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1. EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely Metal-poor Galaxies

   https://doi.org/10.3847/1538-4357/ad06ab  

   Xu, Yi ; Ouchi, Masami ; Isobe, Yuki ; Nakajima, Kimihiko ; Ozaki, Shinobu ; Bouché, Nicolas F. ; Wise, John H. ; Emsellem, Eric ; Kusakabe, Haruka ; Hattori, Takashi ; et al ( January 2024 , The Astrophysical Journal)

   We  present the demography of the dynamics and gas mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of 0.015–0.195Z_⊙and low stellar masses of 10⁴–10⁸M_⊙in the local universe. We conduct deep optical integral field spectroscopy (IFS) for the low-mass EMPGs with the medium-high resolution (R= 7500) grism of the 8 m Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate the Hαemission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the Hαlines by the fitting of three-dimensional disk models. We obtain an average maximum rotation velocity (v_rot) of 15 ± 3 km s⁻¹and an average intrinsic velocity dispersion (σ₀) of 27 ± 10 km s⁻¹for 15 spatially resolved EMPGs out of 33 EMPGs, and find that all 15 EMPGs havev_rot/σ₀< 1 suggesting dispersion-dominated systems. There is a clear decreasing trend ofv_rot/σ₀with the decreasing stellar mass and metallicity. We derive the gas mass fraction (f_gas) for all 33 EMPGs, and find no clear dependence on stellar mass and metallicity. Thesev_rot/σ₀andf_gastrends should be compared with young high-zgalaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe.

    

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2. From Carbon to Cobalt: Chemical Compositions and Ages of z ∼ 0.7 Quiescent Galaxies

   https://doi.org/10.3847/1538-4357/acc176  

   Beverage, Aliza G. ; Kriek, Mariska ; Conroy, Charlie ; Sandford, Nathan R. ; Bezanson, Rachel ; Franx, Marijn ; van der Wel, Arjen ; Weisz, Daniel R. ( May 2023 , The Astrophysical Journal)

   We present elemental abundance patterns (C, N, Mg, Si, Ca, Ti, V, Cr, Fe, Co, and Ni) for a population of 135 massive quiescent galaxies atz∼ 0.7 with ultra-deep rest-frame optical spectroscopy drawn from the LEGA-C survey. We derive average ages and elemental abundances in four bins of stellar velocity dispersion (σ_v) ranging from 150–250 km s⁻¹using a full-spectrum hierarchical Bayesian model. The resulting elemental abundance measurements are precise to 0.05 dex. The majority of elements, as well as the total metallicity and stellar age, show a positive correlation withσ_v. Thus, the highest dispersion galaxies formed the earliest and are the most metal-rich. We find only mild or nonsignificant trends between [X/Fe] andσ_v, suggesting that the average star formation timescale does not strongly depend on velocity dispersion. To first order, the abundance patterns of thez∼ 0.7 quiescent galaxies are strikingly similar to those atz∼ 0. However, at the lowest-velocity dispersions, thez∼ 0.7 galaxies have slightly enhanced N, Mg, Ti, and Ni abundance ratios and earlier formation redshifts than theirz∼ 0 counterparts. Thus, while the higher-mass quiescent galaxy population shows little evolution, the low-mass quiescent galaxies population has grown significantly over the past 6 Gyr. Finally, the abundance patterns of bothz∼ 0 andz∼ 0.7 quiescent galaxies differ considerably from theoretical prediction based on a chemical evolution model, indicating that our understanding of the enrichment histories of these galaxies is still very limited.

    

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3. An Hi-absorption-selected Cold Rotating Disk Galaxy at z ≈ 2.193

   https://doi.org/10.3847/2041-8213/ad65fe  

   Kaur, B. ; Kanekar, N. ; Neeleman, M. ; Rafelski, M. ; Prochaska, J_X ; Dutta, R. ( August 2024 , The Astrophysical Journal Letters)

