Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid

Dark matter halos that reach the HI-cooling mass without prior star formation or external metal pollution represent potential sites for the formation of small Population III galaxies at high redshifts. Such objects are expected to attain total stellar masses of at most $10^6$ solar masses and will therefore typically be extremely faint. Gravitational lensing may in rare cases boost their fluxes to detectable levels, but to find even a small number of such objects requires very large sky areas to be surveyed. Because of this, a small, wide-field telescope can in principle offer better detection prospects than a large telescope with a smaller field of view. Here, we derive the Pop III galaxy properties - in terms of comoving number density, stellar initial mass function and total stellar mass - required to allow gravitational lensing to lift such objects at redshift z = 5-16 above the detection thresholds of blind surveys carried out with the James Webb space telescope (JWST), the Roman space telescope (RST) or Euclid. We find that the prospects for photometric detections of Pop III galaxies are promising, and that they are better for RST than for JWST and Euclid. However, the Pop III galaxies favoured by current simulations have number densities too low to allow spectroscopic detections based on the strength of the HeII1640 emission line in any of the considered surveys unless very high star formation efficiencies (10 per cent) are envoked.Comment: 13 pages, 4 figure

First Light And Reionisation Epoch Simulations (FLARES) XIV: The Balmer/4000~\AA\ Breaks of Distant Galaxies

With the successful launch and commissioning of JWST we are now able to routinely spectroscopically probe the rest-frame optical emission of galaxies at $z>6$ for the first time. Amongst the most useful spectral diagnostics used in the optical is the Balmer/4000~\AA\ break; this is, in principle, a diagnostic of the mean ages of composite stellar populations. However, the Balmer break is also sensitive to the shape of the star formation history, the stellar (and gas) metallicity, the presence of nebular continuum emission, and dust attenuation. In this work we explore the origin of the Balmer/4000~\AA\ break using the SYNTHESIZER synthetic observations package. We then make predictions of the Balmer/4000~\AA\ break using the First Light and Reionisation Epoch Simulations (FLARES) at $5<z<10$. We find that the average break strength weakly correlates with stellar mass and rest-frame far-UV luminosity, but that this is predominantly driven by dust attenuation. We also find that break strength provides a weak diagnostic of the age but performs better as a means to constrain star formation and stellar mass, alongside the UV and optical luminosity, respectively.Comment: 9 pages, 9 figures, submitted to MNRA

JWST reveals a possible z∼11z \sim 11 galaxy merger in triply-lensed MACS0647−-JD

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.Comment: 27 pages, 14 figures, submitted to Natur

A highly magnified star at redshift 6.2

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 arcs1,2. Individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. Recently, several individual stars at redshifts between approximately 1 and 1.5 have been discovered, magnified by factors of thousands, temporarily boosted by microlensing3,4,5,6. Here we report observations of a more distant and persistent magnified star at a redshift of 6.2 ± 0.1, 900 million years after the Big Bang. This star is magnified by a factor of thousands by the foreground galaxy cluster lens WHL0137–08 (redshift 0.566), as estimated by four independent lens models. Unlike previous lensed stars, the magnification and observed brightness (AB magnitude, 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. The delensed absolute UV magnitude, −10 ± 2, is consistent with a star of mass greater than 50 times the mass of the Sun. Confirmation and spectral classification are forthcoming from approved observations with the James Webb Space Telescope. © 2022, The Author(s), under exclusive licence to Springer Nature Limited.The RELICS Hubble Treasury Program (GO 14096) and follow-up programme (GO 15842) consist of observations obtained by the NASA/ESA Hubble Space Telescope (HST). Data from these HST programmes were obtained from the Mikulski Archive for Space Telescopes (MAST), operated by the Space Telescope Science Institute (STScI). Both HST and STScI are operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under NASA contract NAS 5-26555. The HST Advanced Camera for Surveys (ACS) was developed under NASA contract NAS 5-32864. J.M.D. acknowledges the support of project PGC2018-101814-B-100 (MCIU/AEI/MINECO/FEDER, UE) and María de Maeztu, ref. MDM-2017-0765. A.Z. acknowledges support from the Ministry of Science and Technology, Israel. R.W. acknowledges support from NASA JWST Interdisciplinary Scientist grants NAG5-12460, NNX14AN10G and 80NSSC18K0200 from GSFC. E.Z. and A.V. acknowledge funding from the Swedish National Space Board. M.O. acknowledges support from World Premier International Research Center Initiative, MEXT, Japan, and JSPS KAKENHI grant numbers JP20H00181, JP20H05856, JP18K03693. G.M. received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. MARACAS – DLV-896778. P.K. acknowledges support from NSF AST-1908823. Y.J.-T. acknowledges financial support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 898633, and from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). The Cosmic DAWN Center is funded by the Danish National Research Foundation under grant no. 140.Peer reviewe

