The brightest galaxies in the Universe

High-redshift dusty star-forming galaxies, magnified by strong gravitational lensing

My principal research focus is a multi-wavelength study of superbly luminous dusty star-forming galaxies (DSFGs) at redshifts 1 < z < 4. By examining DSFGs that are strongly gravitationally lensed by an intervening cluster or galaxy, one can recover details of the structure of gas and dust distributions and star formation activity at physical scales on the order of 100s of parsecs. This spatial resolution is currently unreachable for existing technologies without the aid of a "cosmic telescope." Through spectral line observations, kinematic properties of the distant source can be inferred, helping to illuminate what drives their intense star formation.

Reconstructing the source-plane structure from an observed image distorted by lensing is far from a trivial task. This significant challenge has led to the advancement of state-of-the-art techniques for modeling isolated galaxy lenses and cluster lenses (see e.g. multiple recent studies based on ALMA observations of SDP.81, Tamura et al. 2015; Rybak et al. 2015).

Recently collected observations include Hubble WFC3 1.6 μm, Jansky Very Large Array 6 GHz, and Atacama Large Millimeter/submillimeter Array Band 3 and 6. Our sources were selected from the Planck all-sky survey, as detailed by Harrington et al. 2016 and Berman et al. 2020, in prep. These hyper-luminous dusty starbursts have been found with overwhelming frequency to be spectacular gravitational lenses, often with near-complete Einstein rings (see our press release from June 2017). Their intrinsic brightness from rapid star formation (on the order of 10,000 solar masses per year) combined with the amplifying effect of gravitational lensing places them amongst the ranks of the most luminous galaxies known at this time. We intend to investigate what drives this massive efficiency in forming stars.

Faraday rotation measure synthesis of nearby edge-on galaxies

As part of a prior project, I studied Faraday rotation in a sample of galaxies from CHANG-ES (Continuum Halos in Nearby Galaxies-- an EVLA Survey), an international collaboration that utilizes the updated Very Large Array in Socorro, NM. Linearly polarized light (produced most commonly as synchrotron radiation) has a characteristic position angle. When the light travels through a magnetized plasma, this intrinsic polarization orientation is altered, in what is known as the Faraday effect.

Linear polarization can be represented equivalently as a superposition of right-hand and left-hand circular polarization, which have slightly disparate indices of refraction in a magnetized medium. In turn, the plane of polarization is rotated by an amount proportional to the wavelength squared (λ2). The corresponding constant of proportionality is known as the rotation measure, or RM. The RM itself is dependent on the electron density and the component of the magnetic field parallel to the line-of-sight.

In measuring this spectral variation of the polarization angle, we have a unique opportunity to probe magnetic fields in nearby galaxies. Of course, for a meaningful detection, we require a sufficiently large bandwidth. It is for this reason that the radio regime is necessary for this study. Moreover, the new capabilities of the Jansky Very Large Array allow for an unmatched level of precision-- at least until the advent of the Square Kilometer Array, which will fundamentally revolutionize the study of Faraday rotation and, in broader terms, our understanding of cosmic magnetism itself.