Search Talks

Simulations with fixed spatial resolution are an excellent tool to investigate the interplay between different phases of gas in and around galaxies because they mitigate the disparity in cell sizes due to density variations in traditional mass-based refinement schemes. Additionally, the moving-mesh technique implemented in Arepo has been shown to minimize numerical mixing and instability suppression. In this talk, I will introduce a new suite of cosmological zoom simulations with 200 pc resolution covering the inner CGM of a Milky Way-mass galaxy, utilizing the full IllustrisTNG galaxy formation model. At this high resolution, we find increased turbulent velocities, many small, cool cloudlets, and a smooth and homogeneous hot phase. I will outline these results and discuss the implications for high- and intermediate-velocity cloud studies and gas mixing in the CGM.

Despite its vast extent—spanning hundreds of kiloparsecs beyond the galactic disk—the circumgalactic medium (CGM) is shaped by microphysical processes operating on much smaller scales. One key example is the coupling between cosmic rays and gas. Under the right conditions, cosmic rays can dominate the pressure support in the CGM of low-redshift L* galaxies. However, this coupling depends sensitively on AU-scale magnetic field fluctuations—well below the resolution limit of modern galaxy-scale simulations. In this talk, I will highlight recent theoretical developments in cosmic-ray transport and their implications for CGM pressure profiles. I’ll also introduce CGSM, a new subgrid model designed to represent unresolved cold gas structures in hydrodynamic simulations, and discuss its potential to bridge the gap between microphysics and galaxy evolution.

The circumgalactic/intergalactic medium (CGM/IGM) represents a significant baryon reservoir for sustaining star formation and provides insights into the inflows, outflows, and feedback history of galaxies.  Star-forming dwarf galaxies, with their shallow potential wells, are predicted to drive metal-enriched gas into the CGM/IGM. Therefore, a census of the CGM around dwarf galaxies can provide insights into the stellar feedback. We present highly sensitive absorption-line measurements in quasar sightlines adjacent to 91 isolated dwarf galaxies with a median stellar mass of M_star/M_sun≈8.4 from the Cosmic Ultraviolet Baryon Survey (CUBS). This survey uses HST absorption spectroscopy to access a range of ion transitions from 0.077

Active Galactic Nuclei (AGN) feedback is known to play a key role in galaxy evolution and in regulating star formation. Studying the interplay between the central AGN and the different gas phases permeating galaxies is crucial to further our understanding of this powerful mechanism. We have observed the central regions of four brightest cluster galaxies at optical wavelengths using the Keck Cosmic Web Imager. With the high-resolution integral field unit data obtained from these observations, we map the fluxes and velocities of both emission lines and stellar absorption lines. This allows for a detailed tracing of gas cooling in galaxy centres. These galaxies have extensive X-ray and radio observations, allowing us to compare the dynamics of different gas phases and to study their interactions. Nebular emission extends up to tens of kiloparsecs from the central cluster galaxies of Abell 1835, PKS 0745-191, Abell 262, and RX J0820.9+0752. With the stellar continua, we map the kinematics and ages of the stars, learning about the systems’ star formation histories. Our findings highlight the complex stellar and gas dynamics which can be induced by radio-mechanical feedback. Surprisingly, three of the four systems have substantial (~ 150 km/s) velocity differences between their central galaxy and its associated nebular gas. This shows that the central galaxy is not at rest with respect to its surrounding nebula. In PKS 0745-191 and Abell 1835, nebular gas is churned up by buoyantly rising bubbles and jets. The churned gas is also surrounded by larger scale, lower velocity dispersion nebular emission. These complex motions will affect thermally unstable cooling, the interactions between the AGN and its atmosphere and how jet energy dissipates in its surroundings. These novel results highlight the deeply complex dynamics of AGN feedback and the multiphase gas in the centre of massive galaxies.

