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All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

A Comparison of HALOE V19 with SAGE II V6.00 Ozone Observations using Trajectory Mapping

We apply trajectory mapping to an eight-year intercomparison of ozone observations from HALOE (V19) and SAGE II (V6.00) for the months March, May, June, September, October, and December from the period December 1991 - October 1999. Our results, which represent the most extensive such intercomparison of these two data sets to date, suggest a root-mean -square difference between the two data sets of greater than 15% below 22 km and of 4 - 12% throughout most of the rest of the stratosphere. In addition, we find a bias with HALOE ozone low relative to SAGE II by 5 - 20% below 22 km between 40degS and 40degN. Biases throughout most of the rest of the stratosphere are nearly nonexistent. Finally, our analysis suggests almost no drift in the bias between the data sets is observed over the period of study. In the course of our study, we also determine that the employment of the Wang-Cunnold criteria is still recommended with the V6.00 SAGE II ozone data. Results with the new versions of the data sets show significant improvement over previous versions, particularly in the elimination of mid-stratospheric biases and the elimination of the previously observed drifts in the biases between the data sets in the lower stratosphere. Since HALOE V19 and V18 ozone are very similar, these changes can likely be attributed to improvements in the SAGE II retrieval.

Morris, Gary A.↗
NASA NTRS2004

The Interaction of Hot and Cold Gas in the Disk and Halo of Galaxies

Most of the thermal energy in the Galaxy and perhaps most of the baryons in the Universe are found in hot (log T approximately 5.5 - 7) gas. Hot gas is detected in the local interstellar medium, in supernova remnants (SNR), the Galactic halo, galaxy clusters and the intergalactic medium (IGM). In our own Galaxy, hot gas exists in large superbubbles up to several hundred pc in diameter that locally dominate the interstellar medium (ISM) and determine its thermal and dynamic evolution. While X-ray observations using ROSAT, Chandra and XMM have allowed us to make dramatic progress in mapping out the morphology of the hot gas and in understanding some of its spectral characteristics, there remain fundamental questions that are unanswered. Chief among these questions is the way that hot gas interacts with cooler phase gas and the effects these interactions have on hot gas energetics. The theoretical investigations we proposed in this grant aim to explore these interactions and to develop observational diagnostics that will allow us to gain much improved information on the evolution of hot gas in the disk and halo of galaxies. The first of the series of investigations that we proposed was a thorough exploration of turbulent mixing layers and cloud evaporation. We proposed to employ a multi-dimensional hydrodynamical code that includes non-equilibrium ionization (NEI), radiative cooling and thermal conduction. These models are to be applied to high velocity clouds in our galactic halo that are seen to have O VI by FUSE (Sembach et ai. 2000) and other clouds for which sufficient constraining observations exist.

Slavin, Jonathan↗
NASA NTRS2003

Evidence for a Significant Intermediate-Age Population in the M31 Halo from Main Sequence Photometry

We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M3l), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at m(sub v) = 30.7 mag. The CMD, constructed from approx. 3 x 10(exp 5) stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as chi square fitting to a finely-spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (approx. 30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] greater than -0.5) population, as well as a significant globular-cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.

Brown, Thomas M.↗
NASA NTRS2004

Cone Model for Halo CMEs: Application to Space Weather Forecasting

In this study, we present an innovative analytical method to determine the angular width and propagation orientation of halo Coronal Mass Ejections (CMEs). The relation of CME actual speed with apparent speed and its components measured at different position angle has been investigated. The present work is based on the cone model proposed by Zhao et al. We have improved this model by: (1) eliminating the ambiguity via a new analytical approach, (2) using direct measurements of projection onto the plane of the sky (POS), and (3) determining the actual radial speeds from projection speeds at different position angles to clarify the uncertainty of projection speeds in previous empirical models. Our analytical approach allows us to use coronagraph data to determine accurately the geometrical features of POS projections, such as major axis, minor axis, and the displacement of the center of its projection, and to determine the angular width and orientation of a given halo CME. Our approach allows for the first time the determination of the actual CME speed, width, and source location by using coronagraph data quantitatively and consistently. The method greatly enhances the accuracy of the derived geometrical and kinematical properties of halo CMEs, and can be used to optimize Space Weather forecasts. The applied model predications are in good agreement with observations.

Xie, Hong↗
NASA NTRS2003

A New Method to Use Chandra Data to Resolve the X-Ray Halos Around Point Sources and Its Application to Cygnus X-1

The excellent angular resolution, good energy resolution and broad energy band make Chandra ACIS the best instrument for studying the X-ray halos around some galactic x-ray point sources caused by the dust scattering of X-rays in the interstellar medium, but direct images of bright sources of b r i g h t sources obtained with ACIS usually from severe pile- UP - Making use of the fact that an isotropic image could be reconstructed from it's projection on any direction, we can reconstruct the images of the X-ray halos from data obtained with the regular HETGS and/or the CC mode. With the reconstructed high resolution images, we can probe the X-ray halos as close as 1 arcsecond to their associated point sources.

Yao, Y.↗
NASA NTRS2003

The Discovery of an Evolving Dust Scattered X-ray Halo Around GRB 031203

We report the first detection of a time-dependent, dust-scattered X-ray halo around a gamma-ray burst. GRB3 031203 was observed by XMM-Newton starting six hours after the burst. The halo appeared as concentric ring-like structures centered on the GRB location. The radii of these structures increased with time as t(sup 1/2), consistent with small-angle X-ray scattering caused by a large column of dust along the line of sight to a cosmologically distant GRB. The rings are due to dust concentrated in two distinct slabs in the Galaxy located at distances of 880 and 1390 pc, consistent with known Galactic features. The halo brightness implies an initial soft X-ray pulse consistent with the observed GRB.

Vaughan, S.↗
NASA NTRS2004

Velocity Structure and Plasma Properties in Halo CMES

We have identified a set of 23 Halo CMEs and 21 Partial Halo CMEs from the LASCO Halo CME Archive for which UVCS spectra exist through July 2002. For each event we have collected basic information such as the event speed, whether or not UVCS caught the bright front, lines detected, Doppler shift and associated flare class. We are currently analyzing the subset for which UVCS caught the CME front. We also obtained excellent observations of some of the spectacular events in November 2003, and we have made theoretical calculations pertaining to CME expansion at the heights observed by UVCS. In one event we were able to analyze the properties of the current sheet in detail.

Raymond, John C.↗
NASA NTRS2005

Cosmic Ray Propagation through the Magnetic Fields of the Galaxy with Extended Halo

In this project we perform theoretical studies of 3-dimensional cosmic ray propagation in magnetic field configurations of the Galaxy with an extended halo. We employ our newly developed Markov stochastic process methods to solve the diffusive cosmic ray transport equation. We seek to understand observations of cosmic ray spectra, composition under the constraints of the observations of diffuse gamma ray and radio emission from the Galaxy. The model parameters are directly are related to properties of our Galaxy, such as the size of the Galactic halo, particle transport in Galactic magnetic fields, distribution of interstellar gas, primary cosmic ray source distribution and their confinement in the Galaxy. The core of this investigation is the development of software for cosmic ray propagation models with the Markov stochastic process approach. Values of important model parameters for the halo diffusion model are examined in comparison with observations of cosmic ray spectra, composition and the diffuse gamma-ray background. This report summarizes our achievement in the grant period at the Florida Institute of Technology. Work at the co-investigator's institution, the University of New Hampshire, under a companion grant, will be covered in detail by a separate report.

Zhang, Ming↗
NASA NTRS2006

The X-ray Halo of GX5-1

Using Chandra observations we have measured the energy-resolved dust-scattered X-ray halo around the low-mass X-ray binary GX5-1, detecting for the first time multiply scattered X-rays from interstellar dust. % e compared the observed X-ray halo at various energies to predictions from a range of dust models. These fits used both smoothly-distributed dust as well as dust in clumped clouds, with CO and 21 cm observations helping to determine the position of the clouds along the line of sight. We found that the BARE-GR-B model of Zubko, Dwek & Arendt (2004) generally led to the best results, although inadequacies in both the overall model and the data limit our conclusions. We did find that the composite dust models of Zubko, Dwek & Arendt (2004), especially the "no carbon" models, gave uniformly poor results. Although models using cloud positions and densities derived naively from CO and 21 cm data gave generally poor results, plausible adjustments to the distance of the largest cloud and the mass of a cloud in the expanding 3 kpc Arm lead to significantly improved fits. We suggest that combining X-ray halo, CO, and 21 cm observations will be a fruitful method to improve our understanding of both the gas and dust phases of the interstellar medium.

