Search

We present a study on stellar properties of Lyman-alpha (Ly α) emitters at 5 < z < 8.2. We use 247 photometrically selected, lensed, high-redshift, low-luminosity galaxy candidates with spectroscopic follow-up. Of these, 38 are confirmed spectroscopically to be between 5 < z < 8.2 via detection of Ly α. For each galaxy and candidate, we estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age with spectral energy distribution fitting. We also measure the UV β slope and luminosity using values from photometry. We find no strong correlation between Ly α equivalent width and any of these properties, as well as no significant difference between the physical properties of Ly α emitters and candidates without Ly α detected. This lack of expected trends may be explained by a combination of the evolving opacity of the intergalactic medium at these redshifts as well as the unique phase space probed by our lensed sample. Via tests on other galaxy samples which show varying strengths of correlations, we conclude that if there exist any relationships between Ly α equivalent width and physical properties in the underlying population of faint galaxies, they are weak correlations. We also present the results of a spectroscopic search for C  iii ] emission in confirmed Ly α emitters at z ∼ 7, finding no C  iii ] detections, but putting constraints on strong active galactic nuclei activity and extreme nebular emission. [ABSTRACT FROM AUTHOR]

We report on a |$\rm {[CII]}_{158\mu \rm {m}}$| search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed Ly α emitting galaxies at z ∼ 7. Our targets are ultraviolet (UV) faint systems with stellar masses on the order of M * ∼ 109 M⊙. We detect a single [C  ii ] line emission (4σ) from the brightest (L ∼ 2.4 × 1010 L ⊙) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (z [C  ii ] = 6.3151 ± 0.0005) for MACS0454-1251 and measure a Ly α velocity offset of |$\Delta v \approx 300 \pm 70 \rm {km\, s}^{-1}$|⁠. The remaining two galaxies we detect no [C  ii ] but provide 3σ upper limits on their [C  ii ] line luminosities which we use to investigate the |$L_{\textrm {[CII]}} - \rm {SFR}$| relation. Overall our single [C  ii ] detection shows agreement with the relation for local dwarf galaxies. Our [C  ii ] deficient galaxies could potentially be exhibiting low metallicities (Z < Z⊙). Another possible explanation for weaker [C  ii ] emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of |$T_{d}=35 \rm {K}$| dust masses (M dust) range from <4.8 × 107 M⊙ to 2.3 × 108 M⊙. Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing [C  ii ] emission. [ABSTRACT FROM AUTHOR]

Early JWST observations that targeted so-called double-break sources (attributed to Lyman and Balmer breaks at z > 7), reported a previously unknown population of very massive, evolved high-redshift galaxies. This surprising discovery led to a flurry of attempts to explain these objects' unexpected existence including invoking alternatives to the standard Λ cold dark matter (ΛCDM) cosmological paradigm. To test these early results, we adopted the same double-break candidate galaxy selection criteria to search for such objects in the JWST images of the CAnadian Near Infrared Imager and Slitless Spectrograph (NIRISS) Unbiased Cluster Survey (CANUCS), and found a sample of 19 sources over five independent CANUCS fields that cover a total effective area of ∼60 arcmin2 at z ∼ 8. However, (1) our spectral energy distribution fits do not yield exceptionally high-stellar masses for our candidates, while (2) spectroscopy of five of the candidates shows that while all five are at high redshifts, their red colours are due to high-equivalent width emission lines in star-forming galaxies rather than Balmer breaks in massive, evolved systems. Additionally, (3) field-to-field variance leads to differences of ∼1.5 dex in the maximum stellar masses measured in the different fields, suggesting that the early single-field JWST observations may have suffered from cosmic variance and/or sample bias. Finally, (4) we show that the presence of even a single massive outlier can dominate conclusions from small samples such as those in early JWST observations. In conclusion, we find that the double-break sources in CANUCS are not sufficiently massive or numerous to warrant questioning the standard ΛCDM paradigm. [ABSTRACT FROM AUTHOR]

