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1. Kinematics, Structure, and Mass Outflow Rates of Extreme Starburst Galactic Outflows

   https://doi.org/10.3847/1538-4357/acc660  

   Perrotta, Serena; Coil, Alison L.; Rupke, David S. N.; Tremonti, Christy A.; Davis, Julie D.; Diamond-Stanic, Aleksandar M.; Geach, James E.; Hickox, Ryan C.; Moustakas, John; Rudnick, Gregory H.; et al (May 2023, The Astrophysical Journal)

   Abstract We present results on the properties of extreme gas outflows in massive (M_*∼ 10¹¹M_⊙), compact, starburst (star formation rate, SFR∼ 200M_⊙yr⁻¹) galaxies atz= 0.4–0.7 with very high star formation surface densities (Σ_SFR∼ 2000M_⊙yr⁻¹kpc⁻²). Using optical Keck/HIRES spectroscopy of 14 HizEA starburst galaxies, we identify outflows with maximum velocities of 820–2860 km s⁻¹. High-resolution spectroscopy allows us to measure precise column densities and covering fractions as a function of outflow velocity and characterize the kinematics and structure of the cool gas outflow phase (T∼ 10⁴K). We find substantial variation in the absorption profiles, which likely reflects the complex morphology of inhomogeneously distributed, clumpy gas and the intricacy of the turbulent mixing layers between the cold and hot outflow phases. There is not a straightforward correlation between the bursts in the galaxies’ star formation histories and their wind absorption line profiles, as might naively be expected for starburst-driven winds. The lack of strong Mgiiabsorption at the systemic velocity is likely an orientation effect, where the observations are down the axis of a blowout. We infer high mass outflow rates of ∼50–2200M_⊙yr⁻¹, assuming a fiducial outflow size of 5 kpc, and mass loading factors ofη∼ 5 for most of the sample. While these values have high uncertainties, they suggest that starburst galaxies are capable of ejecting very large amounts of cool gas that will substantially impact their future evolution. 

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2. Extending the Dynamic Range of Galaxy Outflow Scaling Relations: Massive Compact Galaxies with Extreme Outflows

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

   Davis, Julie D.; Tremonti, Christy A.; Swiggum, Cameren N.; Moustakas, John; Diamond-Stanic, Aleksandar M.; Coil, Alison L.; Geach, James E.; Hickox, Ryan C.; Perrotta, Serena; Petter, Grayson C.; et al (July 2023, The Astrophysical Journal)

   Abstract We investigate galactic winds in the HizEA galaxies, a collection of 46 late-stage galaxy mergers atz= 0.4–0.8, with stellar masses of $\log \left(M_{*}/M_{\odot }\right)=10.4–11.5$, star formation rates (SFRs) of 20–500M_⊙yr⁻¹, and ultra-compact (a few 100 pc) central star-forming regions. We measure their gas kinematics using the Mgiiλλ2796,2803 absorption lines in optical spectra from MMT, Magellan, and Keck. We find evidence of outflows in 90% of targets, with maximum outflow velocities of 550–3200 km s⁻¹. We combine these data with ten samples from the literature to construct scaling relations for outflow velocity versus SFR, star formation surface density (Σ_SFR),M_*, and SFR/M_*. The HizEA galaxies extend the dynamic range of the scaling relations by a factor of ∼2–4 in outflow velocity and an order of magnitude in SFR and Σ_SFR. The ensemble scaling relations exhibit strong correlations between outflow velocity, SFR, SFR/R, and Σ_SFR, and weaker correlations withM_*and SFR/M_*. The HizEA galaxies are mild outliers on the SFR andM_*scaling relations, but they connect smoothly with more typical star-forming galaxies on plots of outflow velocity versus SFR/Rand Σ_SFR. These results provide further evidence that the HizEA galaxies’ exceptional outflow velocities are a consequence of their extreme star formation conditions rather than hidden black hole activity, and they strengthen previous claims that Σ_SFRis one of the most important properties governing the velocities of galactic winds. 

