S344: Dwarf Galaxies: From the Deep Universe to the Present

Pisces A

What looks at first glance like a nearby open star cluster is actually a more distant dwarf galaxy, Pisces A, seen here in an image from the Hubble Space Telescope. (NASA / ESA / E. Tollerud, STScI)

Dwarf galaxies have long served as excellent laboratories for studying star formation, feedback processes, gas kinematics and chemical enrichment in the local Universe. As community interest in dwarfs has gained momentum, the study of dwarf galaxies has broadened to encompass larger questions themed around structure formation, stellar mass assembly and the role environment plays in galaxy evolution. Now that cosmological simulations of structure formation are finally capable of resolving dwarf galaxies in increasingly larger cosmological volumes, dwarf galaxy theories and observations are at a crossroads.

Our growing body of knowledge on dwarfs is diverse and stretches back to early cosmic times. For example, satellites at increasingly lower masses in the Local Group have placed limits on the effects of reionisation. These dwarf galaxies are now not only seen as analogues to galaxies in the early Universe, but also they have become direct probes of the earliest epochs of star formation. Detailed studies of the cold interstellar medium in nearby galaxies made possible by the Herschel Space Observatory and the Atacama Large Millimeter/submillimeter Array (ALMA) can now place constraints on the dust and molecular gas content of low-mass galaxies.

Low-redshift studies have also begun to statistically populate the faint end of the luminosity function, bridging the gap in the baryonic Tully-Fisher relation between dwarf spheroidals and irregulars, but also revealing environmental variations. The expanding physical volume probed by current telescopes means the properties and histories of isolated dwarfs can be compared across environments ranging from dwarf galaxy associations, dwarfs in groups, stellar streams and directly interacting systems. The numbers of observed dwarfs can further be compared to cosmological simulations as direct tests of the Lambda Cold Dark Matter paradigm.

Burgeoning samples of extremely metal-poor star-forming dwarfs have opened new avenues of research on star formation in nearly pristine environments, creating tension with our current understanding of stellar feedback and the retention of baryons at low masses. We are on the threshold of observing and understanding the formation and life cycles of massive stars in metal-poor environments that will connect star-formation conditions locally with intermediate- and high-redshift conditions that probe the physics of early generation stars. The upcoming progress in this area inspired by second-generation, high-multiplexing optical spectrographs, and the ideal laboratories provided by dwarf galaxies, make this a crucial time for bringing together the low metallicity, massive star, and dwarf galaxy communities.

At the same time, advances in observational techniques have moved us into the era of direct observations of dwarf galaxies at high redshift, including studies of dwarfs that are directly contributing to the reionisation of the Universe. For example, dwarf galaxies in the mass range of 107 to 108 MSun are now being studied out to redshift 6; this is an area poised for significant growth. Such observational advances have been paralleled by large chemo- and hydrodynamical simulations that are now resolving structures on dwarf galaxy mass scales over critical cosmic timescales for galaxy evolution.

In this symposium our goal is to integrate the current knowledge of dwarf galaxies across multiple distance scales and multiple communities, not only to build a consistent picture of low-mass systems across cosmic time, but also to relate these observations to cosmological constraints from dwarf galaxy populations. The meeting will incorporate (i) detailed studies of Local Group satellites; (ii) star formation, interstellar medium (ISM) content, feedback, gas kinematics, and chemical enrichment (or lack thereof) in nearby dwarfs; (iii) the interplay of the ISM and massive stars hosted by low-metallicity dwarf galaxies; (iv) the properties of dwarfs at high redshift; and (v) hydrodynamical simulations and cosmological models of low-mass structures.

IAU Symposium 344 coincides with the onset of a number of key ground- and space-based telescopes, including the James Webb Space Telescope, Square Kilometre Array precursor and Jansky Very Large Array continuum and HI surveys, integral field unit surveys, Extremely Large Telescope, Giant Magellan Telescope, Thirty Meter Telescope, Large Synoptic Survey Telescope, full ALMA capabilities, and Gaia. In addition, we’re benefiting from the recent advent of big simulations, such as Illustris and Eagle, capable of resolving the history and structure of dwarf galaxies within a cosmologically representative setting. Thus, discussions on the pivotal challenges and opportunities for dwarf galaxy research in the changing observational landscape will be highly encouraged.

KRISTEN McQUINN is a research scientist at the University of Texas at Austin in the United States. She studies the formation and evolution of low-mass galaxies in the nearby Universe.

SABRINA STIERWALT is a research scientist at the California Institute of Technology and principal investigator of the TiNy Titans Survey of low-redshift pairs of interacting dwarf galaxies.