Resonance Trapping in the Galactic Disc and Halo and its Relation with Moving Groups

NASA Astrophysics Data System (ADS)

Pichardo, Barbara; Moreno, Edmundo; william, schuster B.

2015-08-01

With the use of a detailed Milky Way nonaxisymmetric potential, observationally and dynamically constrained, the eects of the bar and the spiral arms in the Galaxy are studied in the disc and in the stellar halo. Especially the trapping of stars in the disk and Galactic halo by resonances on the Galactic plane created by the Galactic bar has been analysed in detail. To this purpose, a new method is presented to delineate the trapping regions using empirical diagrams of some orbital properties obtained in the Galactic potential. In these diagrams we plot in the inertial Galactic frame a characteristic orbital energy versus a characteristic orbital angular momentum, or versus the orbital Jacobi constant in the reference frame of the bar, when this is the only nonaxisymmetric component in the Galactic potential. With these diagrams some trapping regions are obtained in the disc and halo using a sample of disc stars and halo stars in the solar neighborhood. We compute several families of periodic orbits on the Galactic plane, some associated with this resonant trapping. In particular, we nd that the trapping eect of these resonances on the Galactic plane can extend some kpc from this plane, trapping stars in the Galactic halo. The purpose of our analysis is to investigate if the trapping regions contain some known moving groups in our Galaxy. We have applied our method to the Kapteyn group, a moving group in the halo, and we have found that this group appears not to be associated with a particular resonance on the Galactic plane.

Analytical halo model of galactic conformity

NASA Astrophysics Data System (ADS)

Pahwa, Isha; Paranjape, Aseem

2017-09-01

We present a fully analytical halo model of colour-dependent clustering that incorporates the effects of galactic conformity in a halo occupation distribution framework. The model, based on our previous numerical work, describes conformity through a correlation between the colour of a galaxy and the concentration of its parent halo, leading to a correlation between central and satellite galaxy colours at fixed halo mass. The strength of the correlation is set by a tunable 'group quenching efficiency', and the model can separately describe group-level correlations between galaxy colour (1-halo conformity) and large-scale correlations induced by assembly bias (2-halo conformity). We validate our analytical results using clustering measurements in mock galaxy catalogues, finding that the model is accurate at the 10-20 per cent level for a wide range of luminosities and length-scales. We apply the formalism to interpret the colour-dependent clustering of galaxies in the Sloan Digital Sky Survey (SDSS). We find good overall agreement between the data and a model that has 1-halo conformity at a level consistent with previous results based on an SDSS group catalogue, although the clustering data require satellites to be redder than suggested by the group catalogue. Within our modelling uncertainties, however, we do not find strong evidence of 2-halo conformity driven by assembly bias in SDSS clustering.

Grains in galactic haloes

NASA Technical Reports Server (NTRS)

Ferrara, Andrea; Barsella, Bruno; Ferrini, F.; Greenberg, J. Mayo; Aiello, Santi

1989-01-01

Researchers considered the effect of extensive forces on dust grains subjected to the light and matter distribution of a spiral galaxy (Greenberg et al. (1987), Ferrini et al. (1987), Barsella et al (1988). Researchers showed that the combined force on a small particle located above the plane of a galactic disk may be either attractive or repulsive depending on a variety of parameters. They found, for example, that graphite grains from 20 nm to 250 nm radius are expelled from a typical galaxy, while silicates and other forms of dielectrics, after initial expulsion, may settle in potential minimum within the halo. They discuss only the statistical behavior of the forces for 17 galaxies whose luminosity and matter distribution in the disk, bulge and halo components are reasonably well known. The preliminary results of the study of the motion of a dust grain for NGC 3198 are given.

Uncovering the hidden iceberg structure of the Galactic halo

NASA Astrophysics Data System (ADS)

Moss, Vanessa A.; Di Teodoro, Enrico M.; McClure-Griffiths, Naomi M.; Lockman, Felix; Pisano, D. J.; Price, Daniel; Rees, Glen

2018-01-01

How the Milky Way gets its gas and keeps its measured star formation rate going are both long-standing mysteries in Galactic studies, with important implications for galaxy evolution across the Universe. I will present our recent discovery of two populations of neutral hydrogen (HI) in the halo of the Milky Way: 1) a narrow line-width dense population typical of the majority of bright high velocity cloud (HVC) components, and 2) a fainter, broad line-width diffuse population that aligns well with the population found in very sensitive pointings such as in Lockman et al. (2002). From our existing data, we concluded that the diffuse population likely outweighs the dense HI by a factor of 3. This discovery of diffuse HI, which appears to be prevalent throughout the halo, takes us closer to solving the Galactic mystery of accretion and reveals a gaseous neutral halo hidden from the view of most large-scale surveys. We are currently carrying out deep Parkes observations to investigate these results further, in order to truly uncover the nature of the diffuse HI and determine whether our 3:1 ratio (based on the limited existing data) is consistent with what is seen when Parkes and the 140 ft Green Bank telescope are employed at comparable sensitivity. With these data, through a combination of both known and new sightline measurements, we aim to reveal the structure of the Galactic halo in more detail than ever before.

Chemical Cartography. I. A Carbonicity Map of the Galactic Halo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Young Sun; Kim, Young Kwang; Beers, Timothy C.

We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner- and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner- and outer-halo populations, with peaks at [Fe/H]more » = −1.5 and −2.2, respectively. From consideration of the absolute carbon abundances for our sample, A (C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP- s stars (those with strong overabundances of elements associated with the s -process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP- s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP- s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner- and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.« less

Neutron stars and white dwarfs in galactic halos

NASA Technical Reports Server (NTRS)

Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

1989-01-01

The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

The Profile of the Galactic Halo from Pan-STARRS1 3π RR Lyrae

NASA Astrophysics Data System (ADS)

Hernitschek, Nina; Cohen, Judith G.; Rix, Hans-Walter; Sesar, Branimir; Martin, Nicolas F.; Magnier, Eugene; Wainscoat, Richard; Kaiser, Nick; Tonry, John L.; Kudritzki, Rolf-Peter; Hodapp, Klaus; Chambers, Ken; Flewelling, Heather; Burgett, William

2018-05-01

We characterize the spatial density of the Pan-STARRS1 (PS1) sample of Rrab stars to study the properties of the old Galactic stellar halo. This sample, containing 44,403 sources, spans galactocentric radii of 0.55 kpc ≤ R gc ≤ 141 kpc with a distance precision of 3% and thus is able to trace the halo out to larger distances than most previous studies. After excising stars that are attributed to dense regions such as stellar streams, the Galactic disk and bulge, and halo globular clusters, the sample contains ∼11,000 sources within 20 kpc ≤ R gc ≤ 131 kpc. We then apply forward modeling using Galactic halo profile models with a sample selection function. Specifically, we use ellipsoidal stellar density models ρ(l, b, R gc) with a constant and a radius-dependent halo flattening q(R gc). Assuming constant flattening q, the distribution of the sources is reasonably well fit by a single power law with n={4.40}-0.04+0.05 and q={0.918}-0.014+0.016 and comparably well fit by an Einasto profile with n={9.53}-0.28+0.27, an effective radius r eff = 1.07 ± 0.10 kpc, and a halo flattening of q = 0.923 ± 0.007. If we allow for a radius-dependent flattening q(R gc), we find evidence for a distinct flattening of q ∼ 0.8 of the inner halo at ∼25 kpc. Additionally, we find that the south Galactic hemisphere is more flattened than the north Galactic hemisphere. The results of our work are largely consistent with many earlier results (e.g., Watkins et al.; Iorio et al.). We find that the stellar halo, as traced in RR Lyrae stars, exhibits a substantial number of further significant over- and underdensities, even after masking all known overdensities.

Photoionization in the halo of the Galaxy

NASA Technical Reports Server (NTRS)

Bregman, Joel N.; Harrington, J. Patrick

1986-01-01

The ionizing radiation field in the halo is calculated and found to be dominated in the 13.6-45 eV range by light from O-B stars that escapes the disk, by planetary nebulae at 45-54 eV, by quasars and the Galactic soft X-ray background at 54-2000 eV, and by the extragalactic X-ray background at higher energies. Photoionization models are calculated with this radiation field incident on halo clouds of constant density for a variety of densities, for normal and depleted abundances, and with variations of the incident spectrum. For species at least triply ionized, such as Si IV, C IV, N V, and O VI, the line ratios are determined by intervening gas with the greatest volume, which is not necessarily the greatest mass component. Column densities from doubly ionized species like Si III should be greater than from triply ionized species. The role of photoionized gas in cosmic ray-supported halos and Galactic fountains is discussed. Observational tests of photoionization models are suggested.

Photoionization of the diffuse interstellar medium and galactic halo by OB associtations

NASA Technical Reports Server (NTRS)

Dove, James B.; Shull, J. Michael

1994-01-01

Assuming smoothly varying H I distributions in te Galactic disk, we have calculated the geometry of diffuse II regions due to OB associations in the Galactic plane. Near the solar circle, OB associations with a Lyman continuum (Lyc) photon luminosity Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1), produce H II regions that are density bounded in the vertical direction (H II chimneys) allowing Lyc to escape the gaseous disk and penetrate into the Galactic halo. We provide analytic formulae for the Lyc escape fraction as functions of S(sub 0) O-star catalog of Garmany and a new Lyc stellar stellar Lyc stellar flux calibration, we find a production rate of Lyc photons by OB associations within 2.5 kpc of Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1). Integrating the fraction of Lyc photons that escape the disk over our adopted luminosity function of OB associations, we estimate that approximately 7% of the ionizing photons, or Phi(sub Lyc) = 2.3 x 10(exp 6) cm(exp -2) s(exp -1), escape each side of the H I disk layer and penetrate the diffuse ionized medium ('Reynolds layer'). This flux is sufficient to explain the potoionization of this, although we have not constructed a model for the observed H-alpha emission and pulsar dispersion measures that is fully consistent with the absorption rate of Lyc in the H II layer. Since our quiescent model does not account for the effects of dynamic chimneys and superbubbles, which should enhance Lyc escape, we conclude the O stars are the probable source of ionizing radiation for the Reynolds layer. For a random distribution of OB associations throughout the disk, the Lyc flux is nearly uniform for heights Z is greater than approximately 0.8 kpc above the midplane.

Massive black holes in galactic halos?

NASA Technical Reports Server (NTRS)

Lacey, C. G.; Ostriker, J. P.

1985-01-01

In the present attempt to resolve the problems posed by the composition of dark halos and the heating of stellar disks, under the assumption that galaxy halos are composed of massive black holes, it is noted that the black holes must have masses of the order of one million solar masses. The heating mechanism proposed yields predictions for the dependence of the velocity dispersion on time, and for the shape of the velocity ellipsoid, which are in good agreement with observations. Attention is given to the constraints set by dynamical friction causing black holes to spiral to the Galactic center, by the possible presence of dark matter in dwarf spheroidal galaxies, and by the accretion of interstellar gas by the black holes that produce luminous objects in the Galaxy.

Distant Galactic Halo Substructures Observed by the Palomar Transient Factory

NASA Astrophysics Data System (ADS)

Sesar, Branimir

2013-01-01

Characterization of Galactic halo substructures is important as their kinematic and chemical properties help constrain the properties of the Galactic dark matter halo, the formation history of the Milky Way, and the galaxy formation process in general. The best practical choice for finding distant halo substructures are pulsating RR Lyrae stars, due to their intrinsic brightness (M_V = 0.6 mag) and distinct light curves. I will present kinematic and chemical properties of two distant halo substructures that were traced using RR Lyrae stars observed by the Palomar Transient Factory. One of these substructures, located at 90 kpc from the Sun in the Cancer constellation, consists of two groups of RR Lyrae stars moving away from the Galaxy at ~80 and ~20 km/s, respectively. The second substructure is located at ~65 kpc from the Sun in the Hercules constellation. The kinematics of RR Lyrae stars tracing this substructure suggest a presence of 2 or 3 stellar streams extending in the similar direction on the sky. Due to their spatial extent, both of these substructures are clearly disrupted and would be very difficult to detect using tradiitonal techniques such as the color-magnitude diagram filtering.

IONIZED GAS IN THE FIRST 10 kpc OF THE INTERSTELLAR GALACTIC HALO: METAL ION FRACTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howk, J. Christopher; Consiglio, S. Michelle, E-mail: jhowk@nd.edu, E-mail: smconsiglio@ucla.edu

2012-11-10

We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high-resolution ultraviolet absorption-line spectroscopy of post-asymptotic giant branch stars in the globular clusters Messier 3 [(l, b) = (42.{sup 0}2, +78.{sup 0}7), d = 10.2 kpc, and z = 10.0 kpc] and Messier 5 [(l, b) = (3.{sup 0}9, +46.{sup 0}8), d = 7.5 kpc, and z = +5.3 kpc] with the Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure, or place limits on, the column densities of S I, S II, S III, S IV, Smore » VI, and H I. These clusters also house millisecond pulsars, whose dispersion measures give an electron column density from which we infer the H II column in these directions. We find fractions of S{sup +2} in the WIM for the M 3 and M 5 sight lines x(S{sup +2}) {identical_to} N(S{sup +2})/N(S) = 0.33 {+-} 0.07 and 0.47 {+-} 0.09, respectively, with variations perhaps related to location. With negligible quantities of the higher ionization states, we conclude that S{sup +} and S{sup +2} account for all of the S in the WIM. We extend the methodology to study the ion fractions in the warm and hot ionized gas of the Milky Way, including the high ions Si{sup +3}, C{sup +3}, N{sup +4}, and O{sup +5}. The vast majority of the Galactic ionized gas is warm (T {approx} 10{sup 4} K) and photoionized (the WIM) or very hot (T > 4 Multiplication-Sign 10{sup 5} K) and collisionally ionized. The common tracer of ionized gas beyond the Milky Way, O{sup +5}, traces <1% of the total ionized gas mass of the Milky Way.« less

Unmixing the Galactic halo with RR Lyrae tagging

NASA Astrophysics Data System (ADS)

Belokurov, V.; Deason, A. J.; Koposov, S. E.; Catelan, M.; Erkal, D.; Drake, A. J.; Evans, N. W.

2018-06-01

We show that tagging RR Lyrae stars according to their location in the period-amplitude diagram can be used to shed light on the genesis of the Galactic stellar halo. The mixture of RR Lyrae of ab type, separated into classes along the lines suggested by Oosterhoff, displays a strong and coherent evolution with Galactocentric radius. The change in the RR Lyrae composition appears to coincide with the break in the halo's radial density profile at ˜25 kpc. Using simple models of the stellar halo, we establish that at least three different types of accretion events are necessary to explain the observed RRab behaviour. Given that there exists a correlation between the RRab class fraction and the total stellar content of a dwarf satellite, we hypothesize that the field halo RRab composition is controlled by the mass of the progenitor contributing the bulk of the stellar debris at the given radius. This idea is tested against a suite of cosmological zoom-in simulations of Milky Way-like stellar halo formation. Finally, we study some of the most prominent stellar streams in the Milky Way halo and demonstrate that their RRab class fractions follow the trends established previously.

Chemical trends in the Galactic halo from APOGEE data

NASA Astrophysics Data System (ADS)

Fernández-Alvar, E.; Carigi, L.; Allende Prieto, C.; Hayden, M. R.; Beers, T. C.; Fernández-Trincado, J. G.; Meza, A.; Schultheis, M.; Santiago, B. X.; Queiroz, A. B.; Anders, F.; da Costa, L. N.; Chiappini, C.

2017-02-01

The galaxy formation process in the Λ cold dark matter scenario can be constrained from the analysis of stars in the Milky Way's halo system. We examine the variation of chemical abundances in distant halo stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as a function of distance from the Galactic Centre (r) and iron abundance ([M/H]), in the range 5 ≲ r ≲ 30 kpc and -2.5 < [M/H] < 0.0. We perform a statistical analysis of the abundance ratios derived by the APOGEE pipeline (ASPCAP) and distances calculated by several approaches. Our analysis reveals signatures of a different chemical enrichment between the inner and outer regions of the halo, with a transition at about 15 kpc. The derived metallicity distribution function exhibits two peaks, at [M/H] ˜ -1.5 and ˜-2.1, consistent with previously reported halo metallicity distributions. We obtain a difference of ˜0.1 dex for α-element-to-iron ratios for stars at r > 15 kpc and [M/H] > -1.1 (larger in the case of O, Mg, and S) with respect to the nearest halo stars. This result confirms previous claims for low-α stars found at larger distances. Chemical differences in elements with other nucleosynthetic origins (Ni, K, Na, and Al) are also detected. C and N do not provide reliable information about the interstellar medium from which stars formed because our sample comprises red giant branch and asymptotic giant branch stars and can experience mixing of material to their surfaces.

Studying Dust Scattering Halos with Galactic X-ray Binaries

NASA Astrophysics Data System (ADS)

Beeler, Doreen; Corrales, Lia; Heinz, Sebastian

2018-01-01

Dust is an important part of the interstellar medium (ISM) and contributes to the formation of stars and planets. Since the advent of modern X-ray telescopes, Galactic X-ray point sources have permitted a closer look at all phases of the ISM. Interstellar metals from oxygen to iron — in both gas and dust form — are responsible for absorption and scattering of X-ray light. Dust scatters the light in a forward direction and creates a diffuse halo image surrounding many bright Galactic X-ray binaries. We use all the bright X-ray point sources available in the Chandra HETG archive to study dust scattering halos from the local ISM. We have described a data analysis pipeline using a combination of the data reduction software CIAO and Python. We compare our results from Chandra HETG and ACIS-I observations of a well studied dust scattering halo around GX 13+1, in order to characterize any systematic errors associated with the HETG data set. We describe how our data products will be used to measure ISM scaling relations for X-ray extinction, dust abundance, and dust-to-metal ratios.

ULTRAVIOLET HALOS AROUND SPIRAL GALAXIES. I. MORPHOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hodges-Kluck, Edmund; Cafmeyer, Julian; Bregman, Joel N., E-mail: hodgeskl@umich.edu

2016-12-10

We examine ultraviolet halos around a sample of highly inclined galaxies within 25 Mpc to measure their morphology and luminosity. Despite contamination from galactic light scattered into the wings of the point-spread function, we find that ultraviolet (UV) halos occur around each galaxy in our sample. Around most galaxies the halos form a thick, diffuse disk-like structure, but starburst galaxies with galactic superwinds have qualitatively different halos that are more extensive and have filamentary structure. The spatial coincidence of the UV halos above star-forming regions, the lack of consistent association with outflows or extraplanar ionized gas, and the strong correlationmore » between the halo and galaxy UV luminosity suggest that the UV light is an extragalactic reflection nebula. UV halos may thus represent 10{sup 6}–10{sup 7} M {sub ⊙} of dust within 2–10 kpc of the disk, whose properties may change with height in starburst galaxies.« less

Cosmic stellar relics in the Galactic halo

NASA Astrophysics Data System (ADS)

Salvadori, Stefania; Schneider, Raffaella; Ferrara, Andrea

2007-10-01

We study the stellar population history and chemical evolution of the Milky Way (MW) in a hierarchical Λ cold dark matter model for structure formation. Using a Monte Carlo method based on the semi-analytical extended Press & Schechter formalism, we develop a new code GALAXY MERGER TREE AND EVOLUTION (GAMETE) to reconstruct the merger tree of the Galaxy and follow the evolution of gas and stars along the hierarchical tree. Our approach allows us to compare the observational properties of the MW with model results, exploring different properties of primordial stars, such as their initial mass function and the critical metallicity for low-mass star formation, Zcr. In particular, by matching our predictions to the metallicity distribution function (MDF) of metal-poor stars in the Galactic halo we find that: (i) a strong supernova (SN) feedback is required to reproduce the observed properties of the MW; (ii) stars with [Fe/H] < -2.5 form in haloes accreting Galactic medium (GM) enriched by earlier SN explosions; (iii) the fiducial model (Zcr = 10-4Zsolar, mPopIII = 200 Msolar) provides an overall good fit to the MDF, but cannot account for the two hyper-metal-poor (HMP) stars with [Fe/H] < -5 the latter can be accommodated if Zcr <= 10-6 Zsolar but such model overpopulates the `metallicity desert', that is, the range -5.3 < [Fe/H] < -4 in which no stars have been detected; (iv) the current non-detection of metal-free stars robustly constrains either Zcr > 0 or the masses of the first stars mPopIII > 0.9 Msolar (v) the statistical impact of truly second-generation stars, that is, stars forming out of gas polluted only by metal-free stars, is negligible in current samples; and (vi) independent of Zcr, 60 per cent of metals in the GM are ejected through winds by haloes with masses M < 6 × 109 Msolar, thus showing that low-mass haloes are the dominant population contributing to cosmic metal enrichment. We discuss the limitations of our study and comparison with previous

Galactic googly: the rotation-metallicity bias in the inner stellar halo of the Milky Way

NASA Astrophysics Data System (ADS)

Kafle, Prajwal R.; Sharma, Sanjib; Robotham, Aaron S. G.; Pradhan, Raj K.; Guglielmo, Magda; Davies, Luke J. M.; Driver, Simon P.

2017-09-01

The first and second moments of stellar velocities encode important information about the formation history of the Galactic halo. However, due to the lack of tangential motion and inaccurate distances of the halo stars, the velocity moments in the Galactic halo have largely remained 'known unknowns'. Fortunately, our off-centric position within the Galaxy allows us to estimate these moments in the galactocentric frame using the observed radial velocities of the stars alone. We use these velocities coupled with the hierarchical Bayesian scheme, which allows easy marginalization over the missing data (the proper motion, and uncertainty-free distance and line-of-sight velocity), to measure the velocity dispersions, orbital anisotropy (β) and streaming motion (vrot) of the halo main-sequence turn-off (MSTO) and K-giant (KG) stars in the inner stellar halo (r ≲ 15 kpc). We study the metallicity bias in kinematics of the halo stars and observe that the comparatively metal-rich ([Fe/H] > -1.4) and the metal-poor ([Fe/H] ≤ -1.4) MSTO samples show a clear systematic difference in vrot ˜ 20-40 km s - 1, depending on how restrictive the spatial cuts to cull the disc contamination are. The bias is also detected in KG samples but with less certainty. Both MSTO and KG populations suggest that the inner stellar halo of the Galaxy is radially biased I.e. σr > σθ or σϕ and β ≃ 0.5. The apparent metallicity contrariety in the rotation velocity among the halo sub-populations supports the co-existence of multiple populations in the galactic halo that may have formed through distinct formation scenarios, I.e. in situ versus accretion.

THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: TESTING GALACTIC FOUNTAIN MODELS' X-RAY EMISSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henley, David B.; Shelton, Robin L.; Kwak, Kyujin

2015-02-20

We test the X-ray emission predictions of galactic fountain models against XMM-Newton measurements of the emission from the Milky Way's hot halo. These measurements are from 110 sight lines, spanning the full range of Galactic longitudes. We find that a magnetohydrodynamical simulation of a supernova-driven interstellar medium, which features a flow of hot gas from the disk to the halo, reproduces the temperature but significantly underpredicts the 0.5-2.0 keV surface brightness of the halo (by two orders of magnitude, if we compare the median predicted and observed values). This is true for versions of the model with and without anmore » interstellar magnetic field. We consider different reasons for the discrepancy between the model predictions and the observations. We find that taking into account overionization in cooled halo plasma, which could in principle boost the predicted X-ray emission, is unlikely in practice to bring the predictions in line with the observations. We also find that including thermal conduction, which would tend to increase the surface brightnesses of interfaces between hot and cold gas, would not overcome the surface brightness shortfall. However, charge exchange emission from such interfaces, not included in the current model, may be significant. The faintness of the model may also be due to the lack of cosmic ray driving, meaning that the model may underestimate the amount of material transported from the disk to the halo. In addition, an extended hot halo of accreted material may be important, by supplying hot electrons that could boost the emission of the material driven out from the disk. Additional model predictions are needed to test the relative importance of these processes in explaining the observed halo emission.« less

The Origin of the Hot Gas in the Galactic Halo: Testing Galactic Fountain Models' X-Ray Emission

NASA Astrophysics Data System (ADS)

Henley, David B.; Shelton, Robin L.; Kwak, Kyujin; Hill, Alex S.; Mac Low, Mordecai-Mark

2015-02-01

We test the X-ray emission predictions of galactic fountain models against XMM-Newton measurements of the emission from the Milky Way's hot halo. These measurements are from 110 sight lines, spanning the full range of Galactic longitudes. We find that a magnetohydrodynamical simulation of a supernova-driven interstellar medium, which features a flow of hot gas from the disk to the halo, reproduces the temperature but significantly underpredicts the 0.5-2.0 keV surface brightness of the halo (by two orders of magnitude, if we compare the median predicted and observed values). This is true for versions of the model with and without an interstellar magnetic field. We consider different reasons for the discrepancy between the model predictions and the observations. We find that taking into account overionization in cooled halo plasma, which could in principle boost the predicted X-ray emission, is unlikely in practice to bring the predictions in line with the observations. We also find that including thermal conduction, which would tend to increase the surface brightnesses of interfaces between hot and cold gas, would not overcome the surface brightness shortfall. However, charge exchange emission from such interfaces, not included in the current model, may be significant. The faintness of the model may also be due to the lack of cosmic ray driving, meaning that the model may underestimate the amount of material transported from the disk to the halo. In addition, an extended hot halo of accreted material may be important, by supplying hot electrons that could boost the emission of the material driven out from the disk. Additional model predictions are needed to test the relative importance of these processes in explaining the observed halo emission.

