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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

CoSn-type NiIn1–xSbx (0 ≤ x ≤ 0.17): Site-Selective Substitution, Electronic Structure, Chemical Bonding, and Structural Transformation

CoSn-type intermetallic compounds have emerged as a model platform for Kagome-derived flat-band physics, where subtle chemical perturbations can strongly influence electronic structure and phase stability. Here, we present a combined experimental and theoretical study of Sb-substitution in CoSn-type NiIn1–xSbx (0 ≤ x ≤ 0.17) to elucidate the interplay between site selectivity, solubility limit, chemical bonding, and electronic structure. Rietveld refinements on Neutron powder diffraction data confirmed the selective Sb-substitution at the electron-rich In2 (2d) site forming the honeycomb substructure, while the In1 (1a) site within the Kagome layer remains exclusively occupied by In. Density functional theory (DFT) calculations revealed that pristine CoSn-type NiIn hosts Ni 3d-dominated flat bands near the Fermi level (EF), originating from the Kagome-like Ni substructure. Partial replacement of In by Sb within the honeycomb layer alters these flat-band features below EF, reducing the density of states and suppressing the flat-band topology near the Fermi level. Orbital-resolved electronic structure and chemical-bonding analyses show that Sb-substitution enhances Ni-p-block (In/Sb) covalency and optimizes charge compensation, stabilizing the CoSn-type structure up to the solubility limit x ≈ 0.17. Beyond the limit, the higher-Sb compositions show satellite reflections consistent with an incommensurately modulated phase. These results establish a link between site-selective chemical substitution, bonding optimization, and flat-band electronic structure evolution, providing fundamental insights into how chemical substitution influences the electronic properties of Kagome-based intermetallic compounds.

Roy, Nilanjan [National Institute of Technology Si↗
DOE OSTI2019

Computing Relative Binding Affinity of Ligands to Receptor: An Effective Hybrid Single-Dual-Topology Free-Energy Perturbation Approach in NAMD

An effective hybrid single-dual-topology protocol is designed for the calculation of relative binding affinities of small ligands to a receptor. The protocol was developed as an extension of the NAMD molecular dynamics program, which exclusively supports a dual-topology framework for relative alchemical free-energy perturbation (FEP) calculations. Here, the alchemical end states are represented as two separate molecules sharing a common substructure identified through maximum structural mapping. Within the substructure, an atom-to-atom correspondence is established, and each pair of corresponding atoms is holonomically constrained to share identical coordinates at all time throughout the simulation. The forces are projected and combined at each step for propagation. Following this formulation, a set of illustrative calculations of reliable experiment/simulation data, including relative solvation free energies of small molecules and relative binding affinities of drug compounds to proteins, are presented. To enhance sampling of the dual-topology region, the FEP calculations were carried out within a replica-exchange MD scheme supported by the multiple-copy algorithm module of NAMD, with periodically attempted swapping of the thermodynamic coupling parameter lambda between neighboring states. The findings are consistent with experiments and benchmarks reported in the literature, lending support to the validity of the current protocol. In summary, this hybrid single-dual-topology approach combines the conceptual simplicity of the dual-topology paradigm with the advantageous sampling efficiency of the single-topology method, making it an ideal strategy for high-throughput in silico drug design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Higher Dimensionality in the Mg–Co–B System: Synthesis and Structure of Incommensurate Composite Mg 1+ε Co 4 B 4

