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NASA NTRS1994

Preliminary evidence for dust in galactic halos

I use B and I photometry of distant galaxies observed through the halos of two nearby spiral galaxies, NGC 2835 and NGC 3521, to test for the existence of dust in galactic halos out to at least a radius of 60 kpc. B - I colors of background galaxies in fields centered along the nearby galaxy's major axis at a projected separation of 60 kpc are compared to the colors of background galaxies in fields centered at a projected separation of about 220 kpc. Background galaxies in the fields at smaller projected separations have average B - I colors that are 0.067 +/- 0.033 mag redder than those in the outer fields. Such a result will occur by chance less than 2.2% of the time and so is taken as preliminary evidence that galaxy halos contain more dust at galactic radii of 60 than 220 kpc. A model which assumes that the radial dust profile in galactic disks and halos is a single exponential has a corresponding scale length of 31 +/- 8 kpc. I argue on the basis of the Infrared Astronomy Satellite (IRAS) 100 micron flux maps that absorption by Galactic dust is not responsible for this result and briefly discuss connections between this result and other observations of the baryonic component of galaxy halos.

Zaritsky, Dennis↗
NASA NTRS1994

Synoptic interpretation of measurements from HALOE

The degree to which the Southern Hemisphere polar vortex is isolated against horizontal (isentropic) mixing is investigated using data from the Halogen Occultation Experiment (HALOE), U.K. Meteorological Office (UKMO) potential vorticity (PV), and contour advection diagnostics. Measurements of methane and water vapor taken by HALOE during a disturbed period in the Southern Hemisphere springtime (21 September - 15 October 1992) are interpreted in light of the prevailing synoptic meteorology. Daily fields of winds and PV are shown to be essential in the interpretation of the data. A climatological high pressure region is responsible for a distorted vortex, and a substantial 'vortex stripping' event is present, associated with the early stages of vortex breakdown. This leads to significant temporal, zonal, and altitudinal variations in the distribution of tracers. The authors point out the difficulties this presents for the interpretation of solar occultation data, especially with regard to the use of zonal average time series. Longitude-height methane distributions from two days during the period are examined. Both days show substantial variations in abundance around a latitude circle. In particular, the authors investigate HALOE measurements at 77 deg S on 15 October 1992, which indicate an abundance of methane in the height region 600-2000 K (approximately 30-1 mb) that is more typical of midlatitude air. Similar distributions, observed in the 1991 HALOE data, have previously been interpreted as evidence for the penetration of midlatitude air into the vortex. Gradients of potential vorticity and contour advection diagnositcs are employed to examine whether the UKMO winds are consistent with this hypothesis in 1992. Although midlatitude air is able to penetrate poleward of the main jet core by advection processes alone, an essentially intact inner core of vortex air remains, which does not mix to any great extent with air from lower latitudes. The authors show that the high-latitude HALOE abundances that are typical of midlatitude air were observed in a region of extensive filamentation and mixing, rather than within the inner, more isolated, core.

Bithell, M.↗
NASA NTRS1994

Baryonic dark clusters in galactic halos and their observable consequences

We consider the possibility that approximately 10% of the mass of a typical galaxy halo is in the form of massive (approximately 10(exp 7) solar masses), compact (escape speeds approximately 100 km/s) baryonic clusters made of neutron stars (approximately 10% by mass), black holes (less than or approximately equal to 1%) and brown dwarfs, asteroids, and other low-mass debris (approximately 90%). These general properties are consistent with several different observational and phenomenological constraints on cluster properties subject to the condition that neutron stars comprise approximately 1% of the total halo mass. Such compact, dark clusters could be the sites of a variety of collisional phenomena involving neutron stars. We find that integrated out to the Hubble distance approximately one neutron star-neutron star or neutron star-black hole collision occurs daily. Of order 0.1-1 asteroid-neutron star collisions may also happen daily in the halo of the Milky Way if there is roughly equal cluster mass per logarithmic particle mass interval between asteroids and brown dwarfs. These event rates are comparable to the frequency of gamma-ray burst detections by the Burst and Transient Source Experiment (BATSE) on the Compton Observatory, implying that if dark halo clusters are the sites of most gamma-ray bursts, perhaps approximately 90% of all bursts are extragalactic, but approximately 10% are galactic. It is possible that dark clusters of the kind discussed here could be detected directly by the Infrared Space Observatory (ISO) or Space Infrared Telescope Facility (SIRTF). If the clusters considered in this paper exist, they should produce spatially correlated gravitational microlensing of stars in the Large Magellanic Cloud (LMC). If 10% of the halo is in the form of dark baryonic clusters, and the remaining 90% is in brown dwarfs and other dark objects which are either unclustered or collected into low-mass clusters, then we expect that two events within approximately 1 min of one another are likely to be seen after a total of order 20-30 microlenses have been detected.

