arXiv subjects

Willem B. Hoogendam

Publications and source records attributed to Willem B. Hoogendam.

At least 19 recordsLinked to original sources

arXiv2026

Extreme Stellar Death and Galaxy Feedback at z = 2: A Rest-frame Ultraviolet Characterization of the Strongly Lensed Superluminous Supernova 2025wny

We present photometric and spectroscopic follow-up observations of the strongly-lensed H-poor superluminous supernova (SLSN) 2025wny at $z = 2.0155$. We use integral-field Keck-II/KCWI spectroscopy to obtain rest-frame ultraviolet spectra spanning $11$ to $61$ days after maximum light. We use Pan-STARRS photometry to constrain the brightest image's magnification, finding $μ_A=19.4\pm1.6$, a factor of $\sim$2-4 higher than mass-modeling estimates. We fit the Pan-STARRS photometry with a magnetar energy-injection model including $^{56}$Ni decay using the Modular Open Source Fitter for Transients (MOSFiT); the model can reproduce the near-maximum light curve with parameters typical of local universe SLSNe-I, including a magnetar spin period $P_{\rm spin}=4.1^{+0.7}_{-1.0}\,\mathrm{ms}$ and magnetic field $B_{\perp}=2.4^{+1.1}_{-0.8}\times10^{14}\,\mathrm{G}$; however, the late-time plateau suggests an additional power source. Spectroscopically, iron-group element line blanketing is virtually absent in the rest-frame UV spectra, and the absorption features match previously identified SLSN-I features from abundance tomography. Based on narrow ISM line metallicity estimates, SN 2025wny exploded in a sub-solar-metallicity galaxy. From host-galaxy lines in our rest-frame UV-to-optical spectrum we estimate high-velocity outflows of $\sim$575 km s$^{-1}$ and an exceptionally high Ly$α$ escape fraction of $f_{esc}^{Lyα}=0.23\pm0.03$. SN 2025wny matches lower-redshift SLSNe reasonably well. Upcoming surveys like LSST and Roman will discover additional high-redshift SLSNe, further testing whether SLSNe-I explosions remain consistent at the population level in the early universe.

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arXiv2026

SN2025aico: An Interesting Case Of $^{56}$Ni Mixing, Ejecta Asymmetries, and Dust Formation in a Type IIb Supernova

Stripped-envelope supernovae provide a window into how massive stars lose their layers, mix radioactive material, produce dust, and explode asymmetrically. We present optical, near-infrared (NIR), and mid-infrared (MIR) observations of SN~2025aico, a Type~IIb supernova in LEDA~35384. Our spectroscopic sequence, spanning $+1$ to $+167$ d after explosion, follows its evolution from a photospheric phase exhibiting both hydrogen and helium features to prominent helium emission and, ultimately, nebular-phase ejecta. Using He I $1.083$ and $2.0581\,μ$m transitions, we investigated the kinematics and geometry of the helium-rich material. Both transitions exhibit a three-phase, non-monotonic velocity evolution: an initial rapid decline, a subsequent increase, and an eventual plateau. We interpret this behavior as evidence for limited outward mixing of $^{56}$Ni, such that radioactive energy deposition reaches the outer helium-rich ejecta progressively as the ejecta expand, producing the non-thermal electrons responsible for helium excitation. After $\sim100$ d, both NIR He I transitions develop double-peaked emission profiles. Similar structure in the oxygen emission indicates ejecta asymmetry. Comparison with other supernovae suggests a tentative connection between this structure and explosion energy, potentially linked to the delay between core collapse and explosion. Serendipitous JWST observations at $+124.4$d reveal an infrared excess. Modeling favors warm ($\sim800$--$1500$K) carbon dust newly formed in the ejecta, together with cooler carbon or silicate dust likely associated with pre-existing circumstellar material. SN~2025aico demonstrates how continuous optical-to-MIR observations can connect progenitor evolution, explosion physics, ejecta geometry, and dust production.