Smith, Randall K.↗
NASA NTRS2008

The Quasi-biennial Oscillation and Annual Variations in Tropical Ozone from SHADOZ and HALOE

We examine the tropical ozone mixing ratio perturbation fields generated from a monthly ozone climatology using 1998 to 2006 ozonesonde data from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network and the 13-year satellite record from 1993 to 2005 obtained from the Halogen Occultation Experiment (HALOE). The long time series and high vertical resolution of the ozone and temperature profiles from the SHADOZ sondes coupled with good tropical coverage north and south of the equator gives a detailed picture of the ozone structure in the lowermost stratosphere down through the tropopause where the picture obtained from HALOE measurements is blurred by coarse vertical resolution. Ozone perturbations respond to annual variations in the Brewer-Dobson Circulation (BDC) in the region just above the cold-point tropopause to around 20 km. Annual cycles in ozone and temperature are well correlated. Above 20 km, ozone and temperature perturbations are dominated by the Quasi-biennial Oscillation (QBO). Both satellite and sonde records show good agreement between positive and negative ozone mixing ratio anomalies and alternating QBO westerly and easterly wind shears from the Singapore rawinsondes with a mean periodicity of 26 months for SHADOZ and 25 months for HALOE. There is a temporal offset of one to three months with the QBO wind shear ahead of the ozone anomaly field. The meridional length scales for the annual cycle and the QBO, obtained using the temperature anomalies and wind shears in the thermal wind equation, compare well with theoretical calculations.

Witte, J. C.↗
NASA NTRS2011

Halo Coronal Mass Ejections: Comparing Observations and Models

Since 1996, the SOHO LASCO coronagraphs have detected "halo" CMEs that appear to be directed toward Earth, but information about the size and speed of these events seen face-on has been limited. From a single vantage point along the Sun-Earth line, the primary limitation has been ambiguity in fitting the cone model (or other forward-modeling techniques, e.g., Thernisian et al., 2006). But in the past few years, the STEREO mission has provided a view of Earth-directed events from the side. These events offer the opportunity to compare measurements (width and speed) of halo CMEs observed by STEREO with models that derive halo CME properties. We report here results of such a comparison on a large sample of LASCO CMEs in the STEREO era.

Gilbert, Holly↗
NASA NTRS2016

A Giant Radio Halo in a Low-Mass Sz-selected Galaxy Cluster: ACT-CLJ0256.5+0006

We present the detection of a giant radio halo (GRH) in the Sunyaev-Zel'dovich (SZ)- selected merging galaxy cluster ACT-CL J0256.5+ 0006 (z = 0.363), observed with the Giant Metrewave Radio Telescope at 325 and 610 MHz. We find this cluster to host a faint (S610 = 5.6 +/- 1.4mJy) radio halo with an angular extent of 2.6 arcmin, corresponding to 0.8 Mpc at the cluster redshift, qualifying it as a GRH. J0256 is one of the lowest mass systems, M500, SZ = (5.0 +/- 1.2) × 10(exp14) M, found to host a GRH. We measure the GRH at lower significance at 325 MHz (S325 = 10.3 +/- 5.3mJy), obtaining a spectral index measurement of α610 325 = 1.0+ 0.7 − 0.9. This result is consistent with the mean spectral index of the population of typical radio haloes, alpha = 1.2 +/- 0.2. Adopting the latter value, we determine a 1.4 GHz radio power of P1.4 GHz = (1.0 +/- 0.3) × 10(exp 24)W/Hz, placing this cluster within the scatter of known scaling relations. Various lines of evidence, including the intracluster medium morphology, suggest that ACT-CL J0256.5+ 0006 is composed of two subclusters. We determine a merger mass ratio of 7:4, and a line-of-sight velocity difference of v⊥ = 1880 +/- 210 km/s. We construct a simple merger model to infer relevant time-scales in the merger. From its location on the P1.4GHz-LX scaling relation, we infer that we observe ACT-CL J0256.5+ 0006 just before first core crossing.

Knowles, Kendra↗
NASA NTRS2018

Bow Shock in Merging Cluster A520: The Edge of the Radio Halo and the Electron-Proton Equilibration Timescale

