We present our model and preliminary results from using the 30 richest SDSS redMaPPer clusters and their X-ray follow-up to improve cluster abundance constraints on $\sigma_8$ and $\Omega_m$.
Astronomers have used redshift to quantify distance to objects for over 150 years. Historically, redshift has been calculated by measuring the spectrum of an object and measuring frequency shifts in atomic spectral lines. These so-called spectroscopic redshifts have very low uncertainties but take quite a bit of telescope time and take longer the fainter the object is. Last year, the Dark Energy Survey released their Year 1 data release and revealed that they measured photometry for over 300 million new galaxies. Worse yet, the upcoming Large Synoptic Survey Telescope is estimated to measure photometry for another 20 billion galaxies over its 10-year program. With this many objects, measuring each spectrum is completely unreasonable, however, we need to measure redshifts to do science. After a brief introduction to spectroscopic redshift, I will delve into the various methods that have been developed to measure redshift using photometric data including Bayesian template fitting, machine learning methods, and other more arcane methods.
We measure the scatter in the richness-mass relation for the 30 richest clusters in the redMaPPer catalog for the Sloan Digital Sky Survey (SDSS) using gas mass measurements from the Chandra Xray Observatory. As part of our analysis, we test for the consistency of the mass calibration of the SDSS redMaPPer and Weighing the Giants mass cluster samples. Our results provide the first direct estimate of the scatter in mass of a complete sample of redMaPPer clusters.
I gave a brief overview of my work measuring the richness-mass relation and the cluster gas mass-mass relation with a complete cluster sample to the clusters working group in the Dark Energy Science Collaboration. The talk highlighted some intermediate results in the work that did not include the full scatter model.
For almost 90 years we have expected that the universe has a huge quantity of an invisible form of matter that we have dubbed, dark matter. While we have found more and more convincing evidence that it is there, in the time since, we have learned very little about it. There are currently efforts around the world to attempt to find concrete evidence that dark matter is out there and that the effects that we are seeing are not caused by something else. These include experiments trying to make dark matter, experiments trying to scatter dark matter and experiments looking for the results of dark matter annihilation. In this talk, I will be giving a broad overview of where we stand today in the search for dark matter.
Cosmologists love to compare independent probes of cosmology to get an increasingly better understanding of the universe as a whole. I am currently working on a model to get the true masses of galaxy cluster by jointly fitting several observables that are thought to trace underlying matter. I will be discussing galaxy clusters, why we care about their masses and what we are doing to find their masses.
I will be showing examples of a new class of galaxy discovered only last year called ultra diffuse galaxies. I will show examples of why they were only recently discovered and then discuss how they may help us study the properties of dark matter.