Wasserman, Ira↗
NASA NTRS1994

Observations of stratospheric hydrogen fluoride by halogen occultation experiment (HALOE)

The Halogen Occultation Experiment (HALOE) Hydrogen Fluoride (HF) channel on the Upper Atmospheric Research Satellite (UARS) is providing the first global measurements of stratospheric HF, the dominant flourine reservoir in the atmosphere. This paper describes the latitudinal and seasonal variations of HALOE-observed HF in terms of vertical profiles, altitude/latitude cross sections, and column abundances. The HF global distribution shows a 'tracerlike' structure and its column amount increases with latitude, in agreement with previous aircraft measurements of the HF column amount. A comparison between the HALOE HF column above 20 km and the ATMOS 1985 measurements is used to estimate the annual rate of increase of stratospheric HF. Exponential rates of 4.9-6.6%/yr and linear growth rates of 6-8.6%/yr in 1985 and 4.3-5.5%/yr in 1992-1993 are found. HALOE HF measurements during the 1993 Antarctic spring are briefly described. This species behaves like a conserved tracer and its distribution shows an area of enhanced mixing ratios correlated with the polar vortex that has a clear latitude boundary. Finally, simulated HF distributions by the National Center for Atmospheric Research (NCAR) two-dimensional model are used to compare with HALOE observations of HF. Reasonable agreements in the global structure and the absolute amount of HF are found. The differences between the model and the observed results indicate the need for improving treatment of atmospheric dynamics and fluorine-related chemical parameters in the model simulations.

Luo, M.↗
NASA NTRS1993

Probing the galactic halo with ROSAT

We discuss the current status of ROSAT shadowing observations designed to search for emission from million degree gas in the halo of the Milky Way galaxy. Preliminary results indicate that million degree halo gas is observed in the 1/4 keV band in some directions, most notably toward the Draco cloud at (l,b) = (92 deg, +38 deg), but that the halo emission is patchy and highly anisotropic. Our current understanding of this halo emission is based on a small handful of observations which have been analyzed to date. Many more observations are currently being analyzed or are scheduled for observation within the next year, and we expect our understanding of this component of the galactic halo to improve dramatically in the near future.

Burrows, D. N.↗
NASA NTRS1993

Optimum transfer to a large-amplitude halo orbit for the Solar and Heliospheric Observatory (SOHO) spacecraft

The Solar and Heliospheric Observatory (SOHO), built by the European Space Agency to study the Sun as part of the International Solar-Terrestrial Physics (ISTP) Program, will be launched in July 1995 into a transfer trajectory that terminates in a large-amplitude halo orbit. The spacecraft will enter the halo orbit by performing one insertion maneuver at a specified point on the halo orbit. The position on the halo orbit that requires the least fuel for the insertion maneuver is identified using the planar, circular restricted three-body problem as a model. Fuel costs for halo orbit insertion at other points in the orbit are also identified. Practical trajectories incorporating all significant accelerations are discussed. The use of a lunar swingby to avoid any insertion maneuver is mentioned.

Stalos, S.↗
NASA NTRS1998

HALOE Science Investigation

This cooperative agreement has investigated a number of spectroscopic problems of interest to the Halogen Occultation Experiment (HALOE). The types of studies performed are in two parts, namely, those that involve the testing and characterization of correlation spectrometers and those that provide basic molecular spectroscopic information. In addition, some solar studies were performed with the calibration data returned by HALOE from orbit. In order to accomplish this a software package was written as part of this cooperative agreement. The HALOE spectroscopic instrument package was used in various tests of the HALOE flight instrument. These included the spectral response test, the early stages of the gas response test and various spectral response tests of the detectors and optical elements of the instruments. Considerable effort was also expended upon the proper laboratory setup for many of the prelaunch tests of the HALOE flight instrument, including the spectral response test and the gas response test. These tests provided the calibration and the assurance that the calibration was performed correctly.

