arXiv subjects

Olivier Doré

Publications and source records attributed to Olivier Doré.

At least 37 records · Page 2Linked to original sources

arXiv2025

The End of the Road for Far-infrared Reddening Maps? Evidence for Reddening Errors Driven by Changes in PAH Abundance

Accurate correction for extinction by Galactic dust is essential for studying the extragalactic sky. In the low-extinction regions of the Ursa Major molecular cloud complex, we demonstrate that Galactic dust reddening maps constructed from observations of far-infrared emission are insensitive to variations in the abundance of polycyclic aromatic hydrocarbons (PAHs), and, as a result, to PAH-induced variations in reddening. Using galaxy counts to validate various reddening maps, we find evidence that maps based on far-infrared emission erroneously under-predict reddening compared to stellar reddening maps. This underestimation by far-infrared emission based reddening maps -- representing the largest discrepancy between maps of up to $E(B-V)=0.08$ mag -- is correlated with the relative brightness of PAH emission. Furthermore, we demonstrate theoretically that changes in PAH abundance via accretion from the gas phase is capable of altering extinction significantly with only minor changes to far-infrared emission. We show that modeling the extinction of Ursa Major using both far-infrared and mid-infrared emission more accurately traces dust extinction variations due to changes in PAH abundance. Finally, we discuss how SPHEREx observations of the 3.3 $μ$m PAH feature are a promising way to overcome this limitation of far-infrared emission.

astro-ph.GA↗

arXiv2025

A Fast Bayesian Method for Coherent Gravitational Wave Searches with Relative Astrometry

Using relative stellar astrometry for the detection of coherent gravitational wave sources is a promising method for the microhertz range, where no dedicated detectors currently exist. Compared to other gravitational wave detection techniques, astrometry operates in an extreme high-baseline-number and low-SNR-per-baseline limit, which leads to computational difficulties when using conventional Bayesian search techniques. We extend a technique for efficiently searching pulsar timing array datasets through the precomputation of inner products in the Bayesian likelihood, showing that it is applicable to astrometric datasets. Using this technique, we are able to reduce the total dataset size by up to a factor of $\mathcal{O}(100)$, while remaining accurate to within 1% over two orders of magnitude in gravitational wave frequency. Applying this technique to simulated astrometric datasets for the Kepler Space Telescope and Nancy Grace Roman Space Telescope missions, we obtain forecasts for the sensitivity of these missions to coherent gravitational waves. Due to the low angular sky coverage of astrometric baselines, we find that coherent gravitational wave sources are poorly localized on the sky. Despite this, from $10^{-8}$ Hz to $10^{-6}$ Hz, we find that Roman is sensitive to coherent gravitational waves with an instantaneous strain above $h_0 \simeq 10^{-11.4}$, and Kepler is sensitive to strains above $h_0 \simeq $ $10^{-12.4}$. At this strain, we can detect a source with a frequency of $10^{-7}$ Hz and a chirp mass of $10^9$ $M_\odot$ at a luminosity distance of 3.6 Mpc for Kepler, and 0.3 Mpc for Roman.

astro-ph.IM↗

arXiv2025

The SPHEREx Sky Simulator: Science Data Modeling for the First All-Sky Near-Infrared Spectral Survey

We describe the SPHEREx Sky Simulator, a software tool designed to model science data for NASA's SPHEREx mission that will carry out a series of all-sky spectrophotometric surveys at $\sim$6'' spatial resolution in 102 spectral channels spanning 0.75 to 5 $μ$m. The Simulator software implements models for astrophysical emission, instrument characteristics, and survey strategy to generate realistic infrared sky scenes as they will be observed by SPHEREx. The simulated data includes a variety of realistic noise and systematic effects that are estimated using up-to-date astrophysical measurements and information from pre-launch instrument characterization campaigns. Through the pre-flight mission phases the Simulator has been critical in predicting the impact of various effects on SPHEREx science performance, and has played an important role guiding the development of the SPHEREx data analysis pipeline. In this paper, we describe the \skysim\ architecture, pre-flight instrument and sky models, and summarize high-level predictions from the Simulator, including a pre-launch prediction for the 5$σ$ point source sensitivity of SPHEREx, which we estimate to be $m_{\rm AB}$ 18.5--19 from 0.75 to 3.8~$μ$m and $m_{\rm AB}$ 16.6--18 from 3.8 to 5 $μ$m, with the sensitivity limited by the zodiacal light background at all wavelengths. In the future, on-orbit data will be used to improve the Simulator, which will form the basis of a variety of forward-modeling tools that will be used to model myriad instrumental and astrophysical processes to characterize their systematic effects on our final data products and analyses.

