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The process leading to the formation of the terrestrial planet remains elusive. In a previous publication, we have shown that, if the first generation of planetesimals forms in a ring at about 1 AU and the gas disk's density peaks at the ring location, planetary embryos of a few martian masses can grow and remain in the ring. In this work, we extend our simulations beyond the gas-disk stage, covering 200 Myr and accounting for the phase of giant planet instability, assumed to happen at different times. About half of the simulations form a pair of Venus and Earth analogues and, independently, about 10% form a Mars analogue. We find that the timing of the giant planet instability affects statistically the terrestrial system's excitation state and the timing of the last giant impacts. Hence a late instability (about 60 to 100 Myr after the Solar system's birth) is more consistent with a late Moon-formation time, as suggested by radioactive chronometers. However, the late veneer mass (LVM: mass accreted after the last giant impact) of Earth-sized planets suffering a giant impact after 80 My is usually an order of magnitude lower than the value inferred from geochemistry. In addition, the final angular momentum deficit (AMD) of the terrestrial planets tends to be too high. We tested the effect on the final AMD of the generation of debris during collisions and found that it is too small to change these conclusions. We argue that the best-case scenario is that the Moon-forming event occurred between 50 and 80 My, possibly just following the giant planet instability., Comment: Accepted for publication in Icarus

Chirality is a ubiquitous phenomenon in which a symmetry between left- and right-handed objects is broken, examples in nature ranging from subatomic particles and molecules to living organisms. In particle physics, the weak force is responsible for the symmetry breaking and parity violation in beta decay, but in condensed matter systems interactions that lead to chirality remain poorly understood. Here, we unravel the mechanism of chiral charge density wave formation in the transition-metal dichalcogenide 1T-TiSe2. Using representation analysis, we show that charge density modulations and ionic displacements, which transform as a continuous scalar field and a vector field on a discrete lattice, respectively, follow different irreducible representations of the space group, despite the fact that they propagate with the same wave-vectors and are strongly coupled to each other. This charge-lattice symmetry frustration is resolved by further breaking of all symmetries not common to both sectors through induced lattice distortions, thus leading to chirality. Our theory is verified using Raman spectroscopy and inelastic x-ray scattering, which reveal that all but translation symmetries are broken at a level not resolved by state-of-the-art diffraction techniques., Comment: 10 pages, 3 figures, 1 table

Compilation of papers presented by the VERITAS Collaboration at the 38th International Cosmic Ray Conference (ICRC), held July 26 through August 3, 2023 in Nagoya, Japan., Comment: html page. ICRC 2023, Nagoya, Japan

G106.3$+$2.7, commonly considered a composite supernova remnant (SNR), is characterized by a boomerang-shaped pulsar wind nebula (PWN) and two distinct ("head" & "tail") regions in the radio band. A discovery of very-high-energy (VHE) gamma-ray emission ($E_\gamma > 100$ GeV) followed by the recent detection of ultra-high-energy (UHE) gamma-ray emission ($E_\gamma > 100$ TeV) from the tail region suggests that G106.3$+$2.7 is a PeVatron candidate. We present a comprehensive multi-wavelength study of the Boomerang PWN (100" around PSR J2229+6114) using archival radio and Chandra data obtained from two decades ago, a new NuSTAR X-ray observation from 2020, and upper limits on gamma-ray fluxes obtained by Fermi and VERITAS observatories. The NuSTAR observation allowed us to detect a 51.67 ms spin period from the pulsar PSR J2229+6114 and the PWN emission characterized by a power-law model with $\Gamma = 1.52\pm0.06$ up to 20 keV. Contrary to the previous radio study by Kothes et al. 2006, we prefer a much lower PWN B-field ($B\sim3$ $\mu$G) and larger distance ($d \sim 8$ kpc) based on (1) the non-varying X-ray flux over the last two decades, (2) the energy-dependent X-ray PWN size resulting from synchrotron burn-off and (3) the multi-wavelength spectral energy distribution (SED) data. Our SED model suggests that the PWN is currently re-expanding after being compressed by the SNR reverse shock $\sim 1000$ years ago. In this case, the head region should be formed by GeV--TeV electrons injected earlier by the pulsar propagating into the low density environment.