Benner, D. Chris↗
NASA NTRS1998

A Search for a Near-Infrared Halo Around NGC 4565

We present a near-infrared (3.5-5 micron) search for the integrated emission from low-mass stars and/or brown dwarfs in the halo of the nearby edge-on spiral galaxy NGC 4565. The observation was made with a liquid-helium-cooled rocket-borne telescope using a 256 x 256 InSb array with a pixel scale of 17". Images of NGC 4565 were successfully obtained with sensitivity near the natural background limit. Our search reveals no evidence of a faint halo around the galaxy, in contrast with the previous reports of a halo around NGC 5907. The lower limit of the mass-to-light ratio for the halo of NGC 4565 is 260 (2 delta) in solar units at 3.5-5 microns. This implies that hydrogen-burning stars do not contribute significantly to the mass of the dark halo in NGC 4565.

Uemizu, Kazunori↗
NASA NTRS2004

X-Ray Emission from the Halo of M31

Our goal was to use short (10 ksec) observations of selected fields in the halo of M31, to determine the size and characteristics of its X-ray population and to study the connection between globular clusters and X-ray sources. The program of observations has yet to be successfully completed. We received acceptable data from just 2 of the 5 approved fields. Nevertheless, the results were intriguing and we have submitted a paper based on this data to Nature. We find that the X-ray source density is significantly enhanced in the vicinity of one GC, providing the first observational evidence supporting the ejection hypothesis. We also find additional X-ray sources, including some which are very soft, in large enough numbers to suggest that not all could have been formed in GCs. That is, some must be descended from the same primordial halo population that produced any compact stars comprising part of the halo's dark matter. Extrapolating fiom the X-ray source population, we estimate that stellar remnants and dim old stars in the halo could comprise as much as 25% of the estimated mass (approx. 10(exp 12) Solar Mass) of the halo. These results suggest that the other approved fields should be observed soon and also provide strong motivation for the future XMM-Newton programs.

Mushotzky, Richard↗
NASA NTRS2009

Halo Coronal Mass Ejections and Geomagnetic Storms

In this letter, I show that the discrepancies in the geoeffectiveness of halo coronal mass ejections (CMEs) reported in the literature arise due to the varied definitions of halo CMEs used by different authors. In particular, I show that the low geoeffectiveness rate is a direct consequence of including partial halo CMEs. The geoeffectiveness of partial halo CMEs is lower because they are of low speed and likely to make a glancing impact on Earth. Key words: Coronal mass ejections, geomagnetic storms, geoeffectiveness, halo CMEs.

Gopalswamy, Nat↗
NASA NTRS2012

Inverse Compton X-Ray Halos Around High-z Radio Galaxies: A Feedback Mechanism Powered by Far-Infrared Starbursts or the Cosmic Microwave Background?

We report the detection of extended X-ray emission around two powerful radio galaxies at z approx. 3.6 (4C 03.24 and 4C 19.71) and use these to investigate the origin of extended, inverse Compton (IC) powered X-ray halos at high redshifts. The halos have X-ray luminosities of L(sub X) approx. 3 x 10(exp 44) erg/s and sizes of approx.60 kpc. Their morphologies are broadly similar to the approx.60 kpc long radio lobes around these galaxies suggesting they are formed from IC scattering by relativistic electrons in the radio lobes, of either cosmic microwave background (CMB) photons or far-infrared photons from the dust-obscured starbursts in these galaxies. These observations double the number of z > 3 radio galaxies with X-ray-detected IC halos. We compare the IC X-ray-to-radio luminosity ratios for the two new detections to the two previously detected z approx. 3.8 radio galaxies. Given the similar redshifts, we would expect comparable X-ray IC luminosities if millimeter photons from the CMB are the dominant seed field for the IC emission (assuming all four galaxies have similar ages and jet powers). Instead we see that the two z approx. 3.6 radio galaxies, which are 4 fainter in the far-infrared than those at z 3.8, also have approx.4x fainter X-ray IC emission. Including data for a further six z > or approx. 2 radio sources with detected IC X-ray halos from the literature, we suggest that in the more compact, majority of radio sources, those with lobe sizes < or approx.100-200 kpc, the bulk of the IC emission may be driven by scattering of locally produced far-infrared photons from luminous, dust-obscured starbursts within these galaxies, rather than millimeter photons from the CMB. The resulting X-ray emission appears sufficient to ionize the gas on approx.100-200 kpc scales around these systems and thus helps form the extended, kinematically quiescent Ly(alpha) emission line halos found around some of these systems. The starburst and active galactic nucleus activity in these galaxies are thus combining to produce an even more effective and widespread "feedback" process, acting on the long-term gas reservoir for the galaxy, than either individually could achieve. If episodic radio activity and co-eval starbursts are common in massive, high-redshift galaxies, then this IC-feedback mechanism may play a role in affecting the star formation histories of the most massive galaxies at the present day.

