Search for: All records

We super-resolve the seeing-limited Subaru Hyper Suprime-Cam (HSC) images for 32187 galaxies at $z\sim 2$–5 using three techniques, namely, the classical Richardson–Lucy (RL) point spread function (PSF) deconvolution, sparse modeling, and generative adversarial networks, to investigate the environmental dependence of galaxy mergers. These three techniques generate overall similar high spatial resolution images but with some slight differences in galaxy structures; for example, more residual noises are seen in the classical RL PSF deconvolution. To alleviate the disadvantages of each technique, we create combined images by averaging over the three types of super-resolution images, resulting in galaxy substructures resembling those seen in the Hubble Space Telescope images. Using the combined super-resolution images, we measure the relative galaxy major merger fraction corrected for the chance projection effect, $f_{\rm merger}^{\rm rel,col}$, for galaxies in the $\sim$300 deg$^2$ area data of the HSC Strategic Survey Program and the CFHT Large Area U-band Survey. Our $f_{\rm merger}^{\rm rel,col}$ measurements at $z\sim 3$ validate previous findings showing that $f_{\rm merger}^{\rm rel,col}$ is higher in regions with a higher galaxy overdensity $\delta$ at $z\sim 2$–3. Thanks to the large galaxy sample, we identify a nearly linear increase in $f_{\rm merger}^{\rm rel,col}$ with increasing $\delta$ at $z\sim 4$–5, providing the highest-z observational evidence that galaxy mergers are related to $\delta$. In addition to our $f_{\rm merger}^{\rm rel,col}$ measurements, we find that the galaxy merger fractions in the literature also broadly align with the linear $f_{\rm merger}^{\rm rel,col}$–$\delta$ relation across a wide redshift range of $z\sim 2$–5. This alignment suggests that the linear $f_{\rm merger}^{\rm rel,col}$–$\delta$ relation can serve as a valuable tool for quantitatively estimating the contributions of galaxy mergers to various environmental dependences. This super-resolution analysis can be readily applied to datasets from wide field-of-view space telescopes such as Euclid and Roman.

Observations with the James Webb Space Telescope (JWST) have uncovered numerous faint active galactic nuclei (AGN) atz∼ 5 and beyond. These objects are key to our understanding of the formation of supermassive black holes (SMBHs), their coevolution with host galaxies, as well as the role of AGN in cosmic reionization. Using photometric colors and size measurements, we perform a search for compact red objects in an array of blank deep JWST/NIRCam fields totaling ∼640 arcmin². Our careful selection yields 260 reddened AGN candidates at 4 <z_phot< 9, dominated by a point-source-like central component (〈r_eff〉 < 130 pc) and displaying a dichotomy in their rest-frame colors (blue UV and red optical slopes). Quasar model fitting reveals our objects to be moderately dust-extincted (A_V∼ 1.6), which is reflected in their inferred bolometric luminosities ofL_bol= 10^44–47erg s⁻¹and fainter UV magnitudesM_UV≃ −17 to −22. Thanks to the large areas explored, we extend the existing dusty AGN luminosity functions to both fainter and brighter magnitudes, estimating their number densities to be ×100 higher than for UV-selected quasars of similar magnitudes. At the same time, they constitute only a small fraction of all UV-selected galaxies at similar redshifts, but this percentage rises to ∼10% forM_UV∼ − 22 atz∼ 7. Finally, assuming a conservative case of accretion at the Eddington rate, we place a lower limit on the SMBH mass function atz∼ 5, finding it to be consistent with both theory and previous JWST observations.

