University of Minnesota
School of Physics & Astronomy

Spotlight

Galaxy Evolution

Claudia Scarlata
Claudia Scarlata
                                                       

Claudia Scarlata is an astrophysicist who studies the formation and evolution of galaxies. One question her research examines is the effect of galaxy formation on the so-called “reionization problem.” In the early universe, about 380,000 years after the Big Bang, free protons and electrons combined to form neutral hydrogen. This process produced a photon after-glow known as the Cosmic Microwave Background. A few hundred million years later, the neutral hydrogen was reionized—i.e. it absorbed high energy photons, released its bound electrons and became ionized hydrogen.

This process produced a photon after-glow known as the Cosmic Microwave Background. A few hundred million years later, the neutral hydrogen was reionized—i.e. it absorbed high energy photons, released its bound electrons and became ionized hydrogen. Cosmologists have been trying to understand the source of such a huge number of high-energy photons. Claudia Scarlata’s research focuses on the part that the formation of galaxies played in the reionization epoch.
It is still not know what fraction of high energy photons escaped from forming galaxies into the intergalactic medium. It is not possible to simply study bodies formed during the phase transition epoch because they are too far away. Scarlata uses local galaxies because they are brighter and easier to study their escape fraction. These galaxies are actively forming stars, and offer a good opportunity to observe some escaping ionizing photons. Using data from the Hubble Space Telescope (HST), Scarlata is trying to determine the intrinsic number of ionizing photons, because they have no baseline to study from.

Scarlata and her group also study a kind of galaxies known as a Lyman-alpha emitter. Cosmologists are very interested in them because they could be used to trace the reionization history of the universe. By studying the Lyman-alpha emitters in the local universe, Scarlata is able to figure out how they change as a function of time and to work on problems such as how Lyman alpha photons escape from dusty sources . Using ultra-violet spectroscopy with the help of Hubble telescope, Scarlata is also studying the motion of the neutral gas which is imprinted in the profile of the Lyman-alpha line. Her group found that not only the motion of the gas, but also how the gas is distributed is crucial for the escape of the Lyman-alpha photons.

One of Scarlata’s most significant findings involved Lyman Alpha blobs, which are sources of Lyman- alpha photons, much bigger than normal galaxies. The energy source for Lyman-alpha photons is still a mystery. “We found that there is a high level of polarization in a ring around the blob. This tells us that the Lyman-alpha photons are produced at the center of the blob and then scattered by neutral gas toward the Earth.” This finding helps exclude one previous interpretation that the gas entered galaxies in filaments. Scarlata and collaborators found that it is instead distributed in a more homogenous shell.

Scarlata with the help of an undergrad, Alex Card, used data from the Sloane Digital Sky Survey to look for extreme Lyman-alpha emitters. They have used the Large Binocular Telescope to confirm a few candidates and are working on the properties of the full sample.

Scarlata is also studying the formation of the most massive galaxies using infrared spectroscopy with the HST. She is part of a team who has been awarded more than 1,000 orbits of the HST. She will be continuing this research with Euclid, a European Space Agency (ESA) infrared satellite mission that will be launched in 2020. Euclid has a consortium with 1200 members. NASA recently joined the consortium and Scarlata is one of the American members. The main focus of Euclid is to study dark energy, but because it will cover 15,000 square degrees of the sky, the data will be very useful to Scarlata to study galaxy evolution.