SIMULATING 21CM SKY

Atsushi J. Nishizawa (Nagoya) Kiyotomo Ichiki (Nagoya) Rika Ando (Nagoya)

HI AS A PROBE OF LARGE-SCALE STRUCTURE

Robertson+ ’13

dark

mat

ter h

alo

HI d

ensit

y

z=1

CMB-LENSING IS USEFUL FOR HI

redshift

CMB

Lens

ing

kern

el

EoR

post-EoR decoupling

⌃⇤�1cr (�) =

(�⇤ � �)�

�⇤

• Lensing efficiency for CMB lensing

• It has a maximum at the post-EoR

•Kernel Matches

h(aHIlm + aFGlm )almi = h(aHI

lmalmi = C�HIl

• CMB lens and Galactic foreground is NOT correlated each other

• We are free from the FG!!

•Foreground

-> 田中君のトーク (Tanaka, [AJN]+ 2019)

CMB /Z z⇤

0

dz

H(z)(1 + z)⌃⇤�1

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IS FOREGROUND REALLY NOT THE PROBLEM?

Santos+’05

Gal. Synchrotron

Ext. Gal. PS

Gal. Free-Free

Ext. Gal. F-F

21cm signal

6 orders larger!!

• How much is the effect of foreground on the cross correlation?

• To what extent we need to consider the foreground removal?

SIMULATION - DARK MATTER -• Use Takahashi+ 2017 ray tracing simulation for CMB lensing and DM

★

…

… L=450Mpc/h

14L=6.5Gpc/h

z=7.1

z=1100

……..random Gaussian

• redshift shell 150Mpc/h • source redshifts are

equally spanned from 0.051 to 5.342 (w 150Mpc/h width) and additionally zs=1100

• outputs

�2Dcdm(n, zi)

(n, zi)

CMB(n)

halo(x, M)

SIMULATION - HI PASTING -• HI is pasted to the DM distribution (calibrated with Illustris TNG)

• linear bias • MHI-Mh relation (fitting, scatter, …) • more complex modeling…

�Tb =3

32⇡

hc3A10

kBmp⌫221

(1 + z)2

H(z)⇢̄HI�HI(n, z)

Ando, AJN+ 2019Villaescusa-Navaro+ 2018 (Illustris TNG)

MHI(Mh, z) = M0

✓Mh

Mmin

◆↵

exp

✓�Mmin

Mh

◆�HI = bHI ? �cdm

• linear bias approximation is only valid on large scales (k<0.2 h/Mpc)

SIMULATION - MAPS AND AUTO SPECTRA -

CMB lensing map

Brightness temperature map @ z=1

`(`+ 1)C`

1 10 102 103

`(`+ 1)CHI` [mK2]

ANTENNA NOISE• We approximate the noise as white spectrum • values quoted from Bull et al. 2015 • assume SKA interferometer covers 20,000 deg2 in 10,000 hours • SKA-MID (Wide: Band 1) specifications • Tsys = Tinst + Tsky ~ 20 + 60*(300MHz/nu)^2.5 [K] • generate noise map with random-Gaussian

CN=

T 2

sys

⌫21

ttot

�4Asky

A2

eFoV

1

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100 101 102 103

multipole `

10�5

10�4

10�3

10�2

10�1

100

`(`

+1)

C`

[mK

2 ]

simulated HI @ z=1.0

SKA-MID1 (Intef.) noise

`(`+ 1)CHI` [mK]2

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`(`+ 1)C�HI` [mK]

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GALACTIC FOREGROUND• So far, Galactic synchrotron radiation (most dominant) only, but others are

straightforward to implement. • FG map is based on the Haslam template w/ finer structures from random

Gaussian under position dependent power spectrum. • publicly available code CRIME (Aronso+ 2014)

synchrotron map @ 700 MHz

CROSS CORRELATION• Cross correlation signal is highly contaminated. • it is expected consistent with “zero” but with a huge scatter. • despite the null signal, we anyway need to reduce the level of foreground

CL^HI-KAPPA W/O

FOREGROUND REMOVAL

anything within the error bar can be a statistical fluke!

�2CHI` =

[CHI` ]2 + [C

` +N` ][C

HI` +NHI

` +NFG` ]

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huge!!

IDEAL FOREGROUND REMOVAL• assume that the FG can be removed at %

�T obs

b = �T 21cm

b + (1� ↵)�TFG

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• FG should be removed at 99.9%

CL^HI-KAPPA W/O

FOREGROUND REMOVAL

MASKING?• Half of the sky where the FG is significant is masked (>~100K) • Even after masking, the FG should be removed up to 99.5%

CL^HI-KAPPA W/O

FOREGROUND REMOVAL

SUMMARY• we consider the x-correlation of HI with CMB-lensing

• HI-CMBLens may be the most efficient way to extract cosmological information.

• HI-CMBLens has been expected to be free from FG

• Signal, Noise and FG are all simulated

• To find the signal, FG should be removed at 99.9% (99.5% if half masked)

— Future plan —

• Apply real FG removal method

• Include CMB Lens noise

• use more complex (realistic) HI-pasting model