Danial Langeroodi

We present JWST/MIRI observations of the Type I superluminous supernova (SLSN) 2017gci obtained over 2000 rest-frame days after the supernova (SN) exploded, which represent the latest phase images taken of any known SLSN to date. We find that archival Wide-field Infrared Survey Explorer (WISE) detections of SN 2017gci taken 70–200 days after explosion are most likely explained by an IR dust echo from a ∼10 ⁻⁴ M _⊙ shell of preexisting dust, as opposed to freshly formed dust. New JWST observations reveal mid-infrared emission at the position of SN 2017gci; however, the flux level and spatial offset indicate that this emission is most likely dominated by the host galaxy. We therefore derive upper limits from these observations to constrain dust emission at late times. Radiative transfer modeling of carbonaceous dust shows that warm optically thin dust masses up to 0.18 M _⊙ are excluded at the 3 σ confidence level. However, substantially larger dust masses cannot be ruled out if the dust is optically thick. Infrared detections of other SLSNe have suggested that SLSNe may be highly efficient dust producers. While our constraints are insufficient to determine the total dust yield of SN 2017gci, they indicate that any late-time dust emission must either be modest compared to the most dust-rich SNe or arise from dust that is optically thick. A larger sample of deep infrared observations will be required to determine whether SLSNe are significant contributors to cosmic dust production.

We present new MIRI F560W, F770W, and F1000W imaging of the galaxy GN-z11 at a redshift of 10.603. We report a significant detection (14 σ ) in the F560W and F770W images, and a marginal detection (3.2 σ ) in the F1000W filter. The new MIRI observations cover the optical-red spectral range and significantly extend previous NIRCam wavelength coverage from rest-frame 0.38 μm up to 0.86 μm. In this work, we analyse the spectral energy distribution (SED) combining this new MIRI imaging data with archival NIRSpec/Prism and MRS spectroscopy, and NIRCam imaging, i.e. covering the rest-frame 0.12–0.86 μm. New constraints such as the equivalent widths of the strong optical lines ([O III ] λ 5008, H β and H α ) and the continuum emission at rest-frame 0.48 μm, 0.66 μm, and 0.86 μm, free of emission line contributions, are presented. The continuum emission shows a flat energy distribution, in f _ν , up to 0.5 μm, compatible with the presence of a mixed stellar population of young (4 ± 1 Myr) and mature (63 ± 23 Myr) stars that also account for the [O III ], H β , and H α emission lines. The continuum at rest-frame 0.66 μm shows a 36 ± 3% flux excess above the predicted flux for a mixed stellar population, pointing to the presence of an additional source contributing at these wavelengths. This excess increases to 91 ± 28% at rest-frame 0.86 μm, although with a large uncertainty due to the marginal detection in the F1000W filter. We consider that hot dust emission in the dusty torus around a type 2 active galactic nucleus (AGN) could be responsible for the observed excess. Alternatively, this excess could be due to hot dust emission or a photoluminiscence dust process (Extended Red Emission, ERE) under the extreme UV radiation field, as is observed in local metal-poor galaxies and in young compact starbursts. The presence of a type 1 AGN is not supported by the observed SED as the hot dust emission in luminous high- z quasi-stellar objects (QSOs) contributes at wavelengths above rest-frame 1 μm, and an additional ad hoc red source would be required to explain the observed flux excess at 0.66 and 0.86 μm. Additional deep MIRI imaging covering the rest-frame near-IR is needed to confirm the flux detection at 10 μm, and to discriminate between the different hot dust emission in the extreme starburst and AGN scenarios.

