Rachel Mandelbaum
Professor Carnegie Mellon University
- Pittsburgh PA
Rachel Mandelbaum's research interests are predominantly in the areas of observational cosmology and astrophysics.
Biography
Mandelbaum earned her PhD in Physics from Princeton University in 2006, then was a Hubble Fellow for astrophysics at the Institute for Advanced Study and an associate research scholar in the Department of Astrophysical Sciences at Princeton University. She moved to Carnegie Mellon University in 2012 and has been Department Head in Physics since 2024.
Mandelbaum’s research interests are in the areas of observational cosmology and galaxy studies that constrain our cosmological model, reveal the nature of dark matter and dark energy, and unveil the connection between dark matter and galaxies. Over the course of her career she has moved from carrying out such studies in the Sloan Digital Sky Survey (SDSS), to the Hyper Suprime-Cam Survey (HSC), and is now preparing for the Rubin Observatory Legacy Survey of Space and Time (LSST) and the Nancy Grace Roman Space Telescope. In recent years she has dedicated significant effort towards collaboration leadership, the development of open source software for astronomical simulation and data analysis, and the development of novel analysis tools using machine learning. For example, she has been one of the lead developers of the GalSim library used for image simulations by all current optical and infrared imaging surveys, and is co-PI of the LINCC Frameworks initiative, which is supported by Schmidt Sciences to develop open-source analysis infrastructure for LSST. Much of her work on LSST is carried out within the LSST Dark Energy Science Collaboration, for which she previously served as Analysis Coordinator (2015-2019) and then Spokesperson (2019-2021), but also as part of the Rubin commissioning team and the Rubin Survey Cadence Optimization Committee (SCOC).
Major recognitions of Mandelbaum’s work include the AAS Annie Jump Cannon Prize, the Department of Energy Early Career Award, an Alfred P. Sloan Fellowship, a Simons Investigator Award, and selection as a Fellow of the American Physical Society.
Areas of Expertise
Media Appearances
Genesis Mission Takes on Astronomy’s Growing Computing Challenge
HPCwire online
2026-09-01
HPCwire interviewed Dr. Rachel Mandelbaum, professor of physics and head of the Department of Physics at CMU, about her Genesis Mission project. We discussed why existing approaches are becoming difficult at this scale, how the project could make it easier to work across different astronomical datasets, and the potential role of AI and foundation models.
CMU professor leads research project for Dept. of Energy’s Genesis Mission
Times of Israel online
2026-08-25
“Our team is working on data infrastructure that is going to make it easier for researchers to apply AI to data from multiple sky surveys,” Mandelbaum offered.
Carnegie Mellon Researchers Lead Three DOE Genesis Mission Awards to Advance the Future of AI-Enabled Scientific Discovery
Carnegie Mellon University Profile online
2026-07-22
CMU researchers, led by Rachel Mandelbaum, head of the Department of Physics at CMU’s Mellon College of Science and member of the McWilliams Center for Cosmology and Astrophysics, with partners from the University of Washington and collaborators from SLAC National Accelerator Laboratory, will develop AI-enabled infrastructure that will make it easier for scientists to combine and analyze data from some of the world's largest astronomy experiments.
CMU now offers track in quantum physics, thanks to advocacy from a student
Pittsburgh Post-Gazette online
2024-12-27
These tracks allow students to complete their general degree while gaining additional expertise in an area they’re interested in, said Rachel Mandelbaum, CMU professor and interim head of the physics department.
CMU hosts first-ever Physics Slam
The Tartan online
2022-02-21
Then, Professor Rachel Mandelbaum introduced the audience to weak gravitational lensing, a measurement using data gained from large sky surveys. Weak gravitational lensing can be used to measure masses, specifically of dark matter in the universe. Her lab uses data from the Sloan Digital Sky Survey (SDSS) and the Hyper-SuprimeCam (HSC), which capture detailed images of the galaxy. Professor Mandelbaum’s research asks questions like, “How is dark matter distributed in the universe?” and “What are the main components of the universe?”
Jewish cosmologist is a star at CMU
The Pittsburgh Jewish Chronicle online
2020-08-12
Rachel Mandelbaum has always asked why. “From when I was a pretty young child, I was interested in learning how stuff worked,” she said.
Carnegie Mellon physicist Rachel Mandelbaum named 2019 Simons Investigator
EurekAlert! online
2019-06-24
"I am honored to have been named a Simons Investigator. This source of support will be of great value to my research group during the next five years, which will be particularly exciting times as we explore many questions in cosmology with new datasets," Mandelbaum said.
