We present a Keck/MOSFIRE restoptical composite spectrum of 16 typical gravitationally lensed starforming dwarf galaxies at 1.7 ≲
We present a spectroscopic analysis of Eridanus IV (Eri IV) and Centaurus I (Cen I), two ultrafaint dwarf galaxies of the Milky Way. Using IMACS/Magellan spectroscopy, we identify 28 member stars of Eri IV and 34 member stars of Cen I. For Eri IV, we measure a systemic velocity of
 NSFPAR ID:
 10488523
 Author(s) / Creator(s):
 ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astrophysical Journal
 Volume:
 961
 Issue:
 2
 ISSN:
 0004637X
 Format(s):
 Medium: X Size: Article No. 234
 Size(s):
 ["Article No. 234"]
 Sponsoring Org:
 National Science Foundation
More Like this

Abstract z ≲ 2.6 (z _{mean}= 2.30), all chosen independent of emissionline strength. These galaxies have a median stellar mass of and a median star formation rate of $\mathrm{log}{({M}_{*}/{M}_{\odot})}_{\mathrm{med}}={8.29}_{0.43}^{+0.51}$ . We measure the faint electrontemperaturesensitive [O ${\mathrm{S}\mathrm{F}\mathrm{R}}_{\mathrm{H}\alpha}^{\mathrm{m}\mathrm{e}\mathrm{d}}={2.25}_{1.26}^{+2.15}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}\phantom{\rule{0.25em}{0ex}}{\mathrm{y}\mathrm{r}}^{1}$iii ]λ 4363 emission line at 2.5σ (4.1σ ) significance when considering a bootstrapped (statisticalonly) uncertainty spectrum. This yields a directmethod oxygen abundance of ( $12+\mathrm{log}{(\mathrm{O}/\mathrm{H})}_{\mathrm{direct}}={7.88}_{0.22}^{+0.25}$ ). We investigate the applicability at high ${0.15}_{0.06}^{+0.12}\phantom{\rule{0.33em}{0ex}}{Z}_{\odot}$z of locally calibrated oxygenbased strongline metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strongline ratio. At fixedM _{*}, our composite is well represented by thez ∼ 2.3 directmethod stellar mass—gasphase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories , we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixed $(\mathrm{log}{({M}_{*}/{M}_{\odot})}_{\mathrm{med}}={8.92}_{0.22}^{+0.31})$M _{*}and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [Oii ]λ 3729/[Oii ]λ 3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of ( ${n}_{e}={1}_{0}^{+215}\phantom{\rule{0.33em}{0ex}}{\mathrm{cm}}^{3}$ ) when considering the bootstrapped (statisticalonly) error spectrum. This result suggests that lowermass galaxies have lower densities than highermass galaxies at ${n}_{e}={1}_{0}^{+74}\phantom{\rule{0.33em}{0ex}}{\mathrm{cm}}^{3}$z ∼ 2. 
Abstract We measure the COtoH_{2}conversion factor (
α _{CO}) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from farinfrared emission as a tracer of the gas surface density and assuming a constant dusttometal ratio. In total, we have ∼790 and ∼610 independent measurements ofα _{CO}for CO (2–1) and (1–0), respectively. The mean values forα _{CO (2–1)}andα _{CO (1–0)}are and ${9.3}_{5.4}^{+4.6}$ , respectively. The COintensityweighted mean is 5.69 for ${4.2}_{2.0}^{+1.9}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}\phantom{\rule{0.25em}{0ex}}{\mathrm{pc}}^{2}\phantom{\rule{0.25em}{0ex}}{(\mathrm{K}\phantom{\rule{0.25em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1})}^{1}$α _{CO (2–1)}and 3.33 forα _{CO (1–0)}. We examine howα _{CO}scales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dustmassweighted average interstellar radiation field strength ( ). Among them, $\overline{U}$ , Σ_{SFR}, and the integrated CO intensity ( $\overline{U}$W _{CO}) have the strongest anticorrelation with spatially resolvedα _{CO}. We provide linear regression results toα _{CO}for all quantities tested. At galaxyintegrated scales, we observe significant correlations betweenα _{CO}andW _{CO}, metallicity, , and Σ_{SFR}. We also find that $\overline{U}$α _{CO}in each galaxy decreases with the stellar mass surface density (Σ_{⋆}) in highsurfacedensity regions (Σ_{⋆}≥ 100M _{⊙}pc^{−2}), following the powerlaw relations and ${\alpha}_{\mathrm{CO}\phantom{\rule{0.25em}{0ex}}(2\u20131)}\propto {\mathrm{\Sigma}}_{\star}^{0.5}$ . The powerlaw index is insensitive to the assumed dusttometal ratio. We interpret the decrease in ${\alpha}_{\mathrm{CO}\phantom{\rule{0.25em}{0ex}}(1\u20130)}\propto {\mathrm{\Sigma}}_{\star}^{0.2}$α _{CO}with increasing Σ_{⋆}as a result of higher velocity dispersion compared to isolated, selfgravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα _{CO}. The decrease inα _{CO}at high Σ_{⋆}is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburstlike” conversion factors. 
