From ESO: “Dark Matter Less Influential in Galaxies in Early Universe”

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European Southern Observatory

15 March 2017
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

1
Schematic representation of rotating disc galaxies in the early Universe (right) and the present day (left). Observations with ESO’s Very Large Telescope suggest that such massive star-forming disc galaxies in the early Universe were less influenced by dark matter (shown in red), as it was less concentrated. As a result the outer parts of distant galaxies rotate more slowly than comparable regions of galaxies in the local Universe. Credit: ESO/L. Calçada

2
Schematic representation of rotating disc galaxies in the distant Universe and the present day. Observations with ESO’s Very Large Telescope suggest that such massive star-forming disc galaxies in the early Universe were less influenced by dark matter. As a result the outer parts of distant galaxies rotate more slowly than comparable regions of galaxies in the local Universe. Their rotations curves, rather than being flat, drop with increasing radius. Credit: ESO


Access mp4 video here .
New observations from ESO’s Very Large Telescope have revealed that the outer parts of massive disc galaxies 10 billion years ago were rotating less quickly than the spiral galaxies, like the Milky Way, that we see today. This ESOcast Light summarises the important points of this discovery and the significance of dark matter, and how it is distributed.
The video is available in 4K UHD.
The ESOcast Light is a series of short videos bringing you the wonders of the Universe in bite-sized pieces. The ESOcast Light episodes will not be replacing the standard, longer ESOcasts, but complement them with current astronomy news and images in ESO press releases. Credit: ESO

Editing: Herbert Zodet.
Web and technical support: Mathias André and Raquel Yumi Shida.
Written by: Thomas Barratt and Lauren Fuge.
Music: Jennifer Athena Galatis.
Footage and photos: ESO, The Illustris Project (visualization by Dylan Nelson), L. Calçada and F. Char.
Directed by: Herbert Zodet.
Executive producer: Lars Lindberg Christensen.

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 was published in the journal Nature today.

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.


KMOS


SINFONI

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 information

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)

Links

Research Paper 1
Research Paper 2
Research Paper 3
Research Paper 4

See the full article here .

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