Hyper Suprime-Cam survey maps dark matter in the universe
Phys.org online
2018-09-26
An international group of researchers, including Carnegie Mellon University's Rachel Mandelbaum, released the deepest wide field map of the three-dimensional distribution of matter in the universe ever made and increased the precision of constraints for dark energy with the Hyper Suprime-Cam survey (HSC).
NASA’s Dark-Energy Probe Faces Cost Crisis
Scientific American online
2017-06-06
Those include a survey to measure how the structure of the Universe evolved over time, which will shed light on the nature of dark energy. WFIRST’s data should complement the observations of several other dark-energy explorers set to come online in the early 2020s, such as the European Space Agency’s Euclid probe, says Rachel Mandelbaum, an astrophysicist at Carnegie Mellon University in Pittsburgh, Pennsylvania.
Media
Social
Industry Expertise
Accomplishments
DOE Early Career Award
2012
Kusaka Memorial Prize, Princeton University
2000
Hubble Fellow
2006
AAS Annie Jump Cannon Prize
2011
Alfred P. Sloan Fellow
2013
Falco-DeBenedetti Career Development Professor
2013
Simons Investigator in Astrophysics
2019
Education
Princeton University
Ph.D.
Physics
2006
Princeton University
A.B.
Physics
2000
Event Appearances
Invited Talk,“New Frontier sin Cosmology with the Intrinsic Alignments of Galaxies”
(2022) Kyoto (participated remotely)
Invited Talk on LINCC Frameworks
(2022) LSST Solar System Readiness Sprint Virtual
Invited Review
(2022) EchoIA Kickoff Workshop Virtual
Articles
A Joint Roman Space Telescope and Rubin Observatory synthetic wide-field imaging survey
Monthly Notices of the Royal Astronomical Society2023
We present and validate 20 deg2 of overlapping synthetic imaging surveys representing the full depth of the Nancy Grace Roman Space Telescope High-Latitude Imaging Survey (HLIS) and five years of observations of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). The two synthetic surveys are summarized, with reference to the existing 300 deg2 of LSST simulated imaging produced as part of Dark Energy Science Collaboration (DESC) Data Challenge 2 (DC2). Both synthetic surveys observe the same simulated DESC DC2 universe. For the synthetic Roman survey, we simulate for the first time fully chromatic images along with the detailed physics of the Sensor Chip Assemblies derived from lab measurements using the flight detectors. The simulated imaging and resulting pixel-level measurements of photometric properties of objects span a wavelength range of ∼0.3 to 2.0 μm. We also describe updates to the Roman simulation pipeline, changes in how astrophysical objects are simulated relative to the original DC2 simulations, and the resulting simulated Roman data products. We use these simulations to explore the relative fraction of unrecognized blends in LSST images, finding that 20-30 per cent of objects identified in LSST images with i-band magnitudes brighter than 25 can be identified as multiple objects in Roman images. These simulations provide a unique testing ground for the development and validation of joint pixel-level analysis techniques of ground- and space-based imaging data sets in the second half of the 2020s – in particular the case of joint Roman–LSST analyses.
Analytical weak-lensing shear responses of galaxy properties and galaxy detection
Monthly Notices of the Royal Astronomical Society2023
Shear estimation bias from galaxy detection and blending identification is now recognized as an issue for ongoing and future weak-lensing surveys. Currently, the empirical approach to correcting for this bias involves numerically shearing every observed galaxy and rerunning the detection and selection process. In this work, we provide an analytical correction for this bias that is accurate to subpercent level and far simpler to use. With the interpretation that smoothed image pixel values and galaxy properties are projections of the image signal onto a set of basis functions, we analytically derive the linear shear responses of both the pixel values and the galaxy properties (i.e., magnitude, size and shape) using the shear responses of the basis functions. With these derived shear responses, we correct for biases from shear-dependent galaxy detection and galaxy sample selection. With the analytical covariance matrix of measurement errors caused by image noise on pixel values and galaxy properties, we correct for the noise biases in galaxy shape measurement and the detection/selection process to the second-order in noise. The code used for this paper can carry out the detection, selection, and shear measurement for ∼1000 galaxies per CPU second. The algorithm is tested with realistic image simulations, and we find, after the analytical correction (without relying on external image calibration) for the detection/selection bias of about $-4~{{\%}}$, the multiplicative shear bias is $-0.12 \pm 0.10~{{\%}}$ for isolated galaxies; and about $-0.3 \pm 0.1~{{\%}}$ for blended galaxies with Hyper Suprime-Cam observational condition.
