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We present spatially-resolved rest-frame optical emission line maps of four galaxies at z∼2 observed with Keck/OSIRIS to study the physical conditions of the ISM at Cosmic Noon. Our analysis of strong emission line ratios in these galaxies reveals an offset from the local star-forming locus on the BPT diagram, but agrees with other star-forming galaxies at similar redshifts. Despite the offset towards higher [O III]λ5008/Hβ and [N II]λ6585/Hα, these strong-line ratios remain consistent with or below the maximum starburst threshold even in the inner ∼1 kpc region of the galaxies, providing no compelling evidence for central AGN activity. The galaxies also exhibit flat radial gas-phase metallicity gradients, consistent with previous studies of z∼2 galaxies and suggesting efficient radial mixing possibly driven by strong outflows from intense star formation. Overall, our results reveal the highly star-forming nature of these galaxies, with the potential to launch outflows that flatten metallicity gradients through significant radial gas mixing. Future observations with JWST/NIRSpec are crucial to detect fainter emission lines at higher spatial resolution to further constrain the physical processes and ionization mechanisms that shape the ISM during Cosmic Noon. 

Abstract We present Keck Cosmic Web Imager integral-field unit observations around extended Lyαhalos of 27 typical star-forming galaxies with redshifts 2.0 <z< 3.2 drawn from the MOSFIRE Deep Evolution Field survey. We examine the average Lyαsurface brightness profiles in bins of star formation rate (SFR), stellar mass (M_*), age, stellar continuum reddening, SFR surface density (Σ_SFR), and Σ_SFRnormalized by stellar mass (Σ_sSFR). The scale lengths of the halos correlate with stellar mass, age, and stellar continuum reddening and anticorrelate with SFR, Σ_SFR, and Σ_sSFR. These results are consistent with a scenario in which the down-the-barrel fraction of Lyαemission is modulated by the low-column-density channels in the interstellar medium, and in which the neutral gas covering fraction is related to the physical properties of the galaxies. Specifically, we find that this covering fraction increases with stellar mass, age, andE(B−V) and decreases with SFR, Σ_SFR, and Σ_sSFR. We also find that the resonantly scattered Lyαemission suffers greater attenuation than the (nonresonant) stellar continuum emission, and that the difference in attenuation increases with stellar mass, age, and stellar continuum reddening, and decreases with Σ_sSFR. These results imply that more reddened galaxies have more dust in their circumgalactic medium. 

ABSTRACT We use the large spectroscopic data set of the MOSFIRE Deep Evolution Field survey to investigate the kinematics and energetics of ionized gas outflows. Using a sample of 598 star-forming galaxies at redshift 1.4 < z < 3.8, we decompose [O iii] and $$\rm {H}\,\alpha$$ emission lines into narrow and broad components, finding significant detections of broad components in 10 per cent of the sample. The ionized outflow velocity from individual galaxies appears independent of galaxy properties, such as stellar mass, star formation rate (SFR), and SFR surface density (ΣSFR). Adopting a simple outflow model, we estimate the mass-, energy-, and momentum-loading factors of the ionized outflows, finding modest values with averages of 0.33, 0.04, and 0.22, respectively. The larger momentum- than energy-loading factors, for the adopted physical parameters, imply that these ionized outflows are primarily momentum driven. We further find a marginal correlation (2.5σ) between the mass-loading factor and stellar mass in agreement with predictions by simulations, scaling as ηm$$\propto M_{\star }^{-0.45}$$. This shallow scaling relation is consistent with these ionized outflows being driven by a combination of mechanical energy generated by supernovae explosions and radiation pressure acting on dusty material. In a majority of galaxies, the outflowing material does not appear to have sufficient velocity to escape the gravitational potential of their host, likely recycling back at later times. Together, these results suggest that the ionized outflows traced by nebular emission lines are negligible, with the bulk of mass and energy carried out in other gaseous phases. 

ABSTRACT We report on the discovery of cool gas inflows towards three star-forming galaxies at <z> ∼ 2.30. Analysis of Keck Low-Resolution Imaging Spectrometer spectroscopy reveals redshifted low-ionization interstellar (LIS) metal absorption lines with centroid velocities of 60–130 km s−1. These inflows represent some of the most robust detections of inflowing gas into isolated, star-forming galaxies at high redshift. Our analysis suggests that the inflows are due to recycling metal-enriched gas from previous ejections. Comparisons between the galaxies with inflows and a larger parent sample of 131 objects indicate that galaxies with detected inflows may have higher specific star formation rates (sSFRs) and star-formation-rate surface densities (ΣSFR). However, when additional galaxies without robustly detected inflows based on centroid velocity but whose LIS absorption line profiles indicate large red-wing velocities are considered, galaxies with inflows do not show unique properties relative to those lacking inflows. Additionally, we calculate the covering fraction of cool inflowing gas as a function of red-wing inflow velocity, finding an enhancement in high-sSFR binned galaxies, likely due to an increase in the amount of recycling gas. Together, these results suggest that the low detection rate of galaxies with cool inflows is primarily related to the viewing angle rather than the physical properties of the galaxies. 

