MEET BOB ABRAHAM
Professor and Chair
David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto
Here is a link to my academic CV.
Biography for Public Talks:
Roberto Abraham is a Professor of Astronomy and Chair of the David A. Dunlap Department of Astronomy and Astrophysics at the University of Toronto. He is a Fellow of the Royal Society of Canada and served as President of the Canadian Astronomical Society.
Prof. Abraham was born in Manila, grew up in San Francisco and Vancouver, and obtained his BSc from University of British Columbia before moving to the UK to obtain a doctorate from Oxford. He did postdoctoral work at the National Research Council of Canada's Herzberg Institute and at Cambridge University. Prof. Abraham's work is focused on observations of galaxy formation and evolution and on the development of innovative scientific instruments, such as the Dragonfly Telephoto Array. He has won numerous awards for his work, including the Jackson-Gwilt Medal awarded by the Royal Astronomical Society, the Canadian Astronomical Society's P. G. Martin Award, an NSERC Steacie Memorial Fellowship, a Canada Council for the Arts Killam Research Fellowship, a Premier's Research Excellence Award, and the University of Toronto Outstanding Teaching Award. He has served on the Board of Directors of major international observatories, advised NASA and scientific funding agencies in various capacities and served as Canada's representative on the James Webb Space Telescope Advisory Committee.
In addition to being a professional astronomer, Prof. Abraham has never given up his love of backyard astronomy, which set him on the road to being a scientist at age 12. His secret life as an amateur astronomer has led him to place tremendous value on outreach, and on the role of astronomy in stimulating the growth of scientific literacy. Astronomy is the gateway science for encouraging young people to embark on a host of STEM careers. This enthusiasm for outreach has led to him serve as the Honorary President of the Toronto Centre of the Royal Astronomical Society of Canada for many years. (Here is a Pro Tip: if you love astronomy and you live in Canada, you should definitely be a member of the Royal Astronomical Society of Canada.)
Galaxy Evolution and Novel Astronomical Instruments
Over the course of my career I've worked in many areas of astrophysics, in collaboration with an incredible set of collaborators and students. Most of my work has been on galaxy evolution. To understand how galaxies evolve I've pioneered techniques for using machine vision to classify galaxy shapes, and helped build spectrometers for giant telescopes. Most recently, I have been trying to better understand a host of interesting phenomena that exist in the Universe at low surface brightness levels. My interest (and the community's interest) in this area has been spurred on by many discoveries made using the Dragonfly Telephoto Array, which I developed together with my colleague Pieter van Dokkum at Yale.
To help prospective students better understand the sorts of things I do, the following sections present five 'themes', each with a representative paper, corresponding to areas in which I contribute. Some of the papers described are quite recent, and their impact is just being felt. Others are highly-cited 'classics'. Taken together, they encompass my general areas of research.
THE LOW SURFACE BRIGHTNESS UNIVERSE
Representative paper: Abraham, R. G., & van Dokkum, P. G. (2014). PASP, 126, 55.
“Ultra-Low Surface Brightness Imaging with the Dragonfly Telephoto Array”
This paper introduces the Dragonfly Telephoto Array (Dragonfly), a new design for a telescope optimized for wide-field low surface brightness imaging. It presents the science rationale for surveying the universe at low surface brightness, describes early results, and quantifies the gain in performance (almost a factor of ten) relative to Dragonfly’s nearest competitor. Discoveries made with the Dragonfly Telephoto Array ignited a resurgence of interest in low surface brightness, and since this paper was published the array has grown from 8 to 48 lenses (with the present configuration of the array best described in Danieli et al. 2020). Dragonfly is scheduled to complete the next stage of its evolution in 2022, thanks to a generous grant from the Canada Foundation for Innovation. At that point it will have grown to 168 lenses, and 120 of these will have exquisite made-in-Canada full-aperture tunable ultra-narrow-band interference filters for wide-field emission line mapping.
Representative paper: van Dokkum, P. Abraham, R., et al. (2015). ApJ 798, 45.