Spin nematic (SN) is a magnetic analog of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid. Particularly intriguing is a valence-bond SN, in which spins are quantum entangled to form a multi-polar order without breaking time-reversal symmetry, but its unambiguous experimental realization remains elusive. Here, we establish a SN phase in the square-lattice iridate Sr$_2$IrO$_4$, which approximately realizes a pseudospin one-half Heisenberg antiferromagnet (AF) in the strong spin-orbit coupling limit. Upon cooling, the transition into the SN phase at T$_C$ $\approx$ 263 K is marked by a divergence in the static spin quadrupole susceptibility extracted from our Raman spectra, and concomitant emergence of a collective mode associated with the spontaneous breaking of rotational symmetries. The quadrupolar order persists in the antiferromagnetic (AF) phase below T$_N$ $\approx$ 230 K, and becomes directly observable through its interference with the AF order in resonant x-ray diffraction, which allows us to uniquely determine its spatial structure. Further, we find using resonant inelastic x-ray scattering a complete breakdown of coherent magnon excitations at short-wavelength scales, suggesting a resonating-valence-bond-like quantum entanglement in the AF state. Taken together, our results reveal a quantum order underlying the N\'eel AF that is widely believed to be intimately connected to the mechanism of high temperature superconductivity (HTSC)., Comment: Published in https://www.nature.com/articles/s41586-023-06829-4

We report on multiwavelength target-of-opportunity observations of the blazar PKS 0735+178, located 2.2$^\circ$ away from the best-fit position of the IceCube neutrino event IceCube-211208A detected on December 8, 2021. The source was in a high-flux state in the optical, ultraviolet, X-ray, and GeV gamma-ray bands around the time of the neutrino event, exhibiting daily variability in the soft X-ray flux. The X-ray data from Swift-XRT and NuSTAR characterize the transition between the low-energy and high-energy components of the broadband spectral energy distribution (SED), and the gamma-ray data from Fermi -LAT, VERITAS, and H.E.S.S. require a spectral cut-off near 100 GeV. Both X-ray and gamma-ray measurements provide strong constraints on the leptonic and hadronic models. We analytically explore a synchrotron self-Compton model, an external Compton model, and a lepto-hadronic model. Models that are entirely based on internal photon fields face serious difficulties in matching the observed SED. The existence of an external photon field in the source would instead explain the observed gamma-ray spectral cut-off in both leptonic and lepto-hadronic models and allow a proton jet power that marginally agrees with the Eddington limit in the lepto-hadronic model. We show a numerical lepto-hadronic model with external target photons that reproduces the observed SED and is reasonably consistent with the neutrino event despite requiring a high jet power., Comment: 21 pages, 3 figures, accepted by ApJ

It has been long proposed that, if all the terrestrial planets form within a tiny ring of solid material at around 1 AU, the concentrated mass-distance distribution of the current system can be reproduced. Recent planetesimal formation models also support this idea. In this study, we revisit the ring model by performing a number of high-resolution N-body simulations for 10 Myr of a ring of self-interacting planetesimals, with various radial distributions of the gas disc. We found that even if all the planetesimals form at ~1 AU in a minimum mass solar nebula-like disc, the system tends to spread radially as accretion proceeds, resulting in a system of planetary embryos lacking mass-concentration at ~1 AU. Modifying the surface density of the gas disc into a concave shape with a peak at ~1 AU helps to maintain mass concentrated at ~1 AU and solve the radial dispersion problem. We further propose that such a disc should be short lived (<= 1 Myr) and with a shallower radial gradient in the innermost region (< 1 AU) than previously proposed to prevent a too-rapid growth of Earth. Future studies should extend to ~100 Myr the most promising simulations and address in a self-consistent manner the evolution of the asteroid belt and its role in the formation of the terrestrial planets., Comment: Accepted by Icarus

Iridates have attracted much interest in the last decade for their novel magnetism emerging in the limit of strong spin-orbit coupling and possible unconventional superconductivity. A standard for growing iridate single crystals has been the flux method using platinum crucibles. Here, we show that this widely used method compromises the sample quality by inclusion of platinum impurities. We find that Sr2IrO4 single crystals grown in iridium crucibles show remarkable differences from those grown in platinum crucibles in their sample characterizations using Raman spectroscopy, resistivity, magnetization, optical third harmonic generation, resonant X-ray diffraction, and resonant inelastic X-ray scattering measurements. In particular, we show that several peaks of sizable intensities disappear in the Raman spectra of samples free of platinum impurities, and a significantly larger activation energy is extracted from the resistivity data compared to previously reported values. Furthermore, we find no evidence of the previously reported glide symmetry breaking structural distortions and confirm the I41/acd space group of the lattice symmetry. Although the platinum impurities are not apparent in the magnetic properties and thus went unnoticed in the stoichiometric insulating phase for a long time, their effects can be much more detrimental to transport properties in chemically doped compounds. Therefore, our result suggests using growth methods that avoid platinum impurities for an investigation of intrinsic physical properties of iridates, and possible superconducting phases., Comment: to be published in Physical Review Materials