   We have used the Atacama Large Millimeter/submillimeter Array to map CO(3–2) emission from a galaxy, DLA-B1228g, associated with the high-metallicity damped Lyαabsorber atz≈ 2.1929 toward the QSO PKS B1228–113. At an angular resolution of ≈0.″32 × 0.″24, DLA-B1228g shows extended CO(3–2) emission with a deconvolved size of ≈0.″78 × 0.″18, i.e., a spatial extent of ≈6.4 kpc. We detect extended stellar emission from DLA-B1228g in a Hubble Space Telescope Wide Field Camera 3 F160W image and find that Hαemission is detected in a Very Large Telescope SINFONI image from only one side of the galaxy. While the clumpy nature of the F160W emission and the offset between the kinematic and physical centers of the CO(3–2) emission are consistent with a merger scenario, this appears unlikely due to the lack of strong Hαemission, the symmetric double-peaked CO(3–2) line profile, the high molecular gas depletion timescale, and the similar velocity dispersions in the two halves of the CO(3–2) image. Kinematic modeling reveals that the CO(3–2) emission is consistent with arising from an axisymmetric rotating disk with an exponential profile, a rotation velocity ofv_rot= 328 ± 7 km s⁻¹, and a velocity dispersion ofσ_v= 62 ± 7 km s⁻¹. The high value of the ratiov_rot/σ_v, ≈5.3, implies that DLA-B1228g is a rotation-dominated cold disk galaxy, the second case of a high-zHi-absorption-selected galaxy identified with a cold rotating disk. We obtain a dynamical mass ofM_dyn= (1.5 ± 0.1) × 10¹¹M_⊙, similar to the molecular gas mass of ≈10¹¹M_⊙inferred from earlier CO(1–0) studies; this implies that the galaxy is baryon-dominated in its inner regions.

    

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4. Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy

   https://doi.org/10.1051/0004-6361/202245105  

   Lelli, Federico ; Zhang, Zhi-Yu ; Bisbas, Thomas G. ; Lin, Lingrui ; Papadopoulos, Padelis ; Schombert, James M. ; Di Teodoro, Enrico ; Marasco, Antonino ; McGaugh, Stacy S. ( April 2023 , Astronomy & Astrophysics)

   We study the dynamics of cold molecular gas in two main-sequence galaxies at cosmic noon (zC-488879 at z  ≃ 1.47 and zC-400569 at z  ≃ 2.24) using new high-resolution ALMA observations of multiple 12 CO transitions. For zC-400569 we also reanalyze high-quality H α data from the SINS/zC-SINF survey. We find that (1) both galaxies have regularly rotating CO disks and their rotation curves are flat out to ∼8 kpc contrary to previous results pointing to outer declines in the rotation speed V rot ; (2) the intrinsic velocity dispersions are low ( σ CO  ≲ 15 km s −1 for CO and σ Hα  ≲ 37 km s −1 for H α ) and imply V rot / σ CO  ≳ 17 − 22 yielding no significant pressure support; (3) mass models using HST images display a severe disk-halo degeneracy, that is models with inner baryon dominance and models with “cuspy” dark matter halos can fit the rotation curves equally well due to the uncertainties on stellar and gas masses; and (4) Milgromian dynamics (MOND) can successfully fit the rotation curves with the same acceleration scale a 0 measured at z  ≃ 0. The question of the amount and distribution of dark matter in high- z galaxies remains unsettled due to the limited spatial extent of the available kinematic data; we discuss the suitability of various emission lines to trace extended rotation curves at high z . Nevertheless, the properties of these two high- z galaxies (high V rot / σ V ratios, inner rotation curve shapes, bulge-to-total mass ratios) are remarkably similar to those of massive spirals at z  ≃ 0, suggesting weak dynamical evolution over more than 10 Gyr of the Universe’s lifetime. 

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5. Dwarfs in Void Environments (DIVE): The Stellar Kinematics of Void Dwarf Galaxies Using the Keck Cosmic Web Imager

   https://doi.org/10.3847/1538-4357/acd189  

   de los Reyes, Mithi A. C. ; Kirby, Evan N. ; Zhuang, Zhuyun ; Steidel, Charles C. ; Chen, Yuguang ; Wheeler, Coral ( July 2023 , The Astrophysical Journal)

   Dwarf galaxies located in extremely underdense cosmic voids are excellent test beds for disentangling the effects of large-scale environments on galaxy formation and evolution. We present the first results of the Dwarfs in Void Environments Survey, which has obtained integral field spectroscopy for low-mass galaxies (M_⋆= 10⁷–10⁹M_⊙) located inside (N= 21) and outside (N= 9) cosmic voids using the Keck Cosmic Web Imager. Using measurements of stellar line-of-sight rotational velocityv_rotand velocity dispersionσ_⋆, we test the tidal stirring hypothesis, which posits that dwarf spheroidal galaxies are formed through tidal interactions with more massive host galaxies. We measure low values ofv_rot/σ_⋆≲ 2 for our sample of isolated dwarf galaxies, and we find no trend betweenv_rot/σ_⋆and the distance from a massive galaxy$d_{L^{\star }}$out to$d_{L^{\star }}\sim 10$Mpc. These suggest that dwarf galaxies can become dispersion-supported, “puffy” systems even in the absence of environmental effects like tidal interactions. We also find indications of an upward trend betweenv_rot/σ_⋆and galaxy stellar mass, perhaps implying that stellar disk formation depends on mass rather than environment. Although some of our conclusions may be slightly modified by systematic effects, our main result still holds: that isolated low-mass galaxies may form and remain as puffy systems rather than the dynamically cold disks predicted by classical galaxy formation theory.

    

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