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<jats:title>Abstract</jats:title> <jats:p>Cygnus X-1 is a well-studied persistent black hole X-ray binary. Recently, the three parameters needed to estimate the black hole spin of this system, namely the black hole mass <jats:italic>M</jats:italic>, the orbital inclination <jats:italic>i</jats:italic>, and the source distance <jats:italic>D</jats:italic>, have been updated. In this work we redetermine the spin parameter using the continuum-fitting technique for those updated parameter values. Based on the assumption that the spin axis of the black hole is aligned with the orbital plane, we fit the thermal disk component to a fully relativistic thin accretion disk model. The error in the spin estimate arising from the combined observational uncertainties is obtained via Monte Carlo simulations. We demonstrate that, without considering the counteracting torque effect, the new spin parameter is constrained to be <jats:italic>a</jats:italic> <jats:sub>*</jats:sub> &gt; 0.9985 (3<jats:italic>σ</jats:italic>), which confirms that the spin of the black hole in Cygnus X-1 is extreme.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent observations of the high-mass X-ray binary Cygnus X-1 have shown that both the companion star (41 solar masses) and the black hole (21 solar masses) are more massive than previously estimated. Furthermore, the black hole appears to be nearly maximally spinning. Here, we present a possible formation channel for the Cygnus X-1 system that matches the observed system properties. In this formation channel, we find that the orbital parameters of Cygnus X-1, combined with the observed metallicity of the companion, imply a significant reduction in mass loss through winds relative to commonly used prescriptions for stripped stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We establish that there are two velocity systems along lines of sight that contribute to the emission-line spectrum of the brightest parts of the Orion Nebula. These overlie the Orion-S embedded molecular cloud southwest of the dominant ionizing star (<jats:italic>θ</jats:italic> <jats:sup>1</jats:sup> Ori C). Examination of 10 × 10″ samples of high spectral resolution emission-line spectra of this region reveals it to be of low ionization, with velocities and ionization different from the central part of the nebula. These properties jeopardize earlier determinations of abundance and physical conditions since they indicate that this region is much more complex than has been assumed in analyzing earlier spectroscopic studies and argue for use of very high spectral resolution or known simple regions in future studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a spectroscopic analysis of 7774 Å O <jats:sc>i</jats:sc> triplet abundances, 8498–8662 Å Ca <jats:sc>ii</jats:sc> triplet chromospheric activity, and rotation in the Pleiades open cluster, with the objective of thoroughly examining the O triplet overabundance trends observed in cool open cluster dwarfs, and to thereby make clear the cause of that trend. High-dispersion, contemporaneous spectra of the O <jats:sc>i</jats:sc> triplet, Ca <jats:sc>ii</jats:sc> triplet, and H<jats:italic>α</jats:italic> spectral regions in 41 Pleiades dwarfs were acquired using Hydra on the WIYN 3.5 m telescope. Our Ca <jats:sc>ii</jats:sc> emission equivalent-width data exhibit a strong positive correlation with decreasing <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub>, with the rapidly rotating stars enhanced by up to 50% above the slowly rotating stars. Our triplet [O/H] values exhibit a statistically significant positive correlation with total Ca <jats:sc>ii</jats:sc> triplet emission, and similarly, significant correlations have been found by every study to date that used contemporaneous O triplet abundance and chromospheric activity data, which is strong evidence that chromospheric activity is the cause of the observed overabundance trends. Based on the slowly rotating, low Ca <jats:sc>ii</jats:sc> emission stars in the near-solar range 5450 K &lt; <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> &lt; 6100 K, we find a cluster mean [O/H] = + 0.143 ± 0.061, consistent with the substantial super-solar [O/H] values exhibited by most young ( &lt; 1 Gyr) open clusters. We also find a cluster mean [Fe/H] = + 0.029 ± 0.034, in excellent agreement with previous studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field survey, we investigate the role of the local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [N <jats:sc>ii</jats:sc>]<jats:italic>λ</jats:italic>6584 and H<jats:italic>α</jats:italic>, we measure gas-phase oxygen abundances of 167 galaxies at 1.37 ≤ <jats:italic>z</jats:italic> ≤ 1.7 and 303 galaxies at 2.09 ≤ <jats:italic>z</jats:italic> ≤ 2.61, located in diverse environments. We find that at <jats:italic>z</jats:italic> ∼ 1.5, the average metallicity of galaxies in overdensities with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ∼ 10<jats:sup>9.8</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>, 10<jats:sup>10.2</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙,</jats:sub> and 10<jats:sup>10.8</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> is higher relative to their field counterparts by 0.094 ± 0.051, 0.068 ± 0.028, and 0.052 ± 0.043 dex, respectively. However, this metallicity enhancement does not exist at higher redshift, <jats:italic>z</jats:italic> ∼ 2.3, where, compared to the field galaxies, we find 0.056 ± 0.043, 0.056 ± 0.028, and 0.096 ± 0.034 dex lower metallicity for galaxies in overdense environments with <jats:italic>M</jats:italic> <jats:sub>*</jats:sub> ∼ 10<jats:sup>9.8</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub>, 10<jats:sup>10.2</jats:sup> <jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> and 10<jats:sup>10.7 </jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, respectively. Our results suggest that, at 1.37 ≤ <jats:italic>z</jats:italic> ≤ 2.61, the variation of mass–metallicity relation with local environment is small (&lt;0.1 dex), and reverses at <jats:italic>z</jats:italic> ∼ 2. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the universe evolves to lower redshifts (<jats:italic>z</jats:italic> ≲ 2), the shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Clusters, Clumps, Dust, and Gas in Extreme Star-forming Galaxies (CCDG) survey with the Hubble Space Telescope includes multiwavelength imaging of 13 galaxies less than 100 Mpc away, spanning a range of morphologies and sizes, from blue compact dwarfs to luminous infrared galaxies, all with star formation rates in excess of hundreds of solar masses per year. Images of seven merging galaxies in the CCDG survey were artificially redshifted to compare with galaxies at <jats:italic>z</jats:italic> = 0.5, 1, and 2. Most redshifted tails have surface brightnesses that would be visible at <jats:italic>z</jats:italic> = 0.5 or 1 but not at <jats:italic>z</jats:italic> = 2 due to cosmological dimming. Giant star clumps are apparent in these galaxies; the 51 measured have similar sizes, masses, and colors to clumps in observed high-<jats:italic>z</jats:italic> systems in the UDF, GEMS, GOODS, and CANDELS surveys. These results suggest that some clumpy high-<jats:italic>z</jats:italic> galaxies without observable tidal features could be the result of mergers. The local clumps also have the same star formation rate per unit area and stellar surface density as clumps observed at intermediate and high redshift, so they provide insight into the substructure of distant clumps. A total of 1596 star clusters brighter than <jats:italic>M</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> = −9 were identified within the boundaries of the local clumps. The cluster magnitude distribution function is a power law with approximately the same slope (∼−1 for a plot of number versus log luminosity) for all the galaxies both inside and outside the clumps and independently of clump surface brightness.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of a 10 comoving megaparsec (cMpc)-scale structure traced by massive submillimeter galaxies (SMGs) at <jats:italic>z</jats:italic> ∼ 4.6. These galaxies are selected from an emission line search of ALMA Band 7 observations targeting 184 luminous submillimeter sources (<jats:italic>S</jats:italic> <jats:sub>850<jats:italic>μ</jats:italic>m</jats:sub> ≥ 6.2 mJy) across 1.6 degrees<jats:sup>2</jats:sup> in the COSMOS field. We identify four [C <jats:sc>ii</jats:sc>] emitting SMGs and two probable [C <jats:sc>ii</jats:sc>] emitting SMG candidates at <jats:italic>z</jats:italic> = 4.60–4.64 with velocity-integrated signal-to-noise ratio of S/N &gt; 8. Four of the six emitters are near-infrared blank SMGs. After excluding one SMG whose emission line is falling at the edge of the spectral window, all galaxies show clear velocity gradients along the major axes that are consistent with rotating gas disks. The estimated rotation velocities of the disks are 330–550 km s<jats:sup>−1</jats:sup> and the inferred host dark-matter halo masses are ∼2–8 × 10<jats:sup>12</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. From their estimated halo masses and [C <jats:sc>ii</jats:sc>] luminosity function, we suggest that these galaxies have a high (50%–100%) duty cycle and high (∼0.1) baryon conversion efficiency (SFR relative to baryon accretion rate), and that they contribute ≃2% to the total star formation rate density at <jats:italic>z</jats:italic> = 4.6. These SMGs are concentrated within just 0.3% of the full survey volume, suggesting they are strongly clustered. The extent of this structure and the individual halo masses suggest that these SMGs will likely evolve into members of a ∼10<jats:sup>15</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> cluster at <jats:italic>z</jats:italic> = 0. This survey reveals a synchronized dusty starburst in massive halos at <jats:italic>z</jats:italic> &gt; 4, which could be driven by mergers or fed by smooth gas accretion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Motivated by the recent discovery of a compact object with mass in the range 2.5–2.67 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> in the binary merger GW190814, we revisit the question of the maximum mass of neutron stars (NSs). We use a Markov Chain Monte Carlo approach to generate about two million phenomenological equations of state with and without first-order phase transitions. We fix the crust equation of state and only assume causality at higher densities. We show how a strict upper bound on the maximum NS mass can be inferred from upcoming observation of NS radii and masses. The derived upper bounds depend only on relativity and causality, so it is not affected by nuclear physics uncertainties. We show how a lower limit on the maximum mass of NSs, in combination with upcoming measurements of NS radii by LIGO/Virgo and NICER, would constrain the equation of state of dense matter. Finally, we discuss the implications for GW190814.</jats:p>