Publications
Clicking on any of the links below will redirect you to the abstract and details of my contributions.
Erika L. Wagoner, Eduardo Rozo, Xiao Fang et al
MNRAS, 2021
We implement a linear model for mitigating the effect of observing conditions and other sources of contamination in galaxy clustering analyses. Our treatment improves upon the fiducial systematics treatment of the Dark Energy Survey (DES) Year 1 (Y1) cosmology analysis in four crucial ways. Specifically, our treatment: 1) does not require decisions as to which observable systematics are significant and which are not, allowing for the possibility of multiple maps adding coherently to give rise to significant bias even if no single map leads to a significant bias by itself; 2) characterizes both the statistical and systematic uncertainty in our mitigation procedure, allowing us to propagate said uncertainties into the reported cosmological constraints; 3) explicitly exploits the full spatial structure of the galaxy density field to differentiate between cosmology-sourced and systematics-sourced fluctuations within the galaxy density field; 4) is fully automated, and can therefore be trivially applied to any data set. The updated correlation function for the DES Y1 redMaGiC catalog minimally impacts the cosmological posteriors from that analysis. Encouragingly, our analysis does improve the goodness of fit statistic of the DES Y1 3$\times$2pt data set ($\Delta \chi^2 = -6.5$ with no additional parameters). This improvement is due in nearly equal parts to both the change in the correlation function and the added statistical and systematic uncertainties associated with our method. We expect the difference in mitigation techniques to become more important in future work as the size of cosmological data sets grows.
The University of Arizona Campus Repository, 2020
In the era of large-area surveys, cosmology has seen enormous growth in the amount of available data and a corresponding decrease in the statistical uncertainty of measurements made with this data. The increased precision has led to the discovery of differences between measurements based on the local versus early Universe. One of the most notable differences is a 4.4? tension between the expansion rate of the Universe measured directly with Type Ia supernovae versus that inferred from measurements of the Cosmic Microwave Background (CMB). This tension could be an exciting indication of new physics or a result of unknown systematic uncertainties becoming increasingly important as the statistical uncertainty decreases. In this dissertation, I first explore the possibility of systematic uncertainties due to various observing conditions, such as sky brightness and exposure time. Variations in these conditions lead to variations in the observed density of galaxies, which are difficult to differentiate from variations sourced by cosmology. I introduce a novel method for mitigating the impact of these observing conditions and correctly propagates the uncertainty due to the mitigation into the resulting cosmological analysis. I apply the method to Year 1 (Y1) data from the Dark Energy Survey (DES) and compare the results to the fiducial DES Y1 analysis. I find that this new method results in a modest improvement in the goodness of fit for the recovered cosmological parameters ($\Delta\chi^2=-6.5$ with no additional parameters). Second, I propose a new method for measuring the distance-redshift relation that is independent of both the distance ladder and the theoretical systematics of CMB measurements. I show that such a method is already feasible with existing data, and I forecast the constraining power of this measurement withnear-future data from the Dark Energy Spectroscopic Instrument (DESI). Without any added information, this method applied to DESI data will result in a ~1.3% measurement of the expansion rate. Adding cosmological supernova data improves the constraint to ~0.7%. This level of precision is enough to distinguish between local measurements of the expansion rate and those based on the CMB at high confidence.
Erika L. Wagoner, Eduardo Rozo, Han Aung, & Daisuke Nagai
arXiv e-prints, 2020
The line-of-sight velocity dispersion profile of galaxy clusters exhibits a “kink” corresponding to the spatial extent of orbitinggalaxies. Because the spatial extent of a cluster is correlated with the amplitude of the velocity dispersion profile, we can utilisethis feature as a gravity-calibrated standard ruler. Specifically, the amplitude of the velocity dispersion data allows us to infer thephysical cluster size. Consequently, observations of the angular scale of the “kink” in the profile can be translated into a distancemeasurement to the cluster. Assuming the relation between cluster radius and cluster velocity dispersion can be calibrated fromsimulations, we forecast that with existing data from the Sloan Digital Sky Survey (SDSS) we will be able to measure the Hubbleconstant with3.0 %precision. Implementing our method with data from the Dark Energy Spectroscopic Instrument (DESI)will result in a1.3 %measurement of the Hubble constant. Adding cosmological supernova data improves the uncertainty ofthe DESI measurement to0.7 %. While these error estimates are statistical-only, they provide strong motivation for pursuingthe necessary simulation program required to characterise and calibrate the systematic uncertainties impacting our proposedmeasurement. Whether or not our proposed measurement can in fact result in competitive퐻0constraints will depend on whatthe eventual systematics floor for this method is.
