Image of the inner 3 square degrees of the NGFS survey footprint
compared with the size of the Moon. Low surface brightness dwarf
galaxies are marked by red circles. Gray circles indicate previously
known dwarf galaxies. The dwarf galaxies, which vastly outnumber the
bright galaxies, may be the “missing satellites” predicted by
cosmological simulations.
An astonishing number of faint low surface brightness dwarf galaxies
recently discovered in the Fornax cluster of galaxies may help to solve
the long-standing cosmological mystery of “The Missing Satellites”. The
discovery, made by an international team of astronomers led by Roberto
Muñoz and Thomas Puzia of Pontificia Universidad Católica de Chile, was
carried out using the Dark Energy Camera (DECam) on the 4-m Blanco
telescope at Cerro Tololo Inter-American Observatory (CTIO). CTIO is
operated by the National Optical Astronomy Observatory (NOAO).
Computer simulations of the evolution of the matter distribution in
the Universe predict that dwarf galaxies should vastly outnumber
galaxies like the Milky Way, with hundreds of low mass dwarf galaxies
predicted for every Milky Way-like galaxy. The apparent shortage of
dwarf galaxies relative to these predictions, “the missing satellites
problem,” could imply that the cosmological simulations are wrong or
that the predicted dwarf galaxies have simply not yet been discovered.
The discovery of numerous faint dwarf galaxies in Fornax suggests that
the “missing satellites” are now being found.
The discovery, recently published in the Astrophysical Journal, comes
as one of the first results from the Next Generation Fornax Survey
(NGFS), a study of the central 30 square degree region of the Fornax
galaxy cluster using optical imaging with DECam and near-infrared
imaging with ESO’s VISTA/VIRCam. The Fornax cluster, located at a
distance of 62 million light-years, is the second richest galaxy cluster
within 100 million light-years after the much richer Virgo cluster.
The deep, high-quality images of the Fornax cluster core obtained
with DECam were critical to the recovery of the missing dwarf galaxies.
“With the combination of DECam’s huge field of view (3 square degrees)
and our novel observing strategy and data reduction algorithms, we were
able to detect extremely diffuse low-surface brightness galaxies,”
explained Roberto Muñoz, the lead author of the study.
Because the low surface brightness dwarf galaxies are extremely
diffuse, stargazers residing in one of these galaxies would see a night
sky very different from that seen from Earth. The stellar density of the
faint dwarf galaxies (one star per million cubic parsecs) is about a
million times lower than that in the neighborhood of the Sun, or almost a
billion times lower than in the bulge of the Milky Way.
As a result, “inhabitants of worlds in one of our NGFS ultra-faint
dwarfs would find their sky sparsely populated with visible objects and
extremely boring. They would perhaps not even realize that they live in a
galaxy!” mused coauthor Thomas Puzia.
The large number of dwarf galaxies discovered in the Fornax cluster
echoes the emerging census of satellites of our own Galaxy, the Milky
Way. More than 20 dwarf galaxy companions have been discovered in the
past year, many of which were also discovered with DECam.
Reference:
“Unveiling a Rich System of Faint Dwarf Galaxies in the Next Generation
Fornax Survey,” Roberto P. Muñoz et al., 2015 November 1, Astrophysical
Journal Letters [http://iopscience.iop.org/article/10.1088/2041-8205/813/1/L15, preprint: http://arxiv.org/abs/1510.02475].
Cerro Tololo Inter-American Observatory is managed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.
Science Contact
Dr. Thomas H. Puzia
Pontificia Universidad Católica de Chile
Tel: +56-9-89010007
Email: tpuzia@astro.puc.cl