Astrophysics team lights the way for more accurate model of the universe


Date:
October 19, 2020
Source:
University of Texas at Dallas
Summary:
Scientists demonstrated the first use of a method called
self-calibration to remove contamination from gravitational lensing
signals. The results should lead to more accurate cosmological
models of the universe.



FULL STORY ========================================================================== Light from distant galaxies reveals important information about the
nature of the universe and allows scientists to develop high-precision
models of the history, evolution and structure of the cosmos.


==========================================================================
The gravity associated with massive pockets of dark matter that lie
between Earth and these galaxies, however, plays havoc with those
galactic light signals. Gravity distorts galaxies' light -- a process
called gravitational lensing -- and also slightly aligns the galaxies physically, resulting in additional gravitational lensing light signals
that contaminate the true data.

In a study first published Aug. 5 in The Astrophysical Journal Letters, University of Texas at Dallas scientists demonstrated the first use of a
method called self-calibration to remove contamination from gravitational lensing signals. The results should lead to more accurate cosmological
models of the universe, said Dr. Mustapha Ishak-Boushaki, professor
of physics in the School of Natural Sciences and Mathematics and the corresponding author of the study.

"The self-calibration method is something others proposed about 10 years
ago; many thought it was just a theoretical method and moved away from
it," Ishak- Boushaki said. "But I intuitively felt the promise. After
eight years of persistent investigation maturing the method itself,
and then the last two years applying it to the data, it bore fruit with important consequences for cosmological studies." A Lens on the Universe Gravitational lensing is one of the most promising methods in cosmology
to provide information on the parameters that underlie the current model
of the universe.



==========================================================================
"It can help us map the distribution of dark matter and discover
information about the structure of the universe. But the measurement
of such cosmological parameters can be off by as much as 30% if we do
not extract the contamination in the gravitational lensing signal," Ishak-Boushaki said.

Due to the way distant galaxies form and the environment they form in,
they are slightly physically aligned with the dark matter close to
them. This intrinsic alignment generates additional spurious lensing
signals, or a bias, which contaminate the data from the galaxies and
thus skew the measurement of key cosmological parameters, including those
that describe the amount of dark matter and dark energy in the universe
and how fast galaxies move away from each other.

To complicate matters further, there are two types of intrinsic alignment
that require different methods of mitigation. In their study, the research
team used the self-calibration method to extract the nuisance signals
from a type of alignment called intrinsic shape-gravitational shear,
which is the most critical component.

"Our work significantly increases the chances of success to measure
the properties of dark energy in an accurate way, which will allow us
to understand what is causing cosmic acceleration," Ishak-Boushaki
said. "Another impact will be to determine accurately whether
Einstein's general theory of relativity holds at very large scales in
the universe. These are very important questions." Impact on Cosmology
Several large scientific surveys aimed at better understanding the
universe are in the works, and they will gather gravitational lensing
data. These include the Vera C. Rubin Observatory's Legacy Survey of
Space and Time (LSST), the European Space Agency's Euclid mission and
NASA's Nancy Grace Roman Space Telescope.



==========================================================================
"The big winner here will be these upcoming surveys of gravitational
lensing.

We will really be able to get the full potential from them to understand
our universe," said Ishak-Boushaki, who is a member and a convener of
the LSST's Dark Energy Science Collaboration.

The self-calibration method to remove contaminated signals was first
proposed by Dr. Pengjie Zhang, a professor of astronomy at Shanghai Jiao
Tong University and a co-author of the current study.

Ishak-Boushaki further developed the method and introduced it to the realm
of cosmological observations, along with one of his former students,
Michael Troxel MS'11, PhD'14, now an assistant professor of physics at
Duke University.

Since 2012 the research has been supported by two grants to Ishak-Boushaki
from the National Science Foundation (NSF).

"Not everyone was sure that self-calibration would lead to such an
important result. Some colleagues were encouraging; some were skeptical," Ishak-Boushaki said. "I've learned that it pays not to give up. My
intuition was that if it was done right, it would work, and I'm grateful
to the NSF for seeing the promise of this work."

========================================================================== Story Source: Materials provided
by University_of_Texas_at_Dallas. Original written by Amanda
Siegfried. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Eske M. Pedersen, Ji Yao, Mustapha Ishak, Pengjie Zhang. First
Detection
of the GI-type of Intrinsic Alignments of Galaxies Using the Self-
calibration Method in a Photometric Galaxy Survey. The Astrophysical
Journal, 2020; 899 (1): L5 DOI: 10.3847/2041-8213/aba51b ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019164944.htm

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