Showing papers on "Point source published in 2022"

Incremental Fermi Large Area Telescope Fourth Source Catalog

Abstract: We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi Large Area Telescope (LAT) catalog of γ-ray sources. Based on the first 12 years of science data in the energy range from 50 MeV to 1 TeV, it contains 6658 sources. The analysis improves on that used for the 4FGL catalog over eight years of data: more sources are fit with curved spectra, we introduce a more robust spectral parameterization for pulsars, and we extend the spectral points to 1 TeV. The spectral parameters, spectral energy distributions, and associations are updated for all sources. Light curves are rebuilt for all sources with 1 yr intervals (not 2 month intervals). Among the 5064 original 4FGL sources, 16 were deleted, 112 are formally below the detection threshold over 12 yr (but are kept in the list), while 74 are newly associated, 10 have an improved association, and seven associations were withdrawn. Pulsars are split explicitly between young and millisecond pulsars. Pulsars and binaries newly detected in LAT sources, as well as more than 100 newly classified blazars, are reported. We add three extended sources and 1607 new point sources, mostly just above the detection threshold, among which eight are considered identified, and 699 have a plausible counterpart at other wavelengths. We discuss the degree-scale residuals to the global sky model and clusters of soft unassociated point sources close to the Galactic plane, which are possibly related to limitations of the interstellar emission model and missing extended sources.

QUBIC III: Laboratory characterization

Abstract: A prototype version of the Q & U Bolometric Interferometer for Cosmology (QUBIC) underwent a campaign of testing in the laboratory at Astroparticle Physics and Cosmology in Paris. We report the results of this Technological Demonstrator which successfully shows the feasibility of the principle of Bolometric Interferometry. Characterization of QUBIC includes the measurement of the synthesized beam, the measurement of interference fringes, and the measurement of polarization performance. A modulated and frequency tunable millimetre-wave source in the telescope far-field is used to simulate a point source. The QUBIC pointing is scanned across the point source to produce beam maps. Polarization modulation is measured using a rotating Half Wave Plate. The measured beam matches well to the theoretical simulations and gives QUBIC the ability to do spectro imaging. The polarization performance is excellent with less than 0.5\% cross-polarization rejection. QUBIC is ready for deployment on the high altitude site at Alto Chorillo, Argentina to begin scientific operations.

Strong methane point sources contribute a disproportionate fraction of total emissions across multiple basins in the U.S.

Abstract: Understanding, prioritizing, and mitigating methane (CH4) emissions requires quantifying methane budgets from facility scales to regional scales with the ability to differentiate between source sectors. We deployed a tiered observing system for multiple basins in the United States (San Joaquin Valley, Uintah, Denver-Julesberg, Permian, Marcellus). We quantify strong point source emissions (>10 kg CH4 h-1) using airborne high spatial resolution imaging spectrometers, then attribute them to sectors, and assess their intermittency with multiple revisits. We contextualize these point source emissions by comparing to total basin CH4 fluxes derived from inversion of Sentinel-5p satellite observations. We find that across basins point source make up on average 40% of the regional flux. We sampled some basins several times across multiple months and years and find a distinct bimodal structure to emission lifetimes: the total point source budget is split nearly in half by short- and long-lived emission events. With the increasing airborne and satellite observing capability planned for the near future, tiered observing systems can more fully account and attribute emission sources, which is needed to effectively and efficiently reduce methane emissions.

Non-point contaminant source identification in an aquifer using the ensemble smoother with multiple data assimilation

Abstract: Proper identification of groundwater contaminant sources is vital to assess groundwater contamination. However, the majority of previous studies focuses on point source identification; only a few works have been conducted for non-point source parameter identification. Here, we employ the ensemble smoother with multiple data assimilation (ES-MDA) to simultaneously identify the spatial architecture of non-point contaminant sources and the related release information. Three different shapes of non-point contaminant sources are considered, an ellipse, a circle, and an irregular shape. We test the applicability of the ES-MDA for the simultaneous identification using three scenarios in a synthetic confined aquifer by assimilating concentration observations from all-time steps multiple times. The results demonstrate that the ES-MDA is capable to accurately identify both regular and irregular non-point contaminant source information; the accuracy of the identification can be improved by increasing the number of iterations.

