We measure the COtoH_{2}conversion factor (
Using the Keck Planet Imager and Characterizer, we obtained highresolution (
 Award ID(s):
 1801978
 NSFPAR ID:
 10485107
 Author(s) / Creator(s):
 ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astronomical Journal
 Volume:
 162
 Issue:
 4
 ISSN:
 00046256
 Format(s):
 Medium: X Size: Article No. 148
 Size(s):
 ["Article No. 148"]
 Sponsoring Org:
 National Science Foundation
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Abstract 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 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 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
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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. 
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