“Forty-seven Milky Way-sized, Extremely Diffuse Galaxies in the Coma Cluster”
This paper uses data from the Dragonfly Telephoto Array to uncover the existence of many very large, very low surface brightness galaxies in the Coma cluster. The paper ignited interest in these galaxies, leading to a renaissance in research on the low surface brightness Universe. The ‘ultra-diffuse galaxies’ (UDGs) in Coma (a term coined in the paper) are similar to other types of objects known about since the 1980s, and Dragonfly's main contribution has been to reveal their huge abundances in all environments. Follow-up work on the dynamics of these galaxies was undertaken by our group using the Keck telescope, and by independent groups who leveraged our observations (in particular our ability to control systematics) to discover hundreds more UDGs in Coma, most notably using the 8m Subaru telescope. This shows the beautiful synergy between Dragonfly and 8m-class telescopes when studying relatively distant local objects like the Coma cluster. Each class of telescope has its own area of excellence. For very distant galaxies, large ground-based (e.g. Keck, Gemini) or space-based (e.g. HST and JWST) telescopes are the tools of choice. But when studying large and nearby galaxies, where resolution matters less than control of systematics, and when probing low surface-brightness phenomena on degree-scales, Dragonfly will often outpace even the largest conventional large ground-based and space-based telescopes.
DARK MATTER (TOO MUCH, TOO LITTLE)
Representative paper: van Dokkum, P., Danieli, S., Cohen, Y., Merritt, A., Romanowsky, A., Abraham, R., Brodie, J., Conroy, C., Lokhorst, D., Mowla, L., O’Sullivan, E., and Zhang, J. (2018). Nature, 555, 629.
“A galaxy lacking dark matter”
This paper reported the discovery of a relatively nearby ultra-diffuse galaxy that is lacking in dark matter. The paper was hugely controversial at the time of publication, but after extensive follow-up campaigns (using Keck and VLT spectroscopy, and Hubble Space Telescope imaging) by our group and by others, its results have held up. Ultra-diffuse galaxies now appear to provide evidence that galaxies can have far greater diversity in dark matter content (sometimes far too much, sometimes far too little) than originally expected. You can learn more about it by listening to a CBC Quirks and Quarks episode.
RED NUGGETS IN THE DISTANT UNIVERSE
Representative paper: Damjanov, I., McCarthy, P., Abraham, R. G. et al. (2009). ApJ, 695, 101.
"Red Nuggets at z~1.5: Compact Passive Galaxies and the Formation of the Kormendy Relation"
While leading the Gemini Deep Deep Survey (GDDS; Abraham et al. 2004), together with my colleagues Karl Glazebrook and Pat McCarthy, I proposed, developed, and commissioned a ‘Nod & Shuffle’ mode to control sky systematics in the Gemini Multi-Object Spectrograph (GMOS). This allowed the telescope to obtain redshifts in the hitherto poorly explored "redshift desert" (1 < z < 2) and to discover a surprising abundance of massive galaxies at high redshifts. The GDDS produced thirteen refereed papers and has been cited over 1500 times. The paper noted above is part of the PhD thesis of Ivana Damjanov, one of many graduate students I have been privileged to work with, and learn from. The paper reports the existence of compact red galaxies at intermediate redshifts and introduces the term ‘red nuggets', which is now commonly used to describe these galaxies. Other GDDS highlights include work on the evolving space density of early-type galaxies (Abraham et al. 2007), an influential characterization of the relationship between our sample and cosmological downsizing (Juneau et al. 2005), one of the first studies of the redshift evolution of the mass-metallicity relation (Savaglio et al. 2005), and the discovery of a high abundance of massive quiescent galaxies at z ∼ 1.5 (Glazebrook et al. 2004).
Representative paper: Abraham, R. G., Tanvir, N. R., Santiago, B.X., Ellis, R. S., Glazebrook, I. & van den Bergh, S. (1996). MNRAS, 279, L47.
“Galaxy morphology to I=25 mag in the Hubble Deep Field”
This was the first paper published from the Hubble Deep Field campaign. It presents the Concentration-Asymmetry galaxy classification system that I devised, which has now become a de-facto standard for automated galaxy classification. This work was done in collaboration with my colleagues and friends Richard Ellis, Sidney van den Bergh, and Karl Glazebrook. In 2003 I built on the ideas in this paper by introducing the Gini coefficient as a morphological parameter, which is another morphological system that has become popular. Papers that I wrote which define automated classification schemes (and apply them to deep fields) have been cited over 1000 times, which is notable as citations underestimate the impact of this work, since over time these ideas have been improved upon by others and been incorporated into software packages (e.g. the CAS and Gini-M20 galaxy classification systems) which tend to get cited on their own.
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