Comparison of rotating disc galaxies in the distant Universe and the present day
Comparison of rotating disc galaxies in the distant Universe and the present day
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ESOcast 100 Light: Dark Matter Less Influential in Early Universe (4K UHD)
Comparison of rotating disc galaxies in the distant Universe and the present day
VLT observations of distant galaxies suggest they were dominated by normal matter
Notes
More Informations
Links
Contacts
Reinhard Genzel
Director, Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Germany
Tel: +49 89 30000 3280
Email: genzel@mpe.mpg.de
Natascha M. Forster Schreiber
Senior Scientist, Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Germany
Tel: +49 89 30000 3524
Email: forster@mpe.mpg.de
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
VLT observations of distant galaxies suggest they were dominated by normal matter
New observations indicate that massive,
star-forming galaxies during the peak epoch of galaxy formation, 10
billion years ago, were dominated by baryonic or “normal” matter. This
is in stark contrast to present-day galaxies, where the effects of
mysterious dark matter seem to be much greater. This surprising result
was obtained using ESO’s Very Large Telescope and suggests that dark
matter was less influential in the early Universe than it is today. The
research is presented in four papers, one of which will be published in
the journal Nature this week.
We see normal matter as brightly shining stars, glowing gas and clouds of dust. But the more elusive dark matter
does not emit, absorb or reflect light and can only be observed via its
gravitational effects. The presence of dark matter can explain why the
outer parts of nearby spiral galaxies rotate more quickly than would be expected if only the normal matter that we can see directly were present [1].
Now, an international team of astronomers led by Reinhard Genzel at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany have used the KMOS and SINFONI instruments at ESO’s Very Large Telescope in Chile [2]
to measure the rotation of six massive, star-forming galaxies in the
distant Universe, at the peak of galaxy formation 10 billion years ago.
What they found was intriguing: unlike spiral galaxies in
the modern Universe, the outer regions of these distant galaxies seem to
be rotating more slowly than regions closer to the core — suggesting
there is less dark matter present than expected [3].
“Surprisingly, the rotation velocities are not constant, but decrease further out in the galaxies,” comments Reinhard Genzel, lead author of the Nature paper. “There
are probably two causes for this. Firstly, most of these early massive
galaxies are strongly dominated by normal matter, with dark matter
playing a much smaller role than in the Local Universe. Secondly, these
early discs were much more turbulent than the spiral galaxies we see in
our cosmic neighbourhood.”
Both effects seem to become more marked as astronomers look further
and further back in time, into the early Universe. This suggests that 3
to 4 billion years after the Big Bang,
the gas in galaxies had already efficiently condensed into flat,
rotating discs, while the dark matter halos surrounding them were much
larger and more spread out. Apparently it took billions of years longer
for dark matter to condense as well, so its dominating effect is only
seen on the rotation velocities of galaxy discs today
This explanation is consistent with observations showing that early
galaxies were much more gas-rich and compact than today’s galaxies.
The six galaxies mapped in this study were among a larger sample of a hundred distant, star-forming discs imaged with the KMOS and SINFONI instruments at ESO’s Very Large Telescope
at the Paranal Observatory in Chile. In addition to the individual
galaxy measurements described above, an average rotation curve was
created by combining the weaker signals from the other galaxies. This
composite curve also showed the same decreasing velocity trend away from
the centres of the galaxies. In addition, two further studies of 240
star forming discs also support these findings.
Detailed modelling shows that while normal matter typically accounts
for about half of the total mass of all galaxies on average, it
completely dominates the dynamics of galaxies at the highest redshifts.
Notes
[1] The disc of a spiral galaxy rotates over a timescale of hundreds
of millions of years. Spiral galaxy cores have high concentrations of
stars, but the density of bright matter decreases towards their
outskirts. If a galaxy’s mass consisted entirely of normal matter, then
the sparser outer regions should rotate more slowly than the dense
regions at the centre. But observations of nearby spiral galaxies show
that their inner and outer parts actually rotate at approximately the
same speed. These “flat rotation curves ” indicate that spiral galaxies must contain large amounts of non-luminous matter in a dark matter halo surrounding the galactic disc.
[2] The data analysed were obtained with the integral field spectrometers KMOS and SINFONI at ESO’s Very Large Telescope
in Chile in the framework of the KMOS3D and SINS/zC-SINF surveys. It is
the first time that such a comprehensive study of the dynamics of a
large number of galaxies spanning the redshift interval from z~0.6 to
2.6, or 5 billion years of cosmic time, has been carried out.