Guided by high-temperature in situ X-ray diffraction, the discovery and synthesis of Mg 1+ε Co 4 B 4 (ε ≈ 0.272) using a MgH 2 hydride precursor is reported, along with a detailed crystal structure description and measurement of magnetic properties. The mismatch in lattice periodicities between Mg and Co–B substructures places Mg 1+ε Co 4 B 4 in the family of incommensurate composite crystals and prompted structural refinement in a (3 + 1)-dimensional model. The structure of Mg 1+ε Co 4 B 4 (P4 2 /ncm(00γ)s00s, a = 6.75847(7) Å, c = 3.94007(8) Å, q = (0, 0, 1.2721(3))) was refined from neutron powder diffraction and high-resolution powder X-ray diffraction data and confirmed by scanning transmission electron microscopy and electron diffraction. Mg 1+ε Co 4 B 4 is isostructural to Nd 1+ε Fe 4 B 4 and several related ternary borides with 0.07 ≤ ε ≤ 0.17, with Mg occupying the rare-earth site. Satellite reflections in the electron diffraction patterns hinted at positional modulation of the transition metal–boron substructure by Mg atoms, but this could not be refined from the neutron or X-ray diffraction data. Low-temperature magnetic measurements show no indications of long-range magnetic ordering or superconductivity down to 5 K. DFT calculations confirmed the absence of a magnetically ordered ground state and the stability of a 5:4 supercell (ε = 0.25) relative to the fully commensurate structure. Neutron diffraction and synthesis from elemental Mg demonstrated that Mg 1+ε Co 4 B 4 is not a hydrogen-stabilized phase. Mg 1+ε Co 4 B 4 represents the second compound reported in the Mg–Co–B system and the first superspace symmetry model of a Nd 1+ε Fe 4 B 4 -type incommensurate composite compound refined from powder diffraction data.

chemical structure↗
DOE OSTI2018

Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these interactions in the form of stellar streams, substructures, and chemically distinct stellar components. The impact of dwarf galaxy mergers on the content and morphology of the Galactic disk is still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups, which may have extragalactic origin. However, there is mounting evidence that stellar overdensities at the outer disk/halo interface could have been caused by the interaction of a dwarf galaxy with the disk. Here we report detailed spectroscopic analysis of 14 stars drawn from two stellar overdensities, each lying about 5 kiloparsecs above and below the Galactic plane - locations suggestive of association with the stellar halo. However, we find that the chemical compositions of these stars are almost identical, both within and between these groups, and closely match the abundance patterns of the Milky Way disk stars. This study hence provides compelling evidence that these stars originate from the disk and the overdensities they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Characterization and dynamics of the peculiar stream Jhelum: A tentative role for the Sagittarius dwarf galaxy

Stellar streams are a promising tool to study the Milky Way’s dark matter subhalo population, as interactions with subhalos are expected to leave visible imprints in the streams in the form of substructure. However, there may be other causes of substructure. Here we studied the kinematics and the unusual morphology of the stellar stream Jhelum. Using a combination of ground-based photometry and Gaia EDR3 astrometry, we characterized the morphology of Jhelum. We combined this new data with radial velocities from the literature to perform orbit integrations of the stream in static Galactic potentials. We also carried out N-body simulations in the presence of the Sagittarius dwarf galaxy. The new data reveal a previously unreported tertiary component in the stream, as well as several gaps and a kink-like feature in its narrow component. We find that for a range of realistic Galactic potentials, no single orbit is able to reproduce Jhelum’s radial velocity data entirely. A generic property of the orbital solutions is that they share a similar orbital plane to Sagittarius and this leads to repeated encounters with the stream. Using N-body simulations that include a massive Sagittarius, we explored its effect on Jhelum, and we show that these encounters are able to qualitatively reproduce the narrow and broad components in Jhelum, as well as create a tertiary component in some cases. We also find evidence that such encounters can result in an apparent increase in the velocity dispersion of the stream by a factor up to four due to overlapping narrow and broad components. Our findings suggest that the Jhelum stream is even more complex than once thought; however, its morphology and kinematics can tentatively be explained via the interactions with Sagittarius. In this scenario, the formation of Jhelum’s narrow and broad components occurs naturally, yet some of the smaller gap-like features remain to be explained.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Optical/X-ray/radio view of Abell 1213: A galaxy cluster with anomalous diffuse radio emission