Near-future discovery of point sources of ultra-high-energy neutrinos

Abstract: Upcoming neutrino telescopes may discover ultra-high-energy (UHE) cosmic neutrinos, with energies beyond 100 PeV, in the next 10–20 years. Finding their sources would identify guaranteed sites of interaction of UHE cosmic rays, whose origin is unknown. We search for sources by looking for multiplets of UHE neutrinos arriving from similar directions. Our forecasts are state-of-the-art, geared at neutrino radio-detection in IceCube-Gen2. They account for detector energy and angular response, and for critical, but uncertain backgrounds. Sources at declination of -45° to 0° will be easiest to discover. Discovering even one steady-state source in 10 years would imply that the source has an UHE neutrino luminosity at least larger than about 1043 erg/s (depending on the source redshift evolution). Discovering no transient source would disfavor transient sources brighter than 1053 erg as dominant. Our results aim to inform the design of upcoming detectors.

Inverse moving point source problem for the wave equation

Abstract: In this paper, we consider the problem of identifying a single moving point source for a three-dimensional wave equation from boundary measurements. Precisely, we show that the knowledge of the field generated by the source at six different points of the boundary over a finite time interval is sufficient to determine uniquely its trajectory. We also derive a Lipschitz stability estimate for the inversion.

Technical note: Interpretation of field observations of point-source methane plume using observation-driven large-eddy simulations

Abstract: Abstract. This study demonstrates the ability of large-eddy simulation (LES) forced by a large-scale model to reproduce plume dispersion in an actual field campaign. Our aim is to bring together field observations taken under non-ideal conditions and LES to show that this combination can help to derive point-source strengths from sparse observations. We analyze results from a single-day case study based on data collected near an oil well during the ROMEO campaign (ROmanian Methane Emissions from Oil and gas) that took place in October 2019. We set up our LES using boundary conditions derived from the meteorological reanalysis ERA5 and released a point source in line with the configuration in the field. The weather conditions produced by the LES show close agreement with field observations, although the observed wind field showed complex features due to the absence of synoptic forcing. In order to align the plume direction with field observations, we created a second simulation experiment with manipulated wind fields that better resemble the observations. Using these LESs, the estimated source strengths agree well with the emitted artificial tracer gas plume, indicating the suitability of LES to infer source strengths from observations under complex conditions. To further harvest the added value of LES, higher-order statistical moments of the simulated plume were analyzed. Here, we found good agreement with plumes from previous LES and laboratory experiments in channel flows. We derived a length scale of plume mixing from the boundary layer height, the mean wind speed and convective velocity scale. It was demonstrated that this length scale represents the distance from the source at which the predominant plume behavior transfers from meandering dispersion to relative dispersion.

OUP accepted manuscript

Abstract: Abstract We examined the X-ray and radio spatial structure at the eastern ear of the W 50/SS 433 system to clarify a characteristic feature of the termination region of the SS 433 jet, and found that a hot spot ahead of the filament structure, which is considered to be a terminal shock of the SS 433 eastern jet, is clearly different from a single point source. The detailed spatial structure of the X-ray emission is finely resolved by Chandra observations, showing that there are two sources. By comparing the point-spread function of Chandra with the radial profiles of the two sources, the northern one is clearly more extended than a point source while the other seems marginally extended. Since there are no point sources nearby, the northern hot spot is likely a localized diffuse source. The northern hot spot spatially corresponds to the peak of the radio emission. Its spatial correlation is confirmed by an X-ray image using XMM-Newton. The X-ray spectra of the two sources are reproduced by a single absorbed power-law but the column density of the northern part is larger by a factor of ∼3. When a radiation model comprising synchrotron emission and inverse Compton emission is applied to the spectral energy distribution of the northern hot spot, the emission from this spot can be explained by the radiation from an electron population accelerated up to 30 TeV in a magnetic field strength of B ≲ 50 μG. This model also agrees with the radio and X-ray data, as well as the upper limit of gamma-ray emission obtained by the Fermi satellite.

