SFHs and morphology

The same set of physical processes regulating star formation in galaxies leave both temporal (starbursts, quenching, variability) and spatial (spiral arms, bars, clustered star formation) imprints that we study across galaxy populations. The links between how galaxies formed (i.e. their star formation history) and how they look (i.e. their morphology) therefore hold clues about the way certain physical processes leave imprints on galaxies by affecting their star formation. The causal link between whether star formation activity drives morphological transformation or the other way round remains an open question, and one that I got interested in when I first saw clear coherence between galaxy morphologies and star formation histories for galaxies in CANDELS1.

On the largest scales: While we had seen hints of this in earlier work, we explicitly quantified it using Katachi2, an interpretable neural framework that predicts galaxy SFHs from just gri imaging with accuracies comparable to traditional spectral approaches. More importantly, it can also be used to highlight regions in the input images that drive the predictions, providing novel insights about the morphology-SFH connection and enabling model-building for future surveys with Roman, Rubin & Euclid that do not have a broad wavelength baseline. See the Katachi page for more details.

On a few kpc scales: Varying the strength of stellar feedback and bulge-to-total ratio in an isolated galaxy in the AGORA framework shows distinct signatures in their spatial and temporal power spectra3.

On 10pc-kpc scales: Studying star clusters magnified by gravitational lensing in JWST observations45 (especially with spectra) allows us to study the stellar populations in a variety of cluster environments, ranging from star clusters to nuclear regions to globular clusters in some regions.

  1. Kartheik G. Iyer, Eric Gawiser, Sandra M. Faber, Henry C. Ferguson, Jeyhan Kartaltepe, Anton M. Koekemoer, Camilla Pacifici, and Rachel S. Somerville. Nonparametric Star Formation History Reconstruction with Gaussian Processes. I. Counting Major Episodes of Star Formation. \apj , 879(2):116, July 2019. arXiv:1901.02877, doi:10.3847/1538-4357/ab2052. ↩

  2. Juan Pablo Alfonzo, Kartheik G. Iyer, Masayuki Akiyama, Greg L. Bryan, Suchetha Cooray, Eric Ludwig, Lamiya Mowla, Kiyoaki C. Omori, Camilla Pacifici, Joshua S. Speagle, and John F. Wu. Katachi (形): Decoding the Imprints of Past Star Formation on Present-day Morphology in Galaxies with Interpretable CNNs. \apj , 967(2):152, June 2024. arXiv:2404.05146, doi:10.3847/1538-4357/ad3b95. ↩

  3. Eun-jin Shin, Sandro Tacchella, Ji-hoon Kim, Kartheik G. Iyer, and Vadim A. Semenov. Star Formation Variability as a Probe for the Baryon Cycle within Galaxies. \apj , 947(2):61, April 2023. arXiv:2211.01922, doi:10.3847/1538-4357/acc251. ↩

  4. Lamiya Mowla, Kartheik G. Iyer, Guillaume Desprez, Vicente Estrada-Carpenter, Nicholas S. Martis, Gaël Noirot, Ghassan T. Sarrouh, Victoria Strait, Yoshihisa Asada, Roberto G. Abraham, Gabriel Brammer, Marcin Sawicki, Chris J. Willott, Marusa Bradac, René Doyon, Adam Muzzin, Camilla Pacifici, Swara Ravindranath, and Johannes Zabl. The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST. \apjl , 937(2):L35, October 2022. arXiv:2208.02233, doi:10.3847/2041-8213/ac90ca. ↩

  5. Lamiya Mowla, Kartheik Iyer, Yoshihisa Asada, Guillaume Desprez, Vivian Yun Yan Tan, Nicholas Martis, Ghassan Sarrouh, Victoria Strait, Roberto Abraham, Maruša Bradač, Gabriel Brammer, Adam Muzzin, Camilla Pacifici, Swara Ravindranath, Marcin Sawicki, Chris Willott, Vince Estrada-Carpenter, Nusrath Jahan, Gaël Noirot, Jasleen Matharu, Gregor Rihtaršič, and Johannes Zabl. The Firefly Sparkle: The Earliest Stages of the Assembly of A Milky Way-type Galaxy in a 600 Myr Old Universe. arXiv e-prints, pages arXiv:2402.08696, February 2024. arXiv:2402.08696, doi:10.48550/arXiv.2402.08696. ↩