MACS J0600.1-2008 (MACS0600) is an X-ray-luminous, massive galaxy cluster at $z_{\mathrm{d}}=0.43$, studied previously by the REionization LensIng Cluster Survey and ALMA Lensing Cluster Survey projects which revealed a complex, bimodal mass distribution and an intriguing high-redshift object behind it. Here, we report on the results of a combined analysis of the extended strong lensing (SL), X-ray, Sunyaev–Zeldovich (SZ), and galaxy luminosity-density properties of this system. Using new JWST and ground-based Gemini-N and Keck data, we obtain 13 new spectroscopic redshifts of multiply-imaged galaxies and identify 12 new photometric multiple-image systems and candidates, including two multiply-imaged $z\sim 7$ objects. Taking advantage of the larger areal coverage, our analysis reveals an additional bimodal, massive SL structure which we measure spectroscopically to lie adjacent to the cluster and whose existence was implied by previous SL-modelling analyses. While based in part on photometric systems identified in ground-based imaging requiring further verification, our extended SL model suggests that the cluster may have the second-largest critical area and effective Einstein radius observed to date, $A_{\mathrm{crit}}\simeq 2.16\, \mathrm{arcmin}^2$ and $\theta _{\mathrm{E}}=49.7^{\prime \prime }\pm 5.0^{\prime \prime }$ for a source at $z_{\mathrm{s}}=2$, enclosing a total mass of $M(\lt \theta _{\mathrm{E}})=(4.7\pm 0.7)\times 10^{14}\, \mathrm{M}_{\odot }$. These results are also supported by the galaxy luminosity distribution, and the SZ and X-ray data. Yet another, probably related massive cluster structure, discovered in X-rays 5 arcmin (1.7 Mpc) further north, suggests that MACS0600 is part of an even larger filamentary structure. This discovery adds to several recent detections of massive structures around SL galaxy clusters and establishes MACS0600 as a prime target for future high-redshift surveys with JWST.

The James Webb Space Telescope (JWST) is revolutionizing our knowledge ofz> 5 galaxies and their actively accreting black holes. Using the JWST Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization (UNCOVER) in the lensing field A2744, we report the identification of a sample of little red dots at 3 <z_phot< 7 that likely contain highly reddened accreting supermassive black holes. Using a NIRCam-only selection to F444W < 27.7 mag, we find 26 sources over the ∼45 arcmin²field that are blue in F115W − F200W ∼ 0 (orβ_UV∼ –2.0 forf_λ∝λ^β), red in F200W − F444W = 1−4 (β_opt∼ +2.0), and are dominated by a point-source-like central component. Of the 20 sources with deep Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm coverage, none are detected individually or in a stack. For the majority of the sample, spectral energy distribution fits to the JWST+ALMA observations prefer models with hot dust rather than obscured star formation to reproduce the red NIRCam colors and ALMA 1.2 mm nondetections. While compact dusty star formation cannot be ruled out, the combination of extremely small sizes (〈r_e〉 ≈ 50 pc after correction for magnification), red rest-frame optical slopes, and hot dust can be explained by reddened broad-line active galactic nuclei (AGNs). Our targets have faintM₁₄₅₀≈ −14 to −18 mag but inferred bolometric luminosities ofL_bol= 10⁴³–10⁴⁶erg s⁻¹, reflecting their obscured nature. If the candidates are confirmed as AGNs with upcoming UNCOVER spectroscopy, then we have found an abundant population of reddened luminous AGNs that are at least ten times more numerous than UV-luminous AGNs at the same intrinsic bolometric luminosity.

