Galaxies are central to our understanding of the universe. They trace
the geometry of space-time and give birth to stars and planets. Galaxy
formation theory accurately describes the gravitational amplification of
structure in the matter distribution over cosmic time. Unfortunately, most
of the (dark) mass density in the universe is not normal baryonic
material,
so the theory does not directly predict the observable feature of galaxies --
starlight. Research in Crystal Martin's group focuses on the astrophysics
of galaxy
formation and evolution, trying to understand in detail why the star formation
rate varies widely among galaxies. Central to this work is the idea of
feedback from supernova explosions, which inject energy, momentum, and
heavy elements into the surrounding interstellar gas. The pictures above show
a schematic of the galactic ecosystem, feedback from a young star cluster, and
a galactic-scale starburst wind.
Current work is centered around the following themes:
The environmental dependence of galaxy properties today requires an accelerated
assembly history in high density environments. Protoclusters, the overdense
regions of the universe that ultimately collapse into massive galaxy clusters,
contribute a significant fraction of all cosmic star formation during the
era of reionization. The galaxy overdensity may enhance the escape of ionizing
photons, making protoclusters crucial in driving the timing
and topology of cosmic reionization. We propose to measure the brightest
rest-frame-optical emission lines from spectrosopically-confirmed
galaxies comprising the largest overdensity yet identified near the midpoint
of cosmic reionization, z7OD. Eight protocluster members, identified by
their Lyman-alpha emission, are the primary targets for these NIRSpec MOS
observations, which will measure rest-frame optical emission lines between
the [OII] doublet and hydrogen Balmer alpha lines. We aim to measure the
transmission of the IGM in and around an ionized, cosmic
bubble, determine the physical properties of the galaxies that ionized
the bubble, and compare them to field galaxies at z > 3.37 (observed
simultaneously). We will measure the Lyman-alpha escape fraction and the
Lyman-alpha velocity offset, information required to map spatial
variation in IGM transmission. Protoclusters at this redshift are predicted
to contain significant amount of cold gas, possibly triggering high specific
star formation rates and accelerating the chemical evolution of the galaxies;
ideas we will test by directly measuring diagnostic emission-line ratios.
Which galaxies reionized the universe, how they did it, and why the highest redshift galaxies are so luminous remain fundamental, unanswered questions about the history of the universe. The environment of galaxies must have been very dierent then than today. Yet low mass galaxies today have gas-phase metallicities similar to those in the reionization era; and, in extremely rare cases, are caught forming stars very e ciently, likely due to galaxy interactions. Studying the physical processes at play in these local analogues teaches us how to correctly interpret the extreme emission-line spectra of reionization-era galaxies and generates empirical scaling relations that can be employed in cosmological simulations.
Recent advancements in modeling multiphase winds open the possibility of makding direct comparisons between theoretical predictions and observations. However, developing this interface requires a deeper understanding of how the structure of outflows shape the observed absorption and emission lines profiles, both in integrated spectra and in maps obtained via integral field spectroscopy. Combining new high-resolution emission-line spectra of starbursts galaxies with high S/N ratio spectroscopy of their ultraviolet absorption lines, we can understand the physical origins of the various line components through comparison to a series of increasing more realistic physical models.