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
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
 NSFPAR ID:
 10406532
 Author(s) / Creator(s):
 ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astrophysical Journal
 Volume:
 947
 Issue:
 1
 ISSN:
 0004637X
 Format(s):
 Medium: X Size: Article No. 16
 Size(s):
 Article No. 16
 Sponsoring Org:
 National Science Foundation
More Like this

Abstract 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 the KODIAQZ survey aimed to characterize the cool, photoionized gas at 2.2 ≲
z ≲ 3.6 in 202 Hi selected absorbers with 14.6 ≤ < 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with $\mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}$ at 2.2 ≲ $14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<20$z ≲ 3.6 can be metalrich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyα absorbers (DLAs); it can also be very metalpoor ([X/H] < − 2.4) or even pristine ([X/H] < − 3.8), which is not observed in DLAs but is common in the IGM. For absorbers, the frequency of pristine absorbers is about 1%–10%, while for $16<\mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<20$ absorbers it is 10%–20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δ $14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}\le 16$v < 500 km s^{−1}imply that the metals are poorly mixed in gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲ $14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<20$z ≲ 3.6. We find that the mean metallicity increases withN _{Hi}, consistent with what is found inz < 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲z ≲ 3.6 toz < 1, but the contribution of the absorbers to the total metal budget of the universe at $14.6\le \mathrm{log}{N}_{\mathrm{H}\phantom{\rule{0.25em}{0ex}}\mathrm{I}}<19$z < 1 is a quarter of that at 2.2 ≲z ≲ 3.6. We show that FOGGIE cosmological zoomin simulations have a similar evolution of [X/H] withN _{Hi}, which is not observed in lowerresolution simulations. In these simulations, very metalpoor absorbers with [X/H] < − 2.4 atz ∼ 2–3 are tracers of inflows, while highermetallicity absorbers are a mixture of inflows and outflows. 
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. 
Abstract 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
, and velocity dispersion ${v}_{\mathrm{sys}}={31.5}_{1.2}^{+1.3}\phantom{\rule{0.33em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}$ . Additionally, we measure the metallicities of 16 member stars of Eri IV. We find a metallicity of ${\sigma}_{v}={6.1}_{0.9}^{+1.2}\phantom{\rule{0.33em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}$ , and resolve a dispersion of $[\mathrm{Fe}/\mathrm{H}]={2.87}_{0.07}^{+0.08}$σ _{[Fe/H]}=0.20 ± 0.09. The mean metallicity is marginally lower than all other known ultrafaint dwarf galaxies, making it one of the most metalpoor galaxies discovered thus far. Eri IV also has a somewhat unusual rightskewed metallicity distribution. For Cen I, we find a velocityv _{sys}= 44.9 ± 0.8 km s^{−1}, and velocity dispersion . We measure the metallicities of 27 member stars of Cen I, and find a mean metallicity [Fe/H] = −2.57 ± 0.08, and metallicity dispersion ${\sigma}_{v}={4.2}_{0.5}^{+0.6}\phantom{\rule{0.33em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}$ . We calculate the systemic proper motion, orbit, and the astrophysical Jfactor for each system, the latter of which indicates that Eri IV is a good target for indirect dark matter detection. We also find no strong evidence for tidal stripping of Cen I or Eri IV. Overall, our measurements confirm that Eri IV and Cen I are darkmatterdominated galaxies with properties largely consistent with other known ultrafaint dwarf galaxies. The low metallicity, rightskewed metallicity distribution, and high Jfactor make Eri IV an especially interesting candidate for further followup. ${\sigma}_{[\mathrm{Fe}/\mathrm{H}]}={0.38}_{0.05}^{+0.07}$ 
Abstract We present a Keck/MOSFIRE restoptical composite spectrum of 16 typical gravitationally lensed starforming dwarf galaxies at 1.7 ≲
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.