Cosmology

Maintained by WW

The Cosmic Microwave Background

Istvan Szapudi and his colleagues have recently found strong evidence for correlations between the fluctuations in the Cosmic Microwave Background Radiation and the spatial distribution of high-redshift galaxies. Cosmological theory, specifically the Integrated Sachs-Wolfe effect, states that such a correlation can only exist if the expansion rate of the Universe is increasing with time. This result therefore provides strong support for the existence of Dark Energy as a major constituent of our Universe.

Map of The Cosmic Background Radiation. The dark blue area near the center indicates a weakening of the radiation as as result of its passage though the so-called “Super-Void” - an unusually low-density region of our Universe - about 1.7 billion years ago

Type Ia supernovae

Distant supernovae are brighter than predicted, implying that the universe
expanded more slowly in the past.

John Tonry continues a long-standing collaboration to exploit the "standard candle" property of Type Ia supernovae to probe cosmology. Comparing distance with redshift we have discovered that the Universe is accelerating under the influence of "Dark Energy". We continue to use facilities such as Pan-STARRS and telescopes on Mauna Kea to refine our understanding of the properties of Dark Energy, for example whether it has varied over cosmic time.

Tonry is embarking on a new use of SNIa, this time to determine the properties of "Dark Matter". The ATLAS project is finding many new SNIa every day to redshifts of 0.1, and it is possible to infer the distribution of Dark Matter from its gravitational effect on these SNIa. SNIa can offer the cleanest, most bias-free measurement of this type, but they are so rare that it will require some years for even a massive discovery machine such as ATLAS to find enough of them.

The Hubble Constant

The Hubble Constant H₀ encodes the rate of current expansion of the universe and its value is the subject of intense debate. The value inferred from conditions in the early universe carried forward to the present with the most popular cosmological model disagrees with the value found today. If the disagreement is not due to measurement errors, the implication is that the standard cosmological paradigm requires modification with new physics. Brent Tully and the Cosmicflows team are contributing to this discussion. They measure a value from the observed velocities and distances of galaxies of H₀ = 75 km/s/Mpc, in substantial disagreement with the expectations of the standard model. The case for missing physics ingredients is becoming strong.

HEROES - the Hawaii EROsita Ecliptic-pole Survey

The EROsita X-ray telescope, which will be 25 times more sensitive than ROSAT, is due for launch in April 2019, and is expected to yield vast amounts of data on distant galaxy clusters.
In anticipation of the launch, Len Cowie and his colleagues are currently engaged in a project to obtain visible and infrared images of large numbers of high-redshift galaxies in a 120 square degree region around the North Ecliptic Pole using the CFHT and Subaru telescopes. With these data, combined with the X-ray observations ,they hope to learn about clustering and black hole formation in galaxy clusters out to a redshift of 7 when our Universe was only a small fraction of its current age.

Combined infrared and visible light image
of the central region of the HEROES survey .

Galaxies at z = 6.6

A crucial event in the history of the Universe occurred when ultraviolet radiation from newly forming stars and galaxies became strong enough to reinonize the surrounding intergalactic medium, making it transparent to ultraviolet radiation.. This event is thought to have occurred at a time in the past equivalent to a redshift of about 7. Toni Cowie, Esther Hu and their colleagues are studying this era by using a narrow band filter on the Subaru telescope to search for Lyman-Alpha emitting galaxies at a redshift of 6.6 - the highest redshift accessible in the visible wavelength range. Follow-up spectroscopy of some of these galaxies with the Keck telescope support the theory that it is objects like these which are responsible for the reionization of the Universe.

Redshift-corrected spectrum of the Lyman-alpha
line in an active galaxy.

Submillimeter Quasars

Len Cowie and his colleagues have been measuring submillimeter emission from high-redshift X-ray sources using SCUBA-2 and the Submillimeter Array (SMA) on Mauna Kea, and the Atacama Large Millimeter Array (ALMA) in Chile. They have turned up a wide variety of objects including two examples of a new type of celestial object that shows strong X-ray and submillimeter emission but no detectable infrared or visible light. They are probably high redshift quasars (z~ 4-5) surrounded by unusually thick layers of interstellar gas.

Submillimeter emission (contour lines) and visible radiation (color) from a z = 3.8 quasar. The visible light image was obtained from the Hubble Space Telescope.