Pantheon+ Type Ia Supernova Catalog

• Pantheon+ is a homogenized public compilation containing 1701 light curves of 1550 spectroscopically confirmed Type Ia supernovae, designed to enhance cosmological parameter constraints.
• It integrates data from low-, intermediate-, and high-redshift surveys with meticulous cross-calibration and systematic corrections, notably expanding coverage at z < 0.01.
• The catalog provides complete light-curve products, calibration files, and metadata that enable rigorous inference of H0, dark energy, and other late-universe cosmological parameters.

Searching arXiv for the core Pantheon+ catalog papers and closely related analyses to ground the article in the primary literature. {"query":"Pantheon+ analysis full dataset light-curve release arXiv (Scolnic et al., 2021) redshifts peculiar velocities (Carr et al., 2021) Pantheon+ cosmology Brout 2022", "max_results": 10} {"query":"arXiv Pantheon+ Type Ia supernova catalog 1701 light curves 1550 spectroscopically confirmed SNe Ia", "max_results": 10} The Pantheon+ Type Ia supernova catalog is a homogenized public compilation of 1701 light curves of 1550 unique, spectroscopically confirmed SNe Ia assembled across 18 surveys and spanning $0.001 \le z \le 2.26$. It was constructed as the observational basis for the Pantheon+ cosmology analysis and the SH0ES distance-ladder program, and it extends the original Pantheon sample of 1048 SNe Ia by substantially increasing the low-redshift population, explicitly including objects with $z<0.01$, and releasing the photometry, SALT2 light-curve fits, calibration files, host-galaxy information, redshift products, and covariance ingredients needed for precision inference of $H_0$, $w$, and related late-time cosmological parameters (Scolnic et al., 2021, Carr et al., 2021).

1. Survey synthesis and sample definition

Pantheon+ was assembled from low-, intermediate-, and high-redshift SN Ia programs into a single cross-calibrated dataset. The release includes LOSS1, LOSS2, SOUSA, CSP, CfA1, CfA2, CfA3S+CfA3K, CfA4, LOWZ, CNIa0.02, Foundation, SDSS-II, PS1 Medium-Deep, SNLS, DES 3-year, and HST programs including HDFN, SCP, CANDELS+CLASH, and GOODS+PANS. Large components of the compilation include SDSS-II $(321/499)$, PS1 Medium-Deep $(269/370)$, DES $(203/251)$, Foundation $(179/228)$, and SNLS $(160/239)$, where the paired numbers denote cosmology-sample and full-sample counts. Relative to Pantheon, the largest gains are at very low and low redshift and at intermediate redshift, and those gains are central to the catalog’s later cosmological leverage (Scolnic et al., 2021).

A defining change with respect to Pantheon is the explicit inclusion of SNe with $z<0.01$. The release paper states that this was done so that SN systematic covariance could be included in a joint measurement of the Hubble constant and the dark-energy equation-of-state parameter without excluding the nearest calibrators. In later Pantheon+ analyses, the usable redshift interval is often quoted more precisely as $z<0.01$0, with the low-redshift expansion of the sample repeatedly identified as the principal source of the catalog’s enhanced constraining power (Wang, 2022).

The compilation is not merely a list of standardized distances. It is a survey-synthesis product in which duplicate observations, calibration transfer across photometric systems, peculiar-velocity corrections, host information, and survey-specific bias modeling were organized into a common statistical framework. The release also documents 151 SNe Ia observed by multiple surveys and 12 pairs or triplets of “SN siblings,” meaning distinct SNe in the same host galaxy, so that cross-survey consistency and covariance assignment can be treated explicitly rather than implicitly (Scolnic et al., 2021).

2. Public release, file structure, and observational content

Pantheon+ was released as a full light-curve dataset rather than only a derived Hubble diagram. The public products include photometric light curves for each SN, per-survey calibration definitions and offsets needed to place the data onto common systems, fitted SALT2 parameters and uncertainties, host properties, consolidated redshift and peculiar-velocity lists, and combined FITRES tables with fitted parameters and metadata before and after selection cuts. The main access point is https://pantheonplussh0es.github.io/, and the SNANA distribution contains a dedicated Pantheon+ directory with survey-level subfolders; the full download is linked through Zenodo in the release documentation (Scolnic et al., 2021).

