(Published - 16 January 2019)

Galaxies contain stars. Stars form within a cloud of gas - neutral hydrogen (HI) coalesces to become molecular hydrogen, which collapses to form stars. But how exactly does that happen? What is the the relationship between the neutral hydrogen and the stellar component of the galaxy?

University of the Western Cape (UWC) Astrophysics PhD candidate (and now graduate) Mika Harisetry Rafieferantsoa was determined to find out.

His thesis used state-of-the art hydrodynamic galaxy formation simulations run on UWC supercomputers to investigate the processes that cause galaxies to transform from HI-rich to HI-poor within dense environments, resulting in so-called galaxy conformity.

“Birds of a feather flock together. That is also true with galaxies if we look at their properties. But instead of being the cause, the similarity with their properties is rather thought to be the effect of the flocking and is called galactic conformity. This ‘galactic conformity’ has been observed in galaxy colours, but is also shown to be present in other properties, including the amount of neutral hydrogen in galaxies. We were the first to do such analysis using a hydrodynamical simulation.”

Mika also developed machine learning tools to characterise the connection between HI content and other multi-wavelength properties. These results set the stage for combining MeerKAT HI data with other multi-wavelength survey data to better understand the role of HI in galaxy evolution.

“Due to the effect of gravity, galaxies fall in more massive gravitationally-bound structures. If the medium inside the structure is hot, it tends to strip the gaseous component of the galaxies falling in. It turns out the bigger the structure they fall in, the hotter the medium and the shorter the timescales the gaseous components of the falling galaxies get stripped. We were the first to quantify these timescales using a simulated group of galaxies.”

For someone so successful in his field, it’s refreshing to hear just what motivated him to start studying the stars in the first place: “I decided to enter this field because I like it.”

Simple enough - though the route he took to get there wasn’t quite that simple. Mika was born in Madagascar, where he studied all the way through to his DEA (MSc, basically) in physics. Then he saw a movie about the evolution of the gaseous component of a spiral galaxy from the simulation perspective.

“That was it,” he says. “After that, I wanted to be an expert in that field.”

Looking Ahead In Space And On Earth

It’s an exciting time to be an astrophysicist, Mika notes. South Africa’s MeerKAT radio telescope is set to deliver unprecedented views into the nature of galaxies. Advanced numerical simulations are crucial for interpreting such data within a modern cosmological context.

“I do simulations, but my simulation models have to be constrained with observations. The quality of images from the MeerKAT array is unprecedented and crazy good - and who knows how insane it will be with the SKA?”

Of course, there’s more to life than just science (no matter how awesome it is), and Mika has other interests as well.

“I do many other things - but what I spend most of my time on is playing piano, swimming, playing pool and doing some leather work, like my recently-built laptop case and passport holder.”

So what’s next for Mika?

“I don’t know, really - people usually apply for postdoc but I haven’t. But I am sure of something ,” he says. “I am curious and I am always in search of a way to satisfy that curiosity. I’m also part of a social species, and a thriving society, where every member is important. So I see myself contributing to the wellbeing of society in the years to come, in whatever field that might be.”