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arXiv2026

Nebular Spectra of the Extremely Metal-Poor SN II 2023ufx Over a Year After Explosion: A Massive Progenitor and Unique Circumstellar Environment

We present new observations of the metal-poor ($< 0.1$ $\rm Z_\odot$) Type II supernova 2023ufx and its host galaxy. The deep nebular spectrum, obtained roughly a year after explosion, has a triple-peaked [O I] emission profile suggesting an asymmetric explosion. Comparison to nebular spectra models suggests a zero-age main sequence mass of $ M_{\rm ZAMS} \sim 25-35$ $\rm M_\odot$, which is supported by the low [Ca II]/[O I] emission-line ratio of $\approx0.4$. The diminishing, broad, boxy H$α$ emission and flattening of the light curve in the late ($\sim2$ yr) photometry suggest a complex mass-loss history in the centuries to millennia before explosion. New optical and near-infrared imaging of the host galaxy confirms that it is a dwarf, with a stellar mass of $10^{6.6\pm0.1}$ $\rm M_\odot$ and a SFR of $10^{-2.5\pm0.1}$ $\rm M_\odot$/yr. Results from both SED fitting and galaxy stellar mass-metallicity scaling relations all lead to an environmental metallicity estimate of $0.02-0.07$ $\rm Z_\odot$. Taken together, these observations confirm that SN 2023ufx is the explosion of a very metal-poor, heavily stripped red supergiant.

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arXiv2026

SCAT Data Release 1: 1812 optical spectra of 1331 transients

We present the first data release (DR1) of the Spectroscopic Classification of Astronomical Transients (SCAT) survey, covering the first $\approx 5$ years of observations (March 2018 - January 2023). DR1 includes 1812 spectra of 1331 transients, which we sort into broad spectroscopic classes including supernovae (SNe), transients originating in galactic nuclei, and stellar variability. We collect multi-filter light curves from imaging surveys and fit them with phenomenological models to estimate peak brightnesses and the time of explosion/first-light. Extragalactic transients are matched to candidate host galaxies, and we compare host-galaxy luminosities and projected offsets by SN type. SNe appear to be a reliable way to augment the redshift coverage of nearby ($z\lesssim 0.1$) galaxies in tandem with dedicated redshift surveys. We present new redshifts for roughly half of the SN host galaxies, most of which are low-luminosity dwarfs similar to the Magellanic Clouds ($M_r \gtrsim -18$ mag). This set of transient spectra, light curves, luminosities, redshifts, and host galaxies offers an excellent testbed for real-time photometric/light curve classification pipelines in the modern era of deep and large-area surveys. We conclude with a brief discussion of the provided data products and status of the SCAT survey.

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arXiv2026

The host galaxies of 2003fg-like type Ia supernovae

SN~2003fg-like events are a peculiar type Ia supernova (SN~Ia) subtype characterized by broader light curves, higher near-infrared luminosities, and stronger carbon absorptions at early times. Here we present observations of the largest compilation of 2003fg-like SN Ia host galaxies to date, obtained with Integral Field Spectroscopy (IFS). For 20 objects, we study both the global host-galaxy properties and, for the first time for a sizeable sample, the local environment at the SN position. Globally, 2003fg-like SNe~Ia occur in galaxies with lower stellar mass, lower oxygen abundance, and marginally higher specific star-formation rate (sSFR) than those of normal SNe~Ia, although their hosts are not as extreme in such properties as superluminous SNe, nor representative of metal-poor dwarf-galaxy samples. Locally, the SN positions show lower star-formation-rate, stellar-mass surface densities, and lower sSFR, than normal SN~Ia environments, consistent with a significant preference for the outskirts of their hosts, while their stellar age indicators are typical. The most distinctive local property is metallicity, with 2003fg-like SNe~Ia occupying the most metal-poor environments among SNe~Ia. We also find a tentative positive correlation between the light-curve width and the oxygen abundance for 2003fg-like events. Our results imply that 2003fg-like SNe~Ia arise from the merger of two white dwarfs (WDs) or the core-degenerate scenario, but disfavor the single, rapidly rotating super-M$_{ch}$ C-O WD progenitor, as this channel requires a young stellar population that we do not observe at the SN positions. The preference of 2003fg-like SNe~Ia for low-metallicity environments suggests that they may have been more common in the early Universe. (abridged)

