Kavli Institute for Particle Astrophysics and Cosmology

Toy M., Wiseman P., Sullivan M., Scolnic D., Vincenzi M., Brout D., Davis T.M., Frohmaier C., Galbany L., Lidman C., Lee J., Kelsey L., Kessler R., Möller A., Popovic B., et. al.

ABSTRACT Using 1533 type Ia supernovae (SNe Ia) from the 5-yr sample of the Dark Energy Survey (DES), we investigate the relationship between the projected galactocentric separation of the SNe and their host galaxies and their light curves and standardization. We show, for the first time, that the difference in SN Ia post-standardization brightnesses between high- and low-mass hosts reduces from $0.078\pm 0.011$ mag in the full sample to $0.036 \pm 0.018$ mag for SNe Ia located in the outer regions of their host galaxies, while increasing to $0.100 \pm 0.014$ mag for SNe in the inner regions. The difference in the size of the mass step between inner and outer regions is $0.064\pm 0.023$ mag. In these inner regions, the step can be reduced (but not removed) using a model where the $R_V$ of dust along the line of sight to the SN changes as a function of galaxy properties. We investigate the remaining difference using the distributions of the SN Ia stretch parameter to test the inferred age of SN progenitors. Comparing red (older) environments only, outer regions have a higher proportion of high-stretch SNe and a more homogeneous stretch distribution. However, this effect cannot explain the reduction in significance of any Hubble residual step in outer regions. We conclude that the standardized distances of SNe Ia located in the outer regions of galaxies are less affected by their global host galaxy properties than those in the inner regions.

Shah P., Davis T.M., Vincenzi M., Armstrong P., Brout D., Camilleri R., Galbany L., Gill M.S., Huterer D., Jeffrey N., Lahav O., Lee J., Lidman C., Möller A., Sullivan M., et. al.

ABSTRACT The weak gravitational lensing magnification of Type Ia supernovae (SNe Ia) is sensitive to the matter power spectrum on scales $k\gt 1 h$ Mpc$^{-1}$, making it unwise to interpret SNe Ia lensing in terms of power on linear scales. We compute the probability density function of SNe Ia magnification as a function of standard cosmological parameters, plus an empirical parameter $A_{\rm mod}$ which describes the suppression or enhancement of matter power on non-linear scales compared to a cold dark matter only model. While baryons are expected to enhance power on the scales relevant to SN Ia lensing, other physics such as neutrino masses or non-standard dark matter may suppress power. Using the Dark Energy Survey Year-5 sample, we find $A_{\rm mod} = 0.77^{+0.69}_{-0.40}$ (68 per cent credible interval around the median). Although the median is consistent with unity there are hints of power suppression, with $A_{\rm mod} \lt 1.09$ at 68 per cent credibility.

Golden-Marx J.B., Zhang Y., Ogando R.L., Yanny B., Pereira M.E., Hilton M., Aguena M., Allam S., Andrade-Oliveira F., Bacon D., Brooks D., Rosell A.C., Carretero J., Cheng T., da Costa L.N., et. al.

Abstract Using a sample of 2800 galaxy clusters identified in the Dark Energy Survey across the redshift range 0.20 < z < 0.60, we characterize the hierarchical assembly of Bright Central Galaxies (BCGs) and the surrounding intracluster light (ICL). To quantify hierarchical formation we use the stellar mass - halo mass (SMHM) relation, comparing the halo mass, estimated via the mass-richness relation, to the stellar mass within the BCG+ICL system. Moreover, we incorporate the magnitude gap (M14), the difference in brightness between the BCG (measured within 30 kpc) and 4th brightest cluster member galaxy within 0.5 R200, c, as a third parameter in this linear relation. The inclusion of M14, which traces BCG hierarchical growth, increases the slope and decreases the intrinsic scatter, highlighting that it is a latent variable within the BCG+ICL SMHM relation. Moreover, the correlation with M14 decreases at large radii. However, the stellar light within the BCG+ICL transition region (30 kpc - 80 kpc) most strongly correlates with halo mass and has a statistically significant correlation with M14. Since the transition region and M14 are independent measurements, the transition region may grow due to the BCG’s hierarchical formation. Additionally, as M14 and ICL result from hierarchical growth, we use a stacked sample and find that clusters with large M14 values are characterized by larger ICL and BCG+ICL fractions, which illustrates that the merger processes that build the BCG stellar mass also grow the ICL. Furthermore, this may suggest that M14 combined with the ICL fraction can identify dynamically relaxed clusters.

