Click the links below to find out who I am, what I have accomplished, and what I am currently working on.
Biography
Tyler is the first born child in a family of immigrants from the small island nation Trinidad and Tobago, in the Caribbean. He is from Shirley, NY, where he graduated early from high school at the age of 16. Tyler became very interested in physics due to his early, homegrown passion for astronomy, as well as his high school physics teacher passion for the subject.
He went on to attend Embry-Riddle Aeronautical University in Daytona Beach, FL with the major of Space Physics. There, Tyler was a part of the Honors Program, the National Leadership Honor Society, the National Physics Honor Society, and the McNair Post Baccalaureate Program, a program to help under-represented and first generation college students acquire graduate degrees.
Additionally, Tyler worked in the Space Physics Research Lab under Dr. Matthew Zettergren, and also conducted astrophysical research under Dr. Jason Aufdenberg. Under Dr. Zettergren, he researched electron heating in the upper atmosphere and under Dr. Aufdenberg, he investigated the use of Bayesian statistics to extract stellar parameters from stellar models.
With the knowledge that he gained from his project with Dr. Aufdenberg, Tyler was able to acquire an internship at NASA Johnson Space Center where he worked on determining when parts on the International Space Station would break.
Tyler graduated from Embry-Riddle in 2015 and currently attends Oregon State University as a graduate student in the Department of Physics. He is under the supervision of Dr. Davide Lazzati.
Curriculum Vita
Research
Image Credit: NASA
As a fifth year graduate student, with an expected graduation of June 2021, I have completed all of my classes and I am fully dedicated to conducting research on gamma ray bursts with my advisor Dr. Lazzati. His website is: science.oregonstate.edu/~lazzatid/
Diversity is important to science because people of different backgrounds go through different life experiences and develop new and innovative ways of analyzing and solving problems; this is what makes science exciting and progressive.
In the effort to increase diversity and foster scientific curiosity, I try to engage all members of the public in astronomy. Below are some of my efforts to accomplish this goal as an American Astronomical Society Astronomy Ambassador.
This figure shows the results of the SKIRT radiative transfer simulations of a FIRE-2 galaxy. The top three panels, from left to right, show mock observations of the galaxy without any dust attenuation, with dust attenuation and the dust attenuated image convolved with the point spread function (PSF) that we use. The bottom panel shows how well the statmorph code is able to recover the true profile of the galaxy by accounting for the PSF and fitting the galaxy with a sersic profile.
As a participant of the 2018 Kavli Summer program on Galaxy Formation (https://kspa.soe.ucsc.edu/archives/2018) at the Flatiron Institute, I was able to get my hands dirty with researching galaxy formation physics. Since this isn’t my PhD thesis research I learned a ton about the physics of galaxy formation and the currunt status of the field.
I collaborated with Rachel Cochrane, Chris Hayward, Daniel Angles-Alcazar, and Jennifer Lotz in understanding how Active Galactic Nuclei (AGN) feedback can affect the observed sizes of galaxies. I conducted SKIRT radiative transfer simulations of a set of FIRE-2 zoom-in galaxy simlations. These galaxy simulations include a variety of stellar physics, are done at higher resolution, and include the effects of Black Hole accretion. While they do not include the effects of AGN feedback, we can conduct mock observations of these galaxies, as shown in the figure above, to determine how well they align with observational relationships.
We have found that the galaxies start off in relative agreement with the \(R_e-M_\star\) relationship and the \(\Sigma_1-M_\star\) and \(\Sigma_e-M_\star\) relationships at large redshifts. As the galaxies evolve, they begin to diverge from the observational relationships at \(z \sim 2\). ro this point on the simulated galaxies are too compact compared to observed galaxies.
We anticipate that including AGN feedback in these simulations will allow material to be heated and prevent accretion into the central region of the galaxy. As a result, the galaxies will be less compact and fall into alignment with the various observational relationships. This hypothesis will be tested with a new suite of galalxy simulations that include the effects of AGN feedback.
