abdurro'uf
Lily Whitler
Intae Jung
Gourav Khullar
Ashish Kumar Meena
Pratika Dayal
Kirk S. S. Barrow
Lillian Santos-Olmsted
Adam Casselman
Eros Vanzella
Mario Nonino
Yolanda Jimenez-Teja
Masamune Oguri
Daniel P. Stark
Lukas J. Furtak
Adi Zitrin
Angela Adamo
Gabriel Brammer
Abstract： MACS0647$-$JD is a triply-lensed $z\sim11$ galaxy originally discovered with the Hubble Space Telescope. Here we report new JWST imaging, which clearly resolves MACS0647$-$JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. Both are very small, with stellar masses $\sim10^8\,M_\odot$ and radii $r<100\,\rm pc$. The brighter larger component "A" is intrinsically very blue ($\beta\sim-2.6$), likely due to very recent star formation and no dust, and is spatially extended with an effective radius $\sim70\,\rm pc$. The smaller component "B" appears redder ($\beta\sim-2$), likely because it is older ($100-200\,\rm Myr$) with mild dust extinction ($A_V\sim0.1\,\rm mag$), and a smaller radius $\sim20\,\rm pc$. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be out of phase. With an estimated stellar mass ratio of roughly 2:1 and physical projected separation $\sim400\,\rm pc$, we may be witnessing a galaxy merger 400 million years after the Big Bang. We also identify a candidate companion galaxy C $\sim3\,{\rm kpc}$ away, likely destined to merge with galaxies A and B. The combined light from galaxies A+B is magnified by factors of $\sim$8, 5, and 2 in three lensed images JD1, 2, and 3 with F356W fluxes $\sim322$, $203$, $86\,\rm nJy$ (AB mag 25.1, 25.6, 26.6). MACS0647$-$JD is significantly brighter than other galaxies recently discovered at similar redshifts with JWST. Without magnification, it would have AB mag 27.3 ($M_{UV}=-20.4$). With a high confidence level, we obtain a photometric redshift of $z=10.6\pm0.3$ based on photometry measured in 6 NIRCam filters spanning $1-5\rm\mu m$, out to $4300\,\r{A}$ rest-frame. JWST NIRSpec observations planned for January 2023 will deliver a spectroscopic redshift and a more detailed study of the physical properties of MACS0647$-$JD.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Graham P. Smith
Andrew Robertson
Guillaume Mahler
Matt Nicholl
Dan Ryczanowski
Matteo Bianconi
Keren Sharon
Richard Massey
Johan Richard
Mathilde Jauzac
Abstract： Secure confirmation that a gravitational wave (GW) has been gravitationally lensed would bring together these two pillars of General Relativity for the first time. This breakthrough is challenging for many reasons, including: GW sky localization uncertainties dwarf the angular scale of gravitational lensing, the mass and structure of gravitational lenses is diverse, the mass function of stellar remnant compact objects is not yet well constrained, and GW detectors do not operate continuously. We introduce a new approach that is agnostic to the mass and structure of the lenses, compare the efficiency of different methods for lensed GW discovery, and explore detection of lensed kilonova counterparts as a direct method for localising candidates. Our main conclusions are: (1) lensed neutron star mergers (NS-NS) are magnified into the "mass gap" between NS and black holes, therefore selecting candidates from public GW alerts with high mass gap probability is efficient, (2) the rate of detectable lensed NS-NS will approach one per year in the mid-2020s, (3) the arrival time difference between lensed NS-NS images is $1\,\rm sec\lesssim\Delta t\lesssim1\,year$, and thus well-matched to the operations of GW detectors and optical telescopes, (4) lensed kilonova counterparts are faint at peak (e.g.\ $r_{\rm AB}\simeq24-26$ in the mid-2020s), fade quickly ($d<2\,\rm days$), and are detectable with target of opportunity observations with large wide-field telescopes. For example, just $\lesssim0.25$ per cent of Vera C.\ Rubin Observatory's observing time will be sufficient to follow up one well-localized candidate per year. Our predictions also provide a physically well-defined basis for exploring electromagnetically the exciting new "mass gap" discovery space.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Karina Rojas
Thomas E. Collett
Daniel Ballard
Mark R. Magee
Simon Birrer
Elizabeth Buckley-Geer.
