Table of contents

Dedicated searches generally find a decreasing fraction of obscured active galactic nuclei (AGN) with increasing AGN luminosity. This has often been interpreted as evidence for a decrease of the covering factor of the AGN torus with increasing luminosity, the so-called receding torus models. Using a complete flux-limited X-ray selected sample of 199 AGN, from the Bright Ultra-hard XMM-Newton Survey, we determine the intrinsic fraction of optical type-2 AGN at $0.05\leqslant z\leqslant 1$ as a function of rest-frame 2–10 keV X-ray luminosity from ${10}^{42}$ to ${10}^{45}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$. We use the distributions of covering factors of AGN tori derived from CLUMPY torus models. Since these distributions combined over the total AGN population need to match the intrinsic type-2 AGN fraction, we reveal a population of X-ray undetected objects with high-covering factor tori, which are increasingly numerous at higher AGN luminosities. When these "missing" objects are included, we find that Compton-thick AGN account at most for ${37}_{-10}^{+9}$% of the total population. The intrinsic type-2 AGN fraction is 58 ± 4% and has a weak, non-significant (less than 2σ) luminosity dependence. This contradicts the results generally reported by AGN surveys and the expectations from receding torus models. Our findings imply that the majority of luminous rapidly accreting supermassive black holes at $z\leqslant 1$ reside in highly obscured nuclear environments, but most of them are so deeply embedded that they have so far escaped detection in X-rays in <10 keV wide area surveys.

The Wide-field Infrared Survey Explorer (WISE) is a powerful tool for finding nearby brown dwarfs and searching for new planets in the outer solar system, especially with the incorporation of NEOWISE and NEOWISE-Reactivation data. However, so far, searches for brown dwarfs in WISE data have yet to take advantage of the full depth of the WISE images. To efficiently search this unexplored space via visual inspection, we have launched a new citizen science project, called "Backyard Worlds: Planet 9," which asks volunteers to examine short animations composed of difference images constructed from time-resolved WISE coadds. We report the first new substellar object discovered by this project, WISEA J110125.95+540052.8, a T5.5 brown dwarf located approximately 34 pc from the Sun with a total proper motion of ∼07$\,{\mathrm{yr}}^{-1}$. WISEA J110125.95+540052.8 has a WISE W2 magnitude of $W2=15.37\pm 0.09;$ our sensitivity to this source demonstrates the ability of citizen scientists to identify moving objects via visual inspection that are 0.9 mag fainter than the W2 single-exposure sensitivity, a threshold that has limited prior motion-based brown dwarf searches with WISE.

We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic image obtained by ALMA that includes a large sunspot within the active region AR12470, on 2015 December 16. The 3 mm map has a 300'' × 300'' field of view and 49 × 22 spatial resolution, which is the highest spatial resolution map of an entire sunspot in this frequency range. We find a gradient of 3 mm brightness from a high value in the outer penumbra to a low value in the inner penumbra/outer umbra. Within the inner umbra, there is a marked increase in 3 mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightness in the 1330 and 1400 Å slit-jaw images of the Interface Region Imaging Spectrograph (IRIS), adjacent to a partial lightbridge. This λ = 3 mm brightness enhancement may be an intrinsic feature of the sunspot umbra at chromospheric heights, such as a manifestation of umbral flashes, or it could be related to a coronal plume, since the brightness enhancement was coincident with the footpoint of a coronal loop observed at 171 Å.

We report a survey of molecular gas in galaxies in the XMMXCS J2215.9–1738 cluster at z = 1.46. We have detected emission lines from 17 galaxies within a radius of R₂₀₀ from the cluster center, in Band 3 data of the Atacama Large Millimeter/submillimeter Array, with a coverage of 93–95 GHz in frequency and 2.33 arcmin² in spatial direction. The lines are all identified as CO J = 2–1 emission lines from cluster members at $z\sim 1.46$ by their redshifts and the colors of their optical and near-infrared (NIR) counterparts. The line luminosities reach down to ${L}_{\mathrm{CO}(2\mbox{--}1)}^{\prime }=4.5\times {10}^{9}$ K km s⁻¹ pc². The spatial distribution of galaxies with a detection of CO(2–1) suggests that they disappear from the very center of the cluster. The phase-space diagram showing relative velocity versus cluster-centric distance indicates that the gas-rich galaxies have entered the cluster more recently than the gas-poor star-forming galaxies and passive galaxies located in the virialized region of this cluster. The results imply that the galaxies experienced ram-pressure stripping and/or strangulation during the course of infall toward the cluster center and then the molecular gas in the galaxies at the cluster center was depleted by star formation.