We studied the prominent bow shock in the merging galaxy cluster A520 using a deep Chandra X-ray observation and archival VLA radio data. This shock is a useful diagnostic tool, owing to its clear geometry and relatively high Mach number. At the "nose" of the shock, we measure a Mach number of M=2.4(sup 0.4, sub -0.2). The shock becomes oblique away from the merger axis, with the Mach number falling to approx. 1.6 around 30 deg from the nose. The electron temperature immediately behind the shock nose is consistent with that from the Rankine-Hugoniot adiabat, and is higher (at a 95% confidence) than expected for adiabatic compression of electrons followed by Coulomb electron-proton equilibration, indicating the presence of equilibration mechanisms faster than Coulomb collisions. This is similar to an earlier finding for the Bullet cluster. We also combined four archival VLA data sets to obtain a better image of the cluster's giant radio halo at 1.4 GHz. An abrupt edge of the radio halo traces the shock front, and no emission is detected in the pre-shock region. If the radio edge were due only to adiabatic compression of relativistic electrons in pre-shock plasma, we would expect a pre-shock radio emission detectable in this radio data set; however, an interferometric artifact dominates the uncertainty, so we cannot rule this model out. Other interesting features of the radio halo include a peak at the remnant of the cool core, suggesting that the core used to have a radio minihalo, and a peak marking a possible region of high turbulence.

Wang, Qian H. S.↗
NASA NTRS2026

Gateway Element and Payload Materials Outgassing Analyses: HALO, HERMES, and ERSA

Gateway was intended to be humanity’s first space station around the Moon, but its development has been paused as the National Aeronautics and Space Administration (NASA) shifts focus to achieving the United States’ National Space Policy goals. Instead of an orbiting lunar outpost, NASA will now pursue the development of a lunar surface base to support a sustained human presence on the Moon. Before the program’s pause, Gateway’s Induced Environments team worked to ensure payloads and elements (i.e., modules) complied with induced environment requirements. Methods developed and insights gained from this work will have applicability to NASA’s Moon Base and the potential repurposing of Gateway elements and payloads, as well as to induced environments modeling for future space stations. The Gateway program’s induced environment included molecular contamination, electric thruster plume sputter and redeposition, and lunar dust transfer from the Human Landing System (HLS). Primary sources of external molecular contamination included materials outgassing, chemical thruster plume contamination, and vacuum venting. The focus of this paper will be on element- and payload-level materials outgassing analyses performed for Gateway Configuration 1, extending the previously-developed framework for Gateway system-level external molecular contamination modeling. Gateway Configuration 1 consisted of the Power and Propulsion Element (PPE) and the Habitation and Logistics Outpost (HALO). It also included payloads like the European Radiation Sensor Array (ERSA) attached to PPE and the Heliophysics Environmental and Radiation Measurement Experiment Suite (HERMES) attached to HALO. The element- and payload-level analyses to be introduced in this paper for HALO, HERMES, and ERSA enabled high-fidelity descriptions of Gateway’s external molecular contamination environment. Approaches to geometric modeling, meshing, outgassing rate assignment, molecular transport modeling, and analysis methodology will be presented. Element and payload contaminant deposition onto sensitive Gateway receiver surfaces will be summarized and results compared to induced environment requirements. While these results incorporate refinements made over the course of the program, they were not intended to be final. Therefore, modeling assumptions and inputs, potential improvements, and lessons-learned will be documented to inform future work on Moon Base, repurposed elements and payloads, and other space stations.

Gateway↗
DOE OSTI2025

Dwarf galaxy halo masses from spectroscopic and photometric lensing in DESI and DES

We present the most precise and lowest-mass weak lensing measurements of dwarf galaxies to date, enabled by spectroscopic lenses from the Dark Energy Spectroscopic Instrument (DESI) and photometric lenses from the Dark Energy Survey (DES) calibrated with DESI redshifts. Using DESI spectroscopy from the first data release, we construct clean samples of galaxies with median stellar masses $\log_{10}(M_*/M_{\odot})=8.3-10.1$ and measure their weak lensing signals with sources from DES, KiDS, and SDSS, achieving detections with $S/N$ up to 14 for dwarf galaxies ($\log_{10}(M_*/M_{\odot})<$9.25) -- opening up a new regime for lensing measurements of low-mass systems. Leveraging DES photometry calibrated with DESI, we extend to a photometric dwarf sample of over 700,000 galaxies, enabling robust lensing detections of dwarf galaxies with combined $S/N=38$ and a significant measurement down to $\log_{10}(M_*/M_{\odot})=8.0$. We show that the one-halo regime (scales $\lesssim 0.15h^{-1}\rm Mpc$) is insensitive to various systematic and sample selection effects, providing robust halo mass estimates, while the signal in the two-halo regime depends on galaxy color and environment. These results demonstrate that DESI already enables precise dwarf lensing measurements, and that calibrated photometric samples extend this capability. Together, they pave the way for novel constraints on dwarf galaxy formation and dark matter physics with upcoming surveys like the Vera C. Rubin Observatory's LSST.

