Luminous Galaxies in the Early Universe
The luminous galaxy Arp220, as seen in the visible and near-infrared with Hubble. Astronomers have modeled dusty galaxies in the early universe that are similar to Arp220 but even more extreme in their luminosities, and found that extreme bursts of star formation can explain their huge power output.
"Submillimeter galaxies" (SMGs) are among the most luminous, rapidly star-forming galaxies known. Located so far away that their light has typically been traveling for over ten billion years, they can shine more brightly than a trillion Suns (or about a hundred times the luminosity of the Milky Way). This display of energy is powered by stars forming at a rate of as much as one thousand per year (in the Milky Way, the rate is more like a few stars per year). They are called submilimeter galaxies because they were first detected at submillimeter wavelengths where their copious warm dust, heated by star formation, glows brightly.
In the local universe, we know that the most luminous galaxies are usually merging systems, that is, two galaxies in collision. The dramatic interaction prompts the gas in the galaxies to increase in density as it flows towards their centers, and leads to bursts star formation. Since their discovery, the question about SMGs has been whether they too are in collision, or whether some other process is at work to provide the humongous power outputs observed.
CfA astronomers Chris Hayward, Patrik Jonsson, and Lars Hernquist and their colleagues have completed a series of computer simulations and modeling of galaxy mergers in the early universe. One of the unique features of their study is that they constrain the simulation to duplicate the masses and other general properties of known galaxies, and then see what kinds of collisions result. In this way they can isolate which features are most sensitive to dynamical evolution and the emitted radiation. The scientists report finding that their method closely reproduces the number, spatial distribution, and generic types of SMGs in the early universe. They conclude in particular that the nature of star formation in these objects need not be unusual, contrary to other theories, but that customary processes and limits are at work -- only they are more active. The also conclude that some of the issues associated with these erroneous alternative theories are not due to specific nature of SMGs, but relate to more general issues of understanding star formation in galaxies in general.