James H. H. Chan
Benjamin Clément
José M. Diego
Fabrizio Gentile
Jimena González
Rémy Joseph
Jorge Mastache
Stefan Schuldt
Crescenzo Tortora
Tomás Verdugo
Aprajita Verma
Tansu Daylan
Martin Millon
Neal Jackson
Abstract： We investigate the ability of human 'expert' classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25$\%$ of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, and unlabeled data. We find that experts are extremely good at finding bright, well-resolved Einstein rings, whilst arcs with $g$-band signal-to-noise less than $\sim$25 or Einstein radii less than $\sim$1.2 times the seeing are rarely recovered. Very few non-lenses are scored highly. There is substantial variation in the performance of individual classifiers, but they do not appear to depend on the classifier's experience, confidence or academic position. These variations can be mitigated with a team of 6 or more independent classifiers. Our results give confidence that humans are a reliable pruning step for lens candidates, providing pure and quantifiably complete samples for follow-up studies.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Miriam Golubchik
Adi Zitrin
Justin Pierel
Lukas J. Furtak
Ashish K. Meena
Or Graur
Patrick L. Kelly
Dan Coe
Felipe Andrade-Santos
Maor Asif
Larry D. Bradley
Wenlei Chen
Brenda L. Frye
Sebastian Gomez
Saurabh Jha
Guillaume Mahler
Mario Nonino
Louis-Gregory Strolger
Yuanyuan Su
Abstract： The Reionization Cluster Survey (RELICS) imaged 41 galaxy clusters with the Hubble Space Telescope (HST), in order to detect lensed and high-redshift galaxies. Each cluster was imaged to about 26.5 AB mag in three optical and four near-infrared bands, taken in two distinct visits separated by varying time intervals. We make use of the multiple near-infrared epochs to search for transient sources in the cluster fields, with the primary motivation of building statistics for bright caustic crossing events in gravitational arcs. Over the whole sample, we do not find any significant ($\gtrsim5 \sigma$) caustic crossing events, in line with expectations from semi-analytic calculations but in contrast to what may be naively expected from previous detections of some bright events, or from deeper transient surveys that do find high rates of such events. Nevertheless, we find six prominent supernova (SN) candidates over the 41 fields: three of them were previously reported and three are new ones reported here for the first time. Out of the six candidates, four are likely core-collapse (CC) SNe -- three in cluster galaxies, and among which only one was known before, and one slightly behind the cluster at $z\sim0.6-0.7$. The other two are likely Ia -- both of them previously known, one probably in a cluster galaxy, and one behind it at $z\simeq2$. Our study supplies empirical bounds for the rate of caustic crossing events in galaxy cluster fields to typical HST magnitudes, and lays the groundwork for a future SN rate study.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Seiji Fujimoto
Kotaro Kohno
Masami Ouchi
Masamune Oguri
Vasily Kokorev
Gabriel Brammer
Fengwu Sun
Franz E. Bauer
Gabriel B. Caminha
Bunyo Hatsukade
Johan Richard
Ian Smail
Akiyoshi Tsujita
Yoshihiro Ueda
Ryosuke Uematsu
Adi Zitrin
Dan Coe
Jean-Paul Kneib
Marc Postman
Keiichi Umetsu
Abstract： We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescope} and {\it Spitzer} images. The dust continuum sources belong to a blind sample ($N=141$) with S/N $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($N=39$) with S/N= $4.0-5.0$ screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $\mu$Jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ Jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. The resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at $z=0.6-7.5$ with the $1/V_{\rm max}$ method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) SFRD component contributed by the faint-mm population, including NIR dark objects.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Larry D. Bradley
Dan Coe
Gabriel Brammer
Lukas J. Furtak
Rebecca L. Larson
Felipe Andrade-Santos
Rachana Bhatawdekar