Gupta S., Sridhar N., Sironi L.

ABSTRACT Magnetic reconnection in relativistic plasmas – where the magnetization $\sigma \gg 1$ – is regarded as an efficient particle accelerator, capable of explaining the most dramatic astrophysical flares. We employ two-dimensional (2D) particle-in-cell simulations of relativistic pair-plasma reconnection with vanishing guide field and outflow boundaries to quantify the impact of the energy gain occurring in regions of electric dominance ($E\gt B$) for the early stages of particle acceleration (i.e. the ‘injection’ stage). Given an injection threshold energy $\epsilon ^\ast =\sigma /4$ for the particles that eventually attain energy $\epsilon _{\rm T}$ by time T, we calculate the mean fractional contribution $\zeta (\epsilon ^\ast ,\epsilon _{\rm T})$ by $E\gt B$ fields to particle energization at the time when the threshold $\epsilon ^\ast$ is reached. We find that $\zeta$ monotonically increases with $\sigma$ and $\epsilon _{\rm T}$; for $\sigma \gtrsim 50$ and $\epsilon _{\rm T}/\sigma \gtrsim 8$, we find that $\gtrsim 80~{{\ \rm per\ cent}}$ of the energy gain obtained before reaching $\epsilon ^\ast =\sigma /4$ occurs in $E\gt B$ regions. We find that $\zeta$ is independent of simulation box size $L_x$, as long as $\epsilon _{\rm T}$ is normalized to the maximum particle energy, which scales as $\epsilon _{\rm max}\propto L_{\rm x}^{1/2}$ in 2D. The distribution of energy gains $\epsilon _{\chi }$ acquired in $E\gt B$ regions can be modelled as $\mathrm{ d}N/\mathrm{ d}\epsilon _{\chi }\propto \epsilon _{\chi }^{-0.35}\exp [-(\epsilon _{\chi }/0.06\, \sigma)^{0.5}]$. Our results help assess the role of electric dominance in relativistic reconnection with vanishing guide fields, which is realized in the magnetospheres of black holes and neutron stars.

Dixon M., Mould J., Lidman C., Taylor E.N., Flynn C., Duffy A.R., Galbany L., Scolnic D., Davis T.M., Möller A., Kelsey L., Lee J., Wiseman P., Vincenzi M., Shah P., et. al.

ABSTRACT The present state of cosmology is facing a crisis where there is a fundamental disagreement in measurements of the Hubble constant ($H_{0}$), with significant tension between the early and late Universe methods. Type Ia supernovae (SNe Ia) are important to measuring $H_{0}$ through the astronomical distance ladder. However, there remains potential to better standardize SN Ia light curves by using known dependencies on host galaxy properties after the standard light curve width and colour corrections have been applied to the peak SN Ia luminosities. To explore this, we use the 5-yr photometrically identified SNe Ia sample obtained by the Dark Energy Survey, along with host galaxy spectra obtained by the Australian Dark Energy Survey. Using host galaxy spectroscopy, we find a significant trend with the equivalent width (EW) of the [O ii] $\lambda \lambda$ 3727, 29 doublet, a proxy for specific star formation rate, and Hubble residuals. We find that the correlation with [O ii] EW is a powerful alternative to the commonly used mass step after initial light-curve corrections. Applying this [O ii] EW correction to 20 SNe Ia in calibrator galaxies observed with WiFeS, we examined the impact on SN Ia absolute magnitudes and $H_{0}$. Our [O ii] EW corrections result in $H_{0}$ values ranging between 73.04 and 73.51 $\mathrm{km \, s^{-1} \, Mpc^{-1}}$, with a combined statistical and systematic uncertainty of $\sim 1.31 \, \mathrm{km \, s^{-1} \, Mpc^{-1}}$. However, even with this additional correction, the impact of host galaxy properties in standardizing SNe Ia appears limited in reducing the current tension ($\sim 5\sigma$) with the cosmic microwave background result for $H_{0}$.

Beheshti A., Schaan E., Kosowsky A.

Reefe M., McDonald M., Chatzikos M., Seebeck J., Mushotzky R., Veilleux S., Allen S.W., Bayliss M., Calzadilla M., Canning R., Floyd B., Gaspari M., Hlavacek-Larrondo J., McNamara B., Russell H., et. al.

