Min Su Yun

The superb sensitivity and angular resolution of the next-generation radio telescopes with combined frequency coverage of approximately over 3 orders of magnitude (100 MHz–100 GHz) will sample the radio and far-infrared (FIR) spectral energy distribution (SED) of galaxies and revolutionize the galaxy formation study at the epoch of reionization and beyond. We present a prospect of observing the radio–FIR continuum SEDs of galaxies in the redshift of up to z ≈ 20 based on an ensemble of the simulated “energy balanced” panchromatic SED (from UV to FIR) extended to the radio. For “realistic” populations of UV star-forming galaxies and dusty star-forming galaxies (DSFGs), we simulate their SEDs by accounting for the CMB effect and the radio-IR correlation. The flux density evolution of the UV-bright star-forming galaxies and the DSFGs at the selected observing frequencies covered by the current (ALMA) and next generation (SKA and ngVLA) radio-millimeter telescopes, suggest that massive galaxies ( M _* ≳ 10 ¹⁰ M _⊙ ) are detectable at any redshift (0 < z < 20) in high frequency ( ν > 90GHz). In particular, when operating, the ngVLA high-frequency (≈100 GHz) band is capable of detecting galaxies with M _* ≳ 10 ⁹ M _⊙ almost independently from redshift and the SKA low-frequency observing window (≲1 GHz) has sufficient sensitivity to detect M _* ≳ 10 ¹⁰ M _⊙ DSFGs up to the epoch of reionization ( z = 5 ∼ 7). We also show that the brightness of anomalous microwave emission (AME) in the galaxy SED is insignificant if the galaxies are beyond the local Universe (e.g., z ≳ 0.1).

More than 60 years have passed since the first formal suggestion to use strongly lensed supernovae (SNe) to measure the expansion rate of the Universe through time-delay cosmography. Yet, fewer than 10 such objects have ever been discovered. We consider the merits of a targeted strategy focused on lensed hyperluminous infrared galaxies, which are among the most rapidly star-forming galaxies known in the Universe. With star formation rates (SFRs) ∼200–6000 M _⊙ yr ⁻¹ , the ∼30 objects in the Planck All-Sky Survey to Analyze Gravitationally-lensed Extreme Starbursts are excellent candidates for a case study, in particular, and have already led to the discovery of the multiply imaged SN H0pe. Considering their lens model-corrected SFRs, we estimate their intrinsic SN rates to be an extraordinary 1.8–65 yr ⁻¹ (core-collapse) and 0.2–6.4 yr ⁻¹ (Type Ia). Moreover, these massive starbursts typically have star-forming companions which are unaccounted for in this tally. We demonstrate a strong correlation between Einstein radius and typical time delays, with cluster lenses often exceeding several months (and therefore most favorable for high-precision H ₀ inferences). A multivisit monitoring campaign with a sensitive infrared telescope (namely, JWST) is necessary to mitigate dust attenuation. Nevertheless, a porous interstellar medium and clumpy star formation in these extreme galaxies might produce favorable conditions for detecting SNe as transient point sources. Targeted campaigns of known lensed galaxies to discover new lensed SNe can greatly complement wide-area cadenced surveys. Increasing the sample size helps to realize the potential of SN time-delay cosmography to elucidate the Hubble tension through a single-step measurement, independent of other H ₀ techniques.

