The Virgo Cluster (credit:  Rogelio Bernal Andreo ).

The Virgo Cluster (credit: Rogelio Bernal Andreo).

The Virgo Cluster

Why study one galaxy when you can study a thousand at a time? Galaxies tend to be social creatures, and are often found in groups or clusters where hundreds or even thousands of these galaxies are gravitationally bound together. My research lies with a truly one of a kind system: the Virgo Cluster. It is our richest neighbouring cluster, containing upwards of 4000 galaxy members ranging the full gamut of the Hubble sequence and mass/luminosity range all still churning through the cluster's active dynamical potential and various substructures. Virgo has given researchers a unique opportunity to study galaxy formation and evolution in a dense environment at multiple evolutionary stages My collaborators and I have taken full advantage of this by creating the Spectroscopy and H-band Imaging of Virgo (or SHIVir) survey: a multi-wavelength spectrophotometric campaign making use of a number of 4-8m class telescopes.

Galaxy Masses

One of the challenges in astronomy is that we don’t have direct access to most of the objects we’re studying, yet we want to measure as many of their physical parameters (mass, size, age, etc.) as we can. Currently, everything outside of our Solar System is out of reach. This is definitely true for galaxies, for which we can only hope to collect light. Fortunately, scientists have gotten pretty clever at converting direct observables such as photometry and spectroscopy into quantities such as mass, which are crucial to crack the puzzle of galaxy evolution. Using luminosities, colours, and spectra collected for SHIVir, I’ve built an extensive catalogue of the stellar and dynamical masses of Virgo Cluster galaxies. Dynamical mass, which includes the dark matter component of galaxies, has been computed from kinematics extracted from our spectroscopy. Probing different types of mass profiles in these galaxies allows us to study the interplay between baryonic (normal) and dark matter, and how they drive galaxy evolution.

At the Very Large Telescope on Cerro Paranal, Chile in April 2015.

At the Very Large Telescope on Cerro Paranal, Chile in April 2015.

Scaling Relations

Alright, I’ve built up an extensive and very awesome database of galaxy properties which includes everything from kinematics to stellar mass to surface brightness to size. Now what? Where’s the real science?! This is where scaling relations come into play: strong trends observed between physical properties such as those listed above. An example would be the Tully-Fisher Relation, where we expect a strong correlation between spiral galaxies’ rotational velocity and their luminosity/mass. Galaxies located in very different parts of the Universe fall relatively neatly onto these scaling relations, which tells us that the physical laws and processes which govern galaxy evolution are very similar everywhere in the Universe. Additionally, we can look at correlations between additional properties (colour, morphology, etc.) and exactly how near or far individual galaxies or galaxy types fall from observed best-fit relations or theoretically derived relations. This information allows us to figure out the nitty gritty physics that dictate exactly why a galaxy is the way it is. What makes a spiral a spiral and an elliptical an elliptical? The scatter in the scaling relations likely holds the key to these questions!

Observing Programs

One of the greatest privileges I've has as an astrophysicist is travelling to exotic locations all around the globe. The trips I’ve taken to collect data at observatories are the ones I hold most dear. As we build larger and more expensive telescopes to look deeper into our Universe, it becomes more important than ever to select optimal observing sites. These locations are often very remote and on high mountaintops or plateaus to escape factors such as light pollution, humidity, turbulent atmospheres, and inclement weather. Some of the locations I’ve travelled to include Maunakea in Hawai'i, the Apache Point Observatory in New Mexico, and (my personal favourite, don’t tell the other mountains!) Cerro Paranal on the Atacama Plateau in Chile. Modern day astronomy has mostly bypassed the need to travel on-site to collect data; many observatories have skilled observing technicians working at the telescopes to either collect data for you (queue mode) or assist you during your remote data collection. I myself have controlled the APO’s 3.5m telescope from the comfort of my bedroom some 3,300km away. This has done great things to improve the accessibility of data, and it certainly makes observing a lot more economical! That being said, the experience and skills I’ve acquired during observing trips cannot be overstated, and I highly encourage advisors to send their students on at least one observing trip if at all possible. Completely disconnecting modern astronomy from its romantic roots would be a mistake.