Matus Rybak: research webpage

Astronomer. Studying distant galaxies. Expert on sub-millimetre observations.

Get in touch at mrybak@strw.leidenuniv.nl

About me

I am an observational astronomer, studying how stars formed in early galaxies. I am currently a Senior Research Associate at the Allegro ALMA Regional Center in Leiden.

Veni Fellow, NWO Open XS Grant, Delft Space Institute Seed Grant.

Originally from Slovakia, studied in Scotland, earned my PhD in Bavaria. Now I'm based in Leiden, the Netherlands/

About my research

Research overview

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.

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 lensing and data processing for radio interferometers.

Now I study galaxies in the early Universe, using large interferometers such as ALMA, NOEMA, VLA, and the upcoming DESHIMA spectrometer on the ASTE. In Delft and Leiden, I work closely with Jackie Hodge, Akira Endo and Paul van der Werf.

PRUSSIC - surveying dense gas in high-redshift galaxies

Stars form from very dense gas. In nearby galaxies, we usually trace it using the HCN line, particularly the low-excitation (1-0) transition. But only a handful of high-redshift galaxies have been detected in HCN emission, giving us potentially a very biased view of their star-formation mechanisms.

I am leading the PRUSSIC survey - a comprehensive observing programme targeting HCN emission in high-redshift galaxies using the VLA, ALMA and NOEMA. Surprisingly, our results challenge the idea that high-z galaxies have lots of dense gas (and are thus bright in HCN) - in fact, we find them to be rather faint!

You can read more about PRUSSIC here.

DESHIMA: ultra-wideband spectroscopy in sub-mm

I am co-leading the astronomy programme on DESHIMA, a novel ultra-wideband spectrometer developed at TU Delft and ASTRON (PI: Akira Endo). The prototype of this instrument saw the "first light" in 2017; we have now built a much-improved DESHIMA 2.0. In late 2022, DESHIMA 2.0 will start regular observations on the ASTE telescope in the Atacama desert. Some of its main aims will be: measuring redshifts of distant dusty galaxies, studying thermodynamics and chemistry of extreme starbursts, and mapping the Sunyaev-Zeldovich effect around galaxy clusters.

For a recent overview of DESHIMA 2.0's capabilities, see: Rybak et al. (2021) and Taniguchi et al. (2021).

The quasar that blinked

We have recently detected a "blinking" lensed quasar in our ALMA observations. This blinking is caused by microlensing by stars in the foreground galaxy. But for a source to be microlensed, it has to be very small! Our analysis shows that the mm-wave emission arises from a region <100 AU across: the elusive mm-wave corona, a region of superheated plasma surrounding a supermassive black hole!

This is the first time we can measure the size of the corona directly, without any assumptions about the source properties. You can find the pre-print here.

A Rorschach test galaxy

Do you see a circle in this image? Small galaxies with little dust might play an outsize role in the very early Universe (redshift >6). But they are so far and so faint that it is very difficult to study them. Instead, we can focus on their counterparts at redshift 2 and use gravitational lensing. We used very deep ALMA observations to obtain a faint detection of the [CII] line in one such strongly lensed galaxy, 30x lower than predicted by commonly used models.

You can find the paper here: arXiv:2101.00841 .

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 telescope, 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.

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