We investigate the environmental quenching of galaxies, especially those with stellar masses (M_*) < 10^9.5M_⊙, beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test whether or not such a dwarf QG-massive central galaxy connection exists beyond the local universe. For this purpose, we only need a statistically representative, rather than complete, sample of low-mass galaxies, which enables our study to z ≳ 1.5. For each low-mass galaxy, we measure the projected distance (d_proj) to its nearest massive neighbor (M_* > 10^10.5M_⊙) within a redshift range. At a given z and M_*, the environmental quenching effect is considered to be observed if the d_proj distribution of QGs (${d}_{\mathrm{proj}}^{Q}$) is significantly skewed toward lower values than that of star-forming galaxies (${d}_{\mathrm{proj}}^{\mathrm{SF}}$). For galaxies with 10⁸M_⊙ < M_* < 10¹⁰M_⊙, such a difference between ${d}_{\mathrm{proj}}^{Q}$ and ${d}_{\mathrm{proj}}^{\mathrm{SF}}$ is detected up to z ∼ 1. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii (R_Vir) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, ${d}_{\mathrm{proj}}^{Q}/{R}_{\mathrm{Vir}}$, decreases with satellite M_* at M_* ≲ 10^9.5M_⊙, but increases with satellite M_* at M_* ≳ 10^9.5M_⊙. This trend suggests a smooth, if any, transition of the quenching timescale around M_* ∼ 10^9.5M_⊙ at 0.5 < z < 1.0.

We report the discovery of tidal tails around the Galactic globular cluster NGC 7492, based on the Data Release 1 of the Pan-STARRS1 survey. The tails were detected using a version of the matched filter technique applied to the (g − r, r) and (g − i, i) color–magnitude diagrams. Tidal tails emerging from the cluster extend at least ∼35 in the north–east to south–east direction, equivalent to ∼1.5 kpc in projected length.

The search for habitable exoplanets and life beyond the solar system is one of the most compelling scientific opportunities of our time. Nevertheless, the high cost of building facilities that can address this topic and the keen public interest in the results of such research requires rigorous development of experiments that can deliver a definitive advancement in our understanding. Most work to date in this area has focused on a "systems science" approach of obtaining and interpreting comprehensive data for individual planets to make statements about their habitability and the possibility that they harbor life. This strategy is challenging because of the diversity of exoplanets, both observed and expected, and the limited information that can be obtained with astronomical instruments. Here, we propose a complementary approach that is based on performing surveys of key planetary characteristics and using statistical marginalization to answer broader questions than can be addressed with a small sample of objects. The fundamental principle of this comparative planetology approach is maximizing what can be learned from each type of measurement by applying it widely rather than requiring that multiple kinds of observations be brought to bear on a single object. As a proof of concept, we outline a survey of terrestrial exoplanet atmospheric water and carbon dioxide abundances that would test the habitable zone hypothesis and lead to a deeper understanding of the frequency of habitable planets. We also discuss ideas for additional surveys that could be developed to test other foundational hypotheses in this area.