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arXiv2026

A Two-month, Galaxy-targeted NIR Follow-up of the Sub-solar-mass Gravitational Wave Candidate S251112cm: Probing Electromagnetic Counterpart Scenarios

S251112cm is a nearby ($93 \pm 27$~Mpc) compact-binary merger candidate with a high inferred probability that at least one component is below $1\,M_\odot$. This event provides a rare test case for electromagnetic follow-up of a theoretically predicted but unconfirmed sub-solar-mass merger candidate. Motivated by scenarios predicting NIR-bright emission over weeks to months, we carried out a deep, galaxy-targeted UKIRT $J$-band campaign over approximately two months, prioritizing host candidates by a ranking that combines the three-dimensional localization probability with WISE W1 luminosity as a stellar-mass proxy. Of $\sim9000$ candidate hosts, we monitored 59, corresponding to 7.7\% of the cumulative weighted host prior. Difference imaging reveals no convincing transient down to typical depths of $J\sim22$--23~mag (AB). At this distance, both a Type~Ic-BL supernova template and an AT\,2017gfo-like KN template---including time-shifted variants up to $Δt \sim 60$~days---would have remained above our median depth for multiple epochs within the monitored hosts. Comparison with a canonical KN model grid, summarized through conditional weighted consistent-fraction maps, shows that bright configurations with high dynamical and wind-ejecta masses are strongly disfavored, while less luminous configurations remain largely permissible. While these constraints are host-limited and do not constitute an event-wide exclusion, this campaign provides the first empirical case study of long-baseline, deep NIR follow-up for a sub-solar-mass merger GW class and demonstrates a host-weighted framework applicable to future galaxy-targeted campaigns.

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arXiv2026

JWST Spectroscopy of Type Ia Supernova 2025rbs from Maximum Light to the Nebular Phase

We present JWST observations of the Type Ia supernova (SN Ia) 2025rbs ($D=$14.5 Mpc) at +1, +23, and +84 days after B-band maximum, spanning peak light through a wavelength-dependent transition toward the nebular phase. Combined with ground-based optical and near-infrared (NIR) data, our panchromatic spectra (0.4-14 $μ$m) include the first maximum-light mid-infrared (MIR) spectrum and the earliest MIR spectroscopic sequence of an SN Ia to date. At peak light, the MIR spectrum exhibits a continuum with permitted and forbidden features, including Si II, Ni II, and early-emerging [Ni III-IV] and [Ar II-III]. By +23 days the MIR is dominated by forbidden lines with a weak continuum, and by +84 days it is fully nebular, whereas the optical/NIR spectra remain transitional. The nebular spectrum reveals strongly stratified ejecta, with stable Ni concentrated at the lowest velocities, radioactive Co at intermediate velocities but absent within ~2000 km s$^{-1}$, and Ar occupying an outer shell. We detect small-scale substructure in [Ca IV] 3.21 $μ$m with fractional amplitudes of a few percent and a characteristic velocity scale of ~800 km s$^{-1}$, which may reflect compositional structure, ionization variations, or both. Radiative-transfer calculations substantially underpredict these MIR Mg II features despite approximately reproducing the NIR Mg II 1.0927 $μ$m line, suggesting that the relative strengths of these transitions are sensitive to the treatment of Mg ionization and excitation. These observations demonstrate that MIR spectroscopy beginning near maximum light simultaneously probes the emerging inner ejecta and rapidly fading outer burning products, providing new constraints for explosion and radiative-transfer models.

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arXiv2026

ATLAS22kjn (AT 2022fpx): A Coronal Line Emitter with an Early Light Curve Bump and Mid-Infrared Dust Echo

