arXiv subjects

Hovav Lazare

Publications and source records attributed to Hovav Lazare.

5 recordsLinked to original sources

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-$α$ 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-$α$ 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

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 $B_λ$ 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 $B_{{\rm H}α}\!\simeq\!7$ 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

First galaxy ultraviolet luminosity function limits on dark matter-proton scattering

Scattering between dark matter (DM) and protons leads to suppressed small-scale fluctuations, with implications for a variety of cosmological observables. In this work, we search for evidence of DM-proton scattering with an interaction cross section $σ\!=\!σ_0 (\frac{v}{c})^n$ for $n=0,2$ and $4$, corresponding e.g. to velocity-independent contact interactions from heavy mediators, velocity-dependent pseudoscalar-mediated scattering, and higher-order dipole interactions, respectively, using high-redshift ($z \sim4-10$) ultraviolet galaxy luminosity functions (UVLFs) observed by Hubble Space Telescope (HST). We employ an adjusted implementation of GALLUMI combined with the modified Boltzmann solver CLASS DMeff that accounts for interacting DM, and incorporate UVLF data from both blank and lensed HST fields, alongside Planck CMB data and the Pantheon supernova catalog in a Bayesian analysis framework to set constraints on $σ_0$. Our results show that including lensed UVLF data, which probe fainter galaxies than the blank HST fields and thus smaller scales, leads to a substantial improvement in the constraints on $σ_0$ for $n>0$, surpassing existing bounds from Milky-Way (MW) satellite abundance and CMB anisotropies. For $m_χ = 1\,\rm MeV $, for example, we set the upper bounds at $1.1\times 10^{-25} \, \rm cm^2$ for $n=2$ and $2.1\times 10^{-22} \, \rm cm^2$ for $n=4$. For $n=0$, our bound is within an order of magnitude of those from the Lyman-$α$ forest and MW satellites.

astro-ph.CO↗

arXiv2025

Constraints on the fuzzy dark matter mass window from high-redshift observables

We use a combination of high-redshift observables to extract the strongest constraints to date on the fraction of axion fuzzy dark matter (FDM) in the mass window $10^{-26}\,\mathrm{eV}\!\lesssim\! m_\mathrm{FDM}\!\lesssim\!10^{-23}\,\mathrm{eV}$. These observables include ultraviolet luminosity functions (UVLFs) at redshifts $4-10$ measured by the Hubble Space Telescope, a constraint on the neutral hydrogen fraction from high-redshift quasar spectroscopy, the cosmic microwave background optical depth to reionization measurement from Planck and upper bounds on the 21cm power spectrum from HERA. In order to calculate these signals for FDM cosmology, we use the 21cmFirstCLASS code to interface between AxiCLASS and 21cmFAST and consistently account for the full cosmic history from recombination to reionization. To facilitate a full Bayesian likelihood analysis, we developed a machine-learning based pipeline, which is both accurate, and enables a swift statistical inference, orders of magnitude faster than a brute force approach. We find that FDM of mass $m_\mathrm{FDM} \!= \!10^{-23} \, \mathrm{eV}$ is bound to less than $16\%$ of the total dark matter, where the constrains strengthen towards smaller masses, reaching down to $1\%$ for $m_\mathrm{FDM}\! =\! 10^{-26} \, \mathrm{eV}$, both at $95\%$ confidence level. In addition, we forecast that a future detection of the 21cm power spectrum with HERA will lower the upper bound at $m_\mathrm{FDM}\! =\! 10^{-23} \, \mathrm{eV}$ to $\lesssim\!1\%$.

astro-ph.CO↗

arXiv2024

HERA bound on x-ray luminosity when accounting for population III stars

Recent upper bounds from the Hydrogen Epoch of Reionization Array (HERA) on the cosmological 21-cm power spectrum at redshifts $z \approx 8, 10$, have been used to constrain $L_{\rm X<2 \, keV}/{\rm SFR}$, the soft-band X-ray luminosity measured per unit star formation rate (SFR), strongly disfavoring values lower than $\approx 10^{39.5} \, {\rm erg} \;{\rm s}^{-1} \;{\rm M}_{\odot}^{-1} \;{\rm yr}$. This conclusion is derived from semi-numerical models of the 21-cm signal, specifically focusing on contributions from atomic cooling galaxies that host PopII stars. In this work, we first reproduce the bounds on $L_{\rm X<2 \, keV}/{\rm SFR}$ and other parameters using a pipeline that combines machine learning emulators for the power spectra and the intergalactic medium characteristics, together with a standard Markov chain Monte Carlo parameter fit. We then use this approach when including molecular cooling galaxies that host PopIII stars in the cosmic dawn 21-cm signal, and show that lower values of $L_{\rm X<2 \, keV}/{\rm SFR}$ are hence no longer strongly disfavored. The revised HERA bound does not require high-redshift X-ray sources to be significantly more luminous than high-mass X-ray binaries observed at low redshift.

astro-ph.CO↗