Open Access Publications from the University of California

## Measurements of Secodary Cosmic Microwave Background Anisotropies with the South Pole Telescope

Abstract

The South Pole Telescope is a 10m millimeter-wavelength telescope for finding

galaxy clusters via the thermal Sunyaev-Zel'dovich (tSZ) effect. This thesis is divided into two parts. The

first part describes the development of the kilopixel SPT-SZ receiver and the frequency-domain multiplexor

(fMUX). The second part describes the first SPT power spectrum measurement and the first detection of the

tSZ power spectrum.

The SPT-SZ focal plane consists of 960 spiderweb coupled transition-edge sensors. Due to strong electro-

thermal feedback, these devices have good sensitivity and linearity, though risk spontaneous oscillations.

Adding heat capacity to these devices can ensure stability, so long as the loopgain, $\mathcal{L}$, is less

than $G_\textrm{int}/G_0$, the ratio between the thermal conductances linking the TES to the heat capacity

and linking the heat capacity to the bath. I describe as experimental technique for measuring the

internal thermal structure of these devices, allowing for rapid sensor evaluation.

The fMUX readout system reduces wiring complexity in this receiver by AC-biasing each sensor at a unique

frequency and sending signals from multiple bolometers along one pair of wires. The Series SQUID Arrays

(SSAs) used to read changes in bolometer current are notably non-linear and extremely sensititve to ambient

magnetic fields. The SSAs are housed in compact magnetic shielding modules which reduces their effective

area to 80 $\textrm{m}\Phi_0/\textrm{gauss}$. The SSA are fedback with a flux-locked loop to improve their

linearity and dynamic range, and decrease their input reactance. The FLL is bandwidth of 1 MHz with a

measured loopgain of 10. In the current implementation, this bandwidth is limited between the SQUID input

coil and other reactances, which I study in Chapter \ref{chap:fllstab}.

In the second part of the thesis I present power spectrum measurements for the first 100~deg$^2$ field observed by the SPT. On angular scales where the primary CMB anisotropy is dominant,

$\ell \lesssim 3000$, the SPT power spectrum is consistent with the standard

$\Lambda$CDM cosmology. On smaller scales, we see strong evidence for

a point source contribution, consisteThe South Pole Telescope is a 10m millimeter-wavelength telescope for finding

galaxy clusters via the thermal Sunyaev-Zel'dovich (tSZ) effect. This thesis is divided into two parts. The

first part describes the development of the kilopixel SPT-SZ receiver and the frequency-domain multiplexor

(fMUX). The second part describes the first SPT power spectrum measurement and the first detection of the

tSZ power spectrum.

The SPT-SZ focal plane consists of 960 spiderweb coupled transition-edge sensors. Due to strong electro-

thermal feedback, these devices have good sensitivity and linearity, though risk spontaneous oscillations.

Adding heat capacity to these devices can ensure stability, so long as the loopgain, $\mathcal{L}$, is less

than $G_\textrm{int}/G_0$, the ratio between the thermal conductances linking the TES to the heat capacity

and linking the heat capacity to the bath. I describe as experimental technique for measuring the

internal thermal structure of these devices, allowing for rapid sensor evaluation.

The fMUX readout system reduces wiring complexity in this receiver by AC-biasing each sensor at a unique

frequency and sending signals from multiple bolometers along one pair of wires. The Series SQUID Arrays

(SSAs) used to read changes in bolometer current are notably non-linear and extremely sensititve to ambient

magnetic fields. The SSAs are housed in compact magnetic shielding modules which reduces their effective

area to 80 $\textrm{m}\Phi_0/\textrm{gauss}$. The SSA are fedback with a flux-locked loop to improve their

linearity and dynamic range, and decrease their input reactance. The FLL is bandwidth of 1 MHz with a

measured loopgain of 10. In the current implementation, this bandwidth is limited between the SQUID input

coil and other reactances, which I study in Chapter \ref{chap:fllstab}.

In the second part of the thesis I present power spectrum measurements for the first 100~deg$^2$ field observed by the SPT. On angular scales where the primary CMB anisotropy is dominant,

$\ell \lesssim 3000$, the SPT power spectrum is consistent with the standard

$\Lambda$CDM cosmology. On smaller scales, we see strong evidence for

a point source contribution, consistent with a population of dusty, star-forming galaxies.

I combine the 150 and 220$\,$GHz data to remove the majority of the point source power,

and use the point source subtracted spectrum to detect Sunyaev-Zel'dovich (SZ) power at $2.6 \,\sigma$. At $\ell=3000$, the SZ power in the subtracted bandpowers is $4.2\,$$\pm$$\,1.5\, \mu\rm{K}^2$, which is significantly lower than the power predicted by a

fiducial model using WMAP5 cosmological parameters. t with a population of dusty, star-forming galaxies.

I combine the 150 and 220$\,$GHz data to remove the majority of the point source power,

and use the point source subtracted spectrum to detect Sunyaev-Zel'dovich (SZ) power at $2.6 \,\sigma$. At $\ell=3000$, the SZ power in the subtracted bandpowers is $4.2\,$$\pm$$\,1.5\, \mu\rm{K}^2$, which is significantly lower than the power predicted by a

fiducial model using WMAP5 cosmological parameters.