We introduce genesis-metallicity , a gas-phase metallicity measurement P ython software employing the direct and strong-line methods depending on the available oxygen lines. The nonparametric strong-line estimator is calibrated based on a kernel density estimate in the four-dimensional space of O2 = [O ii ] λλ 3727,29/H β ; O3 = [O iii ] λ 5007/H β ; H β equivalent width EW(H β ); and gas-phase metallicity 12 + log ( O/H) . We use a calibration sample of 1510 galaxies at 0 < z < 10 with direct-method metallicity measurements, compiled from the JWST/NIRSpec and ground-based observations. In particular, we report 122 new NIRSpec direct-method metallicity measurements at z > 1. We show that the O2, O3, and EW(H β ) measurements are sufficient for a gas-phase metallicity estimate that is more accurate than 0.09 dex. Our calibration is universal, meaning that its accuracy does not depend on the target redshift. Furthermore, the direct-method module employs a nonparametric T _e (O ii ) electron temperature estimator based on a kernel density estimate in the five-dimensional space of O2, O3, EW(H β ), T _e (O ii ), and T _e (O iii ). This T _e (O ii ) estimator is calibrated based on 1004 spectra with detections of both [O iii ] λ 4363 and [O ii ] λλ 7320,30, notably reporting 20 new NIRSpec detections of the [O ii ] λλ 7320,30 doublet. We make genesis-metallicity and its calibration data publicly available and commit to keeping both up to date in light of the incoming data.

We present cosmological constraints from eight strongly lensed quasars (hereafter, the TDCOSMO-2025 sample). Building on previous work, our analysis incorporated new deflector stellar velocity dispersions measured from spectra obtained with the James Webb Space Telescope (JWST), the Keck Telescopes, and the Very Large Telescope (VLT), utilizing improved methods. We used integrated JWST stellar kinematics for five lenses, VLT-MUSE for 2, and resolved kinematics from Keck and JWST for RX J1131−1231. We also considered two samples of non-time-delay lenses: 11 from the Sloan Lens ACS (SLACS) sample with Keck-KCWI resolved kinematics; and four from the Strong Lenses in the Legacy Survey (SL2S) sample. We improved our analysis of line-of-sight effects, the surface brightness profile of the lens galaxies, and orbital anisotropy, and corrected for projection effects in the dynamics. Our uncertainties are maximally conservative by accounting for the mass-sheet degeneracy in the deflectors’ mass density profiles. The analysis was blinded to prevent experimenter bias. Our primary result is based on the TDCOSMO-2025 sample, in combination with Ω _m constraints from the Pantheon+ Type Ia supernovae (SN) dataset. In the flat Λ cold dark matter (CDM), we find H ₀ = 71.6 ^+3.9 _−3.3 km s ⁻¹ Mpc ⁻¹ . The SLACS and SL2S samples are in excellent agreement with the TDCOSMO-2025 sample, improving the precision on H ₀ in flat ΛCDM to 4.6%. Using the Dark Energy Survey SN Year-5 dataset (DES-SN5YR) or DESI-DR2 baryonic acoustic oscillations (BAO) likelihoods instead of Pantheon+ yields very similar results. We also present constraints in the open ΛCDM, w CDM, w ₀ w _a CDM, and w _ϕ CDM cosmologies. The TDCOSMO H ₀ inference is robust and consistent across all presented cosmological models, and our cosmological constraints in them agree with those from the BAO and SN.

