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David Rubin

Publications and source records attributed to David Rubin.

At least 19 recordsLinked to original sources
arXiv2026

Supernovae Unite: Combining Pantheon+ and DES-SN5YR

We present the Hubble diagram and cosmological constraints resulting from the combination of the Pantheon+ and DES-SN5YR supernova (SN) samples, which we refer to as Unite. Unite updates Pantheon+, including methodology improvements that the DES sample enabled, and adds the new SN from the DES survey. This represents the most comprehensive and internally consistent SN Ia dataset available, consisting of 2884 likely type Ia supernovae. This work features consistent SN Ia modelling, sample selection, and bias corrections. We also redetermine host-galaxy stellar masses for over 98% of the sample using a consistent framework. Using Unite alone, for a flat universe with a cosmological constant (Flat-$Λ$CDM), we find $Ω_{\rm m} = 0.310^{+0.012}_{-0.011}$. We further present constraints using the Unite sample combined with Cosmic Microwave Background and both DES and DESI Baryon Acoustic Oscillation data. We find strong evidence of tension between CMB measurements and the combined BAO and supernova datasets when fitting a model with constant dark energy equation of state ($w$), which is alleviated when allowing $w$ to vary with time. For a flat universe with dark energy that has a time-evolving equation of state parametrized by $w_0$ and $w_a$ we find $(Ω_{\rm m},w_0,w_a) = (0.305\pm0.004,-0.861^{+0.044}_{-0.042},-0.60^{+0.17}_{-0.19})$ with a dark energy Figure of Merit of 315. This corresponds to a $\sim30\%$ reduction in the area of the $w_0-w_a$ confidence region relative to previous constraints from the combination of DES Y6, DESI-DR2, and CMB data (arXiv:2605.27221). The Bayesian evidence indicates only weak preference for time evolving dark energy, whereas frequentist analyses yield a preference over Flat-$Λ$CDM at a significance of $3.3σ$ ($3.1σ$) when using the maximum $\textit{a posteriori}$ probability (maximum likelihood).

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arXiv2026

Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31

Minute- and sub-minute microlensing provides a direct probe of compact dark matter at asteroid-mass scales, where primordial black holes with MPBH <~ 10^-10 Msol would produce short-duration, finite-source-suppressed amplifications of stars in extragalactic fields. To enable these measurements, we present FLASH: Fast Lensing And Sub-minute High-accuracy photometry with JWST, a pipeline designed to recover such events from JWST/NIRCam imaging by preserving detector-ramp time information and performing high-precision crowded-field photometry. FLASH begins from Level 1 NIRCam data products, applies microlensing-oriented detector calibration (including improved treatment of non-linearity and position-dependent detector calibration), and extracts forced multi-band light curves in crowded fields. We apply the pipeline to two public JWST/NIRCam datasets targeting the disk of M31 with 21.5 s cadence: GO-4735 and GO-2609. Although these observations are suboptimal as a microlensing survey, they provide a stringent test of JWST time-domain performance in a high-surface-brightness, crowded stellar field. Using these data with our own microlensing simulations, we derive the first JWST-based microlensing constraints toward M31, finding fPBH <~ 100 for MPBH~ 10^-9 Msol. Our results demonstrate that JWST is a competitive platform for high-cadence microlensing and that a dedicated, continuous NIRCam monitoring program could substantially improve constraints on compact dark matter below the current ground-based frontier.

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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

Chromatic Effects Across the Roman Focal Plane: Implications for Supernova Photometry and Measurements of Cosmological Parameters

