Astronomers used the Atacama Large Millimeter/submillimeter Array
(ALMA) to identify 39 faint galaxies that are not seen with the Hubble
Space Telescope’s most in-depth view of the Universe, 10 billion
light-years away. They are ten times more numerous than similarly
massive but optically–bright galaxies detected with Hubble. The research
team assumes that these faint galaxies precede massive elliptical
galaxies in the present Universe. However, no significant theories for
the evolution of the Universe have predicted such an abundant population
of star-forming, dark, massive galaxies. The new ALMA results throw
into question our understanding of the early Universe. These results
appear in the latest issue of the journal Nature.
“Previous studies have found extremely active star-forming galaxies
in the early Universe, but their population is quite limited,” says Tao
Wang, lead author of this research at the University of Tokyo, the
French Alternative Energies and Atomic Energy Commission (CEA), and the
National Astronomical Observatory of Japan (NAOJ). “Star formation in
the dark galaxies we identified is less intense, but they are 100 times
more abundant than the extreme starbursts. It is important to study such
a major component of the history of the Universe to comprehend galaxy
formation.”
Wang and his team targeted three ALMA windows to the deep Universe
opened up by the Hubble Space Telescope (HST): the CANDELS fields. The
team discovered 63 extremely red objects in the infrared images taken by
NASA’s Spitzer Space Telescope: they are too red to be detected with
HST. However, Spitzer’s limited spatial resolution prevented astronomers
from identifying their nature.
ALMA detected submillimeter-wave emission from 39 out of the 63 extremely red objects. Thanks to its high resolution and sensitivity, ALMA confirmed that they are massive, star-forming galaxies that are producing stars 100 times more efficiently than the Milky Way. These galaxies are representative of the majority of massive galaxies in the Universe 10 billion years ago, most of which have so far been missed by previous studies.
“By maintaining this rate of star formation, these ALMA-detected
galaxies will likely transform into the first population of massive
elliptical galaxies formed in the early Universe,” says David Elbaz, an
astronomer at CEA, and coauthor on the paper, “But there is a problem.
They are unexpectedly abundant.” The researchers estimated their number
density to be equivalent to 530 objects in a square degree in the sky.
This number density well exceeds predictions from current theoretical
models and computer simulations. Also, according to the widely accepted
model of the Universe with a particular type of dark matter, it is
challenging to build a large number of massive objects in such an early
phase of the Universe. Together, the present ALMA results challenge our
current understanding of the evolution of the Universe.
“Like the galaxy M87, from which astronomers recently obtained the
first-ever image of a black hole, massive elliptical galaxies are
located in the heart of galaxy clusters. Scientist believes that these
galaxies formed most of their stars in the early Universe,” explains
Kotaro Kohno, a professor at the University of Tokyo and member of the
research team. “However, previous searches for the progenitors of these
massive galaxies have been unsuccessful because they were based solely
on galaxies that are easily detectable by HST. The discovery of this
large number of massive, HST-dark galaxies provides direct evidence for
the early assembly of massive galaxies during the first billion years of
the Universe.” More detailed follow-up observations with ALMA and
NASA’s James Webb Space Telescope are essential to provide further
insights into the nature of these galaxies. New studies could enable a
complete view of galaxy formation in the early Universe.”
Contacts
Tao Wang
Postdoctoral fellow
Institute of Astronomy, The University of Tokyo / National Astronomical Observatory of Japan
Email: taowang@ioa.s.u-tokyo.ac.jp
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Masaaki Hiramatsuv Education and Public Outreach Officer, NAOJ Chilev Observatory , Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp
Mariya Lyubenova
ESO Outreach Astronomer
Garching bei München, Germany
Phone: +49 89 32 00 61 88
Email: mlyubeno@eso.org
Iris Nijman
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Cell phone: +1 (434) 249 3423
Email: alma-pr@nrao.edu
Additional Information
Contacts
Tao Wang
Postdoctoral fellow
Institute of Astronomy, The University of Tokyo / National Astronomical Observatory of Japan
Email: taowang@ioa.s.u-tokyo.ac.jp
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Masaaki Hiramatsuv Education and Public Outreach Officer, NAOJ Chilev Observatory , Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp
Mariya Lyubenova
ESO Outreach Astronomer
Garching bei München, Germany
Phone: +49 89 32 00 61 88
Email: mlyubeno@eso.org
Iris Nijman
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Cell phone: +1 (434) 249 3423
Email: alma-pr@nrao.edu
Additional Information
These observation results are published as T. Wang et al. “A dominant
population of optically invisible massive galaxies in the early
Universe” in Nature on August 7, 2019.
The research team members are:
T. Wang (The University of Tokyo/CEA/National Astronomical Observatory
of Japan), C. Schreiber (CEA/Leiden University/Oxford University), D.
Elbaz (CEA), Y. Yoshimura (The University of Tokyo), K. Kohno (The
University of Tokyo), X. Shu (Anhui Normal University), Y. Yamaguchi
(The University of Tokyo), M. Pannella
(Ludwig-Maximilians-Universitat,), M. Franco (CEA), J. Huang (National
Astronomical Observatories of China), C.-F. Lim (Academia Sinica
Institute of Astronomy and Astrophysics), and W.-H. Wang (Academia
Sinica Institute of Astronomy and Astrophysics).
This research was supported by NAOJ ALMA Scientific Research Grant
Number 2017-06B, JSPS KAKENHI (No. JP17H06130), funding from the
European Union Seventh Framework Program (FP7/2007-2013) under grant
agreement No. 312725 (ASTRODEEP), NSFC 11573001, National Basic Research
Program 2015CB857005, and Ministry of Science and Technology of Taiwan
Grant (105-2112-M-001-029-MY3).
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of the European
Organisation for Astronomical Research in the Southern Hemisphere (ESO),
the U.S. National Science Foundation (NSF) and the National Institutes
of Natural Sciences (NINS) of Japan in cooperation with the Republic of
Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
Ministry of Science and Technology (MOST) and by NINS in cooperation
with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and
Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its
Member States; by the National Radio Astronomy Observatory (NRAO),
managed by Associated Universities, Inc. (AUI), on behalf of North
America; and by the National Astronomical Observatory of Japan (NAOJ) on
behalf of East Asia. The Joint ALMA Observatory (JAO) provides the
unified leadership and management of the construction, commissioning,
and operation of ALMA.