Context. Abell 1213, a low-richness galaxy system, is known to host an anomalous radio halo detected in data of the Very Large Array (VLA). It is an outlier with regard to the relation between the radio halo power and the X-ray luminosity of the parent clusters. Aims. Our aim is to analyze the cluster in the optical, X-ray, and radio bands to characterize the environment of its diffuse radio emission and to shed new light on its nature. Methods. We used optical data from the Sloan Digital Sky Survey to study the internal dynamics of the cluster. We also analyzed archival XMM-Newton X-ray data to unveil the properties of its hot intracluster medium. Finally, we used recent data from the LOw Frequency ARray (LOFAR) at 144 MHz, together with VLA data at 1.4 GHz, to study the spectral behavior of the diffuse radio source. Results. Both our optical and X-ray analysis reveal that this low-mass cluster exhibits disturbed dynamics. In fact, it is composed of several galaxy groups in the peripheral regions and, in particular, in the core, where we find evidence of substructures oriented in the NE–SW direction, with hints of a merger nearly along the line of sight. The analysis of the X-ray emission adds further evidence that the cluster is in an unrelaxed dynamical state. At radio wavelengths, the LOFAR data show that the diffuse emission is ~510 kpc in size. Moreover, there are hints of low-surface-brightness emission permeating the cluster center. Conclusions. The environment of the diffuse radio emission is not what we would expect for a classical halo. The spectral index map of the radio source is compatible with a relic interpretation, possibly due to a merger in the N–S or NE–SW directions, in agreement with the substructures detected through the optical analysis. The fragmented, diffuse radio emissions at the cluster center could be attributed to the surface brightness peaks of a faint central radio halo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Large grain CBMM Nb ingot slices: An ideal test bed for exploring the microstructure-electromagnetic property relationships relevant to SRF

High purity (RRR > 200), large grain (> 5-10 cm) niobium ingot slices have been successfully used to fabricate radio frequency (RF) cavities for particle accelerators. They offer significantly reduced fabrication cost by eliminating processing steps and furthermore they provide the opportunity to study the influence of individual grain boundaries in SRF Nb. Here we summarize our measurements of grain boundary (GB) effects on the superconducting properties of large grain high purity niobium sheet manufactured by CBMM. We show by magneto-optical (MO) imaging that GBs allow premature flux penetration, but only when they are oriented close to the direction of the magnetic field. However, even low angle GBs produced by minor deformations commensurate with half-cell forming produce localized flux penetration. The transport properties of grain boundaries were investigated by direct transport across them and evidence for preferential vortex flow along the GBs of SRF Nb was observed for the first time. Using transmission electron microscopy (TEM) and micro crystallographic analysis with electron backscattered diffraction (EBSD), we were able to quantitatively characterize surface substructures that can lead to localized thermal breakdown of superconductivity. Important to these studies was the development of sample preparation techniques that made the cutout single, bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Defining the layers of a sensory cilium with STORM and cryoelectron nanoscopy

Primary cilia carry out numerous signaling and sensory functions, and defects in them, “ciliopathies,” cause a range of symptoms, including blindness. Understanding of their nanometer-scale ciliary substructures and their disruptions in ciliopathies has been hindered by limitations of conventional microscopic techniques. In this work, we have combined cryoelectron tomography, enhanced by subtomogram averaging, with superresolution stochastic optical reconstruction microscopy (STORM) to define subdomains within the light-sensing rod sensory cilium of mouse retinas and reveal previously unknown substructures formed by resident proteins. Domains are demarcated by structural features such as the axoneme and its connections to the ciliary membrane, and are correlated with molecular markers of subcompartments, including the lumen and walls of the axoneme, the membrane glycocalyx, and the intervening cytoplasm. Within this framework, we report spatial distributions of key proteins in wild-type (WT) mice and the effects on them of genetic deficiencies in 3 models of Bardet–Biedl syndrome.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

NEAR-INFRARED K AND L' FLUX RATIOS IN SIX LENSED QUASARS

We examine the wavelength dependence of flux ratios for six gravitationally lensed quasars using K and L' images obtained at the Gemini North 8 m telescope. We select lenses with source redshifts z{sub s} < 2.8 so that K-band images probe rest-frame optical emission from accretion disks, while L'-band images probe rest-frame near-infrared flux emitted (in part) from the more extended surrounding torus. Since the observations correspond to different source sizes, the K and L' flux ratios are sensitive to structure on different scales and may be useful for studying small structure in the lens galaxies. Four of the six lenses show differences between K and L' flux ratios. In HE 0435-1223, SDSS 0246-0825, and HE 2149-2745, the differences may be attributable to known microlensing and/or intrinsic variability. In SDSS 0806+2006, the wavelength dependence is not easily attributed to known variations and may indicate the presence of substructure. By contrast, in Q0142-100 and SBS 0909+523 the K and L' flux ratios are consistent within the uncertainties. We discuss the utility of the current data for studying chromatic effects related to microlensing, dust extinction, and dark matter substructure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