Search for dark matter from the Galactic halo with the IceCube Neutrino Telescope

NASA Astrophysics Data System (ADS)

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; Benzvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Braun, J.; Brown, A. M.; Buitink, S.; Carson, M.; Chirkin, D.; Christy, B.; Clem, J.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; D'Agostino, M. V.; Danninger, M.; Daughhetee, J.; Davis, J. C.; de Clercq, C.; Demirörs, L.; Denger, T.; Depaepe, O.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; Deyoung, T.; Díaz-Vélez, J. C.; Dierckxsens, M.; Dreyer, J.; Dumm, J. P.; Ehrlich, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Foerster, M. M.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Geisler, M.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Heinen, D.; Helbing, K.; Herquet, P.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Homeier, A.; Hoshina, K.; Hubert, D.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Joseph, J. M.; Kampert, K.-H.; Kappes, A.; Karg, T.; Karle, A.; Kelley, J. L.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Krings, T.; Kroll, G.; Kuehn, K.; Kuwabara, T.; Labare, M.; Lafebre, S.; Laihem, K.; Landsman, H.; Larson, M. J.; Lauer, R.; Lünemann, J.; Madsen, J.; Majumdar, P.; Marotta, A.; Maruyama, R.; Mase, K.; Matis, H. S.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Middell, E.; Milke, N.; Miller, J.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nießen, P.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Ono, M.; Panknin, S.; Paul, L.; Pérez de Los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Prikockis, M.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Rizzo, A.; Rodrigues, J. P.; Roth, P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Schmidt, T.; Schoenwald, A.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Slipak, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stephens, G.; Stezelberger, T.; Stokstad, R. G.; Stoyanov, S.; Strahler, E. A.; Straszheim, T.; Stür, M.; Sullivan, G. W.; Swillens, Q.; Taavola, H.; Taboada, I.; Tamburro, A.; Tarasova, O.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Tosi, D.; Turčan, D.; van Eijndhoven, N.; Vandenbroucke, J.; van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Voigt, B.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Wolf, M.; Woschnagg, K.; Xu, C.; Xu, X. W.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.

2011-07-01

Self-annihilating or decaying dark matter in the Galactic halo might produce high energy neutrinos detectable with neutrino telescopes. We have conducted a search for such a signal using 276 days of data from the IceCube 22-string configuration detector acquired during 2007 and 2008. The effect of halo model choice in the extracted limit is reduced by performing a search that considers the outer halo region and not the Galactic Center. We constrain any large-scale neutrino anisotropy and are able to set a limit on the dark matter self-annihilation cross section of ⟨σAv⟩≃10-22cm3s-1 for weakly interacting massive particle masses above 1 TeV, assuming a monochromatic neutrino line spectrum.

Abundances and Evolution of Lithium in the Galactic Halo and Disk

NASA Astrophysics Data System (ADS)

Ryan, Sean G.; Kajino, Toshitaka; Beers, Timothy C.; Suzuki, Takeru Ken; Romano, Donatella; Matteucci, Francesca; Rosolankova, Katarina

2001-03-01

We have measured the Li abundance of 18 stars with -2<~[Fe/H]<~-1 and 6000<~Teff<~6400 K, a parameter range that was poorly represented in previous studies. We examine the Galactic chemical evolution (GCE) of this element, combining these data with previous samples of turnoff stars over the full range of halo metallicities. We find that A(Li) increases from a level of ~2.10 at [Fe/H]=-3.5 to ~2.40 at [Fe/H]=-1.0, where A(Li)=log10(n(Li)/n(H))+12.00. We compare the observations with several GCE calculations, including existing one-zone models and a new model developed in the framework of inhomogeneous evolution of the Galactic halo. We show that Li evolved at a constant rate relative to iron throughout the halo and old disk epochs but that during the formation of young disk stars, the production of Li relative to iron increased significantly. These observations can be understood in the context of models in which postprimordial Li evolution during the halo and old disk epochs is dominated by Galactic cosmic-ray fusion and spallation reactions, with some contribution from the ν-process in supernovae. The onset of more efficient Li production (relative to iron) in the young disk coincides with the appearance of Li from novae and asymptotic giant branch (AGB) stars. The major challenge facing the models is to reconcile the mild evolution of Li during the halo and old disk phases with the more efficient production (relative to iron) at [Fe/H]>-0.5. We speculate that cool-bottom processing (production) of Li in low-mass stars may provide an important late-appearing source of Li, without attendant Fe production, that might explain the Li production in the young disk. Based on observations obtained with the University College London échelle spectrograph (UCLES) on the Anglo-Australian Telescope (AAT) and the Utrecht échelle spectrograph (UES) on the William Herschel Telescope (WHT).

A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars

NASA Astrophysics Data System (ADS)

Carlos, Marília; Karakas, Amanda I.; Cohen, Judith G.; Kobayashi, Chiaki; Meléndez, Jorge

2018-04-01

We determine magnesium isotopic abundances of metal-poor dwarf stars from the galactic halo, to shed light on the onset of asymptotic giant branch (AGB) star nucleosynthesis in the galactic halo and constrain the timescale of its formation. We observed a sample of eight new halo K dwarfs in a metallicity range of ‑1.9 < [Fe/H] < ‑0.9 and 4200 < T eff(K) < 4950, using the HIRES spectrograph at the Keck Observatory (R ≈ 105 and 200 ≤ S/N ≤ 300). We obtain magnesium isotopic abundances by spectral synthesis on three MgH features and compare our results with galactic chemical evolution models. With the current sample, we almost double the number of metal-poor stars with Mg isotopes determined from the literature. The new data allow us to determine the metallicity when the 26Mg abundances start to become important, [Fe/H] ∼ ‑1.4 ± 0.1. The data with [Fe/H] > ‑1.4 are somewhat higher (1–3σ) than previous chemical evolution model predictions, indicating perhaps higher yields of the neutron-rich isotopes. Our results using only AGB star enrichment suggest a timescale for formation for the galactic halo of about 0.3 Gyr, but considering also supernova enrichment, the upper limit for the timescale formation is about 1.5 Gyr. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

New Asymptotic Giant Branch Carbon Stars in the Galactic Halo

NASA Astrophysics Data System (ADS)

Mauron, N.; Gigoyan, K. S.; Kostandyan, G. R.

2018-03-01

For the first time the data on the eight confirmed or candidate carbon (C) stars found mainly from objective-prism plates are presented. By using the Catalina database of lightcurves, we find that all these stars are pulsating, allowing a distance to be estimated through the K-band Period-Luminosity (PL) relation. This relation does not depend on spectral type (M or C) and distances are reliable even for C candidates. Seven stars are more than 10 kpc from the galactic plane, suggesting they do not belong to the galactic disk. We also find one star located at about 180 kpc from the Sun, being one of the most distant star in the Galaxy. Many of these new C stars are relatively blue. Some comments are also provided on seven other known halo carbon stars for which either a pulsation period is obtained, or because they were not included in previous works on halo C stars.

The Halo Occupation Distribution of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Chatterjee, Suchetana; Nagai, D.; Richardson, J.; Zheng, Z.; Degraf, C.; DiMatteo, T.

2011-05-01

We investigate the halo occupation distribution of active galactic nuclei (AGN) using a state-of-the-art cosmological hydrodynamic simulation that self-consistently incorporates the growth and feedback of supermassive black holes and the physics of galaxy formation (DiMatteo et al. 2008). We show that the mean occupation function can be modeled as a softened step function for central AGN and a power law for the satellite population. The satellite occupation is consistent with weak redshift evolution and a power law index of unity. The number of satellite black holes at a given halo mass follows a Poisson distribution. We show that at low redshifts (z=1.0) feedback from AGN is responsible for higher suppression of black hole growth in higher mass halos. This effect introduces a bias in the correlation between instantaneous AGN luminosity and the host halo mass, making AGN clustering depend weakly on luminosity at low redshifts. We show that the radial distribution of AGN follows a power law which is fundamentally different from those of galaxies and dark matter. The best-fit power law index is -2.26 ± 0.23. The power law exponent do not show any evolution with redshift, host halo mass and AGN luminosity within statistical limits. Incorporating the environmental dependence of supermassive black hole accretion and feedback, our formalism provides the most complete theoretical tool for interpreting current and future measurements of AGN clustering.

Formation of the Galactic Stellar Halo: Origin of the Metallicity-Eccentricity Relation.

PubMed

Bekki; Chiba

2000-05-01

Motivated by the recently improved knowledge on the kinematic and chemical properties of the Galactic metal-poor stars, we present the numerical simulation for the formation of the Galactic stellar halo to interpret the observational results. As a model for the Galaxy contraction, we adopt the currently standard theory of galaxy formation based on the hierarchical assembly of the cold dark matter fluctuations. We find, for the simulated stars with &sqbl0;Fe&solm0;H&sqbr0;Galactic halo is a natural consequence of the hierarchical evolution of the subgalactic clumps seeded from the cold dark matter density fluctuations.

The dependence of cosmic ray-driven galactic winds on halo mass

NASA Astrophysics Data System (ADS)

Jacob, Svenja; Pakmor, Rüdiger; Simpson, Christine M.; Springel, Volker; Pfrommer, Christoph

2018-03-01

Galactic winds regulate star formation in disc galaxies and help to enrich the circum-galactic medium. They are therefore crucial for galaxy formation, but their driving mechanism is still poorly understood. Recent studies have demonstrated that cosmic rays (CRs) can drive outflows if active CR transport is taken into account. Using hydrodynamical simulations of isolated galaxies with virial masses between 1010 and 1013 M⊙, we study how the properties of CR-driven winds depend on halo mass. CRs are treated in a two-fluid approximation and their transport is modelled through isotropic or anisotropic diffusion. We find that CRs are only able to drive mass-loaded winds beyond the virial radius in haloes with masses below 1012 M⊙. For our lowest examined halo mass, the wind is roughly spherical and has velocities of ˜20 km s-1. With increasing halo mass, the wind becomes biconical and can reach 10 times higher velocities. The mass loading factor drops rapidly with virial mass, a dependence that approximately follows a power law with a slope between -1 and -2. This scaling is slightly steeper than observational inferences, and also steeper than commonly used prescriptions for wind feedback in cosmological simulations. The slope is quite robust to variations of the CR injection efficiency or the CR diffusion coefficient. In contrast to the mass loading, the energy loading shows no significant dependence on halo mass. While these scalings are close to successful heuristic models of wind feedback, the CR-driven winds in our present models are not yet powerful enough to fully account for the required feedback strength.

Far-IR spectroscopy of the galactic center: Neutral and ionized gas in the central 10 pc of the galaxy

NASA Technical Reports Server (NTRS)

Hollenbach, D. J.; Watson, D. M.; Townes, C. H.; Dinerstein, H. L.; Hollenbach, D.; Lester, D. F.; Werner, M.; Storey, J. W. V.

1983-01-01

The 3P1 - 3P2 fine structure line emission from neutral atomic oxygen at 63 microns in the vicinity of the galactic center was mapped. The emission is extended over more than 4' (12 pc) along the galactic plane, centered on the position of Sgr A West. The line center velocities show that the O I gas is rotating around the galactic center with an axis close to that of the general galactic rotation, but there appear also to be noncircular motions. The rotational velocity at R is approximately 1 pc corresponds to a mass within the central pc of about 3 x 10(6) solar mass. Between 1 and 6 pc from the center the mass is approximately proportional to radius. The (O I) line probability arises in a predominantly neutral, atomic region immediately outside of the ionized central parsec of out galaxy. Hydrogen densities in the (O I) emitting region are 10(3) to 10(6) cm(-3) and gas temperatures are or = 100 K. The total integrated luminosity radiated in the line is about 10(5) solar luminosity, and is a substantial contribution to the cooling of the gas. Photoelectric heating or heating by ultraviolet excitation of H2 at high densities (10(5) cm(-3)) are promising mechanisms for heating of the gas, but heating due to dissipation of noncircular motions of the gas may be an alternative possibility. The 3P1 - 3P0 fine structure line of (O III) at 88 microns toward Sgr A West was also detected. The (O III) emission comes from high density ionized gas (n 10(4) cm(-3)), and there is no evidence for a medium density region (n 10(3) cm(-3)), such as the ionized halo in Sgr A West deduced from radio observations. This radio halo may be nonthermal, or may consist of many compact, dense clumps of filaments on the inner edges of neutral condensations at R or = 2 pc.

Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

NASA Astrophysics Data System (ADS)

Duplessis, Francis; Vachaspati, Tanmay

2017-05-01

Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify and explain a new feature of the Q-statistics that can further enhance its power.

Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duplessis, Francis; Vachaspati, Tanmay, E-mail: fdupless@asu.edu, E-mail: tvachasp@asu.edu

Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify andmore » explain a new feature of the Q-statistics that can further enhance its power.« less

A search for dark matter in the Galactic halo with HAWC

NASA Astrophysics Data System (ADS)

Abeysekara, A. U.; Albert, A.; Alfaro, R.; Alvarez, C.; Arceo, R.; Arteaga-Velázquez, J. C.; Avila Rojas, D.; Ayala Solares, H. A.; Becerril, A.; Belmont-Moreno, E.; BenZvi, S. Y.; Bernal, A.; Brisbois, C.; Caballero-Mora, K. S.; Capistrán, T.; Carramiñana, A.; Casanova, S.; Castillo, M.; Cotti, U.; Cotzomi, J.; De León, C.; De la Fuente, E.; Diaz Hernandez, R.; Dingus, B. L.; DuVernois, M. A.; Díaz-Vélez, J. C.; Engel, K.; Enríquez-Rivera, O.; Fiorino, D. W.; Fleischhack, H.; Fraija, N.; García-González, J. A.; Garfias, F.; González Muñoz, A.; González, M. M.; Goodman, J. A.; Hampel-Arias, Z.; Harding, J. P.; Hernandez, S.; Hernandez-Almada, A.; Hueyotl-Zahuantitla, F.; Hüntemeyer, P.; Iriarte, A.; Jardin-Blicq, A.; Joshi, V.; Kaufmann, S.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linnemann, J. T.; Longinotti, A. L.; Luis-Raya, G.; Luna-García, R.; López-Coto, R.; Malone, K.; Marinelli, S. S.; Martinez, O.; Martinez-Castellanos, I.; Martínez-Castro, J.; Matthews, J. A.; Miranda-Romagnoli, P.; Moreno, E.; Mostafá, M.; Nellen, L.; Newbold, M.; Nisa, M. U.; Noriega-Papaqui, R.; Pelayo, R.; Pretz, J.; Pérez-Pérez, E. G.; Ren, Z.; Rho, C. D.; Rodd, N. L.; Rosa-González, D.; Rosenberg, M.; Ruiz-Velasco, E.; Safdi, B. R.; Salazar, H.; Salesa Greus, F.; Sandoval, A.; Schneider, M.; Sinnis, G.; Smith, A. J.; Springer, R. W.; Surajbali, P.; Taboada, I.; Tibolla, O.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Vianello, G.; Villaseñor, L.; Weisgarber, T.; Westerhoff, S.; Wisher, I. G.; Wood, J.; Yapici, T.; Yodh, G. B.; Younk, P. W.; Zepeda, A.; Zhou, H.; Álvarez, J. D.

2018-02-01

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV – 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Here we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.

THE SEGUE K GIANT SURVEY. III. QUANTIFYING GALACTIC HALO SUBSTRUCTURE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janesh, William; Morrison, Heather L.; Ma, Zhibo

2016-01-10

We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5–125 kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey’s Sloan Extension for Galactic Understanding and Exploration project. Using a position–velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earliermore » work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (∼33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.« less

Using photometrically selected metal-poor stars to study dwarf galaxies and the Galactic stellar halo

NASA Astrophysics Data System (ADS)

Youakim, Kris; Starkenburg, Else; Martin, Nicolas; Pristine Team

2018-06-01

The Pristine survey is a narrow-band photometric survey designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, it has demonstrated great efficiency at finding EMP stars, and also great promise for increasing the current, small sample of the most metal-poor stars. The present sky coverage is ~2500 square degrees in the Northern Galactic Halo, including several individual fields targeting dwarf galaxies. By efficiently identifying member stars in the outskirts of known faint dwarf galaxies, the dynamical histories and chemical abundance patterns of these systems can be understood in greater detail. Additionally, with reliable photometric metallicities over a large sky coverage it is possible to perform a large scale clustering analysis in the Milky Way halo, and investigate the characteristic scale of substructure at different metallicities. This can reveal important details about the process of building up the halo through dwarf galaxy accretion, and offer insight into the connection between dwarf galaxies and the Milky Way halo. In this talk I will outline our results on the search for the most pristine stars, with a focus on how we are using this information to advance our understanding of dwarf galaxies and their contribution to the formation of the Galactic stellar halo.

Discussion on the energy content of the galactic dark matter Bose-Einstein condensate halo in the Thomas-Fermi approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Souza, J.C.C.; Pires, M.O.C., E-mail: jose.souza@ufabc.edu.br, E-mail: marcelo.pires@ufabc.edu.br

We show that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [6] trapped by a self-graviting potential [5], may be stable in the Thomas-Fermi approximation since appropriate choices for the dark matter particle mass and scattering length are made. The demonstration is performed by means of the calculation of the potential, kinetic and self-interaction energy terms of a galactic halo described by a Boehmer-Harko density profile. We discuss the validity of the Thomas-Fermi approximation for the halo system, and show that the kinetic energy contribution is indeed negligible.

"Invisible" Galactic Halos.

ERIC Educational Resources Information Center

Lugt, Karel Vander

1993-01-01

Develops a simple core-halo model of a galaxy that exhibits the main features of observed rotation curves and quantitatively illustrates the need to postulate halos of dark matter. Uses only elementary mechanics. (Author/MVL)

Probing the Interstellar Dust towards the Galactic Centre using X-ray Dust Scattering Halos

NASA Astrophysics Data System (ADS)

Jin, C.; Ponti, G.; Haberl, F.; Smith, R.

2017-10-01

Dust scattering creates an X-ray halo that contains abundant information about the interstellar dust along the source's line-of-sight (LOS), and is most prominent when the LOS nH is high. In this talk, I will present results from our latest study of a bright dust scattering halo around an eclipsing X-ray binary at 1.45 arcmin away from Sgr A*, namely AX J1745.6-2901. This study is based on a large set of XMM-Newton and Chandra observations, and is so-far the best dust scattering halo study of a X-ray transient in the Galactic centre (GC). I will show that the foreground dust of AX J1745.6-2901 can be decomposed into two major thick dust layers. One layer contains (66-81)% of the total LOS dust and is several kpc away from the source, and so is most likely to reside in the Galactic disc. The other layer is local to the source. I will also show that the dust scattering halo can cause the source spectrum to severely depend on the source extraction region. Such spectral bias can be corrected by our new Xspec model, which is likely to be applicable to Sgr A* and other GC sources as well.

XMM-NEWTON MEASUREMENT OF THE GALACTIC HALO X-RAY EMISSION USING A COMPACT SHADOWING CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henley, David B.; Shelton, Robin L.; Cumbee, Renata S.

2015-02-01

Observations of interstellar clouds that cast shadows in the soft X-ray background can be used to separate the background Galactic halo emission from the local emission due to solar wind charge exchange (SWCX) and/or the Local Bubble (LB). We present an XMM-Newton observation of a shadowing cloud, G225.60–66.40, that is sufficiently compact that the on- and off-shadow spectra can be extracted from a single field of view (unlike previous shadowing observations of the halo with CCD-resolution spectrometers, which consisted of separate on- and off-shadow pointings). We analyzed the spectra using a variety of foreground models: one representing LB emission, andmore » two representing SWCX emission. We found that the resulting halo model parameters (temperature T {sub h} ≈ 2 × 10{sup 6} K, emission measure E{sub h}≈4×10{sup −3} cm{sup −6} pc) were not sensitive to the foreground model used. This is likely due to the relative faintness of the foreground emission in this observation. However, the data do favor the existence of a foreground. The halo parameters derived from this observation are in good agreement with those from previous shadowing observations, and from an XMM-Newton survey of the Galactic halo emission. This supports the conclusion that the latter results are not subject to systematic errors, and can confidently be used to test models of the halo emission.« less

A search for dark matter in the Galactic halo with HAWC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abeysekara, A. U.; Albert, A.; Alfaro, R.

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV – 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Heremore » we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.« less

A search for dark matter in the Galactic halo with HAWC

DOE PAGES

Abeysekara, A. U.; Albert, A.; Alfaro, R.; ...

2018-02-23

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV – 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Heremore » we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.« less

The sagittarius tidal stream and the shape of the galactic stellar halo

NASA Astrophysics Data System (ADS)

Newby, Matthew T.

The stellar halo that surrounds our Galaxy contains clues to understanding galaxy formation, cosmology, stellar evolution, and the nature of dark matter. Gravitationally disrupted dwarf galaxies form tidal streams, which roughly trace orbits through the Galactic halo. The Sagittarius (Sgr) dwarf tidal debris is the most dominant of these streams, and its properties place important constraints on the distribution of mass (including dark matter) in the Galaxy. Stars not associated with substructures form the "smooth" component of the stellar halo, the origin of which is still under investigation. Characterizing halo substructures such as the Sgr stream and the smooth halo provides valuable information on the formation history and evolution of our galaxy, and places constraints on cosmological models. This thesis is primarily concerned with characterizing the 3-dimensional stellar densities of the Sgr tidal debris system and the smooth stellar halo, using data from the Sloan Digital Sky Survey (SDSS). F turnoff stars are used to infer distances, as they are relatively bright, numerous, and distributed about a single intrinsic brightness (magnitude). The inherent spread in brightnesses of these stars is overcome through the use of the recently-developed technique of statistical photometric parallax, in which the bulk properties of a stellar population are used to create a probability distribution for a given star's distance. This was used to build a spatial density model for the smooth stellar halo and tidal streams. The free parameters in this model are then fit to SDSS data with a maximum likelihood technique, and the parameters are optimized by advanced computational methods. Several computing platforms are used in this study, including the RPI SUR Bluegene and the Milkyway home volunteer computing project. Fits to the Sgr stream in 18 SDSS data stripes were performed, and a continuous density profile is found for the major Sgr stream. The stellar halo is found to

Millisecond Pulsars, TeV Halos, and Implications For The Galactic Center Gamma-Ray Excess

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hooper, Dan; Linden, Tim

Observations by HAWC indicate that many young pulsars (including Geminga and Monogem) are surrounded by spatially extended, multi-TeV emitting regions. It is not currently known, however, whether TeV emission is also produced by recycled, millisecond pulsars (MSPs). In this study, we perform a stacked analysis of 24 MSPs within HAWC's field-of-view, finding between 2.6-3.2 sigma evidence that these sources are, in fact, surrounded by TeV halos. The efficiency with which these MSPs produce TeV halos is similar to that exhibited by young pulsars. This result suggests that several dozen MSPs will ultimately be detectable by HAWC, including many "invisible" pulsarsmore » without radio beams oriented in our direction. The TeV halos of unresolved MSPs could also dominate the TeV-scale diffuse emission observed at high galactic latitudes. We also discuss the possibility that TeV and radio observations could be used to constrain the population of MSPs that is present in the inner Milky Way, thereby providing us with a new way to test the hypothesis that MSPs are responsible for the Galactic Center GeV excess.« less

Effect of dark matter halo on global spiral modes in a collisionless galactic disk

NASA Astrophysics Data System (ADS)

Ghosh, Soumavo; Saini, Tarun Deep; Jog, Chanda J.