[3] This new result does not call into
question the need for dark matter as a fundamental component of the
Universe or the total amount. Rather it suggests that dark matter was
differently distributed in and around disc galaxies at early times
compared to the present day.
More Informations
This research was presented in a paper entitled “Strongly baryon
dominated disk galaxies at the peak of galaxy formation ten billion
years ago”, by R. Genzel et al., to appear in the journal Nature.
The team is composed of R. Genzel (Max-Planck-Institut für
extraterrestrische Physik, Garching, Germany; University of California,
Berkeley, USA), N.M. Förster Schreiber (Max-Planck-Institut für
extraterrestrische Physik, Garching, Germany), H. Übler
(Max-Planck-Institut für extraterrestrische Physik, Garching, Germany),
P. Lang (Max-Planck-Institut für extraterrestrische Physik, Garching,
Germany), T. Naab (Max-Planck-Institut für Astrophysik, Garching,
Germany), R. Bender (Universitäts-Sternwarte
Ludwig-Maximilians-Universität, München, Germany; Max-Planck-Institut
für extraterrestrische Physik, Garching, Germany), L.J. Tacconi
(Max-Planck-Institut für extraterrestrische Physik, Garching, Germany),
E. Wisnioski (Max-Planck-Institut für extraterrestrische Physik,
Garching, Germany), S.Wuyts (Max-Planck-Institut für extraterrestrische
Physik, Garching, Germany; University of Bath, Bath, UK), T. Alexander
(The Weizmann Institute of Science, Rehovot, Israel), A. Beifiori
(Universitäts-Sternwarte Ludwig-Maximilians-Universität, München,
Germany; Max-Planck-Institut für extraterrestrische Physik, Garching,
Germany), S.Belli (Max-Planck-Institut für extraterrestrische Physik,
Garching, Germany), G. Brammer (Space Telescope Science Institute,
Baltimore, USA), A.Burkert (Max-Planck-Institut für Astrophysik,
Garching, Germany; Max-Planck-Institut für extraterrestrische Physik,
Garching, Germany) C.M. Carollo (Eidgenössische Technische Hochschule,
Zürich, Switzerland), J. Chan (Max-Planck-Institut für
extraterrestrische Physik, Garching, Germany), R. Davies
(Max-Planck-Institut für extraterrestrische Physik, Garching, Germany),
M. Fossati (Max-Planck-Institut für extraterrestrische Physik, Garching,
Germany; Universitäts-Sternwarte Ludwig-Maximilians-Universität,
München, Germany), A. Galametz (Max-Planck-Institut für
extraterrestrische Physik, Garching, Germany; Universitäts-Sternwarte
Ludwig-Maximilians-Universität, München, Germany), S. Genel (Center for
Computational Astrophysics, New York, USA), O. Gerhard
(Max-Planck-Institut für extraterrestrische Physik, Garching, Germany),
D. Lutz (Max-Planck-Institut für extraterrestrische Physik, Garching,
Germany), J.T. Mendel (Max-Planck-Institut für extraterrestrische
Physik, Garching, Germany; Universitäts-Sternwarte
Ludwig-Maximilians-Universität, München, Germany), I. Momcheva (Yale
University, New Haven, USA), E.J. Nelson (Max-Planck-Institut für
extraterrestrische Physik, Garching, Germany; Yale University, New
Haven, USA), A. Renzini (Vicolo dell'Osservatorio 5, Padova, Italy),
R.Saglia (Max-Planck-Institut für extraterrestrische Physik, Garching,
Germany; Universitäts-Sternwarte Ludwig-Maximilians-Universität,
München, Germany), A. Sternberg (Tel Aviv University, Tel Aviv, Israel),
S. Tacchella (Eidgenössische Technische Hochschule, Zürich,
Switzerland), K.Tadaki (Max-Planck-Institut für extraterrestrische
Physik, Garching, Germany) and D. Wilman (Universitäts-Sternwarte
Ludwig-Maximilians-Universität, München, Germany; Max-Planck-Institut
für extraterrestrische Physik, Garching, Germany)
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Links
- Research Paper 1 (Genzel et al., in Nature)
- Research Paper 2
- Research Paper 3
- Research Paper 4
- Photos of the VLT
Contacts
Reinhard Genzel
Director, Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Germany
Tel: +49 89 30000 3280
Email: genzel@mpe.mpg.de
Natascha M. Forster Schreiber
Senior Scientist, Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Germany
Tel: +49 89 30000 3524
Email: forster@mpe.mpg.de
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