In the centres of many galaxy clusters, the hot (approximately 107 kelvin) intracluster medium can become dense enough that it should cool on short timescales1,2. However, the low measured star formation rates in massive central galaxies3–6 and the absence of soft X-ray lines from the cooling gas7–9 suggest that most of this gas never cools. This is known as the cooling flow problem. The latest observations suggest that black hole jets are maintaining the vast majority of gas at high temperatures10–16. A cooling flow has yet to be fully mapped through all the gas phases in any galaxy cluster. Here we present observations of the Phoenix cluster17 using the James Webb Space Telescope to map the [Ne vi] λ 7.652-μm emission line, enabling us to probe the gas at 105.5 kelvin on large scales. These data show extended [Ne vi] emission that is cospatial with the cooling peak in the intracluster medium, the coolest gas phases and the sites of active star formation. Taken together, these imply a recent episode of rapid cooling, causing a short-lived spike in the cooling rate, which we estimate to be 5,000–23,000 solar masses per year. These data provide a large-scale map of gas at temperatures between 105 kelvin and 106 kelvin in a cluster core, and highlight the critical role that black hole feedback has in not only regulating cooling but also promoting it18. Observations of the Phoenix cluster using the James Webb Space Telescope reveal rapid cooling in galaxy cluster cores, driven by black hole jets, with gas temperatures mapped between 105 K and 106 K and cooling rates of 5,000–23,000 M⊙ yr−1.

Camilleri R., Davis T.M., Hinton S.R., Armstrong P., Brout D., Galbany L., Glazebrook K., Lee J., Lidman C., Möller A., Nichol R.C., Sako M., Scolnic D., Shah P., Smith M., et. al.

ABSTRACT We measure the current expansion rate of the Universe, Hubble’s constant $H_0$, by calibrating the absolute magnitudes of supernovae to distances measured by baryon acoustic oscillations (BAO). This ‘inverse distance ladder’ technique provides an alternative to calibrating supernovae using nearby absolute distance measurements, replacing the calibration with a high-redshift anchor. We use the recent release of 1829 supernovae from the Dark Energy Survey spanning $0.01\lt z\lt 1.13$ anchored to the recent baryon acoustic oscillation measurements from Dark Energy Spectroscopic Instrument (DESI) spanning $0.30 \lt z_{\mathrm{eff}}\lt 2.33$. To trace cosmology to $z=0$, we use the third-, fourth-, and fifth-order cosmographic models, which, by design, are agnostic about the energy content and expansion history of the universe. With the inclusion of the higher redshift DESI-BAO data, the third-order model is a poor fit to both data sets, with the fourth-order model being preferred by the Akaike Information Criterion. Using the fourth-order cosmographic model, we find $H_0=67.19^{+0.66}_{-0.64}\mathrm{~km} \mathrm{~s}^{-1} \mathrm{~Mpc}^{-1}$, in agreement with the value found by Planck without the need to assume Flat-$\Lambda$CDM. However, the best-fitting expansion history differs from that of Planck, providing continued motivation to investigate these tensions.

Turner C., Tacchella S., D’Eugenio F., Carniani S., Curti M., Glazebrook K., Johnson B.D., Lim S., Looser T., Maiolino R., Nanayakkara T., Wan J.

ABSTRACT We present a detailed analysis of JWST/NIRSpec and NIRCam observations of ZF-UDS-7329, a massive, quiescent galaxy at redshift $z=3.2$, which has been put forward to challenge cosmology and galaxy formation physics. We study on the impact of different star formation history (SFH) priors, stellar libraries, metallicity, and initial mass function assumptions. Our results show that ZF-UDS-7329, with a formed stellar mass of $M_{\star } \approx 10^{11.4}~{\rm M}_\odot $ (surviving mass $M_{\star \mathrm{,surv}} \approx 10^{11.2}~{\rm M}_\odot $) and a specific star formation rate of $\mathrm{sSFR} \approx 0.03~{\rm Gyr} ^{-1}$, formed efficiently in the first billion years of the Universe. In agreement with previous work, we find that the spectrum is consistent with mass-weighted stellar ages of $1.3{\!-\!}1.8$ Gyr, depending on the SFH prior used. A physically motivated rising SFH prior makes the formation history of ZF-UDS-7329 compatible with stellar mass and star formation rate estimates of $z\gt 6$ galaxies. Using NIRCam imaging, we identify a colour gradient indicative of an old, quiescent bulge and a younger disc component, as expected from a complex formation history. The inferred SFH is consistent a high stellar fraction of $f_{\star }=M_{\star }/(f_b \cdot M_{\rm h}) \approx 100{{\ \rm per\ cent}}$ at $z=7{\!-\!}12$, implying an extremely high integrated star formation efficiency. However, when considering cosmic variance and possible mergers as expected in overdense environments – as traced by ZF-UDS-7329 – the stellar fractions could be reduced to $f_{\star } \approx 50{{\ \rm per\ cent}}$, which is more consistent with galaxy formation models and the stellar-to-halo mass relation at lower redshifts. We conclude that ZF-UDS-7329 forms extremely efficient in the early universe, but does not necessitate unseen galaxies at higher redshifts since the inferred SFR of ancestors are consistent with those seen in $z\gt 6$ galaxies.