Calibration uncertainties are the leading systematics in cosmological analyses using Type Ia supernovae (SNe Ia). For the \textit{Nancy Grace Roman Space Telescope (Roman)}, we quantify the impact of chromatic effects on SNe Ia photometry and derived cosmological parameters, using simulated light curves from the High-Latitude Time Domain Survey. We investigate two sources of wavelength-dependent bias: focal plane array (FPA)-dependent wavelength shifts arising from spatial variations across \textit{Roman's} 18 detectors, and coherent wavelength shifts corresponding to the measured $0.06\%$ uncertainty in absolute filter wavelength calibration. Using simulated SNe Ia light curves, we find that the FPA-dependent shifts -- which range from +6 to -80 $\rm Å$ introduce a redshift-dependent distance modulus bias that, if left uncorrected, propagates to $Δw_0 \sim -0.06$ and $Δw_a = -0.236$, which are larger than the forecast statistical uncertainties of $σ_{\rm stat, w_0} = 0.025$ and $σ_{\rm stat, w_a} = 0.114$, rendering the survey systematics-limited. We probe the impact of chromatic effects by employing detector-specific filter curves that recover unbiased cosmological constraints; to remain below the statistical noise floor, FPA wavelength shifts must be characterized to within 20\%. In contrast, a coherent 0.06\% offset in filter wavelength calibration -- ranging from -3 to -11 $\rm Å$ -- produces negligible redshift-dependent bias, with a minimal spread in $w_a$ ($Δw_a = -0.0004, σ_{w_{a,\rm sys}} = 0.114)$, demonstrating that the achieved pre-launch calibration precision is sufficient for this systematic to remain subdominant. Our results establish that chromatic effects are a required component of SN Ia cosmology with \textit{Roman}.

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arXiv2026

Hawai`i Supernova Flows: Bulk Flow Measurements using SNe Ia in the Optical and NIR

The present day peculiar velocity-field was sourced by primordial density fluctuations and sculpted over the lifespan of the Universe. Cosmological models such as $Λ$CDM make predictions for various statistical properties of peculiar velocities. Bulk flow, the average velocity within a given volume, has an expectation value of $\vec{0}$ due to isotropy, and a variance directly tied to the Hubble constant, the growth-rate of structure, and the matter power spectrum. In this paper, we use the redshifts and optical and near-infrared distance estimates to Type Ia Supernovae (SNe Ia) within subsets of the Hawai`i Supernova Flows dataset to infer the bulk flow within $z \lesssim 0.1$. The inferred speeds vary between ~100 to 400 km/s but are all consistent with the predictions of $Λ$CDM. As a secondary focus, we discuss the systematic uncertainty introduced by the discrete choice of methodology using two bulk flow estimators, two types of SN Ia distance estimators, and data covering two distinct regimes in wavelength space.

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arXiv2026

The Peculiar Growth of Structure: Validating $fσ_8$ Measurements from TITAN Type Ia Supernovae and the Uchuu Simulations

The growth rate of cosmic structure, parameterized by $fσ_8$, is a fundamental test of $Λ$CDM and general relativity. Using Type Ia supernova (SN Ia) peculiar velocities in conjunction with galaxy redshift surveys may be one of the most precise pathways to measuring $fσ_8$ in the local Universe, yet existing analyses have not quantified its systematic uncertainties. Here, we present an end-to-end simulated $fσ_8$ measurement tailored to the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) survey, using ~2000 simulated SNe Ia at $z < 0.067$. We use the Uchuu $N$-body simulations to generate mock galaxy catalogs and SN Ia simulations with realistic, correlated peculiar velocities, and use these catalogs to reconstruct density fields that replicate the 2M++ redshift survey. Using a modified forward likelihood framework across eight mock realizations, we recover $\langle fσ_8 \rangle = 0.429 \pm 0.038$ ($σ_{\rm stat} = 0.030$, $σ_{\rm sys} = 0.023$), consistent with the Uchuu simulation input $fσ_8 = 0.428$ to within 0.1%. The mock-to-mock scatter of 0.031 is consistent with our uncertainties, highlighting the reliability of our error estimates. Our measurement is dominated by the statistical uncertainty, with approximately equal contributions from SN Ia ($σ_{\rm sys}^{\rm SN}=0.017$) and density reconstruction ($σ_{\rm sys}^{\rm recon}=0.016$) systematic uncertainties. The assumed intrinsic scatter model is the largest single systematic contribution, and a different model choice can shift $fσ_8$ to lower values, largely driven by red SNe with a skewed color distribution. Our analysis provides the first systematic uncertainty budget for the "reconstruction-and-scaling" method of measuring $fσ_8$ with SNe Ia, and demonstrates that SNe Ia are a competitive probe of the growth of structure in the local Universe.