Marusa Bradac
Tom Broadhurst
Adam Carnall
Christopher J. Conselice
Jose M. Diego
Brenda Frye
Seiji Fujimoto
Tiger Y. -Y Hsiao
Taylor A. Hutchison
Intae Jung
Guillaume Mahler
Stephan McCandliss
Masamune Oguri
Abstract： JWST was designed to peer into the distant universe and study galaxies nearer the beginning of time than previously. Here we report the discovery of 12 galaxy candidates observed 300-600 Myr after the Big Bang with photometric redshifts between z ~ 8.5-13 measured using JWST NIRCam imaging of the galaxy cluster WHL0137 observed in 8 filters spanning 0.8-5.0 $\mu$m, plus 9 HST filters spanning 0.4-1.7 $\mu$m. Three of these candidates are gravitationally lensed by the foreground galaxy cluster and have magnifications of $\mu \sim 3 - 8$. The remaining nine candidates are located in a second JWST NIRCam module, centered ~29' from the cluster center, with expected magnifications of $\mu$ <~ 1.1. Our sample of high-redshift candidates have observed F200W AB magnitudes between 25.9 and 28.1 mag and intrinsic F200W AB magnitudes between 26.4 and 29.7 mag ($M_{UV}$ = -22.5 to -17). We find the stellar masses of these galaxies are in the range $\log M_{*}/M_{\odot}$ = 8 - 9, and down to 7.5 for the lensed galaxies. All are young with mass-weighted ages < 100 Myr, low dust content $A_V$ < 0.15 mag, and high specific star formation rates sSFR ~10-50 Gyr$^{-1}$ for most. One z ~ 9 candidate is consistent with an age < 5 Myr and a sSFR ~250 Gyr$^{-1}$, as inferred from a strong F444W excess, implying [OIII]+H-beta rest-frame equivalent width ~2000 Angstrom, although an older and redder z~ 10 object is also allowed. Another z~9 candidate ID9356 is lensed into an arc 2.6" long by the effects of strong gravitational lensing ($\mu$~8), and has at least two bright knots of unevenly distributed star formation. This arc is the most spatially-resolved galaxy at z~9 known to date, revealing structures ~30 pc across. Follow-up spectroscopy of WHL0137 with JWST/NIRSpec is planned for later this year, which will validate some of these candidates and study their physical properties in more detail.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Brian Welch
Dan Coe
Jose M. Diego
Adi Zitrin
Erik Zackrisson
Paola Dimauro
Yolanda Jimenez-Teja
Patrick Kelly
Guillaume Mahler
Masamune Oguri
F. X. Timmes
Rogier Windhorst
Michael Florian
S. E. DeMink
Roberto J. Avila
Jay Anderson
Larry Bradley
Keren Sharon
Anton Vikaeus
Stephan McCandliss
Abstract： Galaxy clusters magnify background objects through strong gravitational lensing. Typical magnifications for lensed galaxies are factors of a few but can also be as high as tens or hundreds, stretching galaxies into giant arcs. Individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. Recently, several individual stars at redshift $z \sim 1 - 1.5$ have been discovered, magnified by factors of thousands, temporarily boosted by microlensing. Here we report observations of a more distant and persistent magnified star at redshift $z_{\rm phot} = 6.2 \pm 0.1$, 900 Myr after the Big Bang. This star is magnified by a factor of thousands by the foreground galaxy cluster lens WHL0137--08 ($z = 0.566$), as estimated by four independent lens models. Unlike previous lensed stars, the magnification and observed brightness (AB mag 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. The delensed absolute UV magnitude $M_{UV} = -10 \pm 2$ is consistent with a star of mass $M > 50 M_{\odot}$. Confirmation and spectral classification are forthcoming from approved observations with the James Webb Space Telescope
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Brian Welch
Dan Coe
Erik Zackrisson
S. E. de Mink
Swara Ravindranath
Jay Anderson
Gabriel Brammer
Larry Bradley
Jinmi Yoon
Patrick Kelly
Jose M. Diego
Rogier Windhorst
Adi Zitrin
Paola Dimauro
Yolanda Jimenez-Teja
Abdurro'uf
Mario Nonino
Ana Acebron
Felipe Andrade-Santos
Roberto J. Avila
