Anthony R. Pullen


MS 169-237
JPL, 4800 Oak Grove Dr
Pasadena, CA, 91109
CV


I am currently a NASA Postdoctoral Fellow (NPP) under the mentorship of Olivier Doré at the Jet Propulsion Lab (JPL) in Pasadena, CA. My interests span a wide range of topics in theoretical cosmology and data analysis. Much of my work has involved forecasting the detection capabilities of upcoming probes of cosmology, as well as characterizing systematic effects that can contaminate cosmological parameter estimations. My work has applications to probing cosmology across cosmic time, from inflation through reionization to their imprints on large scale structure today. In addition, I am also interested in probes of dark matter. As a scientist, my hope is to play a part in bringing us closer to understanding our universe.
My research interests include:
    • Intensity Mapping
    • Photometric and Spectroscopic Surveys
    • Reionization, Star Formation, and non-Gaussianity
    • Nonlinear Galaxy Cluster Evolution and Dark Matter
I received my Ph.D. in June 2011 at Caltech, where I studied theoretical cosmology as a member of the Theoretical AstroPhysics Including Relativity (TAPIR) group. During my time at Caltech, I was advised by Profs. Marc Kamionkowski and Christopher M. Hirata. For three years in graduate school I was supported by a NSF fellowship.

Published Work


Intensity Mapping Across Cosmic Times with the Lyman-Alpha Line, A. R. Pullen, Olivier Doré, and Jamie Bock. arXiv:1309.2295

A cartoon of the Lyα emission region around a massive halo, surrounded by the IGM. The four regions are (starting from the inside) the halo, the stellar IGM, the transition zone, and the diffuse IGM. The first two regions are ionized, the transition zone is partially ionized, and the diffuse IGM is neutral. The halo region is denoted by a dashed circle, though the actual regions in ionization equilibrium are denoted as solid circles around the stars.

    

We present a quantitative model of Lyman-alpha (Lyα) emission throughout cosmic history and determine the prospects for intensity mapping of spatial fluctuations in the Lyα signal. Since i) our model assumes at z>6 the minimum star formation required to sustain reionization and ii) is based at z<6 on a luminosity function extrapolated from the few observed bright Lyα emitters, this should be considered a lower limit. Mapping the line emission allows probes of reionization, star formation, and large-scale structure (LSS) as a function of redshift. While Lyα emission during reionization has been studied, we also predict the post-reionization signal to test predictions of the intensity and motivate future intensity mapping probes of reionization. We include emission from massive dark matter halos and the intergalactic medium (IGM) in our model. We find agreement with current, measured luminosity functions of Lyα emitters at z<8. However, diffuse IGM emission, not associated with Lyα emitters, dominates the intensity up to z~10. While our model is applicable for deep-optical or near-infrared observers like the SuMIre survey or the James Webb Space Telescope, only intensity mapping will detect the diffuse IGM emission. We also construct a 3D power spectrum model of the Lyα emission, and characterize possible foreground contamination. Finally, we study the prospects of an intensity mapper for measuring Lyα fluctuations while identifying interloper contamination for removal. Our results suggest that while the reionization signal is challenging, Lyα fluctuations can be an interesting new probe of LSS at late times when used in conjunction with other lines like, e.g., Hα, to monitor low-redshift foreground confusion.

Cross-Correlations as a Cosmological Carbon Monoxide Detector, A. R. Pullen, Tzu-Ching Chang, Olivier Doré, and Adam Lidz. ApJ 768, 15 (2013), arXiv:1211.1397

Limits on <TCO> of CO(1-0) and CO(2-1) over four redshift bins. The solid and dotted lines are the fiducial temperatures according to two different estimates of CO emission, and the dashed line is 10x the estimate shown as the dotted line.

