My name is Justin Robinson, and I am the assistant professor of astronomy at Troy University. My research interests include
extragalactic distance measurements, supermassive black hole mass measurements,
and relationships between active galaxies and supermassive black holes.
AGN Host Galaxies
An active galactic nucleus (AGN) is a supermassive black hole actively
feeding on nearby material. AGN activity generates an enormous amount of
energetic feedback back into the galaxy, which is thought to play a major
role in galaxy evolution over cosmic time. I measure distances to galaxies
which host a supermassive black hole such as this, and also use the behavior
of these environments to measure black hole masses.
The Robert C. Byrd Green Bank Telescpoe is located in the national radio quiet zone in West Virginia.
It is the largest steerable instrument in the world, with a dish 300 feet in diameter and height 485 feet
above the ground. I've used this telescope to observe 21cm radiation from neutral hydrogen in nearby
galaxies hosting an active galactic nucleus (AGN).
"Tully-Fisher Distances and Dynamical Mass Constraints for 24 Host Galaxies of Reverberation-Mapped AGN," Justin H. Robinson,
Misty C. Bentz, Hélène M. Courtois, Megan C. Johnson, D. M. Crenshaw, Beena Meena, Garrett E. Polack, Michele L. Silverstein, Dading Chen 2021, ApJ, 912, 160
I am the vice president of the Troy Astronomical Society (TAS). Formed in 2021, the TAS is a club comprised of amateur astronomers, professional astronomers, physicists, and undergraduates of all majors. During the fall and spring semesters, we hold monthly meetings featuring astronomy talks, recent astronomy news, and observing sessions. Click on the image above to join our Facebook group!
The Tully-Fisher relation shows a correlation between the rotational velocity of a
spiral galaxy (the width of the emission line, corrected for the inclination of the galaxy)
and its absolute magnitude. Therefore, if the rotational velocity is known, then the true
brightness of a galaxy can be achieved.
The Tully-Fisher relation's main importance to extragalactic astronomy is distance measurement.
Because the relation gives absolute magnitude, if we compare that value to the measured apparent
magnitude of the same galaxy, then the distance can be measured (in short, comparing how bright
something actually is to how bright it appears to be shows how far away it must be).
Summer Semester 2022
SCI 2240: Principles of Astronomy: Stars, Galaxies, and Cosmology
T, Th, 10:30am - 12:50pm
SCI L240: Principles of Astronomy: Stars, Galaxies, and Cosmology Lab
T, Th, 2:00pm - 3:50pm
Reverberation Mapping is a technique to measure the mass of an active supermassive black hole.
Light that is ejected from the accretion disk emits in all directions, some towards us, and some
towards the surrounding broad line region clouds. The clouds reflect the incoming light, causing an
echo in the signals we dectect from an AGN: one signal from the light emitted towards us, another
signal from the reflected light. The echo, or reverberation, allows the size of the broad line region
to be measured. The size in combination with the rotation speed of the broad line region clouds allows
the mass of the supermassive black hole to be measured.
I use reverberation mapping data to model the broad line regions in nearby AGN host galaxies.
These models tell us the geometry of the region, how it is oriented with respect to our observing
point of view, and the dynamics of the gas. This allows us not only measure supermassive black hole
masses, but determine if gas is actively rotating around, inflowing towards, or outflowing
away from the black hole.
I was the pilot graduate ambassador for the Georgia Outreach Team for Space (GOT Space). Since the founding of GOT Space in 2018, our team has expanded to ~20 undergraduate and ~10 graduate ambassadors from Georgia State University, Georgia Tech, and Kennesaw State University. We have impacted nearly 3000 K-12 students in 15 schools across 6 Georgia districts (and still counting!). We proudly continue to be partnered with and funded by the Georgia Space Grant Consortium.
For more information on GOT Space, or to request a presentation, please visit our website: