When Did Quiescent Galaxies First Appear and What Quenched Their Star-Formation?

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Galaxies are vast collections of stars, gas, dust, and dark matter, and come in various sizes, shapes, and colors. Understanding how the different types of galaxies formed is one of the major quests in astrophysics. Today, the biggest and heaviest galaxies in the local universe are found to be quiescent (i.e., not forming new stars) and made of very old stars, with typical ages of 12 billion years. To understand how these nearby galaxies formed, their counterparts in the distant, young universe need to be studied as well. Dr. Marchesini and his team will investigate quiescent galaxies over 95% of cosmic history using the highest quality astronomical observations. The findings will be compared with theoretical predictions, providing new clues on what switches off star formation in the early phase of galaxy formation. Besides training graduate and undergraduate students, Dr. Marchesini will implement a summer research program for high-school students, contribute to the professional development of K-12 science teachers, and deliver public lectures. The project includes construction of multi-wavelength photometric catalogs of galaxies using data from the Hubble Frontier Fields, ground-based telescopes (Keck and VLT), and Spitzer-IRAC. The spectral energy distributions of the detected galaxies will be modeled to derive photometric redshifts and stellar population properties. The evolution of the stellar mass function of galaxies since redshift z=7 will be measured, with particular emphasis on the quiescent galaxy population.