Paxton Tomooka, Eduardo Rozo, Erika L. Wagoner, et al
MNRAS, 2020
We study the distribution of line-of-sight velocities of galaxies in the vicinity of SDSS redMaPPer galaxy clusters. Based on their velocities, galaxies can be split into two categories: galaxies that are dynamically associated with the cluster, and random line-of-sight projections. Both the fraction of galaxies associated with the galaxy clusters, and the velocity dispersion of the same, exhibit a sharp feature as a function of radius. The feature occurs at a radial scale $R_{\rm edge} \approx 2.2R_{\rm{\lambda}}$, where $R_{\rm{\lambda}}$ is the cluster radius assigned by redMaPPer. We refer to $R_{\rm edge}$ as the “edge radius.” These results are naturally explained by a model that further splits the galaxies dynamically associated with a galaxy cluster into a component of galaxies orbiting the halo and an infalling galaxy component. The edge radius $R_{\rm edge}$ constitutes a true “cluster edge”, in the sense that no orbiting structures exist past this radius. A companion paper (Aung et al. 2020) tests whether the “halo edge” hypothesis holds when investigating the full three-dimensional phase space distribution of dark matter substructures in numerical simulations, and demonstrates that this radius coincides with a suitably defined splashback radius.
Andrina Nicola [and 14 others including Erika L. Wagoner]
JCAP, 2020
We analyze the clustering of galaxies in the first public data release of the Hyper Suprime-Cam Subaru Strategic Program. Despite the relatively small footprints of the observed fields, the data are an excellent proxy for the very deep photometric datasets that will be acquired by the Large Synoptic Survey Telescope, and are therefore an ideal test bed for the analysis methods being implemented by the LSST Dark Energy Science Collaboration. We select a magnitude limited sample with i<24.5 and analyze it in four tomographic redshift bins covering the range 0.15lesssim zlesssim1.5. We carry out a Fourier-space analysis of the two-point clustering of this sample, including all auto- and cross-correlations between bins. We demonstrate the use of map-level deprojection methods to account for non-physical fluctuations in the galaxy number density caused by observational systematics. Through a halo occupation distribution analysis, we place constraints on the characteristic halo masses of this sample as a function of redshift, finding a good fit up to scales kmax=1 Mpc−1, including both auto- and cross-correlations. Our results show monotonically decreasing average halo masses with increasing redshift, which can be interpreted in terms of the drop-out of red galaxies at high redshifts for a flux-limited sample, consistent with previous analyses. In terms of photometric redshift systematics, we show that additional care is needed in order to marginalize over uncertainties in the redshift distribution in galaxy clustering, even for samples of this small size, and that these uncertainties can be significantly constrained by including cross-bin correlations. We are able to make a ~3σ detection of the effects of lensing magnification in the HSC data. Our results are stable to variations in the amplitude of density fluctuations σ8 and the cold dark matter abundance Ωc and we find constraints that agree well with measurements from Planck and low-redshift probes. Finally, we use our analysis pipeline to study the clustering of galaxies as a function of limiting flux, and provide a simple fitting function for the linear galaxy bias for magnitude limited samples as a function of limiting magnitude and redshift.
