arXiv subjects

Sarah Libanore

Publications and source records attributed to Sarah Libanore.

At least 19 recordsLinked to original sources

arXiv2026

Breaking binary formation mechanism degeneracies with gravitational wave clustering

Thanks to the almost 400 gravitational wave events detected, we are currently able to grasp the fundamental features of black hole mass, spin, and distance distributions. However, such a fast increase in the precision of the measurements does not necessarily correspond to a better theoretical understanding of gravitational wave sources, especially in current scenarios where the number of free parameters is significantly larger than the number of inferred properties of the black hole population. In this work, we showcase how the landscape of theoretical models can be chipped away by complementary data-analysis strategies, in particular by studying the statistical properties of gravitational wave anisotropic distribution. Specifically, we show how gravitational wave clustering is sensitive to two unique features of each binary formation mechanism: the time-delay distribution and the properties of the binary hosts. First, we consider a model-agnostic scenario and show the impact that different time-delay distributions have on the gravitational wave bias. Then, we consider a realistic scenario where gravitational wave events are sourced either by isolated binary evolution or dynamical processes in globular clusters, and study how the gravitational wave bias is unique sensitive to the specific properties of the environment. In both scenarios, we show how the cross-correlation between galaxy and gravitational wave catalogs is able to distinguish between models with different time delays or with different binary sub-populations originated in specific formation channels.

gr-qc↗

arXiv2026

When galaxies burst II. Implications of enhanced burstiness for the 21-cm Cosmic Dawn signal

Recent JWST observations suggest that star formation in the early universe was substantially burstier than assumed in standard models. Such burstiness can be described as a stochastic process characterized by the burst amplitude and the coherence time of star formation epochs. In this paper, we investigate how bursty star formation modifies the 21-cm power spectrum during Cosmic Dawn through its impact on the non-local radiation fields that govern its evolution, namely Lyman-$\alpha$ and X-ray backgrounds. To do so, we introduce an unequal-time correlation in the star-formation-rate density sourcing the two fields and we compute its impact using the analytical framework implemented in the public code Zeus21. We find that the burstiness-induced time correlation produces a shot-noise-like contribution in the Lyman-$\alpha$ and X-ray fields, enhancing both their auto- and cross-power spectra while leaving the global 21-cm signal, $T_{21}(z)$, unchanged. As a result, the 21-cm power spectrum is strongly modified by a shot-noise-like contribution at the beginning of the Cosmic Dawn, where the signal is dominated by lower-mass halos ($M_h\lesssim10^{10}\,M_\odot$), and is boosted by a factor of a few near the Wouthuysen-Field absorption trough. Elsewhere at low redshift, where the clustering signal dominates and larger halos drive the signal, the burstiness component is negligible.

astro-ph.CO↗

arXiv2026

Mitigating galaxy systematics with gravitational wave clustering

Although currently poorly constrained, cosmological ultra-large scales are expected to provide formidable tests not only of General Relativity, but also of the content of $\Lambda$CDM and the Early Universe. However, in this regime, cosmic variance plays a major role in limiting sensitivity, and controlling systematic errors becomes a crucial aspect in preserving the limited information content of current and future observations. Multi-tracer analyses represent a useful technique that simultaneously allows to limit the impact of cosmic variance and mitigate the presence of systematics. In this sense, gravitational waves might represent the perfect alternative tracer of the large-scale structure, since their detection suffers from a set of uncertainties completely different from that of traditional large-scale structure surveys. In this work, we provide a concrete example of how gravitational wave clustering mitigates the presence of systematics, and facilitate the discovery of New Physics signatures. Specifically, we focus on systematics that degrade the constraining power on local Primordial non-Gaussianity for future galaxy surveys; and show how catalogs of gravitational wave events detected by third-generation observatories reduce the impact of systematics while being able to maintain flexibility in the statistical analysis. Additionally, we release a new version of the Multi_CLASS code, which now provides an enhanced level of customization of the different tracers and is compatible with the latest releases of CLASS.

astro-ph.CO↗

arXiv2026

Cosmology with Intensity Mapping via Statistics Beyond the Power Spectrum in the SKAO Era