2017-07-01

Low surface brightness (LSB) galaxies are dominated by dark matter halo from the innermost radii; hence they are ideal candidates to investigate the influence of dark matter on different dynamical aspects of spiral galaxies. Here, we study the effect of dark matter halo on grand-design, m = 2 , spiral modes in a galactic disk, treated as a collisionless system, by carrying out a global modal analysis within the WKB approximation. First, we study a superthin, LSB galaxy UGC 7321 and show that it does not support discrete global spiral modes when modeled as a disk-alone system or as a disk plus dark matter system. Even a moderate increase in the stellar central surface density does not yield any global spiral modes. This naturally explains the observed lack of strong large-scale spiral structure in LSBs. An earlier work (Ghosh et al., 2016) where the galactic disk was treated as a fluid system for simplicity had shown that the dominant halo could not arrest global modes. We found that this difference arises due to the different dispersion relation used in the two cases and which plays a crucial role in the search for global spiral modes. Thus the correct treatment of stars as a collisionless system as done here results in the suppression of global spiral modes, in agreement with the observations. We performed a similar modal analysis for the Galaxy, and found that the dark matter halo has a negligible effect on large-scale spiral structure.

WEAK GALACTIC HALO-DWARF SPHEROIDAL CONNECTION FROM RR LYRAE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fiorentino, Giuliana; Bono, Giuseppe; Monelli, Matteo

2015-01-01

We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in 6 dwarf spheroidals (dSphs) and 11 ultra faint dwarf galaxies (∼1300) show a Gaussian period distribution well peaked around a mean period of (Pab) = 0.610 ± 0.001 days (σ = 0.03). The Halo RRL (∼15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dSphs apart from Sagittariusmore » are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P ≲ 0.48 days and A{sub V} ≥ 0.75 mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered 18 globulars covering a broad range in metallicity (–2.3 ≲ [Fe/H] ≲ –1.1) and hosting more than 35 RRL each. The metallicity turns out to be the main parameter, since only globulars more metal-rich than [Fe/H] ∼ –1.5 host RRL in the HASP region. This finding suggests that dSphs similar to the surviving ones do not appear to be the major building-blocks of the Halo. Leading physical arguments suggest an extreme upper limit of ∼50% to their contribution. On the other hand, massive dwarfs hosting an old population with a broad metallicity distribution (Large Magellanic Cloud, Sagittarius) may have played a primary role in the formation of the Halo.« less

On planetary nebulae as sources of carbon dust: Infrared emission from planetary nebulae of the galactic halo

NASA Technical Reports Server (NTRS)

Dinerstein, Harriet L.; Lester, Daniel F.

1990-01-01

Planetary nebulae of the galactic disk are generally seen to emit a thermal continuum due to dust grains heated by stellar and nebular photons. This continuum typically peaks between 25 and 60 micron m, so that the total power emitted by the dust is sampled well by the broad-band measurements made by IRAS. Researchers examine here the characteristics of the infrared emission from the four planetary nebulae which are believed on the basis of their low overall metallicities to belong to the halo population. These nebulae are of particular interest because they are the most metal-poor ionized nebulae known in our Galaxy, and offer the opportunity to probe possible dependences of the dust properties on nebular composition. Researchers present fluxes extracted from co-addition of the IRAS data, as well as ground-based near infrared measurements. Each of the four halo objects, including the planetary nebula in the globular cluster M15, is detected in at least one infrared band. Researchers compare the estimated infrared excesses of these nebulae (IRE, the ratio of measured infrared power to the power available in the form of resonantly-trapped Lyman alpha photons) to those of disk planetary nebulae with similar densities but more normal abundances. Three of the halo planetaries have IRE values similar to those of the disk nebulae, despite the fact that their Fe- and Si-peak gas phase abundances are factors of 10 to 100 lower. However, these halo nebulae have normal or elevated C/H ratios, due to nuclear processing and mixing in their red giant progenitors. Unlike the other halo planetaries, DDDM1 is deficient in carbon as well as in the other light metals. This nebula has a substantially lower IRE than the other halo planetaries, and may be truly dust efficient. Researchers suggest that the deficiency is due to a lack of the raw material for producing carbon-based grains, and that the main bulk constituent of the dust in these planetary nebulae is carbon.

Constraints on baryonic dark matter in the Galactic halo and Local Group

NASA Technical Reports Server (NTRS)

Richstone, Douglas; Gould, Andrew; Guhathakurta, Puragra; Flynn, Chris

1992-01-01

A four-color method and deep CCD data are used to search for very faint metal-poor stars in the direction of the south Galactic pole. The results make it possible to limit the contribution of ordinary old, metal-poor stars to the dynamical halo of the Galaxy or to the Local Group. The ratio of the mass of the halo to its ordinary starlight must be more than about 2000, unless the halo is very small. For the Local Group, this ratio is greater than about 400. If this local dark matter is baryonic, the process of compact-object formation must produce very few 'impurities' in the form of stars similar to those found in globular clusters. The expected number of unbound stars with MV not greater than 6 within 100 pc of the sun is less than 1 based on the present 90-percent upper limit to the Local Group starlight.

Study of galactic halo F(T,TG) wormhole solutions

NASA Astrophysics Data System (ADS)

Sharif, M.; Nazir, Kanwal

In this paper, we investigate static spherically symmetric wormhole solutions with galactic halo region in the background of F(T,TG) gravity. Here, T represents torsion scalar and TG is teleparallel equivalent Gauss-Bonnet term. For this purpose, we consider a diagonal tetrad and two specific F(T,TG) models. We analyze the wormhole structure through shape function graphically for both models. We also investigate the behavior of null/weak energy conditions. Finally, we evaluate the equilibrium condition to check stability of the wormhole solutions. It is concluded that there exists physically viable wormhole solution only for the first model that turns out to be stable.

Ages, chemistry, and type 1A supernovae: Clues to the formation of the galactic stellar halo

NASA Technical Reports Server (NTRS)

Smecker-Hane, Tammy A.; Wyse, Rosemary F. G.

1993-01-01

We endeavor to resolve two conflicting constraints on the duration of the formation of the Galactic stellar halo - 2-3 Gyr age differences in halo stars, and the time scale inferred from the observed constant values of chemical element abundance ratios characteristic of enrichment by Type II supernovae - by investigating the time scale for the onset of Type Ia supernovae (SNIa) in the currently favored progenitor model - mergers of carbon and oxygen white dwarfs (CO WDs).

HST/COS OBSERVATIONS OF GALACTIC HIGH-VELOCITY CLOUDS: FOUR ACTIVE GALACTIC NUCLEUS SIGHT LINES THROUGH COMPLEX C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shull, J. Michael; Stevans, Matthew; Danforth, Charles

2011-10-01

We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in Complex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), together with new 21 cm spectra from the Green Bank Telescope. The wide spectral coverage and higher signal-to-noise ratio, compared to previous HST spectra, provide better velocity definition of the HVC absorption, additional ionization species (including high ions), and improved abundances in this halo gas. Complex C has a metallicity of 10%-30% solar and a wide range of ions, suggesting dynamical and thermal interactions with hot gas in the Galactic halo. Spectra in the COSmore » medium-resolution G130M (1133-1468 A) and G160M (1383-1796 A) gratings detect ultraviolet absorption lines from eight elements in low-ionization states (O I, N I, C II, S II, Si II, Al II, Fe II, P II) and three elements in intermediate- and high-ionization states (Si III, Si IV, C IV, N V). Our four active galactic nucleus sight lines toward Mrk 817, Mrk 290, Mrk 876, and PG 1259+593 have high-velocity H I and O VI column densities, log N{sub Hi}= 19.39-20.05 and log N{sub Ovi}= 13.58-14.10, with substantial amounts of kinematically associated photoionized gas. The high-ion abundance ratios are consistent with cooling interfaces between photoionized and collisionally ionized gas: N(C IV)/N(O VI) {approx} 0.3-0.5, N(Si IV)/N(O VI) {approx} 0.05-0.11, N(N V)/N(O VI) {approx} 0.07-0.13, and N(Si IV)/N(Si III) {approx}0.2.« less

Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

NASA Astrophysics Data System (ADS)

Martell, S. L.; Smolinski, J. P.; Beers, T. C.; Grebel, E. K.

2011-10-01

We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8 ≤ [Fe/H] ≤ -1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster mass-loss processes. Extrapolating from theoretical models of two-generation globular cluster formation, this result suggests that globular clusters contributed significant numbers of stars to the construction of the Galactic halo: we calculate that a minimum of 17% of the present-day mass of the stellar halo was originally formed in globular clusters. The ratio of CN-strong to CN-normal stars drops with Galactocentric distance, suggesting that the inner-halo population may be the primary repository of these stars. Full Tables 1 and 3 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/534/A136

Ablation from High Velocity Clouds: A Source for Low Velocity Ionized Gas

NASA Astrophysics Data System (ADS)

Shelton, Robin L.; Henley, D. B.; Kwak, K.

2012-05-01

High velocity clouds shed material as they move through the Galaxy. This material mixes with the Galactic interstellar medium, resulting in plasma whose temperature and ionization levels are intermediate between those of the cloud and those of the Galaxy. As time passes, the mixed material slows to the velocity of the ambient gas. This raises the possibility that initially warm (T 10^3 K), poorly ionized clouds moving through hot (T 10^6 K), very highly ionized ambient gas could lead to mixed gas that harbors significant numbers of high ions (O+5, N+4, and C+3) and thus helps to explain the large numbers of low-velocity high ions seen on high latitude lines of sight through the Galactic halo. We have used a series of detailed FLASH simulations in order to track the hydrodynamics of warm clouds embedded in hot Galactic halo gas. These simulations tracked the ablated material as it mixed and slowed to low velocities. By following the ionization levels of the gas in a time-dependent fashion, we determined that the mixed material is rich in O+5, N+4, and C+3 ions and continues to contain these ions for some time after slowing to low velocities. Combining our simulational results with estimates of the high velocity cloud infall rate leads to the finding that the mixed gas can account for 1/3 of the normal-velocity O+5 column density found on high latitude lines of sight. It accounts for lesser fractions of the N+4 and C+3 column densities. We will discuss our high velocity cloud results as part of a composite halo model that also includes cooling Galactic fountain gas, isolated supernova remnants, and ionizing photons.

Herschel Galactic plane survey of ionized gas traced by [NII

NASA Astrophysics Data System (ADS)

Yildiz, Umut; Goldsmith, Paul; Pineda, Jorge; Langer, William

2015-01-01

Far infrared and sub-/millimeter atomic & ionic fine structure and molecular rotational lines are powerful tracers of star formation on both Galactic and extragalactic scales. Although CO lines trace cool to moderately warm molecular gas, ionized carbon [CII] produces the strongest lines, which arise from almost all reasonably warm (T>50 K) parts of the ISM. However, [CII] alone cannot distinguish highly ionized gas from weakly ionized gas. [NII] plays a significant role in star formation as it is produced only in ionized regions; in [HII] regions as well as diffuse ionized gas. The ionization potential of nitrogen (14.5 eV) is greater than that of hydrogen (13.6 eV), therefore the ionized nitrogen [NII] lines reflect the effects of massive stars, with possible enhancement from X-ray and shock heating from the surroundings. Two far-infrared 122 um and 205 um [NII] fine structure spectral lines are targeted via Photodetector Array Camera and Spectrometer (PACS) onboard Herschel Space Observatory. The sample consists of 149 line-of-sight (LOS) positions in the Galactic plane. These positions overlap with the [CII] 158 um observations obtained with the GOT C+ survey. With a reasonable assumption that the emission from both 122 um and 205 um lines originate in the same gas; [NII] 122/205 um line ratio indicates the a good measure of the electron density of each of the LOS positions. [NII] detections are mainly toward the Galactic center direction and the [NII] electron densities are found between 7-50 cm^-3, which is enhanced WIM (Warm Ionized Medium). WIM densities are expected to be much lower (~1 cm-3), therefore non-detections toward the opposite side of the Galactic Center shows abundant of this gas. The pixel to pixel variation of the emission within a single Herschel pointing is relatively small, which is interpreted as the [NII] emission comes from an extended gas. It is important to quantify what fraction of [CII] emission arises in the ionized gas. Thus, with

Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

NASA Technical Reports Server (NTRS)

Maloney, Philip

1992-01-01

Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-velocity Cloud Complex A

NASA Astrophysics Data System (ADS)

Barger, K. A.; Haffner, L. M.; Wakker, B. P.; Hill, Alex. S.; Madsen, G. J.; Duncan, A. K.

2012-12-01

The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin Hα Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km s-1 in the local standard of rest reference frame. These observations include the first full Hα intensity map of Complex A across (\\mathit {l, b}) = (124{^\\circ }, 18{^\\circ }) to (171°, 53°) and deep targeted observations in Hα, [S II] λ6716, [N II] λ6584, and [O I] λ6300 toward regions with high H I column densities, background quasars, and stars. The Hα data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 106 M ⊙. We find that the Bland-Hawthorn & Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 104 K or for gas with a high fraction of singly ionized nitrogen and sulfur.

Properties of the highly ionized disk and halo gas toward two distant high-latitude stars

NASA Technical Reports Server (NTRS)

Savage, Blair D.; Sembach, K. R.

1994-01-01

absorption, part of the C IV absorption, and has very little associated Si IV absorption. In this gas N(C IV)/N(N V) is approximately 1 to 3. This gas is hot (T greater than 2 x 10(exp 5) K) and may be tracing the cooling gas of supernova (SN) bubbles or a Galactic fountain. The relative mixture of these two types of highly ionized gas varies from one sight line to the next. The two sight lines in this study sample halo gas in the solar neighborhood and have a smaller percentage of the more highly ionized gas than inner Galaxy sight lines.

Galactic Halo Stars in Phase Space: A Hint of Satellite Accretion?

NASA Astrophysics Data System (ADS)

Brook, Chris B.; Kawata, Daisuke; Gibson, Brad K.; Flynn, Chris

2003-03-01

The present-day chemical and dynamical properties of the Milky Way bear the imprint of the Galaxy's formation and evolutionary history. One of the most enduring and critical debates surrounding Galactic evolution is that regarding the competition between ``satellite accretion'' and ``monolithic collapse'' the apparent strong correlation between orbital eccentricity and metallicity of halo stars was originally used as supporting evidence for the latter. While modern-day unbiased samples no longer support the claims for a significant correlation, recent evidence has been presented by Chiba & Beers for the existence of a minor population of high-eccentricity metal-deficient halo stars. It has been suggested that these stars represent the signature of a rapid (if minor) collapse phase in the Galaxy's history. Employing velocity and integrals of motion phase-space projections of these stars, coupled with a series of N-body/smoothed particle hydrodynamic chemodynamical simulations, we suggest that an alternative mechanism for creating such stars may be the recent accretion of a polar orbit dwarf galaxy.

Mapping photometric metallicities in the Galactic halo using broadband photometry

NASA Astrophysics Data System (ADS)

Hebenstreit, Samuel David; Nidever, David L.; Munn, Jeffrey A.; Majewski, Steven R.

2018-06-01

An important objective of modern Astrophysics is to trace the history of galaxies and the dynamics of their formations. The outer regions of the Milky Way, including the Galactic halo, could potentially elucidate the evolutionary history of our galaxy. In this study, we make use of extensive DDO51 photometry combined with SDSS broadband photometry to select giant stars reaching to 90 kpc. Photometric metallicities, calibrated by overlapping spectroscopic data (SDSS, APOGEE and LAMOST), and distances are calculated for all giant stars. Using these metallicities and distances, we construct metallicity distribution functions (MDFs) from these stars. We study the MDFs for information pertaining to the accretion history of the Milky Way.

V474 Car: A RARE HALO RS CVn BINARY IN RETROGRADE GALACTIC ORBIT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bubar, Eric J.; Mamajek, Eric E.; Jensen, Eric L. N.

We report the discovery that the star V474 Car is an extremely active, high velocity halo RS CVn system. The star was originally identified as a possible pre-main-sequence star in Carina, given its enhanced stellar activity, rapid rotation (10.3 days), enhanced Li, and absolute magnitude which places it above the main sequence (MS). However, its extreme radial velocity (264 km s{sup -1}) suggested that this system was unlike any previously known pre-MS system. Our detailed spectroscopic analysis of echelle spectra taken with the CTIO 4 m finds that V474 Car is both a spectroscopic binary with an orbital period similarmore » to the photometric rotation period and metal-poor ([Fe/H] {approx_equal}-0.99). The star's Galactic orbit is extremely eccentric (e {approx_equal} 0.93) with a perigalacticon of only {approx}0.3 kpc of the Galactic center-and the eccentricity and smallness of its perigalacticon are surpassed by only {approx}0.05% of local F/G-type field stars. The observed characteristics are consistent with V474 Car being a high-velocity, metal-poor, tidally locked, chromospherically active binary, i.e., a halo RS CVn binary, and one of only a few such specimens known.« less

Baryonic dark clusters in galactic halos and their observable consequences

NASA Technical Reports Server (NTRS)

Wasserman, Ira; Salpeter, Edwin E.

1994-01-01

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

PRESENT-DAY GALACTIC EVOLUTION: LOW-METALLICITY, WARM, IONIZED GAS INFLOW ASSOCIATED WITH HIGH-VELOCITY CLOUD COMPLEX A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barger, K. A.; Haffner, L. M.; Wakker, B. P.

2012-12-20

The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin H{alpha} Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km s{sup -1} in the local standard of rest reference frame. These observations include the first full H{alpha} intensity map of Complex A across (l, b) = (124 Degree-Sign , 18 Degree-Sign ) to (171 Degree-Sign , 53 Degree-Sign ) and deep targeted observationsmore » in H{alpha}, [S II] {lambda}6716, [N II] {lambda}6584, and [O I] {lambda}6300 toward regions with high H I column densities, background quasars, and stars. The H{alpha} data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 10{sup 6} M{sub Sun }. We find that the Bland-Hawthorn and Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 10{sup 4} K or for gas with a high fraction of singly ionized nitrogen and sulfur.« less

Ionized haloes in planetary nebulae: new discoveries, literature compilation and basic statistical properties

NASA Astrophysics Data System (ADS)

Corradi, R. L. M.; Schönberner, D.; Steffen, M.; Perinotto, M.

2003-04-01

We present a comprehensive observational study of haloes around planetary nebulae (PNe). Deep Hα+[NII] and/or [OIII] narrow-band images have been obtained for 35 PNe, and faint extended haloes have been newly discovered in the following 10 objects: Cn 1-5, IC 2165, IC 2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, and possibly IC 1747. New deep images have also been obtained of other known or suspected haloes, including the huge extended emission around NGC 3242 and Sh 2-200. In addition, the literature was searched, and together with the new observations an improved data base containing some 50 PN haloes has been compiled. The halo sample is illustrated in an image atlas contained in this paper, and the original images are made available for use by the scientific community at http://www.ing. iac.es/~rcorradi/HALOES/. The haloes have been classified following the predictions of modern radiation-hydrodynamical simulations that describe the formation and evolution of ionized multiple shells and haloes around PNe. According to the models, the observed haloes have been divided into the following groups: (i) circular or slightly elliptical asymptotic giant branch (AGB) haloes, which contain the signature of the last thermal pulse on the AGB; (ii) highly asymmetrical AGB haloes; (iii) candidate recombination haloes, i.e. limb-brightened extended shells that are expected to be produced by recombination during the late post-AGB evolution, when the luminosity of the central star drops rapidly by a significant factor; (iv) uncertain cases which deserve further study for a reliable classification; (v) non-detections, i.e. PNe in which no halo is found to a level of <~10-3 the peak surface brightness of the inner nebulae. We discuss the properties of the haloes: detection rate, morphology, location of the central stars in the Hertzsprung-Russell diagram, sizes, surface brightness profiles, and kinematical ages. Among the most

A New Determination of the Luminosity Function of the Galactic Halo.

NASA Astrophysics Data System (ADS)

Dawson, Peter Charles

The luminosity function of the galactic halo is determined by subtracting from the observed numbers of proper motion stars in the LHS Catalogue the expected numbers of main-sequence, degenerate, and giant stars of the disk population. Selection effects are accounted for by Monte Carlo simulations based upon realistic colour-luminosity relations and kinematic models. The catalogue is shown to be highly complete, and a calibration of the magnitude estimates therein is presented. It is found that, locally, the ratio of disk to halo material is close to 950, and that the mass density in main sequence and subgiant halo stars with 3 < M(,v) < 14 is about 2 x 10('-5) M(,o) pc('-3). With due allowance for white dwarfs and binaries, and taking into account the possibility of a moderate rate of halo rotation, it is argued that the total density does not much exceed 5 x 10('-5) M(,o) pc('-3), in which case the total mass interior to the sun is of the order of 5 x 10('8) M(,o) for a density distribution which projects to a de Vaucouleurs r(' 1/4) law. It is demonstrated that if the Wielen luminosity function is a faithful representation of the stellar distribution in the solar neighbourhood, then the observed numbers of large proper motion stars are inconsistent with the presence of an intermediate popula- tion at the level, and with the kinematics advocated recently by Gilmore and Reid. The initial mass function (IMF) of the halo is considered, and weak evidence is presented that its slope is at least not shallower than that of the disk population IMF. A crude estimate of the halo's age, based on a comparison of the main sequence turnoff in the reduced proper motion diagram with theoretical models is obtained; a tentative lower limit is 15 Gyr with a best estimate of between 15 and 18 Gyr. Finally, the luminosity function obtained here is compared with those determined in other investigations.

Halo histories versus galaxy properties at z = 0 II: large-scale galactic conformity

NASA Astrophysics Data System (ADS)

Tinker, Jeremy L.; Hahn, ChangHoon; Mao, Yao-Yuan; Wetzel, Andrew R.; Conroy, Charlie

2018-06-01

Using group catalogues from the Sloan Digital Sky Survey (SDSS) Data Release 7, we measure galactic conformity in the local universe. We measure the quenched fraction of neighbour galaxies around isolated primary galaxies, dividing the isolated sample into star-forming and quiescent objects. We restrict our measurements to scales >1 Mpc to probe the correlations between halo formation histories. Over the stellar mass range 109.7 ≤ M*/M⊙ ≤ 1010.9, we find minimal evidence for conformity. We further compare these data to predictions of the halo age-matching model, in which the oldest galaxies are associated with the oldest haloes. For models with strong correlations between halo and stellar age, the conformity is too large to be consistent with the data. Weaker implementations of the age-matching model would not produce a detectable signal in SDSS data. We reproduce the results of Kauffmann et al., in which the star formation rates of neighbour galaxies are reduced around primary galaxies when the primaries are low star formers. However, we find this result is mainly driven by contamination in the isolation criterion; when removing the small fraction of satellite galaxies in the sample, the conformity signal largely goes away. Lastly, we show that small conformity signals, i.e. 2-5 per cent differences in the quenched fractions of neighbour galaxies, can be produced by mechanisms other than halo assembly bias. For example, if passive galaxies occupy more massive haloes than star-forming galaxies of the same stellar mass, a conformity signal that is consistent with recent measurements from PRIMUS (Berti et al.) can be produced.

