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Abstract Dwarf galaxies are dark matter-dominated systems that are sensitive to feedback and display a diversity of baryonic morphologies. This makes them excellent probes for understanding dark matter and galaxy evolution. This work investigates the physical processes that influence the sizes of isolated dwarf galaxies using high-resolution cosmological zoom-in simulations of 39 dwarf galaxies drawn from the Marvelous Massive Dwarfs simulation suite (7.5 <  $\log (M_{\star }/M_{\odot })$ < 9.1). Our simulations show that dwarf galaxies initially form as compact galaxies (R_e < 2 kpc). However, several of these galaxies (54%) experience periods of gradual size growth at relatively stable specific star formation rate, allowing them to become extended galaxies. While previous simulations have struggled to produce dwarf galaxy disks, we find that the growth of rotation-supported stellar disks is the primary means by which isolated dwarfs become extended in size. These stellar disks are formed by mergers with high orbital angular momentum (AM) satellites on high AM (spiraling-in) orbits, which spin up the gas surrounding the central galaxy and contribute ≈30% of the cold gas mass atz= 0. For these systems, star formation in the AM-supported gas and the gradual buildup of stars in the disk result in secular size growth. 

Abstract The observed rotation curves of dwarf galaxies exhibit significant diversity at fixed halo mass, challenging galaxy formation within the cold dark matter (CDM) model. Previous cosmological galaxy formation simulations with baryonic physics fail to reproduce the full diversity of rotation curves, suggesting that there is a flaw in baryonic feedback models, observational bias, or that an alternative to CDM must be invoked. In this work, we use the Marvelous Massive Dwarf zoom-in simulations, a suite of high-resolution dwarf simulations withM₂₀₀ ∼ 10¹⁰–10¹¹ M_⊙andM_* ∼ 10⁷–10⁹ M_⊙, designed to target the mass range where the galaxy rotation curve diversity is maximized, i.e., between $V_{\max }\sim 70$ and 100 km s⁻¹. We add to this a set of low-mass galaxies from the Marvel Dwarf Zoom Volumes to extend the galaxy mass range to lower values. Our fiducial star formation and feedback models produce simulated dwarfs with a broader range of rotation curve shapes, similar to observations. These simulations both create dark matter cores via baryonic feedback, reproducing the slower-rising rotation curves, while also allowing for compact galaxies and steeply rising rotation curves. Our simulated dwarfs also reproduce the observed size–M_*relation, including scatter, producing both extended and compact dwarfs for the first time in simulated field dwarfs. However, the slowly rising and high baryon mass fraction, as well as the steeply rising and low baryon mass fraction, remain missing. We explore star formation and feedback models and conclude that previous simulations may have had feedback that was too strong to produce compact dwarfs. 

Abstract Drawing from the Chandra archive and using a carefully selected set of nearby dwarf galaxies, we present a calibrated high-mass X-ray binary (HMXB) luminosity function in the low-mass galaxy regime and search for an already hinted at dependence on metallicity. Our study introduces a new sample of local dwarf galaxies (D< 12.5 Mpc andM_*< 5 × 10⁹M_⊙), expanding the specific star formation rates (sSFR) and gas-phase metallicities probed in previous investigations. Our analysis of the observed X-ray luminosity function indicates a shallower power-law slope for the dwarf galaxy HMXB population. In our study, we focus on dwarf galaxies that are more representative in terms of sSFR compared to prior work. In this regime, the HMXB luminosity function exhibits significant stochastic sampling at high luminosities. This likely accounts for the pronounced scatter observed in the galaxy-integrated HMXB population’sL_X/SFR versus metallicity for our galaxy sample. Our calibration is necessary to understand the active galactic nuclei content of low-mass galaxies identified in current and future X-ray survey fields and has implications for binary population synthesis models, as well as X-ray-driven cosmic heating in the early Universe.