SDSS-III: MASSIVE SPECTROSCOPIC SURVEYS OF THE DISTANT UNIVERSE, THE MILKY WAY, AND EXTRA-SOLAR PLANETARY SYSTEMS

Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS Data Release 8 (DR8), which was made public in 2011 January and includes SDSS-I and SDSS-II images and spectra reprocessed with the latest pipelines and calibrations produced for the SDSS-III investigations. This paper presents an overview of the four surveys that comprise SDSS-III. The Baryon Oscillation Spectroscopic Survey will measure redshifts of 1.5 million massive galaxies and Ly{alpha} forest spectra of 150,000 quasars, using the baryon acoustic oscillation feature of large-scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z < 0.7 and at z {approx} 2.5. SEGUE-2, an already completed SDSS-III survey that is the continuation of the SDSS-II Sloan Extension for Galactic Understanding and Exploration (SEGUE), measured medium-resolution (R = {lambda}/{Delta}{lambda} {approx} 1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE, the Apache Point Observatory Galactic Evolution Experiment, will obtain high-resolution (R {approx} 30,000), high signal-to-noise ratio (S/N {>=} 100 per resolution element), H-band (1.51 {mu}m < {lambda} < 1.70 {mu}m) spectra of 10{sup 5} evolved, late-type stars, measuring separate abundances for {approx}15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m s{sup -1}, {approx}24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. As of 2011 January, SDSS-III has obtained spectra of more than 240,000 galaxies, 29,000 z {>=} 2.2 quasars, and 140,000 stars, including 74,000 velocity measurements of 2580 stars for MARVELS.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

The LAMOST survey of background quasars in the vicinity of the Andromeda and Triangulum galaxies. II. Results from the commissioning observations and the pilot surveys

We present new quasars discovered in the vicinity of the Andromeda and Triangulum galaxies with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also named the Guoshoujing Telescope, during the 2010 and 2011 observational seasons. Quasar candidates are selected based on the available Sloan Digital Sky Survey, Kitt Peak National Observatory 4 m telescope, Xuyi Schmidt Telescope Photometric Survey optical, and Wide-field Infrared Survey Explorer near-infrared photometric data. We present 509 new quasars discovered in a stripe of ∼135 deg{sup 2} from M31 to M33 along the Giant Stellar Stream in the 2011 pilot survey data sets, and also 17 new quasars discovered in an area of ∼100 deg{sup 2} that covers the central region and the southeastern halo of M31 in the 2010 commissioning data sets. These 526 new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to 3.2. They represent a significant increase of the number of identified quasars in the vicinity of M31 and M33. There are now 26, 62, and 139 known quasars in this region of the sky with i magnitudes brighter than 17.0, 17.5, and 18.0, respectively, of which 5, 20, and 75 are newly discovered. These bright quasars provide an invaluable collection with which to probe the kinematics and chemistry of the interstellar/intergalactic medium in the Local Group of galaxies. A total of 93 quasars are now known with locations within 2.°5 of M31, of which 73 are newly discovered. Tens of quasars are now known to be located behind the Giant Stellar Stream, and hundreds are behind the extended halo and its associated substructures of M31. The much enlarged sample of known quasars in the vicinity of M31 and M33 can potentially be utilized to construct a perfect astrometric reference frame to measure the minute proper motions (PMs) of M31 and M33, along with the PMs of substructures associated with the Local Group of galaxies. Those PMs are some of the most fundamental properties of the Local Group.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Probing for exoplanets hiding in dusty debris disks: Disk imaging, characterization, and exploration with HST/STIS multi-roll coronagraphy