Abstract Cosmic reionization was the last major phase transition of hydrogen from neutral to highly ionized in the intergalactic medium (IGM). Current observations show that the IGM is significantly neutral at
z > 7 and largely ionized byz ∼ 5.5. However, most methods to measure the IGM neutral fraction are highly model dependent and are limited to when the volumeaveraged neutral fraction of the IGM is either relatively low ( ) or close to unity ( ${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\lesssim {10}^{3}$ ). In particular, the neutral fraction evolution of the IGM at the critical redshift range of ${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\sim 1$z = 6–7 is poorly constrained. We present new constraints on at ${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}$z ∼ 5.1–6.8 by analyzing deep optical spectra of 53 quasars at 5.73 <z < 7.09. We derive modelindependent upper limits on the neutral hydrogen fraction based on the fraction of “dark” pixels identified in the Lyα and Lyβ forests, without any assumptions on the IGM model or the intrinsic shape of the quasar continuum. They are the first modelindependent constraints on the IGM neutral hydrogen fraction atz ∼ 6.2–6.8 using quasar absorption measurements. Our results give upper limits of (1 ${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}(z=6.3)<0.79\pm 0.04$σ ), (1 ${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}(z=6.5)<0.87\pm 0.03$σ ), and (1 ${\overline{x}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}(z=6.7)<{0.94}_{0.09}^{+0.06}$σ ). The dark pixel fractions atz > 6.1 are consistent with the redshift evolution of the neutral fraction of the IGM derived from Planck 2018. 
Abstract We present a detection of 21 cm emission from largescale structure (LSS) between redshift 0.78 and 1.43 made with the Canadian Hydrogen Intensity Mapping Experiment. Radio observations acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRGs), emissionline galaxies (ELGs), and quasars (QSOs) from the eBOSS clustering catalogs. We find decisive evidence for a detection when stacking on all three tracers of LSS, with the logarithm of the Bayes factor equal to 18.9 (LRG), 10.8 (ELG), and 56.3 (QSO). An alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1
σ (LRG), 5.7σ (ELG), and 11.1σ (QSO). These are the first 21 cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (Hi ), defined as , where Ω_{Hi}is the cosmic abundance of H ${\mathit{\ue22d}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\equiv {10}^{3}\phantom{\rule{0.25em}{0ex}}{\mathrm{\Omega}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\left({b}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}+\u3008\phantom{\rule{0.25em}{0ex}}f{\mu}^{2}\u3009\right)$i ,b _{Hi}is the linear bias of Hi , and 〈f μ ^{2}〉 = 0.552 encodes the effect of redshiftspace distortions at linear order. We find for LRGs ( ${\mathit{\ue22d}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}={1.51}_{0.97}^{+3.60}$z = 0.84), for ELGs ( ${\mathit{\ue22d}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}={6.76}_{3.79}^{+9.04}$z = 0.96), and for QSOs ( ${\mathit{\ue22d}}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}={1.68}_{0.67}^{+1.10}$z = 1.20), with constraints limited by modeling uncertainties at nonlinear scales. We are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias Δv = − 66 ± 20 km s^{−1}for the QSOs. We split the QSO catalog into three redshift bins and have a decisive detection in each, with the upper bin atz = 1.30 producing the highestredshift 21 cm intensity mapping measurement thus far. 
Abstract The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a twoepisode wind in which the slow, outer wind originated 400 Myr ago (Episode I;
R _{I}= 20 − 50 kpc) and the fast, inner wind is 7 Myr old (Episode II;R _{II}= 0 − 20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phase—the warm, ionized gas—are unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out tor = 30–40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally excited lines are detected throughout the wind, and their line ratios are consistent with 200–400 km s^{−1}shocks that power the ionized gas, withv _{shock}=σ _{wind}. Combining shock models, densitysensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as those of the molecular gas: and ${M}_{\mathrm{II}}^{\mathrm{H}\mathrm{II}}\sim {M}_{\mathrm{II}}^{{\mathrm{H}}_{2}}=(12)\times {10}^{9}\phantom{\rule{0.50em}{0ex}}{M}_{\odot}$ yr^{−1}. The outer wind has slowed, so that $\mathit{dM}/{\mathit{dt}}_{\mathrm{II}}^{\mathrm{H}\mathrm{II}}\sim \mathit{dM}/{\mathit{dt}}_{\mathrm{II}}^{{\mathrm{H}}_{2}}=170250\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ yr^{−1}, but it contains more ionized gas, $\mathit{dM}/{\mathit{dt}}_{\mathrm{I}}^{\mathrm{H}\mathrm{II}}\sim 10\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ ${M}_{\mathrm{I}}^{\mathrm{H}\mathrm{II}}=5\times {10}^{9}$M _{⊙}. The momentum and energy in the recent Episode II wind imply a momentumdriven flow (p “boost” ∼7) driven by the hot ejecta and radiation pressure from the Eddingtonlimited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the circumgalactic medium.