We present the multi-wavelength counterparts of 850-$\mu$m selected submillimetre sources over a 2-deg$^2$ field centred on the North Ecliptic Pole. In order to overcome the large beam size (15 arcsec) of the 850-$\mu$m images, deep optical to near-infrared (NIR) photometric data and arcsecond-resolution 20-cm images are used to identify counterparts of submillimetre sources. Among 647 sources, we identify 514 reliable counterparts for 449 sources (69 per cent in number), based either on probabilities of chance associations calculated from positional offsets or offsets combined with the optical-to-NIR colours. In the radio imaging, the fraction of 850-$\mu$m sources having multiple counterparts is 7 per cent. The photometric redshift, infrared luminosity, stellar mass, star-formation rate (SFR), and the AGN contribution to the total infrared luminosity of the identified counterparts are investigated through spectral energy distribution fitting. The SMGs are infrared-luminous galaxies at an average $\langle z\rangle=2.5$ with $\mathrm{log}_{10} (L_\mathrm{IR}/\mathrm{L}_\odot)=11.5-13.5$, with a mean stellar mass of $\mathrm{log}_{10} (M_\mathrm{star}/\mathrm{M}_\odot)=10.90$ and SFR of $\mathrm{log}_{10} (\mathrm{SFR/M_\odot\,yr^{-1}})=2.34$. The SMGs show twice as large SFR as galaxies on the star-forming main sequence, and about 40 per cent of the SMGs are classified as objects with bursty star formation. At $z\ge4$, the contribution of AGN luminosity to total luminosity for most SMGs is larger than 30 per cent. The FIR-to-radio correlation coefficient of SMGs is consistent with that of main-sequence galaxies at $z\simeq2$., Comment: 24 pages, 16 figures. Accepted for publication in MNRAS

The stellar surface density within the inner 1 kpc ($\Sigma_{1}$) has become a popular tool for understanding the growth of galaxies and its connection with the quenching of star formation. The emerging picture suggests that building a central dense core is a necessary condition for quenching. However, it is not clear whether changes in $\Sigma_{1}$ trace changes in stellar kinematics and the growth of dispersion-dominated bulges. In this paper, we combine imaging from the Sloan Digital Sky Survey with stellar kinematics from the Sydney-AAO Multi-object Integral-field unit (SAMI) and Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) surveys to quantify the correlation between $\Sigma_{1}$ and the proxy for stellar spin parameter within one effective radius ($\lambda_{re}$) for 1599 nearby galaxies. We show that, on the star-forming main sequence and at fixed stellar mass, changes in $\Sigma_{1}$ are mirrored by changes in $\lambda_{re}$. While forming stars, main sequence galaxies remain rotationally-dominated systems, with their $\Sigma_{1}$ increasing but their stellar spin staying either constant or slightly increasing. The picture changes below the main sequence, where $\Sigma_{1}$ and $\lambda_{re}$ are no longer correlated. Passive systems show a narrower range of $\Sigma_{1}$, but a wider range of $\lambda_{re}$ compared to star-forming galaxies. Our results indicate that, from a structural point of view, passive galaxies are a more heterogeneous population than star-forming systems, and may have followed a variety of evolutionary paths. This also suggests that, if dispersion-dominated bulges still grow significantly at $z\sim$0, this generally takes place during, or after, the quenching phase., Comment: 12 pages, 7 figures, 1 table. MNRAS in press

Not only do the sampled terrestrial worlds (Earth, Mars, and asteroid 4 Vesta) differ in their mass-independent (nucleosynthetic) isotopic compositions of many elements (e.g. $\varepsilon^{48}$Ca, $\varepsilon^{50}$Ti, $\varepsilon^{54}$Cr, $\varepsilon^{92}$Mo), the magnitudes of some of these isotopic anomalies also appear to correlate with heliocentric distance. While the isotopic differences between the Earth and Mars may be readily accounted for by the accretion of mostly local materials in distinct regions of the protoplanetary disc, it is unclear whether this also applies to asteroid Vesta. Here we analysed the available data from our numerical simulation database to determine the formation location of Vesta in the framework of three planet-formation models: classical, Grand Tack, and Depleted Disc. We find that Vesta has a high probability of forming locally in the asteroid belt in models where material mixing in the inner disc is limited; this limited mixing is implied by the isotopic differences between the Earth and Mars. Based on our results, we propose several criteria to explain the apparent correlation between the different nucleosynthetic isotopic compositions of the Earth, Mars, and Vesta: (1) these planetary bodies accreted their building blocks in different regions of the disc, (2) the inner disc is characterised by an isotopic gradient, and (3) the isotopic gradient was preserved during the formation of these planetary bodies and was not diluted by material mixing in the disc (e.g. via giant planet migration).