The DECam Local Volume Exploration Survey Data Release 2

Abstract: We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of ∼160,000 exposures that cover >21,000 deg2 of the high-Galactic-latitude (∣b∣ > 10°) sky in four broadband optical/near-infrared filters (g, r, i, z). DELVE DR2 provides point-source and automatic aperture photometry for ∼2.5 billion astronomical sources with a median 5σ point-source depth of g = 24.3, r = 23.9, i = 23.5, and z = 22.8 mag. A region of ∼17,000 deg2 has been imaged in all four filters, providing four-band photometric measurements for ∼618 million astronomical sources. DELVE DR2 covers more than 4 times the area of the previous DELVE data release and contains roughly 5 times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform.

Effects of point source emission heights in WRF–STILT: a step towards exploiting nocturnal observations in models

Abstract: Abstract. An appropriate representation of point source emissions in atmospheric transport models is very challenging. In the Stochastic Time-Inverted Lagrangian Transport model (STILT), all point source emissions are typically released from the surface, meaning that the actual emission stack height plus subsequent plume rise is not considered. This can lead to erroneous predictions of trace gas concentrations, especially during nighttime when vertical atmospheric mixing is minimal. In this study we use two Weather Research and Forecasting (WRF)–STILT model approaches to simulate fossil fuel CO2 (ffCO2) concentrations: (1) the standard “surface source influence (SSI)” approach and (2) an alternative “volume source influence (VSI)” approach where nearby point sources release CO2 according to their effective emission height profiles. The comparison with 14C-based measured ffCO2 data from 2-week integrated afternoon and nighttime samples collected at Heidelberg, 30 m above ground level shows that the root-mean-square deviation (RMSD) between modelled and measured ffCO2 is indeed almost twice as high during the night (RMSD =6.3 ppm) compared to the afternoon (RMSD =3.7 ppm) when using the standard SSI approach. In contrast, the VSI approach leads to a much better performance at nighttime (RMSD =3.4 ppm), which is similar to its performance during afternoon (RMSD =3.7 ppm). Representing nearby point source emissions with the VSI approach could thus be a first step towards exploiting nocturnal observations in STILT. The ability to use nighttime observations in atmospheric inversions would dramatically increase the observational data and allow for the investigation of different source mixtures or diurnal cycles. To further investigate the differences between these two approaches, we conducted a model experiment in which we simulated the ffCO2 contributions from 12 artificial power plants with typical annual emissions of 1 million tonnes of CO2 and with distances between 5 and 200 km from the Heidelberg observation site. We find that such a power plant must be more than 50 km away from the observation site in order for the mean modelled ffCO2 concentration difference between the SSI and VSI approach to fall below 0.1 ppm during situations with low mixing heights smaller than 500 m.

Detecting clusters of galaxies and active galactic nuclei in an eROSITA all-sky survey digital twin