One of the greatest challenges in galaxy evolution over the last decade has been constraining the prevalence of heavily dust-obscured galaxies in the early Universe. At z > 3, these galaxies are increasingly rare, and difficult to identify, as they are interspersed among the more numerous dust-obscured galaxy population at z = 1–3, making efforts to secure confident spectroscopic redshifts expensive, and sometimes unsuccessful. In this work, we present the Extended Mapping Obscuration to Reionization with the Atacama Large Millimeter/submillimeter Array (ALMA; Ex-MORA) Survey—a 2 mm blank-field survey in the COSMOS-Web field, and the largest ever ALMA blank-field survey to date, covering 577 arcmin ² . Ex-MORA is an expansion of the MORA survey designed to identify primarily z > 3 dusty, star-forming galaxies while simultaneously filtering out the more numerous z < 3 population by leveraging the very negative K -correction at observed-frame 2 mm. We identify 37 significant (>5 σ ) sources, 33 of which are robust thermal dust emitters. We measure a median redshift of 〈 z 〉 = 3 . 8 − 1.52 + 1.7 , with two-thirds of the sample at z > 3, and just under half at z > 4, demonstrating the overall success of the 2 mm selection technique. The total integrated z > 3 volume density of Ex-MORA sources is ∼1–3 × 10 ⁻⁵ Mpc ⁻³ , consistent with other surveys of infrared luminous galaxies at similar epochs. We also find that techniques using rest-frame optical emission (or lack thereof) to identify z > 3 heavily dust-obscured galaxies miss at least half of Ex-MORA galaxies. This supports the idea that the dusty galaxy population is heterogeneous, and that synergies across observatories spanning multiple energy regimes are critical to understanding their formation and evolution at z > 3.

We present the neutral gas morphology of four galaxies from z = 0.22 to 0.47 obtained with the COSMOS H i Large Extragalactic Survey (CHILES). The H i is resolved at the highest redshift with the 7 . ″ 5 beam of CHILES and 43 kpc linear scale, with all four galaxies having extended H I . Three are massive galaxies ( M _* > 3 × 10 ¹⁰ M _⊙ ), with H i masses of (1.6–6.7) × 10 ¹⁰ M _⊙ and active star formation (3–30 M _⊙ yr ⁻¹ ). The morphology and kinematics of the galaxies vary from regular to disturbed, including an asymmetric H i disk surrounding the fourth smaller galaxy ( M _* ∼ 10 ⁹ M _⊙ ). CO (1–0) observations of the sample, obtained with the Large Millimeter Telescope, confirm the redshifts of three of the four galaxies, and we derive H ₂ masses of (0.4–5.2) × 10 ¹⁰ M _⊙ . JWST imaging with four combined NIRCam filters reveals disturbed stellar components with compact knots in two of the galaxies. We combine our new higher-redshift galaxies with previously published observations to conduct a more complete study of H i and H ₂ evolution in the redshift range 0–0.5. With our H i flux-limited observations compared to similar lower-redshift galaxies with high stellar mass ( M _* > 10 ¹⁰ M _⊙ ), the results show that the mean H ₂ /H i ratio at the highest redshift is 10.3 ± 3.4, larger than the mean H ₂ /H i ratio in the local Universe.

We exploit a new sample of around 400 bright dusty galaxies from the Atacama Large Millimeter/submillimeter Array (ALMA) CHAMPS Large Program, together with the rich JWST multiband data products in the COSMOS field, to explore and validate new selection methods for identifying dusty star-forming galaxies (DSFGs). Here we present an effective empirical selection criterion based on a newly defined parameter: I ⋆ ≡ log 10 ( M ⋆ ) × log 10 ( SFR ) . Incorporating the m _277W − m _444W color as a second parameter further improves the purity of the selection. We then apply this method to the COSMOS2025 catalog to search for fainter dusty galaxy candidates below the ALMA CHAMPS detection limit and, through a stacking technique, identify a population of high-redshift DSFG candidates with an average flux density of S _1.2mm ≈ 150 μ Jy and a space density of ∼6 × 10 ⁻⁶ Mpc ⁻³ . Three of these galaxies have been spectroscopically confirmed at z _spec = 7.20, 5.85, and 5.04. This faint population seems to have been missed by most of the previous submillimeter/millimeter surveys and ground- and space-based UV−near-IR observations. We then show evidence of a possible evolutionary connection between the z > 10 UV-bright galaxies recently discovered by JWST, the faint dusty z ≈ 6-8 galaxies identified here, and the population of z ≈ 3–5 massive quiescent galaxies; all of them are potentially linked as progenitor−descendant populations based on their abundance, redshifts, and stellar masses. Future spectroscopic campaigns will be essential to confirm the redshifts and physical properties of these massive, faint, high-redshift DSFG candidates.

