September 7 -- Colloquium
Andrew Baker (Rutgers)
Not-So-Dense Gas in Not-So-Distant Galaxies
To understand how galaxies evolve across cosmic time, we must
understand not only their dark matter and their stars, but also
the properties of their interstellar gas, from which new stars
form and into which old stars release the products of their
nucleosynthesis. In normal galaxies like the Milky Way, a majority
of this gas lies at temperatures that are neither hot enough to
ionize hydrogen atoms nor cold enough to permit the formation of
hydrogen molecules. Such material is best traced at radio
wavelengths using the 21cm spin-flip transition of neutral atomic
hydrogen (HI). I will describe what we can learn from observations
of HI emission in galaxies, and how we will use a powerful new
array of 64 radio telescopes in South Africa to observe a single
position on the sky for thousands of hours, thereby probing the
evolution of galaxies' HI reservoirs over the last nine billion
years. This effort, constituting the LADUMA (Looking At the
Distant Universe with the MeerKAT Array) survey, will benefit from
close connections with optical-wavelength observations and
theoretical modelling.
September 8 -- Colloquium
Eric Gawiser (Rutgers)
Probing Dark Energy and Dark Matter with High-Redshift
Galaxies in the Era of Big Data
The spatial clustering of distant galaxies is a powerful probe of
both the nature of those galaxies and of fundamental
physics. I will summarize recent measurements of the
physical properties of high-redshift galaxies made at
Rutgers. Understanding these galaxies allows us to mitigate
systematic errors as we use them to study cosmology.
The HETDEX experiment is using our Bayesian classification method
to discover 700,000 high-redshift Lyman alpha-emitting galaxies
and will use their clustering to determine the dark energy
equation-of-state and to measure the spatial curvature of the
Universe. As the leading example of "Big Data" in astronomy,
the forthcoming Large Synoptic Survey Telescope (LSST) will
produce over 50 petabytes of images. These images will
reveal billions of distant galaxies whose clustering we will use
to determine the evolution of the dark energy equation-of-state,
to seek evidence for modifications to General Relativity, and to
measure the masses of cosmological neutrinos. I will present
a Rutgers study of improvements to the LSST experimental design
that will reduce systematic errors in these measurements.
September 15 -- Juliana Kwan (U. Penn)
Galaxy-galaxy lensing for cosmology in the Dark Energy Survey
The Dark Energy Survey (DES) is an ongoing photometric survey
that will cover 5000 sq deg of the Southern sky over five years
with the aim of determining the origin of cosmic acceleration. Two
of the probes involved in achieving this goal are the large scale
clustering of galaxies and weak gravitational lensing, which are
more powerful when taken in combination, since a number of
parameter degeneracies can be broken by combining probes. Using
measurements of large scale clustering and galaxy-galaxy lensing
of red galaxies identified in the Science Verification area, we
are able to provide some of the first cosmological constraints
from the Dark Energy Survey.
September 29 -- Boris Leistedt (NYU)
Cosmology with large imaging surveys: from precision to
accuracy
I will give an overview of the formidable science that can be
achieved with modern photometric galaxy surveys, and also discuss
the challenges that must be overcome in order to fully exploit
these large data sets. I will present some of the latest results
from the Dark Energy Survey (DES), and highlight the great
opportunities that will come with the LSST. Finally, I will
showcase some of the most advanced statistical methods used to
analyze these surveys. I will present a new approach for robustly
estimating photometric redshifts and their probability
distributions even in the presence of limited, highly
heterogeneous spectroscopic training data.
October 6 -- Mary Putman (Columbia)
Gas Flows on Various Scales
Gas flows into dark matter halos of all mass scales. In
this talk I will discuss the flows relative to the largest and
smallest mass scales. This is the flow of the intergalactic
medium to galaxy clusters traced by Lyman-alpha absorbers and the
flow of gas into a dwarf spiral galaxy at its disk-halo
interface. The latter represents one of the few direct
detections of inflow.
October 13 -- Smita Mathur (OSU)
Missing baryons and missing metals in galaxies: Clues from our
Milky Way
It is well-known that most galaxies are missing most of their
baryonic mass. Perhaps more surprisingly, they also seem to
be missing most of their metals. I will present Chandra
observations probing our Milky Way halo in absorption. Together
with XMM and Suzaku data on emission, our results show that
the Milky Way halo contains a huge reservoir of warm-hot gas that
may account for a large fraction of missing baryons and metals.
I'll review current status of this field, discuss implications of
our results to models of galaxy formation and evolution and
outline paths for future progress.