Spatially resolved scattered-light images of circumstellar debris in exoplanetary systems constrain the physical properties and orbits of the dust particles in these systems. They also inform on co-orbiting (but unseen) planets, the systemic architectures, and forces perturbing the starlight-scattering circumstellar material. Using Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) broadband optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in a sample of 10 circumstellar debris systems and 1 'mature' protoplanetrary disk, all with HST pedigree, using point-spread-function-subtracted multi-roll coronagraphy. These observations probe stellocentric distances ≥5 AU for the nearest systems, and simultaneously resolve disk substructures well beyond corresponding to the giant planet and Kuiper Belt regions within our own solar system. They also disclose diffuse very low-surface-brightness dust at larger stellocentric distances. Herein we present new results inclusive of fainter disks such as HD 92945 (F {sub disk}/F {sub star} = 5 × 10{sup –5}), confirming, and better revealing, the existence of a narrow inner debris ring within a larger diffuse dust disk. Other disks with ring-like substructures and significant asymmetries and complex morphologies include HD 181327, for which we posit a spray of ejecta from a recent massive collision in an exo-Kuiper Belt; HD 61005, suggested to be interacting with the local interstellar medium; and HD 15115 and HD 32297, also discussed in the context of putative environmental interactions. These disks and HD 15745 suggest that debris system evolution cannot be treated in isolation. For AU Mic's edge-on disk, we find out-of-plane surface brightness asymmetries at ≥5 AU that may implicate the existence of one or more planetary perturbers. Time-resolved images of the MP Mus protoplanetary disk provide spatially resolved temporal variability in the disk illumination. These and other new images from our HST/STIS GO/12228 program enable direct inter-comparison of the architectures of these exoplanetary debris systems in the context of our own solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MAPPING THE GALACTIC HALO WITH BLUE HORIZONTAL BRANCH STARS FROM THE TWO-DEGREE FIELD QUASAR REDSHIFT SURVEY

We use 666 blue horizontal branch stars from the 2Qz Redshift Survey to map the Galactic halo in four dimensions (position, distance, and velocity). We find that the halo extends to at least 100 kpc in Galactocentric distance, and obeys a single power-law density profile of index {approx}-2.5 in two different directions separated by about 150{sup 0} on the sky. This suggests that the halo is spherical. Our map shows no large kinematically coherent structures (streams, clouds, or plumes) and appears homogeneous. However, we find that at least 20% of the stars in the halo reside in substructures and that these substructures are dynamically young. The velocity dispersion profile of the halo appears to increase toward large radii while the stellar velocity distribution is non-Gaussian beyond 60 kpc. We argue that the outer halo consists of a multitude of low luminosity overlapping tidal streams from recently accreted objects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE NORTHERN WRAPS OF THE SAGITTARIUS STREAM AS TRACED BY RED CLUMP STARS: DISTANCES, INTRINSIC WIDTHS, AND STELLAR DENSITIES

We trace the tidal Stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Red Clump (RC) stars from the catalog of the Sloan Digital Sky Survey-Data Release 6, in the range 150{sup 0} {approx}< R.A. {approx}< 220{sup 0}, corresponding to the range of orbital azimuth 220{sup 0} {approx}< {Lambda} {approx}< 290{sup 0}. Substructures along the line of sight (los) are identified as significant peaks in the differential star count profiles (SCPs) of candidate RC stars. A proper modeling of the SCPs allows us to obtain (1) {<=}10% accurate, purely differential distances with respect to the main body of Sgr, (2) estimates of the FWHM along the los, and (3) estimates of the local density, for each detected substructure. In the range 255{sup 0} {approx}< {Lambda} {approx}< 290{sup 0} we cleanly and continuously trace various coherent structures that can be ascribed to the Stream, in particular: the well-known northern portion of the leading arm, running from d {approx_equal} 43 kpc at {Lambda} {approx_equal} 290{sup 0} to d {approx_equal} 30 kpc at {Lambda} {approx_equal} 255{sup 0}, and a more nearby coherent series of detections lying at a constant distance d {approx_equal} 25 kpc, that can be identified with a wrap of the trailing arm. The latter structure, predicted by several models of the disruption of Sgr dSph, was never traced before; comparison with existing models indicates that the difference in distance between these portions of the leading and trailing arms may provide a powerful tool to discriminate between theoretical models assuming different shapes of the Galactic potential. A further, more distant wrap in the same portion of the sky is detected only along a couple of los. For {Lambda} {approx}< 255{sup 0} the detected structures are more complex and less easily interpreted. We are confident of being able to trace the continuation of the leading arm down to {Lambda} {approx_equal} 220{sup 0} and d {approx_equal} 20 kpc; the trailing arm is seen up to {Lambda} {approx_equal} 240{sup 0} where it is replaced by more distant structures. Possible detections of more nearby wraps and of the Virgo Stellar Stream are also discussed. These measured properties provide a coherent set of observational constraints for the next generation of theoretical models of the disruption of Sgr.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