The per-object metadata include right ascension and declination for the SN and host, Milky Way $z<0.01$1, heliocentric redshift, CMB-frame redshift, peculiar velocity and its uncertainty, and host-galaxy properties. Host stellar masses are provided for all SNe, while sSFR and morphology are given for $z<0.01$2, measured homogeneously with LePHARE SED fits to GALEX, SDSS, PS1, and 2MASS photometry. FITRES outputs include $z<0.01$3, $z<0.01$4, $z<0.01$5, $z<0.01$6, the corresponding uncertainties and covariances, peak date and uncertainty, fit $z<0.01$7, degrees of freedom, fit probability, signal-to-noise metrics, and host-SN angular separation (Scolnic et al., 2021).

The light-curve release was designed for direct reuse in external pipelines. For FITS delivery, metadata reside in HEAD.FITS and photometry in PHOT.FITS; text releases place metadata in the header and photometry in tabular columns. The photometric columns include MJD, filter, FLUXCAL, FLUXCALERR, magnitude, and magnitude error, with the FLUXCAL zero-point corresponding to $z<0.01$8 mag. The release therefore preserves the ingredients needed to refit light curves, inspect calibration choices, or reconstruct downstream likelihoods, rather than constraining users to a fixed cosmological data vector (Scolnic et al., 2021).

3. Light-curve standardization, calibration, and sample cuts

Pantheon+ uses SALT2, retrained on recalibrated multi-survey photometry, as its common light-curve model. In SALT2 notation, the spectral time-series model is approximately

$z<0.01$9

The fitted light-curve parameters are the amplitude $H_0$0, usually expressed as the rest-frame $H_0$1-band magnitude $H_0$2, the stretch parameter $H_0$3, and the color parameter $H_0$4. The Pantheon+ color law is close to a Cardelli–Clayton–Mathis dust law with $H_0$5, but it deviates below $H_0$6 Å (Rose et al., 2022).

Distance standardization follows a modified Tripp relation. In the release paper, the nominal form is

$H_0$7

while the conventional presentation

$H_0$8

remains useful for interpretation. Pantheon+ adopts nominal global coefficients $H_0$9 and $w$0, and incorporates the canonical host-mass step inside the simulation-based bias correction term $w$1 rather than treating it as a separate additive correction in the nominal analysis (Scolnic et al., 2021).

Cross-survey calibration is a central feature of the catalog. Pantheon+ introduced a survey-spanning recalibration tied to HST CALSPEC standards and retrained SALT2 on the recalibrated inputs. The release documentation highlights specific corrections relative to Pantheon, including SDSS data that had previously been treated as AB despite being in the natural system, and CfA3K/CfA3S data that had previously been treated as natural despite actually being in a standard system. These revisions altered some distance moduli at the few-hundredths-mag level and were one reason for publishing the full calibration definitions together with the data (Scolnic et al., 2021).

The main cosmology sample was defined through explicit quality cuts. These include $w$2, $w$3, $w$4, $w$5 days, at least one observation within $w$6 days after peak, and Milky Way $w$7. Pantheon+ also excludes SNLS and DES SNe at $w$8 in the cosmology sample because of sensitivity to the rest-frame $w$9 band in SALT2 training that cannot be fully cross-calibrated; 59 SNe are removed by this cut. After the full selection sequence, including valid bias-correction region requirements and the condition that light curves pass all 40 systematic perturbations, 1701 light curves remain, of which 151 are duplicates across surveys (Scolnic et al., 2021).

The conservative color cut $(321/499)$0 defines the main cosmological sample but does not exhaust the information in the release. A later Pantheon+ dust analysis reinstated 57 SNe Ia with $(321/499)$1, including objects up to $(321/499)$2, and found that the change in the color-luminosity coefficient above the $(321/499)$3 threshold was consistent with zero, with $(321/499)$4 at $(321/499)$5. That study also argued that line-of-sight $(321/499)$6 is not a single value but forms a distribution, which has direct implications for how Pantheon+ color systematics are interpreted (Rose et al., 2022).

4. Redshift definitions and peculiar-velocity corrections

Pantheon+ distinguishes three redshift conventions. The heliocentric redshift $(321/499)$7 is the observed-frame redshift. The CMB-frame redshift $(321/499)$8 corrects $(321/499)$9 for Solar-system motion relative to the CMB dipole. The Hubble-diagram redshift $(269/370)$0 is the cosmology redshift after removing the host galaxy’s peculiar velocity. The redshift-improvement paper stresses that these transformations must be treated multiplicatively rather than with low-$(269/370)$1 additive approximations (Carr et al., 2021).

