Galaxies in the Local Universe
I use the 305-meter Arecibo , 100-meter Green Bank , and NRAO Very Large Array in my research concerning galaxies within 250 Megaparsecs. Arecibo is a detection machine due to its ability to survey large regions of sky with high sensitivity. I use the data from the Arecibo Legacy Fast ALFA Survey to compute hydrogen masses for nearby galaxies. In particular, astronomers are interested in the density of galaxies per cubic megaparsec for a given HI mass range. How many low mass galaxies? How many high ones? This is used to construct an HI mass function. N-body simulations predict that large amounts of low-mass dark matter halos should inhabit the vincinities of large galaxies. One way of detecting these potentially low-surface brightness objects is through the examination of wide field survey data from Arecibo. Pinning down the low mass end of the HI mass function with better statistics is one goal of modern astrophysics, as it will allow us to compare observations with theoretical predictions.
I'm currently studying the Messier 96 galaxy and environment with the VLA (left). I've used the GBT and currently the VLA for followup observations of different galaxies. The GBT is a fantastic instrument to use for studying galactocentric hydrogen surrounding our galaxy, commonly known as high-velocity clouds. Some HI detections may lie near our own Milky Way galaxy, while others may lie further out into the Local Group. The VLA is a hallmark of modern astronomy, as it allows for high resolution imaging of astronomical objects. I use the VLA to study the dynamics of tidal debris that have no optical counterparts.
The Virgo Cluster, Galaxy Interactions, and Radio Surveys
Most galaxies are found in groups. Large groups, more commonly referred to as clusters,
are fascinating environments to study the evolution and interactions of galaxies. The Virgo cluster is the
nearest large, rich cluster to our own Milky Way galaxy. With over 1000 members, Virgo is a prime target
of many studies in modern astrophysics. My research is completing a survey of Virgo down to a HI mass
of 2 x 107 solar masses. This survey comprises the largest number of HI detections
for Virgo ever published. In addition to publishing a catalog of these observations, I am examining
some of the more interesting detections with followup observations with the GBT and VLA, as well
as optical spectroscopy with the 5-meter Palomar telescope.
Interesting detections abound in Virgo, as the cluster's outer periphery has not yet reached virial equilibrium. The cluster's massive potential and hot intracluster gas has the ability to tear gas from galaxies, through processes such as ram pressure stripping and galaxy harassment. Some of the detections I've examined might be tidal debris from such interactions.
Galaxies in groups and in cluster interact gravitationally with each other, and hydrodynamically with hot gas inbetween. These interactions, including those around NGC 4254 (at right), have been mapped with Arecibo. These long extended gas tails originating from the galaxy are likely due to interactions with the dominate potential well, provided by the 1014 solar masses of the Virgo Cluster.
HI debris left behind from these interactions is being found in the periphery of Virgo. I have mapped some of the isolated objects with the VLA. Other observations from Arecibo and the VLA with collaborators show similar types of "HI Clouds" on larger scales with larger velocity dispersions. These objects are not detected in large numbers as they are likely transient phenomena that disperse within the time it takes to cross the Virgo cluster.
I study galaxies at radio frequencies. Technological advancement and computing power have revolutionized astronomy to the point where we can study large numbers of galaxies and their associated properties. We are learning about a variety of different galaxies, their environments, distance, masses, and kinematics. My research with large radio surveys utilizes the 305-meter Arecibo radio telescope to survey large areas of sky and study the cold neutral hydrogen gas content of galaxies. I have used the Arecibo Legacy Fast ALFA survey to obtain data with a L-band multibeam receiver system.
My science and software development stem from these current and future radio surveys. I have written software used by all team members for visualization and reduction of the survey datasets. In addtion, I created online databases that distribute the data to the astronomical community and web services of the Virtual Observatory.