FIBRILLAR CHROMOSPHERIC SPICULE-LIKE COUNTERPARTS TO AN EXTREME-ULTRAVIOLET AND SOFT X-RAY BLOWOUT CORONAL JET

We observe an erupting jet feature in a solar polar coronal hole, using data from Hinode/Solar Optical Telescope (SOT), Extreme Ultraviolet Imaging Spectrometer (EIS), and X-Ray Telescope (XRT), with supplemental data from STEREO/EUVI. From extreme-ultraviolet (EUV) and soft X-ray (SXR) images we identify the erupting feature as a blowout coronal jet: in SXRs it is a jet with a bright base, and in EUV it appears as an eruption of relatively cool ({approx}50,000 K) material of horizontal size scale {approx}30'' originating from the base of the SXR jet. In SOT Ca II H images, the most pronounced analog is a pair of thin ({approx}1'') ejections at the locations of either of the two legs of the erupting EUV jet. These Ca II features eventually rise beyond 45'', leaving the SOT field of view, and have an appearance similar to standard spicules except that they are much taller. They have velocities similar to that of 'type II' spicules, {approx}100 km s{sup -1}, and they appear to have spicule-like substructures splitting off from them with horizontal velocity {approx}50 km s{sup -1}, similar to the velocities of splitting spicules measured by Sterling et al. Motions of splitting features and of other substructures suggest that the macroscopic EUV jet is spinning or unwinding as it is ejected. This and earlier work suggest that a subpopulation of Ca II type II spicules are the Ca II manifestation of portions of larger scale erupting magnetic jets. A different subpopulation of type II spicules could be blowout jets occurring on a much smaller horizontal size scale than the event we observe here.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A COMBINED LOW-RADIO FREQUENCY/X-RAY STUDY OF GALAXY GROUPS. I. GIANT METREWAVE RADIO TELESCOPE OBSERVATIONS AT 235 MHz AND 610 MHz

We present new Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz of 18 X-ray bright galaxy groups. These observations are part of an extended project, presented here and in future papers, which combines low-frequency radio and X-ray data to investigate the interaction between central active galactic nuclei (AGNs) and the intra-group medium (IGM). The radio images show a very diverse population of group-central radio sources, varying widely in size, power, morphology, and spectral index. Comparison of the radio images with Chandra and XMM-Newton X-ray images shows that groups with significant substructure in the X-ray band and marginal radio emission at {approx}>1 GHz host low-frequency radio structures that correlate with substructures in IGM. Radio-filled X-ray cavities, the most evident form of AGN/IGM interaction in our sample, are found in half of the systems and are typically associated with small, low-, or mid-power double radio sources. Two systems, NGC5044 and NGC4636, possess multiple cavities, which are isotropically distributed around the group center, possibly due to group weather. In other systems the radio/X-ray correlations are less evident. However, the AGN/IGM interaction can manifest itself through the effects of the high-pressure medium on the morphology, spectral properties, and evolution of the radio-emitting plasma. In particular, the IGM can confine fading radio lobes in old/dying radio galaxies and prevent them from dissipating quickly. Evidence for radio emission produced by former outbursts that co-exist with current activity is found in six groups of the sample.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A COSMIC COINCIDENCE: THE POWER-LAW GALAXY CORRELATION FUNCTION