A Low-metallicity Molecular Cloud in the Lower Galactic Halo

NASA Astrophysics Data System (ADS)

Hernandez, Audra K.; Wakker, Bart P.; Benjamin, Robert A.; French, David; Kerp, Juergen; Lockman, Felix J.; O'Toole, Simon; Winkel, Benjamin

2013-11-01

We find evidence for the impact of infalling, low-metallicity gas on the Galactic disk. This is based on FUV absorption line spectra, 21 cm emission line spectra, and far-infrared (FIR) mapping to estimate the abundance and physical properties of IV21 (IVC135+54-45), a galactic intermediate-velocity molecular cloud that lies ~300 pc above the disk. The metallicity of IV21 was estimated using observations toward the subdwarf B star PG1144+615, located at a projected distance of 16 pc from the cloud's densest core, by measuring ion and H I column densities for comparison with known solar abundances. Despite the cloud's bright FIR emission and large column densities of molecular gas as traced by CO, we find that it has a sub-solar metallicity of log (Z/Z ⊙) = -0.43 ± 0.12 dex. IV21 is thus the first known sub-solar metallicity cloud in the solar neighborhood. In contrast, most intermediate-velocity clouds (IVC) have near-solar metallicities and are believed to originate in the Galactic Fountain. The cloud's low metallicity is also atypical for Galactic molecular clouds, especially in light of the bright FIR emission which suggest a substantial dust content. The measured I 100 μm/N(H I) ratio is a factor of three below the average found in high latitude H I clouds within the solar neighborhood. We argue that IV21 represents the impact of an infalling, low-metallicity high-velocity cloud that is mixing with disk gas in the lower Galactic halo. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from MAST at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program No. 12275. The Green Bank Telescope is part of the National Radio Astronomy Observatory which is a Facility of the National Science Foundation, operated by Associated Universities, Inc.

Palomar 13: An Unusual Stellar System in the Galactic Halo

NASA Astrophysics Data System (ADS)

Côté, Patrick; Djorgovski, S. G.; Meylan, G.; Castro, Sandra; McCarthy, J. K.

2002-08-01

We report the first results of a program to study the internal kinematics of globular clusters in the outer halo of the Milky Way. Using the Keck telescope and High Resolution Echelle Spectrometer, we have measured precise radial velocities for 30 candidate red giants in the direction of Palomar 13, an object traditionally cataloged as a compact, low-luminosity globular cluster. We have combined these radial velocities with published proper motion membership probabilities and new CCD photometry from the Keck and Canada-France-Hawaii telescopes to isolate a sample of 21 probable members. We find a systemic velocity of s=24.1+/-0.5 km s-1 and a projected, intrinsic velocity dispersion of σp=2.2+/-0.4 km s-1. Although modest, this dispersion is nevertheless several times larger than that expected for a globular cluster of this luminosity and central concentration. Taken at face value, it implies a mass-to-light ratio of ΥV=40+24-17 based on the best-fit King-Michie model. The surface density profile of Palomar 13 also appears unusual compared to most Galactic globular clusters; depending upon the details of background subtraction and model-fitting, Palomar 13 either contains a substantial population of ``extratidal'' stars, or is considerably more spatially extended than previously suspected. The full surface density profile is equally well fitted by a King-Michie model having a high concentration and large tidal radius, or by a Navarro-Frenk-White model. We examine-and tentatively reject-a number of possible origins for the observed characteristics of Palomar 13 (e.g., velocity ``jitter'' among the red giant branch stars, spectroscopic binary stars, nonstandard mass functions, modified Newtonian dynamics) and conclude that the two leading explanations are either catastrophic heating during a recent perigalacticon passage or the presence of a dark matter halo. The available evidence therefore suggests that Palomar 13 is either a globular cluster that is now in

Ultra Light Axionic Dark Matter: Galactic Halos and Implications for Observations with Pulsar Timing Arrays

NASA Astrophysics Data System (ADS)

de Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Shive, Hsi-Yu; Lazkoz, Ruth

2018-01-01

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors alternative candidates such as light axionic dark matter that naturally arise in string theory. Cosmological N-body simulations have shown that axionic dark matter forms a solitonic core of size of ≃ 150 pc in the innermost region of the galactic halos. The oscillating scalar field associated to the axionic dark matter halo produces an oscillating gravitational potential that induces a time dilation of the pulse arrival time of ≃ 400 ns/(m_B/10^{-22} eV) for pulsar within such a solitonic core. Over the whole galaxy, the averaged predicted signal may be detectable with current and forthcoming pulsar timing array telescopes.

VizieR Online Data Catalog: The SEGUE K giant survey. III. Galactic halo (Janesh+, 2016)

NASA Astrophysics Data System (ADS)

Janesh, W.; Morrison, H. L.; Ma, Z.; Rockosi, C.; Starkenburg, E.; Xue, X. X.; Rix, H.-W.; Harding, P.; Beers, T. C.; Johnson, J.; Lee, Y. S.; Schneider, D. P.

2016-03-01

We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration (SEGUE) project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (~33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity. (2 data files).

New Halo Stars of the Galactic Globular Clusters M3 and M13 in the LAMOST DR1 Catalog

NASA Astrophysics Data System (ADS)

Navin, Colin A.; Martell, Sarah L.; Zucker, Daniel B.

2016-10-01

M3 and M13 are Galactic globular clusters with previous reports of surrounding stellar halos. We present the results of a search for members and extratidal cluster halo stars within and outside of the tidal radius of these clusters in the LAMOST Data Release 1. We find seven candidate cluster members (inside the tidal radius) of both M3 and M13, respectively. In M3 we also identify eight candidate extratidal cluster halo stars at distances up to ˜9.8 times the tidal radius, and in M13 we identify 12 candidate extratidal cluster halo stars at distances up to ˜13.8 times the tidal radius. These results support previous indications that both M3 and M13 are surrounded by extended stellar halos, and we find that the GC destruction rates corresponding to the observed mass loss are generally significantly higher than theoretical studies predict.

The global dark halo structure of the Andromeda galaxy

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Chiba, Masashi

2014-01-01

We set new limits on the global shape of the dark halo in the Andromeda galaxy based on axisymmetric mass models constructed by Hayashi & Chiba (2012). This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Based on the application of our models to latest kinematical data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield not a spherical but a prolate shape for its dark halo. We also find that the prolate dark halo is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their galactic host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web.

Using artificial neural networks to constrain the halo baryon fraction during reionization

NASA Astrophysics Data System (ADS)

Sullivan, David; Iliev, Ilian T.; Dixon, Keri L.

2018-01-01

Radiative feedback from stars and galaxies has been proposed as a potential solution to many of the tensions with simplistic galaxy formation models based on Λcold dark matter, such as the faint end of the ultraviolet (UV) luminosity function. The total energy budget of radiation could exceed that of galactic winds and supernovae combined, which has driven the development of sophisticated algorithms that evolve both the radiation field and the hydrodynamical response of gas simultaneously, in a cosmological context. We probe self-feedback on galactic scales using the adaptive mesh refinement, radiative transfer, hydrodynamics, and N-body code RAMSES-RT. Unlike previous studies which assume a homogeneous UV background, we self-consistently evolve both the radiation field and gas to constrain the halo baryon fraction during cosmic reionization. We demonstrate that the characteristic halo mass with mean baryon fraction half the cosmic mean, Mc(z), shows very little variation as a function of mass-weighted ionization fraction. Furthermore, we find that the inclusion of metal cooling and the ability to resolve scales small enough for self-shielding to become efficient leads to a significant drop in Mc when compared to recent studies. Finally, we develop an artificial neural network that is capable of predicting the baryon fraction of haloes based on recent tidal interactions, gas temperature, and mass-weighted ionization fraction. Such a model can be applied to any reionization history, and trivially incorporated into semi-analytical models of galaxy formation.

A Hot Gaseous Galaxy Halo Candidate with Mg X Absorption

NASA Astrophysics Data System (ADS)

Qu, Zhijie; Bregman, Joel N.

2016-12-01

The hot gas in galaxy halos may account for a significant fraction of missing baryons in galaxies, and some of these gases can be traced by high ionization absorption systems in QSO UV spectra. Using high S/N Hubble Space Telescope/Cosmic Origins Spectrograph spectra, we discovered a high ionization state system at z = 1.1912 in the sightline toward LBQS 1435-0134, and two-component absorption lines are matched for Mg x, Ne viii, Ne VI, O VI, Ne v, O v, Ne IV, O IV, N IV, O III, and H I. Mg x, detected for the first time (5.8σ), is a particularly direct tracer of hot galactic halos, as its peak ion fraction occurs near 106.1 K, about the temperature of a virialized hot galaxy halo of mass ˜ 0.5{M}* . With Mg x and Ne viii, a photoionization model cannot reproduce the observed column densities with path lengths of galaxy halos. For collisional ionization models, one or two-temperature models do not produce acceptable fits, but a three-temperature model or a power-law model can produce the observed results. In the power-law model, {dN}/{dT}={10}4.4+/- 2.2-[Z/X]{T}1.55+/- 0.41 with temperatures in the range of {10}4.39+/- 0.13 {{K}}\\lt T\\lt {10}6.04+/- 0.05 {{K}}, the total hydrogen column density is 8.2× {10}19(0.3 {Z}⊙ /Z) {{cm}}-2 and the positive power-law index indicates most of the mass is at the high temperature end. We suggest that this absorption system is a hot volume-filled galaxy halo rather than interaction layers between the hot halo and cool clouds. The temperature dependence of the column density is likely due to the local mixture of multiple phase gases.

Revealing the Ionization Properties of the Magellanic Stream Using Optical Emission

NASA Astrophysics Data System (ADS)

Barger, K. A.; Madsen, G. J.; Fox, A. J.; Wakker, B. P.; Bland-Hawthorn, J.; Nidever, D.; Haffner, L. M.; Antwi-Danso, Jacqueline; Hernandez, Michael; Lehner, N.; Hill, A. S.; Curzons, A.; Tepper-García, T.

2017-12-01

The Magellanic Stream, a gaseous tail that trails behind the Magellanic Clouds, could replenish the Milky Way (MW) with a tremendous amount of gas if it reaches the Galactic disk before it evaporates into the halo. To determine how the Magellanic Stream’s properties change along its length, we have conducted an observational study of the Hα emission, along with other optical warm ionized gas tracers, toward 39 sight lines. Using the Wisconsin Hα Mapper telescope, we detect Hα emission brighter than 30–50 mR in 26 of our 39 sight lines. This Hα emission extends over 2^\\circ away from the H I emission. By comparing {I}{{H}α } and {I}[{{O}{{I}}]}, we find that regions with {log}{N}{{H}{{I}}}/{{cm}}-2≈ 19.5{--}20.0 are 16%–67% ionized. Most of the {I}{{H}α } along the Magellanic Stream are much higher than expected if the primary ionization source is photoionization from Magellanic Clouds, the MW, and the extragalactic background. We find that the additional contribution from self ionization through a “shock cascade” that results as the Stream plows through the halo might be sufficient to reproduce the underlying level of Hα emission along the Stream. In the sparsely sampled region below the South Galactic Pole, there exists a subset of sight lines with uncharacteristically bright emission, which suggest that gas is being ionized further by an additional source that could be a linked to energetic processes associated with the Galactic center.

A Modified Kinematic Model of Neutral and Ionized Gas in Galactic Center

NASA Astrophysics Data System (ADS)

Krishnarao, Dhanesh; Benjamin, Robert A.; Haffner, L. Matthew

2018-01-01

Gas near the center of the Milky Way is very complex across all phases (cold, warm, neutral, ionized, atomic, molecular, etc.) and shows strong observational evidence for warping, lopsided orientations and strongly non-circular kinematics. Historically, the kinematic complexities were modeled with many discrete features involved with expulsive phenomena near Galactic Center. However, much of the observed emission can be explained with a single unified and smooth density structure when geometrical and perspective effects are accounted for. Here we present a new model for a tilted, elliptical disk of gas within the inner 2 kpc of Galactic center based on the series of models following Burton & Liszt (1978 - 1992, Papers I- V). Machine learning techniques such as the Histogram of Oriented Gradients image correlation statistic are used to optimize the geometry and kinematics of neutral and ionized gas in 3D observational space (position,position, velocity). The model successfully predicts emission from neutral gas as seen by HI (Hi4Pi) and explains anomalous ionized gas features in H-Alpha emission (Wisconsin H-Alpha Mapper) and UV absorption lines (Hubble Space Telescope - Space Telescope Imaging Spectrograph). The modeled distribution of this tilted gas disk along with its kinematics of elliptical x1 orbits can reveal new insight about the Galactic Bar, star formation, and high-velocity gas near Galactic Center and its relation with the Fermi Bubble.

The ionizing radiation of Seyfert 2 galactic nuclei

NASA Technical Reports Server (NTRS)

Ho, Luis C.; Shields, Joseph C.; Filippenko, Alexei V.

1993-01-01

We report the discovery of a nonrandom trend in the dispersion of emission-line intensity ratios for Seyfert 2 galaxies. The sense of this pattern suggests the influence of a single physical parameter, the hardness of the ionizing continuum, which controls the heating energy per ionizing photon. We compare the observed line ratios with new photoionization calculations and find that the observed distributions can be reproduced if the ionizing continuum is parametrized by a power law. Our results also suggest an inverse correlation between luminosity and continuum hardness for Seyfert 2 nuclei; if true, this trend extends a similar pattern known in quasars and Seyfert 1 galaxies to active galactic nuclei of lower luminosity. Samples of Seyfert 2 nuclei with improved selection uniformity are desirable for elaboration of these findings.

The Gaia-ESO Survey: A globular cluster escapee in the Galactic halo

NASA Astrophysics Data System (ADS)

Lind, K.; Koposov, S. E.; Battistini, C.; Marino, A. F.; Ruchti, G.; Serenelli, A.; Worley, C. C.; Alves-Brito, A.; Asplund, M.; Barklem, P. S.; Bensby, T.; Bergemann, M.; Blanco-Cuaresma, S.; Bragaglia, A.; Edvardsson, B.; Feltzing, S.; Gruyters, P.; Heiter, U.; Jofre, P.; Korn, A. J.; Nordlander, T.; Ryde, N.; Soubiran, C.; Gilmore, G.; Randich, S.; Ferguson, A. M. N.; Jeffries, R. D.; Vallenari, A.; Allende Prieto, C.; Pancino, E.; Recio-Blanco, A.; Romano, D.; Smiljanic, R.; Bellazzini, M.; Damiani, F.; Hill, V.; de Laverny, P.; Jackson, R. J.; Lardo, C.; Zaggia, S.

2015-03-01

A small fraction of the halo field is made up of stars that share the light element (Z ≤ 13) anomalies characteristic of second generation globular cluster (GC) stars. The ejected stars shed light on the formation of the Galactic halo by tracing the dynamical history of the clusters, which are believed to have once been more massive. Some of these ejected stars are expected to show strong Al enhancement at the expense of shortage of Mg, but until now no such star has been found. We search for outliers in the Mg and Al abundances of the few hundreds of halo field stars observed in the first eighteen months of the Gaia-ESO public spectroscopic survey. One halo star at the base of the red giant branch, here referred to as 22593757-4648029 is found to have [ Mg/Fe ] = -0.36 ± 0.04 and [ Al/Fe ] = 0.99 ± 0.08, which is compatible with the most extreme ratios detected in GCs so far. We compare the orbit of 22593757-4648029 to GCs of similar metallicity andfind it unlikely that this star has been tidally stripped with low ejection velocity from any of the clusters. However, both chemical and kinematic arguments render it plausible that the star has been ejected at high velocity from the anomalous GC ω Centauri within the last few billion years. We cannot rule out other progenitor GCs, because some may have disrupted fully, and the abundance and orbital data are inadequate for many of those that are still intact. Based on data acquired by the Gaia-ESO Survey, programme ID 188.B-3002. Observations were made with ESO Telescopes at the La Silla Paranal Observatory.Appendix A is available in electronic form at http://www.aanda.org

Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos

NASA Astrophysics Data System (ADS)

Oppenheimer, Benjamin D.; Segers, Marijke; Schaye, Joop; Richings, Alexander J.; Crain, Robert A.

2018-03-01

Proximity zone fossils (PZFs) are ionization signatures around recently active galactic nuclei (AGNs) where metal species in the circumgalactic medium remain overionized after the AGNs have shut off due to their long recombination time scales. We explore cosmological zoom hydrodynamic simulations, using the EAGLE (Evolution and Assembly of GaLaxies and their Environments) model paired with a non-equilibrium ionization and cooling module including time-variable AGN radiation to model PZFs around star-forming disc galaxies in the z ˜ 0.2 Universe. Previous simulations typically underestimated the O VI content of galactic haloes, but we show that plausible PZF models increase O VI column densities by 2 - 3 × to achieve the levels observed around COS-Halos star-forming galaxies out to 150 kpc. Models with AGN bolometric luminosities ≳ 1043.6erg s- 1, duty cycle fractions ≲ 10 per cent, and AGN lifetimes ≲ 106 yr are the most promising, because their supermassive black holes grow at the cosmologically expected rate and they mostly appear as inactive AGN, consistent with COS-Halos. The central requirement is that the typical star-forming galaxy hosted an active AGN within a time-scale comparable to the recombination time of a high metal ion, which for circumgalactic O VI is ≈107 yr. H I, by contrast, returns to equilibrium much more rapidly due to its low neutral fraction and does not show a significant PZF effect. O VI absorption features originating from PZFs appear narrow, indicating photoionization, and are often well aligned with lower metal ion species. PZFs are highly likely to affect the physical interpretation of circumgalactic high ionization metal lines if, as expected, normal galaxies host flickering AGN.

Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo

NASA Astrophysics Data System (ADS)

Cojocaru, Elena-Ruxandra

2016-09-01

White dwarfs are fossil stars that can encode valuable information about the formation, evolution and other properties of the different Galactic stellar populations. They are the direct descendants of main-sequence stars with masses ranging from ∼0.8 M⊙ to ∼10 M⊙, which means that over 95% of the stars in our Galaxy will eventually become white dwarfs. This fact, correlated with the excellent quality of modern white dwarf cooling models, clearly marks their potential as cosmic clocks for estimating the ages of Galactic stellar populations, as well as place white dwarfs as privileged objects in understanding several actual astrophysical problems. Stellar population synthesis methods (Tinsley, 1968) use theoretical evolutionary sequences to reproduce luminosities, temperatures and other parameters building up to a synthetic population that can be readily compared to an observed sample of stars. Such techniques are perfect for the study of the different white dwarf populations in our Galaxy and their strength has only grown in recent years, fueled both by improved evolutionary sequences and detailed cooling tracks and also by the ever growing samples of white dwarfs identified through modern survey missions. In particular, the work presented in this thesis uses an updated population synthesis code based on previous versions of the code from our group (García-Berro et al., 1999; Torres et al., 2002; García-Berro et al., 2004; Torres et al., 2005; Camacho et al., 2014). Our synthetic population code, based on Monte Carlo statistical techniques, has been extensively used in the study of the disk (García-Berro et al., 1! 999; Torres et al., 2001; Torres & García-Berro, 2016) and halo (Torres et al., 2002; García-Berro et al., 2004) single white-dwarf population, white dwarf plus main sequence stars (Camacho et al., 2014), as well as open clusters such as NGC 6791 (García-Berro et al., 2010; García-Berro et al., 2011) or globular clusters, as 47 Tuc (Garc

Is the Milky Way's hot halo convectively unstable?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henley, David B.; Shelton, Robin L., E-mail: dbh@physast.uga.edu

2014-03-20

We investigate the convective stability of two popular types of model of the gas distribution in the hot Galactic halo. We first consider models in which the halo density and temperature decrease exponentially with height above the disk. These halo models were created to account for the fact that, on some sight lines, the halo's X-ray emission lines and absorption lines yield different temperatures, implying that the halo is non-isothermal. We show that the hot gas in these exponential models is convectively unstable if γ < 3/2, where γ is the ratio of the temperature and density scale heights. Usingmore » published measurements of γ and its uncertainty, we use Bayes' theorem to infer posterior probability distributions for γ, and hence the probability that the halo is convectively unstable for different sight lines. We find that, if these exponential models are good descriptions of the hot halo gas, at least in the first few kiloparsecs from the plane, the hot halo is reasonably likely to be convectively unstable on two of the three sight lines for which scale height information is available. We also consider more extended models of the halo. While isothermal halo models are convectively stable if the density decreases with distance from the Galaxy, a model of an extended adiabatic halo in hydrostatic equilibrium with the Galaxy's dark matter is on the boundary between stability and instability. However, we find that radiative cooling may perturb this model in the direction of convective instability. If the Galactic halo is indeed convectively unstable, this would argue in favor of supernova activity in the Galactic disk contributing to the heating of the hot halo gas.« less

Dynamics of the CMZ - Giant Magnetic Loops Connection in the Galactic Center

NASA Astrophysics Data System (ADS)

Langer, William

2012-10-01

Understanding the mass transfer and dynamics among the Galactic Center, the disk, and the halo of the Milky Way is fundamental to the study of the evolution of galaxies and star formation. Several giant molecular loops (GML), detected in CO maps of the Galactic Center, are likely the result of the magnetic Parker instability. We have new evidence of a possible dynamical connection between these loops and the Central Molecular Zone (CMZ) from a sparse [CII] sampling from our Herschel Open Time Key Project GOT C+. The CMZ-GML region is dynamically active and is likely to have a significant ionized component. However, we have no information on the distribution and dynamics of the ionized gas. The fine-structure lines of [NII] are key probes of the warm ionized medium (WIM) and along with the [CII] can isolate the different ionization components. We have a Herschel OT2 Priority 1 program to map the GML and the CMZ-GML connection in [CII] in more detail. However, we did not propose needed [NII] observations due to an incomplete analysis of our limited GOT C+ data at the time. Here we propose to observe with the SOFIA/GREAT instrument, [NII] in the CMZ-GML interface region using the L1b band, and serendipitously CO (16-15) using band L2. With this data, combined with our Herschel HIFI [CII], Mopra 12CO (1-0) and 13CO (1-0), and HI, we will characterize these important ISM components and their motions in these Galactic Center features. These observations of the nearest such regions of galactic center activity, also have bearing on the dynamics of other galactic nuclei.

RR Lyrae in XSTPS: The halo density profile in the north galactic cap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faccioli, L.; Smith, M. C.; Yuan, H.-B.

We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ≈376.75 deg{sup 2} at α ≈ 150° and δ ≈ 27° down to a magnitude limit of i ≈ 19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more thanmore » 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. and Sesar et al. RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.« less

RR Lyrae in XSTPS: The Halo Density Profile in the North Galactic Cap

NASA Astrophysics Data System (ADS)

Faccioli, L.; Smith, M. C.; Yuan, H.-B.; Zhang, H.-H.; Liu, X.-W.; Zhao, H.-B.; Yao, J.-S.

2014-06-01

We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ≈376.75 deg2 at α ≈ 150° and δ ≈ 27° down to a magnitude limit of i ≈ 19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. and Sesar et al. RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.

The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

NASA Astrophysics Data System (ADS)

Terebey, S.; Fich, M.; Taylor, R.

1999-12-01

A summary of research activities carried out in this eighth and final progress report. The final report includes: this summary document, copies of three published research papers, plus a draft manuscript of a fourth research paper entitled "The Contribution of Ionizing Stars to the FarInfrared and Radio Emission in the Milky Way; Evidence for a Swept-up Shell and Diffuse Ionized Halo around the W4 Chimney/Supershell." The main activity during the final quarterly reporting period was research on W4, including analysis of the radio and far-infrared images, generation of shell models, a literature search, and preparation of a research manuscript. There will be additional consultation with co-authors prior to submission of the paper to the Astrophysical Journal. The results will be presented at the 4th Tetons Summer Conference on "Galactic Structure, Stars, and the ISM" in May 2000. In this fourth and last paper we show W4 has a swept-up partially ionized shell of gas and dust which is powered by the OCl 352 star cluster. Analysis shows there is dense interstellar material directly below the shell, evidence that that the lower W4 shell "ran into a brick wall" and stalled, whereas the upper W4 shell achieved "breakout" to form a Galactic chimney. An ionized halo is evidence of Lyman continuum leakage which ionizes the WIM (warm ionized medium). It has long been postulated that the strong winds and abundant ionizing photons from massive stars are responsible for much of the large scale structure in the interstellar medium (ISM), including the ISM in other galaxies. However standard HII region theory predicts few photons will escape the local HII region. The significance of W4 and this work is it provides a direct example of how stellar winds power a galactic chimney, which in turn leads to a low density cavity from which ionizing photons can escape to large distances to ionize the WIM.

