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1. The Faintest Dwarf Galaxies

   https://doi.org/10.1146/annurev-astro-091918-104453  

   Simon, Joshua D. (August 2019, Annual Review of Astronomy and Astrophysics)

   The lowest luminosity ([Formula: see text] L[Formula: see text]) Milky Way satellite galaxies represent the extreme lower limit of the galaxy luminosity function. These ultra-faint dwarfs are the oldest, most dark matter–dominated, most metal-poor, and least chemically evolved stellar systems known. They therefore provide unique windows into the formation of the first galaxies and the behavior of dark matter on small scales. In this review, we summarize the discovery of ultra-faint dwarfs in the Sloan Digital Sky Survey in 2005 and the subsequent observational and theoretical progress in understanding their nature and origin. We describe their stellar kinematics, chemical abundance patterns, structural properties, stellar populations, orbits, and luminosity function, as well as what can be learned from each type of measurement. We conclude the following: ▪ In most cases, the stellar velocity dispersions of ultra-faint dwarfs are robust against systematic uncertainties such as binary stars and foreground contamination. ▪ The chemical abundance patterns of stars in ultra-faint dwarfs require two sources of r-process elements, one of which can likely be attributed to neutron star mergers. ▪ Even under conservative assumptions, only a small fraction of ultra-faint dwarfs may have suffered significant tidal stripping of their stellar components. ▪ Determining the properties of the faintest dwarfs out to the virial radius of the Milky Way will require very large investments of observing time with future telescopes. Finally, we offer a look forward at the observations that will be possible with future facilities as the push toward a complete census of the Local Group dwarf galaxy population continues. 

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2. Cosmology with Multiple Galaxies

   https://doi.org/10.3847/1538-4357/ad4969  

   Chawak, Chaitanya; Villaescusa-Navarro, Francisco; Echeverri-Rojas, Nicolás; Ni, Yueying; Hahn, ChangHoon; Anglés-Alcázar, Daniel (July 2024, The Astrophysical Journal)

   Abstract Recent works have discovered a relatively tight correlation between Ω_mand the properties of individual simulated galaxies. Because of this, it has been shown that constraints on Ω_mcan be placed using the properties of individual galaxies while accounting for uncertainties in astrophysical processes such as feedback from supernovae and active galactic nuclei. In this work, we quantify whether using the properties of multiple galaxies simultaneously can tighten those constraints. For this, we train neural networks to perform likelihood-free inference on the value of two cosmological parameters (Ω_mandσ₈) and four astrophysical parameters using the properties of several galaxies from thousands of hydrodynamic simulations of the CAMELS project. We find that using properties of more than one galaxy increases the precision of the Ω_minference. Furthermore, using multiple galaxies enables the inference of other parameters that were poorly constrained with one single galaxy. We show that the same subset of galaxy properties are responsible for the constraints on Ω_mfrom one and multiple galaxies. Finally, we quantify the robustness of the model and find that without identifying the model range of validity, the model does not perform well when tested on galaxies from other galaxy formation models. 

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3. Weighing in Dwarf Galaxies

   Muhammad, A (January 2025, volume 245 of American Astronomical Society Meeting Abstracts, 359.10, January 2025)

   Telescopes such as the Rubin Observatory and Euclid Space telescopes find more and more low mass galaxies as time passes by. However, the link between small dwarf galaxy light and star mass is currently unclear. We recently found out that there are clear differences between stellar mass depending on star formation history (SFH), according to an article published by Mithi A. C. de los Reyes. This is shown in artificial data and we can show this using real observed data. Therefore, using the Galaxy And Mass Assembly (GAMA) survey, we will compare mass estimates for small dwarf galaxies with the utilization of four different methods. We seek to find out if these methods agree. Or do they not agree? What happens when a galaxy is so small it only has a few million suns of stars inside? Are there stars missing? Using jupyter notebooks and python, we can compare the GAMA data and make plots and comparisons to answer these questions. 

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4. Galaxies Going Bananas: Inferring the 3D Geometry of High-redshift Galaxies with JWST-CEERS

   https://doi.org/10.3847/1538-4357/ad1a13  

   Pandya, Viraj; Zhang_张, Haowen 昊文; Huertas-Company, Marc; Iyer, Kartheik G; McGrath, Elizabeth; Barro, Guillermo; Finkelstein, Steven L; Kümmel, Martin; Hartley, William G; Ferguson, Henry C; et al (February 2024, The Astrophysical Journal)

   Abstract The 3D geometries of high-redshift galaxies remain poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently and robustly infer the 3D shapes of star-forming galaxies in James Webb Space Telescope Cosmic Evolution Early Release Science observations with $\log M_{*}/M_{\odot }=9.0–10.5$atz= 0.5–8.0. We reproduce previous results from the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in a fraction of the computing time and constrain the mean ellipticity, triaxiality, size, and covariances with samples as small as ∼50 galaxies. We find high 3D ellipticities for all mass–redshift bins, suggesting oblate (disky) or prolate (elongated) geometries. We break that degeneracy by constraining the mean triaxiality to be ∼1 for $\log M_{*}/M_{\odot }=9.0–9.5$dwarfs atz> 1 (favoring the prolate scenario), with significantly lower triaxialities for higher masses and lower redshifts indicating the emergence of disks. The prolate population traces out a “banana” in the projected $b/a–\log a$diagram with an excess of low-b/a, large- $\log a$galaxies. The dwarf prolate fraction rises from ∼25% atz= 0.5–1.0 to ∼50%–80% atz= 3–8. Our results imply a second kind of disk settling from oval (triaxial) to more circular (axisymmetric) shapes with time. We simultaneously constrain the 3D size–mass relation and its dependence on 3D geometry. High-probability prolate and oblate candidates show remarkably similar Sérsic indices (n∼ 1), nonparametric morphological properties, and specific star formation rates. Both tend to be visually classified as disks or irregular, but edge-on oblate candidates show more dust attenuation. We discuss selection effects, follow-up prospects, and theoretical implications. 

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5. Dynamical Regularities in Rotating Galaxies

   McGaugh, S.S.; Lelli, F.; Li, P.; Schombert, J.M. (September 2019, Galactic Dynamics in the Era of Large Surveys)

   Galaxies are observed to obey a strict set of dynamical scaling relations. We review these relations for rotationally supported disk galaxies spanning many decades in mass, surface brightness, and gas content. The behavior of these widely varied systems can be summarized with a handful of empirical laws connected by a common acceleration scale. 

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