Matus Rybak: research webpage

Sterrewacht Leiden

About me & my research

About me

Postdoctoral researcher at the Leiden Observatory, working in Jacqueline Hodge's group. I got my MPhys at the University of St Andrews (UK) and my PhD at the Max Planck Institute for Astrophysics (Germany). My PhD supervisors were Simona Vegetti and Simon White.

Research overview

My research focuses on high-resolution observations of dusty, intensely star-forming galaxies that existed some 10 - 12 billion years ago (redshift 2-5), at a time when the galaxies were forming new stars at the peak rate. Our understanding of the processes behind this intense star formation is still very limited.

I spent my PhD working on gravitational lens modelling of radio/mm-wave interferometric observations, which provided an unprecedented resolution in these elusive objects - all the way down to 50 pc!

Now I work on deep ALMA and ancillary observations of redshift ~3 galaxies from the ALESS sample. I am a Principal Investigator of several approved project on ALMA (7 in total), NOEMA (2) and VLA (1).

Thermodynamics of distant star factories

Dusty galaxies that existed some 10 billion years ago are the most intensely star-forming objects in the entire history of the Universe, forging new stars from their gas at incredible pace. The gas thermodynamics - density, temperature, external radiation - are the key to understanding these extreme galaxies. We used ALMA observations of dust, CO and C+ in a gravitationally lensed galaxy SDP.81 to map the gas properties inside a dusty starburst for the first time!

You can find the pre-print here: arXiv:1912.12538 .

Bright beacons: oxygen emission in distant galaxies

How can we study galaxies that lived only 1 billion years after the Big Bang? We need bright emission lines. For over 20 years, theory predicted that distant, dusty galaxies will be very bright in the atomic oxygen emission. With the new receiver on APEX telescope, we have successfully confirmed this! This opens new doors to studying the early Universe.

Pre-print: arXiv:1912.07652 .

APEX telesccope, credit: Carlos Duran

What drives the [CII]/FIR deficit in high-redshift starbursts?

[CII] 158-micron emission line is an extremely bright emission line, allowing us to study high-redshift galaxies. But linking the [CII] emission to star-formation is very difficult, as the [CII] emission does not increase proportionally to the star-formation rate (the so-called [CII]/FIR deficit).

We obtained first resolved maps of the [CII]/FIR deficit in non-lensed, redshift 3 galaxies - ALESS 49.1 and ALESS 57.1. These reveal a very strong [CII]/FIR deficit (see below). Using resolved CO observations in the same galaxies, we found that this is due to very strong radiation from young stars, which heats up the gas to very high temperatures, thermally saturating the [CII] emission.

You can find the pre-print here: arXiv:1901.10027 , and the final paper here: ApJ 876 112.

SDP.81: disentangling a high-refshift starburst

SDP.81 is a redshift-3 dusty, star-forming galaxy. It was selected as a target of the first ALMA Long Baseline Campaign. Using the superb resolution of ALMA and an extra boost due to the gravitational lensing, this allows the most detailed look into a galaxy that existed some 10 billion years ago!

We managed to obtain the first high-resolution (~50 parsec) reconstruction of the dust continuum in two different frequency bands, and multiple CO lines at 100-pc resolution! Our reconstruction shows clumpy dust clouds heated by intense UV radiation from the new-born stars.

A press release by MPA Garching.

RXJ 1131: resolving the molecular gas in a lensed quasar

RXJ 1131 is a beautiful, relatively nearby (z~0.658) lensed quasar. Its four bright images are regularly monitored in an effort to constrain the Hubble constant.

Using ALMA Cycle 2 observations of the CO emission, we found a beautiful, thick Einstein ring! I reconstructed the CO emission and its velocity structure in the source-plane, revealing a large disc of molecular gas with structure reminiscent of spiral arms and a gaseous bar. The full paper can be found here.

Figure: Reconstruction of the CO (2-1) emission in RXJ 1131. Left - surface brightness density; notice the irregular structure of the gas! Right - map of the gas velocity, showing an ordered rotation.

Where do isolated massive stars come from?

With William Lucas and Ian Bonnell (St Andrews), we looked at the seemingly isolated, very massive stars in the vicinity of the 30 Doradus star-forming region. Did they form where they are now, or do they actually originate from 30 Doradus?

In fact, the center of 30 Doradus actually consists of two stellar clusters, which might be in a process of merging. Simulating cluster mergers, we found that these apparently isolated stars might have originated in 30 Doradus. You can find the paper here.

Other writing and activities

I sometimes type up an article for a more general audience. For the English-speakers, you can have a look at my cover article on the missing satellites and dark matter substructure in the MPG's Offspring (page 18).

Long ago, I wrote a number of Slovak-language articles for TriCeleStrnast.

I have been a reviewer for astronomy journals MNRAS and ApJ since spring 2017.

In Leiden, I run semi-regular monthly careers talk for postdocs and PhD students.