The cosmological distribution of neutral hydrogen (HI) during the post-reionization era is highly non-Gaussian due to the underlying non-linear structure formation, complex galaxy biasing, and potential primordial non-Gaussianity. One needs higher-order (beyond two-point) statistics to maximally extract the non-Gaussian information out of the 21-cm intensity maps. This chapter summarizes the potential of several higher-order statistics, including voxel intensity distribution, emission line stacking, probability density functions, $\ell_1$-norm, bispectrum, and various marked statistics. Additionally, image-based morphological descriptors, such as the Largest Cluster Statistic, local dimensions, and Minkowski functionals, etc., can potentially characterize the morphology and geometry of the cosmic web encoded in the 21-cm intensity maps. This chapter presents forecasts of the detectability of these higher-order statistics in the context of the future SKAO observations. These forecasts incorporate instrumental noise, observational effects, and, in some cases, foreground removal in their analyses. With its unprecedented sensitivity, the future SKAO 21-cm observations will enable us to measure these higher-order statistics more precisely, possibly helping to break degeneracies between astrophysical and cosmological parameters, and maximizing the science outcome from these surveys.

astro-ph.CO↗

arXiv2026

Cosmology with Multi-Wavelength Line Intensity Mapping Synergies in the SKAO Era

Line intensity mapping (LIM) has emerged as a powerful tool for surveying the large-scale structure of the Universe across cosmic time by measuring spatial fluctuations in the cumulative emission of spectral lines from unresolved sources or the intergalactic medium. Besides the most abundant 21-cm hyperfine line of neutral hydrogen, there are bright far-infrared fine-structure lines like [CII] 158 $\mu$m, [OIII] 88 $\mu$m, [NII] 122/205 $\mu$m, and [OI] 63 $\mu$m, as well as mid-/high-$J$ CO rotational transitions, hydrogen Ly$\alpha$ and H$\alpha$ as potential LIM probes. A key opportunity lies in combining and cross-correlating 21-cm intensity maps from SKAO with other line intensity maps, targeted by a range of ongoing and forthcoming LIM experiments that probe overlapping cosmic volumes. Cross-correlation between 21-cm maps and other line tracers mitigates uncorrelated systematics and enhances sensitivity to the underlying matter distribution, while multi-line analyses help disentangle cosmological and astrophysical parameters. Beyond cross-power spectra, higher-order and morphological statistics -- such as cross-bispectra, marked correlations, and morphological measures -- capture non-Gaussian features and the environmental dependence of structure formation. This chapter explores the synergies that can be achieved by combining SKAO observations with other line-intensity mapping experiments, demonstrating how such joint analyses can unlock new insights into galaxy evolution and cosmology.

astro-ph.CO↗

arXiv2026

Using SKAO to Understand the Clustering of Gravitational Wave Sources

Coalescing Binary Black Holes (BBHs) trace the Large-Scale Structure (LSS) of the Universe, and their clustering properties can be extracted from Gravitational Wave (GW) data. Next-generation detectors, such as the Einstein Telescope and Cosmic Explorer, will enable statistical studies of GW sources thanks to the massive number of detected events. However, such events will still suffer from significant instrumental and theoretical uncertainties. Cross-correlating GW maps with other LSS surveys provides a promising strategy to mitigate these limitations. The SKA-Mid intensity mapping and radio continuum surveys offer ideal datasets for cross-correlation studies with GWs (SKAO$\times$ET2CE). Their wide sky coverage and deep redshift sensitivity will allow precise probing of the epochs and environments where stellar BBHs form most efficiently. In this chapter, we forecast the potential of cross-correlation angular power spectra to extract information on the distribution and clustering properties of GW events. First, we model the number density and bias of three independent tracers: GW sources, neutral hydrogen intensity maps, and radio galaxies. We estimate the constraining power of SKA-Mid$\times$ET2CE on the GW clustering bias, which carries information on the origin of GW progenitors, e.g., whether they formed through stellar evolution or are primordial black holes. Finally, we develop a semi-analytic model for GW events hosted by SKAO galaxies as a function of the time-delay distribution between the binary formation and merger, which is still largely uncertain to date. We forecast the signal-to-noise ratio of their cross-correlation with SKA-Mid, and demonstrate that SKA-Mid$\times$ET2CE will foster our understanding of the time-delay distribution.