We present an analysis of ATLAS22kjn (AT 2022fpx), whose high-ionisation coronal lines (CLs) and pre-peak light curve bump provide distinctive opportunities to investigate the physical mechanisms powering tidal disruption events (TDEs). In addition to CLs, the optical spectra show common TDE features, including a strong, blue continuum and broad Balmer and He II lines. The CLs appear before UV/optical light curve peak, preceding the detection of X-rays by $\sim 300$ days and persisting after X-rays are no longer detected, suggesting the X-ray emission is obscured at both early and late times. Using the CL luminosities, we constrain the temperature evolution of the ionising source, finding a decrease of $\lesssim 10 \%$ over 500 days. In the UV/optical light curve, we observe a $9 \substack{+4 \\ -2}$ day bump that peaks $125 \substack{+5 \\ -3}$ rest-frame days before the peak of the main flare. Although we cannot definitively determine the origins of the bump, we find that its timescale and luminosity are most consistent with theoretical predictions for a precursor feature produced by a stream-stream collision or a wind-stream collision. ATLAS22kjn also shows a prominent dust echo in its mid-infrared (MIR) light curves, indicating a high dust covering fraction $f_c \simeq 0.40 \pm 0.03$, similar to the covering fractions of other CL-emitting TDEs. From the multi-wavelength observations of ATLAS22kjn, we estimate the size and relative radii of the emission regions in its nuclear environment and determine that the CL region lies between the broad line region and the MIR-emitting dust. ATLAS22kjn demonstrates the importance of multi-wavelength and early-time observations, and the utility of CLEs in characterising the otherwise unobservable EUV/ultrasoft X-ray emission of TDEs.

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arXiv2026

AT2021yky: A Fast-Rising Optical Transient with Evolving Broad Hydrogen Emission Consistent with an Ambiguous Nuclear Transient

Nuclear transients are powerful probes of supermassive black hole properties, offering insight into black hole mass, accretion physics, and the structure of galactic nuclei. Among these, a growing class of events cannot be classified as either tidal disruption events (TDEs) or active galactic nuclei (AGN) flares, and their physical origins remain poorly understood. We present a multi-wavelength photometric and spectroscopic analysis of AT2021yky (ZTF21abzciqh), an ambiguous nuclear transient (ANT) at a redshift of $z = 0.076$. AT2021yky reached a peak bolometric luminosity of $L_{\rm peak} = (4.1 \pm 1.1) \times 10^{43}~\mathrm{erg~s^{-1}}$, with a rise-time of $18.2 \pm 0.7$ days. The early-time UV/optical emission is well described by a blackbody with a temperature of $T \simeq 1.4 \times 10^{4}$ K, cooler than most optically selected TDEs. No X-ray emission from the transient is detected, with a $3σ$ limit of $L_X \lesssim 3.4 \times 10^{41}$ erg s$^{-1}$ near peak. Spectroscopic observations reveal a largely featureless blue continuum with broad (FWHM$\sim 11,000$ km s$^{-1}$) H$α$ emission line that appears around 20$-$40 days post-peak. The host-galaxy emission-line ratios indicate the presence of an AGN, though the absence of optical or mid-IR variability and a non-AGN mid-IR color suggest it is weak. AT2021yky exhibits a rapid rise time comparable to that of luminous fast blue optical transients (LFBOTs), while its decay timescale and late-time broad H$α$ emission resemble those observed in TDEs. However, its cooler blackbody temperature and the absence of He II and Balmer emission lines other than H$α$ instead favour its classification as an ANT.

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arXiv2026

Decadal pre-explosion activity and circumstellar interaction in a supernova

When a massive star explodes as a supernova, crucial information about its immediate environment is lost within hours. Here we report rapid optical observations from Lulin Observatory of the broad-lined Type Ic supernova SN 2026gzf, beginning 1.25 hours after Einstein Probe detected the X-ray transient EP260321a. Our data led to the discovery of the optical counterpart and showed a luminous blue first-day excess that cannot be reproduced by standard radioactive models. We find that interaction between the ejecta and $\approx 0.02$ M$_{\odot}$ of circumstellar material accounts for the early excess. Archival Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) images show variability at the explosion site over the previous $\sim 12$ years, with the source brightening by a factor of $\sim 1.5$ in the final $\sim 3$ years before explosion, providing rare evidence for pre-explosion activity in a stripped-envelope progenitor system. The precursor brightening suggests enhanced eruptive mass loss during late-stage oxygen burning before core collapse, while an additional silicon-burning episode shortly before explosion may have created the compact nearby material responsible for the X-ray shock-breakout signal. SN 2026gzf therefore offers the first view of how a stripped progenitor modifies its immediate environment shortly before death, linking long-term precursor variability, circumstellar interaction and the explosion itself.

