arXiv subjects

Jillian Paulin

Publications and source records attributed to Jillian Paulin.

7 recordsLinked to original sources

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}.

astro-ph.CO↗

arXiv2026

Calibration-Induced Systematics in SALT3 Training and Their Impact on Dark Energy Constraints from Stage IV Supernova Surveys

In the coming years, the Vera Rubin Observatory's Legacy Survey of Space and Time (Rubin-LSST) and the Nancy Grace Roman Space Telescope's (Roman) High Latitude Time Domain Survey (HLTDS) are expected to discover more than a million Type Ia supernovae (SNe Ia), several orders of magnitude more than current samples and with a tighter control on systematic uncertainties. One of the largest systematic uncertainties in cosmological analyses with SNe Ia is the accuracy of the spectro-photometric model for SNe Ia time series data, which depends on the photometric calibration of the surveys. To quantify the impact of this uncertainty, we analyze simulated Rubin-LSST and HLTDS data, perturb the photometric zero-points and filter mean wavelengths, and propagate these systematics to spectral model recovery, estimated distances, and dark energy figure of merit (FoM) based on the $w_0 w_a$CDM model. Zero-point shifts of 5 mmag and filter mean wavelength shifts of 5 angstrom lead to a $\sim 50\%$ decrease in the FoM relative to a statistical-only case when calibration uncertainties are propagated only through light-curve fitting. The same calibration shifts applied only during model training produce a smaller $\sim 13\%$ degradation. Contrary to previous analyses, calibration uncertainties in light-curve fitting dominate over those from model training. Their effect during light-curve fitting varies smoothly with redshift and is nearly degenerate with cosmology, preventing mitigation through self-calibration. Finally, we show that the FoM dependence on the size of the calibration uncertainties (in the range of expected sizes) is roughly linear.

astro-ph.CO↗

arXiv2026

Supermassive Dark Stars and their remnants as a possible solution to three recent cosmic dawn puzzles

The James Webb Space Telescope (JWST) has begun to revolutionize our view of the Cosmos. The discovery of Blue Monsters (i.e., ultra-compact yet very bright high-z galaxies) and the Little Red Dots (i.e., very compact dustless strong Balmer break cosmic dawn sources) pose significant challenges to pre-JWST era models of the assembly of first stars and galaxies. In addition, JWST data further strengthen the problem posed by the origin of the supermassive black holes that power the most distant quasars observed. Stars powered by Dark Matter annihilation (i.e., Dark Stars) can form out of primordial gas clouds during the cosmic dawn era and subsequently might grow via accretion and become supermassive. In this paper we argue that Supermassive Dark Stars (SMDSs) offer natural solutions to the three puzzles mentioned above.

astro-ph.GA↗

arXiv2025

Spectroscopic Supermassive Dark Star candidates

Dark Stars, i.e. early stars composed almost entirely of hydrogen and helium but powered by Dark Matter, could form in zero metallicity clouds located close to the center of high redshift Dark Matter halos. In 2023 three of us identified (in a PNAS work) the first three photometric Dark Star candidates: JADES-GS-z11-0, JADES-GS-z12-0, and JADES-GS-z13-0. We report here our results of a followup analysis based on available NIRSpec JWST data. We find that JADES-GS-z11-0 and JADES-GS-z-13-0 are spectroscopically consistent with a Dark Star interpretation. Moreover, we find two additional spectroscopic Dark Star candidates: JADES-GS-z14-0 and JADES-GS-z-14-1, with the former being the most distant luminous object ever observed. We furthermore identify a feature in its spectrum indicative of the smoking gun signature of Dark Stars: the He II$λ$1640 absorption line. In view ALMA's recent identification of a probable OIII nebular emission line in the spectrum of JADES-GS-z14-0, the simple interpretation of this object as an isolated Dark Star is unlikely. If both spectral features survive follow-up observations it would imply a Dark Star embedded in a metal rich environment, requiring theoretical refinements of the formation of evolution of Dark Stars, which in previous studies were assumed to form in isolation, without any companions.

astro-ph.CO↗

arXiv2023

UHZ1 and the other three most distant quasars observed: possible evidence for Supermassive Dark Stars

The James Webb Space Telescope (JWST) has recently uncovered a new record-breaking quasar, UHZ1, at a redshift of $z\sim10$. This discovery continues JWST's trend of confronting the expectations from the standard $Λ$CDM model of cosmology with challenges. Namely, too many very massive galaxies and quasars have been observed at very high redshifts, when the universe was only a few hundred million years old. We have previously shown that Supermassive Dark Stars (SMDSs) may offer a solution to this puzzle. These fascinating objects would be the first stars in the universe, growing to be $\sim 10^5-10^7 M_{\odot}$ and shining as bright as $10^9$ suns. Unlike Population III stars (the major alternative proposed model for the first stars in the universe, which would also have zero metallicity and would be powered by nuclear fusion), SMDSs would be powered by dark matter heating (e.g. dark matter annihilation) and would be comparatively cooler. At the ends of their lives (when they run out of dark matter fuel), SMDSs would directly collapse into black holes, thus providing possible seeds for the first quasars. Previous papers have shown that to form at $z\sim10$, UHZ1 would require an incredibly massive seed ($\sim 10^4 -10^5 M_{\odot}$), which was assumed to be a Direct Collapse Black Hole (DCBH). In this paper, we demonstrate that Supermassive Dark Stars (SMDSs) offer an equally valid solution to the mystery of the first quasars, by examining the four most distant known quasars: UHZ1, J0313-1806, J1342+0928, and J1007+2115, with particular emphasis on UHZ1.

astro-ph.GA↗

arXiv2023

Supermassive Dark Star candidates seen by JWST?

The first generation of stars in the Universe is yet to be observed. There are two leading theories for those objects that mark the beginning of the cosmic dawn: hydrogen burning Population~III stars and Dark Stars, made of hydrogen and helium but powered by Dark Matter heating. The latter can grow to become supermassive ($M_\star\sim 10^6\Msun$) and extremely bright ($L\sim 10^9L_\odot$). We show that each of the following three objects: JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0 (at redshifts $z\in[11,14]$) are consistent with a Supermassive Dark Star interpretation, thus identifying, for the first time, Dark Star candidates.

astro-ph.CO↗

arXiv2022

Analytic Approximations for the Velocity Suppression of Dark Matter Capture

Compact astrophysical objects have been considered in the literature as dark matter (DM) probes, via the observational effects of annihilating captured DM. In this respect, Population III (Pop III) stars are particularly interesting candidates, since they form at high redshifts, in very high DM density environments. It is customary to assume such a star would form roughly at the center of a DM halo, and, as such, have no rotational velocity. In this paper, we break from this assumption and explore the effects we can expect to observe if a Pop III star forms at some distance away from the center of the halo and thus has a non-zero rotational velocity. The capture rate of DM in such a star is suppressed by a predictable amount. We develop and validate an analytical expression for the capture rate suppression factor and re-evaluate the bounds placed on the DM-nucleon cross section as a result of DM capture. We find that our previous results, obtained under the assumption of star formed within the central 10 AU of the DM mini-halo are essentially unchanged, even when considering the possible rotational velocities for those central stars.

astro-ph.CO↗