    

We present a new procedure to measure the large-scale carbon monoxide (CO) emissions across cosmic history. As a tracer of large-scale structure (LSS), the CO gas content as a function of redshift can be quantified by its three-dimensional fluctuation power spectra. Furthermore, cross-correlating CO emission with other LSS tracers offers a way to measure the emission as a function of scale and redshift. Here we introduce the model relevant for such a cross-correlation measurement between CO and other LSS tracers, and between different CO rotational lines. We propose a novel use of Cosmic Microwave Background (CMB) data and attempt to extract redshifted CO emissions embedded in the Wilkinson Microwave Anisotropy Probe (WMAP) dataset. We cross-correlate the all-sky WMAP7 data with LSS data sets, namely, the photometric quasar sample and the luminous red galaxy sample from the Sloan Digital Sky Survey Data Release 6 and 7 respectively. We are unable to detect a cross-correlation signal with either CO(1-0) nor CO(2-1) lines, mainly due to the instrumental noise in the WMAP data. However, we are able to rule out models more than three times greater than our more optimistic model. We discuss the cross-correlation signal from the thermal Sunyaev-Zeldovich effect and dust as potential contaminants, and quantify their impact for our CO measurements. We discuss forecasts for current CMB experiments and a hypothetical future CO focused experiment, and propose to cross-correlate CO temperature data with the Hobby-Eberly Telescope Dark Energy Experiment Lyα-emitter sample, for which a signal-to-noise ratio of 58 is possible.

Systematic Effects in Large-Scale Angular Power Spectra of Phoometric Quasars and Implications for Constraining Primordial Nongaussianity, A. R. Pullen and C. M. Hirata. Accepted for publication to PASP. arXiv:1212.4500

The measured cross-correlation angular power spectra between QSO redshift slices z=1.2 and 1.7 from the Richards 2008 quasar catalog before mode projecting systematic effects. The crosses are the measured spectra with 1σ errors and the solid lines are the predicted spectra. Note that the predicted spectra are not exactly zero at smaller scales because the redshift distributions have small overlaps.

    

Primordial non-Gaussianity of local type is predicted to lead to enhanced halo clustering on very large scales. Photometric quasars, which can be seen from cosmological redshifts z>2 even in wide-shallow optical surveys, are promising tracers for constraining non-Gaussianity using this effect. However, large-scale systematics can also mimic this signature of non-Gaussianity. In order to assess the contribution of systematic effects, we cross-correlate overdensity maps of photometric quasars from the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) in different redshift ranges. We find that the maps are significantly correlated on large scales, even though we expect the angular distributions of quasars at different redshifts to be uncorrelated. This implies that the quasar maps are contaminated with systematic errors. We investigate the use of external templates that provide information on the spatial dependence of potential systematic errors to reduce the level of spurious clustering in the quasar data. We find that templates associated with stellar density, the stellar color locus, airmass, and seeing are major contaminants of the quasar maps, with seeing having the largest effect. Using template projection, we are able to decrease the significance of the cross-correlation measurement on the largest scales from 9.2σ to 5.4σ. Although this is an improvement, the remaining cross-correlation suggests the contamination in this quasar sample is too great to allow a competitive constraint on fNL by correlations internal to this sample. The SDSS quasar catalog exhibits spurious number density fluctuations of ~2% rms, and we need a contamination level less than 1% (0.6%) in order to measure values of fNL less than 100 (10). Properly dealing with these systematics will be paramount for future large scale structure surveys that seek to constrain non-Gaussianity.

Non-Detection of a Statistically Anisotropic Power Spectrum in Large-Scale Structure, A. R. Pullen and C. M. Hirata. JCAP 1005, 27 (2010), arXiv:1003.0673

The quadrupole anisotropy parameters for each multipole marginalized over redshift slice with 1-sigma errors. The top panel includes errors calculated from the Fisher matrix. The bottom panel includes errors calculated using N-body simulations. Note that both results are consistent within two sigma with the null result, shown as the dashed line in both plots.

