Lammim Ahad gives a colloquium on simulating galaxies in clusters

On November 28, Dr. Syeda Lammim Ahad, an independent postdoctoral fellow at the Waterloo Centre for Astrophysics, University of Waterloo, Canada, spoke at the first colloquium organized by the Center for Astronomy, Space Science, and Astrophysics (CASSA) at Independent University, Bangladesh (IUB).

Approximately 50 students and researchers participated in the event, 10 of whom joined online. Among the attendees were 17 students from ongoing IUB course, Atmospheric and Space Physics, who participated as part of their final exam syllabus. These students were majoring in Physics, Computer Science, or Electrical and Electronic Engineering, with some also minoring in Astronomy and Astrophysics.

Faculty members from IUB included Professor Dr. Arshad Momen, Director of the Office for Graduate Studies, Research, and Industrial Relations, and Dr. Jewel Kumar Ghosh, an assistant professor researching string theory in the Department of Physical Sciences. In addition to IUB students, a few students from other universities in Dhaka also attended.

In the colloquium, Lammim primarily presented her PhD research in simple terms in Bangla to provide undergraduate students of Physics, Mathematics, Engineering, and Computer Science with a general understanding of her work. The title of her talk was ‘Galaxy Evolution in Dense Environments: Insights from Hydrodynamic Simulations and Multi-Wavelength Observations‘ (presentation slides here).

Modern astronomy has four equally important pillars: simulation, observation, instrumentation, and theory. Theoretical astronomers use relevant physical equations to simulate different regions of the universe at various epochs using supercomputers. Meanwhile, observational astronomers focus on building various telescopes to compare their observations with these simulations. The data from telescopes are also analyzed using supercomputers. Science progresses by identifying matches or discrepancies between theoretical simulations and observations.

In her 2021 paper, Lammim presented a comparison between observations and a large-scale simulation. This simulation, known as Hydrangea, required high-performance supercomputers and took at least a year to complete. Scientists spend nearly a decade preparing the relevant equations for such a simulation. While the simulation itself takes about a year to run, the resulting data can fuel research for decades; Lammim’s work is an example of such research.

Her work revealed that the characteristics of stars in various galaxy clusters simulated in Hydrangea align closely with observed realities. She also identified the variations in the mass of dark matter and the stellar mass evolution of galaxies within clusters—findings that scientists were already aware of from observations—further validating the simulation’s accuracy.

Lammim then briefly discussed her 2023 and 2024 papers. In many galaxy clusters, there are stars that are not part of any specific galaxy but instead move independently in intergalactic space. The light emitted by these stars is called intracluster light (ICL). When such stars are found in galaxy groups (containing hundreds of galaxies) instead of clusters (containing thousands of galaxies), the light is referred to as intragroup light (IGL). While X-ray telescopes can detect the intracluster gas in galaxy clusters, this gas often does not align with the distribution of dark matter. In contrast, ICL tends to align more closely with dark matter. Since dark matter cannot be directly observed, ICL or IGL can be used to infer its distribution.

In her 2023 paper, Lammim prepared mock observations of nearly 500 galaxy clusters from the Hydrangea simulation. She examined various characteristics of IGL and highlighted the observational biases and limitations in measuring these characteristics from real data.

Due to time constraints, she couldn’t elaborate much on her 2024 paper, which explores the reasons behind the declining star formation rates in galaxies within ancient proto-clusters (around 10 billion years old).

Lammim emphasized that high-performance computing (HPC) can enable advanced astronomy research from Bangladesh. She also expressed her willingness to involve Bangladeshi students in her various projects. IUB’s CASSA has an HPC, which can be utilized to analyze data from various observations and simulations. Following the lecture, many students expressed interest in working under the guidance of Lammim on her research.

As an associate member of CASSA, Lammim showed interest in future collaborations on various research projects. She also discussed the potential for workshops and mini-courses through CASSA.