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arXiv2026

Discovery and Analysis of a Type II Supernova Candidate at z = 3.19 from JWST's COSMOS-Web Survey

The launch of the James Webb Space Telescope (JWST) has enabled the discovery of a small but increasing sample of high-redshift core-collapse supernovae (CC SNe), which provide new tests of massive star evolution in the early Universe. In this study, we report the discovery of SN 2023aeaf in COSMOS-Web survey observations, which at $z = 3.195$ has one of the highest SN spectroscopic redshifts to date. Using two epochs of JWST photometry separated by $\sim$1 month in the rest frame, we photometrically classify SN 2023aeaf by comparing the JWST photometry to spectrophotometric CC SN and Type Ia (SN Ia) models and UV observations of SNe from the Swift telescope, finding that SN 2023aeaf is highly likely to be a Type II SN. A spectrum of the SN$+$host galaxy was also obtained $\sim$30 rest-frame days after discovery but shows no clearly identifiable SN features, with H$α$ emission from the host potentially masking emission from the SN. Although the limited photometric coverage prevents strong constraints on the explosion properties, we find that the data are most consistent with a $\sim$12$M_\odot$ progenitor with $\sim$0.5$M_{\odot}$ of circumstellar material. We next use the host-galaxy spectrum and photometry to model the host spectral energy distribution (SED) using the Prospector Bayesian inference framework. We find that the host is a star-forming galaxy with a sSFR of $ \log_{10}(\rm sSFR/yr^{-1})= -10.17^{+0.13}_{-0.10}$, a stellar mass of $\log(M_\star/M_\odot) = 9.04^{+0.03}_{-0.04}$, and a gas-phase metallicity of $12 +{\rm log_{10}}({\rm O/H}) = 7.82\pm0.02$. SN 2023aeaf joins a growing sample of early Universe CC SNe with high luminosities, dense CSM, and low-metallicity environments.

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arXiv2026

Supernova 2025wny: High-angular resolution Keck/NIRC2 observations and preliminary lens modeling

Multiply imaged, gravitationally lensed supernovae are rare but powerful tools for providing independent measurements on cosmological parameters. Supernova (SN) 2025wny ("SN Winny") is the first gravitationally-lensed Type I superluminous supernova and the first lensed supernova in a galaxy-scale system that is suitable for time-delay cosmography studies. In this work, we present high-resolution $K_p$-band adaptive optics imaging of SN Winny obtained with the near-infrared camera (NIRC2) on the W. M. Keck II telescope. With exquisite image quality (FWHM$\approx0.^{\prime\prime}065$) we determine and make use of the precise astrometric positions of the five multiple images as constraints for our lens mass models. With lenstronomy and Glee, we parameterize the total mass of the system with a singular isothermal ellipsoid, a singular isothermal sphere, and external shear. The two independent models are in excellent agreement and reproduce the observed image positions with sub-milli-arcsecond residuals. The inferred projected total masses enclosed within the Einstein radii of the primary and secondary lens galaxies are M$_1$ = 4.44$^{+0.06}_{-0.05}\times10^{11} M_\odot$ and M$_2$ = 0.96$^{+0.02}_{-0.02}\times10^{11} M_\odot$, respectively. Likewise, the inferred effective velocity dispersion of the primary lens is $σ_{1} = $ 277.4$^{+0.9}_{-0.7}$ km/s, consistent with the independent spectroscopic measurement made by DESI of $σ_{\star,1} = $ 298$\,\pm\,37$ km/s. Our modeling results are also consistent with previous results for the same system with data from the Large Binocular Telescope (LBT), using the same lens modeling codes. We also corroborate their finding that the SN multiple image A has an anomalous excess of flux by a factor of ~2-3 beyond what our smooth mass models predict.

