In
1969, the astrophysicists Rashid Sunyaev and Yakov Zel'dovich realized
that the then recently discovered cosmic microwave background radiation
(CMBR) would be distorted by hot cosmic gas. Hot electrons in the
intergalactic medium preferentially scatter the light in one direction,
causing a change in the brightness of the CMBR towards clusters of
galaxies where electrons should be abundant. They showed that the
effect would reveal the large-scale structure of the universe, the
nature of the CMBR, cosmological parameters like the Hubble constant,
and physical conditions in galaxy clusters.
The effect, now known as the effect (SZSunyaev-Zel'dovich E), was
first spotted in 1978 after much searching. Both space- and ground-based
instruments, including the Planck satellite, the South Pole Telescope
(SPT), and others have released new catalogs of galaxy clusters selected
using the SZE. CfA astronomers Matt Ashby, Matt Bayliss, Richard
Foley, Christine Jones, Steve Murray, Brian Stalder, Tony Stark, and
Alexey Vikhlinin were part of a large team that used the SPT to examine
the SZE signatures of forty-six X-ray selected groups and clusters of
galaxies. The X-ray observations are some of the most sensitive ever
used to search for clusters; the most distant of the galaxy clusters
detected to date from a cosmic epoch six billion years after the big
bang.
The team reports generally very good agreement between the
cosmological parameters they measure and those reported by other means,
in particular the latest results from the Planck satellite study of the
CMBR. However the agreement is not perfect: the team reports an
unexpectedly weak SZE signal for less massive galaxy clusters. Although
they did identify and measure several potential sources of
contamination, the discrepancy is not easily explained away. They
suggest one possibility: dust within the clusters is reducing the SZE
signal. For now, the reason remains unknown; this mystery will be
addressed in subsequent, deeper, more sensitive SZE observations planned
for the SPT.
Reference(s):
"Analysis of Sunyaev–Zel'dovich Effect Mass–Observable Relations Using
South Pole Telescope Observations of an X-ray Selected Sample of
Low-Mass Galaxy Clusters and Groups," J. Liu et al., MNRAS, 448, 2085, 2015