Using the Planck 2018 dipole, with $(269/370)$2 km s$(269/370)$3 toward $(269/370)$4, Pantheon+ adopts the exact special-relativistic relation

$(269/370)$5

where $(269/370)$6 and $(269/370)$7 is the angle between the dipole direction and the SN line of sight. The cosmology redshift is then obtained through

$(269/370)$8

with $(269/370)$9 derived from the host peculiar velocity using the relativistic one-dimensional Doppler formula (Carr et al., 2021).

The peculiar-velocity field is based on 2M++ and Carrick et al. reconstruction, evaluated in redshift space, with the calibrated form

$(203/251)$0

and the Pantheon+ redshift paper adopts the updated value $(203/251)$1. The reconstruction volume extends to $(203/251)$2, and beyond that radius the catalog uses a decaying bulk-flow term consistent with $(203/251)$3CDM expectations rather than setting peculiar velocities to zero. The release also standardizes the sign convention so that $(203/251)$4 denotes motion away from the observer (Carr et al., 2021).

The scale of the redshift cleanup was substantial. The redshift-audit paper reports 5 cases of missing or incorrect heliocentric corrections, 44 incorrect or missing supernova coordinates, 230 missing heliocentric or CMB-frame redshifts, and 1200 missing redshift uncertainties; 990 unique heliocentric redshifts were updated. The reported absolute corrections span $(203/251)$5 with $(203/251)$6. Despite that extensive bookkeeping revision, the paper reports that the cosmological impact was much smaller than the then-current uncertainties in $(203/251)$7 and $(203/251)$8, which is one indication that Pantheon+’s primary role is not only to increase sample size but also to regularize redshift conventions and uncertainty propagation across heterogeneous surveys (Carr et al., 2021).

5. The catalog as a cosmological likelihood

Pantheon+ distances are routinely analyzed through the distance-modulus relation

$(203/251)$9

with flat-$(179/228)$0CDM background evolution commonly written as

$(179/228)$1

When SN distances are used without an external absolute calibration, the observable is effectively $(179/228)$2, so $(179/228)$3 and the absolute magnitude $(179/228)$4 are fully degenerate and only relative distances are constrained. Pantheon+ analyses therefore separate uncalibrated SN-only inference from Cepheid-anchored analyses that fix the absolute scale through SH0ES (Wang, 2022).

Tomographic analyses have made the catalog’s internal leverage especially explicit. In equal-redshift binning, the first interval, $(179/228)$5, contains 1021 SNe Ia and dominates the constraining power of the whole sample. Using Pantheon+ without SH0ES calibration, one analysis reports $(179/228)$6 for the full sample and only a $(179/228)$7 lower bound on $(179/228)$8; with SH0ES calibration, the same study finds $(179/228)$9 and $(160/239)$0. Across both equal-redshift and equal-count tomographic schemes, that work reports no obvious evidence for evolution of $(160/239)$1 or $(160/239)$2 at the $(160/239)$3 confidence level. In a broader multiprobe $(160/239)$4CDM fit combining Pantheon+ with Planck 2018 CMB, BAO, cosmic chronometers, DES Y1 two-point functions, and related data, the strongest quoted constraint is $(160/239)$5 km s$(160/239)$6 Mpc$(160/239)$7 without SH0ES calibration and $(160/239)$8 km s$(160/239)$9 Mpc$z<0.01$0 when the Cepheid anchor is included (Wang, 2022).

Pantheon+ has also been used as a relative-distance component in joint late-universe analyses with absolute probes. In a gravitational-wave standard-siren study, a subset of 1590 SNe Ia was used after removing all data with $z<0.01$1 to reduce sensitivity to peculiar velocities. There the SN likelihood constrains shape parameters while GW sirens provide the absolute scale, and the joint dataset yields approximately $z<0.01$2 precision on $z<0.01$3, approximately $z<0.01$4 on $z<0.01$5, and approximately $z<0.01$6 on $z<0.01$7 in the flat $z<0.01$8CDM extension (Zheng et al., 2024).

Methodologically, Pantheon+ has become a benchmark dataset for model-independent compression and reconstruction. A recent compression study showed that the Pantheon+ distance-redshift relation can be represented by eleven Gaussian-distributed $z<0.01$9 values with full covariance, reproducing the corresponding full distance-modulus analyses within the statistical sampling noise of the chains. For flat $z<0.01$00CDM with Pantheon+ alone, the compressed analysis gives $z<0.01$01 versus $z<0.01$02 from the full $z<0.01$03 likelihood, and the same work argues that the compressed 11-dimensional likelihood is operationally lossless for downstream inference in flat $z<0.01$04CDM, flat $z<0.01$05CDM, and non-parametric $z<0.01$06 reconstructions (Wang et al., 18 May 2026).