astro-ph.IM↗

arXiv2025

The Spectroscopic Stage-5 Experiment

The existence, properties, and dynamics of the dark sectors of our universe pose fundamental challenges to our current model of physics, and large-scale astronomical surveys may be our only hope to unravel these long-standing mysteries. In this white paper, we describe the science motivation, instrumentation, and survey plan for the next-generation spectroscopic observatory, the Stage-5 Spectroscopic Experiment (Spec-S5). Spec-S5 is a new all-sky spectroscopic instrument optimized to efficiently carry out cosmological surveys of unprecedented scale and precision. The baseline plan for Spec-S5 involves upgrading two existing 4-m telescopes to new 6-m wide-field facilities, each with a highly multiplexed spectroscopic instrument capable of simultaneously measuring the spectra of 13,000 astronomical targets. Spec-S5, which builds and improves on the hardware used for previous cosmology experiments, represents a cost-effective and rapid approach to realizing a more than 10$\times$ gain in spectroscopic capability compared to the current state-of-the-art represented by the Dark Energy Spectroscopic Instrument project (DESI). Spec-S5 will provide a critical scientific capability in the post-Rubin and post-DESI era for advancing cosmology, fundamental physics, and astrophysics in the 2030s.

astro-ph.CO↗

arXiv2025

Mapping Galactic Dust Emission and Extinction with HI, HII, and H$_2$

Neutral hydrogen (HI) emission closely traces the dust column density at high Galactic latitudes and is thus a powerful tool for predicting dust extinction. However, the relation between HI column density $N_{\rm HI}$ and high-latitude dust emission observed by Planck has large-scale residuals at the level of $\lesssim 20\%$ on tens of degree scales. In this work, we improve HI-based dust templates in the north/south Galactic poles covering a sky fraction of $f_{\rm sky}=13.5\%/11.0\%$ (5577/4555\,deg$^2$) by incorporating data from ionized (HII) and molecular (H$_2$) gas phases. We make further improvements by employing a clustering analysis on the HI spectral data to identify discrete clouds with distinct dust properties. However, only a modest reduction in fitting residuals is achieved. We quantify the contributions to these residuals from variations in the dust-to-gas ratio, dust temperature and opacity, and magnetic field orientation using ancillary datasets. Although residuals in a few particular regions can be attributed to these factors, no single explanation accounts for the majority. Assuming a constant dust temperature along each line of sight, we derive an upper limit on the high-latitude dust temperature variation of $σ_T<1.28$K, lower than the temperature variation reported in previous studies. Joint analysis of multiple existing and upcoming datasets that trace Galactic gas and dust properties is needed to clarify the origins of the variation of gas and dust properties found here and to significantly improve gas-based extinction maps.

astro-ph.GA↗

arXiv2025

The Radio and Microwave Sky as Seen by Juno on its Mission to Jupiter

We present six nearly full-sky maps made from data taken by radiometers on the Juno satellite during its 5-year flight to Jupiter. The maps represent integrated emission over $\sim 4\%$ passbands spaced approximately in octaves between 600 MHz and 21.9 GHz. Long time-scale offset drifts are removed in all bands, and, for the two lowest frequency bands, gain drifts are also removed from the maps via a self-calibration algorithm similar to the NPIPE pipeline used by the Planck collaboration. We show that, after this solution is applied, statistical noise in the maps is consistent with thermal radiometer noise and expected levels of correlated noise on the gain and noise drift solutions. We verify our map solutions with several consistency tests and end-to-end simulations. We also estimate the level of systematic pixelization noise and polarization leakage via simulations.

astro-ph.IM↗

arXiv2024

Linear Relativistic Corrections in the Spherical Fourier-Bessel Power Spectrum

The three-dimensional galaxy power spectrum is a powerful probe of primordial non-Gaussianity and additional general relativistic (GR) effects on large scales, which can be constrained by the current and upcoming large-scale structure surveys. In this work, we calculate the linear-order relativistic power spectrum in the spherical Fourier-Bessel (SFB) basis, a coordinate system that preserves the geometry of the curved sky and fully accounts for the wide-angle effect. In particular, we model the GR effects present in the discrete SFB power spectrum, which is a more efficient and stable decomposition of the galaxy density field compared to the continuous SFB basis in the presence of radial windows. To validate our GR calculations, we introduce a mapping between the angular power spectrum and the SFB power spectrum, and we compare our calculations with outputs from CLASS. We discuss the rich pattern of GR effects in the SFB basis and compare the GR effects to the local primordial non-Gaussianity (PNG) effect. The Doppler and lensing effects have different angular and Fourier dependence compared to the PNG in the SFB basis, while the gravitational potential term is more degenerate with the PNG and comparable to a signal of $f_{\rm NL}\sim 1$. We also discuss the potential opportunities of extracting the lensing effect through SFB modes in upcoming LSS surveys.