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3. Physical Properties of Massive Compact Starburst Galaxies with Extreme Outflows

   https://doi.org/10.3847/1538-4357/ac2fa4  

   Perrotta, Serena; George, Erin R.; Coil, Alison L.; Tremonti, Christy A.; Rupke, David S. N.; Davis, Julie D.; Diamond-Stanic, Aleksandar M.; Geach, James E.; Hickox, Ryan C.; Moustakas, John; et al (December 2021, The Astrophysical Journal)

   Abstract We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (M_*∼ 10¹¹M_⊙), compact starburst galaxies atz= 0.4–0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean Σ_SFR∼ 2000M_⊙yr⁻¹kpc⁻²) and powerful galactic outflows (maximum speedsv₉₈∼ 1000–3000 km s⁻¹). Our unique data set includes an ensemble of both emission ([Oii]λλ3726,3729, Hβ, [Oiii]λλ4959,5007, Hα, [Nii]λλ6549,6585, and [Sii]λλ6716,6731) and absorption (Mgiiλλ2796,2803, and Feiiλ2586) lines that allow us to investigate the kinematics of the cool gas phase (T∼ 10⁴K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (mediann_e∼ 530 cm⁻³), and high metallicity (solar or supersolar). We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [Sii]nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape. 

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4. Spatially Resolved Circumgalactic Medium around a Star-forming Galaxy Driving a Galactic Outflow at z  ≈ 0.8

   https://doi.org/10.3847/1538-4357/add0b9  

   Shaban, Ahmed; Bordoloi, Rongmon; O’Meara, John M; Sharon, Keren; Tejos, Nicolas; Lopez, Sebastian; Ledoux, Cédric; Barrientos, L Felipe; Rigby, Jane R (June 2025, The Astrophysical Journal)

   Abstract We report the small-scale spatial variation in cool (T ∼ 10⁴K) Mgiiabsorption detected in the circumgalactic medium (CGM) of a star-forming galaxy atz ≈ 0.8. The CGM of this galaxy is probed by a spatially extended bright background gravitationally lensed arc atz= 2.76. The background arc continuously samples the CGM of the foreground galaxy at a range of impact parameters between 54 and 66 kpc. The Mgiiabsorption strengths vary by more than a factor of 2 within these ranges. A power-law fit to the fractional variation of absorption strengths yields a coherence length of 5.8 kpc within this range of impact parameters. This suggests a high degree of spatial coherence in the CGM of this galaxy. The host galaxy is driving a strong galactic outflow with a mean outflow velocity ≈ −179 km s⁻¹and mass outflow rate ${\dot{M}}_{\mathrm{out}}\ge 64_{-27}^{+31}$M_⊙yr⁻¹traced by blueshifted Mgiiand Feiiabsorption lines. The galaxy itself has a spatially extended emission halo with a maximum spatial extent of ≈33 kpc traced by [Oii], [Oiii], and Hβemission lines. The extended emission halo shows kinematic signatures of corotating halo gas with solar metallicity. Taken together, these observations suggest evidence of a baryon cycle that is recycling the outflowing gas to form the next generation of stars. 

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5. A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): JWST Discovers an Overdensity around a Metal Absorption-selected Galaxy at z ∼ 5.5

   https://doi.org/10.3847/2041-8213/acfee3  

   Wu, Yunjing; Wang, Feige; Cai, Zheng; Fan, Xiaohui; Finlator, Kristian; Yang, Jinyi; Hennawi, Joseph F; Sun, Fengwu; Champagne, Jaclyn B; Lin, Xiaojing; et al (October 2023, The Astrophysical Journal Letters)

   Abstract The launch of JWST opens a new window for studying the connection between metal-line absorbers and galaxies at the end of the Epoch of Reionization. Previous studies have detected absorber–galaxy pairs in limited quantities through ground-based observations. To enhance our understanding of the relationship between absorbers and their host galaxies atz> 5, we utilized the NIRCam wide-field slitless spectroscopy to search for absorber-associated galaxies by detecting their rest-frame optical emission lines (e.g., [OIII] + Hβ). We report the discovery of a Mgii-associated galaxy atz= 5.428 using data from the JWST ASPIRE program. The Mgiiabsorber is detected on the spectrum of quasar J0305–3150 with a rest-frame equivalent width of 0.74 Å. The associated galaxy has an [OIII] luminosity of 10^42.5erg s⁻¹with an impact parameter of 24.9 pkpc. The joint Hubble Space Telescope–JWST spectral energy distribution (SED) implies a stellar mass and star formation rate ofM_*≈ 10^8.8M_⊙, star-formation rate  ≈ 10M_⊙yr⁻¹. Its [OIII] equivalent width and stellar mass are typical of [OIII] emitters at this redshift. Furthermore, connecting the outflow starting time to the SED-derived stellar age, the outflow velocity of this galaxy is ∼300 km s⁻¹, consistent with theoretical expectations. We identified six additional [OIII] emitters with impact parameters of up to ∼300 pkpc at similar redshifts (∣dv∣ < 1000 km s⁻¹). The observed number is consistent with that in cosmological simulations. This pilot study suggests that systematically investigating the absorber–galaxy connection within the ASPIRE program will provide insights into the metal-enrichment history in the early Universe. 

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