Simulating the large-scale structure of HI intensity maps

Seehars, Sebastian; Paranjape, Aseem; Witzemann, Amadeus; Réfrégier, Alexandre; Amara, Adam; Akeret, Joël

doi:10.1088/1475-7516/2016/03/001

Cited by 24 publications

(30 citation statements)

References 150 publications

(279 reference statements)

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“…As discussed in the introduction, the shape and amplitude of the function MHI(M, z) is of primary importance for future surveys that aim at putting constraints on the cosmological parameters using intensity mapping. We now compare our findings with the theoretical model of Bagla et al (2010), which has been commonly used in the literature to perform forecasts (Camera et al 2013;Bull et al 2015;Villaescusa-Navarro et al 2014, 2015bCarucci et al 2015;Villaescusa-Navarro et al 2015a) and to create mock 21cm intensity mapping maps (Seehars et al 2015). Bagla et al (2010) proposed a functional form for the MHI(M, z) function as follows…”

Section: Comparison With Theoretical Models and Implications For Intementioning

confidence: 97%

Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

Villaescusa-Navarro¹,

Planelles²,

Borgani³

et al. 2016

Mon. Not. R. Astron. Soc.

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By means of zoom-in hydrodynamic simulations we quantify the amount of neutral hydrogen (HI) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics (SPH), include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split in two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analyzed to account for HI self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter halos monotonically increases with the halo mass and can be well described by a power-law of the form M HI (M, z) ∝ M 3/4 . Our results point out that AGN feedback reduces both the total halo mass and its HI mass, although it is more efficient in removing HI. We conclude that AGN feedback reduces the neutral hydrogen mass of a given halo by ∼ 50%, with a weak dependence on halo mass and redshift. The spatial distribution of neutral hydrogen within halos is also affected by AGN feedback, whose effect is to decrease the fraction of HI that resides in the halo inner regions. By extrapolating our results to halos not resolved in our simulations we derive astrophysical implications from the measurements of Ω HI (z): halos with circular velocities larger than ∼ 25 km/s are needed to host HI in order to reproduce observations. We find that only the model with AGN feedback is capable of reproducing the value of Ω HI b HI derived from available 21cm intensity mapping observations.

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Section: Comparison With Theoretical Models and Implications For Intementioning

confidence: 97%

Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

Villaescusa-Navarro¹,

Planelles²,

Borgani³

et al. 2016

Mon. Not. R. Astron. Soc.

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“…In the above expressions, n(M ) denotes the dark matter halo mass function [taken to have the Sheth-Tormen (Sheth & Tormen 2002) form in the present study], and b(M, z) (Scoccimarro et al 2001) is the corresponding halo bias. From the above expression for the power spectrum, we can define the the angular power spectrum, denoted by C 's (e.g., Battye et al 2012;Seehars et al 2016) which is given by:…”

Section: Fisher Matrix Forecastsmentioning

confidence: 99%

“…Typically, threedimensional analyses of clustering in wide-field surveys require the assumption of an underlying cosmological model. This requirement is circumvented by performing a tomographic analysis with the angular correlation function (or power spectrum) within bins of redshift (e.g., Seehars et al 2016;Nicola et al 2014). Using the angular power spectrum, denoted by C (z), is thus effectively suited to obtaining meaningful cosmological forecasts from an intensity mapping survey.…”