astro-ph.CO↗

arXiv2026

When galaxies burst: enhanced shot-noise for line-intensity mapping in the JWST era

Recent JWST observations indicate that star formation at $z\!\sim\!4-6$ is more stochastic than previously assumed, with rms log-SFR scatter $\sim\!0.6$ dex at $M_h\!\sim\!10^{11}M_{\odot}$, growing toward smaller halos and time-correlated on $\sim\!25$ Myr. This is significantly higher than the typical $\sim\!0.3$ dex phenomenological lognormal scatter assumed in standard line-intensity mapping (LIM) forecasts. We propagate the JWST-era burstiness through to the LIM shot-noise power spectrum and show that the result is a simple multiplicative correction: the deterministic shot noise multiplied by a line-dependent boost factor $B_\lambda$ derived in closed form by convolving the SFR correlation function with the stellar-population-synthesis kernel of each line. At $z\!\sim\!6$, we find $B_{{\rm H}\alpha}\!\simeq\!7$ and $B\!\sim\!2.5$-$3.5$ for longer-window tracers ([CII], CO, UV) - factors of $\sim\!2$-$5$ above the standard prescription, and growing further toward higher redshift. The enhancement transforms the LIM landscape: it improves auto-spectrum detectability and suppresses lower-redshift interloper contamination, but degrades cosmological applications such as BAO that rely on a clean clustering measurement. Crucially, it also opens a new use of LIM as a diagnostic of high-redshift star-formation physics beyond the regime of individually resolved galaxies: redshift tomography of a single line constrains the amplitude and mass dependence of the burstiness, while cross-line shot-noise correlations probe its time coherence.

astro-ph.GA↗

arXiv2026

Reionization Bubbles from Real-Space Cross Correlations of Line Intensity Maps

We propose a new way to reconstruct the ionized-bubble size distribution during the Epoch of Reionization (EoR) through the real-space cross-correlation of 21-cm and star-forming line-intensity maps. Understanding the evolution and timing of the EoR is crucial for both astrophysics and cosmology, and a wealth of information on the first sources can be extracted from the study of ionized bubbles. Nevertheless, directly mapping bubbles is challenging due to the high redshifts involved, possible selection biases, and foregrounds in 21-cm maps. Here, we exploit the real-space cross-correlation $\xi_{21,\nu}$ between 21-cm and line-intensity mapping (LIM) signals to reconstruct the evolution of bubble sizes during reionization. For the first time, we show that $\xi_{21,\nu}(r)$ departs from a saturation level for each separation $r$ when bubbles of size $r$ begin to form, providing a handle for the onset of bubbles of each radius. Moreover, we demonstrate that $\xi_{21,\nu}$ evolves from positive to negative as the EoR progresses, reaching a minimum (i.e. maximum anti-correlation) when bubbles of radius $r$ reach peak abundance. We show that these results are robust to changes in the astrophysical model as well as the timing/topology of reionization. This real-space observable complements usual Fourier-space estimators by capturing the localized nature of bubbles, offering new insights into the sources driving cosmic reionization.

astro-ph.CO↗

arXiv2025

A New Boundary Condition on Reionization

The epoch of reionization (EoR) marks the last phase transition of hydrogen in our Universe, as it evolves from cold and neutral to hot and ionized in the intergalactic medium (IGM). While its endpoint and duration can be estimated from current observations, albeit with large uncertainties, there is no known avenue to constrain its onset. We propose a novel method based on the Pearson cross-correlation coefficient between 21-cm brightness temperature maps and line-intensity maps tracing star-formation (e.g., [OIII], CO, [CII]). This real-space estimator evolves from negative to positive as X-ray heating progresses, and saturates prior to the EoR. We predict a sharp drop from saturation during the earliest EoR stages, when the IGM ionized fraction is $x_{\rm HII}\lesssim 10\%$. We show that in standard scenarios, where IGM heating precedes reionization, the drop is a clear, model-robust signature that the EoR is still in its early stages, even when $\bar{x}_{\rm HII}$ cannot be measured precisely. This information is not accessible through the detection of an anticorrelation alone, which only indicates that reionization is ongoing. To assess the detectability of this feature, we provide a preliminary estimate of its signal-to-noise ratio in our fiducial scenario, assuming SPHEREx-like and SKAO-like noise levels, indicating that it is within reach of next-generation surveys. The detection of the Pearson drop therefore will provide a unique anchor for the EoR onset, and an upper bound on $x_{\rm HII}$, complementing existing probes and tightening constraints on early galaxy formation models.