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arXiv2026

ASAS-SN Rates IV: Constraints on the Kilonova Rate

Kilonovae (KNe) are the electromagnetic signatures of neutron star mergers and are likely the dominant site of cosmic $r$-process nucleosynthesis. However, their intrinsic rate remains poorly constrained due to a paucity of confirmed events. We use the All-Sky Automated Survey for Supernovae (ASAS-SN) to place limits on the rate of bright, nearby KNe over an 11-year baseline ranging from 2014 to 2024. To evaluate the survey's completeness for KNe, we employ an injection-recovery simulation using a shock-cooling cocoon model calibrated to the early blue emission of the only well-sampled KN, SSS17a (AT 2017gfo). Finding no KNe within the survey, we calculate a $2σ$ ($\sim95\%$) upper limit on the local volumetric KN rate of $R_{\mathrm{KN}} < 4400\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}$. Despite ASAS-SN's shallower limiting magnitude compared to other time-domain searches, its continuous, high-cadence, all-sky monitoring yields a constraint that is competitive with the strongest results from electromagnetic surveys but remains a factor of 18 higher than the LIGO-Virgo-KAGRA GWTC-4 estimate of the binary neutron star merger rate.

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arXiv2026

Contemporaneous Optical and Near-Infrared Observations of the Interstellar Comet 3I/ATLAS Pre- and Post-Perihelion

Interstellar objects provide a unique view into the formation of other star systems. Here we present spectroscopic observations of the recently discovered interstellar object 3I/ATLAS between a heliocentric distance of $3.7$ to $1.8$~au on either side of its travels through perihelion. We obtained several observations with the Keck-I/LRIS, Keck-II/NIRES, Gemini/GMOS, and UH88/SNIFS spectrographs, covering a wavelength range of $0.3 - 2.5~\mathrm{μm}$. We report the continued emission of both Ni and CN, along with post-perihelion detections of Fe and a weak detection of $\mathrm{C_3}$. We determine the spectral slope across optical and NIR wavelengths and find a positive spectral slope in the optical, with values ranging from $\sim 21 - 27\%$ in the blue regions ($0.4 - 0.55~\mathrm{μm}$) to $\sim 6 - 10\%$ in the red ($0.65 - 0.9~\mathrm{μm}$) regions. In contrast, the NIR showed a negative spectral slope of $\sim -0.9 \%$ between $0.9 - 1.5~\mathrm{μm}$ and $\sim -2.3\%$ between $1.9 - 2.5~\mathrm{μm}$. 3I/ATLAS shows a clear turnover in its spectral shape at $\sim 1.1~\mathrm{μm}$, corresponding to scattered light from the dusty coma. Finally, in the NIR, we do not find an increase in the depth of the water features identified in an earlier NIR observation of 3I/ATLAS. Our observations of 3I/ATLAS in the NIR show a similar shape to the NIR spectrum of 2I/Borisov as it approached perihelion.

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arXiv2026

AT 2024ahzi: A Type IIP Supernova Discovered by the LSST Commissioning Camera

As part of its commissioning, the Vera C. Rubin Observatory observed several fields repeatedly for a month with ComCam, an instrument that uses the same hardware as the LSST camera but covers a smaller field of view. We photometrically classify AT 2024ahzi, a transient discovered by ComCam, as a Type IIP supernova (SN IIP) using both ComCam and DECam photometry. We find that the duration, luminosity, and color of AT 2024ahzi's photometric plateau are all consistent with those from a large sample of SNe II. By comparing its multi-band light curves to SN II models and analytic relations, we place constraints on the SN progenitor, explosion dynamics, and circumstellar environment. We argue that the progenitor has an extended density profile indistinguishable from a slowly accelerating CSM. We discuss how a similar workflow can identify and characterize future Rubin SNe II.

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arXiv2026

Pre-perihelion Emergence of the CN Gas Coma in 3I/ATLAS Temporally and Spatially Resolved by the 7-Dimensional Telescope

