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Constraining the X-ray reflection in low accretion-rate active galactic nuclei using XMM-Newton, NuSTAR, and Swift
No full textAn interesting feature of active galactic nuclei (AGN) accreting at low rates is the weakness of the reflection features in their X-ray spectra, which may result from the gradual disappearance of the torus with decreasing accretion rates. It has been suggested that low-luminosity AGN (LLAGN) would exhibit a different reflector configuration than high-luminosity AGN, covering a smaller fraction of the sky or simply having less material. Additionally, we note that the determination of the spectral index (Γ) and the cut-off energy of the primary power-law emission is affected by the inclusion of reflection models, showing their importance in studying accretion mechanisms. This is especially valid in the case of the LLAGN which has previously shown a high dispersion in the relation between Γ and the accretion rate.
Aims. Our purpose is to constrain the geometry and column density of the reflector in a sample of LLAGN covering a broad X-ray range of energy by combining data from XMM-Newton+ NuSTAR + Swift. The spectral analysis also allows us to investigate the accretion mechanism in LLAGN.
Methods. We used XMM-Newton+ NuSTAR + Swift observations of a hard X-ray flux-limited sample of 17 LLAGN from BASS/DR2 with accretion rates of λ_(Edd) = L_(Bol)/L_(Edd) < 10⁻³. We fit all spectra using the reflection model for torus (BORUS) and accretion disk (XILLVER) reflectors.
Results. We found a tentative correlation between the torus column density and the accretion rate, with LLAGN showing a lower column density than the high-luminosity objects. We also confirm the relation between Γ and λ_(Edd), with a smaller scatter than previously reported, thanks to the inclusion of high-energy data and the reflection models. Our results are consistent with a break at λ_(Edd) ∼ 10⁻³, which is suggestive of a different accretion mechanism compared with higher accretion AGN
Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations
No full textLyman-break galaxy (LBG) candidates at z ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z ≲ 7) may also mimic the near-infrared (near-IR) colors of z > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ≈ 5.1. We also present a tentative 2.6σ SCUBA-2 detection at 850 μm around a recently identified z ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ∼ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ∼ 4–6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations
Two-phonon scattering in nonpolar semiconductors: A first-principles study of warm electron transport in Si
No full textThe ab initio theory of charge transport in semiconductors typically employs the lowest-order perturbation theory in which electrons interact with one phonon (1ph). This theory is accepted to be adequate to explain the low-field mobility of nonpolar semiconductors but has not been tested extensively beyond the low-field regime. Here, we report first-principles calculations of the electric field dependence of the electron mobility of Si as described by the warm electron coefficient β. Although the 1ph theory overestimates the low-field mobility by only around 20%, it overestimates β by over a factor of two over a range of temperatures and crystallographic axes. We show that the discrepancy in β is reconciled by the inclusion of on-shell iterated two-phonon (2ph) scattering processes, indicating that scattering from higher-order electron-phonon interactions is non-negligible even in nonpolar semiconductors. Further, a ∼20% underestimate of the low-field mobility with 2ph scattering suggests that nontrivial cancellations may occur in the perturbative expansion of the electron-phonon interaction
Observation of triple J/ψ meson production in proton-proton collisions
No full textProtons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be 272+141−104(stat)±17(syst)fb, and compared it to theoretical expectations for triple-J/ψ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double-and triple-parton scattering are the dominant contributions for the measured process
The Evolution and Mass Dependence of Galaxy Cluster Pressure Profiles at 0.05 ≤ z ≤ 0.60 and 4 × 10¹⁴ M_⊙ ≤ M₅₀₀ ≤ 30 × 10¹⁴ M_⊙
