Research
Apertif: What govens star formation in dwarf galaxies?Apertif is a new phased-array feed system for WSRT that will greatly expand its field of view and increase its survey speed. The planned surveys will detect and resolve the neutral hydrogen (HI) disks in hundreds of dwarf galaxies. I will use both Halpha imaging and the sensitive Apertif continuum maps to measure the star formation in dwarf galaxies, connecting it to the HI and state of the gas. I am especially interested in ultra-diffuse galaxies, and what we can learn about a field population of this newly reconized class of dwarf galaxy using HI surveys.
ALFALFA: A Rich HI Dataset
My research focuses on using data from the ALFALFA survey to understand galaxy evolution and formation. The Arecibo Legacy Fast ALFA (ALFALFA) survey is a blind extragalactic neutral hydrogen (HI) survey that aims to map 7000 square degrees of sky using the Arecibo L-band Feed Array. You can find out more on the ALFALFA homepage. I am involved in several projects that make use of unique datasets from the ALFALFA survey. These projects include the Survey of HI in Extremely Low-mass Dwarfs (SHIELD), a multiwavelength study of a dozen of the lowest HI mass dwarf galaxies from ALFALFA led by Prof. John Cannon, and HIghMass, a survey of galaxies discovered by ALFALFA with very massive HI disks and very high gas-fractions. You can use the links on the right to explore these projects in more detial.
The Hunt for Missing Galaxies
My main focus (and thesis research) focuses on the hunt for minihalos within ALFALFA. There is a long standing discrepancy between the number of low mass dark matter halos predicted by simulations and the number of low mass galaxies observed in the Universe. We generally understand this discrepancy to be the result of the fact that not all dark matter halos host luminous galaxies, and the lowest mass halos are the most susceptible to the loss of their baryons. While we understand the big picture, there is still a lot to be learned from the details. We have made progress on the details recently with the discovery of the ultra-faint dwarf galaxies around the Milky Way. However, with the exception of Leo T, these new galaxies are located within the virial radius of the Milky Way, making it difficult to disentagle evolutionary from environmental effects.
The discovery of Leo T opened the possibility to finding new low mass galaxies in the Local Group through their gas content. Leo T was discovered in SDSS images but is barely within the detection limits for SDSS. However, its HI content is easily detectable in a sensitive HI survey such as ALFALFA. The recent discovery of Leo P, first as an HI detection within the ALFALFA survey, and then as a confirmed optical galaxy validates the idea that new gas-rich galaxies can be found within the Local Group through their gas content.
I have developed a specialized source-finding algorithm for the ALFALFA survey data to find HI clouds that are the best candidates to represent gas rich nearby low mass galaxies. Currently, I have a catalog of 90+ candidates from 53% of the final ALFALFA survey (~3700 square degrees). I am starting a campaign to understand these sources and confirm their nature, including optical imaging to search for stellar counterparts and JVLA observations to understand the details of the HI distribution.