astro-ph.CO↗

arXiv2024

Exact Modeling of Power Spectrum Multipole through Spherical Fourier-Bessel Basis

The three-dimensional galaxy power spectrum is a powerful probe of primordial non-Gaussianity and additional general relativistic effects, which become important on large scales. At the same time, wide-angle (WA) effects due to differing lines-of-sight (LOS) on the curved sky also become important with large angular separation. In this work, we accurately model WA and Doppler effects using the spherical Fourier-Bessel (SFB) formalism, before transforming the result into the commonly used power spectrum multipoles (PSM). This mapping from the SFB power spectrum to PSM represents a new way to non-perturbatively model WA and GR effects present in the PSM, which we validate with log-normal mocks. Moreover, for the first time, we can compute the analytical PSM Gaussian covariance on large scales, exactly including WA-induced mode-couplings, without resorting to any plane-parallel approximations.

astro-ph.CO↗

arXiv2024

The relative constraining power of the high-$z$ 21-cm dipole and monopole signals

The 21-cm background is a promising probe of early star formation and black hole activity. While a slew of experiments on the ground seek to detect the 21-cm monopole and spatial fluctuations on large $\sim 10$ arcminute scales, little work has been done on the prospects for detecting the 21-cm dipole signal or its utility as a probe of early galaxies. Though an intrinsically weak signal relative to the monopole, its direction is known well from the cosmic microwave background and wide-field surveys, plus as a relative measurement the dipole could help relax instrumental requirements. In order to understand the constraining power of the dipole, in this work we perform parameter inference on mock datasets that include the dipole, monopole, or both signals. We find that while the monopole does provide the best constraints for a given integration time, constraints from a dipole measurement are competitive, and can in principle constrain the cosmic star formation rate density and efficiency of X-ray photon production in early $z \sim 15$ galaxies to better than a factor of $\sim 2$. This result holds for most of the available prior volume, which is set by constraints on galaxy luminosity functions, the reionization history, and upper limits from 21-cm power spectrum experiments. We also find that predictions for the monopole from a dipole measurement are robust to different choices of signal model. As a result, the 21-cm dipole signal is a valuable target for future observations and offers a robust cross-check on monopole measurements.

astro-ph.CO↗

arXiv2024

Bayesian Multi-line Intensity Mapping

Line intensity mapping (LIM) has emerged as a promising tool for probing the 3D large-scale structure through the aggregate emission of spectral lines. The presence of interloper lines poses a crucial challenge in extracting the signal from the target line in LIM. In this work, we introduce a novel method for LIM analysis that simultaneously extracts line signals from multiple spectral lines, utilizing the covariance of native LIM data elements defined in the spectral--angular space. We leverage correlated information from different lines to perform joint inference on all lines simultaneously, employing a Bayesian analysis framework. We present the formalism, demonstrate our technique with a mock survey setup resembling the SPHEREx deep field observation, and consider four spectral lines within the SPHEREx spectral coverage in the near infrared: H$α$, $[$\ion{O}{3}$]$, H$β$, and $[$\ion{O}{2}$]$. We demonstrate that our method can extract the power spectrum of all four lines at the $\gtrsim 10σ$ level at $z<2$. For the brightest line, H$α$, the $10σ$ sensitivity can be achieved out to $z\sim3$. Our technique offers a flexible framework for LIM analysis, enabling simultaneous inference of signals from multiple line emissions while accommodating diverse modeling constraints and parameterizations.

astro-ph.CO↗

arXiv2024

Fast Theoretical Predictions for Spherical Fourier Analysis of Large-Scale Structures

