Upcoming observations of large areas of sky (e.g. DES, Euclid) are expected to tell us about dark energy, through observations of the exact shapes of distant galaxies. This is possible because distant galaxies appear distorted by "gravitational lensing", due to the bending of light by the gravitational pull of matter (see figure below). Similarly, street lamps seen through a bathroom window appear distorted due to the varying thickness of the glass; by analysing the apparent shapes of the street lamps we could deduce the variations in the thickness of the glass. Lensing effects can also be observed by just using a candle and wine glass (credit Phil Marshall, Stanford University).
Credit: HST, with red ovals added by Sarah Bridle
We can use the images of distant galaxies to discover the distribution of matter in the Universe. This can tell us about dark energy because the dark matter clusters together. As time passes the dark matter clusters into tighter clumps, but if there is significant dark energy then the rate of clumping slows down. Therefore we can use gravitational lensing to learn about the dark matter and dark energy in our Universe. Estimation of photometric redshift is key to this work.
There are several effects that can contaminate the gravitational lensing signal. The telescope and atmosphere distort the images of distant galaxies, as illustrated in the figure below. Furthermore, as galaxies form they become coherently distorted. We are developing methods to combat these potential problems to unleash the full potential of gravitational lensing to crack the biggest problem in cosmology.
|Taken from the GREAT08 Handbook by Bridle et al. AOAS.|
Page last modified on 16 jul 10 15:14 by Fabrizio Sidoli