Sarah Gallagher

Associate Professor, Department of Physics and Astronomy University of Western Ontario

  • London ON

Professor Gallagher's research focuses on investigating the nature of winds from luminous quasars

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Biography

Dr. Sarah Gallagher is a Professor of Physics and Astronomy and the Director of the Institute for Earth and Space Exploration at Western University. Her astrophysics research focuses on studying growing supermassive black holes at the centres of distant galaxies and the interactions between galaxies in crowded environments. She has over 120 refereed papers that include data from 10 different space observatories, and her research has been recognized with an Ontario Early Career Researcher Award and a Western University Faculty Scholar Award. From 2018-2022, she served as the first Science Advisor to the President of the Canadian Space Agency. In this role, she advised the CSA Executive Committee on space science investments and capacity development and sat on the Departmental Science Advisor Network. She is active in science policy and an advocate for creating a diverse and inclusive space science community. She regularly talks to the public about astronomy and space, and is currently serving as the President of the Canadian Astronomical Society.

Industry Expertise

Education/Learning
Research

Areas of Expertise

Science Policy
Physics Education
Astrophysics
Black Holes
Space Science

Accomplishments

Faculty Scholar Award

University of Western Ontario

2016 - 2018

Faculty of Science Outreach Award

University of Western Ontario

2010

Early Researcher Award

Ontario Ministry of Research & Innovation, 2010 - 2014

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Education

Yale University

B.A.

Physics

1995

Penn State

Ph.D.

Astronomy and Astrophysics

2002

Affiliations

  • Mauna Kea Spectroscopic Explorer Science Team : Member 2014 - Present
  • Joint Committee on Space Astronomy : Member 2015 - 2017
  • Canadian Astronomical Society (CASCA) Board : Directory 2014 - 2017
  • Canadian Time Allocation Committee (CanTAC) : Chair 2013 - 2014 & Member 2011 - 2014
  • Space Telescope User's Committee 2009 - 2011
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Languages

  • English
  • French

Media Appearances

‘Hole’ lotta force: Punching holes in the theory of General Relativity

Western News  

2015-11-19

One of these regarded the description of an object collapsing under its own gravitational pull. If the object is sufficiently dense, no force is strong enough to counteract the attraction of gravitation, and it collapses all the way down to a point. According to Einstein’s theory, the endpoint of this collapse is a singularity, which can be described as a ‘tear’ in spacetime. A singularity is often hidden inside a black hole whose size is set as the region where the gravitational pull is so strong that even light cannot escape from it...

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Ancient Galaxies Finally Get Together

Sky & Telescope  

2010-02-24

Four members of the Hickson Compact Group 31 (and also known as NGC 1471), are coming together in a space about 75,000 light-years across — less than the diameter of the much larger Milky Way. "They each have a mass about one-tenth of the Milky Way," says Sarah Gallagher (University of Western Ontario), "so they're on the high-mass side of what would be called dwarf galaxies." Two components, A and C, are the brightest of the bunch. They have a visual magnitude of 13½, putting them within the grasp of a large amateur telescope...

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Astronomers Find Dust in the Wind of Black Holes

NASA Jet Propulsion Laboratory  

2007-10-09

"Quasars are like the Cookie Monster," said co-author Sarah Gallagher of the University of California at Los Angeles, who is currently a visiting astronomer at the University of Western Ontario, Canada. "They are messy eaters, and they can consume less matter than they spit out in the form of winds."...

