We report the discovery of MAGAZ3NE J095924+022537, a spectroscopically confirmed protocluster at
We present a multiwavelength analysis of the galaxy cluster SPTCL J06074448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope at
 NSFPAR ID:
 10401696
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astrophysical Journal
 Volume:
 944
 Issue:
 2
 ISSN:
 0004637X
 Format(s):
 Medium: X Size: Article No. 164
 Size(s):
 ["Article No. 164"]
 Sponsoring Org:
 National Science Foundation
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Abstract around a spectroscopically confirmed $z={3.3665}_{0.0012}^{+0.0009}$UVJ quiescent ultramassive galaxy (UMG; ) in the COSMOS UltraVISTA field. We present a total of 38 protocluster members (14 spectroscopic and 24 photometric), including the UMG. Notably, and in marked contrast to protoclusters previously reported at this epoch that have been found to contain predominantly starforming members, we measure an elevated fraction of quiescent galaxies relative to the coeval field ( ${M}_{\star}\phantom{\rule{0.25em}{0ex}}={2.34}_{0.34}^{+0.23}\times {10}^{11}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ versus ${73.3}_{16.9}^{+26.7}\mathrm{\%}$ for galaxies with stellar mass ${11.6}_{4.9}^{+7.1}\mathrm{\%}$M _{⋆}≥ 10^{11}M _{⊙}). This high quenched fraction provides a striking and important counterexample to the seeming ubiquitousness of starforming galaxies in protoclusters atz > 2 and suggests, rather, that protoclusters exist in a diversity of evolutionary states in the early universe. We discuss the possibility that we might be observing either “early mass quenching” or nonclassical “environmental quenching.” We also present the discovery of MAGAZ3NE J100028+023349, a second spectroscopically confirmed protocluster, at a very similar redshift of . We present a total of 20 protocluster members, 12 of which are photometric and eight spectroscopic including a poststarburst UMG ( $z={3.3801}_{0.0281}^{+0.0213}$ ). Protoclusters MAGAZ3NE J0959 and MAGAZ3NE J1000 are separated by 18′ on the sky (35 comoving Mpc), in good agreement with predictions from simulations for the size of “Coma”type cluster progenitors at this epoch. It is highly likely that the two UMGs are the progenitors of Brightest Cluster Galaxies seen in massive virialized clusters at lower redshift. ${M}_{\star}={2.95}_{0.20}^{+0.21}\times {10}^{11}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ 
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 We present the
z ≈ 6 type1 quasar luminosity function (QLF), based on the PanSTARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars atz ≈ 5.7–6.2, with −28 ≲M _{1450}≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate thez ≈ 6 QLF over −28 ≲M _{1450}≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z ) ∝ 10^{k(z−6)};k = −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of , a faintend slope of ${M}^{*}={26.38}_{0.60}^{+0.79}\phantom{\rule{0.25em}{0ex}}\mathrm{mag}$ , and a steep brightend slope of $\alpha ={1.70}_{0.19}^{+0.29}$ . Based on our new QLF model, we determine the quasar comoving spatial density at $\beta ={3.84}_{1.21}^{+0.63}$z ≈ 6 to be . In comparison with the literature, we find the quasar density to evolve with a constant value of $n({M}_{1450}<26)={1.16}_{0.12}^{+0.13}\phantom{\rule{0.25em}{0ex}}{\mathrm{cGpc}}^{3}$k ≈ −0.7, fromz ≈ 7 toz ≈ 4. Additionally, we derive an ionizing emissivity of , based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. at ${\u03f5}_{912}(z=6)={7.23}_{1.02}^{+1.65}\times {10}^{22}\phantom{\rule{0.25em}{0ex}}\mathrm{erg}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}\phantom{\rule{0.25em}{0ex}}{\mathrm{Hz}}^{1}\phantom{\rule{0.25em}{0ex}}{\mathrm{cMpc}}^{3}$z ≈ 6, we calculate an Hi photoionizing rate of Γ_{H I}(z = 6) ≈ 6 × 10^{−16}s^{−1}, strongly disfavoring a dominant role of quasars in hydrogen reionization. 
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. ${\sigma}_{[\mathrm{Fe}/\mathrm{H}]}={0.38}_{0.05}^{+0.07}$ 
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