Abstract： The gravitationally lensed star WHL0137-LS, nicknamed Earendel, was identified with a photometric redshift $z_{phot} = 6.2 \pm 0.1$ based on images taken with the Hubble Space Telescope. Here we present James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) images of Earendel in 8 filters spanning 0.8--5.0$\mu$m. In these higher resolution images, Earendel remains a single unresolved point source on the lensing critical curve, increasing the lower limit on the lensing magnification to $\mu > 4000$ and restricting the source plane radius further to $r < 0.02$ pc, or $\sim 4000$ AU. These new observations strengthen the conclusion that Earendel is best explained by an individual star or multiple star system, and support the previous photometric redshift estimate. Fitting grids of stellar spectra to our photometry yields a stellar temperature of $T_{\mathrm{eff}} \simeq 13000$--16000 K assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from $\log(L) = 5.8$--6.6 $L_{\odot}$, which is in the range where one expects luminous blue variable stars. Follow-up observations, including JWST NIRSpec scheduled for late 2022, are needed to further unravel the nature of this object, which presents a unique opportunity to study massive stars in the first billion years of the universe.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Yunchong Zhang
Viraj Manwadkar
Michael D. Gladders
Gourav Khullar
Håkon Dahle
Kate A. Napier
Guillaume Mahler
Keren Sharon
Owen S. Matthews Acuña
Finian Ashmead
William Cerny
Juan Remolina Gonzàlez
Katya Gozman
Benjamin C. Levine
Daniel Marohnic
Michael N. Martinez
Kaiya Merz
Yue Pan
Jorge A. Sanchez
Isaac Sierra
Abstract： We report the discovery of five bright strong gravitationally-lensed galaxies at $3 < z < 4$: COOL J0101$+$2055 ($z = 3.459$), COOL J0104$-$0757 ($z = 3.480$), COOL J0145$+$1018 ($z = 3.310$), COOL J0516$-$2208 ($z = 3.549$), and COOL J1356$+$0339 ($z = 3.753$). These galaxies have magnitudes of $r_{\rm AB}, z_{\rm AB} < 21.81$ mag and are lensed by galaxy clusters at $0.26 < z < 1$. This sample doubles the number of known bright lensed galaxies with extended arcs at $3 < z < 4$. We characterize the lensed galaxies using ground-based grz/giy imaging and optical spectroscopy. We report model-based magnitudes and derive stellar masses, dust content, and star-formation rates via stellar-population synthesis modeling. Building lens models based on ground-based imaging, we estimate source magnifications ranging from $\sim$29 to $\sim$180. Combining these analyses, we derive demagnified stellar masses ranging from $\rm log_{10}(M_{*}/M_{\odot}) \sim 9.7 - 11.0$ and star formation rates in the youngest age bin ranging from $\rm log_{10}(SFR/(M_{\odot}\cdot yr^{-1})) \sim 0.4 - 1.6$, placing the sample galaxies on the massive end of the star-forming main sequence in this redshift interval. In addition, three of the five galaxies have strong Ly$\alpha$ emissions, offering unique opportunities to study Ly$\alpha$ emitters at high redshift in future work.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Caitlin M. Casey
Jeyhan S. Kartaltepe
Nicole E. Drakos
Maximilien Franco
Santosh Harish
Louise Paquereau
Olivier Ilbert
Caitlin Rose
Isabella G. Cox
James W. Nightingale
Brant E. Robertson
John D. Silverman
Anton M. Koekemoer
Richard Massey
Henry Joy McCracken
Jason Rhodes
Hollis B. Akins
Aristeidis Amvrosiadis
Rafael C. Arango-Toro
Micaela B. Bagley
Abstract： We present the survey design, implementation, and outlook for COSMOS-Web, a
255 hour treasury program conducted by the James Webb Space Telescope in its
first cycle of observations. COSMOS-Web is a contiguous 0.54 deg$^2$ NIRCam
imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach
5$\sigma$ point source depths ranging $\sim$27.5-28.2 magnitudes. In parallel,
we will obtain 0.19 deg$^2$ of MIRI imaging in one filter (F770W) reaching
5$\sigma$ point source depths of $\sim$25.3-26.0 magnitudes. COSMOS-Web will
build on the rich heritage of multiwavelength observations and data products
available in the COSMOS field. The design of COSMOS-Web is motivated by three
primary science goals: (1) to discover thousands of galaxies in the Epoch of
Reionization ($6
Peer Review Status:Awaiting Review
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