The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

NASA Technical Reports Server (NTRS)

Terebey, S.; Fich, M.; Taylor, R.

1999-01-01

A summary of research activities carried out in this eighth and final progress report. The final report includes: this summary document, copies of three published research papers, plus a draft manuscript of a fourth research paper entitled "The Contribution of Ionizing Stars to the FarInfrared and Radio Emission in the Milky Way; Evidence for a Swept-up Shell and Diffuse Ionized Halo around the W4 Chimney/Supershell." The main activity during the final quarterly reporting period was research on W4, including analysis of the radio and far-infrared images, generation of shell models, a literature search, and preparation of a research manuscript. There will be additional consultation with co-authors prior to submission of the paper to the Astrophysical Journal. The results will be presented at the 4th Tetons Summer Conference on "Galactic Structure, Stars, and the ISM" in May 2000. In this fourth and last paper we show W4 has a swept-up partially ionized shell of gas and dust which is powered by the OCl 352 star cluster. Analysis shows there is dense interstellar material directly below the shell, evidence that that the lower W4 shell "ran into a brick wall" and stalled, whereas the upper W4 shell achieved "breakout" to form a Galactic chimney. An ionized halo is evidence of Lyman continuum leakage which ionizes the WIM (warm ionized medium). It has long been postulated that the strong winds and abundant ionizing photons from massive stars are responsible for much of the large scale structure in the interstellar medium (ISM), including the ISM in other galaxies. However standard HII region theory predicts few photons will escape the local HII region. The significance of W4 and this work is it provides a direct example of how stellar winds power a galactic chimney, which in turn leads to a low density cavity from which ionizing photons can escape to large distances to ionize the WIM.

The Chandra Dust-scattering Halo of Galactic Center Transient Swift J174540.7–290015

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corrales, L. R.; Mon, B.; Haggard, D.

We report the detection of a dust-scattering halo around a recently discovered X-ray transient, Swift J174540.7–290015, which in early 2016 February underwent one of the brightest outbursts ( F {sub X} ≈ 5 × 10{sup −10} erg cm{sup −2} s{sup −1}) observed from a compact object in the Galactic Center field. We analyze four Chandra images that were taken as follow-up observations to Swift discoveries of new Galactic Center transients. After adjusting our spectral extraction for the effects of detector pile-up, we construct a point-spread function for each observation and compare it to the GC field before the outburst. Wemore » find residual surface brightness around Swift J174540.7–290015, which has a shape and temporal evolution consistent with the behavior expected from X-rays scattered by foreground dust. We examine the spectral properties of the source, which shows evidence that the object transitioned from a soft to hard spectral state as it faded below L {sub X} ∼ 10{sup 36} erg s{sup −1}. This behavior is consistent with the hypothesis that the object is a low-mass X-ray binary in the Galactic Center.« less

Diffuse low-ionization gas in the galactic halo casts doubts on z ≃ 0.03 WHIM detections

NASA Astrophysics Data System (ADS)

Nicastro, F.; Senatore, F.; Gupta, A.; Mathur, S.; Krongold, Y.; Elvis, M.; Piro, L.

2016-05-01

In this Letter, we demonstrate that the two claims of z ≃ 0.03 O VII K α absorption lines from Warm Hot Intergalactic Medium (WHIM) along the lines of sight to the blazars H 2356-309 (Buote et al.; Fang et al.) and Mkn 501 (Ren, Fang & Buote) are likely misidentifications of the z = 0 O II K β line produced by a diffuse Low-Ionization Metal Medium in the Galaxy's interstellar and circum-galactic mediums. We perform detailed modelling of all the available high signal-to-noise Chandra Low Energy Transmission Grating (LETG) and XMM-Newton Reflection Grating Spectrometer (RGS) spectra of H 2356-309 and Mkn 501 and demonstrate that the z ≃ 0.03 WHIM absorption along these two sightlines is statistically not required. Our results, however, do not rule out a small contribution from the z ≃ 0.03 O VII K α absorber along the line of sight to H 2356-309. In our model the temperature of the putative z = 0.031 WHIM filament is T = 3 × 105 K and the O VII column density is N_{O VII} ≲ 4× 10^{15} cm-2, twenty times smaller than the O VIIcolumn density previously reported, and now more consistent with the expectations from cosmological hydrodynamical simulations.

The Mysterious 6565 Å Absorption Feature of the Galactic Halo

NASA Astrophysics Data System (ADS)

Sethi, Shiv K.; Shchekinov, Yuri; Nath, Biman B.

2017-12-01

We consider various possible scenarios to explain the recent observation of what has been called a broad Hα absorption in our Galactic halo, with peak optical depth τ ≃ 0.01 and equivalent width W≃ 0.17 \\mathringA . We show that the absorbed feature cannot arise from the circumgalactic and ISM Hα absorption. As the observed absorption feature is quite broad ({{Δ }}λ ≃ 30 \\mathringA ), we also consider CNO lines that lie close to Hα as possible alternatives to explain the feature. We show that such lines could also not account for the observed feature. Instead, we suggest that it could arise from diffuse interstellar bands (DIBs) carriers or polyaromatic hydrocarbons (PAHs) absorption. While we identify several such lines close to the Hα transition, we are unable to determine the molecule responsible for the observed feature, partly because of selection effects that prevent us from identifying DIBs/PAHs features close to Hα using local observations. Deep integration of a few extragalactic sources with high spectral resolution might allow us to distinguish between different possible explanations.

Probing the interstellar dust towards the Galactic Centre: dust-scattering halo around AX J1745.6-2901

NASA Astrophysics Data System (ADS)

Jin, Chichuan; Ponti, Gabriele; Haberl, Frank; Smith, Randall

2017-07-01

AX J1745.6-2901 is an X-ray binary located at only 1.45 arcmin from Sgr A⋆, showcasing a strong X-ray dust-scattering halo. We combine Chandra and XMM-Newton observations to study the halo around this X-ray binary. Our study shows two major thick dust layers along the line of sight (LOS) towards AX J1745.6-2901. The LOS position and NH of these two layers depend on the dust grain models with different grain size distributions and abundances. But for all the 19 dust grain models considered, dust layer-1 is consistently found to be within a fractional distance of 0.11 (mean value: 0.05) to AX J1745.6-2901 and contains only (19-34) per cent (mean value: 26 per cent) of the total LOS dust. The remaining dust is contained in layer-2, which is distributed from the Earth up to a mean fractional distance of 0.64. A significant separation between the two layers is found for all the dust grain models, with a mean fractional distance of 0.31. Besides, an extended wing component is discovered in the halo, which implies a higher fraction of dust grains with typical sizes ≲590 Å than considered in current dust grain models. Assuming AX J1745.6-2901 is 8 kpc away, dust layer-2 would be located in the Galactic disc several kpc away from the Galactic Centre (GC). The dust scattering halo biases the observed spectrum of AX J1745.6-2901 severely in both spectral shape and flux, and also introduces a strong dependence on the size of the instrumental point spread function and the source extraction region. We build xspec models to account for this spectral bias, which allow us to recover the intrinsic spectrum of AX J1745.6-2901 free from dust-scattering opacity. If dust layer-2 also intervenes along the LOS to Sgr A⋆ and other nearby GC sources, a significant spectral correction for the dust-scattering opacity would be necessary for all these GC sources.

The Galactic Magnetic Field and its lensing of Ultrahigh Energy and Galactic Cosmic Rays

NASA Astrophysics Data System (ADS)

Farrar, Glennys

2015-08-01

It has long been recognized that magnetic fields play an important role in many astrophysical environments, but the magnetic field strength and structure has only been quantitatively determined for relatively few systems beyond our solar system.Our understanding of the Galactic magnetic field (GMF) has improved tremendously in recent years. The Jansson-Farrar (2012) (JF12) GMF model is the most realistic and comprehensive model available. It was constrained by fitting all-sky Faraday Rotation Measures of ~40k extragalactic sources, simultaneously with WMAP polarized (Q,U) and total synchrotron emission maps - together providing a total of more than 10,000 independent datapoints, each with measured astrophysical variance. In addition to disk and toroidal halo components, a previously overlooked coherent poloidal halo field proves to be necessary to account for the RM, Q and U data. Moreover a “striated” random component is needed in addition to a fully random component, in both disk and halo.The talk will give a concise review of the JF12 model and its derivation, with emphasis on which features of the GMF are well or poorly established. I will show that the data unambiguously demand a large scale coherent component to the halo field which is a diverging-spiral centered on the Galactic center, with field lines running from Southern to Northern hemispheres. The puzzles posed by the large scale coherent halo and disk magnetic fields, and their possible origins, will be discussed.Having a good model of the Galactic magnetic field is crucial for determining the sources of UHECRs, for modeling the transport of Galactic CRs (the halo field provides a heretofore-overlooked escape route for by diffusion along its field lines), and for calculating the background to dark matter and CMB-cosmology studies. I will present new results on the lensing effect of the GMF on UHECRs, which produces multiple images and dramatic magnification and demagnification that varies with

The large, oxygen-rich halos of star-forming galaxies are a major reservoir of galactic metals.

PubMed

Tumlinson, J; Thom, C; Werk, J K; Prochaska, J X; Tripp, T M; Weinberg, D H; Peeples, M S; O'Meara, J M; Oppenheimer, B D; Meiring, J D; Katz, N S; Davé, R; Ford, A B; Sembach, K R

2011-11-18

The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of intergalactic gas, but its mass, heavy element enrichment, and relation to galaxy properties are poorly constrained by observations. In a survey of the outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope, we detected ubiquitous, large (150-kiloparsec) halos of ionized oxygen surrounding star-forming galaxies; we found much less ionized oxygen around galaxies with little or no star formation. This ionized CGM contains a substantial mass of heavy elements and gas, perhaps far exceeding the reservoirs of gas in the galaxies themselves. Our data indicate that it is a basic component of nearly all star-forming galaxies that is removed or transformed during the quenching of star formation and the transition to passive evolution.

A high-velocity black hole on a Galactic-halo orbit in the solar neighbourhood.

PubMed

Mirabel, I F; Dhawan, V; Mignani, R P; Rodrigues, I; Guglielmetti, F

2001-09-13

Only a few of the dozen or so known stellar-mass black holes have been observed away from the plane of the Galaxy. Those few could have been ejected from the plane as a result of a 'kick' received during a supernova explosion, or they could be remnants of the population of massive stars formed in the early stages of evolution of the Galaxy. Determining their orbital motion should help to distinguish between these options. Here we report the transverse motion (in the plane of the sky) for the black-hole X-ray nova XTE J1118+480 (refs 2, 3, 4, 5), from which we derive a large space velocity. This X-ray binary system has an eccentric orbit around the Galactic Centre, like most objects in the halo of the Galaxy, such as ancient stars and globular clusters. The properties of the system suggest that its age is comparable to or greater than the age of the Galactic disk. Only an extraordinary 'kick' from a supernova could have launched the black hole into an orbit like this from a birthplace in the disk of the Galaxy.

IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, Thomas; Girichidis, Philipp; Gatto, Andrea

2015-11-10

The halo of the Milky Way contains a hot plasma with a surface brightness in soft X-rays of the order 10{sup −12} erg cm{sup −2} s{sup −1} deg{sup −2}. The origin of this gas is unclear, but so far numerical models of galactic star formation have failed to reproduce such a large surface brightness by several orders of magnitude. In this paper, we analyze simulations of the turbulent, magnetized, multi-phase interstellar medium including thermal feedback by supernova explosions as well as cosmic-ray feedback. We include a time-dependent chemical network, self-shielding by gas and dust, and self-gravity. Pure thermal feedback alonemore » is sufficient to produce the observed surface brightness, although it is very sensitive to the supernova rate. Cosmic rays suppress this sensitivity and reduce the surface brightness because they drive cooler outflows. Self-gravity has by far the largest effect because it accumulates the diffuse gas in the disk in dense clumps and filaments, so that supernovae exploding in voids can eject a large amount of hot gas into the halo. This can boost the surface brightness by several orders of magnitude. Although our simulations do not reach a steady state, all simulations produce surface brightness values of the same order of magnitude as the observations, with the exact value depending sensitively on the simulation parameters. We conclude that star formation feedback alone is sufficient to explain the origin of the hot halo gas, but measurements of the surface brightness alone do not provide useful diagnostics for the study of galactic star formation.« less

Galactic dual population models of gamma-ray bursts

NASA Technical Reports Server (NTRS)

Higdon, J. C.; Lingenfelter, R. E.

1994-01-01

We investigate in more detail the properties of two-population models for gamma-ray bursts in the galactic disk and halo. We calculate the gamma-ray burst statistical properties, mean value of (V/V(sub max)), mean value of cos Theta, and mean value of (sin(exp 2) b), as functions of the detection flux threshold for bursts coming from both Galactic disk and massive halo populations. We consider halo models inferred from the observational constraints on the large-scale Galactic structure and we compare the expected values of mean value of (V/V(sub max)), mean value of cos Theta, and mean value of (sin(exp 2) b), with those measured by Burst and Transient Source Experiment (BATSE) and other detectors. We find that the measured values are consistent with solely Galactic populations having a range of halo distributions, mixed with local disk distributions, which can account for as much as approximately 25% of the observed BATSE bursts. M31 does not contribute to these modeled bursts. We also demonstrate, contrary to recent arguments, that the size-frequency distributions of dual population models are quite consistent with the BATSE observations.

The Prolate Dark Matter Halo of the Andromeda Galaxy

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Chiba, Masashi

2014-07-01

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi & Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

The Segue K giant survey. II. A catalog of distance determinations for the Segue K giants in the galactic halo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Xiang-Xiang; Rix, Hans-Walter; Ma, Zhibo

2014-04-01

We present an online catalog of distance determinations for 6036 K giants, most of which are members of the Milky Way's stellar halo. Their medium-resolution spectra from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration are used to derive metallicities and rough gravity estimates, along with radial velocities. Distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g – r){sub 0} color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to properly propagate the errors in metallicities, magnitudes,more » and colors into distance uncertainties. We also fold in prior information about the giant-branch luminosity function and the different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays a small role in the distance estimates, but that neglecting the luminosity prior could lead to a systematic distance modulus bias of up to 0.25 mag, compared to the case of using the luminosity prior. We find a median distance precision of 16%, with distance estimates most precise for the least metal-poor stars near the tip of the red giant branch. The precision and accuracy of our distance estimates are validated with observations of globular and open clusters. The stars in our catalog are up to 125 kpc from the Galactic center, with 283 stars beyond 50 kpc, forming the largest available spectroscopic sample of distant tracers in the Galactic halo.« less

Moving Groups in the Milky Way Halo and Disk Induced by the Bar and Spiral Arms

NASA Astrophysics Data System (ADS)

Schuster, William John

2015-08-01

In a previous study (Moreno et al. 2015), the use of a detailed Milky Way potential (observationally and dynamically constrained) has shown that the Galactic bar is able to efficiently concentrate stars of the stellar halo and disk into several main resonances. With the tools introduced here, the Galactic bar is shown to produce significant phase-space structure attracting stars to several main resonances. This new study is dedicated to the study of known groups of the Galactic halo and disk, and their relation to these resonances. Stars belonging to some known halo and disk moving groups have settled down along these bar resonant families, showing, in some cases, a likely Galactic secular origin. In general, the 2D resonant orbits of the disk produced by the bar, seem to dominate at large scale-heights (several kiloparsecs) into the Galactic halo. In particular, provisionally six of the members of the Kapteyn halo moving group seem to be associated with one of these resonances, and also the Groombridge 1830 (Eggen 1996a; Eggen & Sandage 1959) and especially the newer halo moving groups G21-22 and G18-39 (Silva et al. 2012) show some correlation with these resonances suggesting possible secular origins, while the halo moving group Ross 451 (Eggen 1996b) does not show any such correlation, indicating a more probable cosmological (non-secular) ancestry. All Galactic disk moving groups (such as Arcturus, Hercules, Castor, IC 2391, Hyades, Pleiades, and Ursa Major) show considerable association with these resonances.

Formation and Maintenance of Galactic Warps in Triaxial Halos

NASA Astrophysics Data System (ADS)

Jeon, M. W.; Kim, S. S.; Ann, H. B.

2008-10-01

We investigate the evolution of the self-gravitating disk in a fixed axisymmetric halo with a torus of late cosmic infall that is tilted relative to the initial disk. This is an extension to the study by Shen & Sellwood (2006). We find that the magnitude of the warp is suppressed by a factor of ˜ 2 when the halo is moderately oblate while the magnitude of the warp periodically oscillates when the halo is moderately prolate.

Duration of the Early Galactic Formation Epoch: HST Photometry for Red-Horizontal Branch Clusters in the Outer Halo

NASA Astrophysics Data System (ADS)

Hesser, J. E.; Stetson, P. B.; McClure, R. D.; van den Bergh, S.; Bolte, M.; Harris, W. E.; van den Berg, D. A.; Bell, R. A.; Fahlman, G. G.; Richer, H. B.; Bond, H. E.

1997-12-01

Last year we presented evidence from HST photometry of the low-metallicity cluster NGC 2419 (M_V = -9.5, R_⊙ ~ 90 kpc, [Fe/H] = -2.2) that globular cluster formation began at essentially the same time throughout a region of the Galactic halo now almost 200 kpc in diameter (Harris et al. 1997 AJ 114, 1030). We now turn to the time spread of halo formation, with the ultimate aim of addressing the relative roles of mergers over the first 4 or more Gyrs (Searle & Zinn 1978, ApJ, 225, 357; Lee, Demarque & Zinn 1994 ApJ, 423, 248) versus models favoring a rapid collapse (Eggen, Lynden-Bell & Sandage 1962, ApJ, 236, 748; Stetson, VandenBerg & Bolte 1996, PASP, 108, 560), or some combination of those and other processes. We provide the first reliable measurements from the giant branch through the main-sequence turnoffs of red-horizontal-branch clusters in the outer halo, which are frequently postulated to be younger than most other globular clusters. From WFPC2 F555W (`V') and F814W (`I') photometry for Pal 3 (M_V = -5.2, R_⊙ ~ 87 kpc), Pal 4 (M_V = -5.8, R_⊙ ~ 98 kpc), and Eridanus (M_V = -4.8, R_⊙ ~ 78 kpc), all with [Fe/H] ~ -1.5, we estimate their relative ages by making differential comparisons among them and with respect to inner-halo objects of, presumably, comparable chemical compositions. It seems likely at this stage of our analysis that (a) the three clusters are the same age to our measurement precision of ~ 1 Gyr, and, (b) the CMDs of all three outer halo clusters differ from those of M 3 and M 5 (our template clusters of similar metallicity), in the sense that the outer halo clusters are younger by ~ 3 Gyr, or they are ~ 0.5 dex more metal-rich than currently thought. Large uncertainties in chemical compositions (He, [alpha /Fe], [CNO/Fe]) for outer halo and template clusters alike mask the true interpretation.

ON THE ORIGINS OF THE DIFFUSE H{alpha} EMISSION: IONIZED GAS OR DUST-SCATTERED H{alpha} HALOS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seon, Kwang-Il; Witt, Adolf N., E-mail: kiseon@kasi.re.kr

2012-10-20

It is known that the diffuse H{alpha} emission outside of bright H II regions not only are very extended, but also can occur in distinct patches or filaments far from H II regions, and the line ratios of [S II] {lambda}6716/H{alpha} and [N II] {lambda}6583/H{alpha} observed far from bright H II regions are generally higher than those in the H II regions. These observations have been regarded as evidence against the dust-scattering origin of the diffuse H{alpha} emission (including other optical lines), and the effect of dust scattering has been neglected in studies on the diffuse H{alpha} emission. In thismore » paper, we reexamine the arguments against dust scattering and find that the dust-scattering origin of the diffuse H{alpha} emission cannot be ruled out. As opposed to the previous contention, the expected dust-scattered H{alpha} halos surrounding H II regions are, in fact, in good agreement with the observed H{alpha} morphology. We calculate an extensive set of photoionization models by varying elemental abundances, ionizing stellar types, and clumpiness of the interstellar medium (ISM) and find that the observed line ratios of [S II]/H{alpha}, [N II]/H{alpha}, and He I {lambda}5876/H{alpha} in the diffuse ISM accord well with the dust-scattered halos around H II regions, which are photoionized by late O- and/or early B-type stars. We also demonstrate that the H{alpha} absorption feature in the underlying continuum from the dust-scattered starlight ({sup d}iffuse galactic light{sup )} and unresolved stars is able to substantially increase the [S II]/H{alpha} and [N II]/H{alpha} line ratios in the diffuse ISM.« less

The prolate dark matter halo of the Andromeda galaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashi, Kohei; Chiba, Masashi, E-mail: k.hayasi@astr.tohoku.ac.jp, E-mail: chiba@astr.tohoku.ac.jp

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for itsmore » dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.« less

Emission from the Ionized Gaseous Halos of Low-redshift Galaxies and Their Neighbors

NASA Astrophysics Data System (ADS)

Zhang, Huanian; Zaritsky, Dennis; Behroozi, Peter

2018-07-01

Using a sample of nearly half a million galaxies, intersected by over 8 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we extend our previous study of the recombination radiation emitted by the gaseous halos of nearby galaxies. We identify an inflection in the radial profile of the Hα+N[II] radial emission profile at a projected radius of ∼50 kpc and suggest that beyond this radius the emission from ionized gas in spatially correlated halos dominates the profile. We confirm that this is a viable hypothesis using results from a highly simplified theoretical treatment in which the dark matter halo distribution from cosmological simulations is straightforwardly populated with gas. Whether we fit the fraction of halo gas in a cooler (T = 12,000 K), smooth (c = 1) component (0.26 for galaxies with {M}* ={10}10.88 M ⊙ and 0.34 for those with {M}* ={10}10.18 M ⊙) or take independent values of this fraction from published hydrodynamical simulations (0.19 and 0.38, respectively), this model successfully reproduces the radial location and amplitude of the observed inflection. We also observe that the physical nature of the gaseous halo connects to primary galaxy morphology beyond any relationship to the galaxy’s stellar mass and star formation rate. We explore whether the model reproduces behavior related to the central galaxy’s stellar mass, star formation rate, and morphology. We find that it is unsuccessful in reproducing the observations at this level of detail and discuss various shortcomings of our simple model that may be responsible.

Globular cluster systems - Comparative evolution of Galactic halos

NASA Astrophysics Data System (ADS)

Harris, William E.

Space distributions, metallicity/age distributions, and kinematics are considered for the Milky Way halo system. Comparisons are made with other systems, and time scales for dynamical evolution are considered. It is noted that the globular cluster subsystems of halos resemble each other more closely than their parent galaxies do; this forms a reasonable basis for supposing that they represent a kind of underlying unity in the protogalaxy formation process.

Radiation hydrodynamical instabilities in cosmological and galactic ionization fronts

NASA Astrophysics Data System (ADS)

Whalen, Daniel J.; Norman, Michael L.

2011-11-01

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25-500 solar masses, with H(II) regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.

