YSM Issue 90.5

FOCUS
astronomy
into many different wavelengths, or colors.
Objects moving away from the Milky Way
emit less intense light and subsequently undergo
a shift in wavelength toward the red
end of the color spectra where wavelengths
are longer. Therefore, a galaxy with a larger
redshift is moving further away. By gathering
this information, the researchers were better
able to understand the position of potential
satellite galaxies, filling in the missing gap in
knowledge about whether these galaxies are
indeed satellites of a central galaxy.
However, using this process to obtain redshifts
comes with its own set of difficulties.
For example, spectroscopy is expensive and
time consuming. In addition, the slower
that a galaxy moves, the fainter and harder
it becomes to detect the redshifts. Though
the research team was able to target over
17,000 redshifts, the spectra obtained may
be not only from galaxies themselves, but
also from stars and other objects. Therefore,
they needed to further filter out the
redshifts corresponding to galaxies from
those caused by other natural phenomena.
To create a more efficient system for detecting
redshifts of galaxies, the researchers
observed the relative wavelengths of satellite
galaxies and their redshift range. They
found a range in which the redshifts were
similar among satellites, indicating that
redshifts in this range were the most likely
to correspond to satellite galaxies. By going
back over their collected sample of redshifts
and selecting redshifts that fell within
the “satellite galaxy” range, they were able
to leave out redshift data from unwanted
sources. Using this refined redshift information,
researchers were able to locate 25
satellites from analog galaxies, providing
us a new perspective on the nature of many
potential satellite galaxies in the universe.
The SAGA continues
IMAGE COURTESY OF NASA
►The Milky Way Galaxy has long been studied,
and houses numerous satellite galaxies.
While the study has surprised the research
team, there still remains much to
uncover, and they are just getting started.
The team is leading in this field—there
is no other research team doing such an
ambitious project. Once the SAGA is completed,
scientists will better understand
the Milky Way from a cosmological standpoint
and how it compares to other analogs.
“We’re really proud of the progress
we made and we are well underway in answering
the question of how atypical our
galaxy may be,” Geha said.
With a goal of analyzing 100 analog
IMAGE COURTESY OF WIKIMEDIA COMMONS
►Using optical telescopes, more than
10,000 distant galaxies can be seen.
galaxies similar to the Milky Way, the researchers
are already analyzing the data
of other analogs for their satellites. With
more efficient methods for detecting redshifts,
the team can more effectively locate
even the faintest satellites. While Geha is
not certain what the rest of their data will
indicate once they finish analyzing all satellite
galaxies, she believes it might take as
few as two to four years to finish the survey
and make more conclusions. “Once
the SAGA Survey is complete, I think
we will really understand our galaxy in a
much broader context,” Geha said. Until
then, the SAGA continues in uncovering
the mystery of our galaxy.
ABOUT THE AUTHOR
JESSICA TRINH
The Milky Way Galaxy—an outlier?
The process of obtaining redshift information
to determine satellite galaxies is
a slow process, but it comes with a great
payoff. The team’s analyses of these satellite
galaxies have revealed an interesting finding:
the analog galaxies contain mostly star
forming satellite galaxies. Unlike the Milky
Way, the results from the 8 analog galaxies
indicated 26 of the 27 satellite galaxies are
actively forming stars. “If more information
supports this finding, we need to start
reevaluating how we view our own satellite
galaxies in the Milky Way,” Wechsler said.
JESSICA TRINH is a sophomore Neuroscience major in Branford College.
She is the Vice President of Synapse and is excited to teach middle schoolers
about STEM. She also teaches health education in New Haven middle schools,
nutrition counseling at HAVEN Free Clinic, and is currently leading a research
project on nutrition.
THE AUTHOR WOULD LIKE TO THANK Dr. Marla Geha and Dr. Risa
Wechsler for their time and enthusiasm for sharing their research.
FURTHER READING
Geha, M., Wechsler, R.H., Mao, Y.Y., et al. 2017. “The SAGA Survey I: Satellite
Galaxy Populations Around Eight Milky Way Analogs. The Astrophys. J. 847, 1-21.
Geha, M., Wechsler, R.H., Bernstein, R., et al. 2017. The SAGA Survey.
Retrieved from http://sagasurvey.org
14 Yale Scientific Magazine December 2017 www.yalescientific.org