Dr. Amir Hajian from the Canadian Institute for Theoretical Astrophysics led a study using a cross-correlation technique to examine the star formation history of the Universe. The results from the study detected a very strong correlation between two maps of the sky, observed at different frequencies.

The study is the first of its kind to detect this correlation. Hajian and his colleagues took data collected from two telescopes, the Atacama Cosmology Telescope (ACT) and the Balloon-borne Large-Aperture Sub-millimeter Telescope (BLAST), and using cross frequency correlations found that the information collected shed light on some basic questions regarding the evolution of galaxies in the universe, such as: what is the spatial distribution of galaxies (or how are they clustered), and do the properties of the dusty galaxies evolve in time?

ACT is located on Cerro Toco in the Atacama Desert in northern Chile. This six-meter telescope is one of the highest permanent ground-based telescopes in the world, sitting at an altitude of 5190 meters.

In 2008 ACT started collecting data at millimeter wavelengths. The data produced images of radiation emitted from the comic microwave background (CMB). In addition to collecting information on early radiation signals, the telescope also provided arc-minute resolution observations of secondary CMB anisotropies, and extragalactic point-source populations that dominate power at small angular scales in the sky.

In 2006, BLAST (a 2 meter sub millimeter telescope that hangs from a high altitude balloon), in its third launch (second scientific launch) collected data from 120,000 feet above Antarctica for a total of 11 days.

During the launch, BLAST peered into the distant Universe at wavelengths that are nearly unattainable from the ground.

Sensitive to light at wavelengths just below 1mm (sub millimetre and infra-red radiations), the telescope was able to determine the spectrum of light emitted from distant galaxies at very early times in the history of the Universe.

Hajian and his colleagues took overlapping observations from both ACT and BLAST to examine possible correlations. They used observations taken from a region near the south ecliptic pole (SEP) that covered approximately 9 square degrees in the sky. The region examined is relatively free of dust emissions from the Milky Way, and was therefore a suitable area for studying the spatial clustering of dusty star forming galaxies without interruption from our own galaxy.

The cross-correlation of these two maps of the sky demonstrated a strong connection between both sets of data, providing an abundance of information on star formation history. The team discovered that the information provided by BLAST could be interpreted as a detection of the unresolved sources of dusty star forming galaxies picked up by the microwave maps from ACT. In other words, the galaxies that ACT could not detect individually were indirectly detected when cross-examined with data collected from BLAST.

These findings are particularly significant because they are the first to detect a strong correlation between two maps of the sky, observed at different frequencies, thus proving the technique of cross-correlating CMB and infra-red data to be a highly effective method for examining galaxies at different redshifts. The detection of these correlations helps to provide a more robust history of early to present day star formation.

In addition to further understanding and constructing this history, the study also measured important statistical properties of dusty galaxy populations called ‘clustering’. Measuring the clustering of galaxies is extremely important since these measurements are expected to help trace underlying dark matter distribution (clustering of sources can be related to the clumping of dark matter).

Studies of this kind will help scientists find key answers to questions about the masses of dark matter halos that host these dusty galaxies.

It will also help to further our understanding of the star formation history of the Universe and construct accurate ‘clustering’ models of the dusty galaxies as a function of redshifts.

Reference and figures: http://arxiv.org/abs/1101.1517