Abstract: Context. The extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spectrum-Roentgen-Gamma (SRG) observatory is revolutionizing X-ray astronomy. The mission provides unprecedented samples of active galactic nuclei (AGN) and clusters of galaxies, with the potential of studying astrophysical properties of X-ray sources and measuring cosmological param- eters using X-ray-selected samples with higher precision than ever before. Aims. We aim to study the detection, and the selection of AGN and clusters of galaxies in the first eROSITA all-sky survey, and to characterize the properties of the source catalog. Methods. We produced a half-sky simulation at the depth of the first eROSITA survey (eRASS1), by combining models that truthfully represent the population of clusters and AGN. In total, we simulated 1116758 clusters and 225583320 AGN. We ran the standard eROSITA detection algorithm, optimized for extragalactic sources. We matched the input and the source catalogs with a photon-based matching algorithm. Results. We perfectly recovered the bright AGN and clusters. We detected half of the simulated AGN with flux larger than 2 × 10 − 14 ergs − 1 cm − 2 as point sources and half of the simulated clusters with flux larger than 3 × 10 − 13 ergs − 1 cm − 2 as extended sources in the 0.5–2.0keV band. We quantified the detection performance in terms of completeness, false detection rate, and con- tamination. We studied the population in the source catalog according to multiple cuts of source detection and extension likelihood. We find that the latter is suitable for removing contamination, and the former is very e ffi cient in minimizing the false detection rate. We find that the detection of clusters of galaxies is mainly driven by flux and exposure time. It additionally depends on secondary e ff ects, such as the size of the clusters on the sky plane and their dynamical state. The cool core bias mostly a ff ects faint clusters classified as point sources, while its impact on the extent-selected sample is small. We measured the fraction of the area covered by our simulation as a function of limiting flux. We measured the X-ray luminosity of the detected clusters and find that it is compatible with the simulated values. Conclusions. We discuss how to best build samples of galaxy clusters for cosmological purposes, accounting for the nonuniform depth of eROSITA. This simulation provides a digital twin of the real eRASS1.

Underwater Sound Source Localization Based on Passive Time-Reversal Mirror and Ray Theory

Abstract: This study investigates the performance of a passive time-reversal mirror (TRM) combined with acoustic ray theory in localizing underwater sound sources with high frequencies (3–7 kHz). The TRM was installed on a floating buoy and comprised four hydrophones. The ray-tracing code BELLHOP was used to determine the transfer function between a sound source and a field point. The transfer function in the frequency domain obtained from BELLHOP was transformed into the time domain. The pressure field was then obtained by taking the convolution of the transfer function in the time domain with the time-reversed signals that were received by the hydrophones in the TRM. The location with the maximum pressure value was designated as the location of the source. The performance of the proposed methodology for source localization was tested in a towing tank and in the ocean. The aforementioned tests revealed that even when the distances between a source and the TRM were up to 1600 m, the distance deviations between estimated and actual source locations were mostly less than 2 m. Errors originated mainly from inaccurate depth estimation, and the literature indicates that they can be reduced by increasing the number of TRM elements and their apertures.

Testing source confusion and identification capability in Cherenkov Telescope Array data

Abstract: The Cherenkov Telescope Array will provide the deepest survey of the Galactic Plane performed at very-high-energy gamma-rays. Consequently, this survey will unavoidably face the challenge of source confusion, i.e., the non-unique attribution of signal to a source due to multiple overlapping sources. Among the known populations of Galactic gamma-ray sources and given their extension and number, pulsar wind nebulae (PWNe, and PWN TeV halos) will be the most affected. We aim to probe source confusion of TeV PWNe in forthcoming CTA data. For this purpose, we performed and analyzed simulations of artificially confused PWNe with CTA. As a basis for our simulations, we applied our study to TeV data collected from the H.E.S.S. Galactic Plane Survey for ten extended and two point-like firmly identified PWNe, probing various configurations of source confusion involving different projected separations, relative orientations, flux levels, and extensions among sources. Source confusion, defined here to appear when the sum of the Gaussian width of two sources is larger than the separation between their centroids, occurred in ∼30% of the simulations. For this sample and 0.5○ of average separation between sources, we found that CTA can likely resolve up to 60% of those confused sources above 500 GeV. Finally, we also considered simulations of isolated extended sources to see how well they could be matched to a library of morphological templates. The outcome of the simulations indicates a remarkable capability (more than 95% of the cases studied) to match a simulation with the correct input template in its proper orientation.

