分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yun Wang
Zhongxu Zhai
Anahita Alavi
Elena Massara
Alice Pisani
Andrew Benson
Christopher M. Hirata
Lado Samushia
David H. Weinberg
James Colbert
Olivier Doré
Tim Eifler
Chen Heinrich
Shirley Ho
Elisabeth Krause
Nikhil Padmanabhan
David Spergel
Harry I. Teplitz
摘要： The Nancy Grace Roman Space Telescope will conduct a High Latitude Spectroscopic Survey (HLSS) over a large volume at high redshift, using the near-IR grism (1.0-1.93 $\mu$m, $R=435-865$) and the 0.28 deg$^2$ wide field camera. We present a reference HLSS which maps 2000 deg$^2$ and achieves an emission line flux limit of 10$^{-16}$ erg/s/cm$^2$ at 6.5$\sigma$, requiring $\sim$0.6 yrs of observing time. We summarize the flowdown of the Roman science objectives to the science and technical requirements of the HLSS. We construct a mock redshift survey over the full HLSS volume by applying a semi-analytic galaxy formation model to a cosmological N-body simulation, and use this mock survey to create pixel-level simulations of 4 deg$^2$ of HLSS grism spectroscopy. We find that the reference HLSS would measure $\sim$ 10 million H$\alpha$ galaxy redshifts that densely map large scale structure at $z=1-2$ and 2 million [OIII] galaxy redshifts that sparsely map structures at $z=2-3$. We forecast the performance of this survey for measurements of the cosmic expansion history with baryon acoustic oscillations and the growth of large scale structure with redshift space distortions. We also study possible deviations from the reference design, and find that a deep HLSS at $f_{\rm line}>7\times10^{-17}$erg/s/cm$^2$ over 4000 deg$^2$ (requiring $\sim$1.5 yrs of observing time) provides the most compelling stand-alone constraints on dark energy from Roman alone. This provides a useful reference for future optimizations. The reference survey, simulated data sets, and forecasts presented here will inform community decisions on the final scope and design of the Roman HLSS.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： 21 cm intensity mapping (IM) has the potential to be a strong and unique probe of cosmology from redshift of order unity to redshift potentially as high as 30. For post-reionization 21 cm observations, the signal is modulated by the thermal and dynamical reaction of gas in the galaxies to the passage of ionization fronts during the Epoch of Reionization. In this work, we investigate the impact of inhomogeneous reionization on the post-reionization 21 cm power spectrum and the induced shifts of cosmological parameters at redshifts $3.5 \lesssim z \lesssim 5.5$. We make use of hydrodynamics simulations that could resolve small-scale baryonic structure evolution to quantify HI abundance fluctuation, while semi-numerical large box 21cmFAST simulations capable of displaying inhomogeneous reionization process are deployed to track the inhomogeneous evolution of reionization bubbles. We find the inhomogeneous reionization effect could impact the HI power spectrum up to tens of percent level and shift cosmological parameters estimation from sub-percent to tens percent in the observation of future post-reionization 21 cm intensity mapping experiments SKA-LOW and PUMA. In particular, the shift is up to 0.033 in the spectral index $n_s$ and 0.025 eV in the sum of the neutrino masses $\sum m_\nu$ depending on the reionization model and the observational parameters. We discuss strategies to mitigate and separate these biases.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The amplitude of the metagalactic ultraviolet background (UVB) at large-scales is impacted by two factors. First, it naturally attenuates at scales larger than mean-free-path of UVB photons due to the absorption by neutral intergalactic medium. Second, there are discrete and rare ionizing sources distributing in the Universe, emitting the UVB photons, and thus enhancing the local UVB amplitude. Therefore, for cosmological probe that is sensitive to the UVB amplitude and capable of detecting the large scale like Lyman-$\alpha$ forest spectrum, the fluctuation due to the clustering of ionizing sources becomes a significant factor for Lyman-$\alpha$ flux transmission and leave imprints on Lyman-$\alpha$ flux power spectrum at these large scales. In this work, we make use of a radiative transfer model that parametrizes the UVB source distribution by its bias $b_{\rm j}$ and shot noise $\overline{n}_{\rm j}$. We estimate the constraints on this model through the cross-correlation between Lyman-$\alpha$ forest survey and galaxy survey, using the DESI Lyman-$\alpha$ forest survey and the Roman Space Telescope emission line galaxy survey as an example. We show the detection sensitivity improvement for UVB parameters from disjoint to maximal overlap of DESI+Roman survey strategy. We also show that the degeneracy of two ionizing source parameters can be broken by increasing the overlapping survey area. Our results motivate survey strategies more dedicated to probe the UVB large-scale fluctuations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we present the formalism of simulating Lyman-$\alpha$ emission and polarization around reionization ($z$ = 8) from a plane-parallel ionization front. We accomplish this by using a Monte Carlo method to simulate the production of a Lyman-$\alpha$ photon, its propagation through an ionization front, and the eventual escape of this photon. This paper focuses on the relation of the input parameters