Dark photons are hypothetical massive vector particles that could mix with ordinary photons. The simplest theoretical model is fully characterised by only two parameters: the mass of the dark photon m$_{\gamma^{\mathrm{D}}}$ and its mixing parameter with the photon, $\varepsilon$. The sensitivity of the SHiP detector is reviewed for dark photons in the mass range between 0.002 and 10 GeV. Different production mechanisms are simulated, with the dark photons decaying to pairs of visible fermions, including both leptons and quarks. Exclusion contours are presented and compared with those of past experiments. The SHiP detector is expected to have a unique sensitivity for m$_{\gamma^{\mathrm{D}}}$ ranging between 0.8 and 3.3$^{+0.2}_{-0.5}$ GeV, and $\varepsilon^2$ ranging between $10^{-11}$ and $10^{-17}$.

We present geometric and dynamical modeling of the broad line region for the multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The dataset includes photometric and spectroscopic monitoring in the optical and ultraviolet, covering the H$\beta$, C IV, and Ly$\alpha$ broad emission lines. We find an extended disk-like H$\beta$ BLR with a mixture of near-circular and outflowing gas trajectories, while the C IV and Ly$\alpha$ BLRs are much less extended and resemble shell-like structures. There is clear radial structure in the BLR, with C IV and Ly$\alpha$ emission arising at smaller radii than the H$\beta$ emission. Using the three lines, we make three independent black hole mass measurements, all of which are consistent. Combining these results gives a joint inference of $\log_{10}(M_{\rm BH}/M_\odot) = 7.64^{+0.21}_{-0.18}$. We examine the effect of using the $V$ band instead of the UV continuum light curve on the results and find a size difference that is consistent with the measured UV-optical time lag, but the other structural and kinematic parameters remain unchanged, suggesting that the $V$ band is a suitable proxy for the ionizing continuum when exploring the BLR structure and kinematics. Finally, we compare the H$\beta$ results to similar models of data obtained in 2008 when the AGN was at a lower luminosity state. We find that the size of the emitting region increased during this time period, but the geometry and black hole mass remain unchanged, which confirms that the BLR kinematics suitably gauge the gravitational field of the central black hole., Comment: 26 pages, 19 figures, 1 table, accepted for publication in ApJ

We report velocity-delay maps for prominent broad emission lines, Ly_alpha, CIV, HeII and H_beta, in the spectrum of NGC5548. The emission-line responses inhabit the interior of a virial envelope. The velocity-delay maps reveal stratified ionization structure. The HeII response inside 5-10 light-days has a broad single-peaked velocity profile. The Ly_alpha, CIV, and H_beta responses peak inside 10 light-days, extend outside 20 light-days, and exhibit a velocity profile with two peaks separated by 5000 km/s in the 10 to 20 light-day delay range. The velocity-delay maps show that the M-shaped lag vs velocity structure found in previous cross-correlation analysis is the signature of a Keplerian disk with a well-defined outer edge at R=20 light-days. The outer wings of the M arise from the virial envelope, and the U-shaped interior of the M is the lower half of an ellipse in the velocity-delay plane. The far-side response is weaker than that from the near side, so that we see clearly the lower half, but only faintly the upper half, of the velocity--delay ellipse. The delay tau=(R/c)(1-sin(i))=5 light-days at line center is from the near edge of the inclined ring, giving the inclination i=45 deg. A black hole mass of M=7x10^7 Msun is consistent with the velocity-delay structure. A barber-pole pattern with stripes moving from red to blue across the CIV and possibly Ly_alpha line profiles suggests the presence of azimuthal structure rotating around the far side of the broad-line region and may be the signature of precession or orbital motion of structures in the inner disk. Further HST observations of NGC 5548 over a multi-year timespan but with a cadence of perhaps 10 days rather than 1 day could help to clarify the nature of this new AGN phenomenon., Comment: 19 pages, 9 figures, ApJ in press