Quantitative comparison of methods used to estimate methane emissions from small point sources

Abstract: Abstract. Recent interest in quantifying trace gas emissions from point sources, such as measuring methane (CH4) emissions from oil and gas wells, has resulted in several methods being used to estimate emissions from sources with emission rates below 200g CH4 hour−1. The choice of measurement approach depends on how close observers can get to the source, the instruments available and the meteorological/micrometeorological conditions. As such, static chambers, dynamic chambers, HiFlow measurements, Gaussian plume modelling and backward Lagrangian stochastic (bLs) models have all been used, but there is no clear understanding of the accuracy or precision of each method. To address this, we copy the experimental design for each of the measurement methods to make single field measurements of a known source, to simulate single measurement field protocol, and then make repeat measurements to generate an understanding of the accuracy and precision of each method. Here, for comparison, we present estimates for the percentage difference between the measured emission and the known emission, A, and the average percentage difference for three repeat measurements, Ar , for emissions of 200 g CH4 h−1. Our results show that, even though the dynamic chamber repeatedly underestimates the emission, it is the most accurate for a single measurement and the accuracy improves with subsequent measurements (A = −11 %, Ar = −10 %). The single HiFlow emission estimate was also an underestimate, however, poor instrument precision resulted in reduced accuracy of emission estimate to becomes less accurate after repeat measurements (A = −16 %, Ar = −18 %). Of the far field methods, the bLs method underestimated emissions both for single and repeat measurements (A = −11 %, Ar = −7 %) while the GP method significantly overestimated the emissions (A = 33 %, Ar = 29 %) despite using the same meteorological and concentration data as input. Additionally, our results show that the accuracy and precision of the emission estimate increases as the flow rate of the source is increased for all methods. To our knowledge this is the first time that methods for measuring CH4 emissions from point sources less than 200 g CH4 h−1 have been quantitively assessed against a known reference source and each other.

Analytical solution for transport of pollutant from time-dependent locations along groundwater

Abstract: The present work derives analytical solutions of advection–dispersion equation (ADE) with temporal coefficients, and a pollutant’s point source moving linearly along the axis of a one-dimensional semi-infinite domain. The source is considered a varying and a uniform pulse source, respectively. The dispersion of pollutant originating from a varying pulse source may be supposed to occur along groundwater flow domain, and that from a uniform pulse source in an open medium like air or along a river flow. The location of the input concentration that is the pollutant’s concentration emanating from the source in an open medium or that reaching the groundwater domain being infiltrated from its source on the ground, is considered moving linearly along the flow direction. The motion of the source is described through an asymptotically increasing temporal function. The illustration of the analytical solution clearly reflects this feature. It also renders that the concentration pattern of the proposed solution is proximal to that of an existing solution obtained with the stationary source. The pertinent existing solutions may also be derived from the proposed solutions. The proposed solutions are found approximate but it is also found that the error of approximation of one of them is too small to have any effect on the concentration pattern. To get these solutions, firstly, the moving source is reduced into a stationary source at the origin, then the governing equations including the ADE, are made free from the three temporal functions, one occurring in the time-dependent position of the source, and the other two as the coefficients of the ADE. In this process, three new position variables, and a new time variable are introduced using as many coordinate transformations. Then the Laplace Integral Transformation Technique (LITT) is used to get the final solutions. The solution in Laplacian domain with uniform pulse source is obtained as a special case of that with the varying pulse source.

Finite-Difference Simulation for Infrasound Generated by Finite-Extent Ground Motions

Abstract: Underground explosions can produce infrasound in the atmosphere, and the wavefield characteristics are often governed by the ground surface motions. Finite-difference methods are popular for infrasound simulation as their generality and robustness allow for complex atmospheric structures and surface topography. A simple point-source approximation is often used because infrasound wavelengths tend to be large relative to the source dimensions. However, this assumption may not be able to capture the complexity of explosion-induced ground motions if the surface area is not compact, and appropriate source models must be incorporated into the finite-difference simulations for accurate infrasound prediction. In this study, we develop a point source representation of the complex ground motions for infrasound sources. Instead of a single point source, we use a series of point sources distributed over the source area. These distributed point sources can be equivalent to air volume changes produced by the ground motions in the atmosphere. We apply the distributed point-source method to a series of buried chemical explosions conducted during the Source Physics Experiment Phase I. Epicentral ground-motion measurements during the experiments provide a way to calculate accurate distributed point sources. We validate and evaluate the accuracy of distributed point source approach for infrasound simulations by direct comparison with acoustic observations in the field experiment.

