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Research Fellows Directory

James Geach

Dr James Geach

Research Fellow


University of Hertfordshire

Research summary

One of the biggest questions astronomers face is "how did galaxies form and

evolve?" Our own Milky Way is one of billions of galaxies that have evolved

into a 'zoo' of types over a time-span equivalent to nearly three times the

age of the Earth.

Astronomers have used two main tools to study the evolution of galaxies: their

total mass in stars and the rate at which they are forming new stars. Over the

past two decades, we have learned a great deal about galaxy evolution from

these simple observations, by measuring how these parameters have varied over

cosmic history.

But there is a vital ingredient that is missing: molecular gas. New stars are

formed from vast reservoirs of molecular hydrogen; it is this that fuels the

observed star formation rates of galaxies, and from which future stellar mass

is assembled. Without observations of the gas itself, we have an incomplete

view of the evolution of galaxies. Until recently, however, molecular gas in

the distant Universe has been extremely difficult to detect.

Why is this important? The main process governing galaxy growth can be thought

of as a gas cycle: galaxies can accrete gas from the intergalactic medium via

gravity, turning some of that gas into new stars. However, gas can also be

prevented from forming stars, or even be ejected from the galaxy due to

'feedback' from powerful winds blown by new stars, the detonation of

supernovae, and outflows associated with the growth of central massive black

holes. This idea is central to our current model of galaxy formation, but the

complex mixture of astrophysics is poorly understood.

The physics of the gas cycle is encoded in the molecular gas content of

galaxies. This is the "missing link" of galaxy evolution, and the subject of

my research proposal. The goal is to measure how the molecular gas content of

Milky Way-like galaxies has evolved over cosmic time and investigate the

astrophysics of how the stars we see today were forged from primordial gas


Interests and expertise (Subject groups)

Grants awarded

Exploring the molecular Universe: the missing link of galaxy formation

Scheme: University Research Fellowship

Dates: Oct 2013 - Sep 2018

Value: £410,935.93