About Me

Welcome to my webpage! I am Martje, a PhD candidate at Leiden Observatory, in the Netherlands. I work on the formation and evolution of galaxies, with a particular interest in the stellar and kinematic properties of distant quiescent galaxies. My advisor is Mariska Kriek.

Research Interests:
I have broad interests in galaxy formation and evolution. More specifically, I use absorption spectroscopy to unravel the early formation and evolution of distant massive galaxies by studying their (stellar) kinematics and stellar population characteristics. For more details, see my Research section.

Publications:
Here are ADS links to my first-author or co-author papers.

Education:

  • 2023 - Present: PhD candidate in Astronomy, Leiden Observatory, supervised by Mariska Kriek.
  • 2021 - 2023: MSc in Astronomy, Leiden University
  • 2017-2021: BSc in Astronomy at Leiden University

Research

Dynamical properties of distant quiescent galaxies with JWST/NIRSpec MSA

As a part of the JWST-SUSPENSE and JWST-IMFERNO programs, I am working on understanding the dynamical properties of distant quiescent galaxies at cosmic noon. Such dynamical measurements help us understand how these galaxies formed, quenched and evolved into the massive elliptical galaxies we see in the local Universe. Furthermore, their dynamical masses provide independent methods of constraining their dark matter content and initial mass function (IMF). To measure these kinematic properties I have developed a novel method to measure spatially resolved stellar kinematics for distant quiescent galaxies observed with JWST/NIRSpec MSA. This method takes into account the complex JWST/NIRSpec MSA instrumental effects, as well as the morphological properties of the galaxies, and allows us to measure rotation curves and velocity dispersion profiles. I am currently working on extending this method to include Jeans Anistropic Modelling (JAM) to infer dynamical masses and orbital anisotropies for distant quiescent galaxies.

This work was published in Slob et al. (2025).

Star-formation histories of distant quiescent galaxies

In Cycle 1 of JWST, we obtained 16 hours of NIRSPec/MSA data for the JWST-SUSPENSE program, which obtained ultra-deep high-resolution spectra for a sample of 20 quiescent galaxies at z=1-3. Using the full SED fitting code Prospector we obtained detailed star-formation histories (SFHs) and stellar population parameters for these galaxies. From these SFHs we find that distant quiescent galaxies form earlier and over shorter star-formation timescales compared to low redshifts. However, from the detailed chemical abundance patterns of the galaxies in this sample, we find that the SFH timescales inferred from full SED fitting are too extended, and must have instead formed within very short timescales (~500 Myr). This discrepancy points to shortcomings in current stellar population models and SED fitting techniques when applied to these high-quality JWST data, and paves an exciting path forwards of understanding the rapid evolution of these galaxies.

This work was published in Slob et al. (2024) and Beverage, Slob et al. (2025).

Identifying the youngest radio galaxies using LOFAR surveys.

Our understanding of how a radio galaxy evolves remains embarrassingly incomplete. In particular, the first stages of radio galaxy evolution are ill-understood, with far too many small radio galaxy precursors identified relative to the number of giant radio galaxies. These precursors are peaked-spectrum (PS) sources, and can be identified by their compact sizes and turnover in the radio SED. One competing theory for the origin of these PS sources is that these galaxies are not small due to youth but instead because they are confined to small scales by a dense environment ("frustrated").

In this project, we used the International LOFAR telescope, in particular data produced by the LOFAR all-sky survey (LoTSS) and its lowest frequency counterpart (LoLSS), to select the largest sample of these young radio galaxy candidates in the Northern Hemisphere at the time. With this sample we inferred how the luminosity function and number densities of these PS sources evolve over redshift compared to the general radio galaxy population, and found that the PS phase is extremely short compared to the rest of a radio galaxy's lifetime. This showed that the majority of our sample are indeed the young precursors to radio galaxies.

This work was published in Slob et al. (2022).