Colour image of galaxy cluster MCS J0416.1–2403, annotated
Mass map of galaxy cluster MCS J0416.1–2403 using strong and weak lensing
Stunning new observations from Frontier Fields
Astronomers using the NASA/ESA Hubble Space Telescope have mapped the mass within a galaxy cluster more precisely than ever before. Created using observations from Hubble's Frontier Fields observing programme, the map shows the amount and distribution of mass within MCS J0416.1–2403, a massive galaxy cluster found to be 160 trillion times the mass of the Sun. The detail in this mass map was made possible thanks to the unprecedented depth of data provided by new Hubble observations, and the cosmic phenomenon known as strong gravitational lensing.
Measuring the amount and distribution of mass within distant objects
in the Universe can be very difficult. A trick often used by astronomers
is to explore the contents of large clusters of galaxies by studying
the gravitational effects they have on the light from very distant
objects beyond them. This is one of the main goals of Hubble's Frontier Fields,
an ambitious observing programme scanning six different galaxy clusters
— including MCS J0416.1–2403, the cluster shown in this stunning new
image [1].
Large clumps of mass in the Universe warp and distort the space-time
around them. Acting like lenses, they appear to magnify and bend light
that travels through them from more distant objects [2].
Despite their large masses, the effect of galaxy clusters on their
surroundings is usually quite minimal. For the most part they cause what
is known as weak lensing,
making even more distant sources appear as only slightly more
elliptical or smeared across the sky. However, when the cluster is large
and dense enough and the alignment of cluster and distant object is
just right, the effects can be more dramatic. The images of normal
galaxies can be transformed into rings and sweeping arcs of light, even
appearing several times within the same image. This effect is known as strong lensing,
and it is this phenomenon, seen around the six galaxy clusters targeted
by the Frontier Fields programme, that has been used to map the mass
distribution of MCS J0416.1–2403, using the new Hubble data.
"The depth of the data lets us see very faint objects and has
allowed us to identify more strongly lensed galaxies than ever before,"
explains Mathilde Jauzac of Durham University, UK, and Astrophysics
& Cosmology Research Unit, South Africa, lead author of the new
Frontier Fields paper. "Even though strong lensing magnifies the
background galaxies they are still very far away and very faint. The
depth of these data means that we can identify incredibly distant
background galaxies. We now know of more than four times as many
strongly lensed galaxies in the cluster than we did before."
Using Hubble's Advanced Camera for Surveys,
the astronomers identified 51 new multiply imaged galaxies around the
cluster, quadrupling the number found in previous surveys and bringing
the grand total of lensed galaxies to 68. Because these galaxies are
seen several times this equates to almost 200 individual strongly lensed
images which can be seen across the frame. This effect has allowed
Jauzac and her colleagues to calculate the distribution of visible and
dark matter in the cluster and produce a highly constrained map of its
mass [3].
"Although we’ve known how to map the mass of a cluster using
strong lensing for more than twenty years, it’s taken a long time to get
telescopes that can make sufficiently deep and sharp observations, and
for our models to become sophisticated enough for us to map, in such
unprecedented detail, a system as complicated as MCS J0416.1–2403," says team member Jean-Paul Kneib.
By studying 57 of the most reliably and clearly lensed galaxies, the
astronomers modelled the mass of both normal and dark matter within MCS
J0416.1-2403. "Our map is twice as good as any previous models of this cluster!" adds Jauzac.
The total mass within MCS J0416.1-2403 — modelled to be over 650 000
light-years across — was found to be 160 trillion times the mass of the
Sun. This measurement is several times more precise than any other
cluster map, and is the most precise ever produced [4].
By precisely pinpointing where the mass resides within clusters like
this one, the astronomers are also measuring the warping of space-time
with high precision.
"Frontier Fields' observations and gravitational lensing
techniques have opened up a way to very precisely characterise distant
objects — in this case a cluster so far away that its light has taken
four and a half billion years to reach us," adds Jean-Paul Kneib. "But,
we will not stop here. To get a full picture of the mass we need to
include weak lensing measurements too. Whilst it can only give a rough
estimate of the inner core mass of a cluster, weak lensing provides
valuable information about the mass surrounding the cluster core."