Nora Elisa Chisari [and 30 others including Erika L. Wagoner]
ApJS, 2019
The Core Cosmology Library (CCL) provides routines to compute basic cosmological observables to a high degree of accuracy, which have been verified with an extensive suite of validation tests. Predictions are provided for many cosmological quantities, including distances, angular power spectra, correlation functions, halo bias, and the halo mass function through state-of-the-art modeling prescriptions available in the literature. Fiducial specifications for the expected galaxy distributions for the Large Synoptic Survey Telescope (LSST) are also included, together with the capability of computing redshift distributions for a user-defined photometric redshift model. A rigorous validation procedure, based on comparisons between CCL and independent software packages, allows us to establish a well-defined numerical accuracy for each predicted quantity. As a result, predictions for correlation functions of galaxy clustering, galaxy─galaxy lensing, and cosmic shear are demonstrated to be within a fraction of the expected statistical uncertainty of the observables for the models and in the range of scales of interest to LSST. CCL is an open source software package written in C, with a Python interface and publicly available at https://github.com/LSSTDESC/CCL.
Sarah J. Schmidt, Erika L. Wagoner, Jennifer A. Johnson, et al
MNRAS, 2016
We present the effective temperatures ($T_{\rm eff}$), metallicities, and colours in SDSS, 2MASS, and WISE filters, of a sample of 3834 late-K and early-M dwarfs selected from the Sloan Digital Sky Survey APOGEE spectroscopic survey ASPCAP catalog. We confirm that ASPCAP $T_{\rm eff}$ values between 3550 K$<T_{\rm eff}<$4200 K are accurate to $\sim$100 K compared to interferometric $T_{\rm eff}$ values. In that same $T_{\rm eff}$ range, ASPCAP metallicities are accurate to 0.18 dex between $-1.0<$[M/H]$<0.2$. For these cool dwarfs, nearly every colour is sensitive to both $T_{\rm eff}$ and metallicity. Notably, we find that $g-r$ is not a good indicator of metallicity for near-solar metallicity early-M dwarfs. We confirm that $J-K_S$ colour is strongly dependent on metallicity, and find that $W1-W2$ colour is a promising metallicity indicator. Comparison of the late-K and early-M dwarf colours, metallicities, and $T_{\rm eff}$ to those from three different model grids shows reasonable agreement in $r-z$ and $J-K_S$ colours, but poor agreement in $u-g$, $g-r$, and $W1-W2$. Comparison of the metallicities of the KM dwarf sample to those from previous colour-metallicity relations reveals a lack of consensus in photometric metallicity indicators for late-K and early-M dwarfs. We also present empirical relations for $T_{\rm eff}$ as a function of $r-z$ colour combined with either [M/H] or $W1-W2$ colour, and for [M/H] as a function of $r-z$ and $W1-W2$ colour. These relations yield $T_{\rm eff}$ to $\sim$100 K and [M/H] to $\sim$0.18 dex precision with colours alone, for $T_{\rm eff}$ in the range of 3550–4200 K and [M/H] in the range of $-$0.5–0.2.
The Ohio State University Knowledge Bank, 2014
M dwarfs have expected lifetimes of at least 15 Gyr for the main phase of their lives, which is longer than the current age of the Universe. The chemical composition of the surface of an M dwarf, which is nearly constant during this main phase, is the same as the nearby gas of the galaxy in which it formed and at the time that it formed, so M dwarfs create a “fossil record” with which to examine the history and evolution of their host galaxies. This makes M dwarfs extremely important for study, but we do not see enough M dwarfs with few heavy elements, which are the oldest of the M dwarfs, to match predictions of compositions of stars for the local stellar neighborhood. Distances for these M dwarfs are important to accurately determine the extent of this deficiency, but these are difficult to determine accurately for the older M dwarfs that are of the most interest. M dwarfs, and especially older M dwarfs, are also observationally difficult to study in general because they are very dim compared to other stars. In this thesis, we test two different stellar isochrone models, the one by the Dartmouth group and the one by the Padova group, which we will later use to calculate M dwarf distances and investigate the observed discrepancy further. We find that the Padova group’s model ts better with spectroscopic and photometric data taken from two stellar surveys of the Galaxy, APOGEE and SDSS. We then suggest improvements on the tests we have completed and detail the next steps we hope to take in our investigation. We hope that this deep study of M dwarfs will provide more insights into the chemical evolution of the Milky Way, and allow models of stellar formation and Galactic chemical evolution to be improved upon for future use.