On-going or soon to come cosmological large-scale structure surveys such as DESI, SPHEREx, Euclid, or the High-Latitude Spectroscopic Survey of the Nancy Grace Roman Space Telescope promise unprecedented measurement of the clustering of galaxies on large scales. When quantified with the Cartesian Fourier basis, the measurement of these large scales requires the introduction of so-called wide-angle corrections. By contrast, the measurement of the power spectrum in a spherical Fourier Bessel (SFB) basis does not require such corrections and naturally accounts for the spherical survey geometries. Here, we develop and implement a fast code to construct the SFB power spectrum and investigate how line of sight effects, physics such as non-Gaussianity, and differing survey geometries affect SFB power spectrum estimates. We then leverage our program to predict the tightness of cosmological constraints from realistic survey specifications using a Fisher matrix formalism.

astro-ph.CO↗

arXiv2024

SPHEREx: NASA's Near-Infrared Spectrophotmetric All-Sky Survey

SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and ices Explorer, is a NASA MIDEX mission planned for launch in 2024. SPHEREx will carry out the first all-sky spectral survey at wavelengths between 0.75 micron and 5 micron with spectral resolving power ~40 between 0.75 and 3.8 micron and ~120 between 3.8 and 5 micron At the end of its two-year mission, SPHEREx will provide 0.75-to-5 micron spectra of each 6.2"x6.2" pixel on the sky - 14 billion spectra in all. This paper updates an earlier description of SPHEREx presenting changes made during the mission's Preliminary Design Phase, including a discussion of instrument integration and test and a summary of the data processing, analysis, and distribution plans.

astro-ph.IM↗

arXiv2024

Wide-Angle Effects in the Power Spectrum Multipoles in Next-Generation Redshift Surveys

As galaxy redshift surveys expand to larger areas on the sky, effects coming from the curved nature of the sky become important, introducing wide-angle (WA) corrections to the power spectrum multipoles at large galaxy-pair separations. These corrections particularly impact the measurement of physical effects that are predominantly detected on large scales, such the local primordial non-Gaussianities. In this paper, we examine the validity of the perturbative approach to modeling WA effects in the power spectrum multipoles for upcoming surveys by comparing to measurements on simulated galaxy catalogs using the Yamamoto estimator. We show that on the scales $k \lesssim 2π/χ$, where $χ$ is the comoving distance to the galaxies, the estimated power spectrum monopole differs by up to $5\%$ from the second-order perturbative result, with similar absolute deviations for higher multipoles. To enable precision comparison, we pioneer an improved treatment of the $μ$-leakage effects in the Yamamoto estimator. Additionally, we devise a solution to include $f_{\rm NL}$ in the perturbative WA calculations, avoiding divergences in the original framework through the integral constraint. This allows us to conclude that WA effects can mimic a $f_{\rm NL}\sim5$ signal in the lowest SPHEREx redshift bin. We recommend using non-perturbative methods to model large scale power spectrum multipoles for $f_{\rm NL}$ measurements. A companion paper, Wen et al. 2024, addresses this by introducing a new non-perturbative method going through the spherical Fourier-Bessel basis.

astro-ph.CO↗

arXiv2024

Validation of Spherical Fourier-Bessel power spectrum analysis with lognormal simulations and eBOSS DR16 LRG EZmocks

Tuning into the bass notes of the large-scale structure requires careful attention to geometrical effects arising from wide angles. The spherical Fourier-Bessel (SFB) basis provides a harmonic-space coordinate system that fully accounts for all wide-angle effects. To demonstrate the feasibility of the SFB power spectrum, in this paper we validate our SFB pipeline by applying it to lognormal, and both complete and realistic EZmock simulations that were generated for eBOSS DR16 LRG sample. We include redshift space distortions and the local average effect (aka integral constraint). The covariance matrix is obtained from 1000 EZmock simulations, and inverted using eigenvalue decomposition.

astro-ph.IM↗

arXiv2023

The Galaxy Bispectrum in the Spherical Fourier-Bessel Basis

The bispectrum, the three-point correlation in Fourier space, is a crucial statistic for studying many effects targeted by the next-generation galaxy surveys, such as primordial non-Gaussianity (PNG) and general relativistic (GR) effects on large scales. In this work we develop a formalism for the bispectrum in the Spherical Fourier-Bessel (SFB) basis - a natural basis for computing correlation functions on the curved sky, as it diagonalizes the Laplacian operator in spherical coordinates. Working in the SFB basis allows for line-of-sight effects such as redshift space distortions (RSD) and GR to be accounted for exactly, i.e without having to resort to perturbative expansions to go beyond the plane-parallel approximation. Only analytic results for the SFB bispectrum exist in the literature given the intensive computations needed. We numerically calculate the SFB bispectrum for the first time, enabled by a few techniques: We implement a template decomposition of the redshift-space kernel $Z_2$ into Legendre polynomials, and separately treat the PNG and velocity-divergence terms. We derive an identity to integrate a product of three spherical harmonics connected by a Dirac delta function as a simple sum, and use it to investigate the limit of a homogeneous and isotropic Universe. Moreover, we present a formalism for convolving the signal with separable window functions, and use a toy spherically symmetric window to demonstrate the computation and give insights into the properties of the observed bispectrum signal. While our implementation remains computationally challenging, it is a step toward a feasible full extraction of information on large scales via a SFB bispectrum analysis.