Analytical Modeling of Acoustic Emission Due to an Internal Point Source in a Transversely Isotropic Cylinder

Abstract: In this paper, the displacement fields responsible for acoustic emission (AE), excited from a point source in a transversely isotropic cylinder, are derived by solving the Navier-Lamé (NL) equation. The point source as an internal defect is represented by a spatiotemporal concentrated force. The introduction of three potentials correlated with the point source to displacement field vector decouples the coupled NL equation in cylindrical coordinates. Under these conditions, we solve the radial, tangential, and axial displacement fields. Analytical simulations of AE were carried out at several point source locations. Our results demonstrate that analytical modeling is a powerful tool for characterizing AE features generated from an internal defect source.

A Compound Poisson Generator Approach to Point-source Inference in Astrophysics

Abstract: The identification and description of point sources is one of the oldest problems in astronomy; yet, even today the correct statistical treatment for point sources remains one of the field's hardest problems. For dim or crowded sources, likelihood based inference methods are required to estimate the uncertainty on the characteristics of the source population. In this work, a new parametric likelihood is constructed for this problem using Compound Poisson Generator (CPG) functionals which incorporate instrumental effects from first principles. We demonstrate that the CPG approach exhibits a number of advantages over Non-Poissonian Template Fitting (NPTF) - an existing method - in a series of test scenarios in the context of X-ray astronomy. These demonstrations show that the effect of the point-spread function, effective area, and choice of point-source spatial distribution cannot, generally, be factorised as they are in NPTF, while the new CPG construction is validated in these scenarios. Separately, an examination of the diffuse-flux emission limit is used to show that most simple choices of priors on the standard parameterisation of the population model can result in unexpected biases: when a model comprising both a point-source population and diffuse component is applied to this limit, nearly all observed flux will be assigned to either the population or to the diffuse component. A new parametrisation is presented for these priors which properly estimates the uncertainties in this limit. In this choice of priors, CPG correctly identifies that the fraction of flux assigned to the population model cannot be constrained by the data.

Update of the CLRP monte carlo TG-43 parameter database for high-energy brachytherapy sources.

Abstract: PURPOSE To update and extend version 2 of the Carleton Laboratory for Radiotherapy Physics (CLRP) TG-43 dosimetry database (CLRP_TG43v2) for 33 high-energy (HE, ⩾50 keV) brachytherapy sources (1 169 Yb, 23 192 Ir, 5 137 Cs, and 4 60 Co) using egs_brachy, an open-source EGSnrc application. A comprehensive dataset of TG-43 parameters is compiled, including detailed source descriptions, dose-rate constants, radial dose functions, 1D and 2D anisotropy functions, along-away dose-rate tables, Primary and Scatter Separated (PSS) dose tables, and mean photon energies escaping each source. The database also documents the source models which will be freely distributed with egs_brachy. ACQUISITION AND VALIDATION METHODS Datasets are calculated after a recoding of the source geometries using the egs++ geometry package and its egs_brachyextensions. Air kerma per history is calculated in a 10× 10 ×0.05 cm3 voxel located 100 cm from the source along the transverse axis and then corrected for the lateral and thickness dimensions of the scoring voxel to give the air kerma on the central axis at a point 100 cm from the source's mid-point. Full-scatter water phantoms with varying voxel resolutions in cylindrical coordinates are used for dose calculations. Most data (except for 60 Co) are based on the assumption of charged particle equilibrium and ignore the potentially large effects of electron transport very close to the source and dose from initial beta particles. These effects are evaluated for four representative sources. For validation, data are compared to those from CLRP_TG43v1 and published data. DATA FORMAT AND ACCESS Data are available at https://physics.carleton.ca/clrp/egs_brachy/seed_database_v2 or http://doi.org/10.22215/clrp/tg43v2 including in Excel (.xlsx) spreadsheets, and are presented graphically in comparisons to previously published data for each source. POTENTIAL APPLICATIONS The CLRP_TG43v2 database has applications in research, dosimetry, and brachytherapy planning. This comprehensive update provides the medical physics community with more precise and in some cases more accurate Monte Carlo (MC) TG-43 dose calculation parameters, as well as fully benchmarked and described source models which are distributed with egs_brachy. This article is protected by copyright. All rights reserved.