The team will continue to study the cluster using ultra-deep Hubble
imaging and detailed strong and weak lensing information to map the
outer regions of the cluster as well as its inner core, and will thus be
able to detect substructures in the cluster's surroundings. They will
also take advantage of X-ray measurements of hot gas and spectroscopic
redshifts to map the contents of the cluster, evaluating the respective
contribution of dark matter, gas and stars [5].
Combining these sources of data will further enhance the detail of
this mass distribution map, showing it in 3D and including the relative
velocities of the galaxies within it. This paves the way to
understanding the history and evolution of this galaxy cluster.
The results of the study will be published online in Monthly Notices of the Royal Astronomical Society on 24 July 2014.
Notes
[1] The cluster is also known as MACS J0416.1–2403.
[2] The warping of space-time by large objects in the
Universe was one of the predictions of Albert Einstein’s theory of
general relativity.
[3] Gravitational lensing is one of the few methods
astronomers have to find out about dark matter. Dark matter, which makes
up around three quarters of all matter in the Universe, cannot be seen
directly as it does not emit or reflect any light, and can pass through
other matter without friction (it is collisionless). It interacts only
by gravity, and its presence must be deduced from its gravitational
effects.
[4] The uncertainty on the measurement is only around
0.5%, or 1 trillion times the mass of the sun. This may not seem
precise but it is for a measurement such as this.
[5] NASA's Chandra X-ray Observatory
was used to obtain X-ray measurements of hot gas in the cluster and
ground based observatories provide the data needed to measure
spectroscopic redshifts.
Notes for editors
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The international team of astronomers in this study consists of M. Jauzac (Durham University, UK and Astrophysics & Cosmology Research Unit, South Africa);
B. Clement (University of Arizona, USA); M. Limousin (Laboratoire
d’Astrophysique de Marseille, France and University of Copenhagen,
Denmark); J. Richard (Université Lyon, France); E. Jullo (Laboratoire
d’Astrophysique de Marseille, France); H. Ebeling (University of Hawaii,
USA); H. Atek (Ecole Polytechnique Fédérale de Lausanne, Switzerland);
J.-P. Kneib (Ecole Polytechnique Fédérale de Lausanne, Switzerland and
Laboratoire d’Astrophysique de Marseille, France); K. Knowles
(University of KwaZulu-Natal, South Africa); P. Natarajan (Yale
University, USA); D. Eckert (University of Geneva, Switzerland); E.
Egami (University of Arizona, USA); R. Massey (Durham University, UK);
and M. Rexroth (Ecole Polytechnique Fédérale de Lausanne, Switzerland).
More information
Image credit: ESA/Hubble, NASA, HST Frontier Fields
Acknowledgement: Mathilde Jauzac (Durham University, UK and Astrophysics & Cosmology Research Unit, South Africa) and Jean-Paul Kneib (École Polytechnique Fédérale de Lausanne, Switzerland)
Links
- Images of Hubble
- Paper in Monthly Notices of the Royal Astronomical Society
- Science paper
- University of Hawaii Institute for Astronomy press release
Contacts
Mathilde JauzacDurham University, Institute for Computational Cosmology
Durham, United Kingdom
Tel: +33 6 52 67 15 39 (France)
Cell: +44 7445 218614 (UK)
Email: mathilde.jauzac@dur.ac.uk
Jean-Paul Kneib
École Polytechnique Fédérale de Lausanne, Observatoire de Sauverny
Versoix, Switzerland
Tel: +41 22 3792473
Cell: +33 695 795 392
Email: jean-paul.kneib@epfl.ch
Eric Jullo
Laboratoire d'Astrophysique de Marseille
Marseille, France
Tel: +33 4 91 05 5951
Email: eric.jullo@lam.fr
Johan Richard
Centre de Recherche Astronomique de Lyon, Observatoire de Lyon
Lyon, France
Tel: +33 478 868 378
Email: johan.richard@univ-lyon1.fr
Georgia Bladon
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Tel: +44 7816291261
Email: gbladon@partner.eso.org
Source: ESA/Hubble - Space Telescope