Small, Ian↗
NASA NTRS2013

Discovery of a Giant Radio Halo in a New Planck Galaxy Cluster PLCKG171.9-40.7

We report the discovery of a giant radio halo in a new, hot, X-ray luminous galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was found using Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz, and in the 1.4 GHz data from a NRAO Very Large Array Sky Survey pointing that we have reanalyzed. The diffuse radio emission is coincident with the cluster X-ray emission, has an extent of approx.1 Mpc and a radio power of approx. 5×10(exp 24)W/Hz at 1.4 GHz. Its integrated radio spectrum has a slope of alpha approx. = 1.8 between 235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of the archival XMMNewton X-ray data shows that the cluster is hot (approx. 10 keV) and disturbed, consistent with X-ray selected clusters hosting radio halos. This is the first giant radio halo discovered in one of the new clusters found by Planck.

Giacintucci, Simona↗
NASA NTRS2019

The X-Ray Halo Scaling Relations of Supermassive Black Holes

We carry out a comprehensive Bayesian correlation analysis between hot halos and direct masses of supermassive black holes (SMBHs), by retrieving the X-ray plasma properties (temperature, luminosity, density, pressure, and masses) over galactic to cluster scales for 85 diverse systems. We find new key scalings, with the tightest relation being −, followed by −. The tighter scatter (down to 0.2 dex) and stronger correlation coefficient of all the X-ray halo scalings compared with the optical counterparts (as the −) suggest that plasma halos play a more central role than stars in tracing and growing SMBHs (especially those that are ultramassive). Moreover, correlates better with the gas mass than dark matter mass. We show the important role of the environment, morphology, and relic galaxies/coronae, as well as the main departures from virialization/self-similarity via the optical/X-ray fundamental planes. We test the three major channels for SMBH growth: hot/Bondi-like models have inconsistent anticorrelation with X-ray halos and too low feeding; cosmological simulations find SMBH mergers as subdominant over most of cosmic time and too rare to induce a central-limit-theorem effect; the scalings are consistent with chaotic cold accretion, the rain of matter condensing out of the turbulent X-ray halos that sustains a long-term self-regulated feedback loop. The new correlations are major observational constraints for models of SMBH feeding/feedback in galaxies, groups, and clusters (e.g., to test cosmological hydrodynamical simulations), and enable the study of SMBHs not only through X-rays, but also via the Sunyaev–Zel'dovich effect (Compton parameter), lensing (total masses), and cosmology (gas fractions).

Supermassive black holes↗
NASA NTRS2008

Subregions of Motion and Elliptic Halo Orbits in the Elliptic Restricted Three-Body Problem

In this paper we present regions of motion and periodic orbits in the spatial elliptic restricted three body problem (ER3BP). Periodic orbits and regions of motion are fundamental keys to understand any dynamical system; for this reason the Hill's surfaces or the families of halo orbits have been extensively studied in the frame of the circular restricted three body problem. It is our opinion that their natural extensions to the ER3BP have not been studied enough. We divide the position space into forbidden subregions, subregions of motion and low-velocity subregions.We use these notions to define necessary condition for a transfer trajectory in the ER3BP. Also we compute branches of elliptic halo orbits bifurcating from halo orbits in the circular restricted three body problem. The new periodic orbits have principal periods and stability properties different from those of the originating halo orbit.