Weak lensing tomographic redshift distribution inference for the Hyper Suprime-Cam Subaru Strategic Program three-year shape catalogue
Monthly Notices of the Royal Astronomical Society2023
We present posterior sample redshift distributions for the Hyper Suprime-Cam Subaru Strategic Program Weak Lensing three-year (HSC Y3) analysis. Using the galaxies’ photometry and spatial cross-correlations, we conduct a combined Bayesian Hierarchical Inference of the sample redshift distributions. The spatial cross-correlations are derived using a subsample of Luminous Red Galaxies (LRGs) with accurate redshift information available up to a photometric redshift of z < 1.2. We derive the photometry-based constraints using a combination of two empirical techniques calibrated on spectroscopic- and multiband photometric data that covers a spatial subset of the shear catalog. The limited spatial coverage induces a cosmic variance error budget that we include in the inference. Our cross-correlation analysis models the photometric redshift error of the LRGs to correct for systematic biases and statistical uncertainties. We demonstrate consistency between the sample redshift distributions derived using the spatial cross-correlations, the photometry, and the posterior of the combined analysis. Based on this assessment, we recommend conservative priors for sample redshift distributions of tomographic bins used in the three-year cosmological Weak Lensing analyses.
A general framework for removing point spread function additive systematics in cosmological weak lensing analysis
Monthly Notices of the Royal Astronomical Society2023
Cosmological weak lensing measurements rely on a precise measurement of the shear two-point correlation function (2PCF) along with a deep understanding of systematics that affect it. In this work, we demonstrate a general framework for detecting and modeling the impact of PSF systematics on the cosmic shear 2PCF, and mitigating its impact on cosmological analysis. Our framework can detect PSF leakage and modeling error from all spin-2 quantities contributed by the PSF second and higher moments, rather than just the second moments, using the cross-correlations between galaxy shapes and PSF moments. We interpret null tests using the HSC Year 3 (Y3) catalogs with this formalism, and find that leakage from the spin-2 combination of PSF fourth moments is the leading contributor to additive shear systematics, with total contamination that is an order of magnitude higher than that contributed by PSF second moments alone. We conducted a mock cosmic shear analysis for HSC Y3, and find that, if uncorrected, PSF systematics can bias the cosmological parameters Ωm and S8 by ∼0.3σ. The traditional second moment-based model can only correct for a 0.1σ bias, leaving the contamination largely uncorrected. We conclude it is necessary to model both PSF second and fourth moment contamination for HSC Y3 cosmic shear analysis. We also reanalyze the HSC Y1 cosmic shear analysis with our updated systematics model, and identify a 0.07σ bias on Ωm when using the more restricted second moment model from the original analysis. We demonstrate how to self-consistently use the method in both real space and Fourier space, assess shear systematics in tomographic bins, and test for PSF model overfitting.
The Dark Energy Survey Year 3 and eBOSS: constraining galaxy intrinsic alignments across luminosity and colour space
Monthly Notices of the Royal Astronomical Society2023
We present direct constraints on galaxy intrinsic alignments using the Dark Energy Survey Year 3 (DES Y3), the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) and its precursor, the Baryon Oscillation Spectroscopic Survey (BOSS). Our measurements incorporate photometric red sequence (redMaGiC) galaxies from DES with median redshift z ∼ 0.2 − 1.0, luminous red galaxies (LRGs) from eBOSS at z ∼ 0.8, and also a SDSS-III BOSS CMASS sample at z ∼ 0.5. We measure two point intrinsic alignment correlations, which we fit using a model that includes lensing, magnification and photometric redshift error. Fitting on scales 6 < rp < 70 Mpc/h, we make a detection of intrinsic alignments in each sample, at 5σ − 22σ (assuming a simple one parameter model for IAs). Using these red samples, we measure the IA-luminosity relation. Our results are statistically consistent with previous results, but offer a significant improvement in constraining power, particularly at low luminosity. With this improved precision, we see detectable dependence on colour between broadly defined red samples. It is likely that a more sophisticated approach than a binary red/blue split, which jointly considers colour and luminosity dependence in the IA signal, will be needed in future. We also compare the various signal components at the best fitting point in parameter space for each sample, and find that magnification and lensing contribute |$\sim 2-18~{{\%}}$| of the total signal. As precision continues to improve, it will certainly be necessary to account for these effects in future direct IA measurements. Finally, we make equivalent measurements on a sample of Emission Line Galaxies (ELGs) from eBOSS at z ∼ 0.8. We constrain the NLA amplitude to be |$A_1=0.07^{+0.32}_{-0.42}$| (|A1| < 0.78 at 95 % CL).