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arXiv2026

Gravitational Lenses in UNIONS and Euclid (GLUE) I: A Search for Strong Gravitational Lenses in UNIONS with Subaru, CFHT, and Pan-STARRS Data

We present the results of our pipeline for discovering strong gravitational lenses in the ongoing Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). We successfully train the deep residual neural network (ResNet) based on CMU-Deeplens architecture, which is designed to detect strong lenses in ground-based imaging surveys. We train on images of real strong lenses and deploy on a sample of 8 million galaxies in areas with full coverage in the g, r, and i filters, the first multi-band search for strong gravitational lenses in UNIONS. Following human inspection and grading, we report the discovery of a total of 1346 new strong lens candidates of which 146 are grade A, 199 grade B, and 1001 grade C. Of these candidates, 283 have lens-galaxy spectroscopic redshifts from the Sloan Digital Sky Survey (SDSS) and an additional 297 from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1). We find 15 of these systems display evidence of both lens and source galaxy redshifts in spectral superposition. We additionally report the spectroscopic confirmation of seven lensed sources in highquality systems, all with z > 2.1, using the Keck Near-Infrared Echelle Spectrograph (NIRES) and Gemini Near-Infrared Spectrograph (GNIRS).

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arXiv2026

Testing $Λ$CDM versus dynamical dark energy in one year: A DESI spectroscopic follow-up program for Rubin supernovae

Combined cosmological probes currently indicate that best-fit values in the $w_0-w_a$ parametrization of dynamical dark energy deviate from $Λ$CDM by $\sim3σ$. In this work, we present a supernova survey capable of measuring dynamical dark energy at the $>5σ$ level with just one year of data, starting in 2027. We first show that with the present values of $w_0$ and $w_a$, new SNe Ia at redshifts $z\lesssim0.6$ near dark energy-matter equality would add the most constraining power. This is well within reach of the Vera C. Rubin Observatory and the Dark Energy Spectroscopic Instrument (DESI). Because cosmology measurements with SNe Ia quickly become systematics-limited, we focus on eliminating key systematics by using only a spectroscopically confirmed and volume-limited sample. In our proposed survey, SN alerts from Rubin would actively re-prioritize the scheduling of already-planned DESI tile visits. This would yield 7 500 near-peak transient spectra in one year without delaying DESI's primary survey. We forecast that if current best-fit $w_0-w_a$ values persist, combining just our volume-limited subset of 2 300 new SNe Ia at $z<0.3$ with current SN, BAO, and CMB data would push the tension with $Λ$CDM beyond $5σ$. This applies across a wide range of assumed uncertainties. To further circumvent systematics, we explore how DESI enables spectroscopic standardization via machine learning, offering a path toward a cosmology measurement independent of light-curve-based standardization. Finally, we discuss how early results from this program could inform future dark energy experiments.

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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

The Carousel Lens II: Cosmological Constraints with GIGA-Lens

The nature of dark matter and dark energy are among the central questions in cosmology. Strong gravitational lenses with multiple source planes provide a geometric probe of cosmology: the ratio of deflection angles at different redshifts depends only on angular-diameter distances, constraining the matter density $Ω_m$ and the dark energy equation of state $w$. However, constraints from this technique have historically lagged behind those from the CMB, SNe Ia, and BAO. In this work, we present new cosmological constraints from the Carousel Lens, a cluster-scale lens with more than 40 extended images from 11 spectroscopically confirmed sources. Its relaxed core and rich set of extended images behind the main halo make it particularly suitable for cosmological inference. Using the GIGA-Lens pipeline, we construct a pixel-level lens model including six HST-detected sources and four mass components. From this model, we obtain $w$CDM constraints of $Ω_m = 0.34^{+0.16}_{-0.13}$ and $w = -1.31^{+0.35}_{-0.32}$ from the Carousel Lens alone, accounting for both statistical and systematic uncertainties. We further project that including four additional known higher-redshift sources, assuming similar fractional uncertainties, could improve the constraining power by ~80%, bringing the precision close to that of the CMB and SNe Ia. For an evolving dark energy model ($w_0w_a$CDM), the Carousel Lens alone yields constraints comparable to the CMB, providing an independent and complementary probe alongside SN Ia and BAO. While currently systematic uncertainties dominate, which we quantify through simulations, our results demonstrate that relaxed multi-source-plane cluster lenses can deliver competitive cosmological constraints. Further improvements are expected from reductions in systematics and from incorporating higher-redshift sources (known and new) with high-resolution imaging.