A Wide-Field Photometric Survey for Extratidal Tails Around Five Metal-Poor Globular Clusters in the Galactic Halo

NASA Astrophysics Data System (ADS)

Chun, Sang-Hyun; Kim, Jae-Woo; Sohn, Sangmo T.; Park, Jang-Hyun; Han, Wonyong; Kim, Ho-Il; Lee, Young-Wook; Lee, Myung Gyoon; Lee, Sang-Gak; Sohn, Young-Jong

2010-02-01

Wide-field deep g'r'i' images obtained with the Megacam of the Canada-France-Hawaii Telescope are used to investigate the spatial configuration of stars around five metal-poor globular clusters M15, M30, M53, NGC 5053, and NGC 5466, in a field-of-view ~3°. Applying a mask filtering algorithm to the color-magnitude diagrams of the observed stars, we sorted cluster's member star candidates that are used to examine the characteristics of the spatial stellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensity contours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensity features over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observed extratidal features show signatures of tidal tails tracing the clusters' orbits, inferred from their proper motions, and effects of dynamical interactions with the Galaxy. Our findings include detections of a tidal bridge-like feature and an envelope structure around the pair of globular clusters M53 and NGC 5053. The observed radial surface density profiles of target clusters have a deviation from theoretical King models, for which the profiles show a break at 0.5-0.7rt , extending the overdensity features out to 1.5-2rt . Both radial surface density profiles for different angular sections and azimuthal number density profiles confirm the overdensity features of tidal tails around the five metal-poor globular clusters. Our results add further observational evidence that the observed metal-poor halo globular clusters originate from an accreted satellite system, indicative of the merging scenario of the formation of the Galactic halo. Based on observations carried out at the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France, and the University of Hawaii. This is part of the

Possible existence of wormholes in the central regions of halos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahaman, Farook, E-mail: rahaman@iucaa.ernet.in; Salucci, P., E-mail: salucci@sissa.it; INFN, Sezione di Trieste, Via Valerio 2, 34127, Trieste

2014-11-15

An earlier study (Rahaman, et al., 2014 and Kuhfittig, 2014) has demonstrated the possible existence of wormholes in the outer regions of the galactic halo, based on the Navarro–Frenk–White (NFW) density profile. This paper uses the Universal Rotation Curve (URC) dark matter model to obtain analogous results for the central parts of the halo. This result is an important compliment to the earlier result, thereby confirming the possible existence of wormholes in most of the spiral galaxies. - Highlights: • Earlier we showed possible existence of wormholes in the outer regions of halo. • We obtain here analogous results for themore » central parts of the galactic halo. • Our result is an important compliment to the earlier result. • This confirms possible existence of wormholes in most of the spiral galaxies.« less

The role of neutron star mergers in the chemical evolution of the Galactic halo

NASA Astrophysics Data System (ADS)

Cescutti, G.; Romano, D.; Matteucci, F.; Chiappini, C.; Hirschi, R.

2015-05-01

Context. The dominant astrophysical production site of the r-process elements has not yet been unambiguously identified. The suggested main r-process sites are core-collapse supernovae and merging neutron stars. Aims: We explore the problem of the production site of Eu. We also use the information present in the observed spread in the Eu abundances in the early Galaxy, and not only its average trend. Moreover, we extend our investigations to other heavy elements (Ba, Sr, Rb, Zr) to provide additional constraints on our results. Methods: We adopt a stochastic chemical evolution model that takes inhomogeneous mixing into account. The adopted yields of Eu from merging neutron stars and from core-collapse supernovae are those that are able to explain the average [Eu/Fe]-[Fe/H] trend observed for solar neighbourhood stars, the solar abundance of Eu, and the present-day abundance gradient of Eu along the Galactic disc in the framework of a well-tested homogeneous model for the chemical evolution of the Milky Way. Rb, Sr, Zr, and Ba are produced by both the s- and r-processes. The r-process yields were obtained by scaling the Eu yields described above according to the abundance ratios observed in r-process rich stars. The s-process contribution by spinstars is the same as in our previous papers. Results: Neutron star binaries that merge in less than 10 Myr or neutron star mergers combined with a source of r-process generated by massive stars can explain the spread of [Eu/Fe] in the Galactic halo. The combination of r-process production by neutron star mergers and s-process production by spinstars is able to reproduce the available observational data for Sr, Zr, and Ba. We also show the first predictions for Rb in the Galactic halo. Conclusions: We confirm previous results that either neutron star mergers on a very short timescale or both neutron star mergers and at least a fraction of Type II supernovae have contributed to the synthesis of Eu in the Galaxy. The r

Comparison between UBV- and RGU-photometrically determined density functions for the photometric disk and halo and between the corresponding mean isodensity behaviour in the halo close to the galactic north-pole (SA 57)

NASA Astrophysics Data System (ADS)

Fenkart, R.; Esin-Yilmaz, F.

1985-10-01

SA 57, RG U-photometrically treated by Fenkart (1967), is the third field of the Basle Halo Program (BHP) we investigate by applying the RG U-methods for the separation of the (photometric) populations disk and halo and for the determination of their space densities analogously in UBV in order to compare the results independently obtained in both systems. Figures 1 and 2 give the V- and G-fractioned two-colour diagrams of the same 1179 stars treated in UBV and RG U, respectively. On their basis, the logarithmic space density functions of both populations have been calculated for the overall (3m to 8m ) and for the 1m -intervals absolute magnitudes M(V) and M(G). They are tabulated in tables II and III and plotted in figures 3 and 4, respectively (a : disk, b : halo). The overall density functions for the disk and for the halo are compared between the systems in figures Sa and b, respectively. The mean misidentification-rate per system (MMRS) is 7.3 %, lying between the ones for SA 54(9.2 %) and for SA 82(4.5 %) (Fenkart and Esin-Yilmaz, 1983 and 1984, respectively) and close to the mean for all three investigations (7.0 ± 2.4 %) The direction to SA 57 lies almost in the middle of the sector of the northern galactic meridian which is limited by the directions to SA 54 and to SA 82. Our results permit, together with the ones obtained in these limiting directions, the comparison of the mean isodensity-patterns obtained in both systems within this sector. They are completely parallel and blend in perfectly with the mean (RG U-) isodensity-pattern of the - partly overlapping - sector between SA 51 and SA 57 obtained by Fenkart and Karaall (1984) (Fig. 6). The appendices describe shortly the involved methods (A) and refer to related work by other authors in the direction to the galactic north-pole (B).

Unveiling the stellar halo with TGAS

NASA Astrophysics Data System (ADS)

Veljanoski, Jovan; Posti, L.; Helmi, A.; Breddels, M. A.

2018-04-01

The detailed study of the Galactic stellar halo may hold the key to unlocking the assembly history of the Milky Way. Here, we present a machine learning model for selecting metal poor stars from the TGAS catalogue using 5 dimensional phase-space information, coupled with optical and near-IR photometry. We characterise the degree of substructure in our halo sample in the Solar neighbourhood by measuring the velocity correlation function.

Wandering Supermassive Black Holes in Milky-Way-mass Halos

NASA Astrophysics Data System (ADS)

Tremmel, Michael; Governato, Fabio; Volonteri, Marta; Pontzen, Andrew; Quinn, Thomas R.

2018-04-01

We present a self-consistent prediction from a large-scale cosmological simulation for the population of “wandering” supermassive black holes (SMBHs) of mass greater than 106 M ⊙ on long-lived, kpc-scale orbits within Milky Way (MW)-mass galaxies. We extract a sample of MW-mass halos from the ROMULUS25 cosmological simulation, which is uniquely able to capture the orbital evolution of SMBHs during and following galaxy mergers. We predict that such halos, regardless of recent merger history or morphology, host an average of 5.1 ± 3.3 SMBHs, including their central black hole, within 10 kpc from the galactic center and an average of 12.2 ± 8.4 SMBHs total within their virial radius, not counting those in satellite halos. Wandering SMBHs exist within their host galaxies for several Gyr, often accreted by their host halo in the early Universe. We find, with >4σ significance, that wandering SMBHs are preferentially found outside of galactic disks.

Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359

NASA Technical Reports Server (NTRS)

Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin

1995-01-01

We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a signal-to-noise ratio of approximately 50:1. We detect interstellar lines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) = 15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greater than 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/- 0.02. Assuming solar reference abundances, the diffuse clouds containing Mg, S, and Ge along the sight line have average logarithmic depletions D(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2 +/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smaller than is typical of diffuse clouds in the solar vicinity. Galactic rotational modeling of the N v profiles indicates that the highly ionized gas traced by this ion has a scale height of approximately 1 kpc if gas at large z-distances corotates with the underlying disk gas. Rotational modeling of the Si iv and C iv profiles measured by the IUE satellite yields similar scale height estimates. The scale height results contrast with previous studies of highly ionized gas in the outer Milky Way that reveal a more extended gas distribtion with h approximately equals 3-4 kpc. We detect a high-velocity feature in N v and Si II v(sub LSR) approximately equals + 125 km/s) that is probably created in an interface between warm and hot gas.

Tests and consequences of disk plus halo models of gamma-ray burst sources

NASA Technical Reports Server (NTRS)

Smith, I. A.

1995-01-01

The gamma-ray burst observations made by the Burst and Transient Source Experiment (BATSE) and by previous experiments are still consistent with a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo model. Testable predictions and consequences of the disk plus halo model are discussed here; tests performed on the expanded BATSE database in the future will constrain the allowed model parameters and may eventually rule out the disk plus halo model. Using examples, it is shown that if the halo has an appropriate edge, BATSE will never detect an anisotropic signal from the halo of the Andromeda galaxy. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the 'disk' population rises as the detector sensitivity improves. A careful reexamination of the numbers of bursts in the two populations for the pre-BATSE databases could rule out this class of models. Similarly, it is predicted that different satellites will observe different relative numbers of bursts in the two classes for any model in which there are two different spatial distribiutions of the sources, or for models in which there is one spatial distribution of the sources that is sampled to different depths for the two classes. An important consequence of the disk plus halo model is that for the birthrate of the halo sources to be small compared to the birthrate of the disk sources, it is necessary for the halo sources to release many orders of magnitude more energy over their bursting lifetime than the disk sources. The halo bursts must also be much more luminous than the disk bursts; if this disk-halo model is correct, it is necessary to explain why the disk sources do not produce halo-type bursts.

An improved catalog of halo wide binary candidates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Christine; Monroy-Rodríguez, Miguel A., E-mail: chris@astro.unam.mx

2014-08-01

We present an improved catalog of halo wide binaries compiled from an extensive literature search. Most of our binaries stem from the common proper motion binary catalogs by Allen et al. and Chanamé and Gould, but we have also included binaries from the lists of Ryan and Zapatero-Osorio and Martín. All binaries were carefully checked and their distances and systemic radial velocities are included when available. Probable membership to the halo population was tested by means of reduced proper motion diagrams for 251 candidate halo binaries. After eliminating obvious disk binaries, we ended up with 211 probable halo binaries, 150more » of which have radial velocities available. We compute galactic orbits for these 150 binaries and calculate the time they spend within the galactic disk. Considering the full sample of 251 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law f(a) ∼ a {sup –1} (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their entire lives within z = ±500 pc, this limit is found to be 19,000 AU (0.09 pc), while for the 50 most halo-like binaries, those that spend on average only 18% of their lives within z = ±500 pc, the limit is 63,000 AU (0.31 pc). In a companion paper, we employ this catalog to establish limits on the masses of the halo massive perturbers (massive compact halo objects).« less

DETECTING TRIAXIALITY IN THE GALACTIC DARK MATTER HALO THROUGH STELLAR KINEMATICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rojas-Nino, Armando; Valenzuela, Octavio; Pichardo, Barbara

Assuming the dark matter halo of the Milky Way to be a non-spherical potential (i.e., triaxial, prolate, oblate), we show how the assembling process of the Milky Way halo may have left long-lasting stellar halo kinematic fossils due to the shape of the dark matter halo. In contrast with tidal streams, which are associated with recent satellite accretion events, these stellar kinematic groups will typically show inhomogeneous chemical and stellar population properties. However, they may be dominated by a single accretion event for certain mass assembling histories. If the detection of these peculiar kinematic stellar groups were confirmed, they wouldmore » be the smoking gun for the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.« less

Constraining the contribution of active galactic nuclei to reionization

NASA Astrophysics Data System (ADS)

Hassan, Sultan; Davé, Romeel; Mitra, Sourav; Finlator, Kristian; Ciardi, Benedetta; Santos, Mario G.

2018-01-01

Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionize the Universe. We assess the viability of this scenario using a semi-numerical framework for modelling reionization, to which we add a quasar contribution by constructing a Quasar Halo Occupancy Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth τe, neutral fraction and ionizing emissivity. Such a model predicts τe too low by ∼2σ relative to Planck constraints, and reionizes the Universe at z ≲ 5. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionizing emissivity at z ∼ 5. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match τe albeit with late reionization; however, such evolution is inconsistent with observations at z ∼ 4-6 and poorly motivated physically. These results arise because AGN are more biased towards massive haloes than typical reionizing galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionizing bubbles that are reflected in ∼×2 more 21 cm power on all scales. A model with equal part galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21 cm experiments such as Hydrogen Epoch of Reionization Array and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionizing photon budget for reionization.

Parameters of Six Selected Galactic Potential Models

NASA Astrophysics Data System (ADS)

Bajkova, Anisa; Bobylev, Vadim

2017-11-01

This paper is devoted to the refinement of the parameters of the six three-component (bulge, disk, halo) axisymmetric Galactic gravitational potential models on the basis of modern data on circular velocities of Galactic objects located at distances up to 200 kpc from the Galactic center. In all models the bulge and disk are described by the Miyamoto-Nagai expressions. To describe the halo, the models of Allen-Santillán (I), Wilkinson-Evans (II), Navarro- Frenk-White (III), Binney (IV), Plummer (V), and Hernquist (VI) are used. The sought-for parameters of potential models are determined by fitting the model rotation curves to the measured velocities, taking into account restrictions on the local dynamical matter density p⊙ - 0.1M⊙ pc-3 and the vertical force |Kz=1.1|/2πG = 77M⊙ pc-2. A comparative analysis of the refined potential models is made and for each of the models the estimates of a number of the Galactic characteristics are presented.

Absolute proper motions to B approximately 22.5: Evidence for kimematical substructure in halo field stars

NASA Technical Reports Server (NTRS)

Majewski, Steven R.; Munn, Jeffrey A.; Hawley, Suzanne L.

1994-01-01

Radial velocities have been obtained for six of nine stars identified on the basis of similar distances and common, extreme transverse velocities in the proper motion survey of Majewski (1992) as a candidate halo moving group at the north Galactic pole. These radial velocities correspond to velocities perpendicular to the Galactic plane which span the range -48 +/- 21 to -128 +/- 9 km/sec (but a smaller range, -48 +/- 21 to -86 +/- 19 km/sec, when only our own measurements are considered), significantly different than the expected distribution, with mean 0 km/sec, for a random sample of either halo or thick disk stars. The probability of picking such a set of radial velocities at random is less than 1%. Thus the radial velocity data support the hypothesis that these stars constitute part of a halo moving group or star stream at a distance of approximately 4-5 kpc above the Galactic plane. If real, this moving group is evidence for halo phase space substructure which may be the fossil remains of a destroyed globular cluster, Galactic satellite, or Searle & Zinn (1978) 'fragment.'

Bright gamma-ray Galactic Center excess and dark dwarfs: Strong tension for dark matter annihilation despite Milky Way halo profile and diffuse emission uncertainties

NASA Astrophysics Data System (ADS)

Abazajian, Kevork N.; Keeley, Ryan E.

2016-04-01

We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma Ray Space Telescope. The range of particle annihilation rate and masses expand when including these unknowns. However, two of the most precise empirical determinations of the Milky Way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy analyses for single-channel dark matter annihilation models. The GCE and dwarf tension can be alleviated if: one, the halo is very highly concentrated or strongly contracted; two, the dark matter annihilation signal differentiates between dwarfs and the GC; or, three, local stellar density measures are found to be significantly lower, like that from recent stellar counts, increasing the local dark matter density.

An extremely primitive star in the Galactic halo.

PubMed

Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; Monaco, Lorenzo; Spite, Monique; Spite, François; Ludwig, Hans-G; Cayrel, Roger; Zaggia, Simone; Hammer, François; Randich, Sofia; Molaro, Paolo; Hill, Vanessa

2011-08-31

The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z < 1.5 × 10(-5), it has been suggested that low-mass stars cannot form from the primitive interstellar medium until it has been enriched above a critical value of Z, estimated to lie in the range 1.5 × 10(-8) to 1.5 × 10(-6) (ref. 8), although competing theories claiming the contrary do exist. (We use 'low-mass' here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (≤ 6.9 × 10(-7), which is 4.5 × 10(-5) times that of the Sun) and a chemical pattern typical of classical extremely metal-poor stars--that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium.

The HALO / HALO-2 Supernova Neutrino Detectors

NASA Astrophysics Data System (ADS)

Yen, Stanley; HALO Collaboration; HALO-2 Collaboration

2016-09-01

The Helium and Lead Observatory (HALO) is a dedicated supernova neutrino detector in SNOLAB, which is built from 79 tons of surplus lead and the helium-3 neutron detectors from the SNO experiment. It is sensitive primarily to electron neutrinos, and is thus complementary to water Cerenkov and organic scintillation detectors which are primarily sensitive to electron anti-neutrinos. A comparison of the rates in these complementary detectors will enable a flavor decomposition of the neutrino flux from the next galactic core-collapse supernova. We have tentative ideas to build a 1000-ton HALO-2 detector in the Gran Sasso laboratory by using the lead from the decommissioned OPERA detector. We are exploring several neutron detector technologies to supplement the existing helium-3 detectors. We welcome new collaborators to join us. This research is supported by the NRC and NSERC (Canada), the US DOE and NSF, and the German RISE program.

The end of the MACHO era, revisited: New limits on MACHO masses from halo wide binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monroy-Rodríguez, Miguel A.; Allen, Christine, E-mail: chris@astro.unam.mx

2014-08-01

In order to determine an upper bound for the mass of the massive compact halo objects (MACHOs), we use the halo binaries contained in a recent catalog by Allen and Monroy-Rodríguez. To dynamically model their interactions with massive perturbers, a Monte Carlo simulation is conducted, using an impulsive approximation method and assuming a galactic halo constituted by massive particles of a characteristic mass. The results of such simulations are compared with several subsamples of our improved catalog of candidate halo wide binaries. In accordance with Quinn et al., we also find our results to be very sensitive to the widestmore » binaries. However, our larger sample, together with the fact that we can obtain galactic orbits for 150 of our systems, allows a more reliable estimate of the maximum MACHO mass than that obtained previously. If we employ the entire sample of 211 candidate halo stars we, obtain an upper limit of 112 M{sub ☉}. However, using the 150 binaries in our catalog with computed galactic orbits, we are able to refine our fitting criteria. Thus, for the 100 most halo-like binaries we obtain a maximum MACHO mass of 21-68 M{sub ☉}. Furthermore, we can estimate the dynamical effects of the galactic disk using binary samples that spend progressively shorter times within the disk. By extrapolating the limits obtained for our most reliable—albeit smallest—sample, we find that as the time spent within the disk tends to zero, the upper bound of the MACHO mass tends to less than 5 M{sub ☉}. The non-uniform density of the halo has also been taken into account, but the limit obtained, less than 5 M{sub ☉}, does not differ much from the previous one. Together with microlensing studies that provide lower limits on the MACHO mass, our results essentially exclude the existence of such objects in the galactic halo.« less

Finding the Edge of the Galactic Wind's Influence

NASA Astrophysics Data System (ADS)

Werk, Jessica; Prochaska, J. Xavier; Tumlinson, Jason; Tripp, Todd; Thom, Christopher; Ford, Amanda Brady

2011-08-01

Brand new results from the HST Cosmic Origins Spectrograph on the low-z IGM combined with low-resolution optical spectroscopy of galaxy absorbers indicate that there is a correlation between the total star formation rates of L* galaxies and the strength of the OVI absorption in their halos out to 150 kpc. That diffuse, highly-ionized metals surrounding L* galaxies are a sensitive function of recent star formation suggests we may be seeing the effects of feedback in action in the far reaches of a galaxy's halo. Here, we propose to examine this correlation over a broader range of parameters, for galaxies with luminosities ranging from 0.01 L* to L*, having data- rich QSO sightlines passing through their halos at impact parameters up to 300 kpc. Using a combination of GMOS-S imaging and multi-slit spectroscopy, we will determine the star formation rates and metallicities of galaxies from the recently-published LCO/WFCCD redshift survey. We will use existing UV spectral data for the 14 QSO sightlines to analyze the OVI absorption in the circumgalactic medium of the surveyed galaxies. Our goal is to measure the radius at which OVI absorption no longer correlates with galaxy SFR. This observational estimate for the extent to which galactic winds propagate will provide robust constraints on the simulations that model their effects.

Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way

NASA Astrophysics Data System (ADS)

Dumas, Julie; Newberg, Heidi Jo; Niedzielski, Bethany; Susser, Adam; Thompson, Jeffery M.; Weiss, Jake; Lewis, Kim M.

2016-06-01

One prediction of axion dark matter models is they can form Bose-Einstein condensates and rigid caustic rings as a halo collapses in the non-linear regime. In this thesis, we undertake the first study of a caustic ring model for the Milky Way halo (Duffy & Sikivie 2008), paying particular attention to observational consequences. We first present the formalism for calculating the gravitational acceleration of a caustic ring halo. The caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. We show that this halo can reasonably match the known Galactic rotation curve. We are not able to confirm or rule out an association between the positions of the caustic rings and oscillations in the observed rotation curve, due to insufficient rotation curve data. We explore the effects of dark matter caustic rings on dwarf galaxy tidal disruption with N-body simulations. Simulations of the Sagittarius (Sgr) dwarf galaxy in a caustic ring halo potential, with disk and bulge parameters that are tuned to match the Galactic rotation curve, match observations of the Sgr trailing tidal tails as far as 90 kpc from the Galactic center. Like the Navarro-Frenk-White (NFW) halo, they are, however, unable to match the leading tidal tail. None of the caustic, NFW, or triaxial logarithmic halos are able to simultaneously match observations of the leading and trailing arms of the Sagittarius stream. We further show that simulations of dwarf galaxies that move through caustic rings are qualitatively similar to those moving in a logarithmic halo. This research was funded by NSF grant AST 10-09670, the NASA-NY Space Grant, and the American Fellowship from AAUW.

The Impact of Starbursts on the Gaseous Halos of Galaxies

NASA Astrophysics Data System (ADS)

Heckman, Timothy

2009-07-01

Perhaps the most important {yet uncertain} aspects of galaxy evolution are the processes by which galaxies accrete gas and by which the resulting star formation and black hole growth affects this accreting gas. It is believed that both the form of the accretion and the nature of the feedback change as a function of the galaxy mass. At low mass the gas comes in cold and the feedback is provided by massive stars. At high mass, the gas comes in hot, and the feedback is from an AGN. The changeover occurs near the mass where the galaxy population transitions from star-forming galaxies to red and dead ones. The population of red and dead galaxies is building with cosmic time, and it is believed that feedback plays an imporant role in this process: shutting down star formation by heating and/or expelling the reservoir of cold halo gas. To investigate these ideas, we propose to use COS far-UV spectra of background QSOs to measure the properties of the halo gas in a sample of galaxies near the transition mass that have undergone starbursts within the past 100 Myr to 1 Gyr. The galactic wind associated with the starburst is predicted to have affected the properties of the gaseous halo. To test this, we will compare the properties of the halos of the post-starburst galaxies to those of a control sample of galaxies matched in mass and QSO impact parameter. Do the halos of the post-starburst galaxies show a higher incidence rate of Ly-Alpha and metal absorption-lines? Are the kinematics of the halo gas more disturbed in the post-starbursts? Has the wind affected the ionization state and/or the metallicity of the halo? These data will provide fresh new insights into the role of feedback from massive stars on the evolution of galaxies, and may also offer clues about the properties of the QSO metal absorption-line systems at high-redshift.

The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae

NASA Astrophysics Data System (ADS)

Iorio, G.; Belokurov, V.; Erkal, D.; Koposov, S. E.; Nipoti, C.; Fraternali, F.

2018-02-01

We exploit the first Gaia data release to study the properties of the Galactic stellar halo as traced by RR Lyrae. We demonstrate that it is possible to select a pure sample of RR Lyrae using only photometric information available in the Gaia+2MASS catalogue. The final sample contains about 21 600 RR Lyrae covering an unprecedented fraction ( ˜ 60 per cent) of the volume of the Galactic inner halo (R < 28 kpc). We study the morphology of the stellar halo by analysing the RR Lyrae distribution with parametric and non-parametric techniques. Taking advantage of the uniform all-sky coverage, we test halo models more sophisticated than usually considered in the literature, such as those with varying flattening, tilts and/or offset of the halo with respect to the Galactic disc. A consistent picture emerges: the inner halo is well reproduced by a smooth distribution of stars settled on triaxial density ellipsoids. The shortest axis is perpendicular to the Milky Way's disc, while the longest axis forms an angle of ˜70° with the axis connecting the Sun and the Galactic Centre. The elongation along the major axis is mild (p = 1.27), and the vertical flattening is shown to evolve from a squashed state with q ≈ 0.57 in the centre to a more spherical q ≈ 0.75 at the outer edge of our data set. Within the radial range probed, the density profile of the stellar halo is well approximated by a single power law with exponent α = -2.96. We do not find evidence of tilt or offset of the halo with respect to the Galaxy's disc.