Ma H., Takeuchi T.T., Cooray S., Zhu Y.

ABSTRACT A direct approach to studying the galaxy–halo connection is to analyse groups and clusters of galaxies that trace the underlying dark matter haloes, emphasizing the importance of identifying galaxy clusters and their associated brightest cluster galaxies (BCGs). In this work, we test and propose a robust density-based clustering algorithm that outperforms the traditional Friends-of-Friends (FoF) algorithm in the currently available galaxy group/cluster catalogues. Our new approach is a modified version of the Ordering Points To Identify the Clustering Structure (OPTICS) algorithm, which accounts for line-of-sight positional uncertainties due to redshift space distortions by incorporating a scaling factor, and is thereby referred to as sOPTICS. When tested on both a galaxy group catalogue based on semi-analytic galaxy formation simulations and observational data, our algorithm demonstrated robustness to outliers and relative insensitivity to hyperparameter choices. In total, we compared the results of eight clustering algorithms. The proposed density-based clustering method, sOPTICS, outperforms FoF in accurately identifying giant galaxy clusters and their associated BCGs in various environments with higher purity and recovery rate, also successfully recovering 115 BCGs out of 118 reliable BCGs from a large galaxy sample. Furthermore, when applied to an independent observational catalogue without extensive re-tuning, sOPTICS maintains high recovery efficiency, confirming its flexibility and effectiveness for large-scale astronomical surveys.

Albakry M. ., Alkhatib I., Alonso-González D., Amaral D. ., Anczarski J., Aralis T., Aramaki T., Arnquist I. ., Ataee Langroudy I., Azadbakht E., Bathurst C., Bhattacharyya R., Biffl A. ., Brink P. ., Buchanan M., et. al.

This article presents constraints on dark-matter-electron interactions obtained from the first underground data-taking campaign with multiple SuperCDMS HVeV detectors operated in the same housing. An exposure of 7.63  g−days is used to set upper limits on the dark-matter-electron scattering cross section for dark matter masses between 0.5 and 1000  MeV/c2, as well as upper limits on dark photon kinetic mixing and axionlike particle axioelectric coupling for masses between 1.2 and 23.3  eV/c2. Compared to an earlier HVeV search, sensitivity was improved as a result of an increased overburden of 225 meters of water equivalent, an anticoincidence event selection, and better pile-up rejection. In the case of dark-matter-electron scattering via a heavy mediator, an improvement by up to a factor of 25 in cross section sensitivity was achieved. Published by the American Physical Society 2025

Qu F.J., Millea M., Schaan E.

Future low-noise cosmic microwave background (CMB) lensing measurements from e.g., CMB-S4 will be polarization dominated, rather than temperature dominated. In this new regime, statistically optimal lensing reconstructions outperform the standard quadratic estimator, but their sensitivity to extragalactic polarized foregrounds has not been quantified. Using realistic simulations of polarized radio and infrared point sources, we show for the first time that optimal Bayesian lensing from a CMB-S4-like experiment is insensitive to the expected level of polarized extragalactic foregrounds after masking, as long as an accurate foreground power spectrum is included in the analysis. For more futuristic experiments where these foregrounds could cause a detectable bias, we propose a new method to jointly fit for lensing and the Poisson foregrounds, generalizing the bias hardening from the standard quadratic estimator to Bayesian lensing. Published by the American Physical Society 2025

Dome T., Martin-Alvarez S., Tacchella S., Yuan Y., Sijacki D.