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arXiv2026

Union3.1: Self-consistent Measurements of Host Galaxy Properties for 2000 Type Ia Supernovae

The determination of distances using time-series photometry of Type Ia supernovae (SNe Ia) relies on a ~5% empirical correction related to the properties of their host galaxies, e.g., global stellar mass. It is therefore crucial for unbiased cosmology inference that host galaxy properties be self-consistently determined across the full range of redshifts probed, which we undertake in this study for approximately 2000 SNe in the Union3 compilation (now Union3.1). We use aperture-matched, homogeneously-reduced, optical-infrared photometry from the DESI Legacy Imaging Surveys to derive global galaxy properties using the stellar population synthesis and SED-fitting code Prospector. We find that the host masses of $z<0.10$ SNe in Union3 were, on average, overestimated relative to the rest of the sample, while the opposite was true for $z<0.15$ SNe in Pantheon+. After correction, the two studies' average distance modulus estimated for low-redshift SNe, previously $>0.03$ mag discrepant, come into 0.01 mag agreement. We then update the UNITY SN analysis and find that the uncertainties on all standardization parameters shrink to 0.6-0.9x their previous sizes. For flat-$Λ$CDM, we find $Ω_m=0.344^{+0.026}_{-0.025}$, a -0.3$σ$ shift from Union3. We then combine with measurements of Baryon Acoustic Oscillations (BAO) and the Cosmic Microwave Background (CMB) exactly as done by DESI DR2 and find $w_0=-0.719\pm0.084$, $w_a=-0.95^{+0.29}_{-0.26}$, corresponding to 3.4$σ$ evidence against a cosmological constant (down from 3.8$σ$). We also update the DESI combined probe analysis using our correction to Pantheon+ and the recent DES-SN5YR Dovekie recalibration, finding $3.2σ$ (up from 2.8$σ$) and 3.4$σ$ (down from 4.2$σ$) evidence against a cosmological constant in the $w_0w_a$ plane, altogether marking a significantly improved consistency across SN analyses.

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arXiv2026

Banana Split: Improved Cosmological Constraints with Two Light-Curve-Shape and Color Populations Using Union3.1+UNITY1.8

SNe Ia have been used to provide key constraints on the equation-of-state parameter of dark energy. They are generally standardized under the assumption that they belong to a single population, with luminosities standardized in a continuous (roughly linear) fashion using the observed light-curve timescale. We update the Union3+UNITY1.5 SN cosmology analysis in light of increasing evidence for at least two core populations of SNe Ia and apply this "UNITY1.8" model to the updated "Union3.1" compilation (Hoyt et al. 2026). In addition to finding evidence for two different light-curve-shape (x1) distributions, we also find that the color distributions are different, that the light-curve-shape/magnitude standardization relations are different, and that these populations have different distributions across host-galaxy stellar mass and redshift. Importantly, we find that the residual host-mass luminosity step found in prior SN Ia cosmology analyses is now consistent with zero for unreddened SNe. We report a significantly tightened constraint on the split in the red-color standardization between SNe in low- and high-mass galaxies. We find that the estimated uncertainties shrink on cosmological parameters when fitting the same SNe assuming two modes versus one mode. We confirm similar trends in simulated data when running both versions of UNITY on the same (two-mode) simulations. For a flat LambdaCDM cosmology, we find Om = 0.334+0.025-0.024 from SNe alone; for a flat w0-wa cosmology, we find w0 = -0.760+0.084-0.082 and wa = -0.79+0.28-0.30 when including SNe, BAO, and CMB. In the 2D w0-wa plane, adding SNe to BAO and compressed CMB increases the tension with flat LambdaCDM from 2.1 sigma to 2.6 sigma.