Prospects for detecting supersymmetric dark matter in the Galactic halo.

PubMed

Springel, V; White, S D M; Frenk, C S; Navarro, J F; Jenkins, A; Vogelsberger, M; Wang, J; Ludlow, A; Helmi, A

2008-11-06

Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species. In this case, annihilation of dark matter in the halo of the Milky Way should produce gamma-rays at a level that may soon be observable. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model.

A survey for dwarf galaxy remnants around 14 globular clusters in the outer halo

NASA Astrophysics Data System (ADS)

Sollima, A.; Martínez Delgado, D.; Muñoz, R. R.; Carballo-Bello, J. A.; Valls-Gabaud, D.; Grebel, E. K.; Santana, F. A.; Côté, P.; Djorgovski, S. G.

2018-06-01

We report the results of a systematic photometric survey of the peripheral regions of a sample of 14 globular clusters in the outer halo of the Milky Way at distances dGC > 25 kpc from the Galactic Centre. The survey is aimed at searching for the remnants of the host satellite galaxies where these clusters could originally have been formed before being accreted on to the Galactic halo. The limiting surface brightness varies within our sample, but reaches μV, lim = 30-32 mag arcsec-2. For only two globular clusters (NGC 7492 and Whiting 1; already suggested to be associated with the Sagittarius galaxy), we detect extended stellar populations that cannot be associated with either the clusters themselves or with the surrounding Galactic field population. We show that the lack of substructures around globular clusters at these Galactocentric distances is still compatible with the predictions of cosmological simulations whereby in the outer halo the Galactic globular cluster system is built up through hierarchical accretion at early epochs.

Research Progresses of Halo Streams in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Xi-long, Liang; Jing-kun, Zhao; Yu-qin, Chen; Gang, Zhao

2018-01-01

The stellar streams originated from the Galactic halo may be detected when they pass by the solar neighborhood, and they still keep some information at their birth times. Thus, the investigation of halo streams in the solar neighborhood is very important for understanding the formation and evolution of our Galaxy. In this paper, the researches of halo streams in the solar neighborhood are briefly reviewed. We have introduced the methods how to detect the halo streams and identify their member stars, summarized the progresses in the observation of member stars of halo streams and in the study of their origins, introduced in detail how to analyze the origins of halo streams in the solar neighborhood by means of numerical simulation and chemical abundance, and finally discussed the prospects of the LAMOST and GAIA in the research of halo streams in the solar neighborhood.

The age of the galactic disk

NASA Technical Reports Server (NTRS)

Sandage, Allan

1988-01-01

The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk, permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc.

Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

NASA Technical Reports Server (NTRS)

Suchkov, Anatoly A.; Balsara, Dinshaw S.; Heckman, Timothy M.; Leitherner, Claus

1994-01-01

There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and

The COS-Halos Survey: Metallicities in the Low-redshift Circumgalactic Medium

NASA Astrophysics Data System (ADS)

Prochaska, J. Xavier; Werk, Jessica K.; Worseck, Gábor; Tripp, Todd M.; Tumlinson, Jason; Burchett, Joseph N.; Fox, Andrew J.; Fumagalli, Michele; Lehner, Nicolas; Peeples, Molly S.; Tejos, Nicolas

2017-03-01

We analyze new far-ultraviolet spectra of 13 quasars from the z˜ 0.2 COS-Halos survey that cover the H I Lyman limit of 14 circumgalactic medium (CGM) systems. These data yield precise estimates or more constraining limits than previous COS-Halos measurements on the H I column densities {N}{{H}{{I}}}. We then apply a Monte-Carlo Markov chain approach on 32 systems from COS-Halos to estimate the metallicity of the cool (T˜ {10}4 K) CGM gas that gives rise to low-ionization state metal lines, under the assumption of photoionization equilibrium with the extragalactic UV background. The principle results are: (1) the CGM of field L* galaxies exhibits a declining H I surface density with impact parameter {R}\\perp (at > 99.5 % confidence), (2) the transmission of ionizing radiation through CGM gas alone is 70 ± 7% (3) the metallicity distribution function of the cool CGM is unimodal with a median of {10}-0.51 {Z}⊙ and a 95% interval ≈ 1/50 {Z}⊙ to > 3 {Z}⊙ ; the incidence of metal-poor (< 1/100 {Z}⊙ ) gas is low, implying any such gas discovered along quasar sightlines is typically unrelated to L* galaxies; (4) we find an unexpected increase in gas metallicity with declining {N}{{H}{{I}}} (at > 99.9 % confidence) and, therefore, also with increasing {R}\\perp ; the high metallicity at large radii implies early enrichment; and (5) a non-parametric estimate of the cool CGM gas mass is {M}{CGM}{cool}=(9.2+/- 4.3)× {10}10 {M}⊙ , which together with new mass estimates for the hot CGM may resolve the galactic missing baryons problem. Future analyses of halo gas should focus on the underlying astrophysics governing the CGM, rather than processes that simply expel the medium from the halo. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with

Sagittarius A* as an origin of the Galactic PeV cosmic rays?

NASA Astrophysics Data System (ADS)

Fujita, Yutaka; Murase, Kohta; Kimura, Shigeo S.

2017-04-01

Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ("Pevatron"). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 107 yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.

Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate

NASA Astrophysics Data System (ADS)

Indriolo, Nick; Neufeld, D. A.; Gerin, M.; Schilke, P.; Benz, A. O.; Winkel, B.; Menten, K. M.; Chambers, E. T.; Black, John H.; Bruderer, S.; Falgarone, E.; Godard, B.; Goicoechea, J. R.; Gupta, H.; Lis, D. C.; Ossenkopf, V.; Persson, C. M.; Sonnentrucker, P.; van der Tak, F. F. S.; van Dishoeck, E. F.; Wolfire, Mark G.; Wyrowski, F.

2015-02-01

In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζH) and molecular hydrogen fraction (f_H_2). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f_H_2 in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = -15.75 (ζH = 1.78 × 10-16 s-1) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H_3^+ observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Reionization and the Abundance of Galactic Satellites

NASA Astrophysics Data System (ADS)

Bullock, James S.; Kravtsov, Andrey V.; Weinberg, David H.

2000-08-01

One of the main challenges facing standard hierarchical structure formation models is that the predicted abundance of Galactic subhalos with circular velocities vc~10-30 km s-1 is an order of magnitude higher than the number of satellites actually observed within the Local Group. Using a simple model for the formation and evolution of dark halos, based on the extended Press-Schechter formalism and tested against N-body results, we show that the theoretical predictions can be reconciled with observations if gas accretion in low-mass halos is suppressed after the epoch of reionization. In this picture, the observed dwarf satellites correspond to the small fraction of halos that accreted substantial amounts of gas before reionization. The photoionization mechanism naturally explains why the discrepancy between predicted halos and observed satellites sets in at vc~30 km s-1, and for reasonable choices of the reionization redshift (zre~5-12) the model can reproduce both the amplitude and shape of the observed velocity function of galactic satellites. If this explanation is correct, then typical bright galaxy halos contain many low-mass dark matter subhalos. These might be detectable through their gravitational lensing effects, through their influence on stellar disks, or as dwarf satellites with very high mass-to-light ratios. This model also predicts a diffuse stellar component produced by large numbers of tidally disrupted dwarfs, perhaps sufficient to account for most of the Milky Way's stellar halo.

Unified halo-independent formalism from convex hulls for direct dark matter searches

NASA Astrophysics Data System (ADS)

Gelmini, Graciela B.; Huh, Ji-Haeng; Witte, Samuel J.

2017-12-01

Using the Fenchel-Eggleston theorem for convex hulls (an extension of the Caratheodory theorem), we prove that any likelihood can be maximized by either a dark matter 1- speed distribution F(v) in Earth's frame or 2- Galactic velocity distribution fgal(vec u), consisting of a sum of delta functions. The former case applies only to time-averaged rate measurements and the maximum number of delta functions is (Script N‑1), where Script N is the total number of data entries. The second case applies to any harmonic expansion coefficient of the time-dependent rate and the maximum number of terms is Script N. Using time-averaged rates, the aforementioned form of F(v) results in a piecewise constant unmodulated halo function tilde eta0BF(vmin) (which is an integral of the speed distribution) with at most (Script N-1) downward steps. The authors had previously proven this result for likelihoods comprised of at least one extended likelihood, and found the best-fit halo function to be unique. This uniqueness, however, cannot be guaranteed in the more general analysis applied to arbitrary likelihoods. Thus we introduce a method for determining whether there exists a unique best-fit halo function, and provide a procedure for constructing either a pointwise confidence band, if the best-fit halo function is unique, or a degeneracy band, if it is not. Using measurements of modulation amplitudes, the aforementioned form of fgal(vec u), which is a sum of Galactic streams, yields a periodic time-dependent halo function tilde etaBF(vmin, t) which at any fixed time is a piecewise constant function of vmin with at most Script N downward steps. In this case, we explain how to construct pointwise confidence and degeneracy bands from the time-averaged halo function. Finally, we show that requiring an isotropic Galactic velocity distribution leads to a Galactic speed distribution F(u) that is once again a sum of delta functions, and produces a time-dependent tilde etaBF(vmin, t) function

The age of the galactic disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sandage, A.

The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk,more » permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc.« less

A RELATION BETWEEN THE WARM NEUTRAL AND IONIZED MEDIA OBSERVED IN THE CANADIAN GALACTIC PLANE SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foster, T.; Kothes, R.; Brown, J. C., E-mail: Tyler.Foster@nrc-cnrc.gc.ca

2013-08-10

We report on a comparison between 21 cm rotation measure (RM) and the optically thin atomic hydrogen column density (N{sub H{sub I}}({tau} {yields} 0)) measured toward unresolved extragalactic sources in the Galactic plane of the northern sky. H I column densities integrated to the Galactic edge are measured immediately surrounding each of nearly 2000 sources in 1 arcmin 21 cm line data, and are compared to RMs observed from polarized emission of each source. RM data are binned in column density bins 4 Multiplication-Sign 10{sup 20} cm{sup -2} wide, and one observes a strong relationship between the number of hydrogenmore » atoms in a 1 cm{sup 2} column through the plane and the mean RM along the same line of sight and path length. The relationship is linear over one order of magnitude (from 0.8 to 14 Multiplication-Sign 10{sup 21} atoms cm{sup -2}) of column densities, with a constant RM/N{sub H{sub I}}{approx} -23.2 {+-} 2.3 rad m{sup -2}/10{sup 21} atoms cm{sup -2}, and a positive RM of 45.0 {+-} 13.8 rad m{sup -2} in the presence of no atomic hydrogen. This slope is used to calculate a mean volume-averaged magnetic field in the second quadrant of (B{sub Parallel-To }) {approx}1.0 {+-} 0.1 {mu}G directed away from the Sun, assuming an ionization fraction of 8% (consistent with the warm-neutral medium; WNM). The remarkable consistency between this field and (B) = 1.2 {mu}G found with the same RM sources and a Galactic model of dispersion measures (DMs) suggests that electrons in the partially ionized WNM are mainly responsible for pulsar DMs, and thus the partially ionized WNM is the dominant form of the magneto-ionic interstellar medium.« less

Fast dynamos, cosmic rays, and the Galactic magnetic field

NASA Technical Reports Server (NTRS)

Parker, E. N.

1992-01-01

It is suggested here that the dynamo believed to be responsible for the magnetic field of the Galaxy is a fast dynamo due to the dynamical reconnection of the azimuthal field of the Galaxy as the field is deformed by the instability of the gaseous disk and the rapid inflation of magnetic lobes by the cosmic-ray gas to form the Galactic halo. The reconnection of adjacent lobes carries out both the alpha effect and field dissipation essential for the existence of the Galactic alpha-omega dynamo. The azimuthal field is generated primarily in the gaseous disk, while the alpha effect is carried out in the halo.

The Second Galactic Center Black Hole? A Possible Detection of Ionized Gas Orbiting around an IMBH Embedded in the Galactic Center IRS13E Complex

NASA Astrophysics Data System (ADS)

Tsuboi, Masato; Kitamura, Yoshimi; Tsutsumi, Takahiro; Uehara, Kenta; Miyoshi, Makoto; Miyawaki, Ryosuke; Miyazaki, Atsushi

2017-11-01

The Galactic Center is the nuclear region of the nearest spiral galaxy, the Milky Way, and contains the supermassive black hole with M˜ 4× {10}6 {M}⊙ , Sagittarius A* (Sgr A*). One of the basic questions about the Galactic Center is whether or not Sgr A* is the only “massive” black hole in the region. The IRS13E complex is a very intriguing infrared (IR) object that contains a large dark mass comparable to the mass of an intermediate mass black hole (IMBH) from the proper motions of the main member stars. However, the existence of the IMBH remains controversial. There are some objections to accepting the existence of the IMBH. In this study, we detected ionized gas with a very large velocity width ({{Δ }}{v}{FWZI}˜ 650 km s-1) and a very compact size (r˜ 400 au) in the complex using the Atacama Large Millimeter/submillimeter Array (ALMA). We also found an extended component connecting with the compact ionized gas. The properties suggest that this is an ionized gas flow on the Keplerian orbit with high eccentricity. The enclosed mass is estimated to be {10}4 {M}⊙ by the analysis of the orbit. The mass does not conflict with the upper limit mass of the IMBH around Sgr A*, which is derived by the long-term astrometry with the Very Long Baseline Array (VLBA). In addition, the object probably has an X-ray counterpart. Consequently, a very fascinating possibility is that the detected ionized gas is rotating around an IMBH embedded in the IRS13E complex.

A Discovery of a Compact High Velocity Cloud-Galactic Supershell System

NASA Astrophysics Data System (ADS)

Park, Geumsook; Koo, Bon-Chul; Kang, Ji-hyun; Gibson, Steven J.; Peek, Joshua Eli Goldston; Douglas, Kevin A.; Korpela, Eric J.; Heiles, Carl E.

2017-01-01

High velocity clouds (HVCs) are neutral hydrogen (HI) gas clouds having very different radial velocities from those of the Galactic disk material. While some large HVC complexes are known to be gas streams tidally stripped from satellite galaxies of the Milky Way, there are relatively isolated and small angular-sized HVCs, so called “compact HVCs (CHVCs)”, the origin of which remains controversial. There are about 300 known CHVCs in the Milky Way, and many of them show a head-tail structure, implying a ram pressure interaction with the diffuse Galactic halo gas. It is, however, not clear whether CHVCs are completely dissipated in the Galactic halo to feed the multi-phase circumgalactic medium or they can survive their trip through the halo and collide with the Galactic disk. The colliding CHVCs may leave a gigantic trail in the disk, and it had been suggested that some of HI supershells that require ≧ 3 x 1052 erg may be produced by the collision of such HVCs.Here we report the detection of a kiloparsec (kpc)-size supershell in the outskirts of the Milky Way with the compact HVC 040+01-282 (hereafter, CHVC040) at its geometrical center using the “Inner-Galaxy Arecibo L-band Feed Array” HI 21 cm survey data. The morphological and physical properties of both objects suggest that CHVC040, which is either a fragment of a nearby disrupted galaxy or a cloud that originated from an intergalactic accreting flow, collided with the disk ˜5 Myr ago to form the supershell. Our results show that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk.

How do stars affect ψDM halos?

NASA Astrophysics Data System (ADS)

Chan, James H. H.; Schive, Hsi-Yu; Woo, Tak-Pong; Chiueh, Tzihong

2018-04-01

Wave dark matter (ψDM) predicts a compact soliton core and a granular halo in every galaxy. This work presents the first simulation study of an elliptical galaxy by including both stars and ψDM, focusing on the systematic changes of the central soliton and halo granules. With the addition of stars in the inner halo, we find the soliton core consistently becomes more prominent by absorbing mass from the host halo than that without stars, and the halo granules become "non-isothermal", "hotter" in the inner halo and "cooler" in the outer halo, as opposed to the isothermal halo in pure ψDM cosmological simulations. Moreover, the composite (star+ψDM) mass density is found to follow a r-2 isothermal profile near the half-light radius in most cases. Most striking is the velocity dispersion of halo stars that increases rapidly toward the galactic center by a factor of at least 2 inside the half-light radius caused by the deepened soliton gravitational potential, a result that compares favorably with observations of elliptical galaxies and bulges in spiral galaxies. However in some rare situations we find a phase segregation turning a compact distribution of stars into two distinct populations with high and very low velocity dispersions; while the high-velocity component mostly resides in the halo, the very low-velocity component is bound to the interior of the soliton core, resembling stars in faint dwarf spheroidal galaxies.

Simulating Halos with the Caterpillar Project

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-04-01

The Caterpillar Project is a beautiful series of high-resolution cosmological simulations. The goal of this project is to examine the evolution of dark-matter halos like the Milky Ways, to learn about how galaxies like ours formed. This immense computational project is still in progress, but the Caterpillar team is already providing a look at some of its first results.Lessons from Dark-Matter HalosWhy simulate the dark-matter halos of galaxies? Observationally, the formation history of our galaxy is encoded in galactic fossil record clues, like the tidal debris from disrupted satellite galaxies in the outer reaches of our galaxy, or chemical abundance patterns throughout our galactic disk and stellar halo.But to interpret this information in a way that lets us learn about our galaxys history, we need to first test galaxy formation and evolution scenarios via cosmological simulations. Then we can compare the end result of these simulations to what we observe today.This figure illustrates the difference that mass resolution makes. In the left panel, the mass resolution is 1.5*10^7 solar masses per particle. In the right panel, the mass resolution is 3*10^4 solar masses per particle [Griffen et al. 2016]A Computational ChallengeDue to how computationally expensive such simulations are, previous N-body simulations of the growth of Milky-Way-like halos have consisted of only one or a few halos each. But in order to establish a statistical understanding of how galaxy halos form and find out whether the Milky Ways halo is typical or unusual! it is necessary to simulate a larger number of halos.In addition, in order to accurately follow the formation and evolution of substructure within the dark-matter halos, these simulations must be able to resolve the smallest dwarf galaxies, which are around a million solar masses. This requires an extremely high mass resolution, which adds to the computational expense of the simulation.First OutcomesThese are the challenges faced by

One dark matter mystery: halos in the cosmic web

NASA Astrophysics Data System (ADS)

Gaite, Jose

2015-01-01

The current cold dark matter cosmological model explains the large scale cosmic web structure but is challenged by the observation of a relatively smooth distribution of matter in galactic clusters. We consider various aspects of modeling the dark matter around galaxies as distributed in smooth halos and, especially, the smoothness of the dark matter halos seen in N-body cosmological simulations. We conclude that the problems of the cold dark matter cosmology on small scales are more serious than normally admitted.

The Physical Nature of the Circum-Galactic Medium

NASA Astrophysics Data System (ADS)

Faucher-Giguere, Claude-Andre

The installation of the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) as part of its last servicing mission has revolutionized the study of gas in and around galaxies through the study of ultra-violet (UV) diagnostics. These diagnostics are enabling studies of gas flows in and out of low-redshift, evolved galaxies that are not feasible from the ground. Despite the great observational advances made possible with COS, it is necessary to complement the high-quality spectra with theoretical modeling sufficiently accurate for robust and complete physical interpretation so that the full scientific potential of the mission can be realized. The clear correlation between O VI absorption in galactic halos and the specific star formation rate of central galaxies revealed by COS, in particular, highlights the close connection between circum-galactic gas and galaxies. It is now also appreciated that the gaseous halos of galaxies contain a total mass and a mass in metals that are at least comparable to (and likely significantly greater than) the total and metal masses in the interstellar medium of galaxies. The circum-galactic medium (CGM) is thus intimately related to galaxy evolution, including the transformation of blue star-forming disks into red passive ellipticals. However, the physical origin of observed galaxy-halo gas correlations and of halo gas in general is presently not understood. We will model the CGM of low-redshift galaxies probed by HST observations with cosmological simulations of unprecedented resolution and with much more physically predictive models of star formation and stellar and black hole feedback than previously available. Our simulations will also employ a numerical solver that resolves all the main historical differences between grid- and particle-based hydrodynamical codes. Importantly, we will process all of our simulations with radiative transfer calculations to faithfully map the simulations to observable quantities, a

An explosion model for the formation of the radio halo of NGC 891

NASA Astrophysics Data System (ADS)

You, Jun-han; Allen, R. J.; Hu, Fu-xing

1987-06-01

The explosion model for the formation of the radio halo of NGC 891 proposed here are mainly based on two physical assumptions: a) the relativistic electrons belong to two families, a halo family and a disk family: the disk family originating in supernova events throughout the disk and the halo family, in a violent explosion of the galactic nucleus in the distant past. b) Energy equipartition, that is, the magnetic energy density be proportional to the number density of stars. On these two assumptions, the main observed features of the radio halo of NGC 891 can be satisfactorily explained.

An explosion model for the formation of the radio halo of NGC 891

NASA Astrophysics Data System (ADS)

You, Jun-Han; Allen, R. J.; Hu, Fu-Xing

1986-06-01

The explosion model for the formation of the radio halo of NGC 891 proposed here is mainly based on two physical assumptions: (1) the relativistic electrons belong to two families, a halo family and a disk family, the disk family originating in supernova events throughout the disk, and the halo family in a violent explosion of the galactic nucleus in the distant past; and (2) energy equipartition, where the magnetic energy density is proportional to the number density of stars. On these two assumptions, the main observed features of the radio halo of NGC 891 can be satisfactorily explained.

TeV Gamma Rays From Galactic Center Pulsars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hooper, Dan; Cholis, Ilias; Linden, Tim

Measurements of the nearby pulsars Geminga and B0656+14 by the HAWC and Milagro telescopes have revealed the presence of bright TeV-emitting halos surrounding these objects. If young and middle-aged pulsars near the Galactic Center transfer a similar fraction of their energy into TeV photons, then these sources could dominate the emission that is observed by HESS and other ground-based telescopes from the innermost ~10^2 parsecs of the Milky Way. In particular, both the spectral shape and the angular extent of this emission is consistent with TeV halos produced by a population of pulsars. The overall flux of this emission requiresmore » a birth rate of ~100-1000 neutron stars per Myr near the Galactic Center, in good agreement with recent estimates.« less

Planck early results. XXIV. Dust in the diffuse interstellar medium and the Galactic halo

NASA Astrophysics Data System (ADS)

Planck Collaboration; Abergel, A.; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bhatia, R.; Blagrave, K.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Cabella, P.; Cantalupo, C. M.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Challinor, A.; Chamballu, A.; Chiang, L.-Y.; Chiang, C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Gasperis, G.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Jaffe, A. H.; Joncas, G.; Jones, A.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knox, L.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leonardi, R.; Leroy, C.; Linden-Vørnle, M.; Lockman, F. J.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Maino, D.; Mandolesi, N.; Mann, R.; Maris, M.; Marshall, D. J.; Martin, P.; Martínez-González, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Osborne, S.; Pajot, F.; Paladini, R.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pinheiro Gonçalves, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, P.; Smoot, G. F.; Starck, J.-L.; Stivoli, F.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Torre, J.-P.; Tristram, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

2011-12-01

This paper presents the first results from a comparison of Planck dust maps at 353, 545 and 857GHz, along with IRAS data at 3000 (100 μm) and 5000GHz (60 μm), with Green Bank Telescope 21-cm observations of Hi in 14 fields covering more than 800 deg2 at high Galactic latitude. The main goal of this study is to estimate the far-infrared to sub-millimeter (submm) emissivity of dust in the diffuse local interstellar medium (ISM) and in the intermediate-velocity (IVC) and high-velocity clouds (HVC) of the Galactic halo. Galactic dust emission for fields with average Hi column density lower than 2 × 1020 cm-2 is well correlated with 21-cm emission because in such diffuse areas the hydrogen is predominantly in the neutral atomic phase. The residual emission in these fields, once the Hi-correlated emission is removed, is consistent with the expected statistical properties of the cosmic infrared background fluctuations. The brighter fields in our sample, with an average Hi column density greater than 2 × 1020 cm-2, show significant excess dust emission compared to the Hi column density. Regions of excess lie in organized structures that suggest the presence of hydrogen in molecular form, though they are not always correlated with CO emission. In the higher Hi column density fields the excess emission at 857 GHz is about 40% of that coming from the Hi, but over all the high latitude fields surveyed the molecular mass faction is about 10%. Dust emission from IVCs is detected with high significance by this correlation analysis. Its spectral properties are consistent with, compared to the local ISM values, significantly hotter dust (T ~ 20K), lower submm dust opacity normalized per H-atom, and a relative abundance of very small grains to large grains about four times higher. These results are compatible with expectations for clouds that are part of the Galactic fountain in which there is dust shattering and fragmentation. Correlated dust emission in HVCs is not detected

Effect of the cosmological constant on halo size

NASA Astrophysics Data System (ADS)

Kulchoakrungsun, Ekapob; Lam, Adrian; Lowe, David A.