astro-ph.CO↗

arXiv2025

oLIMpus: An Effective Model for Line Intensity Mapping Auto- and Cross- Power Spectra in Cosmic Dawn and Reionization

Line-intensity mapping (LIM) is emerging as a powerful probe of the high-redshift Universe, with a growing number of LIM experiments targeting various spectral lines deep into the epochs of reionization and cosmic dawn. A key remaining challenge is the consistent and efficient modeling of the diverse emission lines and of the observables of different surveys. Here, we present oLIMpus, a fully analytical effective model to study LIM auto- and cross- power spectra. Our work builds on the 21-cm effective model presented in Zeus21, applying it to star-forming lines and improving it in different aspects. Our code accounts for shot noise and linear redshift-space distortions and it includes by default prescriptions for OII, OIII, H$\alpha$, H$\beta$, CII, CO line luminosities, together with the 21-cm model inherited from Zeus21. Beyond auto- and cross-power spectra, oLIMpus can produce mock coeval boxes and lightcones, and with a computational time of $\sim s$ it is ideal for parameter-space exploration and inference. Its modular implementation makes it easy to customize and extend, enabling various applications, such as MCMC analyses and consistent multi-line cross-correlations.

astro-ph.CO↗

arXiv2025

Joint 21-cm and CMB Forecasts for Constraining Self-Interacting Massive Neutrinos

Self-interacting neutrinos provide an intriguing extension to the Standard Model, motivated by both particle physics and cosmology. Recent cosmological analyses suggest a bimodal posterior for the coupling strength $G_{\rm eff}$, favoring either strong or moderate interactions. These interactions modify the scale-dependence of the growth of cosmic structures, leaving distinct imprints on the matter power spectrum at small scales, $k\,>\,0.1\,{\rm Mpc}^{-1}$. For the first time, we explore how the 21-cm power spectrum from the cosmic dawn and the dark ages can constrain the properties of self-interacting, massive neutrinos. The effects of small-scale suppression and enhancement in the matter power spectrum caused by self-interacting neutrinos propagate to the halo mass function, shaping the abundance of small- and intermediate-mass halos. It is precisely these halos that host the galaxies responsible for driving the evolution of the 21-cm signal during the cosmic dawn. We find that HERA at its design sensitivity can improve upon existing constraints on $G_{\rm eff}$ and be sensitive to small values of the coupling, beyond the reach of current and future CMB experiments. Crucially, we find that the combination of HERA and CMB-S4 can break parameter degeneracies, significantly improving the sensitivity to $G_{\rm eff}$ over either experiment alone. Finally, we investigate the prospects of probing neutrino properties with futuristic Lunar interferometers, accessing the astrophysics-free 21-cm power spectrum during the dark ages. The capability of probing small scales of these instruments will allow us to reach a percent-level constraint on the neutrino self-coupling.

astro-ph.CO↗

arXiv2024

Towards a multi-tracer neutrino mass measurement with line-intensity mapping

Accurately determining neutrino masses is a main objective of contemporary cosmology. Since massive neutrinos affect structure formation and evolution, probes of large scale structure are sensitive to the sum of their masses. In this work, we explore future constraints on $\sum m_\nu$ utilizing line-intensity mapping (LIM) as a promising emerging probe of the density of our Universe, focusing on the fine-structure [CII] line as an example, and compare these constraints with those derived from traditional galaxy surveys. Additionally, we perform a multi-tracer analysis using velocity tomography via the kinetic Sunyaev-Zeldovich and moving lens effects to reconstruct the three-dimensional velocity field. Our forecasts indicate that the next-generation AtLAST detector by itself can achieve $\sigma_{\Sigma m_\nu} \sim 50$ meV sensitivity. Velocity tomography will further improve these constraints by 4%. Incorporating forecasts for CMB-S4 and DESI-BAO in a comprehensive multi-tracer analysis, while setting a prior on the optical depth to reionization $\tau$ derived using 21-cm forecasted observations, to break degeneracies, we find that a $\gtrsim5\sigma$ detection of $\sum m_\nu\!\sim\! 60$ meV, under the normal hierarchy, is within reach with LIM. Even without a $\tau$ prior, our combined forecast reaches $\sigma_{\Sigma m_\nu} \!\sim\! 18$ meV.