We model the evolution of galaxy clustering through cosmic time to investigate the nature of the power-law shape of {xi}(r), the galaxy two-point correlation function. While {xi}(r) at large scales is set by primordial fluctuations, departures from a power law are governed by galaxy pair counts at small scales, subject to nonlinear dynamics. We assume that galaxies reside within dark matter halos and subhalos. Therefore, the shape of the correlation function at small scales depends on the amount of halo substructure. We use a semi-analytic substructure evolution model to study subhalo populations within host halos. We find that tidal mass loss and, to a lesser extent, dynamical friction dramatically deplete the number of subhalos within larger host halos over time, resulting in a {approx}90% reduction by z = 0 compared to the number of distinct mergers that occur during the assembly of a host halo. We show that these nonlinear processes resulting in this depletion are essential for achieving a power law {xi}(r). We investigate how the shape of {xi}(r) depends on subhalo mass (or luminosity) and redshift. We find that {xi}(r) breaks from a power law at high masses, implying that only galaxies of luminosities {approx}< L{sub *} should exhibit power-law clustering. Moreover, we demonstrate that {xi}(r) evolves from being far from a power law at high redshift, toward a near power-law shape at z = 0. We argue that {xi}(r) will once again evolve away from a power law in the future. This is in large part caused by the evolving competition between the accretion and destruction rates of subhalos over time, which happen to strike just the right balance at z {approx} 0. We then investigate the conditions required for {xi}(r) to be a power law in a general context. We use the halo model, along with simple parameterizations of the halo occupation distribution, to probe galaxy occupation at various masses and redshifts. We show that the key ingredients determining the shape of {xi}(r) are the fraction of galaxies that are satellites, the relative difference in mass between the halos of isolated galaxies and halos that contain a single satellite on average, and the rareness of halos that host galaxies. These pieces are intertwined and we find no simple, universal rule for which a power law {xi}(r) will occur. However, we do show that the physics responsible for setting the galaxy content of halos do not care about the conditions needed to achieve a power law {xi}(r) and that these conditions are met only in a narrow mass and redshift range. We conclude that the power-law nature of {xi}(r) for L{sub *} and fainter galaxy samples at low redshift is a cosmic coincidence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

STRUCTURE AND POPULATION OF THE NGC 55 STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY

As part of our survey of galactic stellar halos, we investigate the structure and stellar populations of the northern outer part of the stellar halo in NGC 55, a member galaxy of the Sculptor Group, using deep and wide-field V- and I-band images taken with Subaru/Suprime-Cam. Based on the analysis of the color-magnitude diagrams for red giant branch (RGB) stars, we derive a tip of RGB based distance modulus to the galaxy of (m - M){sub 0} = 26.58 {+-} 0.11(d = 2.1 {+-} 0.1 Mpc). From the stellar density maps, we detect the asymmetrically disturbed, thick disk structure and two metal-poor overdense substructures in the north region of NGC 55, which may correspond to merger remnants associated with hierarchical formation of NGC 55's halo. In addition, we identify a diffuse metal-poor halo extended out to at least z {approx} 16 kpc from the galactic plane. The surface brightness profiles toward the z-direction perpendicular to the galactic plane suggest that the stellar density distribution in the northern outer part of NGC 55 is described by a locally isothermal disk at z {approx}< 6 kpc and a likely diffuse metal-poor halo with V-band surface brightness of {mu}{sub V} {approx}> 32 mag arcsec{sup -2}, where old RGB stars dominate. We derive the metallicity distributions (MDs) of these structures on the basis of the photometric comparison of RGB stars with the theoretical stellar evolutionary models. The MDs of the thick disk structures show the peak and mean metallicity of [Fe/H]{sub peak} {approx} -1.4 and [Fe/H]{sub mean} {approx} -1.7, respectively, while the outer substructures show more metal-poor features than the thick disk structure. Combined with the current results with our previous study for M31's halo, we discuss the possible difference in the formation process of stellar halos among different Hubble types.

79 ASTRONOMY AND ASTROPHYSICS↗