We propose to build and operate a detector that, for the first time, will measure the process $pp\to\nu X$ at the LHC and search for feebly interacting particles (FIPs) in an unexplored domain. The TI18 tunnel has been identified as a suitable site to perform these measurements due to very low machine-induced background. The detector will be off-axis with respect to the ATLAS interaction point (IP1) and, given the pseudo-rapidity range accessible, the corresponding neutrinos will mostly come from charm decays: the proposed experiment will thus make the first test of the heavy flavour production in a pseudo-rapidity range that is not accessible by the current LHC detectors. In order to efficiently reconstruct neutrino interactions and identify their flavour, the detector will combine in the target region nuclear emulsion technology with scintillating fibre tracking layers and it will adopt a muon identification system based on scintillating bars that will also play the role of a hadronic calorimeter. The time of flight measurement will be achieved thanks to a dedicated timing detector. The detector will be a small-scale prototype of the scattering and neutrino detector (SND) of the SHiP experiment: the operation of this detector will provide an important test of the neutrino reconstruction in a high occupancy environment., Comment: Letter of Intent

Many theories beyond the Standard Model postulate short-range modifications to gravity which produce deviations of Newton's gravitational potential from a strict $1/r$ dependence. It is common to analyze experiments searching for these modifications using a potential of the form $V^{\prime}(r)=-\frac{GMm}{r} [1+\alpha \exp{(-r/\lambda)}]$. The best present constraints on $\alpha$ for $\lambda <100$\,nm come from neutron scattering and often employ comparisons of different measurements of the coherent neutron scattering amplitudes $b$. We analyze the internal consistency of existing data from two different types of measurements of low energy neutron scattering amplitudes: neutron interferometry, which involves squared momentum transfers $q^{2}=0$, and neutron gravity reflectometry, which involves squared momentum transfers $q^{2}=8mV_{opt}$ where $m$ is the neutron mass and $V_{opt}$ is the neutron optical potential of the medium. We show that the fractional difference $\frac{\Delta b}{|b|}$ averaged over the 7 elements where high precision data exists on the same material from both measurement methods is $[2.2 \pm 1.4] \times 10^{-4}$. We also show that $\frac{\Delta b}{|b|}$ for this data is insensitive both to exotic Yukawa interactions and also to the electromagnetic neutron-atom interactions proportional to the neutron-electron scattering length $b_{ne}$ and the neutron polarizability scattering amplitude $b_{pol}$. This result will be useful in any future global analyses of neutron scattering data to determine $b_{ne}$ and bound $\alpha$ and $\lambda$. We also discuss how various neutron interferometric and scattering techniques with cold and ultracold neutrons can be used to improve the precision of $b$ measurements and make some specific proposals., Comment: 13 pages, 1 figure

The application of machine learning (ML) methods to the analysis of astrophysical datasets is on the rise, particularly as the computing power and complex algorithms become more powerful and accessible. As the field of ML enjoys a continuous stream of breakthroughs, its applications demonstrate the great potential of ML, ranging from achieving tens of millions of times increase in analysis speed (e.g., modeling of gravitational lenses or analysing spectroscopic surveys) to solutions of previously unsolved problems (e.g., foreground subtraction or efficient telescope operations). The number of astronomical publications that include ML has been steadily increasing since 2010. With the advent of extremely large datasets from a new generation of surveys in the 2020s, ML methods will become an indispensable tool in astrophysics. Canada is an unambiguous world leader in the development of the field of machine learning, attracting large investments and skilled researchers to its prestigious AI Research Institutions. This provides a unique opportunity for Canada to also be a world leader in the application of machine learning in the field of astrophysics, and foster the training of a new generation of highly skilled researchers., Comment: White paper E015 submitted to the Canadian Long Range Plan LRP2020

We model the ultraviolet spectra of the Seyfert 1 galaxy NGC~5548 obtained with the Hubble Space Telescope during the 6-month reverberation-mapping campaign in 2014. Our model of the emission from NGC 5548 corrects for overlying absorption and deblends the individual emission lines. Using the modeled spectra, we measure the response to continuum variations for the deblended and absorption-corrected individual broad emission lines, the velocity-dependent profiles of Ly$\alpha$ and C IV, and the narrow and broad intrinsic absorption features. We find that the time lags for the corrected emission lines are comparable to those for the original data. The velocity-binned lag profiles of Ly$\alpha$ and C IV have a double-peaked structure indicative of a truncated Keplerian disk. The narrow absorption lines show delayed response to continuum variations corresponding to recombination in gas with a density of $\sim 10^5~\rm cm^{-3}$. The high-ionization narrow absorption lines decorrelate from continuum variations during the same period as the broad emission lines. Analyzing the response of these absorption lines during this period shows that the ionizing flux is diminished in strength relative to the far-ultraviolet continuum. The broad absorption lines associated with the X-ray obscurer decrease in strength during this same time interval. The appearance of X-ray obscuration in $\sim\,2012$ corresponds with an increase in the luminosity of NGC 5548 following an extended low state. We suggest that the obscurer is a disk wind triggered by the brightening of NGC 5548 following the decrease in size of the broad-line region during the preceding low-luminosity state., Comment: 50 pages, 30 figures, uses aastex62.cls. Accepted for publication in ApJ, 07/06/2019. High-level products page in MAST will go live after 7/15/2019. Replaced Figure 4 on 7/12/2019 to be more red/green color-blind friendly

