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J.M. Moran (CfA)
The Expanded Very Large Array (EVLA) was one of the major facility initiatives recommended by the Astronomy and Astrophysics Survey Committee of the NRC in its report, ``Astronomy and Astrophysics for the New Millennium.'' The strong recommendation for the EVLA was based on the importance and breadth of science that can be done by this new instrument, and its ability to complement the science of other major new instruments such as the Atacama Large Millimeter Array (ALMA) and the Next Generation Space Telescope.
The most exciting science of the EVLA can be divided into four major categories in which such a powerful new centimeter-wavelength interferometer can make major contributions. These are (1) the Magnetic Universe --- measuring the strength and topology of magnetic fields; (2) the Obscured Universe --- unbiased surveys and imaging of dust-obscured objects; (3) the Transient Universe --- rapid response to and imaging of transient objects; and (4) the Evolving Universe --- tracking the formation and evolution of objects ranging from stars to spiral galaxies and active galactic nuclei.
As an example taken from the Evolving Universe, consider the study of star-forming galaxies at high redshift. Low-order CO transitions will be shifted into the EVLA band (below 50 GHz) for redshifts of a few; measurements of these transitions in conjunction with higher order transitions seen by ALMA will give direct information about the excitation conditions in star-forming regions at redshifts of z~4 and beyond. Radio synchrotron emission and thermal free-free emission will be detectable out to z\approx 2--5 from ultraluminous infrared galaxies having star-formation rates on the order of 100M\odot~yr-1, providing direct estimates of the massive star-formation rate as well as the temperature and density of the interstellar medium.