A comparison between the measured FIRE-2 galaxy half light radii and the observational van der Wel relationship between the half light radii and the stellar mass of a galaxy.
This figure shows the comparison between the measured density within 1 kpc of the FIRE-2 galaxy and the Barro et. al. \(\Sigma_1-M_\star\) relationship.
Here, we show the comparison between the measured density fo the FIRE-2 galaxies within the half light radius and the Barro et. al. \(\Sigma_e-M_\star\) relationship.
Time integrated polarization, polarization angle, and light curve peak luminosity as a function of observer viweing angle for 2 synthetic GRBs that we used the MCRaT code on.
The MCRaT code has been improved by implementing the full Klein-Nishina scattering cross section and polarization through the Stokes parameters. These additions to the code allow us to simulate the time integrated and time resolved polarization expected from relativistic outflows.
We ran the MCRaT code on two different GRB jets, the 16TI simulation had a steady jet and the 40sp_down simulation had a pulsed jet. We find that in both cases, the time integrated polarization increases with the observer viewing angle. At large viewing angles, however, the polarization decreases due to the fact that the photons are not fully decoupled from the flow.
Additionally, with our Monte Carlo methods, we are able to produce time resolved polarization predictions expected from LGRBs which can help distinguish various models for GRB radiation mechanisms. This is especially important as future detectors are expected to have better polarization measurement capabilities compared to current GRB detectors.
The 16TI light curve and polarization at an oberver viewing angle of 7\(^\circ\). The polarization percentage of this GRB is very low due to the fact that it has a steady jet and very little angular structure.
We find that the time resolved polarization in the 16TI simulation is very small due to the lack of structure in the jet. On the other hand, the 40sp_down simulation has alot of spatial and temporal structure and we find that there are time periods in the light curve where the polarization gets as high as ~8%. Additionally, the polarization angle is observed to change as a function of time as different shells of material move into the line fo sight of the observer.
Here, we plot the variable time binned light curve of the 40sp_down GRB simulation. There is much variability in the ight curve and at the beginning of the GRB the detected polarization is relatively high and is very statistically significant.
To show the evolution of the polarization angle \(\chi\) we rebin the 40sp_down light curve into uniform 0.5 s bins. At the beginning of the light curve, there is a clear evolution in \(\chi\) from 90\(^\circ\) to 0\(^\circ\) to -90\(^\circ\) at the beginning of the light curve.
While these results are interesting, we need to conduct large domain GRB jet simulations in order to ensure that photons at large viewing angles are decoupled from the flow. This will allow us to make better predictions of the expected polarization signatures seen from the photospheric model.
This figure shows the light curves, plotted in black, and the time resolved peak energies, shown in red, for various Gamma Ray Bursts observed by the FERMI satellite. Some of the Gamma Ray Bursts exhibit a hard-to-soft peak energy evolution; however, for some Gamma Ray Bursts, the peak energy follows the evolution of the light curve. This figure is from the following paper: A&A 588, A135 (2016)
DOI: 10.1051/0004-6361/201527509
For the summer of 2017, as an NSF EAPSI Fellow, I was in Japan at the Astrophysical Big Bang Laboratory (ABBL) in RIKEN to forge new collaborations through understanding radiation transport in Gamma Ray Bursts. The ABBL website is: nagataki-lab.riken.jp.
While at RIKEN, I was also investigating the connection between the time resolved spectral peak energy and the isotropic luminosity. As shown in the figure above, the peak energy track the luminosity sometimes, while other times the peak energy just follows a hard-to-soft evolution. Up until my radiation transfer simulations, this effect has not been able to even be reproduced. Thus, due to my simulations, I have the unique opportunity to understand this seemingly erratic behavior between the peak energy and the luminosity.