We use CANUCS JWST/NIRCam imaging of galaxies behind the gravitationally-lensing cluster MACS J0417.5-1154 to investigate star formation burstiness in low-mass (M ⋆ ∼ 108 M⊙) galaxies at z ∼ 4.7–6.5. Our sample of 123 galaxies is selected using the Lyman break selection and photometric emission-line excess methods. Sixty per cent of the 123 galaxies in this sample have Hα-to-UV flux ratios that deviate significantly from the range of Hα-to-UV ratio values consistent with smooth and steady star formation histories. This large fraction indicates that the majority of low-mass galaxies is experiencing bursty star formation histories at high redshift. We also searched for interacting galaxies in our sample and found that they are remarkably common (⁠|$\sim 40~{{\ \rm per\ cent}}$| of the sample). Compared to non-interacting galaxies, interacting galaxies are more likely to have very low Hα-to-UV ratios, suggesting that galaxy–galaxy interactions enhance star formation burstiness and enable faster quenching (with time-scales of ≲100 Myr) that follows the rapid rise of star formation activity. Given the high frequency of galaxy–galaxy interactions and the rapid SFR fluctuations they appear to cause, we conclude that galaxy–galaxy interactions could be a leading cause of bursty star formation in low-mass, high- z galaxies. They could thus play a significant role in the evolution of the galaxy population at early cosmological times. [ABSTRACT FROM AUTHOR]

Using CANUCS imaging we found an apparent major merger of two |$z$| ∼ 5 ultra-low-mass galaxies (M ⋆∼107M⊙ each) that are doubly imaged and magnified ∼12–15× by the lensing cluster MACS 0417. Both galaxies are experiencing young (∼100 Myr), synchronised bursts of star formation with log (sSFR/Gyr−1) ∼1.3–1.4, yet SFRs of just ∼0.2M⊙ yr−1. They have sub-solar (Z ∼ 0.2Z⊙) gas-phase metallicities and are connected by an even more metal-poor star-forming bridge. The galaxy that forms from the merger will have a mass of at least M ⋆∼2 × 107 M⊙, at least half of it formed during the interaction-induced starburst. More than half of the ionizing photons produced by the system (before and during the merger) will have been produced during the burst. This system provides the first detailed look at a merger involving two high- |$z$| ultra-low-mass galaxies of the type believed to be responsible for reionizing the Universe. It suggests that such galaxies can grow via a combination of mass obtained through major mergers, merger-triggered starbursts, and long-term in-situ star formation. If such high- |$z$| mergers are common, then merger-triggered starbursts could be significant contributors to the ionizing photon budget of the Universe. [ABSTRACT FROM AUTHOR]

We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 < z < 9 galaxies with spectroscopic redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with Bagpipes, using six NIRCam imaging bands spanning the wavelength range 0.8–5 μ m. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of [O iii ]+H β reaching up to ∼3000–4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ∼0.5–1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars. [ABSTRACT FROM AUTHOR]

We present size measurements of 78 high-redshift (z ≥ 5.5) galaxy candidates from the Reionization Lensing Cluster Survey (RELICS). These distant galaxies are well resolved due to the gravitational lensing power of foreground galaxy clusters, imaged by the Hubble Space Telescope and the Spitzer Space Telescope. We compute sizes using the forward-modelling code lenstruction and account for magnification using public lens models. The resulting size–magnitude measurements confirm the existence of many small galaxies with effective radii R eff < 200 pc in the early Universe, in agreement with previous studies. In addition, we highlight compact and highly star-forming sources with star formation rate surface densities |$\Sigma _\text{SFR}\gt 10\, \mathrm{M}_\odot \, \text{yr}^{-1}\, \text{kpc}^{-2}$| as possible Lyman continuum leaking candidates that could be major contributors to the process of reionization. Future spectroscopic follow-up of these compact galaxies (e.g. with the James Webb Space Telescope) will further clarify their role in reionization and the physics of early star formation. [ABSTRACT FROM AUTHOR]

