AAAS 2015 Science Symposium

Building Galaxies: Some Assembly Required

Investigating how galaxies, the building blocks of our Universe, are built is one of the fundamental pursuits of modern astronomy. We believe that galaxies and their central black holes have been assembled initially via collisions and mergers, and gas accretion from the large-scale structure, and then via secular internal processes, such as bars and spiral arms, that are seen to the present epoch. Scientists are now making exciting progress on key questions about the detailed history of how disk, elliptical, dwarf and irregular galaxies – the Hubble sequence of galaxies – formed, what the role of the dark matter and dark energy was, and how the first galaxies and the black holes that they host formed. Progress is being guided by increasingly sophisticated high performance computer simulations, and by a wealth of data acquired with new centimeter to millimeter wavelength telescopes – the Atacama Large Millimeter/submillimeter Array, the Karl G. Jansky Very Large Array, and the Green Bank Telescope – and by ground- and space-based observatories such as the W.M. Keck Observatory, the Hubble Space Telescope, the Spitzer Space Telescope, and others. This symposium brings together six leading scientists to present the latest results in this field, as indicated by observations with orders of magnitude better sensitivity, broader wavelength coverage, and significantly increased imaging and spectral resolution compared to the best that was available just a few years ago.

Organizer: Mark T. Adams, NRAO

Speakers

1. Felix J. Lockman (NRAO)

Making the Milky Way Galaxy: A Work in Progress

The Milky Way was formed by collapse of gas into a stellar disk within an extensive halo of dark matter. While most stars in the Milky Way were formed in the distant past, the process continues to this day, fueled by accretion of fresh gas. I will discuss recent radio-wavelength observations of a very large cloud of gas on a collision course with the Milky Way, bringing in enough new gas to make more than a million solar systems like our own. Its origin and fate are uncertain.

2. Kartik Sheth (NRAO)

The Assembly of Disk Galaxies Over the Last 12 Billion Years of Cosmic Time

New results will be presented from the Atacama Large Millimeter/submillimeter Array that are enabling astronomers to trace the evolution of the gas fraction in disk galaxies using molecular gas and dust continuum observations, constrain the star formation rate, and establish how disk galaxies are assembled. The most massive galaxies formed first, whereas the lowest mass galaxies formed and developed much later and more gradually.

3. Claudia Scarlata (University of Minnesota)

The Evolution of Massive Galaxies with Cosmic Time: Recent Survey Results

This presentation will describe recent developments in our understanding of the formation and evolution of massive galaxies over the last 10 billion years. Despite their homogeneity in the local Universe, increasing evidence suggests that these galaxies have been continuously evolving. I will present an overview of recent results based on high-resolution images and spectra, acquired with the Hubble Space Telescope, that enable scientists to follow the evolution of these galaxies.

4. Eric Wilcots (University of Wisconsin)

Galaxy Growth: The Impact of Neighbors on Galaxy Evolution

Galaxies prefer to live near each other in groups and clusters. I will describe how these environments impacts the growth and evolution of galaxies using new results from a neutral gas survey with the Arecibo telescope and the Sloan Digital Sky Survey. These data show that more massive galaxies live at the centers of groups and are largely devoid of atomic gas, having lost it during their journey through the group and via interactions, or via consumption by star formation.

5. Ximena Fernandez (Columbia University)

A New Era in Radio Astronomy: Imaging Neutral Hydrogen Beyond the Local Universe

Gas is the fuel for star formation and a key ingredient in galaxy assembly. We can now obtain radio-wavelength images of the neutral gas in galaxies in our cosmic neighborhood and back across cosmic time to when the Universe was only two thirds its current age. I will discuss how these radio-wavelength data are helping astronomers study gas accretion and removal processes that are constraining cosmological simulations and improving our understanding of how galaxies grow and evolve.

6. Priyamvada Natarajan (Yale University)

Formation of the First Stars and the First Black Holes

This talk will present our understanding of how the first black hole seeds and first stars formed. While the growth of dark matter haloes is driven by gravity and well understood, the baryonic physics governing the formation and growth of stars, black holes, and galaxies is more complex and requires combining different physics spanning a large range of scales. There has been tremendous theoretical and computational progress on the formation of the first structures in the early Universe.

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