Over the past year, JWST has uncovered galaxies at record-breaking distances up to z ∼ 13. The JWST UNCOVER (ultra-deep NIRSpec and NIRcam observations before the epoch of reionization) program has obtained ultra-deep multiwavelength NIRCam imaging of the massive galaxy cluster A2744 over ∼45 arcmin2 down to ∼29.5 AB mag. Here, we present a robust ultraviolet (UV) luminosity function derived through lensing clusters at 9 < z < 12. Using comprehensive end-to-end simulations, we account for all lensing effects and systematic uncertainties in deriving both the amplification factors and the effective survey volume. Our results confirm the intriguing excess of UV-bright galaxies (MUV <−20 AB mag) previously reported at z > 9 in recent JWST studies. In particular, a double power-law (DPL) describes better the bright end of the luminosity function compared to the classical Schechter form. The number density of these bright galaxies is 10–100 times larger than theoretical predictions and previous findings based on Hubble Space Telescope (HST) observations. Additionally, we measure a star formation rate density of ρSFR = 10−2.64 M⊙ yr−1 Mpc−3 at these redshifts, which is 4–10 times higher than galaxy formation models that assume a constant star formation efficiency. Future wide-area surveys and accurate modelling of lensing-assisted observations will reliably constrain both the bright and the dim end of the UV luminosity function at z > 9, which will provide key benchmarks for galaxy formation models.

We present JWST NIRSpec prism spectroscopy of lensed galaxies atz≳ 9 found behind the massive galaxy cluster Abell 2744 in the UNCOVER Cycle 1 Treasury Program. We confirm the redshift via emission lines and/or the Lyαbreak for 10 galaxies atz= 8.50–13.08 down toM_V= −17.3. We achieve a 100% confirmation rate forz> 9 candidates reported in H. Atek et al. Using six sources with multiple line detections, we find that offsets in redshift estimates between the lines and the Lyαbreak alone can be ±0.2, raising caution in designing future follow-up spectroscopy for the break-only sources with the Atacama Large Millimeter/submillimeter Array. With spec-z-confirmed sources in UNCOVER and the literature, we derive lower limits on the rest-frame ultraviolet (UV) luminosity function (LF) atz≃ 9–12 and find that these lower limits agree with recent photometric measurements. We identify at least two unambiguous and several possible active galactic nucleus (AGN) systems based on X-ray, broad Hβ, high ionization lines, and excess in the UV LF. This requires the AGN LFs atz≃ 9–10 to be comparable or even higher than the X-ray AGN LF estimated atz∼ 6 and suggests a plausible cause of the high abundance ofz> 9 galaxies claimed in the recent photometric measurements is AGNs. One UV-luminous source is confirmed at the same redshift as a broad-line AGN atz= 8.50 with a physical separation of 380 kpc in the source plane. These two sources show emission blueward of Lyα, indicating a giant ionized bubble enclosing them with a radius of 7.69 ± 0.18 pMpc. Our results imply that AGNs have a nonnegligible contribution to cosmic reionization.

We analyze the evolution of massive (log₁₀[M_⋆/M_⊙] > 10) galaxies atz∼ 1–4 selected from JWST Cosmic Evolution Early Release Survey (CEERS). We infer the physical properties of all galaxies in the CEERS NIRCam imaging through spectral energy distribution (SED) fitting withdense basisto select a sample of high-redshift massive galaxies. Where available we include constraints from additional CEERS observing modes, including 18 sources with MIRI photometric coverage, and 28 sources with spectroscopic confirmations from NIRSpec or NIRCam WFSS. We sample the recovered posteriors in stellar mass from SED fitting to infer the volume densities of massive galaxies across cosmic time, taking into consideration the potential for sample contamination by active galactic nuclei. We find that the evolving abundance of massive galaxies tracks expectations based on a constant baryon conversion efficiency in dark matter halos forz∼ 1–4. At higher redshifts, we observe an excess abundance of massive galaxies relative to this simple model, resulting in a shallower decline of observed volume densities of massive galaxies. These higher abundances can be explained by modest changes to star formation physics and/or the efficiencies with which star formation occurs in massive dark matter halos, and are not in tension with modern cosmology.