Abstract We obtained Keck/DEIMOS spectra of 556 individual red giant branch stars in four spectroscopic fields spanning 13−31 projected kpc along the northeast (NE) shelf of M31. We present the first detection of a complete wedge pattern in the space of projected M31-centric radial distance versus line-of-sight velocity for this feature, which includes the returning stream component of the shelf. This wedge pattern agrees with expectations of a tidal shell formed in a radial merger and provides strong evidence in favor of predictions of Giant Stellar Stream (GSS) formation models in which the NE shelf originates from the second orbital wrap of the tidal debris. The observed concentric wedge patterns of the NE, west (W), and southeast (SE) shelves corroborate this interpretation independently of the models. We do not detect a kinematical signature in the NE shelf region corresponding to an intact progenitor core, favoring GSS formation models in which the progenitor is completely disrupted. The shelf’s photometric metallicity ([Fe/H] phot ) distribution implies that it is dominated by tidal material, as opposed to the phase-mixed stellar halo or the disk. The metallicity distribution ([Fe/H] phot = −0.42 ± 0.01) also matches the GSS, and consequently the W and SE shelves, further supporting a direct physical association between the tidal features. 

Abstract We present observations of CO(3−2) in 13 main-sequence z = 2.0–2.5 star-forming galaxies at log ( M * / M ⊙ ) = 10.2 – 10.6 that span a wide range in metallicity (O/H) based on rest-optical spectroscopy. We find that L CO ( 3 − 2 ) ′ /SFR decreases with decreasing metallicity, implying that the CO luminosity per unit gas mass is lower in low-metallicity galaxies at z ∼ 2. We constrain the CO-to-H 2 conversion factor ( α CO ) and find that α CO inversely correlates with metallicity at z ∼ 2. We derive molecular gas masses ( M mol ) and characterize the relations among M * , SFR, M mol , and metallicity. At z ∼ 2, M mol increases and the molecular gas fraction ( M mol / M * ) decreases with increasing M * , with a significant secondary dependence on SFR. Galaxies at z ∼ 2 lie on a near-linear molecular KS law that is well-described by a constant depletion time of 700 Myr. We find that the scatter about the mean SFR− M * , O/H− M * , and M mol − M * relations is correlated such that, at fixed M * , z ∼ 2 galaxies with larger M mol have higher SFR and lower O/H. We thus confirm the existence of a fundamental metallicity relation at z ∼ 2, where O/H is inversely correlated with both SFR and M mol at fixed M * . These results suggest that the scatter of the z ∼ 2 star-forming main sequence, mass–metallicity relation, and M mol – M * relation are primarily driven by stochastic variations in gas inflow rates. We place constraints on the mass loading of galactic outflows and perform a metal budget analysis, finding that massive z ∼ 2 star-forming galaxies retain only 30% of metals produced, implying that a large mass of metals resides in the circumgalactic medium. 

Abstract We present the COSMOS Spectroscopic Redshift Compilation encompassing ∼20 yr of spectroscopic redshifts within a 10 deg²area centered on the 2 deg²COSMOS legacy field. This compilation contains 487,666 redshifts of 266,284 unique objects from 138 individual programs up toz ∼ 8 with median stellar mass ∼10^8.4–10¹⁰M_⊙(redshift dependent). Rest-frameNUVrJcolors and star formation rate–stellar mass correlations show that the compilation primarily contains low-to-intermediate-mass star-forming and massive, quiescent galaxies atz < 1.25 and mostly low-mass bursty star-forming galaxies atz > 2. Sources in the compilation cover a diverse range of environments, including protoclusters such as “Hyperion.” The full compilation is 50% spectroscopically complete byi ∼ 23.4 mag andK_s ∼ 21.6 mag; however, this is redshift dependent. Spatially, the compilation is >50% (>30%) complete within the central (outer) region limited toi < 24 mag andK_s < 22.5 mag, separately. We demonstrate how the compilation can be used to validate photometric redshifts and investigate calibration metrics. By training self-organizing maps on COSMOS2020/Classic and projecting the compilation onto it, we find key subpopulations currently lacking spectroscopic coverage, includingz < 1 intermediate-mass quiescent and low-/intermediate-mass bursty star-forming galaxies,z ∼ 2 massive quiescent galaxies, andz > 3 massive star-forming galaxies. This highlights how combining self-organizing maps with our compilation can provide guidance for future spectroscopic observations to get a complete spectroscopic view of galaxy populations. Lastly, the compilation will undergo periodic data releases incorporating new spectroscopic redshifts and providing a lasting legacy resource for the community.