While the reverberation mapping technique is the best available method for measuring black hole mass in active galactic nuclei (AGN) beyond the local volume, this method has been mainly applied to relatively low-to-moderate luminosity AGNs at low redshift. We present the strategy of the Seoul National University AGN Monitoring Project, which aims at measuring the time delay of the \Hb\ line emission with respect to AGN continuum, using a sample of relatively high luminosity AGNs out to z $\sim$0.5. We present simulated cross correlation results based on a number of mock light curves, in order to optimally determine monitoring duration and cadence. We describe our campaign strategy based on the simulation results and the availability of observing facilities. We present the sample selection, and the properties of the selected 100 AGNs, including the optical luminosity, expected time lag, black hole mass, and Eddington ratio., Comment: 10 pages, 11 figures, JKAS in press

We present an unprecedented view on the morphology and kinematics of the extended narrow-line region (ENLR) and molecular gas around the prototypical hyper-luminous quasar 3C273 ($L\sim10^{47}$ erg/s at z=0.158) based on VLT-MUSE optical 3D spectroscopy and ALMA observations. We find that: 1) The ENLR size of 12.1$\pm$0.2kpc implies a smooth continuation of the size-luminosity relation out to large radii or a much larger break radius as previously proposed. 2) The kinematically disturbed ionized gas with line splits reaching 1000km/s out to 6.1$\pm$1.5kpc is aligned along the jet axis. 3) The extreme line broadening on kpc scales is caused by spatial and spectral blending of many distinct gas clouds separated on sub-arcsecond scales with different line-of-sight velocities. The ENLR velocity field combined with the known jet orientation rule out a simple scenario of a radiatively-driven radial expansion of the outflow. Instead we propose that a pressurized expanding hot gas cocoon created by the radio jet is impacting on an inclined gas disk leading to transverse and/or backflow motion with respect to our line-of-sight. The molecular gas morphology may either be explained by a density wave at the front of the outflow expanding along the jet direction as predicted by positive feedback scenario or the cold gas may be trapped in a stellar over-density caused by a recent merger event. Using 3C273 as a template for observations of high-redshift hyper-luminous AGN reveals that large-scale ENLRs and kpc scale outflows may often be missed due to the brightness of the nuclei and the limited sensitivity of current near-IR instrumentation., Comment: 15 pages, 6 figures, accepted for publication in ApJ

A search for the rare decay $K_L \!\to\! \pi^0 \nu \overline{\nu}$ was performed. With the data collected in 2015, corresponding to $2.2 \times 10^{19}$ protons on target, a single event sensitivity of $( 1.30 \pm 0.01_{\rm stat} \pm 0.14_{\rm syst} ) \times 10^{-9}$ was achieved and no candidate events were observed. We set an upper limit of $3.0 \times 10^{-9}$ for the branching fraction of $K_L \!\to\! \pi^0 \nu \overline{\nu}$ at the 90% confidence level (C.L.), which improved the previous limit by almost an order of magnitude. An upper limit for $K_L \!\to\! \pi^0 X^0$ was also set as $2.4 \times 10^{-9}$ at the 90% C.L., where $X^0$ is an invisible boson with a mass of $135~{\rm MeV}/c^2$., Comment: 6 pages, 4 figures; published version, no change in the results. Fig. 1, Fig. 2, and Fig. 3 were revised, and Fig. 4 presenting the $K_L \!\to\! \pi^0 X^0$ limit as a function of the $X^0$ mass was added