We present the first results from the Web Epoch of Reionization LyαSurvey (WERLS), a spectroscopic survey of Lyαemission using Keck I/MOSFIRE and LRIS. WERLS targets bright (J< 26) galaxy candidates with photometric redshifts of 5.5 ≲z≲ 8 selected from pre-JWST imaging embedded in the Epoch of Reionization (EoR) within three JWST deep fields: CEERS, PRIMER, and COSMOS-Web. Here, we report 11z∼ 7–8 Lyαemitters (LAEs; three secure and eight tentative candidates) detected in the first five nights of WERLS MOSFIRE data. We estimate our observed LAE yield is ∼13%, which is broadly consistent with expectations assuming some loss from redshift uncertainty, contamination from sky OH lines, and that the Universe is approximately half-ionized at this epoch, whereby observable Lyαemission is unlikely for galaxies embedded in a neutral intergalactic medium. Our targets are selected to be UV-bright, and span a range of absolute UV magnitudes with −23.1 <M_UV< −19.8. With two LAEs detected atz= 7.68, we also consider the possibility of an ionized bubble at this redshift. Future synergistic Keck+JWST efforts will provide a powerful tool for pinpointing beacons of reionization and mapping the large-scale distribution of mass relative to the ionization state of the Universe.

We report the discovery of 15 exceptionally luminous 10 ≲z≲ 14 candidate galaxies discovered in the first 0.28 deg²of JWST/NIRCam imaging from the COSMOS-Web survey. These sources span rest-frame UV magnitudes of −20.5 >M_UV> −22, and thus constitute the most intrinsically luminousz≳ 10 candidates identified by JWST to date. Selected via NIRCam imaging, deep ground-based observations corroborate their detection and help significantly constrain their photometric redshifts. We analyze their spectral energy distributions using multiple open-source codes and evaluate the probability of low-redshift solutions; we conclude that 12/15 (80%) are likely genuinez≳ 10 sources and 3/15 (20%) likely low-redshift contaminants. Three of ourz∼ 12 candidates push the limits of early stellar mass assembly: they have estimated stellar masses ∼ 5 × 10⁹M_⊙, implying an effective stellar baryon fraction ofϵ_⋆∼ 0.2−0.5, whereϵ_⋆≡M_⋆/(f_bM_halo). The assembly of such stellar reservoirs is made possible due to rapid, burst-driven star formation on timescales < 100 Myr where the star formation rate may far outpace the growth of the underlying dark matter halos. This is supported by the similar volume densities inferred forM_⋆∼ 10¹⁰M_⊙galaxies relative toM_⋆∼ 10⁹M_⊙—both about 10⁻⁶Mpc⁻³—implying they live in halos of comparable mass. At such high redshifts, the duty cycle for starbursts would be of order unity, which could cause the observed change in the shape of the UV luminosity function from a double power law to a Schechter function atz≈ 8. Spectroscopic redshift confirmation and ensuing constraints of their masses will be critical to understand how, and if, such early massive galaxies push the limits of galaxy formation in the Lambda cold dark matter paradigm.

We present the first detection of the [N ii] 122 $\mu$m and [O iii] 52 $\mu$m lines for a reionization-epoch galaxy. Based on these lines and previous [C ii] 158 $\mu$m and [O iii] 88 $\mu$m measurements, using two different radiative transfer models of the interstellar medium, we estimate an upper limit on electron density of ≲500 cm−3 and an approximate gas-phase metallicity of Z/Z⊙ ∼ 1.1 ± 0.2 for A1689-zD1, a gravitationally lensed dusty galaxy at z = 7.133. Other measurements or indicators of metallicity so far in galaxy interstellar media at z ≳ 6 are typically an order of magnitude lower than this. The unusually high metallicity makes A1689-zD1 inconsistent with the fundamental metallicity relation, although there is likely significant dust obscuration of the stellar mass, which may partly resolve the inconsistency. Given a solar metallicity, the dust-to-metals ratio is a factor of several lower than expected, hinting that galaxies beyond z ∼ 7 may have lower dust formation efficiency. Finally, the inferred nitrogen enrichment compared to oxygen, on which the metallicity measurement depends, indicates that star formation in the system is older than about 250 Myr, pushing the beginnings of this galaxy to z > 10.