Kinematically Complex Circumgalactic Gas Around a Low-mass Galaxy: Filamentary Inflow and Counterrotation in J0910b

Year: 2025 DOI: 10.3847/1538-4357/ae10b2

We present the first detailed, spatially resolved study of the circumgalactic medium (CGM) surrounding the low-mass, low-redshift star-forming galaxy J0910b (SDSS J091458.61+110845.1; M⋆ ∼ 109.2 M⊙, z = 0.096), focusing on its gas dynamics, ionization mechanisms, and kinematics. J0910b is the lowest-mass galaxy in our low-redshift CGM survey using the Keck Cosmic Web Imager (KCWI). Using KCWI integral field spectroscopy and CLOUDY modeling, we map the ionization structure and velocity field of the CGM through Hα, [O III] λ5007, and [O II] λλ3727, 3729 emission. We detect a predominantly cool (T ∼ 10⁴ K) ionized halo extending to ∼35 kpc (∼0.35 Rvir), with a complex structure including a counterrotating component and two filamentary inflows. The counterrotating CGM contains ∼7.4 × 10⁹ M⊙ of ionized gas—nearly 5 times the stellar mass—and exhibits a positive radial metallicity gradient, rising from 0.2 Z⊙ at 9 kpc to 0.65 Z⊙ at 16 kpc. Velocity dispersion maps reveal a shell-like structure near the interstellar medium-CGM interface, suggesting feedback-driven outflows that redistributed enriched gas. In contrast, the filaments show low metallicities (∼0.07 Z⊙), high specific angular momentum (j ∼ 3.7 × 10³ kpc km s−1), and an accretion rate of 0.05 M⊙ yr−1, consistent with an intergalactic origin. Together, these components reveal a dynamically rich CGM. The counterrotating gas dominates the halo’s mass, accounts for ∼33% of the cosmic baryon budget, and must be continuously replenished (tcool ∼ 0.3–2 Myr). These results suggest a long-lived, regulated CGM that governs star formation through angular momentum exchange and gas recycling.