astro-ph.CO↗

arXiv2024

Does it matter? A more careful treatment of density fluctuations in 21-cm simulations

The cosmological 21-cm signal is sourced from hyperfine transitions in neutral hydrogen atoms. Yet, although the abundance of hydrogen atoms follows the baryon density field, semi-numerical codes that simulate the 21-cm signal simplify their treatment as if all the matter in the Universe was in the form of collisionless cold dark matter (CDM). This is usually done by evolving the density field via a scale-independent growth factor (SIGF). In this work, we separate the baryons from CDM and evolve the two species with a proper scale-dependent growth factor (SDGF). By incorporating the SDGF in the 21cmFirstCLASS code, we demonstrate the effect that baryons and CDM have on the 21-cm signal at the linear dark ages epoch and the subsequent non-linear epochs of cosmic dawn and reionization. Our analysis shows that the baryonic nature of hydrogen cannot be ignored during the dark ages, and that non-linear effects in density-field evolution must be accounted for after stars have formed. Furthermore, we discuss how the 21-cm signal is modified at lower redshifts, where ground-based 21-cm interferometers are mostly sensitive, due to the choice of working with either the "linear" or "non-linear" matter over-density (that is, the over-density as computed from linear perturbation theory, and non-linear perturbation theory, respectively) in the extended Press-Schechter formalism. Our code is publicly available at https://github.com/jordanflitter/21cmFirstCLASS.

astro-ph.CO↗

arXiv2024

Gravitational wave background from primordial black holes in globular clusters

Primordial black holes still represent a viable candidate for a significant fraction, if not for the totality, of dark matter. If these compact objects have masses of order tens of solar masses, their coalescence can be observed by current and future ground-based gravitational wave detectors. Therefore, finding new gravitational wave signatures associated with this dark matter candidate can either lead to their detection or help constraining their abundance. In this work we consider the phenomenology of primordial black holes in dense environments, in particular globular clusters. We model the internal structure of globular clusters in a semi-analytical fashion, and we derive the expected merger rate. We show that, if primordial black holes are present in globular clusters, their contribution to the GW background can be comparable to other well-known channels, such as early- and late-time binaries, thus enhancing the detectability prospects of primordial black holes and demonstrating that this contribution needs to be taken into account.

astro-ph.CO↗

arXiv2024

Upcoming searches for decaying dark matter with ULTRASAT ultraviolet maps

Decaying dark matter (DDM) can be tested via different astrophysical and cosmological probes. In particular, particles in the $\sim$ 9.5 - 30 eV mass range that decay into monochromatic photons, would contribute to the extragalactic background light (EBL) in the ultraviolet (UV) bandwidth. In this work, we show that an intriguing improvement to the constraints on such DDM models can come from broadband UV surveys, such as GALEX or the upcoming ULTRASAT satellite. These provide diffuse light maps of the UV EBL, integrated over a wide redshift range. The cross correlation between intensity fluctuations in these maps with a reference spectroscopic galaxy survey, can be used to reconstruct the redshift evolution of the EBL intensity; in this way, it is also possible to detect signatures of contributions from DDM. We forecast the constraining power of (GALEX+ULTRASAT)$\times$DESI, and we show they will be able to detect DDM with decay rate up to $\mathcal{O}(10^{-26}\,{\rm s})$. In the context of axion-like particles (ALP), our forecasts can be converted to constraints on the ALP-photon coupling; our results show this technique will test ALP with coupling $\lesssim\mathcal{O}(10^{-12}\,{\rm GeV^{-1}})$, more than an order of magnitude better than current bounds in this mass range.

astro-ph.CO↗

arXiv2024

Constraining $z\lesssim 2$ ultraviolet emission with the upcoming ULTRASAT satellite