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Style

Availability

  • Keynote
  • Moderator
  • Panelist
  • Host/MC

Fees

$0 to $2500*Will consider certain engagements for no fee

Articles

Examining the Role of Environment in a Comprehensive Sample of Compact Groups

The Astronomical Journal

2012

Compact groups, with their high number densities, small velocity dispersions, and an interstellar medium that has not been fully processed, provide a local analog to conditions of galaxy interactions in the earlier universe. The frequent and prolonged gravitational encounters that occur in compact groups affect the evolution of the constituent galaxies in a myriad of ways, for example, gas processing and star formation. Recently, a statistically significant "gap" has been discovered in the mid-infrared (MIR: 3.6-8 μm) IRAC color space of compact group galaxies. This gap is not seen in field samples and is a new example of how the compact group environment may affect the evolution of member galaxies. In order to investigate the origin and nature of this gap, we have compiled a larger sample of 37 compact groups in addition to the original 12 groups studied by Johnson et al. (yielding 174 individual galaxies with reliable MIR photometry). We find that a statistically significant deficit of galaxies in this gap region of IRAC color space is persistent in the full sample, lending support to the hypothesis that the compact group environment inhibits moderate specific star formation rates. Using this expanded sample, we have more fully characterized the distribution of galaxies in this color space and quantified the low-density region more fully with respect to MIR bluer and MIR redder colors. We note a curvature in the color-space distribution, which is fully consistent with increasing dust temperature as the activity in a galaxy increases. This full sample of 49 compact groups allows us to subdivide the data according to physical properties of the groups. An analysis of these subsamples indicates that neither projected physical diameter nor density shows a trend in color space within the values represented by this sample. We hypothesize that the apparent lack of a trend is due to the relatively small range of properties in this sample, whose groups have already been pre-selected to be compact and dense. Thus, the relative influence of stochastic effects (such as the particular distribution and amount of star formation in individual galaxies) becomes dominant. We analyze spectral energy distributions of member galaxies as a function of their location in color space and find that galaxies in different regions of MIR color space contain dust with varying temperatures and/or polycyclic aromatic hydrocarbon emission.

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The Next Generation Atlas of Quasar Spectral Energy Distributions from Radio to X-Rays

The Astrophysical Journal Supplement Series

2011

We have produced the next generation of quasar spectral energy distributions (SEDs), essentially updating the work of Elvis et al. by using high-quality data obtained with several space- and ground-based telescopes, including NASA's Great Observatories. We present an atlas of SEDs of 85 optically bright, non-blazar quasars over the electromagnetic spectrum from radio to X-rays. The heterogeneous sample includes 27 radio-quiet and 58 radio-loud quasars. Most objects have quasi-simultaneous ultraviolet-optical spectroscopic data, supplemented with some far-ultraviolet spectra, and more than half also have Spitzer mid-infrared Infrared Spectrograph spectra. The X-ray spectral parameters are collected from the literature where available. The radio, far-infrared, and near-infrared photometric data are also obtained from either the literature or new observations. We construct composite SEDs for radio-loud and radio-quiet objects and compare these to those of Elvis et al., finding that ours have similar overall shapes, but our improved spectral resolution reveals more detailed features, especially in the mid- and near-infrared.

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Dusty Tori of Luminous Type 1 Quasars at z~2

The Astrophysical Journal

2011

We present Spitzer infrared (IR) spectra and ultraviolet (UV) to mid-IR spectral energy distributions (SEDs) of 25 luminous type 1 quasars at z ~ 2. In general, the spectra show a bump peaking around 3 μm and the 10 μm silicate emission feature. The 3 μm emission is identified with hot dust emission at its sublimation temperature. We explore two approaches to modeling the SED: (1) using the CLUMPY model SED from Nenkova et al. and (2) the CLUMPY model SED and an additional blackbody component to represent the 3 μm emission. In the first case, a parameter search of ~1.25 million CLUMPY models shows that (1) if we ignore the UV-to-near-IR SED, models fit the 2-8 μm region well, but not the 10 μm feature; (2) if we include the UV-to-near-IR SED in the fit, models do not fit the 2-8 μm region. The observed 10 μm features are broader and shallower than those in the best-fit models in the first approach. In the second case, the shape of the 10 μm feature is better reproduced by the CLUMPY models. The additional blackbody contribution in the 2-8 μm range allows CLUMPY models dominated by cooler temperatures (T < 800 K) to better fit the 8-12 μm SED. A centrally concentrated distribution of a small number of torus clouds is required in the first case, while in the second case the clouds are more spread out radially. The temperature of the blackbody component is ~1200 K as expected for graphite grains.

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