Research Program

My research focuses on using cosmic surveys to understand the fundamental nature of dark matter. Dark matter makes up roughly 25% of the universe, yet we know very little about its composition. My research program combines two astrophysical techniques to understand the nature of dark matter. Indirect Detection searches for Standard Model particles produced through the annihilation or decay of dark matter in regions of high density. Gravitational Probes extract information about the fundamental interactions of dark matter from its distribution and clustering.

To better understand the nature of dark matter, I am heavily involved in the development, operation, and analysis of large cosmic survey experiments. Specifically, I am a member of the Fermi Large Area Telescope (Fermi-LAT), a space-based gamma-ray detector; the Dark Energy Survey (DES), a ground-based optical/near-infrared imaging survey; and the LSST Dark Energy Science Collaboration (DESC), a scientific collaboration associated with the next-generation Large Synoptic Survey Telescope (LSST).

Cosmic surveys provide an enormous amount of data and there are many opportunities for student research at all levels. If you are interested in studying dark matter or near-field cosmology, please contact me.

Recent Results

Searching for Milky Way Stellar Streams

Stellar streams are created when satellite galaxies and star clusters are disrupted by the gravitational potential field of the Milky Way. These streams of stars provide a direct measurement of the local gravitational acceleration near the stream. As such, stellar streams can be used to constrain the size and shape of the Milky Way's dark matter halo. In addition, one key prediction of the cold, collisionless dark matter paradigm is that dark matter should clump on scales much smaller than the smallest known galaxies. These dark matter "subhalos" could be detected through their gravitational influence on stellar streams. We have searched for new stellar streams using the wide area, precisely calibrated data from the Dark Energy Survey (DES). Using the first three years of DES data, we have discovered nearly a dozen new stellar streams. These discoveries increase the known population of stellar streams by ~50%.

The DES stellar stream discoveries accompany the first public release of DES data. I am heavily involved in the production, validation, and distribution of high-level DES data products as the founder and "coordinator emeritus" of the DES Science Release working group.

Publications:

  • Shipp, Drlica-Wagner, Balbinot, et al. (2018), [1801.03097]

Ultra-Low Noise Skipper CCDs

Silicon charged coupled devices (CCDs) have ubiquitous use in astronomy and cosmology. CCDs make use of the photoelectric effect to convert photons into electrons, which can be digitized to yield precise measurements of astrophysical objects. CCDs are also extremely sensitive particle detectors and can be used to search for dark matter and coherent neutrino scattering. State-of-the-art scientific CCDs have a root-mean-squared (rms) electronic readout noise of ~3 electrons per pixel. This noise sets a technical limit on the sensitivity of CCDs both for very faint astronomical sources and very rare particle searches. At Fermilab, we have developed a "Skipper" CCD readout structure to overcome the conventional limit on readout noise. Skipper CCDs are able to non-destructively read the charge in a single pixel multiple times. This allows us to reduce the readout noise by the square root of the number of reads. We have recently shown that Skipper CCDs can reach a readout noise of 0.068 e- rms/pix. This technical achievment has exciting implications for rare particle searches and cosmology! If you are interested in reading more about the Skipper CCDs, check out this article in Symmetry Magazine.

Publications:

  • Tiffenberg, Sofo-Haro, Drlica-Wagner et al. (2017) PRL 119, 131802 [1706.00028]

Searching for Ultra-Faint Milky Way Satellite Galaxies

Our Milky Way is surrounded by many small satellite galaxies. These galaxies are the most ancient, least chemically enriched, and most dark-matter-dominated systems known. Our understanding of these galaxies was greatly increased by the Sloan Digital Sky Survey (SDSS), which roughly doubled the known population of Milky Way satellites. However, the total number of known satellite galaxies was still much smaller than predicted by simulations of cold dark matter. One factor in the disagreement between simulations and observations is that SDSS only observed a third of the sky. The Dark Energy Survey (DES) is in the process of observing roughly 5000 square degrees of the southern hemisphere to unprecedented depth. My work has focused on using DES and other imaging surveys with DECam to increase the number of known satellite galaxies. The first round of discoveries with DES generated quite a bit of excitement.

As a member of the DES Collaboration, I am heavily involved in the data processing, specifically artifact masking and removal. Additionally, I help to lead the effort to validate the DES data for high-level science. In my spare time, I like to tinker with the DECam liquid nitrogen system. I've put together an introduction to DES computing and DES research at Fermilab here: "Getting Started with DES at Fermilab".

Publications:

  • Drlica-Wagner, Bechtol, Allam, et al. ApJL, 833, 5 (2016), [1609.02148]
  • Drlica-Wagner, Bechtol, Rykoff, et al., ApJ, 813, 109 (2015) [1508.03622]
  • Bechtol, Drlica-Wagner, Balbinot, et al., ApJ, 807, 50 (2015) [1503.02584]

Searching for Dark Matter Annihilation with the Fermi-LAT

My research seeks to better understand the dark matter that constitutes nearly 85% of the matter density of the Universe. Currently, I am searching for evidence of dark matter in gamma rays, using the Fermi Large Area Telescope (LAT). I am specifically interested in observations of nearby clumps of dark matter, such as the dwarf satellite galaxies of our own Milky Way. Dwarf galaxies are rich in dark matter but lack astrophysical gamma-ray production, making them prime candidates for dark matter detection. Additionally, numerical simulations predict that many more dwarf galaxies are yet undiscovered. Dark matter decay or annihilation in these galaxies would cause them to shine as unassociated gamma-ray sources.

As a member of the Fermi-LAT Collaboration, I enjoyed working to improve the LAT gamma-ray reconstruction software and increasing the performance of the instrument. I work on implementing multivariate classification algorithms into the LAT gamma-ray event selection. Much of the work that I do bridges the fields of particle physics and astrophysics.

Publications:

  • Fermi-LAT Collaboration ApJ 834, 2 (2017) [1611.03184]
  • Drlica-Wagner, Albert, Bechtol, et al. ApJL 809, 4 (2015) [1503.02632]
  • Fermi-LAT Collaboration PRL 115, 231301 (2015) [1503.02641]
  • Fermi-LAT Collaboration PRD 89, 042001 (2014) [1310.0828]

Past Research

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X-ray Astronomy and Observational Cosmology

The nature of dark energy, the mysterious component driving the accelerating expansion of the Universe, is one of the foremost questions in physics today. I sought to examine this question through the formation and growth of massive clusters of galaxies. These galaxy clusters are one of the most powerful probes of dark energy, since they are the largest gravitationally bound objects in the Universe and can be observed over cosmological times. The summer before graduate school, I was involved in a project which used observations from the Chandra and ROSAT X-ray telescopes to simultaneously constrain cosmology and the X-ray scaling relations of massive clusters. Additionally, this work was used to constrain the dark energy equation of state and set upper limits on neutrino mass.

The Advanced Pair Telescope (APT)

Gamma rays are produced by the most energetic phenomena in the Universe. At the lowest energies (<20 MeV), gamma rays are observed by Compton scattering telescopes, while at the highest energies (>100 GeV) they can be observed by ground-based Cherenkov telescopes. However, before the launch of the Fermi Large Area Telescope (LAT), the energy range between 100 MeV and 100 GeV was largely unexplored. While the LAT has unprecedented angular and energy resolution, its effective area is still quite small compared to ground-based arrays. Using Geant4, a software toolkit for high energy physics, I examined the potential for a large effective area space-based successor to the LAT. I developed simple and robust algorithms for reconstructing the incident direction of gamma rays and optimized the instrumental design subject to the constraints of a space-based mission.

Antibiotic Resistance

Infectious diseases are responsible for nearly one-third of all deaths worldwide. As an undergraduate research associate at the Public Health Research Institute, I investigated the transmission of infectious diseases in the New York City metropolitan area. I implemented multivariate clustering algorithms to map the spread of various genetic strains of Mycobacterium tuberculosis. These genetic maps were complimentary to spatial maps developed by hospitals and can help to identify the source and spreading mechanism of an outbreak. Additionally, I investigated the role of the virulence regulator gene in the human colonization of the Staphylococcus aureus bacterium. Staphylococcus aureus is one of the top five causes of hospital-contracted infections, and it is estimated that nearly 20% of the human population are long term carriers of Staphylococcus. Interestingly, we found that less virulent strains may be favored in infections, potentially due to the fact that they elicit a less severe host immune response.


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