of ionization front speed $U$, blackbody temperature $T_{\rm bb}$, and neutral hydrogen density $n_{\rm HI}$, on intensity $I$ and polarized intensity $P$ as seen by a distant observer. The resulting values of intensity range from $3.18\times 10^{-14}$ erg/cm$^{2}$/s/sr to $1.96 \times 10^{-9}$ erg/cm$^{2}$/s/sr , and the polarized intensity ranges from $5.73\times 10^{-17}$ erg/cm$^{2}$/s/sr to $5.31 \times 10^{-12}$ erg/cm$^{2}$/s/sr. We found that higher $T_{\rm bb}$, higher $U$, and higher $n_{\rm HI}$ contribute to higher intensity, as well as polarized intensity, though the strongest dependence was on the hydrogen density. The dependence of viewing angle of the front is also explored. We present tests to support the validity model, which makes the model suitable for further use in a following paper where we will calculate the intensity and polarized intensity power spectrum on a full reionization simulation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The relative velocity between baryons and dark matter in the early Universe can suppress the formation of small-scale baryonic structure and leave an imprint on the baryon acoustic oscillation (BAO) scale at low redshifts after reionization. This "streaming velocity" affects the post-reionization gas distribution by directly reducing the abundance of pre-existing mini-halos ($\lesssim 10^7 M_{\bigodot}$) that could be destroyed by reionization and indirectly modulating reionization history via photoionization within these mini-halos. In this work, we investigate the effect of streaming velocity on the BAO feature in HI 21 cm intensity mapping after reionization, with a focus on redshifts $3.5\lesssim z\lesssim5.5$. We build a spatially modulated halo model that includes the dependence of the filtering mass on the local reionization redshift and thermal history of the intergalactic gas. In our fiducial model, we find isotropic streaming velocity bias coefficients $b_v$ ranging from $-0.0043$ at $z=3.5$ to $-0.0273$ at $z=5.5$, which indicates that the BAO scale is stretched (i.e., the peaks shift to lower $k$). In particular, streaming velocity shifts the transverse BAO scale between 0.121% ($z=3.5$) and 0.35% ($z=5.5$) and shifts the radial BAO scale between 0.167% ($z=3.5$) and 0.505% ($z=5.5$). These shifts exceed the projected error bars from the more ambitious proposed hemispherical-scale surveys in HI (0.13% at $1\sigma$ per $\Delta z = 0.5$ bin).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The clustering signals of galaxy clusters are known to be powerful tools for self-calibrating the mass-observable relation and are complementary to cluster abundance and lensing. In this work, we explore the possibility of combining three correlation functions -- cluster lensing, the cluster-galaxy cross-correlation function, and the galaxy auto-correlation function -- to self-calibrate optical cluster selection bias, the boosted clustering and lensing signals in a richness-selected sample mainly caused by projection effects. We develop mock catalogues of redMaGiC-like galaxies and redMaPPer-like clusters by applying Halo Occupation Distribution (HOD) models to N-body simulations and using counts-in-cylinders around massive haloes as a richness proxy. In addition to the previously known small-scale boost in projected correlation functions, we find that the projection effects also significantly boost 3D correlation functions out to scales 100 $h^{-1} \mathrm{Mpc}$. We perform a likelihood analysis assuming survey conditions similar to that of the Dark Energy Survey (DES) and show that the selection bias can be self-consistently constrained at the 10% level. We discuss strategies for applying this approach to real data. We expect that expanding the analysis to smaller scales and using deeper lensing data would further improve the constraints on cluster selection bias.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： This is the second paper in a series whose aim is to predict the power spectrum of intensity and polarized intensity from cosmic reionization fronts. After building the analytic models for intensity and polarized intensity calculations in paper I, here we apply these models to simulations of reionization. We construct a geometric model for identifying front boundaries, calculate the intensity and polarized intensity for each front, and compute a power spectrum of these results. This method was applied to different simulation sizes and resolutions, so we ensure that our results are convergent. We find that the power spectrum of fluctuations at $z=8$ in a bin of width $\Delta z=0.5$ ($\lambda/\Delta\lambda=18$) is $\Delta_\ell \equiv [\ell(\ell+1)C_\ell/2\pi]^{1/2}$ is $3.2\times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the intensity $I$, $7.6\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the $E$-mode polarization, and $5.8\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the $B$-mode polarization at $\ell=1.5\times10^4$. After computing the power spectrum, we compare results to detectable scales and discuss implications for observing this signal based on a proposed experiment. We find that, while fundamental physics does not exclude this kind of mapping from being attainable, an experiment would need to be highly ambitious and require significant advances to make mapping Lyman-$\alpha$ polarization from cosmic reionization fronts a feasible goal.
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