A complementary line of work uses Pantheon+ to interrogate dark-energy reconstruction rather than only parametric fits. In combinations with DESI DR2 BAO and Planck distance priors, one study reports a Pantheon+ SN-only flat-$z<0.01$07CDM preference of $z<0.01$08, reduced to $z<0.01$09 after flux averaging, and finds a localized non-parametric deviation in the reconstructed dark-energy density ratio $z<0.01$10 at $z<0.01$11, where Pantheon+ gives $z<0.01$12 without flux averaging and $z<0.01$13 with flux averaging. The authors argue that this pattern correlates with Pantheon+’s higher $z<0.01$14 preference relative to DESI DR2 BAO and may reflect the projection of inter-probe $z<0.01$15 differences into $z<0.01$16 rather than unambiguous evidence for dynamical dark energy (Wang et al., 13 Apr 2026).

6. Internal consistency tests, systematics debates, and contested interpretations

Pantheon+ is frequently described as a standard-candle dataset, but several analyses emphasize that it is more precisely a standardized-distance dataset whose interpretation depends on calibration, dust modeling, and population stability. A Gaussian-process study using cosmic-chronometer reconstructions of $z<0.01$17 as a model-independent baseline found that Pantheon+ SNe Ia are consistent with being standard candles within $z<0.01$18 globally, while also reporting a localized departure near $z<0.01$19 at the level of a few hundredths of a magnitude. The same work notes that because the released Pantheon+ distances treat $z<0.01$20, $z<0.01$21, and $z<0.01$22 as redshift-independent, any true evolution in these relations could imprint as $z<0.01$23 (Rana, 23 Sep 2025).

Directional analyses have produced one of the clearest examples of how the same catalog can support seemingly contradictory claims. A local-universe study restricted to 501 Pantheon+ SNe in $z<0.01$24 reports a statistically significant dipole variation of $z<0.01$25 at more than $z<0.01$26 confidence, with dipole direction $z<0.01$27, bulk-flow speed $z<0.01$28 km s$z<0.01$29 at an effective distance $z<0.01$30 Mpc, and a model-independent local $z<0.01$31 km s$z<0.01$32 Mpc$z<0.01$33 at $z<0.01$34 (Lopes et al., 2024). By contrast, a later anisotropy study using Pantheon+ over the broader sky and simulating 2000 directions concludes that present SN Ia samples cannot robustly determine the direction of an anisotropy of $z<0.01$35, attributing the instability to the intrinsic $z<0.01$36–$z<0.01$37 degeneracy of SN light-curve distances, intrinsic scatter $z<0.01$38 mag, total per-object $z<0.01$39 scatter of approximately $z<0.01$40–$z<0.01$41 km s$z<0.01$42 Mpc$z<0.01$43, and highly nonuniform sky coverage (Quintana-Estellés et al., 18 May 2026). These studies use different redshift ranges and inferential targets, so the apparent tension is methodological as well as physical.

Pantheon+ has also been drawn into broader model-selection debates. One study uses the catalog to compare flat $z<0.01$44CDM against the $z<0.01$45 universe and reports BIC values of $z<0.01$46 and $z<0.01$47, respectively favoring $z<0.01$48 at about $z<0.01$49 versus $z<0.01$50 under that paper’s assumptions. The same paper explicitly notes, however, that $z<0.01$51 is not the consensus cosmological standard model and that its physical underpinnings and consistency with all cosmological probes are actively debated (Chandak et al., 5 Feb 2026). The significance of such results therefore lies less in redefining the catalog than in showing that Pantheon+ is now sufficiently precise to serve as a discriminant in nonstandard model tests.

Taken together, these studies indicate that Pantheon+ is both a mature cosmological resource and an object lesson in how precision SN cosmology depends on the coupling between calibration, covariance, redshift treatment, dust, and model assumptions. Its enlarged low-$z<0.01$52 sample, public light-curve release, and covariance-aware construction make it unusually reusable; its continuing role in debates over luminosity evolution, anisotropy, dark-energy reconstruction, and model selection shows that the catalog is not only a data release but also a platform for stress-testing the methodology of late-universe cosmology (Scolnic et al., 2021, Rana, 23 Sep 2025, Quintana-Estellés et al., 18 May 2026).