Section: Introductionmentioning

confidence: 99%

Impact of astrophysics on cosmology forecasts for 21 cm surveys

Padmanabhan

Réfrégier

Amara

2019

Monthly Notices of the Royal Astronomical Society

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We use the results of previous work building a halo model formalism for the distribution of neutral hydrogen, along with experimental parameters of future radio facilities, to place forecasts on astrophysical and cosmological parameters from next generation surveys. We consider 21 cm intensity mapping surveys conducted using the BINGO, CHIME, FAST, TianLai, MeerKAT and SKA experimental configurations. We work with the 5-parameter cosmological dataset of {Ω m , σ 8 , h, n s , Ω b } assuming a flat ΛCDM model, and the astrophysical parameters {v c,0 , β} which represent the cutoff and slope of the HI-halo mass relation. We explore (i) quantifying the effects of the astrophysics on the recovery of the cosmological parameters, (ii) the dependence of the cosmological forecasts on the details of the astrophysical parametrization, and (iii) the improvement of the constraints on probing smaller scales in the HI power spectrum. For an SKA I MID intensity mapping survey alone, probing scales up to max = 1000, we find a factor of 1.1 − 1.3 broadening in the constraints on Ω b and Ω m , and of 2.4 − 2.6 on h, n s and σ 8 , if we marginalize over astrophysical parameters without any priors. However, even the prior information coming from the present knowledge of the astrophysics largely alleviates this broadening. These findings do not change significantly on considering an extended HIHM relation, illustrating the robustness of the results to the choice of the astrophysical parametrization. Probing scales up to max = 2000 improves the constraints by factors of 1.5-1.8. The forecasts improve on increasing the number of tomographic redshift bins, saturating, in many cases, with 4 -5 redshift bins. We also forecast constraints for intensity mapping with other experiments, and draw similar conclusions.

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“…Ideally, one would use a calibration of the conditional mass function needed above directly from high-resolution N -body simulations (Angulo et al 2014). In this work, we use the approximation discussed by Seehars et al (2016) which uses the conditional mass function obtained from the ellipsoidal collapse model (Sheth & Tormen 2002). Consider a region (say, a cell in a simulation volume) which has a mass M cell and let δL,0 be the corresponding density contrast in the initial conditions linearly extrapolated to z = 0.…”

Section: Appendix A: Semi-analytical Halo Fieldmentioning

confidence: 99%

“…In the actual simulation, there would be scatter in the value of f coll for the same M cell and δNL. Although this scatter is non-trivial for halo masses approaching the cell size due to mass conservation, for large enough cell sizes it is possible to account for the scatter at a given redshift by simply Poisson-sampling the halo mass function (Sheth & Lemson 1999a,b;Seehars et al 2016). For multiple redshifts, one should in principle generate merger trees to avoid artificial appearance and disappearance of haloes as the density evolves (see, e.g.…”

Section: Appendix A: Semi-analytical Halo Fieldmentioning

confidence: 99%

Photon number conservation and the large-scale 21 cm power spectrum in semi-numerical models of reionization

Choudhury

Paranjape

2019

2019 URSI Asia-Pacific Radio Science Conference (AP-RASC)

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Semi-numerical models of the reionization of neutral hydrogen (HI) based on the excursion set (ES) approach are known to violate photon number conservation at the few per cent level. In this work, we highlight a more severe, previously unrecognized shortcoming of ES models: the large-scale 21 cm power spectrum (equivalently, HI bias b HI ) is a relatively strong function of the spatial resolution used to generate ES ionization maps. We trace this problem to the fact that photon non-conservation in these models arises from a resolution-dependent mixture of spatially resolved, photon non-conserving bubbles, and partially ionized grid cells which are perfectly photon-conserving by construction. We argue that this inevitably leads to a resolutiondependence of b HI , with the correct, converged value only emerging at very coarse resolution. Quantitatively, we find that b HI can be non-converged by as much as ∼ 20-25% in conservative ES implementations with grid sizes ∆x = 5-10h −1 cMpc, even when photon non-conservation is as small as ∼ 3-4%. Thus, although numerically efficient, ES ionization maps coarse enough to produce a converged HI bias would wash out all topological features of the ionization field at scales k 0.05h/cMpc. We therefore present a new, explicitly photon conserving (PC) semi-numerical algorithm which distributes photons isotropically around sources while also accounting for anisotropic overlaps between nearby bubbles. Our PC algorithm predicts a resolution-independent value of b HI consistent with the result of low-resolution ES maps, thus serving as a useful compromise between standard ES implementations and more expensive radiative transfer simulations.

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Simulating the large-scale structure of HI intensity maps

Cited by 24 publications

References 150 publications

Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

Impact of astrophysics on cosmology forecasts for 21 cm surveys

Photon number conservation and the large-scale 21 cm power spectrum in semi-numerical models of reionization

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