Abstract We study star formation variability, or burstiness, as a method to constrain and compare different galaxy formation models at high redshift using the Azahar simulation suite. The models range from magneto-hydrodynamics with turbulence-driven star formation to more sophisticated setups incorporating radiative transfer and cosmic ray physics. Analysing a sample of galaxies at redshifts z = 4 − 10, we find that including both radiative transfer and cosmic rays results in more regular star formation periodicity, as revealed by the Lomb-Scargle periodogram. While both radiative transfer and cosmic rays amplify star formation stochasticity, their combination leads to the largest scatter in burst intensity and the most pronounced deviations from the star-forming main sequence. To compare this comprehensive model against observations, we generate a mock spectrum of a low-mass galaxy during a mini-quenching event at z = 7.5. The resulting spectrum aligns well with the low-mass quiescent galaxy JADES-GS-z7-01-QU observed at z = 7.3, though discrepancies attributed to stellar metallicity suggest it may have a composite nature. Our findings highlight the importance of including complex physical processes like cosmic rays and radiative transfer in simulations to accurately capture the bursty nature of star formation in early galaxy formation. Future JWST observations, particularly of the scatter around the star-forming main sequence, might provide critical constraints for numerical models of galaxy formation at high redshift.

Guy J., Gontcho S.G., Armengaud E., Brodzeller A., Cuceu A., Font-Ribera A., Herrera-Alcantar H.K., Karaçaylı N.G., Muñoz-Gutiérrez A., Pieri M.M., Pérez-Ràfols I., Ramírez-Pérez C., Ravoux C., Rich J., Walther M., et. al.

Abstract Baryon Acoustic Oscillations can be measured with sub-percent precision above redshift two with the Lyman-α (Lyα) forest auto-correlation and its cross-correlation with quasar positions. This is one of the key goals of the Dark Energy Spectroscopic Instrument (DESI) which started its main survey in May 2021. We present in this paper a study of the contaminants to the Lyα forest which are mainly caused by correlated signals introduced by the spectroscopic data processing pipeline as well as astrophysical contaminants due to foreground absorption in the intergalactic medium. Notably, an excess signal caused by the sky background subtraction noise is present in the Lyα auto-correlation in the first line-of-sight separation bin. We use synthetic data to isolate this contribution, we also characterize the effect of spectro-photometric calibration noise, and propose a simple model to account for both effects in the analysis of the Lyα forest. We then measure the auto-correlation of the quasar flux transmission fraction of low redshift quasars, where there is no Lyα forest absorption but only its contaminants. We demonstrate that we can interpret the data with a two-component model: data processing noise and triply ionized Silicon and Carbon auto-correlations. This result can be used to improve the modeling of the Lyα auto-correlation function measured with DESI.

Kong H., Ross A.J., Honscheid K., Lang D., Porredon A., de Mattia A., Rezaie M., Zhou R., Schlafly E.F., Moustakas J., Rosado-Marin A., Aguilar J., Ahlen S., Brooks D., Chaussidon E., et. al.

Abstract We use the forward modeling pipeline, Obiwan, to study the imaging systematics of the Luminous Red Galaxies (LRGs) targeted by the Dark Energy Spectroscopic Instrument (DESI). Imaging systematics refers to the false fluctuation of galaxy densities due to varying observing conditions and astrophysical foregrounds corresponding to the imaging surveys from which DESI LRG target galaxies are selected. We update the Obiwan pipeline, which we previously developed to simulate the optical images used to target DESI data, to further simulate WISE images in the infrared. This addition allows simulating the DESI LRGs sample, which utilizes WISE data in the target selection. Deep DESI imaging data combined with a method to account for biases in their shapes is used to define a truth sample of potential LRG targets. We inject these data evenly throughout the DESI Legacy Imaging Survey footprint at declinations between -30 and 32.375 degrees. We simulate a total of 15 million galaxies to obtain a simulated LRG sample (Obiwan LRGs) that predicts the variations in target density due to imaging properties. We find that the simulations predict the trends with depth observed in the data, including how they depend on the intrinsic brightness of the galaxies. We observe that faint LRGs are the main contributing source of the imaging systematics trend induced by depth. We also find significant trends in the data against Galactic extinction that are not predicted by Obiwan. These trends depend strongly on the particular map of Galactic extinction chosen to test against, implying systematic contamination in the Galactic extinction maps is a likely root cause (e.g., Cosmic-Infrared Background, dust temperature correction). We additionally observe a morphological change of the DESI LRGs population evidenced by a correlation between OII emission line average intensity and the size of the z-band PSF. This effect most likely results from uncertainties in background subtraction. The detailed findings we present should be used to guide any observational systematics mitigation treatment for the clustering of the DESI LRGs sample.