astro-ph.CO↗

arXiv2023

Constraining effective neutrino species with bispectrum of large scale structures

Relativistic and free-streaming particles like neutrinos leave imprints in large scale structures (LSS), providing probes of the effective number of neutrino species $N_{\rm eff}$. In this paper, we use the Fisher formalism to forecast $N_{\rm eff}$ constraints from the bispectrum (B) of LSS for current and future galaxy redshift surveys, specifically using information from the baryon acoustic oscillations (BAOs). Modeling the galaxy bispectrum at the tree-level, we find that adding the bispectrum constraints to current CMB constraints from Planck can improve upon the Planck-only constraints on $N_{\rm eff}$ by about 10\% -- 40\% depending on the survey. Compared to the Planck + power spectrum (P) constraints previously explored in the literature, using Planck+P+B provides a further improvement of about 5\% -- 30\%. Besides using BAO wiggles alone, we also explore using the total information which includes both the wiggles and the broadband information (which is subject to systematics challenges), generally yielding better results. Finally, we exploit the interference feature of the BAOs in the bispectrum to select a subset of triangles with the most information on $N_{\rm eff}$. This allows for the reduction of computational cost while keeping most of the information, as well as for circumventing some of the shortcomings of applying directly to the bispectrum the current wiggle extraction algorithm valid for the power spectrum. In sum, our study validates that the current Planck constraint on $N_{\rm eff}$ can be significantly improved with the aid of galaxy surveys before the next-generation CMB experiments like CMB-Stage 4.

astro-ph.CO↗

arXiv2023

Gravitational Wave Detection with Relative Astrometry using Roman's Galactic Bulge Time Domain Survey

Gravitational waves (GWs) are a new avenue of observing our Universe. So far, we have seen them in the ~10-100 Hz range, and there are hints that we might soon detect them in the nanohertz regime. Multiple efforts are underway to access GWs across the frequency spectrum; however, parts of the frequency space are currently not covered by any planned or future observatories. Photometric surveys can bridge the microhertz gap in the spectrum between LISA and Pulsar Timing Arrays (PTAs) through relative astrometric measurements. Similar to PTA measurements, these astrometric measurements rely on the correlated spacetime distortions produced by gravitational waves at Earth, which induce coherent, apparent stellar position changes on the sky. To detect microhertz GWs with an imaging survey, a combination of high relative astrometric precision, a large number of observed stars, and a high cadence of exposures are needed. Roman's proposed core community survey, the Galactic Bulge Time Domain Survey (RGBTDS), would have all of these components. RGBTDS would be sensitive to GWs with frequencies ranging from $7.7\times 10^{-8}$ Hz to $5.6\times 10^{-4}$ Hz, which opens up a unique GW observing window for supermassive black hole binaries and their waveform evolution. We note that small changes to the survey could enhance Roman's sensitivity to GWs, making it possible to observe the GW background signal that PTAs have recently hinted at with an SNR $\sim$ 70.

astro-ph.GA↗

arXiv2022

Constraining the Stochastic Gravitational Wave Background with Photometric Surveys

The detection of the Stochastic Gravitational Wave Background (SGWB) is essential for understanding black hole populations, especially for supermassive black hole binaries. The recent promising results from various Pulsar Timing Array (PTA) collaborations allude to an imminent detection. In this paper, we investigate the relative astrometric gravitational wave detection method, which can contribute to SGWB studies in the microhertz range. We consider the Roman Space Telescope and Gaia as candidates and quantitatively discuss the survey sensitivity in both the frequency and spatial domains. We emphasize the importance of survey specific constraints on performance estimates by considering mean field of view (FoV) signal subtraction and angular power spectrum binning. We conclude that if the SGWB is at a similar level as in PTA estimates, both Roman and Gaia have the potential to detect this frequency-domain power excess. However, both Roman and Gaia are subject to FoV limitations, and are unlikely to be sensitive to the spatial pattern of the SGWB.

gr-qc↗