We present time-series medium-band (R~20-40) observations of the third interstellar object 3I/ATLAS (C/2025 N1) obtained with the 7-Dimensional Telescope (7DT), enabling spatially resolved monitoring of its gas and dust activity from 2025 July to September. The m400-band image (lambda_c = 400 nm, Delta lambda approx 25 nm) reveals the emergence of pronounced and spatially extended CN emission at heliocentric distances r_h < 3 au. This onset is consistently identified across multiple diagnostics, including a break in the light-curve evolution, excess reflectance, inward expansion of annular excess beyond 10,000-20,000 km, growth of the coma half-light radius from ~11,000 to ~19,000 km, and a rapid rise in the CN production rate Q_CN relative to Af rho. We further separate the CN-emitting and dust-scattered components through two-dimensional surface-brightness fitting into inner (dust) and outer (gas) components. The outer component preserves a nearly constant profile shape, varying only in normalization, implying relatively fast expansion of CN-bearing molecules. Together, these results reveal a transition in the optical from dust-dominated scattering at large heliocentric distances to volatile-driven, gas-dominated activity as 3I/ATLAS enters the inner Solar System. The timing and characteristics of the CN activation resemble the volatile enhancement observed in 2I/Borisov, suggesting that both known active interstellar objects exhibit comparable activation behavior at heliocentric distances of ~2-3 au.

astro-ph.EP↗

arXiv2026

BlastBerries: How Supernovae Affect Lyman Continuum Escape Fractions and Ionizing Photon Production in Local Analogs of High-Redshift Galaxies

While compact, star-forming galaxies are believed to play a key role in cosmic reionization, the physical mechanisms enabling the escape of ionizing photons through the galactic interstellar medium remain unclear. Supernova (SN) feedback is one possible mechanism for clearing neutral gas channels to allow the escape of Lyman continuum photons. Here, we use SN discoveries in low-redshift analogs of high-redshift star-forming galaxies -- Green Pea galaxies and their even lower-redshift counterparts, Blueberry (BB) galaxies -- to understand how SNe shape the properties of their host galaxies at high redshifts. We cross-match 1242 BB galaxies with transient discovery reports and identify 11 SNe, ten of which are likely core-collapse SNe, and compare their hosts to the larger BB population. We find that SN-hosting BBs exhibit elevated star formation rates, burstier star formation histories within the last $\sim$50 Myr, and higher stellar masses. We estimate the occurrence rates of SNe in BB galaxies, finding that the SN rate may be slightly suppressed in BBs compared to field galaxies of similar mass, but we are unable to fully control for observational uncertainties. Finally, SN hosts show bluer UV slopes than non-host BB galaxies at 2.1$σ$ significance and lower ionizing photon production efficiency at 7.9$σ$ significance; the former result offers modest support for the hypothesis that SN-driven feedback plays a role in facilitating the escape of ionizing photons, while the latter may imply that SN-driven quenching decreases the rate of ionizing photon production in compact star-forming galaxies during the epoch of reionization.

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arXiv2026

Supernova Rates and Luminosity Functions from ASAS-SN III: Over a Decade of Type Ia SNe and Their Subtypes

We present volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the All-Sky Automated Survey for Supernovae (ASAS-SN), covering the 11-year period from 2014 to 2024. By combining the 2014--2017 $V$-band sample with the 2018--2024 $g$-band sample, we construct a large statistical dataset of $1776$ SNe Ia. We compute completeness corrections based on injection-recovery simulations of the ASAS-SN light curves, taking into account the variations in light curve shapes. For our standard sample ($M_{g,\mathrm{peak}}<-16.0$ mag), we extract a total volumetric SN Ia rate of $R_{\mathrm{tot}} = (2.55 \pm 0.12) \times 10^4\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h_{70}^3$ at a median redshift of $z=0.029$. With a statistical uncertainty of $4.7\%$, this is the most precise local measurement to date. While the "normal" SNe Ia account for $(92.7 \pm 1.9)\%$ of this rate, the total LF reveals immense diversity, with $M_{g,\mathrm{peak}}$ spanning over five magnitudes. The LF of SNe Iax is also broad and rises toward lower luminosities, resulting in a likely lower limit of $(4.3 \pm 1.8)\%$ of the total rate. We place strong constraints on the rate of SNe Ia-CSM, finding they account for only $(0.036 \pm 0.017)\%$ of the total local rate. Finally, we find that the low-luminosity 02es-like SNe are $7 \pm 5$ times more common than the luminous 03fg-like SNe. This places demographic constraints on models proposing a physical continuum for these two subtypes, implying that any common channel for the two classes must strongly favor lower-luminosity explosions.

astro-ph.HE↗