No full textWe have combined X-ray observations from Chandra with Sunyaev–Zel’dovich effect data from Planck and Bolocam to measure intracluster medium pressure profiles from 0.03 R₅₀₀ ≤ R ≤ 5 R₅₀₀ for a sample of 21 low-z galaxy clusters with a median redshift of〈z〉= 0.08 and a median mass of =〈M₅₀₀〉= 6.1 × 10¹⁴ M_⊙ and a sample of 19 mid-z galaxy clusters with〈z〉= 0.50 and〈M₅₀₀〉= 10.6 × 10¹⁴ M_⊙. The mean scaled pressure in the low-z sample is lower at small radii and higher at large radii, a trend that is accurately reproduced in similarly selected samples from The Three Hundred simulations. This difference appears to be primarily due to dynamical state at small radii, evolution at intermediate radii, and a combination of evolution and mass dependence at large radii. Furthermore, the overall flattening of the mean scaled pressure profile in the low-z sample compared to the mid-z sample is consistent with expectations due to differences in the mass accretion rate and the fractional impact of feedback mechanisms. In agreement with previous studies, the fractional scatter about the mean scaled pressure profile reaches a minimum of ≃20% near 0.5 R₅₀₀. This scatter is consistent between the low-z and mid-z samples at all radii, suggesting it is not strongly impacted by sample selection, and this general behavior is reproduced in The Three Hundred simulations. Finally, analytic functions that approximately describe the mass and redshift trends in mean pressure profile shape are provided
Engineered zero-dispersion microcombs using CMOS-ready photonics
No full textNormal group velocity dispersion (GVD) microcombs offer high comb line power and high pumping efficiency compared to bright pulse microcombs. The recent demonstration of normal GVD microcombs using CMOS foundry-produced microresonators is an important step toward scalable production. However, the chromatic dispersion of CMOS devices is large and impairs the generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a coupled-ring resonator configuration. Operating in the turnkey self-injection locking mode, the resonator is integrated in a hybrid manner with a semiconductor laser pump to produce high-power efficiency combs spanning a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb lines. Fast, linear optical sampling of the comb waveform is used to observe the rich set of near-zero GVD comb behaviors, including soliton molecules, switching waves (platicons), and their hybrids. Tuning of the 20 GHz repetition rate by electrical actuation enables servo locking to a microwave reference, which simultaneously stabilizes the comb repetition rate, offset frequency, and temporal waveform. This integrated hybrid system could be used in coherent communications or for ultrastable microwave signal generation by two-point optical frequency division
Weak gravitational lensing shear estimation with metacalibration for the Roman High-Latitude Imaging Survey
No full textWe investigate the performance of the metacalibration shear calibration framework using simulated imaging data for the Nancy Grace Roman Space Telescope (Roman) reference High-Latitude Imaging Survey (HLIS). The weak lensing programme of Roman requires the mean weak lensing shear estimate to be calibrated within about 0.03 per cent. To reach this goal, we can test our calibration process with various simulations and ultimately isolate the sources of residual shear biases in order to improve our methods. In this work, we build on the HLIS image simulation pipeline to incorporate several more realistic processing-pipeline updates. We show the first metacalibration results for 6 deg2 of the simulated reference HLIS and compare them to measurements on simpler, faster Roman-like image simulations. We neglect the impact of blending of objects. We find in the simplified simulations metacalibration can calibrate shapes to within m = (−0.01 ± 0.10) per cent. When applied to the current most-realistic version of the simulations, the precision is much lower, with estimates of m = (−0.76 ± 0.43) per cent for joint multiband multi-epoch measurements and m = (−1.13 ± 0.60) per cent for multiband coadd measurements. These results are all consistent with zero within 1–2σ, indicating we are currently limited by our simulated survey volume. Further work on testing the shear calibration methodology is necessary at the precision of the Roman requirements, in particular in the presence of blending. Current results demonstrate, however, that metacalibration can work on undersampled space-based Roman imaging data at levels comparable to requirements of current weak lensing surveys