Treiber, Helena [Princeton U., Astrophys. Sci. Dep↗
DOE OSTI2026

Brightest Cluster Galaxy ellipticity as proxy for halo shape: Orientation bias, assembly bias, and potential selection effects in SZ-selected clusters

The orientation of triaxial galaxy clusters with respect to the line-of-sight is expected to be one of the prime sources of scatter and potential bias in optical observables (e.g., richness and weak-lensing signal) of galaxy clusters. In this work, we use the observed shape of the central Brightest Cluster Galaxy (BCG) as proxy for the orientation along the line-of-sight for clusters selected via the Sunyaev-Zel'dovich (SZ) effect from the South Pole Telescope (SPT) and Atacama Cosmology Telescope (ACT) surveys, matched to optically selected clusters from the Dark Energy Survey Year 3 (DES). We construct two samples of clusters that are designed to be identical in SZ mass estimate and redshift but with the roundest vs. the most elliptical BCGs, which we expect to correspond to BCGs (and clusters) with major axes aligned along the line-of-sight vs. in the plane of the sky, respectively. We find that the optical richness of round-BCG clusters is $\sim 10$% larger than that of elliptical-BCG clusters, in agreement with the expectation from projection effects and presenting the first such detection in data. The density profiles, however, are not in agreement with the expectation from projection effects: the 1-halo term (below $6~h^{-1}\rm{Mpc}$) of both the weak-lensing and galaxy density profiles are the same for the subsamples, contrary to previous studies based on X-ray selected clusters. In the 2-halo regime (above $6~h^{-1}\rm{Mpc}$), we find a significant excess of the elliptical-BCG cluster profiles compared to the round-BCG cluster profiles, which is the opposite of the expectation from numerical simulations. We hypothesize that the intrinsic shape of the BCG reflects not just the orientation angle, but also intrinsic properties of the cluster which can affect both the SZ signal and the amplitude of the 2-halo term.

Srinivasan, Radhakrishnan [SUNY, Stony Brook] (ORC↗
DOE OSTI2024

Differentiable stochastic halo occupation distribution

ABSTRACT In this work, we demonstrate how differentiable stochastic sampling techniques developed in the context of deep reinforcement learning can be used to perform efficient parameter inference over stochastic, simulation-based, forward models. As a particular example, we focus on the problem of estimating parameters of halo occupation distribution (HOD) models that are used to connect galaxies with their dark matter haloes. Using a combination of continuous relaxation and gradient re-parametrization techniques, we can obtain well-defined gradients with respect to HOD parameters through discrete galaxy catalogue realizations. Having access to these gradients allows us to leverage efficient sampling schemes, such as Hamiltonian Monte Carlo, and greatly speed up parameter inference. We demonstrate our technique on a mock galaxy catalogue generated from the Bolshoi simulation using a standard HOD model and find near-identical posteriors as standard Markov chain Monte Carlo techniques with an increase of ∼8× in convergence efficiency. Our differentiable HOD model also has broad applications in full forward model approaches to cosmic structure and cosmological analysis.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Galactic Bar Resonances with Diffusion: An Analytic Model with Implications for Bar–Dark Matter Halo Dynamical Friction

Abstract The secular evolution of disk galaxies is largely driven by resonances between the orbits of “particles” (stars or dark matter) and the rotation of non-axisymmetric features (spiral arms or a bar). Such resonances may also explain kinematic and photometric features observed in the Milky Way and external galaxies. In simplified cases, these resonant interactions are well understood: for instance, the dynamics of a test particle trapped near a resonance of a steadily rotating bar is easily analyzed using the angle-action tools pioneered by Binney, Monari, and others. However, such treatments do not address the stochasticity and messiness inherent to real galaxies—effects that have, with few exceptions, been previously explored only with complex N -body simulations. In this paper, we propose a simple kinetic equation describing the distribution function of particles near an orbital resonance with a rigidly rotating bar, allowing for diffusion of the particles’ slow actions. We solve this equation for various values of the dimensionless diffusion strength Δ, and then apply our theory to the calculation of bar–halo dynamical friction. For Δ = 0, we recover the classic result of Tremaine and Weinberg that friction ultimately vanishes, owing to the phase mixing of resonant orbits. However, for Δ > 0, we find that diffusion suppresses phase mixing, leading to a finite torque. Our results suggest that stochasticity—be it physical or numerical—tends to increase bar–halo friction, and that bars in cosmological simulations might experience significant artificial slowdown, even if the numerical two-body relaxation time is much longer than a Hubble time.

79 ASTRONOMY AND ASTROPHYSICS↗