We present a detailed analysis of J154506, a strongly lensed submillimetre galaxy (SMG) behind the Lupus-I molecular cloud, and a characterisation of its physical properties using a combination of new and archival data, including VLT/MUSE and FORS2 optical data. We identify two high-significance (S/N > 5) emission lines at 97.0 and 145.5 GHz, corresponding to CO(4-3) and CO(6-5), respectively, in spectral scans from the Atacama Compact Array (ACA) and the Large Millimetre Telescope (LMT), as well as the [CII] 158 μm fine-structure line at 400 GHz observed with the Atacama Pathfinder Experiment (APEX). These detections yield a spectroscopic redshift of z _spec = 3.7515 ± 0.0005. We also report the detection of [CI], HCN(4-3), and two H ₂ O ⁺ transitions, further confirming the redshift and providing insights into the physical properties of J154506. By modelling sub-arcsecond resolution (0.75″) ALMA Band 6 and 7 continuum data in the uv -plane, we derive an average magnification factor of 6.0 ± 0.4, and our analysis reveals a relatively cold dust (38 K) in a starburst galaxy (∼ 900 M _⊙ yr ⁻¹ ) with a high intrinsic dust mass (∼ 2.5 × 10 ⁹ M _⊙ ) and infrared (IR) luminosity (∼ 6 × 10 ¹² L _⊙ ). Non-local thermodynamic equilibrium radiative transfer modelling of the joint dust spectral energy distribution (SED) and CO line excitation suggests the dust continuum emission is primarily associated with relatively diffuse regions with molecular gas densities of 10 ² −10 ⁴ cm ⁻³ , rather than compact, high-pressure environments typical of extreme starbursts or active galactic nuclei (AGNs). This interpretation is supported by the close-to-unity ratio between the dust and gas kinetic temperatures, which argues against highly energetic heating mechanisms. The CO excitation ladder peaks close to CO(5-4) and is dominated by slightly denser molecular gas. Our results underscore the unique power of far-IR and submillimetre observations to both uncover and characterise scarce, strongly lensed, high-redshift galaxies, even when they are obscured by foreground molecular clouds.

We present 21 transients from our three-epoch, four-band NIRCam observations covering 14.16 arcmin ² in the Spitzer IRAC Dark Field (IDF), taken by the JWST Prime Extragalactic Areas for Reionization and Lensing Science program with a time cadence of ∼6 months. A separate Hubble Space Telescope program provided Advanced Camera for Surveys optical imaging contemporaneous with the second and third epochs of the NIRCam observations. The NIRSpec spectroscopy on three transients confirmed a Type Ia supernova at z = 1.63 and the host galaxies of the other two at z = 2.64 and 1.90, respectively. Combining these with the photometric redshifts ( z _ph ) of the host galaxies in the rest of the sample, we find that the transients are in either a “mid- z ” group at z > 1.6 with M _V ≲ − 16.0 mag or a “low- z ” group at z < 0.4 with M _H ≳ − 14.0 mag. The mid- z transients are consistent with supernovae. In contrast, the low- z transients’ luminosities fall in the range of the so-called “gap transients” between supernovae and novae. However, this latter conclusion is only tentative due to possible catastrophic failures in z _ph that could bias them to low- z . Conversely, if they are indeed at z < 0.4, it would be worth studying similar transients in the future. Our work further demonstrates the power of NIRCam in transient science and also shows that it would be more fruitful to carry out a long-term monitoring program with more passbands, a higher cadence, and prompt follow-up spectroscopy. Being in the continuous viewing zone of the JWST, the IDF is an ideal field for this purpose.