X-ray and infrared surveys provide efficient, and to some degree complementary, means of detecting and characterising active galactic nuclei (AGNs), with the infrared also providing an important probe of the host galaxies. To this end we combine the deepest X-ray survey from the Chandra Deep Field-South (CDF-S) ‘7-Ms’ survey with the deepest mid-infrared (5.6 μm) image from the JWST/MIRI Deep Imaging Survey (MIDIS) in the Hubble Ultra-Deep Field (HUDF) to study the infrared counterparts and point-source emission of 31 X-ray sources with a median, intrinsic, rest-frame X-ray luminosity of log ₁₀ ( L _Xc ^{0.5−7 keV} ) = 42.04 ± 0.22 erg s ⁻¹ . The sample includes 24 AGNs with a redshift range, set by the X-ray detectability, of z ≃ 0.5−3, with the bulk of the sources lying at z ≃ 1−2, i.e. around the epoch of cosmic noon. Through a multi-wavelength morphological decomposition, employing three separate classifications (visual, parametric, and non-parametric), we separate (where present) the luminosity of the point-like AGN component from the remainder of the host-galaxy emission. The unprecedented mid-infrared sensitivity and imaging resolution of MIRI allows, in many cases, for the direct characterisation of point-like (i.e. unresolved) components in the galaxies’ emission. We establish a broad agreement between the three morphological classifications. At least 70% of the X-ray sources, including some classified as galaxies, show unresolved emission in the MIRI images, with the unresolved-to-total flux fraction at rest-frame 2 μm ranging from ∼0.2 to ∼0.9. At high X-ray luminosities (log ₁₀ ( L _Xc ) > 43 erg s ⁻¹ ), we derive a consistent rest-frame near-infrared 2 μm point-source luminosity to that derived for local AGNs, whilst at lower X-ray luminosities we identify an excess in the 2 μm emission compared to pre-JWST studies. We speculate that this offset may be driven by a combination of Compton-thick AGN components and nuclear starburst, merger-driven activity. Our observations highlight the complex nature of X-ray sources in the distant Universe and demonstrate the power of JWST/MIRI in quantifying their nuclear infrared emission.

Massive, high-redshift ( z > 2) quiescent galaxies represent crucial tests of early galaxy formation and evolutionary mechanisms through their cosmic number densities and stellar mass functions (SMFs). We explore a sample of 743 massive (M _∗ > 10 ^9.5 M _⊙ ) quiescent galaxies from z = 2 − 7 in over 800 arcmin ² of NIRCam imaging from a compilation of public JWST fields (with a total area > 5× previous JWST studies). We compute and report their cosmic number densities, stellar mass functions, and cosmic stellar mass density. We confirm a significant overabundance of massive quiescent galaxies relative to a range of cosmological hydrodynamical simulations and semi-analytic models (SAMs). We find that no simulations or SAMs accurately reproduce the SMF for massive quiescent galaxies at any redshift within the interval z = 2 − 5. This shows that none of these models’ feedback prescriptions are fully capturing high-z galaxy quenching, challenging the standard formation scenarios. We find a greater abundance of lower-mass (M _∗ < 10 ¹⁰ M _⊙ ) quiescent galaxies than has been previously found, highlighting the importance of specific-star-formation rate cuts rather than simple colour selection. We show the importance of this selection bias, alongside individual field-to-field variations caused by cosmic variance, in varying the observed quiescent galaxy SMF, especially at higher z. We also find a steeper increase in the cosmic stellar mass density for massive quiescent galaxies than has been seen previously, with ρ _* ∝ (1 + z ) ^{−7.2 ± 0.3} , indicating the dramatic increase in the importance of galaxy quenching within these epochs.

We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., “IIn-like”) in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by W. V. Jacobson-Galán et al., this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at 10¹⁶ cm, consistent with substantial progenitor mass-loss rates of ∼10⁻⁴–10⁻⁵ M _⊙ yr⁻¹ (v _w < 50 km s⁻¹) in the final centuries to millennia before explosion.