PAHs, hydrocarbons, and dimethylsulfides in Asteroid Ryugu samples A0106 and C0107 and the Orgueil (CI1) meteorite
No full textEvaluating the molecular distribution of organic compounds in pristine extraterrestrial materials is cornerstone to understanding the abiotic synthesis of organics and allows us to better understand the molecular diversity available during the formation of our solar system and before the origins of life on Earth. In this work, we identify multiple organic compounds in solvent extracts of asteroid Ryugu samples A0106 and C0107 and the Orgueil meteorite using two-dimensional gas chromatography and time-of-flight high resolution mass spectrometry (GC×GC–HRMS). Our analyses found similarities between the molecular distribution of organic compounds in Ryugu and the CI carbonaceous chondrite Orgueil. Specifically, several PAHs and organosulfides were found in Ryugu and Orgueil suggesting an interstellar and parent body origin for these compounds. We also evaluated the common relationship between Ryugu, Orgueil, and comets, such as Wild-2; however, until comprehensive compound-specific isotopic analyses for these organic species are undertaken, and until the effects of parent body processes and Earth’s weathering processes on meteoritic organics are better understood, their parent–daughter relationships will remain unanswered. Finally, the study of organic compounds in Ryugu samples and the curation practices for the future preservation of these unvaluable materials are also of special interest for future sample return missions, including NASA’s OSIRIS-REx asteroid sample return mission
Vibrational dynamics in the undercooled liquid of ultra-fragile metallic glasses
No full textThe lattice vibrational dynamics in ultra-fragile Pt₅₇Cu₂₃P₂₀ and Pt₆₀Cu₂₀P₂₀ glasses were investigated using in situ inelastic neutron scattering to measure the evolution of the phonon density of states (DOS) through the glass transition, into the undercooled liquid phase, and through crystallization. The phonon DOS curves are remarkably similar for the undercooled liquids and the amorphous solids. The vibrational entropy was obtained with these phonon DOS curves, and changes in vibrational entropy caused by the glass transition are less than 0.05 k_B/atom. For these highly fragile metal/metalloid glasses, the excess vibrational entropy of the undercooled liquid is about 0.5–1.5 J mol⁻¹ K⁻¹, compared to 0.1 J mol⁻¹ K⁻¹ reported earlier for stronger Cu–Zr glasses. Our work suggests that, consistent with our previous report for less fragile metallic glasses, the fraction of the total excess entropy that is vibrational is small, and the discontinuity in excess entropy at the glass transition is mainly due to configurational entropy
Direct observation of the local microenvironment in inhomogeneous CO₂ reduction gas diffusion electrodes via versatile pOH imaging
No full textWe report how the micrometer-scale morphology of a carbon dioxide reduction (CO₂R) gas diffusion electrode (GDE) affects the mass transport properties and with it, the local CO₂R performance. We developed a technique to probe the microenvironment in a CO₂R GDE via local pOH imaging with time- and three-dimensional spatial, micrometer-scale resolution. The local activity of hydroxide anions (OH⁻), represented by the pOH value, around a GDE in contact with an aqueous electrolyte is a crucial parameter that governs the catalytic activity and CO₂R selectivity. Here, we use fluorescence confocal laser scanning microscopy (CLSM) to create maps of the local pOH around a copper GDE by combining two ratiometric fluorescent dyes, one of which is demonstrated as a pOH sensor for the first time in this work. We observe that the local pOH decreases when current is applied due to the creation of OH⁻ as a byproduct of CO₂R. Interestingly, the pOH is lower inside microtrenches compared to the electrode surface and decreases further as trenches become more narrow due to enhanced trapping of OH−. We support our experimental results with multiphysics simulations that correlate exceptionally well with measurements. These simulations additionally suggest that the decreased pOH inside microcavities in the surface of a CO2R GDE leads to locally enhanced selectivity towards multicarbon (C₂₊) products. This study suggests that narrow microstructures on the length scale of 5 μm in a GDE surface serve as local CO₂R hotspots, and thus highlights the importance of a GDE's micromorphology on the CO₂R performance