Research

I'm studying the megaparsec-scale environments of hyperluminous quasars (QSOs) at the peak epochs of star formation and black hole accretion (2 < z < 3). My work has primarily been done using optical images and spectra from the LRIS instrument on the 10-m Keck 1 telescope at the W.M. Keck Observatory, but I am also utilizing data from the Hubble Space Telescope and the newly-commissioned near-infrared imager and spectrograph MOSFIRE, for which I was part of the instrument team.

My current research falls under several related topics, which I describe below (on the left). On the right, you can find a glossary of terms involved in my research, just in case you have not spent the better part of your life neck-deep in extragalactic astronomy (ie. Mom, Dad, this part's for you).

A list of my publications can be found on my CV or at the ADS.

Host Halos of HLQSOs

Hyperluminous QSOs (HLQSOs) are extremely bright and exceedingly rare; these objects are brighter than 10^14 solar luminosities, and there are likely only a few dozen of them in the observable universe.

By studying the spatial and velocity distribution of galaxies near the HLQSOs, we were able to determine that the HLQSOs sit in dark-matter halos of similar masses to those hosting lower-luminosity AGN and typical star-forming galaxies at these redshifts. In addition, we found that the HLQSOs are associated with high local densities of galaxies, which suggests that recent galaxy mergers are more important than halo mass in producing efficient (ie. hyperluminous) black-hole accretion. (see paper)

The IGM Near HLQSOs

HLQSOs produce intense ionizing fields that can exceed the UVB by factors of ~1000x over scales of an Mpc or more. This makes the fields around HLQSOs excellent places to look for fluorescent emission, where ionizing photons are reprocessed by dense Hydrogen gas and reemitted as Lya photons. Using narrow-band filters tuned to the Lya line at the redshift of the HLQSOs, we have identified ~1000 Lyman-alpha emitters (LAEs) that may be exhibiting fluorescent emission, and we have obtained ~400 spectra of the Lya lines.

The Lya luminosity function and distribution of Lya equivalent widths (far exceeding those seen in star-forming galaxies in many cases) show strong evidence for fluorescent emission in many of our candidates, and the distribution of these candidates (in redshift and the plane of the sky) implies that the HLQSOs in our sample have lifetimes between 1 and 20 Myr. (see paper)

Furthermore, our Lya spectra reveal rich properties in their line profiles (multi-peaked emission, red- and blue-dominant peaks, etc.) that may tell us about their kinematics and the effects of radiative transfer. With continuing MOSFIRE observations, we will further probe the physical properties of these objects.

The Case of HS1549+1919

HS1549+1919 is the brightest of our HLQSOs, and the field around it is particularly rich with LAEs, continuum-selected galaxies, and lower-luminosity AGN--in fact, the richness of the field indicates than it may be a high-redshift proto-cluster. Via a medley of ground- and space-based observations covering the UV to MIR, we are taking a census of the populations and properties of this fascinating region of the universe.

More coming soon...

MOSFIRE

As a member of the MOSFIRE instrument team, I helped calibrate and commission the instrument, focusing in particular in the modeling of the instrument flexure (as it lies at the Cassegrain focus of the Keck 1 telescope) and calibrating the flexure compensation system.

MOSFIRE is now fully operational and taking beautiful NIR spectra and images (with minimal residual flexure). Check astro-ph or the ADS for recent results!

Glossary

AGN - An AGN is an Active Galactic Nucleus, which is a very bright component at the center of a galaxy that we can identify from its spectrum. AGN are powered by the accretion of material onto a supermassive black hole. Seeing an AGN thus means that its black hole is in the process of growing (and potentially affecting its galaxy with the light and material it emits).

QSO - Also known as a quasar, a QSO is the brightest type of AGN when viewed in optical light. QSOs are among the brightest objects in the universe, and can outshine their host galaxies by 10-1000x! Because QSOs are rare and powerful, it is important to know how they form and how they affect their surroundings.

Dark Matter Halo - A dark matter halo is a particularly dense clump of dark matter that has formed through gravitational attraction. These clumps of dark matter are able to capture large amounts of gas that form stars and galaxies (and feed QSOs). While we can't measure the amount of dark matter in a galaxy's halo directly, we know that more massive dark matter halos cluster together more than less massive halos. By measuring how galaxies and QSOs cluster, we can then infer the mass of their dark matter halos.

IGM - While some gas falls into dark matter halos to form stars, much of the gas in the universe lies in the seemingly empty spaces between galaxies (particularly when the universe was young); this gas is called the Intergalactic Medium (IGM). The IGM helps us understand how gas gets into and out of galaxies, but studying it requires special techniques because the gas in the IGM does not emit much light on its own.

Lya - Lyman-alpha emission is light emitted by a Hydrogen atom (the most abundant element in the universe) when it undergoes a specific transition from its first excited state to its ground state. Hydrogen atoms in this excited state are especially common when an energetic object is nearby (such as a newborn star or a QSO), so measuring Lya emission can reveal regions that are being affected by QSOs or where stars are being formed.