The Extragalactic Background Light (EBL) carries a huge astrophysical and cosmological content: its frequency spectrum and redshift evolution are determined by the integrated emission of unresolved sources, these being galaxies, active galactic nuclei, or more exotic components. The near-UV region of the EBL spectrum is currently not well constrained, yet a significant improvement can be expected thanks to the soon-to-be launched Ultraviolet Transient Astronomy Satellite (ULTRASAT). Intended to study transient events in the $2300-2900\,{\rm \r{A}}$ observed band, this detector will provide wide field maps, tracing the UV intensity fluctuations on the largest scales. In this paper, we suggest how to exploit ULTRASAT to reconstruct the redshift evolution of the UV-EBL volume emissivity. We build upon the work of Chiang et al. (2019), where the Clustering-Based Redshift (CBR) technique was used to study diffuse light maps from GALEX. Their results showed the capability of the cross correlation between GALEX and SDSS spectroscopic catalogs in constraining the UV emissivity, highlighting how CBR is sensitive only to the extragalactic emissions, avoiding foregrounds and Galactic contributions. In our analysis, we introduce a framework to forecast the CBR constraining power when applied to ULTRASAT and GALEX in cross correlation with the 5-year DESI spectroscopic survey. We show that these will yield a strong improvement in the measurement of the UV-EBL volume emissivity. For $\lambda = 1500\,{\rm \r{A}}$,non-ionizing continuum below $z \sim 2$, we forecast a $1\sigma$ uncertainty $\lesssim 26\%\,(9\%)$ with conservative (optimistic) bias priors using ULTRASAT full-sky map; similar constraints can be obtained from its low-cadence survey, which will provide a smaller but deeper map. We finally discuss how these results will foster our understanding of UV-EBL models.

astro-ph.CO↗

arXiv2023

Effects of feedback-free starburst galaxies on the 21-cm signal and reionization history

Different star-formation models at Cosmic Dawn produce detectable signatures in the observables of upcoming 21-cm experiments. In this work, we consider the physical scenario of feedback-free starbursts (FFB), according to which the star-formation efficiency (SFE) is enhanced in sufficiently massive halos at early enough times, thus explaining the indication from the James Webb Space Telescope for an excess of bright galaxies at $z \geq 10$. We model the contribution of FFBs to popII SFE and compute the impact these have on the 21-cm global signal and power spectrum. We show that FFBs affect the evolution of the brightness temperature and the 21-cm power spectrum, but they only have a limited effect on the neutral hydrogen fraction. We investigate how the observables are affected by changes in the underlying star formation model and by contribution from popIII stars. Finally, we forecast the capability of next-generation Hydrogen Epoch of Reionization Array (HERA) to detect the existence of FFB galaxies via power spectrum measurements. Our results show the possibility of a significant detection, provided that popII stars are the main drivers of lowering the spin temperature. Efficient popIII star formation will make the detection more challenging.

astro-ph.CO↗

arXiv2023

Signatures of primordial black holes in gravitational wave clustering

The possible existence of primordial black holes (PBHs) is an open question in modern cosmology. Among the probes to test it, gravitational waves (GW) coming from their mergers constitute a powerful tool. In this work, we study how stellar mass PBH binaries could affect measurements of the clustering of merger events in future GW surveys. We account for PBH binaries formed both in the early and late Universe and show that the power spectrum modification they introduce can be detected at $\sim 2σ-3σ$ (depending on some assumptions) whenever PBH mergers make up at least $\sim 60\%$ of the overall number of detected events. By adding cross-correlations with galaxy surveys, this threshold is lowered to $\sim 40\%$. In the case of a poor redshift determination of GW sources, constraints are degraded by about a factor of 2. Assuming a theoretical model for the PBH merger rate, we can convert our results to constraints on the fraction of dark matter in PBHs, $f_{\rm PBH}$. Finally, we perform a Bayesian model selection forecast and confirm that the analysis we develop could be able to detect $\sim30M_\odot$ PBHs if they account for $f_{\rm PBH}\sim 10^{-4}-10^{-3}$, depending on the model uncertainty considered, being thus competitive with other probes.

astro-ph.CO↗