We present spatially resolved ALMA observations of the CO $J=3-2$ emission line in two massive galaxies at z = 2.5 on the star-forming main sequence. Both galaxies have compact dusty star-forming cores with effective radii of ${R}_{{\rm{e}}}=1.3\pm 0.1\,\mathrm{kpc}$ and ${R}_{{\rm{e}}}=1.2\pm 0.1\,\mathrm{kpc}$ in the 870 μm continuum emission. The spatial extent of star-forming molecular gas is also compact with ${R}_{{\rm{e}}}=1.9\pm 0.4\,\mathrm{kpc}$ and ${R}_{{\rm{e}}}=2.3\pm 0.4\,\mathrm{kpc}$, but more extended than the dust emission. Interpreting the observed position–velocity diagrams with dynamical models, we find the starburst cores to be rotation dominated with the ratio of the maximum rotation velocity to the local velocity dispersion of ${v}_{\max }/{\sigma }_{0}={7.0}_{-2.8}^{+2.5}$ (${v}_{\max }={386}_{-32}^{+36}$ km s⁻¹) and ${v}_{\max }/{\sigma }_{0}={4.1}_{-1.5}^{+1.7}$ (${v}_{\max }={391}_{-41}^{+54}$ km s⁻¹). Given that the descendants of these massive galaxies in the local universe are likely ellipticals with $v/\sigma$ nearly an order of magnitude lower, the rapidly rotating galaxies would lose significant net angular momentum in the intervening time. The comparisons among dynamical, stellar, gas, and dust mass suggest that the starburst CO-to-H₂ conversion factor of ${\alpha }_{\mathrm{CO}}=0.8\,{M}_{\odot }$ (K km s⁻¹ pc⁻²)⁻¹ is appropriate in the spatially resolved cores. The dense cores are likely to be formed in extreme environments similar to the central regions of local ultraluminous infrared galaxies. Our work also demonstrates that a combination of medium-resolution CO and high-resolution dust continuum observations is a powerful tool for characterizing the dynamical state of molecular gas in distant galaxies.

Hot Jupiters have proven themselves to be a rich class of exoplanets that test our theories of planetary evolution and atmospheric dynamics under extreme conditions. Here, we present three-dimensional magnetohydrodynamic simulations and analytic results that demonstrate that a dynamo can be maintained in the thin, stably stratified atmosphere of a hot Jupiter, independent of the presumed deep-seated dynamo. This dynamo is maintained by conductivity variations arising from strong asymmetric heating from the planets' host star. The presence of a dynamo significantly increases the surface magnetic field strength and alters the overall planetary magnetic field geometry, possibly affecting star–planet magnetic interactions.

Recent work suggests that strong emission line, star-forming galaxies (SFGs) may be significant Lyman continuum leakers. We combine archival Hubble Space Telescope broadband ultraviolet and optical imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman continuum (LyC) emission from homogeneously selected z ∼ 2.5 SFGs. We detect no escaping Lyman continuum from SFGs selected on [O ii] nebular emission (N = 208) and, within a narrow redshift range, on [O iii]/[O ii]. We measure 1σ upper limits to the LyC escape fraction relative to the non-ionizing UV continuum from [O ii] emitters, f_esc ≲ 5.6%, and strong [O iii]/[O ii] > 5 ELGs, f_esc ≲ 14.0%. Our observations are not deep enough to detect f_esc ∼ 10% typical of low-redshift Lyman continuum emitters. However, we find that this population represents a small fraction of the star-forming galaxy population at z ∼ 2. Thus, unless the number of extreme emission line galaxies grows substantially to z ≳ 6, such galaxies may be insufficient for reionization. Deeper survey data in the rest-frame ionizing UV will be necessary to determine whether strong line ratios could be useful for pre-selecting LyC leakers at high redshift.

Recent detailed observations of the radio-loud quasar 3C 186 indicate the possibility that a supermassive recoiling black hole is moving away from the host galaxy at a speed of nearly 2100 km s⁻¹. If this is the case, we can model the mass ratio and spins of the progenitor binary black hole using the results of numerical relativity simulations. We find that the black holes in the progenitor must have comparable masses with a mass ratio $q={m}_{1}/{m}_{2}\gt 1/4$ and the spin of the primary black hole must be ${\alpha }_{2}={S}_{2}/{m}_{2}^{2}\gt 0.5$. The final remnant of the merger is bounded by ${\alpha }_{f}\gt 0.5$, and at least 4% of the total mass of the binary system is radiated into gravitational waves. We consider four different pre-merger scenarios that further narrow those values. Assuming, for instance, a cold accretion driven merger model, we find that the binary had comparable masses with $q={0.58}_{-0.19}^{+0.39}$ and the normalized spins of the larger and smaller black holes were ${\alpha }_{1}={0.93}_{-0.31}^{+0.05}$ and ${\alpha }_{2}={0.93}_{-0.10}^{+0.06}$. We can also estimate the final recoiling black hole spin ${\alpha }_{f}={0.91}_{-0.05}^{+0.02}$ and that the system radiated ${8.6}_{-1.8}^{+1.0} \%$ of its total mass, making the merger of those black holes the most energetic event ever observed.