    

We search a sample of photometric luminous red galaxies (LRGs) measured by the Sloan Digital Sky Survey (SDSS) for a quadrupolar anisotropy in the primordial power spectr um, in which P(k) is an isotropic power spectrum P(k) multiplied by a quadrupolar modulation pattern. We first place limits on the 5 coefficients of a general quadrupole anisotropy. We also consider axisymmetric quadrupoles of th e form P(k) = P(k){1 + g*[cos2θ-1/3]} where θ is the angle between k and n the axis of the anisotropy. When we force the symmetry axis to be in the direction (l,b)=(94o,26o) identified in the Groeneboom et al. analysis of the cosmic microwave background, we find g*=0.006±0.036 (1 σ). With uniform priors on n and g* we find that -0.41 < g* < +0.38 with 95% probability, with the wide range due mainly to the large uncertainty of asymmetries aligned with the Galactic Plane. In none of these three analyses do we detect evidence for quadrupolar power anisotropy in large scale structure.

Cosmic Microwave Background Statistics for a Direction-Dependent Primordial Power Spectrum, A. R. Pullen and M. Kamionkowski. Phys. Rev. D 76, 103529 (2007), arXiv:0709.1144

Two realizations of a CMB temperature map. The top panel is a realization when there are no violations of statistical isotropy. The bottom panel exhibits statistical isotropy violation in the direction of the galactic poles with a power quadrupole of 2.

Statistical isotropy of primordial perturbations is a common assumption in cosmology, but it is an assumption that should be tested. To this end, we develop cosmic microwave background statistics for a primordial power spectrum that depends on the direction, as well as the magnitude, of the Fourier wavevector. We first consider a simple estimator that searches in a model-independent way for anisotropy in the square of the temperature (and/or polarization) fluctuation. We then construct the minimum-variance estimators for the coefficients of a spherical-harmonic expansion of the direction-dependence of the primordial power spectrum. To illustrate, we apply these statistics to an inflation model with a quadrupole dependence of the primordial power spectrum on direction and find that a power quadrupole as small as 2.0% can be detected with the Planck satellite.

Search with EGRET for a Gamma Ray Line from the Galactic Center, A. R. Pullen, R. Chary, and M. Kamionkowski. Phys. Rev. D 76, 063006 (2007), arXiv:astro-ph/0610295

The 2σ upper limits to the velocity-averaged cross section <σv> as a function of WIMP mass for various dark-matter halo models, including the Kravtsov a (Ka) and b (Kb) profiles, the Navarro-Frenk-White profile (NFW), and the isothermal profile (Iso).

We search data from the Energetic Gamma Ray Experiment Telescope (EGRET) for a gamma-ray line in the energy range 0.1-10 GeV from the 10 X 10 degree region around the Galactic center. Our null results lead to upper limits to the line flux from the Galactic center. Such lines may have appeared if the dark matter in the Galactic halo is composed of weakly-interacting massive particles (WIMPs) in the mass range 0.1-10 GeV. For a given dark-matter-halo model, our null search translates to upper limits to the WIMP two-photon annihilation cross section as a function of WIMP mass. We show that for a toy model in which Majorana WIMPs in this mass range annihilate only to electron-positron pairs, these upper limits supersede those derived from measurements of the 511-keV line and continuum photons from internal bremsstrahlung at the Galactic center.

Teaching


2009-2010: Physics 1abc: Newtonian Mechanics, Electromagnetism, and Relativity: Caltech
  • Lectured for the freshman general physics course for non-majors.
  • Demonstrated solving classical mechanics problems to students.
  • Explained concepts in electromagnetism and special relativity to students.
  • Monitored continuously the progress of students.
  • Offered help after class.
  • Assisted in grading final exams.
2008-2009: Physics 2ab: Waves, Quantum Mechanics, and Statistical Physics: Caltech
  • Instructed recitations for the sophomore general physics course for non-majors.
  • Performed two lectures in thermal physics for 150 students.
  • Demonstrated solving problems in quantum physics, thermal physics, and wave phenomena to students.
  • Monitored continuously the progress of students.
  • Offered help after class.
  • Assisted in grading quizzes and homework and in leading quiz reviews.
  • Received emails from students praising my methods.
Last Updated: Sept, 2013