mission design↗
NASA NTRS1977

The galactic halo question: New size constraints from galactic gamma-ray data

The SAS-2 gamma-ray data is analyzed making use of recent CO line emission and other data for determining the large-scale distribution of galactic gas. A nonuniform distribution of cosmic rays in the galaxy is implied. This fact rules out large trapping halo models and extragalactic origin models. Detailed models of diffusion halos of various sizes perpendicular to the galactic plane are considered. In such models, the scale perpendicular to the plane has a strong effect in determining the radial distribution of cosmic rays. Such radial distributions are calculated for cylindrical coordinate models. The implied gamma-ray longitude distributions are then calculated and compared with the SAS-2 data for goodness-of-fit. Assuming the sources to be supernova remnants or pulsars, cosmic ray nucleon halo models with scale heights greater than 3 kpc are found to provide a poor fit to the gamma-ray longitude data (probability of 6% or less). Thin halo, or source dominated diffusion models are found to provide a good fit to the gamma-ray data, with an upper limit scale height of approximately 3 kpc.

Stecker, F. W.↗
NASA NTRS1977

Cosmic rays in a dynamical halo. I - Age and matter traversal distributions and anisotropy for nuclei. II - Electrons

Recent measurements of the mean lifetime of galactic cosmic rays (at least 10 million yr) have suggested a dynamical halo model of cosmic-ray confinement to the Galaxy. A one-dimensional version of the model is analyzed to determine the ranges of parameters required to give self-consistent values of the mean lifetime, matter traversed, anisotropy, and interstellar gamma-ray flux. It is found that the ranges of the parameters are: disk scale height of 4000-10,000 pc, average convection velocity of no more than 60 km/s, and diffusion coefficient of (3-10) by 10 to the 28th power sq cm/sec for particles with charges of the order of 10 GV. Some consequences for this model of a much shorter lifetime are also discussed. The energy spectrum and spatial distribution of electrons in the dynamical halo model are considered. A gradual steepening of the electron energy spectrum beginning at several GeV energy is found, as indicated by observations. The decrease of electron density with height in the halo depends on the particle energy and may be much steeper than that for nuclei. The models give a halo with a scale height of the order of 3 kpc for several-GeV electrons, which is shown to be consistent with radio observations.

Owens, A. J.↗
NASA NTRS1978

On the stability of disklike galaxies in massive halos

Results are reported for a series of disk-galaxy simulations carried out as part of a systematic search for disk-galaxy models that show little change over the time of several galactic rotations. Systems in a given fixed external field, such as might be provided by a massive halo, are considered. The analysis is performed in terms of two parameters: the fraction of the total mass that resides in the active disk and the velocity dispersion in the active disk. The amount of halo mass required to stabilize a disk with a given velocity dispersion is investigated along with the question of whether any amount of halo mass can stabilize a completely 'cold' disk galaxy. The experimental results are quoted as growth rates estimated from plots of the amplitudes of Fourier analyses of the density in each of a set of narrow annuli, and systematic trends in the dependence of growth rates on the adjustable parameters are examined. It is shown that a massive inert halo contributes to the stability of disk-galaxy models, but some velocity dispersion is required.

Miller, R. H.↗
NASA NTRS1982

Remote sensing studies of lunar dark-halo impact craters - Preliminary results and implications for early volcanism

A summary of the nature and origin of lunar dark-halo craters is presented. New remote sensing data for dark-haloed impact craters were obtained and interpreted. A variety of spectral, thermal, radar, and photogeologic data are presented which confirm the hypothesis that Copernicus H crater excavated mare basalt from beneath lighter deposits emplaced by the Copernicus impact event. Multispectral imagery suggests that analogous impact re-exposure of basaltic material on the ejecta blankets of other large Copernican and Eratosthenian craters resulted in the formation of other dark-halo craters. Preliminary analyses of near-infrared spectra of dark-haloed impact craters in the Schickard-Schiller region are consistent with the hypothesis that basaltic material was excavated from beneath light plains. These light plains may have been emplaced as a result of the Orientale impact event. Additional evidence is presented which suggests that both pre- and post-Orientale volcanic activity was more prevalent in this region than has previously been recognized.

Hawke, B. R.↗