On the emergent structures at cosmic dawn

Recent developments have granted us the means necessary for studying the emergence of the very first luminous structures in the Universe. The beckoning of the first generation of stars marks the end of the cosmic dark ages – thus entering into the cosmic dawn. Contemporary cosmology provides us with a theoretical framework reaching all the way from the early fluctuations associated with cosmic inflation to the era where stars and galaxies form in large-scale structures. In this thesis we review some of this framework in order to understand the basis for forming the first stars and galaxies in Universe. Dark matter halos forming at very early times acts as host for these emerging stars and galaxies, comprised solely of pristine gas left over from the big bang. Some of these dark matter halos also provide the environments necessary for the formation of direct collapse black holes – the possible seeds for supermassive black holes observed in active galactic nuclei existing when the Universe was less than a billion years old. Grasping the mechanisms behind the formation of such high-redshift objects provides us with important information regarding the prospects for detecting them with current and nascent instruments. The James Webb space telescope is now pushing the frontier with regards to redshift by observing galaxies forming within the first few hundred million years of the Universe. At these distances, such intrinsically small stellar systems are exceedingly dim. In order to reach the very first instances of star formation we therefore often rely on gravitational lensing in order to magnify the flux from these objects above the detection thresholds of our telescopes – clearly demonstrating gravitational lensing as a necessity when aiming to unveil cosmic dawn in its entirety

The information paradox - Horizon structures and its effects on the quasinormal mode gravitational radiation from binary merger ringdowns : Gravitational echoes from reflective near horizon structures

Classical theory cannot provide a satisfying scenario for a unitary thermodynamic evolution of black holes. To preserve information one requires quantum mechanical effects on scales reaching beyond the traditional horizon radius. Therefore, common to many of the theories attempting to resolve the paradox is the existence of exotic horizon structures. The recent advent of gravitational wave astronomy provides a possible means for detecting the existence of such structures through gravitational wave emission in the ringdown phase of binary black hole mergers. Such emission is described by quasinormal modes (QNMs) in which the gravitational waves originates outside the black hole, in the vicinity of the photon spheres. Requiring reflective properties of the horizon structure results in the existence of gravitational echoes that may be detected by facilities such as LIGO etc.. This thesis studies geodesic motion of such echoes in the equatorial plane of a rotating black hole. Depending on the extent of the horizon structure, and the particular mode of emission, one can expect different timescales for the echoes. For a horizon structure extending    outside the traditional horizon of a  ,  black hole one would ideally find echoes appearing as integer multiples of  after the primary signal. The time delay is expected to increase by at least an order of magnitude if one lets . The expected echo timescales for gravitational waves emitted from any point around the black hole, in arbitrary modes, is an interesting further study

On the emergent structures at cosmic dawn

Recent developments have granted us the means necessary for studying the emergence of the very first luminous structures in the Universe. The beckoning of the first generation of stars marks the end of the cosmic dark ages – thus entering into the cosmic dawn. Contemporary cosmology provides us with a theoretical framework reaching all the way from the early fluctuations associated with cosmic inflation to the era where stars and galaxies form in large-scale structures. In this thesis we review some of this framework in order to understand the basis for forming the first stars and galaxies in Universe. Dark matter halos forming at very early times acts as host for these emerging stars and galaxies, comprised solely of pristine gas left over from the big bang. Some of these dark matter halos also provide the environments necessary for the formation of direct collapse black holes – the possible seeds for supermassive black holes observed in active galactic nuclei existing when the Universe was less than a billion years old. Grasping the mechanisms behind the formation of such high-redshift objects provides us with important information regarding the prospects for detecting them with current and nascent instruments. The James Webb space telescope is now pushing the frontier with regards to redshift by observing galaxies forming within the first few hundred million years of the Universe. At these distances, such intrinsically small stellar systems are exceedingly dim. In order to reach the very first instances of star formation we therefore often rely on gravitational lensing in order to magnify the flux from these objects above the detection thresholds of our telescopes – clearly demonstrating gravitational lensing as a necessity when aiming to unveil cosmic dawn in its entirety

Finding Lensed Direct-collapse Black Holes and Supermassive Primordial Stars

Direct-collapse black holes (DCBHs) may be the seeds of the first quasars, over 200 of which have now been detected at z &gt; 6. The James Webb Space Telescope (JWST) could detect DCBHs in the near-infrared (NIR) at z less than or similar to 20 and probe the evolution of primordial quasars at their earliest stages, but only in narrow fields that may not capture many of them. Wide-field NIR surveys by Euclid and the Nancy Grace Roman Space Telescope (RST) would enclose far greater numbers of DCBHs but only directly detect them at z less than or similar to 6-8 because of their lower sensitivities. However, their large survey areas will cover thousands of galaxy clusters and massive galaxies that could gravitationally lens flux from DCBHs, boosting them above current Euclid and RST detection limits and revealing more of them than could otherwise be detected. Here, we estimate the minimum number density of strongly lensed DCBHs and supermassive primordial stars required for detection in surveys by Euclid, RST, and JWST at z less than or similar to 20. We find that for reasonable estimates of host halo numbers RST, Euclid, and JWST could potentially find hundreds of strongly lensed DCBHs at z = 7-20. RST would detect the most objects at z less than or similar to 10 and JWST would find the most at higher redshifts. Lensed supermassive primordial stars could potentially also be found, but in fewer numbers because of their short lifetimes