We present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 6 ≲ z ≲ 8 galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and Spitzer-RELICS surveys. We measure photometry using T-PHOT and perform spectral energy distribution fitting using EAzY and BAGPIPES. Of the 207 candidates for which we could successfully measure (or place limits on) Spitzer fluxes, 23 were demoted to likely z < 4. Among the high-z candidates, we find intrinsic stellar masses between 1 × 106M⊙ and 4 × 109M⊙, and rest-frame UV absolute magnitudes between −22.6 and −14.5 mag. While our sample is mostly comprised of galaxies, it extends to. Our sample spans ∼4 orders of magnitude in stellar mass and star formation rates, and exhibits ages that range from maximally young to maximally old. We highlight 11 z ≥ 6.5 galaxies with detections in Spitzer/IRAC imaging, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. Among these is PLCKG287+32-2013, one of the brightest z ∼ 7 candidates known (AB mag 24.9 at 1.6 μm) with a Spitzer 3.6 μm flux excess suggesting strong [O iii ] + H-β emission (∼1000 Å rest-frame equivalent width). We discuss the possible uses and limits of our sample and present a public catalog of Hubble + Spitzer photometry along with physical property estimates for all objects in the sample. Because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

Recent observations have revealed the presence of strong C  iii ] emission (EW |$_{\rm {C\,{\small III}]}}\gt 20$|  Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to understand the nature of these line emitters, we have initiated a survey targeting C  iii ] emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2–8 × 107 M⊙) and J 125-band flux excesses indicative of intense [O  iii ] + H β emission (EW |$_{\rm {[O\,{\small III}]+H\,\beta }}$| = 500–2000 Å), similar to what has been observed at z > 6. We detect C  iii ] emission in three of the four sources, with the C  iii ] EW reaching values seen in the reionization era (EW |$_{\rm {C\,{\small III}]}}\simeq 17\!-\!22$|  Å) in the two sources with the strongest optical line emission (EW |$_{\rm {[O\,{\small III}]+H\,\beta }}\simeq 2000$|  Å). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest C  iii ] emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense C  iii ] and optical line emission for extremely young (2–3 Myr) and metal-poor (0.06–0.08 Z⊙) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which C  iii ] has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using C  iii ] to measure redshifts of objects with IRAC excesses indicating EW |$_{\rm {[O\,{\small III}]+H\,\beta }}\simeq 2000$|  Å, providing a method of spectroscopic confirmation independent of Ly α. [ABSTRACT FROM AUTHOR]

This paper presents multiwavelength photometric catalogues of the last two Hubble Frontier Fields (HFFs), the massive galaxy clusters Abell 370 and RXC J2248.7−4431. The photometry ranges from imaging performed on the Hubble Space Telescope to ground-based Very Large Telescope and Spitzer /Infrared Array Camera, in collaboration with the ASTRODEEP team, and using the ASTRODEEP pipeline. While the main purpose of this paper is to release the catalogues, we also perform, as a proof of concept, a brief analysis of z > 6 objects selected using dropout method, as well as spectroscopically confirmed sources and multiple images in both clusters. While dropout methods yield a sample of high- z galaxies, the addition of longer wavelength data reveals that as expected the samples have substantial contamination at the ∼30–45 per cent level by dusty galaxies at lower redshifts. Furthermore, we show that spectroscopic redshifts are still required to unambiguously determine redshifts of multiply imaged systems. Finally, the now publicly available ASTRODEEP catalogues were combined for all HFFs and used to explore stellar properties of a large sample of 20 000 galaxies across a large photometric redshift range. The powerful magnification provided by the HFF clusters allows for an exploration of the properties of galaxies with intrinsic stellar masses as low as M * ≳ 107 M⊙ and intrinsic star formation rates ∼0.1–1 M⊙ yr−1 at z  > 6. [ABSTRACT FROM AUTHOR]

Primordial neutral atomic gas, mostly composed of hydrogen, is the raw material for star formation in galaxies. However, there are few direct constraints on the amount of neutral atomic hydrogen (H I) in galaxies at early cosmic times. We analyzed James Webb Space Telescope (JWST) near-infrared spectroscopy of distant galaxies, at redshifts ≳8. From a sample of 12 galaxies, we identified three that show strong damped Lyman-a absorption due to H I in their local surroundings. The galaxies are located at spectroscopic redshifts of 8.8, 10.2, and 11.4, corresponding to 400 to 600 million years after the Big Bang. They have H I column densities ≳1022 cm−2, which is an order of magnitude higher than expected for a fully neutral intergalactic medium, and constitute a gas-rich population of young star-forming galaxies. [ABSTRACT FROM AUTHOR]