The circum-galactic medium (CGM) is at the nexus of the gas inflows and outflows that regulate galaxy evolution. Consequently, the CGM provides an ideal laboratory for studying galaxy fueling, feedback, and interactions. In the last decade, the simultaneous availability of UV spectra from the Cosmic Origins Spectrograph, deep integral field spectrographs, and wide galaxy redshift surveys have revolutionized our ability to characterize the CGM empirically. I will review recent progress enabled by the Cosmic Ultraviolet Baryon Survey (CUBS) and MUSE Quasar Blind Emitter Survey (MUSEQuBES), which combine these data for 31 intermediate redshift quasar fields. These surveys simultaneously provide for the first studies of physical conditions and abundances of the CGM and IGM around low-mass dwarf galaxies that constrain the physical conditions and abundances of the gas while also enabling the discovery of giant rest-frame optical emission nebulae around quasar hosts. I will highlight enlightening case studies, including filamentary accretion from 100 kpc scales into the ISM of a massive quasar host confirmed by down-the-barrel inflows observed in the UV and the first studies of relative abundances in the CGM/IGM around isolated dwarf galaxies that reveal surprisingly high metallicity and low [C/O] and [N/O] ratios, suggestive of core-collapse supernova outflows with modest mass loading.

Despite a growing body of observational and theoretical work, the connection between galactic-scale feedback processes, the underlying distribution of gas in the circumgalactic medium (CGM), and host galaxy properties remains uncertain. Focusing on the latter two points, we present new results on the spatial structure and kinematics of Ly$\alpha$ and several far-UV metallic ions in the CGM of Keck Baryonic Structure Survey (KBSS) galaxies using rest-frame far-UV spectra of foreground/background galaxy pairs with angular separations $\le 30$ arcsec. Medium resolution ($R\simeq 1500$) Keck/KCWI and Keck/LRIS spectra of 736 background galaxies with $\langle z_{\rm bg}\rangle=2.58 \pm 0.38$ probe sightlines through 1033 foreground galaxies ($\langle z_{\rm fg}\rangle=2.03 \pm 0.36$) at projected distances $8\leq D_{\rm tran}/\mathrm{kpc}\leq250$. For each ion, we measure rest-frame equivalent widths ($W_{\lambda}$) as a function of $D_{\rm tran}$; we observe higher ionization species (C IV) decrease less rapidly and extend to larger $D_{\rm tran}$ compared to low ions (O I, C II, Si II). Splitting the pair sample into subsets based on foreground galaxy properties, we find $W_\lambda(\text{C IV})$ exhibits a strong dependence on stellar mass ($M_*$) and a weaker dependence on star formation rate. Similarly, $W_\lambda(\text{Ly}\alpha)$ increases with $M_*$, albeit with more scatter. In 2D, we map the excess Ly$\alpha$ and C IV absorption as functions of line-of-sight velocity and $D_{\rm tran}$ and fit the observed Ly$\alpha$ map with a simple two-component model. Combining the 1D and 2D trends, we discuss the improved constraints these results place on CGM gas-phase kinematics in the context of previous studies at $z\sim 2$.

The baryon cycle of a galaxy involves a dynamic interplay between its star-forming disk and the environment of its virial halo, or circumgalatic medium. Simulations and observations agree that winds are a key seeding mechanism for the CGM, which serves as a reservoir for metals produced in disks. Cool clouds are predicted to form in the CGM from cooling halo gas, and are observed in absorbing sightlines to background quasars. This cloud growth may be accelerated by the action of winds. However, directly imaging the cold-hot interaction is extremely challenging, as most of the cooling channels lie in the UV and X-ray. I will present a deep image of OVI 1032, 1038 A and Lyman-alpha in the footprint of a prominent galactic wind. The OVI-emitting gas follows the morphology observed in lines at optical wavelengths. This represents only the second image of OVI in the halo or CGM of a galaxy, and is a signpost of cloud growth at large radii as the wind and CGM interact. This detection will help motivate further attempts to image the CGM-in-formation with existing or future facilities. It will also help inform models and simulations of the wind-CGM interaction.