We present an analysis of rest-frame optical and far-infrared continuum emission in three luminous submillimeter galaxies (SMGs) at 3.0 ≲ z ≲ 4.5. The SMGs are spatially resolved down to 400–500 pc ( ∼ 0 . ″ 05 ) resolution by James Webb Space Telescope and Atacama Large Millimeter/submillimeter Array observations. Despite similarities in their observed far-infrared properties (flux density, infrared luminosity, and effective radius), the three SMGs exhibit heterogeneous morphologies both across wavelengths and among the sources themselves. While two of them (AzTEC-4 and AzTEC-8) show a disk-like structure in the optical continuum, AzTEC-1 is dominated by a highly concentrated component with a Sérsic index of n = 5.4, where its far-infrared continuum emission is clumpy and less concentrated. AzTEC-4, which is confirmed to be at z = 4.198, shows a two-arm spiral of dust, but not in the stellar distribution. These three SMGs exemplify that multiple physical mechanisms exist in triggering starbursts in luminous SMGs at high redshift: secular instability in gas disks (AzTEC-4) in addition to possible minor mergers (AzTEC-8), and a combination of the efficient gas supply to the central core induced by a gas-rich major merger and the re-formation of a cold gas disk (AzTEC-1).

Investigating the processes by which galaxies rapidly build up their stellar mass during the peak of their star formation ( z = 2–3) is crucial to advancing our understanding of the assembly of large-scale structures. We report the discovery of one of the most gas- and dust-rich protocluster core candidates, PJ0846+15 (J0846), from the Planck All-Sky Survey to Analyze Gravitationally lensed Extreme Starbursts (PASSAGES) sample. The exceedingly high total star formation rate (SFR) uncorrected for lensing magnification ( μ ) of μ SFR = 3990 0 − 12900 + 23000 M ⊙ yr ⁻¹ is the result of a foreground cluster lensing at least 11 dusty star-forming galaxies between z = 2.660 and 2.669, where the intrinsic value is estimated to be SFR = 520 0 − 2000 + 3200 M ⊙ yr ⁻¹ . Atacama Large Millimeter/submillimeter Array observations uncovered 18 CO(3–2) emission-line detections, some of which are multiply imaged systems, lensed by a foreground cluster at z = 0.77. We present the first multiwavelength characterization of this field, constructing a lens model that predicts that these 11 galaxies ( μ ≃ 1.5–25) are contained within a projected physical extent of 280 × 150 kpc, with a velocity dispersion of σ _v = 246 ± 72 km s ⁻¹ . J0846 exhibits the rare case of a protocluster candidate whose core is strongly lensed, offering a magnified view of the rapid stellar buildup within an overdense environment at Cosmic Noon.

We present the COSMOS Spectroscopic Redshift Compilation encompassing ∼20 yr of spectroscopic redshifts within a 10 deg ² area centered on the 2 deg ² COSMOS legacy field. This compilation contains 487,666 redshifts of 266,284 unique objects from 138 individual programs up to z ∼ 8 with median stellar mass ∼10 ^8.4 –10 ¹⁰ M _⊙ (redshift dependent). Rest-frame NUVrJ colors and star formation rate–stellar mass correlations show that the compilation primarily contains low-to-intermediate-mass star-forming and massive, quiescent galaxies at z < 1.25 and mostly low-mass bursty star-forming galaxies at z > 2. Sources in the compilation cover a diverse range of environments, including protoclusters such as “Hyperion.” The full compilation is 50% spectroscopically complete by i ∼ 23.4 mag and K _s ∼ 21.6 mag; however, this is redshift dependent. Spatially, the compilation is >50% (>30%) complete within the central (outer) region limited to i < 24 mag and K _s < 22.5 mag, separately. We demonstrate how the compilation can be used to validate photometric redshifts and investigate calibration metrics. By training self-organizing maps on COSMOS2020/Classic and projecting the compilation onto it, we find key subpopulations currently lacking spectroscopic coverage, including z < 1 intermediate-mass quiescent and low-/intermediate-mass bursty star-forming galaxies, z ∼ 2 massive quiescent galaxies, and z > 3 massive star-forming galaxies. This highlights how combining self-organizing maps with our compilation can provide guidance for future spectroscopic observations to get a complete spectroscopic view of galaxy populations. Lastly, the compilation will undergo periodic data releases incorporating new spectroscopic redshifts and providing a lasting legacy resource for the community.