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arXiv2026

Three-dimensional scene reconstruction using Roman slitless spectra

The Nancy Grace Roman Space Telescope will carry out a wide-field imaging and slitless spectroscopic survey of Type Ia Supernovae to improve our understanding of dark energy. Crucial to this endeavor is obtaining supernova spectra uncontaminated by light from their host galaxies. However, obtaining such spectra is made more difficult by the inherent problem in wide-field slitless spectroscopic surveys: the blending of spectra of close objects. The spectrum of a supernova will blend with the host galaxy, even from regions distant from the supernova on the sky. If not properly removed, this contamination will introduce systematic bias when the supernova spectra are later used to determine intrinsic supernova parameters and to infer the parameters of dark energy. To address this problem we developed an algorithm that makes use of the spectroscopic observations of the host galaxy at all available observatory roll angles to reconstruct a three-dimensional (3d; 2d spatial, 1d spectral) representation of the underlying host galaxy that accurately matches the 2d slitless spectrum of the host galaxy when projected to an arbitrary rotation angle. We call this ``scene reconstruction''. The projection of the reconstructed scene can be subtracted from an observation of a supernova to remove the contamination from the underlying host. Using simulated Roman data, we show that our method has extremely small systematic errors and significantly less random noise than if we subtracted a single perfectly aligned spectrum of the host obtained before or after the supernova was visible.

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arXiv2025

Cosmology Constraints from Type Ia Supernova Simulations of the Nancy Grace Roman Space Telescope Strategy Recommended by the High Latitude Time Domain Survey Definition Committee

Within the next few years, the upcoming Nancy Grace Roman Space Telescope will be gathering data for the High Latitude Time Domain Survey (HLTDS) that will be used to significantly improve the Type Ia supernova measurement of the dark energy equation of state parameters w0 and wa. Here we generate a catalog-level simulation of the in-guide strategy recommended by the HLTDS definition committee, and determine dark energy parameter constraints using a detailed analysis that includes light curve fitting, photometric redshifts and classification, BEAMS formalism, systematic uncertainties, and cosmology fitting. After analysis and selection requirements, the sample includes 10,000 Roman SNe Ia that we combine with 4,400 events from LSST. The resulting dark energy figure of merit is well above the NASA mission requirement of 326, with the caveat that SN Ia model training systematics have not been included.

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arXiv2025

Union Through UNITY: Cosmology with 2,000 SNe Using a Unified Bayesian Framework

Type Ia supernovae (SNe Ia) were instrumental in establishing the acceleration of the universe's expansion. By virtue of their combination of distance reach, precision, and prevalence, they continue to provide key cosmological constraints, complementing other cosmological probes. Individual SN surveys cover only over about a factor of two in redshift, so compilations of multiple SN datasets are strongly beneficial. We assemble an up-to-date "Union" compilation of 2087 cosmologically useful SNe Ia from 24 datasets ("Union3"). We take care to put all SNe on the same distance scale and update the light-curve fitting with SALT3 to use the full rest-frame optical. Over the next few years, the number of cosmologically useful SNe Ia will increase by more than a factor of ten, and keeping systematic uncertainties subdominant will be more challenging than ever. We discuss the importance of treating outliers, selection effects, light-curve shape and color populations and standardization relations, unexplained dispersion, and heterogeneous observations simultaneously. We present an updated Bayesian framework, called UNITY1.5 (Unified Nonlinear Inference for Type-Ia cosmologY), that incorporates significant improvements in our ability to model selection effects, standardization, and systematic uncertainties compared to earlier analyses. As an analysis byproduct, we also recover the posterior of the SN-only peculiar-velocity field, although we do not interpret it in this work. We compute updated cosmological constraints with Union3 and UNITY1.5, finding weak 1.7--2.6 sigma tension with LambdaCDM and possible evidence for thawing dark energy (w0 > -1, wa < 0). We release our SN distances, light-curve fits, and UNITY1.5 framework to the community.