October 20 -- Shy Genel (CCA)
Lagrangian analysis of cosmological simulations
Galaxies form hierarchically and at any given cosmic epoch z>0, the material making up z=0 galaxies may be spread over many Megaparsecs and in numerous progenitor galaxies. Cosmological simulations provide us with the ability to follow the time evolution of the individual 'mass elements' that make up galaxies, referred to as Lagrangian analysis. I will discuss two applications of such an approach, one focusing on the evolution in the gas phase with results on the angular momentum content of galaxies, and one focusing on the evolution in the stellar phase with implications for our understanding of stellar IMF variations.
October 27 -- Steve Boada (Rutgers)
Measuring the scatter in the cluster optical richness-mass
relation with machine learning
I will discuss the work that I did for my PhD thesis while at Texas A&M. I studied the applicability of the upcoming Hobby Eberly Dark Energy Experiment (HETDEX) to calibrating the optical richness-mass relationship of galaxy clusters. The study was conducted in two parts: Firstly, I used a set of detailed mock observations to estimate the number of clusters observed and their associated parameters. Then I used a traditional scaling relation and a machine learning approach to estimate each cluster's total mass. Secondly, I used a set of real observations to apply the methods developed previously to ten clusters selected from the SDSS. I will discuss the results of this work and look forward to HETDEX.
November 3 -- Marla Geha (Yale)
The Satellite Populations of Milky Way-like Galaxies
The properties of the
Milky Way's satellite galaxies provide critical clues to how
galaxies form and test the nature of dark matter. However, the
number of Milky Way satellites and their properties do not fully
agree with well-established cosmological models. The SAGA
(Satellites Around Galactic Analogs) Project is a long-term
program to find satellites around 100 Milky Way analogs. Our
survey has so far determined complete luminosity functions down
to M_r = -12 for eight Milky Way analogs. We find a wide range
of satellite number and properties. I will discuss how these
results potentially change the physical interpretation of
measurements based only on the Milky Way's satellites.
Thursday Nov. 10 -- Special Seminar
Karl Gebhardt
Rutgers 250 Fellow
From Black Holes to Dark Energy, with a journey from New
Jersey to Texas
The nature of dark energy and the roles of black holes and dark matter have been and will continue to be major outstanding issues for understanding our universe. I will summarize initial results and prospect for three major observing campaigns regarding each of these issues. HETDEX is our large dark energy program that is recently starting taking data. The main focus is to measure any evolution of dark energy. It is a 4-year observing campaign. I will present the initial analysis and demonstrate we are on our way to making the most precise measure of the universe expansion rate.
December 1 -- Francis-Yan Cyr-Racine
ETHOS - From dark particle physics to the matter distribution
of the Universe and beyond
The fundamental properties of dark matter can affect structure
formation in our Universe in subtle ways. Unfortunately, many dark
matter theories make similar predictions for how structure
assembles on large and small scales, leading to a large degeneracy
in model space. Motivated by this, we formulate an effective
theory of structure formation (ETHOS) that enables cosmological
structure formation to be computed in a vast array of
microphysical model of dark matter physics. This framework maps
the detailed microphysical theories of particle dark matter
interactions into the physical effective parameters that shape the
linear matter power spectrum and the self-interaction transfer
cross section of non-relativistic dark matter. These are the input
to structure formation simulations, which follow the evolution of
the cosmological and galactic dark matter distributions.
These effective parameters in ETHOS allow the classification of
dark matter theories according to their structure formation
properties rather than their intrinsic particle properties, paving
the way for future simulations to span the space of viable dark
matter physics relevant for structure formation. We discuss how
this framework can help understanding how dark matter microphysics
affects structure formation on small scales.
December 7 -- Jo Dunkley
December 8 -- Michael Tremmel
How to Quench a Galaxy
Galaxy "Genetic Modification" (GM) is a breakthrough method that
provides the ability to conduct controlled experiments with fully
cosmological simulations (Roth+ 2016). This approach is
implemented, along with a new sub-grid model for Supermassive
Black Hole (SMBH) physics that I have developed, into a series of
controlled experiments on a halo with virial of 10^12 Msun at z =
2. I show that the interaction between SMBH feedback and merger
history determine whether and for how long star formation is
quenched at high redshift. I further test these results in the
Romulus Simulations, a new set of large-scale cosmological
simulations run at the same resolution and with the same physics
as the GM runs, showing how merger history informs the evolving
population of quenched galaxies. I also predict the the observable
properties of `rejuvenated' galaxies, that quench for a time and
then come back onto the main sequence.