We present a structural and morphological catalogue for 45 million objects selected from the first year of data from the Dark Energy Survey (DES). Single Sersic fits and non-parametric measurements are produced for g, r and i filters. The parameters from the best-fitting Sersic model (total magnitude, half-light radius, Sersic index, axis ratio and position angle) are measured with Galfit; the non-parametric coefficients (concentration, asymmetry, clumpiness, Gini, M20) are provided using the Zurich Estimator of Structural Types (ZEST+). To study the statistical uncertainties, we consider a sample of state-of-the-art image simulations with a realistic distribution in the input parameter space and then process and analyse them as we do with real data: this enables us to quantify the observational biases due to PSF blurring and magnitude effects and correct the measurements as a function of magnitude, galaxy size, Sersic index (concentration for the analysis of the non-parametric measurements) and ellipticity. We present the largest structural catalogue to date: we find that accurate and complete measurements for all the structural parameters are typically obtained for galaxies with SExtractor MAG AUTO I < 21. Indeed, the parameters in the filters i and r can be overall well recovered up to MAG AUTO < 21.5, corresponding to a fitting completeness of ~90% below this threshold, for a total of 25 million galaxies. The combination of parametric and non-parametric structural measurements makes this catalogue an important instrument to explore and understand how galaxies form and evolve. The catalogue described in this paper will be publicly released alongside the Dark Energy Survey collaboration Y1 cosmology data products at the following URL: https://des.ncsa.illinois.edu/releases/y1a1/gold/morphology., Comment: Accepted for publication in MNRAS. 26 pages, 16 figures. Catalogue data are available at https://des.ncsa.illinois.edu/releases/y1a1/gold/morphology

The Seyfert 1 galaxy Arp 151 was monitored as part of three reverberation mapping campaigns spanning $2008-2015$. We present modeling of these velocity-resolved reverberation mapping datasets using a geometric and dynamical model for the broad line region (BLR). By modeling each of the three datasets independently, we infer the evolution of the BLR structure in Arp 151 over a total of seven years and constrain the systematic uncertainties in non-varying parameters such as the black hole mass. We find that the BLR geometry of a thick disk viewed close to face-on is stable over this time, although the size of the BLR grows by a factor of $\sim 2$. The dynamics of the BLR are dominated by inflow and the inferred black hole mass is consistent for the three datasets, despite the increase in BLR size. Combining the inference for the three datasets yields a black hole mass and statistical uncertainty of $\log_{10}($M$_{\rm BH}/\rm{M}_{\odot})=6.82^{+0.09}_{-0.09}$ with a standard deviation in individual measurements of 0.13 dex., Comment: 21 pages, 8 figures, 2 tables. Accepted for publication in ApJ

We report on H${\alpha}$ + [NII] imaging of the Arp 202 interacting pair and its tidal dwarf galaxy (TDG) candidate as well as a GMOS long slit spectrum from the TDG candidate, observed with the Gemini North telescope. Our H${\alpha}$ + [NII] imaging reveals the TDG to have an elongated structure, $\sim$ 1.9 kpc in length with the two principal star forming knots at either end. Our observations also show the TDG candidate has a recessional V$_{H\alpha}$ $\sim$ 3032 km s$^{-1}$, within 100 km s$^{-1}$ of the parent pair's mean velocity and an oxygen abundance of 12+log(O/H) = 8.10$\pm$0.41. The TDG's oxygen abundance is in good agreement with that of a star forming region in NGC 2719A, one of the parent galaxies, which has an estimated oxygen abundance of 12+log(O/H) = 8.05$\pm$0.41. The TDG's V$_{H\alpha}$ and oxygen abundance confirm previous results validating the candidate as a TDG. The absence of detectable emission from the TDG in $\textit{Spitzer}$ 3.6 $\mu$m and 4.5 $\mu$m images together with the lack of absorption lines and weak continuum in the spectrum is consistent with absence of an old population ($\gtrsim$ 0.5 Gyr). The location of the TDG within the interaction debris and the absence of indicators of an old stellar population in the TDG are consistent with a scenario in which the TDG is formed from HI stripped from the parent galaxies and within the extended dark matter halo of one of the parents as proposed by (Bournaud et al. 2003; Duc et al. 2004)., Comment: 13 pages, 6 figures

Water megamasers from circumnuclear disks in galaxy centers provide the most accurate measurements of supermassive black hole masses and uniquely probe the sub-parsec accretion processes. At the same time, these systems offer independent crucial constraints of the Hubble Constant in the nearby universe, and thus, the arguably best single constraint on the nature of dark energy. The chances of finding these golden standards are however abysmally low, at an overall =< 3% for any level of water maser emission detected at 22 GHz, and =< 1% for those exhibiting the disk-like configuration. We provide here a thorough summary of the current state of the detection of water megamaser disks, along with a novel investigation of the likelihood of increasing their detection rates based on a multivariate parameter analysis of optical and mid-infrared photometric properties of the largest database of galaxies surveyed for the 22 GHz emission. We find that galaxies with water megamaser emission tend to associate with strong emission in all WISE mid-infrared wavelengths, with the strongest enhancement in the W4 band, at 22 micron, as well as with previously proposed and newly found indicators of AGN strength in the mid-infrared, such as red W1-W2 and W1-W4 colors, and the integrated mid-infrared luminosity of the host galaxy. These trends offer a potential boost of the megamaser detection rates to 6 - 15%, or a factor of 2-8 relative to the current rates, depending on the chosen sample selection criteria, while fostering real chances for discovering >= 20 new megamaser disks., Comment: 23 pages, 3 tables, 10 figures. Accepted by ApJ