JWST Imaging of Earendel, the Extremely Magnified Star at Redshift z = 6.2

Full list of authors: Welch, Brian; Coe, Dan; Zackrisson, Erik; de Mink, S. E.; Ravindranath, Swara; Anderson, Jay; Brammer, Gabriel; Bradley, Larry; Yoon, Jinmi; Kelly, Patrick; Diego, Jose M.; Windhorst, Rogier; Zitrin, Adi; Dimauro, Paola; Jimenez-Teja, Yolanda; Abdurro'uf; Nonino, Mario; Acebron, Ana; Andrade-Santos, Felipe; Avila, Roberto J.; Bayliss, Matthew B.; Benitez, Alex; Broadhurst, Tom; Bhatawdekar, Rachana; Bradac, Marusa; Caminha, Gabriel B.; Chen, Wenlei; Eldridge, Jan; Farag, Ebraheem; Florian, Michael; Frye, Brenda; Fujimoto, Seiji; Gomez, Sebastian; Henry, Alaina; Hsiao, Tiger Y-Y; Hutchison, Taylor A.; James, Bethan L.; Joyce, Meridith; Jung, Intae; Khullar, Gourav; Larson, Rebecca L.; Mahler, Guillaume; Mandelker, Nir; McCandliss, Stephan; Morishita, Takahiro; Newshore, Rosa; Norman, Colin; O'Connor, Kyle; Oesch, Pascal A.; Oguri, Masamune; Ouchi, Masami; Postman, Marc; Rigby, Jane R.; Ryan, Russell E., Jr.; Sharma, Soniya; Sharon, Keren; Strait, Victoria; Strolger, Louis-Gregory; Timmes, F. X.; Toft, Sune; Trenti, Michele; Vanzella, Eros; Vikaeus, Anton.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.The gravitationally lensed star WHL 0137–LS, nicknamed Earendel, was identified with a photometric redshift zphot = 6.2 ± 0.1 based on images taken with the Hubble Space Telescope. Here we present James Webb Space Telescope (JWST) Near Infrared Camera images of Earendel in eight filters spanning 0.8–5.0 μm. 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 μ > 4000 and restricting the source plane radius further to r < 0.02 pc, or ∼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 Teff ≃ 13,000–16,000 K, assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from $\mathrm{log}(L)=5.8$ to 6.6 L⊙, 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. © 2022. The Author(s). Published by the American Astronomical Society.E.Z. acknowledges support from the Swedish National Space Board. M.B. acknowledges support from the Slovenian national research agency ARRS through grant N1-0238. A.Z. acknowledges support by grant No. 2020750 from the United States–Israel Binational Science Foundation (BSF) and grant No. 2109066 from the United States National Science Foundation (NSF) and by the Ministry of Science & Technology, Israel. M.T. acknowledges support by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) through project No. CE170100013. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant No. 140. J.M.D. acknowledges the support of projects PGC2018-101814-B-100 and MDM-2017-0765. Y.J.-T. acknowledges financial support from the European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement No. 898633, the MSCA IF Extensions Program of the Spanish National Research Council (CSIC), and the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). P.A.O. acknowledges support by the Swiss National Science Foundation through project grant 200020_207349.Peer reviewe

Balmer breaks in simulated galaxies at z &gt; 6

Photometric observations of the spectroscopically confirmed $z\approx 9.1$ galaxy MACS1149-JD1 have indicated the presence of a prominent Balmer break in its spectral energy distribution, which may be interpreted as due to very large fluctuations in its past star formation activity. In this paper, we investigate to what extent contemporary simulations of high-redshift galaxies produce star formation rate variations sufficiently large to reproduce the observed Balmer break of MACS1149-JD1. We find that several independent galaxy simulations are unable to account for Balmer breaks of the inferred size, suggesting that MACS1149-JD1 either must be a very rare type of object or that our simulations are missing some key ingredient. We present predictions of spectroscopic Balmer break strength distributions for $z\approx 7-9$ galaxies that may be tested through observations with the upcoming James Webb Space Telescope and also discuss the impact that various assumptions on dust reddening, Lyman continuum leakage and deviations from a standard stellar initial mass function would have on the results.Comment: 11 pages, 8 figures. Accepted for publication in MNRA