We present a sample of six F200W and three F277W dropout sources identified as 16 < z < 25 galaxy candidates using the deepest JWST/NIRCam data to date (5σ depths ∼31.5 mag at ≥2 μm), provided by the MIRI Deep Imaging Survey and the Next Generation Deep Extragalactic Exploratory Public survey. We estimate ultraviolet (UV) luminosity functions and densities at z ∼ 17 and z ∼ 25. The number density of galaxies with absolute magnitudes of −19 < M _UV < −18 at z ∼ 17 (z ∼ 25) is a factor of 4 (25) smaller than at z ∼ 12; the luminosity density presents a similar evolution. Compared to state-of-the-art galaxy simulations, we find the need for an enhanced UV-photon production at z = 17–25 in M _DM = 10^8.5−9.5 M _⊙ dark matter halos, provided by an increase in the star formation efficiency at early times and/or by intense compact starbursts with enhanced emissivity linked to strong burstiness, low or primordial gas metallicities, and/or a top-heavy initial mass function. There are a few robust theoretical predictions for the evolution of galaxies above z ∼ 20 in the literature; however, the continuing rapid drop in the halo mass function would predict a more rapid evolution than we observe if photon production efficiencies remained constant. Our z > 16 candidates present mass-weighted ages around 30 Myr, and attenuations A(V) < 0.1 mag. Their average stellar mass is M _⋆ ∼ 10⁷ M _⊙, implying a stellar-to-baryon mass fraction around 10% if the emissivity increases with redshift, or significantly higher otherwise. Three candidates present very blue UV spectral slopes (β ∼ −3) compatible with Population III young (≲10 Myr) stars and/or high escape fractions of ionizing photons; the rest have β ∼ −2.5 similar to the z = 10–12 samples.

We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM) of B14-65666, a source identified as a Lyman-break and interacting galaxy at a redshift of z = 7.15. We detect the Hα line emission in this system, revealing a spatially resolved structure of the Hα-emitting gas, which consists of two distinct galaxies, E and W, at a projected distance of 0.4 arcsec apart (i.e., 2.2 kpc). One of the galaxies (E) is very compact (upper limit for the effective radius of 63 pc) in the rest-frame ultraviolet light, while the other galaxy (W) is more extended (effective radius of 348 pc), showing a clumpy structure reminiscent of a tidal tail. The total Hα luminosity implies that the system is forming stars at a rate of 76 ± 8 M_⊙ yr⁻¹ and 30 ± 4 M_⊙ yr⁻¹ for E and W galaxies, respectively. The ionizing photon production efficiency, log(ζ_ion), for galaxies E and W, has values of 25.1 ± 0.1 Hz erg⁻¹ and 25.5 ± 0.1 Hz erg⁻¹, which is within the range measured in galaxies at similar redshifts. The high values derived for the Hα equivalent widths (832 ± 100 and 536 ± 78 Å) and the distinct locations of the E and W galaxies in the log(ζ_ion) – equivalent width (Hα) plane indicate that the system is dominated by a young (under 10 Myr) stellar population. The overall spectral-energy distribution suggests that in addition to a young stellar population, the two galaxies may have mature (over 100 Myr) stellar populations and very different dust attenuations, with galaxy E showing a larger attenuation (A_V = 1.5 mag) compared to the almost dust-free (A_V = 0.1 mag) galaxy W. The derived star formation rate (SFR) and stellar masses identify the two galaxies as going through a starburst phase characterized by a specific SFR (sSFR) of 40–50 Gyr⁻¹. Galaxy E has an extreme stellar mass surface density (6 × 10⁴ M_⊙ pc⁻²), close to that of the nuclei of low-z galaxies, while galaxy W (10³ M_⊙ pc⁻²) is consistent with the surface densities measured in galaxies at these redshifts. The kinematics of the ionized gas traced by the Hα line show a velocity difference of 175 ± 28 km s⁻¹ between the two components of B14-65666 and a broader profile for galaxy W (312 ± 44 km s⁻¹) relative to galaxy E (243 ± 41 km s⁻¹). The detailed study of B14-65666 shows that the complex stellar and interstellar medium structure in merging galaxy systems was already in place by the Epoch of Reionization. The general properties of B14-65666 agree with those predicted for massive merging systems at redshifts of 7 and above in the FIRSTLIGHT cosmological simulations. The in-depth study of systems such as B14-65666 reveal how galaxy mergers in the early Universe drive intense star formation, shape the interstellar medium, and influence the buildup of stellar mass, just 700–800 Myr after the Big Bang.