We present the variability and time lag measurements of PG 0934+013 based on a photometric and spectroscopic monitoring campaign over a two year period. We obtained 46 epochs of data from the spectroscopic campaign, which was carried out using the Southern African Large Telescope with $\sim$1 week cadence over two sets of 4 month-long observing period, while we obtained 80 epochs of \textit{B}-band imaging data using a few 1-m class telescopes. Due to the seven month gap between the two observing periods, we separately measured the time lags of broad emission lines including H$\beta$, by comparing the emission line light curve with the \textit{B}-band continuum light curve using the cross-correlation function techniques. We determined the H$\beta$ lag, $\tau_{\rm cent} = 8.46^{+2.08}_{-2.14}$ days in the observed-frame based on Year 2 data, while the time lag from Year 1 data was not reliably determined. Using the rms spectrum of Year 2 data, we measured the \Hb\ line dispersion \sigmaline = 668 $\pm$ 44 \kms\ after correcting for the spectral resolution. Adopting a virial factor f = 4.47 from Woo et al. 2015, we determined the black hole mass M$_{BH}$ = $3.13 ^{+0.91} _{-0.93} \times 10^{6}$ \msun based on the \Hb\ time lag and velocity., Comment: 13 pages, 10 figures, ApJ in press

During the Space Telescope and Optical Reverberation Mapping Project (STORM) observations of NGC 5548, the continuum and emission-line variability became de-correlated during the second half of the 6-month long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as a part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than being due to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all the three observations: the UV emission line flux decrease, the soft-excess increase, and the emission line anomaly., Comment: ApJ in press. Replaced with the accepted version

The SHiP experiment is designed to search for very weakly interacting particles beyond the Standard Model which are produced in a 400 GeV/c proton beam dump at the CERN SPS. An essential task for the experiment is to keep the Standard Model background level to less than 0.1 event after $2\times 10^{20}$ protons on target. In the beam dump, around $10^{11}$ muons will be produced per second. The muon rate in the spectrometer has to be reduced by at least four orders of magnitude to avoid muon-induced combinatorial background. A novel active muon shield is used to magnetically deflect the muons out of the acceptance of the spectrometer. This paper describes the basic principle of such a shield, its optimization and its performance., Comment: 8 pages, 5 figures; added clarifications to the penalty function and emphasized that we care about neutrino interactions in the air

We present the results of an optical spectroscopic monitoring program targeting NGC 5548 as part of a larger multi-wavelength reverberation mapping campaign. The campaign spanned six months and achieved an almost daily cadence with observations from five ground-based telescopes. The H$\beta$ and He II $\lambda$4686 broad emission-line light curves lag that of the 5100 $\AA$ optical continuum by $4.17^{+0.36}_{-0.36}$ days and $0.79^{+0.35}_{-0.34}$ days, respectively. The H$\beta$ lag relative to the 1158 $\AA$ ultraviolet continuum light curve measured by the Hubble Space Telescope is roughly $\sim$50% longer than that measured against the optical continuum, and the lag difference is consistent with the observed lag between the optical and ultraviolet continua. This suggests that the characteristic radius of the broad-line region is $\sim$50% larger than the value inferred from optical data alone. We also measured velocity-resolved emission-line lags for H$\beta$ and found a complex velocity-lag structure with shorter lags in the line wings, indicative of a broad-line region dominated by Keplerian motion. The responses of both the H$\beta$ and He II $\lambda$4686 emission lines to the driving continuum changed significantly halfway through the campaign, a phenomenon also observed for C IV, Ly $\alpha$, He II(+O III]), and Si IV(+O IV]) during the same monitoring period. Finally, given the optical luminosity of NGC 5548 during our campaign, the measured H$\beta$ lag is a factor of five shorter than the expected value implied by the $R_\mathrm{BLR} - L_\mathrm{AGN}$ relation based on the past behavior of NGC 5548., Comment: 22 pages, 13 figures, accepted to ApJ