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Research

I am interested in the evolution of galaxies and the processes which drive that evolution. For this, I study the active phases of galaxies: mergers, starbursts, and active galactic nuclei (AGN). I analyze both observations (primarily radio-through-optical) and N-body simulations to understand how mergers drive the growth of stellar mass and black holes, and how feedback processes may eventually halt that growth. Below are thematic summaries of my interests.

For students interested in working with me, I have a list of possible projects.

Topics

Dynamical Models of Galaxy Mergers

The redistribution of stars and consumption of gas by star formation and AGN during galaxy interactions and mergers have a strong influence on the properties of the galaxies involved, driving significant morphological transformation. I am matching dynamical models to observations of local mergers in order to facilitate detailed comparisons between numerical models of star formation and the actual star formation taking place in these systems. This modeling effort will accurately timestamp individual systems, something not previously available for a sample of galaxy mergers.

The image to the left shows the optical image of an ongoing galaxy interaction, between NGC 5257 and NGC 5258, as seen by the Hubble Space Telescope. Below the HST image is a N-body simulation of a galaxy merger which has been matched to the observed morphology and kinematics of the system. This model was presented in my 2013 paper listed below and is representative of the modeling of galaxy mergers.

Papers

The Interstellar Medium of Luminous Infrared Galaxies

There exist populations of galaxies where the bulk of their energy is emitted in the infrared. The “Luminous Infrared Galaxies” (LIRGs) are powered by a combination of star formation and AGN. In addition to the numerical simulations described above, I am also investigating the atomic and molecular gas properties of these systems via radio and mm observations of atomic and molecular gas tracers. These observations are being studied to understand the properties of the fuel available for star formation and AGN fueling. As part of this effort I am also performing a survey of the neutral hydrogen in U/LIRGs to obtain kinematics for the above dynamical modeling, and to determine the distribution of the atomic gas in these systems. Additionally, I am using emission from molecules such as CO, HCN, and HCO+ to study the physical conditions in the gas directly associated with star formation.

The figure to the left shows the galaxy-integrated ratio of the luminosity in the 1–0 transition of the HCN and HCO+ molecules as a function of the dominance of an active galactic nucleus in the mid-infrared, from my 2015 paper (linked below). In the paper, we were unable to find a single physical process which explained the relationship of the global HCN/HCO+ ratio. I am now pursuing resolved observations of these molecular lines with the Atacama Large Millimeter/submillimeter Array to further understand the emission from these tracer molecules.

Papers

Dwarf Galaxy Interactions

Little is known about interactions between dwarf galaxies, compared to more massive galaxies. However, by number, mergers between dwarfs are expected to be more frequent than mergers between massive galaxies, but it is unclear how these interactions will affect the star formation rates, stellar masses, and gas content of dwarfs. I am part of the TiNy Titans (TNT) survey of local dwarf galaxies. Our SDSS-selected sample of isolated dwarf galaxy pairs and a matched sample of non-isolated pairs and individual dwarfs is being used to study the effect of interactions and mergers on dwarf galaxies. Additionally, we are using large-volume cosmological simulations to obtain theoretical predictions for these interactions. I am pursuing optical integral field unit observations of dwarf-dwarf mergers and dynamical models for individual pairs.

Papers

Active Galactic Nuclei

While it only takes a relatively small amount of gas to fuel a supermassive black hole, the energy output can potentially affect the entire host galaxy. I am interested in the interactions between radio jets and the ambient host galaxy, as well as the broadband emission from AGN and their hosts. Studying the broadband emission can disentangle the power sources of these systems: star formation vs AGN activity.

Additionally, I am interested in studying the rare examples of “dual AGN” – galaxy mergers where both supermassive black holes are simultaneously accreting. These systems may provide critical information on the role of AGN feedback in galaxy evolution. I am part of an international team, working on the optical integral field unit and millimeter spectral line observations of these objects.

The figure to the left shows the radio-through-mid-infrared spectral energy distribution (SED) of the radio galaxy Cygnus A. Additionally, the figure shows model fits to the SED, which I used to disentangle the AGN and starburst contribution to the far-infrared emission. I found that the bulk of the infrared could be explained with dust heated by the AGN, but that some of the infrared is the rest of ongoing star formation.

Papers

Collaborations

I am a member of several collaborations which are focused on merger-driven galaxy evolution. These projects have or are in the process of assembling large multi-wavelength imaging and spectroscopic datasets to facilitate the studies described above. In all collaborations I am actively working on (sub)mm and optical observations as well as numerical modeling of the ongoing mergers.

GOALS: The Great Observatories All-sky LIRG Survey

http://goals.ipac.caltech.edu

GOALS is a multiwavelength survey of the most IR luminous galaxies in the nearby universe. The aim of GOALS is to study extreme star formation, AGN, and merger-driven galaxy evolution. I am leading aspects of the (sub)mm studies of the ISM of GOALS galaxies as well as dynamical modeling of the mergers. I am also working on observations and analysis of optical integral field spectroscopy.

TNT: TiNy Titans

https://lavinia.as.arizona.edu/~tinytitans/

TNT is focused on interactions and mergers of dwarf galaxies in the nearby universe. Our understanding of dwarf galaxy interactions is limited, compared to our understanding of massive galaxies. Yet dwarf-dwarf interactions may be better analogs to hierarchical assembly at high redshift. I am actively involved in numerical modeling of local dwarf-dwarf mergers and am leaving an integral field spectroscopy program on TNT galaxies.

MODA: Multiwavelength Observations of Dual AGN

website coming soon

MODA is focused on detailed multi-wavelength studies of the few confirmed dual AGN systems (mergers hosting two AGN with separations less than 10 kpc). The aim of MODA is to understand the impact of AGN on merger-driven galaxy evolution at the phase of a merger where the galaxies are near coalescence and nuclear feedback is expected to have its strongest influence. I am performing (sub)mm and optical integral field spectroscopic observations of these systems, and dynamical modeling of the host mergers.

Publications

A list of my publications is available in my CV, on NASA ADS (peer reviewed), on arXiv/astro-ph, and via my ORCID (0000-0003-3474-1125).

PhD Dissertation

A copy of my PhD dissertation, “The Dynamics and Cold Gas Content of Luminous Infrared Galaxy Mergers in the Local Universe” can be downloaded from the Library at the University of Virginia.

Software Distribution

Many of the scripts I use for processing and analysis are available in a github repository. That repository is a collecting point for several sets of code focused on observing, numerical simulations, and preparing talks and papers. Additional software I have made available includes:

I also host a few sets of potentially useful document templates: