The Dark Energy Spectroscopic InstrumentFrom 2014-2018 I was the Co-Spokesperson for the DESI Collaboration, and many members of the group are now doing science with early data from the survey. DESI built a new spectrograph (actually 10 of them!), which have now been installed on the Mayall Telescope at Kitt Peak in Arizona. You can see me talking about DESI at the telescope itself here (from the BCC documentary "Mystery of Dark Energy"). DESI can take spectra for 5000 objects at a time, and will do a five-year survey, which as of May 2021 has just begun!. DESI will take spectra for ~ 35 million galaxies and quasars, about 10 times more than currently exist from all other instruments. This will allow us to make a 3D map of structure in the Universe, covering roughly 1/3 of the sky (14K sq. degrees) and map the cosmic expansion history to very high precision. This will allow precise tests that can distinguish different models to explain why the Universe is accelerating, and will also give us a much better understanding of the connection between galaxies and dark matter. In the group we are also very interested in what we can learn from DESI observations in the local Universe and within the Milky Way itself.
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The Dark Energy SurveyI have been a member of the Dark Energy Survey since its inception in 2004. DES has now completed a six-year imaging survey (2013-2019), mapping roughly 300 million galaxies over 1/8 of the sky. DES is aimed at measuring the properties of dark energy using galaxy clustering, weak gravitational lensing, galaxy clusters, and supernovae. These techniques are particularly powerful in combination, and we recently measured the local matter density and amount of structure in the Universe more precisely than ever before. The science we can do with DES goes beyond this; for example in 2015-16 we doubled the number of known dwarf galaxies in the Milky Way! My group is also playing a major role in simulating the survey with cosmological N-body simulations and models of the galaxy population. These models are key to making predictions from our cosmological models, so that we can use measurements of galaxies to determine how our Universe evolved. Results from 3 years of DES data are immenent, and many group members have played leading roles in these measurements and their interpretation.
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The SAGA Survey: Satellites Around Galactic AnalogsThe Milky Way galaxy is our home — and the best observed galaxy in the Universe. It is host to two dozen known dwarf galaxy satellites. The properties of these satellite galaxies provide clues to galaxy formation at low masses and to the nature of dark matter. However, to apply our detailed knowledge of Milky Way satellites to broader questions of galaxy formation and dark matter properties requires an improved understanding of the Milky Way’s place in the Universe — how do the properties of the Milky Way and its satellites compare to other similar galaxies? Marla Geha and I initiated this collaboration to determine the satellite content for a large sample of analogs to our own galaxy, compare them with the properties of Milky Way satellites and with a large sample of simulated Milky Way analogs, and to use these observations and simulations together to test physical models for galaxy formation and dark matter. Our Stage II results, which present discoveries of new satellites around 36 Milky Way twins, are now available! We are nearly done taking data for our full sample of 100 systems!
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The Rubin Observatory's Legacy Survey of Space and TimeThe Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will produce the deepest, widest image of the Universe, using a new 3.2 Gigapixel Camera (currently being built at SLAC) and an 8.4 meter mirror on a new telescope in Chile. With a ten year survey expected to start in ~2024, it will observe more than 10 billion galaxies, over half the sky, producing ~20TB of data every night. I am involved in the LSST Dark Energy Science Collaboration which will use data from the LSST survey to learn about dark energy, dark matter, and the evolution of the Universe, and am also on the LSST Scientific Advisory Committee.
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The Dark Sky SimulationsWe had an INCITE 2014 allocation on the Titan Supercomputer, to run several large simulations using the 2HOT N-body code, with Sam Skillman, Mike Warren, Matt Turk and others. We ran two trillion particle N-body simulations in 2014, along with several other smaller boxes. A trillion particles is the largest number of particles ever run in an N-body simulation. These large numbers of particles are needed to simultaneously resolve large volumes and the detailed structure of dark matter halos.
We have made a significant amount of our data publicly available, and plan to release more data soon. We are actively doing science with these boxes, including recent work on the concentration dependence of the galaxy-halo connection, and techniques for distinguishing the redshift space distortions from non-linear bias. |