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arXiv2025

Fishing for the Optimal Roman High Latitude Time Domain Survey: Cosmological Constraints for 1,000 Possible Surveys

The upcoming Nancy Grace Roman Space Telescope is set to conduct a generation-defining SN Ia cosmology measurement with its High Latitude Time Domain Survey (HLTDS). However, between optical elements, exposure times, cadences, and survey areas, there are many survey parameters to consider. This work was part of a Roman Project Infrastructure Team effort to help the Core Community Survey (CCS) Committee finalize the HLTDS recommendation to the Roman Observations Time Allocation Committee. We simulate 1,000 surveys, with and without a conservative (volume-limited) version of the Vera C. Rubin Observatory Deep Drilling Field SNe Ia, and compute Fisher-matrix-analysis Dark Energy Task Force Figures of Merit (FoM, based on w0-wa constraints) for each. We investigate which survey parameters correlate with FoM, as well as the dependence of the FoM values on calibration uncertainties and the SN dispersion model. The exact optimum depends on the assumed dispersion model and whether Rubin DDF SNe Ia are also considered, but ~20% time in prism, ~30--40% time in Wide imaging and the remainder in Deep imaging seems most promising. We also advocate for "interlaced" cadences where not every filter is used in every cadence step to reduce overheads while maintaining a good cadence and increasing the number of filters compared to the Rose et al. (2021) reference survey (the prism has proportionately lower overheads and can be used for each cadence step). We show simulated light curves and spectra for the baseline HLTDS CCS recommendation and release distance-modulus covariance matrices for all surveys to the community.

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arXiv2024

Picture Perfect: Photometric Transient Classification Using the ParSNIP Model with Roman Hourglass Simulations

The Roman Space Telescope, equipped with a 2.4 meter primary mirror and optical--NIR wide-field camera, promises to revolutionize our understanding of dark energy, exoplanets, and infrared astrophysics. One of the Roman Core Community Surveys is the High Latitude Time Domain Survey (HLTDS), which will measure more than 10,000 SN Ia light curves but obtain a fraction of this number with spectra. The remaining SNe will have to be photometrically classified to achieve the full potential of the Roman HLTDS. To investigate transient yields and classifications, Rose et al. (in prep.) updated the Photometric LSST Astronomical Time-series Classification Challenge (PLAsTiCC) framework (originally developed for the Vera Rubin Observatory) for the Roman HLTDS. This study leverages this Roman Hourglass dataset to train and evaluate the ParSNIP (Parameterized Supernova Identification Pipeline) model. We employ this model to classify various transient types from photometric data, paying particular attention to the types most represented in the dataset: normal SNe Ia, 91bg-like SNe Ia, SNe Iax, and CC SNe. The ParSNIP model performance is assessed through confusion matrices and ROC curves across different redshift ranges. Our analysis reveals that while the model performs robustly at higher redshifts (with the AUC for classification varying between 0.9 and 0.95 in the range 0.5 < z < 2), its accuracy dips at the lowest redshifts of the survey, likely due to limited training data. These findings underscore the importance of ensuring adequate representation of classes in the training set. This work underscores the value of machine learning models for next-generation surveys, paving the way for future studies with the Roman Space Telescope for survey optimization, cosmological forecasts, and synergies with other surveys.

astro-ph.IM↗
arXiv2024

Hawai'i Supernova Flows: A Peculiar Velocity Survey Using Over a Thousand Supernovae in the Near-Infrared

We introduce the Hawai'i Supernova Flows project and present summary statistics of the first 1,217 astronomical transients observed, 668 of which are spectroscopically classified Type Ia Supernovae (SNe Ia). Our project is designed to obtain systematics-limited distances to SNe Ia while consuming minimal dedicated observational resources. To date, we have performed almost 5,000 near-infrared (NIR) observations of astronomical transients and have obtained spectra for over 200 host galaxies lacking published spectroscopic redshifts. In this survey paper we describe the methodology used to select targets, collect/reduce data, calculate distances, and perform quality cuts. We compare our methods to those used in similar studies, finding general agreement or mild improvement. Our summary statistics include various parametrizations of dispersion in the Hubble diagrams produced using fits to several commonly used SN Ia models. We find the lowest dispersions using the \texttt{SNooPy} package's EBV\_model2, with a root mean square (RMS) deviation of 0.165 mag and a normalized median absolute deviation (NMAD) of 0.123 mag. The full utility of the Hawai'i Supernova Flows data set far exceeds the analyses presented in this paper. Our photometry will provide a valuable test bed for models of SN Ia incorporating NIR data. Differential cosmological studies comparing optical samples and combined optical and NIR samples will have increased leverage for constraining chromatic effects like dust extinction. We invite the community to explore our data by making the light curves, fits, and host galaxy redshifts publicly accessible.

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