Peter Ferguson

About Me

At Chisos basin in Big Bend

Hi, I am a 5th year graduate student at Texas A&M currently working with Dr. Jennifer Marshall and Dr. Louis Strigari. Currently my research involves using photometric and spectroscopic surveys such as the DECam Local Volume Exploration (DELVE ), the Dark Energy Survey (DES) or the Southern Stellar Stream Spectroscopic Survey (S5) to explore the (sub)structure of the Milky Way Halo. Additionally, I am working as part of the Munnerlyn instrumentation lab developing TCal a mobile spectrophotometric calibration unit for imaging systems to enhance scientific return from large surveys such as the LSST at VRO. I also am extremely interested in spatial statistics, and data vizualization. For more information see the Research section below or my CV

In my free time I play ultimate frisbee, listen to music and figure out how to spend more time in places like Big Bend.

I can be reached at petersferguson "at" tamu.edu

Science

A up to date-ish list of publications can be found at this ADS library --> (My Publications)

A few short descriptions of projects I have worked on are below.

The Jet stream in DELVE

Currently I am working on characterizing Milky Way stellar streams in the DELVE WIDE footprint. In particular, I have focused on using the DELVE data to better understand the Jet stream. On the left I am showing a matched filter map showing the Jet stream clearly. The discovery extent of the stream is shown between the orange points, and the blue points show the new extent based off my analysis.
For the Jet stream we discover an additional length of 18 degrees (bringing the total length to ~29 degrees). Additionally, we are able to measure a distance gradient along the stream using Blue Horizontal Branch stars, finding that over the known extent the stream ranges in distance from 27-34 kpc. We quantitatively model the spatial density of the stream identifying variations in density such as gaps and peaks, as well as two features off the main track of the stream. Then, we use Gaia EDR3 to measure the proper motion of this stellar stream for the first time. Finally, we model the orbit of the Jet stream finding it is on a retrograde orbit with a pericenter of 12.7 kpc. Taken together these measurements indicate the Jet stream is likely to be one of the best known streams for constraining dark matter substructure in the Milky Way.
For more information check out our paper (Ferguson et. al. 2021 )

The DECam Local Volume Exploration survey DELVE

DELVE is a large photometric survey using observations taken by DECam on the 4-m Blanco telescope at Cerro Tololo Inter-American Observatory. This survey uses public archival data plus 126 nights of dedicated observations to homogeneously and contiguously map the southern sky.

The survey is broken up into 3 components:
  • WIDE: a wide field survey (~15,000 deg2) of the high-Galactic-latitude southern sky. This portion is focused on identifying new halo substructures such as satellite dwarf galaxies and stellar clusters (Mau et. al 2020 , Cerny et. al. 2021) and stellar streams (Ferguson et. al. 2021 )
  • MC: A deeper survey of the outskirts of the Magellanic Clouds with a focus on identifying new substructure and inferring spatially resolved stellar formation histories.
  • DEEP: A much deeper survey of 4 isolated Magellanic analogs in the Local Volume.

I have mostly been involved with the data validation and calibration of the DELVE-WIDE catalog, as well as developing the morphological classifier that we used for DELVE DR1. Data from our first data release can be publicly accessed at Astro Data Lab. For more information on DELVE and DELVE DR1 see our data release paper (Drlica-Wagner et. al. 2021).

The geometry of the core of the Sagittarius Dwarf

One set of tools we use to study Galactic structure are RR Lyrae variable type stars because of the low (~5%) uncertainties on their distance from us. For this project we used RR Lyrae stars to trace the core of the disrupting dwarf galaxy Sagittarius (Sgr). I developed a simple model and hierarchical framework to characterize the geometry of Sgr using the RR Lyrae population. We derived distances to a sample of RR Lyrae in the central core of the Sgr dwarf galaxy from OGLE (Optical Gravitational Lensing Experiment) data, and used these 3D tracers along with RR Lyrae from Gaia DR2 (for which we only had precise 2D information) to measure the shape of the stellar distribution in the central ~2 kpc of Sgr. The best-fitting distribution is found to be highly triaxial with axis ratios 1:0.76:0.43, and can be used to constrain the Sgr progenitor or central dark matter distribution assuming dynamic equilibrium. Interestingly, the major axis is aligned nearly perpendicular to the Galactic Center. This result may be compared to cosmological simulations which generally predict that the major axis of the dark matter distribution of subhalos is aligned with the Galactic Center.

  • Paper
  • Here I am showing an animation of the best fit ellipsoid (green), with the 3D OGLE RR Lyrae shown in black and the projection of this ellipsoid onto the observer plane (blue) as well as the 2D Gaia RR Lyrae(red).

    Stellar Streams in the Dark energy Survey

    I worked on associating the new streams found in the Dark Energy Survey with previously known streams, and investigated the distribution of stream orbits looking for progenitors/ evidence of the vast polar structure(VPOS). The image to the left steps through different distance modulus(distances from us), the lines that come and go are streams seen in the Dark Energy Survey(Image credit:Alex Dirlica-Wagner).

  • Press Release
  • Paper
  • Instrumentation

    TCal: a spectrophotometric calibration instrument for imaging systems

    As part of the Munnelyn Instrumentation Lab, I am developing calibration instrument TCal, similar to DeCal. This instrument will be used to characterize that will be used to characterize the throughput as a function of wavelength of imaging systems at observatories around the world. This will improve the science return from large scale surveys such as the LSST at the Vera Rubin Observatory, by placing survey follow-up resources on a common photometric baseline, thus reducing the systematic error due to combining observations from multiple telescopes. To characterize as system we use a 2nm wide monochromater based tunable light source to illuminate the target system to be calibrated and our monitor CCD. The monitor CCD is calibrated in the lab using a NIST photodiode. So, the ratio between the signal in the target and monitor is a measurement of throughput of the target system at a given wavelength. By repeating this measurement at different wavelengths ranging from 300-1000 nm we are able to fully characterize the throughput of an instrument + telescope system as a function of wavelength.

  • SPIE 2018-(Paper)(Poster)
  • SPIE 2020-(Paper)(Poster)
  • K2F2 (Two K-band filters on FLAMINGOS-2)

    I comissioned two new medium band infrared filters, K-blue and K-red, installed on FLAMINGOS-2(F2) at Gemini South an 8 meter telescope on Cerro Panchon in Chile. Additionally, I investigated how thermal emission from the telescope affects the observed sky brightness in the K-band. The plot on the left shows how the emission between 2200 and 2400 Angstroms(the blue line) is much brighter than the predicted sky(the black line). If we include in our model a component that is blackbody emission at the ambient temperature of the telescope the model (red line) is a much better fit to the data.