SZFitter

Abstract

Galaxy clusters are some of the largest
known structures in the universe. Studying them observationally and
theoretically can provide a lot of information on how these clusters form and
are structured. One way to study them is through the so-called
Sunyaev-Zel’dovich (SZ) effect, which is an interaction between the cosmic
microwave background (CMB) and hot electrons in the cluster medium. The SZ effect
can be further broken down into a thermal component (tSZ) arising from the
random motion of the electrons, and a kinematic component (kSZ) arising from
the bulk motion of the cluster medium, making it a good probe for several
properties of the cluster. The SZ effect can be observed as a distortion of the
CMB spectrum using submillimeter spectrometry. However, at many submillimeter
frequencies radiation is absorbed strongly by the atmosphere. This makes it
hard to interpret the measured SZ signal, and measurements require long
observation times in order to reach a sufficient signal-to-noise ratio. In this
thesis, we present a framework that simulates a submillimeter spectrometer
observation of the tSZ effect including noise factors. It then fits a model tSZ
signal to the noisy signal. This allows us to investigate the relation between
observation time, noise and retrievability of cluster properties. We simulate a
galaxy cluster with an electron temperature 𝑇𝑒 = 15.3 keV and central optical depth 𝜏𝑒 = 0.0172 with two simulated DESHIMA-type filterbanks spanning
different frequency ranges. For each filterbank we perform 20 simulations with
an observation time of 16 hours each, and 20 simulations of 32 hours. We fit
every simulation separately, but average over simulations to obtain an
expectation value for 𝑇𝑒
and 𝜏𝑒 given a filterbank
and observation time. We also repeat each fit over rebinned copies of the noisy
spectra, combining 7 data points into each bin. All tested combinations of
filterbanks and observation times produce fits with results that are consistent
with the input parameters. The 160-320 GHz filterbank consistently gives lower
errors than the 220-440 GHz filterbank. From rebinning, we do not find any
significant improvement or degradation of the quality of the fits. The
estimates obtained from rebinned data deviate very little from the original
estimates, by at most 5%, and show no change in consistency. From this result,
we conclude that SZ observations using DESHIMA 2.0 could provide estimates on cluster
parameters. These estimates are already consistent after 16 or 32 hours of
observation time. However, we recommend a new filterbank design that covers
160-320 GHz since the error on estimates using this range are smaller than the
errors obtained using the original 220-440 GHz filterbank. This is likely due
to the atmosphere absorbing much less radiation at this frequency range.
Additionally, the results from rebinning show that this new filterbank could
contain fewer filters with a lower resolving power without degradation of fit
quality.