Hamid Hassani

University of Alberta

Hamid Hassani, is a PhD student in Physics at the University of Alberta, focuses on the observational study of galaxy evolution. His research leverages multi-wavelength observations, spanning ultraviolet to infrared and sub-millimeter spectra, to deeply probe star formation processes. Hamid holds a Master of Science in Astronomy and Astrophysics, where he explored the interplay between star formation and magnetic fields in the interstellar medium of Magellanic Clouds. He used radio continuum observations of these dwarf galaxies to map non-thermal synchrotron emission and magnetic fields with unprecedented resolution.

As he embarked on his PhD journey, Hamid became a part of the international collaboration, The PHANGS (Physics at High Angular Resolution in Nearby Galaxies). He actively participated in the first cycle of observations using the JWST (James Webb Space Telescope), focusing on 19 nearby galaxies within a distance of 20 Mpc. In his landmark study on the first four galaxies observed by JWST, Hamid concentrated on identifying sources at the mid-infrared band, specifically at 21μm. The question he had in mind was about the bright sources in these galaxies: what are they, and where are they located? Developing a sophisticated source detection algorithm, he found over 1000 21μm sources in these galaxies. Most of these were HII regions or active star formation regions, with the remainder being stars or background galaxies. He then integrated observations from the HST’s five bands with JWST’s eight bands, ranging from 2μm to 21μm, to understand the physical properties of these massive star-forming regions, including their age, stellar mass, and metallicity. His findings revealed that these regions are predominantly young, mostly below 8 Myr, with stellar masses ranging between 100 to 100,000 solar masses.

A significant aspect of Hamid’s paper, also illustrated in the figure, is the finding that no bright embedded sources of star formation were found beyond the centers of galaxies (L (21um) ~ 19 W/Hz). Embedded star formation, which refers to the formation of stars in their very early stages (less than 2 Myr), can be identified by bright mid-infrared emission (21μm in this case) and faint optical emission (Hα emission). This implies that embedded sources are relatively uncommon and not consistently linked with intense CO emission beyond the center of galaxies, at a physical scale of about 50 parsecs, as one might anticipate in regions where young, massive stars are forming.

The figure displays a correlation between the luminosity of the Hα line, corrected for attenuation effects, and the 21 μm luminosity density. The age of the star-forming regions is indicated by a color bar, providing a visual representation of varying ages. Additionally, the stellar mass in each region is shown by the size of each point in the graph. A black dashed line on the figure marks a specific threshold, below which a 21 μm source is considered to have faint Hα emission. Meanwhile, a red line represents the average ratio of Hα to 21 μm luminosity (L_Hα/ν_Lν,F(21μm)) at 0.05. The figure also includes a critical vertical line set at 10^19 W Hz^−1, identifying the brightness level below which the study seeks embedded sources, which are young star-forming regions still enveloped in dust and gas.

These results were published in The Astrophysical Journal Letters in February 2023, under the title “PHANGS–JWST First Results: The 21 μm Compact Source Population.” You can find the paper here.

Besides his academic pursuits, Hamid is also a dedicated student activist and advocate, deeply committed to addressing the needs of students in Alberta, Canada. He is actively involved with the Graduate Student Association (GSA) at the University of Alberta, serving as the Vice-President External. In this role, Hamid advocates for graduate student concerns, such as affordable education and housing, not only at the municipal government level but also at the provincial level. Additionally, he plays significant roles as both chair and vice-chair in a few student organizations across the city and province. Through these engagements, he effectively voices and addresses the interests and needs of over 20,000 graduate students, striving to enhance the experiences and well-being of both domestic and international students within the broader academic community.