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The Simons Observatory

Analysis of Small Aperture Telescopes

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Tomoki Terasaki (UTokyo)

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Cosmic Microwave Background

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How did the Universe start?

- Primordial Gravitational Wave　

What is the dark matter/energy?

• ΛCDM parameters

Other cosmological questions

- Mass of neutrino, SZ-effect, transients

Large angular scale observation

High resolution observation

Credit: ESO

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The Simons Observatory

Next generation’s CMB experiment

• Organized 2016, deployed 2023

Members

• >400 researchers from >90 institutes

Site

• Cerro Toco, Atacama, Chile @5,200 m elevation

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Small and Large Aperture Telescopes

SAT

LAT

Large angular scale observation

High resolution observation

• 42-cm aperture
• FOV: 35 deg
• # of detectors in total
• ~ 30,000 (nominal 3 SATs)
• ~ 60,000 (+ 1 x JP & 2 x UK)

• 6-m aperture of primary mirror

SAT receiver

(Galitzki et al 2024)

LAT receiver

(Zhu et al 2021)

arXiv:2405.05550

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B-mode search

nK-order signal

- Large number of high-sensitivity detectors

Large angular scale

- Overcome atmospheric fluctuation

Multipole moment ℓ

Angle scale of pattern

0.1 deg

1 deg

10 deg

Our goal

Large angular scale

Challenges

Current measurements of B-modes

Compiled by Y. Chinone

r = 0.01

r = 0

nK-order

signal

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SAT instruments for B-modes

Focal plane (backside)

w/ 12096 optical dets

High-density, high-sensitivity focal plane

• Background-limited sensitivity
• Microwave multiplexing readout
• 910 multiplex readout

Broadband HWP

SC-Mag. bearing

Polarization Modulator

Half Wave Plate

• 3 stacked sapphire + AR coating

Superconducting magnetic bearing

• Continuous rotation at 2Hz

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Polarization is up-converted to ~8Hz

• Avoid atmospheric fluctuation (~1Hz)

One Pixel

(Dichroic&dual-pol.)

35 cm

6 mm

50 cm

SAT receiver

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SAT array for B-modes

90/150 GHz (MF)

220/280 GHz (UHF)

30/40 GHz (LF)

+ two more under development

Frequency [GHz]

RMS of Brightness [μKRJ]

Spectrum of CMB and foregrounds

under development

> 60,000!!

B. Prasad (13102-71)

M. Higuchi (13102-181)

The first 3 SATs (MF1, MF2, and UHF) has been deployed in the past year!

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SAT Deployment Summary

In-lab run

Deployment: Integrate, system checkout

Commissioning: Measure performance

SAT-MF1

(90/150 GHz)

SAT-MF2

(90/150 GHz)

SAT-UHF

(220/280 GHz)

• First light Oct 2023

- First light Dec 2023

- Mounted on platform 　Apr 2024

Apr 2023

Jul

Oct

Jan 2024

Apr

Pre-deployment test

Pre-deployment test

Pre-deployment test

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Analysis procedure (Very Simple)

Calibration

Observation

TOD analysis

Map-making

Power Spectrum

Pointing, relative gain, and detector angle

1hour observation with constant elevation scan with el = 50/60 deg and Δaz=40 deg

Demodulate the TOD as it is modulated by HWP

And apply TOD filtering to mitigate any systematics.

Reconstruct the map with the pointing and timestamp information.

Coadd maps from many observations and calculate the power spectrum.

Early results 1 (Beam and pointing)

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Consistent with the design values.

(90 GHz) FWHM=27.4’

(150 GHz) FWHM=17.6’

Pointing of

active detectors

(SAT-MF2)

First Light of Jupiter

(SAT-MF1)

90 GHz band

150 GHz band

Achieving our goal of yield (80%).

Most of detectors are background limited.

[deg]

[deg]

preliminary

preliminary

preliminary

preliminary

Early results 2 (Polarization)

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Credit: H.Nakata

Demodulation of linear polarization

Noise spectrum of demodulated signal

Demodulation of polarized signal is working well. For angle calibration with wiregrid see↓

The spectrum is white in the frequency range of > 3 mHz

🡺 Little mode loss even at lowest multipole moment (ℓ)

preliminary

preliminary

Early results 3 (Galactic plane)

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j

Galactic longitude [deg]

Galactic latitude [deg]

SO

Planck

Q

U

Planck NPIPE (2020)

preliminary

preliminary

Summary

• SO SATs started observation!!
• The analysis is very simple thanks to the HWPs!!
• Great maps (and power spectra) are coming out! Stay tuned!
• Systematic study are going on.

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