In this Letter, we report a significant recovery of the linear baryonic acoustic oscillation (BAO) signature by applying the isobaric reconstruction algorithm to the nonlinear matter density field. Assuming only the longitudinal component of the displacement being cosmologically relevant, this algorithm iteratively solves the coordinate transform between the Lagrangian and Eulerian frames without requiring any specific knowledge of the dynamics. For dark matter field, it produces the nonlinear displacement potential with very high fidelity. The reconstruction error at the pixel level is within a few percent and is caused only by the emergence of the transverse component after the shell-crossing. As it circumvents the strongest nonlinearity of the density evolution, the reconstructed field is well described by linear theory and immune from the bulk-flow smearing of the BAO signature. Therefore, this algorithm could significantly improve the measurement accuracy of the sound horizon scale s. For a perfect large-scale structure survey at redshift zero without Poisson or instrumental noise, the fractional error ${\rm{\Delta }}s/s$ is reduced by a factor of ∼2.7, very close to the ideal limit with the linear power spectrum and Gaussian covariance matrix.

The fast radio bursts (FRBs) 110220 and 140514 were detected at telescope pointing locations within 9 arcmin of each other over three years apart, both within the same 14.4 arcmin beam of the Parkes radio telescope. Nevertheless, they generally have not been considered to be from the same source because of a vastly different dispersion measure (DM) for the two bursts by over $380\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$. Here, we consider the hypothesis that these two FRBs are from the same neutron star embedded within a supernova remnant (SNR) that provides an evolving DM as the ejecta expands and becomes more diffuse. Using such a model and the observed DM change, it can be argued that the corresponding SN must have occurred within $\approx 10.2$ years of FRB 110220. Furthermore, constraints can be placed on the SN ejecta mass and explosion energy, which appear to require a stripped-envelope (Type Ib/c) SN and/or a very energetic explosion. A third FRB from this location would be even more constraining, allowing the component of the DM due to the SNR to be separated from the unchanging DM components due to the host galaxy and intergalactic medium. In the future, if more FRBs are found to repeat, the sort of arguments presented here can be used to test the young neutron star progenitor hypothesis for FRBs.

CO is an important component in many ${{\rm{N}}}_{2}/{\mathrm{CH}}_{4}$ atmospheres, including Titan, Triton, and Pluto, and has also been detected in the atmosphere of a number of exoplanets. Numerous experimental simulations have been carried out in the laboratory to understand the chemistry in ${{\rm{N}}}_{2}/{\mathrm{CH}}_{4}$ atmospheres, but very few simulations have included CO in the initial gas mixtures. The effect of CO on the chemistry occurring in these atmospheres is still poorly understood. We have investigated the effect of CO on both gas and solid phase chemistry in a series of planetary atmosphere simulation experiments using gas mixtures of CO, ${\mathrm{CH}}_{4}$, and ${{\rm{N}}}_{2}$ with a range of CO mixing ratios from 0.05% to 5% at low temperature (∼100 K). We find that CO affects the gas phase chemistry, the density, and the composition of the solids. Specifically, with the increase of CO in the initial gases, there is less ${{\rm{H}}}_{2}$ but more ${{\rm{H}}}_{2}{\rm{O}}$, HCN, ${{\rm{C}}}_{2}{{\rm{H}}}_{5}{\rm{N}}/\mathrm{HCNO}$, and ${\mathrm{CO}}_{2}$ produced in the gas phase, while the density, oxygen content, and degree of unsaturation of the solids increase. The results indicate that CO has an important impact on the chemistry occurring in our experiments and accordingly in planetary atmospheres.