Removal of point source leakage from time-order data filtering

Abstract: Time-ordered data (TOD) from ground-based CMB experiments is usually filtered before map-making to reduce the contamination from ground and atmospheric emissions. However, when the observation region contains strong point sources, the filtering process will cause a considerable leakage around the point sources, which should be eliminated to provide a clean CMB polarization map for scientific purposes. The method we introduce in this work, which we refer to as “template fitting,” is capable of removing these leakage signals in the pixel domain, meeting the requirement of measuring the primordial gravitational waves from CMB-B modes for at least r < 0.005, while also avoiding time-consuming operations on the TOD.

Unresolved z ∼ 8 Point Sources and Their Impact on the Bright End of the Galaxy Luminosity Function

Abstract: The distribution and properties of the first galaxies and quasars are critical pieces of the puzzle in understanding galaxy evolution and cosmic reionization. Previous studies have often excluded unresolved sources as potential low-redshift interlopers. We combine broadband color and photometric redshift analysis with morphological selections to identify a robust sample of candidates consistent with unresolved point sources at redshifts z ∼ 8 using deep Hubble Space Telescope images. We also examine G141 grism spectroscopic data to identify and eliminate dwarf star contaminants. From these analyses, we identify three bright (M UV ≲ −22 AB mag) dropout point sources at 7.5 < z < 8.1. Spectral energy distribution analyses suggest that these sources are either quasars or compact star-forming galaxies. The flux captured by the IRAC 4.5 μm channel suggests that they have moderate Hβ + [O III] equivalent widths. We calculate the number density of point sources at z ∼ 7–8, and find that a double-power-law model well describes the point-source distribution. We then extend our analysis to estimate the combined point-source + galaxy luminosity function and find that the point sources have a nonnegligible contribution to the bright-end excess. The fact that the point sources dominate only at M UV ≲ −22 suggests that their contribution to cosmic reionization is likely limited. While spectroscopic follow-up is needed to confirm the nature of these point sources, this work demonstrates that the inclusion of Lyman-dropout point sources is necessary for a complete census of early galaxies at the epoch of cosmic reionization.

Quantifying CO emission rates of industrial point sources from Tropospheric Monitoring Instrument observations

Abstract: Abstract This work demonstrates for the first time the capability of routine Tropospheric Monitoring Instrument (TROPOMI) operations to quantify CO emission rates down to industrial point sources. We have quantified the CO emission rates of four industrial point sources in Asia, namely Qianlishan Industrial Park (39.9° N, 106.9° E), Jiuyuan Industrial Park (40.7° N, 109.7° E) and Botian Industrial Park (42.2° N, 125.2° E) in China and the Jindal factory (15.2° N, 76.7° E) in India, with TROPOMI CO observations from 2017 to 2020. Qianlishan Industrial Park is a missing source in the emission inventory and we quantify it to be ∼14.0 kg s −1 . Our estimates for the other three sources vary between 14.4 and 34.3 kg s −1 , within 37%–69% of the inventory values. The plume inversion methods are presented in a manner that can be easily used with other fine-scale emission plumes observed from space. Although only a small number of CO plumes per year for any given industrial point source can be observed under conditions suitable for estimation of emission rates, there are many industrial point sources that can be captured by a good TROPOMI footprint. This work affirms that a constellation of future CO satellites could monitor individual CO point source emissions to support environmental policies.