In 2018 I was also accepted to participate in the NASA Fermi Summer School, where I learned a lot about the gamma ray observations that take place to produce results like what is presented in the figure above. I have lots of ideas to try to connect the observed \(E_p\) - \(L_\mathrm{iso}\) tracking to the angle dependence of the tracking that I see in my simulations. One of these ideas is exemplified below, where I conducted a very preliminary analysis of GRB 080916C to try to determine the observed angle from the jet axis. I calculates the spearman rank coefficient, \(r_s\), between \(E_p\) and \(L_\mathrm{iso}\) for the GRB and compared it to \(r_s\) measured from my 16TI simulation at different viewing angles for the GRB. In this test analysis, it seems as though GRB 080916C was observed at ~2\(^\circ\) off axis, however a more stringent, self consistent analysis that includes errors need to be done.
This figure shows the comparison between the calculated \(r_s\), between \(E_p\) and \(L_\mathrm{iso}\), for GRB 080916C and my 16TI simulation at various observer viewing angles. This suggests that GRB 080916C was observed at ~2\(^\circ\) off axis.
Monte carlo radiation transfer through gamma ray bursts
The left panel of the video shows photons, in red, being injected into and propagating through a Gamma Ray Burst outflow, plotted in purple/blue. The top right panel shows how the spectrum of those photons change as the photons interact with the matter in the jet. The bottom right panel shows the average temperatures of the photons, in red, and the matter surrounding the photons, in blue.
The video shown above shows one of my Monte Carlo simulations in which photons are injected into a Gamma Ray Burst outflow and then individually scatter and propagate each photon until the end of the outflow becomes optically thin and the photons ideally escape. The spectrum of those photons changes as the photons continually interact with the matter in the jet. As the photons propagate through the expanding jet, the coupling between the counterparts of the jet gradually decrease. This is shown in the plot of the photon and matter temperatures.
The background fluid properties are acquired from hydrodynamic simulations of Gamma Ray Bursts, and my Monte Carlo code allows the photons to interact with the fluid thus allowing us to investigate how a realistic jet outflow affects the produced Gamma Ray Burst spectrum. This is integral to understanding the full Gamma Ray Burst picture.
Thus far, we have applied the MCRaT code to the analysis of special relativistic hydrodynamic simulations of Gamma Ray Bursts with a constant supply of energy, as seen in the video above, and simulations where the energy supplied to the jet is variable. Both analysis have already provided a better footing to compare simulations with observations and get a refined idea of how simulations need to be improved in order to better match nature.
The results that I have acquired using MCraT are contained in 2 papers that I have written. More information can be found on my resume.
My code is hosted on GitHub at: github.com/lazzati-astro/MCRaT. I have implemented the full Klein-Nishina cross section and polarization in the code. Future work will include a variety of emission and absorption processes occurring as the photons travel through the Gamma Ray Burst jet as well as applying the analysis to Short Gamma Ray Bursts.
Additionaly, my python code to analyze the results of MCRaT will be uploaded as well to github. More information will follow soon.
For the Total Solar Eclipse on August 21st 2017, I conducted a variety of astronomy outreach events including the aforementioned Astronomy Open House. I am a NASA Oregon Space Grant Consortium Astronomer-In-Residence, to answer any questions members of the public may have about the event, and I have been interviewed for a video on the eclipse which was produced by the local community library.
Oregon State University also had a festival on the weekend leading up to the eclipse. I, and many others, hosted activities as well as night observations for the thousands of people that came to this spectacular event. More information can be found at: communications.oregonstate.edu/space
Myself and another graduate student, Atul Chhotray, host an event where members of the public can come to the Physics Department and participate in cool physics demos in addition to going to the rooftop and star gazing through the telescopes that we will have set up. This is the first event of its type at OSU that is open to the public. We work with the local library, the local amateur astronomy club, and other community organizations.
Information for this event can be found on Facebook at facebook.com/osuastronights/.
Due to the high number of requests from the Astronomy Open Houses, we have started an Astronomy Club to bring together members of the community with an interest in astronomy. The website for the club is: osuastronomyclub.wordpress.com/
Image Credit: F. Espanak