2018-04-01

In this work, we consider the effect of the cosmological constant on galactic halo size. As a model, we study the general relativistic derivation of orbits in the Schwarzschild-de Sitter metric. We find that there exists a length scale rΛ corresponding to a maximum size of a circular orbit of a test mass in a gravitationally bound system, which is the geometric mean of the cosmological horizon size squared and the Schwarzschild radius. This agrees well with the size of a galactic halo when the effects of dark matter are included. The size of larger structures such as galactic clusters and superclusters are also well-approximated by this scale. This model provides a simplified approach to computing the size of such structures without the usual detailed dynamical models. Some of the more detailed approaches that appear in the literature are reviewed, and we find the length scales agree to within a factor of order one. Finally, we note the length scale associated with the effects of MOND or Verlinde’s emergent gravity, which offer explanations of the flattening of galaxy rotation curves without invoking dark matter, may be expressed as the geometric mean of the cosmological horizon size and the Schwarzschild radius, which is typically 100 times smaller than rΛ.

Statistics of Dark Matter Halos from Gravitational Lensing.

PubMed

Jain; Van Waerbeke L

2000-02-10

We present a new approach to measure the mass function of dark matter halos and to discriminate models with differing values of Omega through weak gravitational lensing. We measure the distribution of peaks from simulated lensing surveys and show that the lensing signal due to dark matter halos can be detected for a wide range of peak heights. Even when the signal-to-noise ratio is well below the limit for detection of individual halos, projected halo statistics can be constrained for halo masses spanning galactic to cluster halos. The use of peak statistics relies on an analytical model of the noise due to the intrinsic ellipticities of source galaxies. The noise model has been shown to accurately describe simulated data for a variety of input ellipticity distributions. We show that the measured peak distribution has distinct signatures of gravitational lensing, and its non-Gaussian shape can be used to distinguish models with different values of Omega. The use of peak statistics is complementary to the measurement of field statistics, such as the ellipticity correlation function, and is possibly not susceptible to the same systematic errors.

On the origin of the warm-hot absorbers in the Milky Way's halo

NASA Astrophysics Data System (ADS)

Marasco, A.; Marinacci, F.; Fraternali, F.

2013-08-01

Disc galaxies like the Milky Way are expected to be surrounded by massive coronae of hot plasma that may contain a significant fraction of the so-called missing baryons. We investigate whether the local (|vLSR| < 400 km s-1) warm-hot absorption features observed towards extra-Galactic sources or halo stars are consistent with being produced by the cooling of the Milky Way's corona. In our scheme, cooling occurs at the interface between the disc and the corona and it is triggered by positive supernova feedback. We combine hydrodynamical simulations with a dynamical 3D model of the galactic fountain to predict the all-sky distribution of this cooling material, and we compare it with the observed distribution of detections for different `warm' (Si III, Si IV, C II, C IV) and `hot' (O VI) ionized species. The model reproduces the position-velocity distribution and the column densities of the vast majority of warm absorbers and about half of O VI absorbers. We conclude that the warm-hot gas responsible for most of the detections lies within a few kiloparsec from the Galactic plane, where high-metallicity material from the disc mixes efficiently with the hot corona. This process provides an accretion of a few M⊙ yr- 1 of fresh gas that can easily feed the star formation in the disc of the Galaxy. The remaining O VI detections are likely to be a different population of absorbers, located in the outskirts of the Galactic corona and/or in the circumgalactic medium of nearby galaxies.

Relativistic Dark Matter at the Galactic Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amin, Mustafa A.; /Stanford U., Phys. Dept. /KIPAC, Menlo Park; Wizansky, Tommer

2007-11-16

In a large region of the supersymmetry parameter space, the annihilation cross section for neutralino dark matter is strongly dependent on the relative velocity of the incoming particles. We explore the consequences of this velocity dependence in the context of indirect detection of dark matter from the galactic center. We find that the increase in the annihilation cross section at high velocities leads to a flattening of the halo density profile near the galactic center and an enhancement of the annihilation signal.

Ordinary Dark Matter versus Mysterious Dark Matter in Galactic Rotation

NASA Astrophysics Data System (ADS)

Gallo, C. F.; Feng, James

2008-04-01

To theoretically describe the measured rotational velocity curves of spiral galaxies, there are two different approaches and conclusions. (1) ORDINARY DARK MATTER. We assume Newtonian gravity/dynamics and successfully find (via computer) mass distributions in bulge/disk configurations that duplicate the measured rotational velocities. There is ordinary dark matter within the galactic disk towards the cooler periphery which has lower emissivity/opacity. There are no mysteries in this scenario based on verified physics. (2) MYSTERIOUS DARK MATTER. Others INaccurately assume the galactic mass distributions follow the measured light distributions, and then the measured rotational velocity curves are NOT duplicated. To alleviate this discrepancy, speculations are invoked re ``Massive Peripheral Spherical Halos of Mysterious Dark Matter.'' But NO matter has been detected in this UNtenable Halo configuration. Many UNverified ``Mysteries'' are invoked as necessary and convenient. CONCLUSION. The first approach utilizing Newtonian gravity/dynamics and searching for the ordinary mass distributions within the galactic disk simulates reality and agrees with data.

Review of the fermionic dark matter model applied to galactic structures

NASA Astrophysics Data System (ADS)

Krut, A.; Argüelles, C. R.; Rueda, J.; Ruffini, R.

2015-12-01

Baryonic components (e.g. bulge and disk) of galactic structures are assumed to be embedded in an isothermal dark matter halo of fermionic nature. Besides the Pauli principle only gravitational interaction is considered. Using the underlying Fermi-Dirac phase space distribution, typical of collisionless relaxation processes, it yields an one-parameter family of scaled solutions which reproduces the observed flat rotation curves in galaxies, and additionally predicts a degenerate core through their centers. In order to provide the right DM halo properties of galaxies a set of four parameters (particle mass, degeneracy parameter at the galactic center, central density and the velocity dispersion) is necessary. The more general density profile shows three regimes depending on radius: an almost uniform very dense quantum core followed by a steep fall, a plateau in the diluted regime and a Boltzmannian tail representing the halo. In contrast to purely Boltzmannian configurations the fermionic DM model containing a quantum core allows to determine the particle mass. We show that the quantum core can be well approximated by a polytrope of index n = 3/2, while the halo can be perfectly described by an isothermal sphere with a halo scale length radius equal to approximately 3/4 of the King-radius.

Review of the fermionic dark matter model applied to galactic structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krut, A.; Argüelles, C. R.; Rueda, J.

2015-12-17

Baryonic components (e.g. bulge and disk) of galactic structures are assumed to be embedded in an isothermal dark matter halo of fermionic nature. Besides the Pauli principle only gravitational interaction is considered. Using the underlying Fermi-Dirac phase space distribution, typical of collisionless relaxation processes, it yields an one-parameter family of scaled solutions which reproduces the observed flat rotation curves in galaxies, and additionally predicts a degenerate core through their centers. In order to provide the right DM halo properties of galaxies a set of four parameters (particle mass, degeneracy parameter at the galactic center, central density and the velocity dispersion)more » is necessary. The more general density profile shows three regimes depending on radius: an almost uniform very dense quantum core followed by a steep fall, a plateau in the diluted regime and a Boltzmannian tail representing the halo. In contrast to purely Boltzmannian configurations the fermionic DM model containing a quantum core allows to determine the particle mass. We show that the quantum core can be well approximated by a polytrope of index n = 3/2, while the halo can be perfectly described by an isothermal sphere with a halo scale length radius equal to approximately 3/4 of the King-radius.« less

The Dual Origin Of Stellar Halos

NASA Astrophysics Data System (ADS)

Zolotov, Adi

In the dominant Lambda+Cold Dark Matter cosmological paradigm, galaxy stellar halos are thought to form hierarchically from multiple accretion events, starting from the first structures to collapse in the Universe. This dissertation aims to make the first detailed theoretical predictions for the origin of galactic stellar halos. We focus on understanding the physical processes involved in halo formation using high-resolution, N-body + Smooth Particle Hydrodynamic simulations of disk galaxies in a cosmological context. These self-consistent simulations are used to study the competing importance of dissipative processes and dissipationless mergers in the formation of stellar halos. The relative contribution of each mechanism, and its specific role in assembling the inner and outer regions of halos is explored, as a function of galaxy mass and merging history. We show that the presence of both accreted and in situ stars in halos is a generic feature of galaxy formation. For L* galaxies, the relative contribution of each stellar population to a halo is shown to be a function of a galaxy's accretion history. Galaxies with recent mergers, like M31, will host relatively few in situ stars, while galaxies with more quiescent recent histories, like the Milky Way, will likely have a larger relative contribution from an in situ population. We show that in situ halo stars are more [alpha/Fe]-rich than accreted stars at the high [Fe/H] end of a halo's metallicity distribution function. In lower mass galaxies, M ˜ 1010 M, in situ stars dominate the stellarmass of halos. In these galaxies, in situ halo stars are, on average, younger and more metal-rich than accreted halo stars. Because in situ stars are dominant, these trends result in halos that are more metal-rich than simple accretion models predict. The halos of low mass galaxies do not extend out to the virial radii of the primary, as they do in more massive galaxies. We find that the ratio of luminous-halo mass to total

Dissecting the large-scale galactic conformity

NASA Astrophysics Data System (ADS)

Seo, Seongu

2018-01-01

Galactic conformity is an observed phenomenon that galaxies located in the same region have similar properties such as star formation rate, color, gas fraction, and so on. The conformity was first observed among galaxies within in the same halos (“one-halo conformity”). The one-halo conformity can be readily explained by mutual interactions among galaxies within a halo. Recent observations however further witnessed a puzzling connection among galaxies with no direct interaction. In particular, galaxies located within a sphere of ~5 Mpc radius tend to show similarities, even though the galaxies do not share common halos with each other ("two-halo conformity" or “large-scale conformity”). Using a cosmological hydrodynamic simulation, Illustris, we investigate the physical origin of the two-halo conformity and put forward two scenarios. First, back-splash galaxies are likely responsible for the large-scale conformity. They have evolved into red galaxies due to ram-pressure stripping in a given galaxy cluster and happen to reside now within a ~5 Mpc sphere. Second, galaxies in strong tidal field induced by large-scale structure also seem to give rise to the large-scale conformity. The strong tides suppress star formation in the galaxies. We discuss the importance of the large-scale conformity in the context of galaxy evolution.

Ghostly Halos in Dwarf Galaxies: a probe of star formation in the Early Universe

NASA Astrophysics Data System (ADS)

Kang, Hoyoung; Ricotti, Massimo

2016-01-01

We carry out numerical simulations to characterize the size, stellar mass, and stellar mass surface density of extended stellar halos in dwarf galaxies as a function of dark matter halo mass. We expect that for galaxies smaller than a critical value, these ghostly halos will not exist because the smaller galactic subunits that build it up, do not form any stars. The detection of ghostly halos around isolated dwarf galaxies is a sensitive test of the efficiency of star formation in the first galaxies and of whether ultra-faint dwarf satellites of the Milky Way are fossils of the first galaxies.

The white dwarf luminosity function - A possible probe of the galactic halo

NASA Technical Reports Server (NTRS)

Tamanaha, Christopher M.; Silk, Joseph; Wood, M. A.; Winget, D. E.

1990-01-01

The dynamically inferred dark halo mass density, amounting to above 0.01 solar masses/cu pc at the sun's Galactocentric radius, can be composed of faint white dwarfs provided that the halo formed in a sufficiently early burst of star formation. The model is constrained by the observed disk white dwarf luminosity function which falls off below log (L/solar L) = -4.4, due to the onset of star formation in the disk. By using a narrow range for the initial mass function and an exponentially decaying halo star formation rate with an e-folding time equal to the free-fall time, all the halo dark matter is allowed to be in cool white dwarfs which lie beyond the falloff in the disk luminosity function. Although it is unlikely that all the dark matter is in these dim white dwarfs, a definite signature in the low-luminosity end of the white dwarf luminosity function is predicted even if they comprise only 1 percent of the dark matter. Current CCD surveys should answer the question of the existence of this population within the next few years.

Discovery of Ionized Gas Associated with the Tilted Inner Disk of the Milky Way

NASA Astrophysics Data System (ADS)

Haffner, L. Matthew; Benjamin, Robert A.; Krishnarao, Dhanesh

2018-01-01

The complex distribution and motion of gas within the central few kiloparsecs of our Galaxy does not follow the more regular patterns seen throughout the rest of its gaseous disk. Sensitive observations of the neutral and molecular gas over the past 40 years reveal emission intensities and velocities that are far from symmetric about the Galactic equator and the line at zero longitude. Burton and Liszt (1978-1992) show that much of the anomalous behavior is well explained by an elliptical disk, tilted with respect to the Galactic plane and our line of sight.Using the Wisconsin Hα Mapper (WHAM), we report the discovery of ionized gas near the Galactic center (l = 0° - 14° b = -8° to +4°) with a distribution and velocities also explained by this creative model. Emission from distant regions near the Galactic plane is typically blocked by a thick band of interstellar dust. However, a portion of the tilted disk is behind Baade's Window, a hole in the thick dust near the Galactic center. Combined with the unparalleled sensitivity of the WHAM Sky Survey (IHα ~ 0.1 R; EM ~ 0.2 pc cm-6), we are able to trace the distribution and kinematics of the ionized phase of this structure for the first time. The relationship between this multi-phase inner disk, outflow from the Galactic center, and the Fermi bubbles is not yet clear.In several directions around the disk, WHAM captures emission from Hα, Hβ, and several ions (N, S, and O) to explore the state and source of the ionized gas. [N II]/Hα, [S II]/Hα, and [S II]/[N II] line ratios are much different than classical H II regions and diffuse gas near the plane but are similar to those seen at high-|z| (> 1.5 kpc) in the Perseus arm. We will also compare this emission to multi-phase absorption components revealed in a recent UV absorption-line study through the low halo (z ~ -1 kpc) in this direction (Savage et al. 2017) and to emission seen near nuclear regions of other spiral galaxies, where high low-ionization

PROBING THE STRUCTURE AND KINEMATICS OF THE TRANSITION LAYER BETWEEN THE MAGELLANIC STREAM AND THE HALO IN H I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nigra, Lou; Stanimirovic, Snezana; Gallagher, John S. III

2012-11-20

The Magellanic Stream (MS) is a nearby laboratory for studying the fate of cool gas streams injected into a gaseous galactic halo. We investigate properties of the boundary layer between the cool MS gas and the hot Milky Way halo with 21 cm H I observations of a relatively isolated cloud having circular projection in the northern MS. Through averaging and modeling techniques, our observations, obtained with the Robert C. Byrd Green Bank Telescope, reach unprecedented 3{sigma} sensitivity of {approx}1 Multiplication-Sign 10{sup 17} cm{sup -2}, while retaining the telescope's 9.'1 resolution in the essential radial dimension. We find an envelopemore » of diffuse neutral gas with FWHM of 60 km s{sup -1}, associated in velocity with the cloud core having FWHM of 20 km s{sup -1}, extending to 3.5 times the core radius with a neutral mass seven times that of the core. We show that the envelope is too extended to represent a conduction-dominated layer between the core and the halo. Its observed properties are better explained by a turbulent mixing layer driven by hydrodynamic instabilities. The fortuitous alignment of the NGC 7469 background source near the cloud center allows us to combine UV absorption and H I emission data to determine a core temperature of 8350 {+-} 350 K. We show that the H I column density and size of the core can be reproduced when a slightly larger cloud is exposed to Galactic and extragalactic background ionizing radiation. Cooling in the large diffuse turbulent mixing layer envelope extends the cloud lifetime by at least a factor of two relative to a simple hydrodynamic ablation case, suggesting that the cloud is likely to reach the Milky Way disk.« less

A HIGH-VELOCITY BULGE RR LYRAE VARIABLE ON A HALO-LIKE ORBIT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunder, Andrea; Storm, J.; Rich, R. M.

2015-07-20

We report on the RR Lyrae variable star, MACHO 176.18833.411, located toward the Galactic bulge and observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay, which has the unusual radial velocity of −372 ± 8 km s{sup −1} and true space velocity of −482 ± 22 km s{sup −1} relative to the Galactic rest frame. Located less than 1 kpc from the Galactic center and toward a field at (l, b) = (3, −2.5), this pulsating star has properties suggesting it belongs to the bulge RR Lyrae star population, yet a velocity indicating it is abnormal,more » at least with respect to bulge giants and red clump stars. We show that this star is most likely a halo interloper and therefore suggest that halo contamination is not insignificant when studying metal-poor stars found within the bulge area, even for stars within 1 kpc of the Galactic center. We discuss the possibility that MACHO 176.18833.411 is on the extreme edge of the bulge RR Lyrae radial velocity distribution, and also consider a more exotic scenario in which it is a runaway star moving through the Galaxy.« less

What to expect from dynamical modelling of galactic haloes - II. The spherical Jeans equation

NASA Astrophysics Data System (ADS)

Wang, Wenting; Han, Jiaxin; Cole, Shaun; More, Surhud; Frenk, Carlos; Schaller, Matthieu

2018-06-01

The spherical Jeans equation (SJE) is widely used in dynamical modelling of the Milky Way (MW) halo potential. We use haloes and galaxies from the cosmological Millennium-II simulation and hydrodynamical APOSTLE (A Project of Simulations of The Local Environment) simulations to investigate the performance of the SJE in recovering the underlying mass profiles of MW mass haloes. The best-fitting halo mass and concentration parameters scatter by 25 per cent and 40 per cent around their input values, respectively, when dark matter particles are used as tracers. This scatter becomes as large as a factor of 3 when using star particles instead. This is significantly larger than the estimated statistical uncertainty associated with the use of the SJE. The existence of correlated phase-space structures that violate the steady-state assumption of the SJE as well as non-spherical geometries is the principal source of the scatter. Binary haloes show larger scatter because they are more aspherical in shape and have a more perturbed dynamical state. Our results confirm that the number of independent phase-space structures sets an intrinsic limiting precision on dynamical inferences based on the steady-state assumption. Modelling with a radius-independent velocity anisotropy, or using tracers within a limited outer radius, result in significantly larger scatter, but the ensemble-averaged measurement over the whole halo sample is approximately unbiased.

The Impact of Galactic Winds on the Angular Momentum of Disk Galaxies in the Illustris Simulation

NASA Astrophysics Data System (ADS)

DeFelippis, Daniel; Genel, Shy; Bryan, Greg L.; Fall, S. Michael

2017-05-01

Observed galactic disks have specific angular momenta similar to expectations for typical dark matter halos in ΛCDM. Cosmological hydrodynamical simulations have recently reproduced this similarity in large galaxy samples by including strong galactic winds, but the exact mechanism that achieves this is not yet clear. Here we present an analysis of key aspects contributing to this relation: angular momentum selection and evolution of Lagrangian mass elements as they accrete onto dark matter halos, condense into Milky-Way-scale galaxies, and join the z = 0 stellar phase. We contrast this evolution in the Illustris simulation with that in a simulation without galactic winds, where the z = 0 angular momentum is ≈ 0.6 {dex} lower. We find that winds induce differences between these simulations in several ways: increasing angular momentum, preventing angular momentum loss, and causing z = 0 stars to sample the accretion-time angular momentum distribution of baryons in a biased way. In both simulations, gas loses on average ≈ 0.4 {dex} between accreting onto halos and first accreting onto central galaxies. In Illustris, this is followed by ≈ 0.2 {dex} gains in the “galactic wind fountain” and no further net evolution past the final accretion onto the galaxy. Without feedback, further losses of ≈ 0.2 {dex} occur in the gas phase inside the galaxies. An additional ≈ 0.15 {dex} difference arises from feedback preferentially selecting higher angular momentum gas at accretion by expelling gas that is poorly aligned. These and additional effects of similar magnitude are discussed, suggesting a complex origin of the similarity between the specific angular momenta of galactic disks and typical halos.

Galactic conformity measured in semi-analytic models

NASA Astrophysics Data System (ADS)

Lacerna, I.; Contreras, S.; González, R. E.; Padilla, N.; Gonzalez-Perez, V.

2018-03-01

We study the correlation between the specific star formation rate of central galaxies and neighbour galaxies, also known as `galactic conformity', out to 20 h^{-1} {Mpc} using three semi-analytic models (SAMs, one from L-GALAXIES and other two from GALFORM). The aim is to establish whether SAMs are able to show galactic conformity using different models and selection criteria. In all the models, when the selection of primary galaxies is based on an isolation criterion in real space, the mean fraction of quenched (Q) galaxies around Q primary galaxies is higher than that around star-forming primary galaxies of the same stellar mass. The overall signal of conformity decreases when we remove satellites selected as primary galaxies, but the effect is much stronger in GALFORM models compared with the L-GALAXIES model. We find this difference is partially explained by the fact that in GALFORM once a galaxy becomes a satellite remains as such, whereas satellites can become centrals at a later time in L-GALAXIES. The signal of conformity decreases down to 60 per cent in the L-GALAXIES model after removing central galaxies that were ejected from their host halo in the past. Galactic conformity is also influenced by primary galaxies at fixed stellar mass that reside in dark matter haloes of different masses. Finally, we explore a proxy of conformity between distinct haloes. In this case, the conformity is weak beyond ˜3 h^{-1} {Mpc} (<3 per cent in L-GALAXIES, <1-2 per cent in GALFORM models). Therefore, it seems difficult that conformity is directly related with a long-range effect.

Halo-independence with quantified maximum entropy at DAMA/LIBRA

NASA Astrophysics Data System (ADS)

Fowlie, Andrew

2017-10-01

Using the DAMA/LIBRA anomaly as an example, we formalise the notion of halo-independence in the context of Bayesian statistics and quantified maximum entropy. We consider an infinite set of possible profiles, weighted by an entropic prior and constrained by a likelihood describing noisy measurements of modulated moments by DAMA/LIBRA. Assuming an isotropic dark matter (DM) profile in the galactic rest frame, we find the most plausible DM profiles and predictions for unmodulated signal rates at DAMA/LIBRA. The entropic prior contains an a priori unknown regularisation factor, β, that describes the strength of our conviction that the profile is approximately Maxwellian. By varying β, we smoothly interpolate between a halo-independent and a halo-dependent analysis, thus exploring the impact of prior information about the DM profile.

Exact axially symmetric galactic dynamos

NASA Astrophysics Data System (ADS)

Henriksen, R. N.; Woodfinden, A.; Irwin, J. A.

2018-05-01

We give a selection of exact dynamos in axial symmetry on a galactic scale. These include some steady examples, at least one of which is wholly analytic in terms of simple functions and has been discussed elsewhere. Most solutions are found in terms of special functions, such as associated Lagrange or hypergeometric functions. They may be considered exact in the sense that they are known to any desired accuracy in principle. The new aspect developed here is to present scale-invariant solutions with zero resistivity that are self-similar in time. The time dependence is either a power law or an exponential factor, but since the geometry of the solution is self-similar in time we do not need to fix a time to study it. Several examples are discussed. Our results demonstrate (without the need to invoke any other mechanisms) X-shaped magnetic fields and (axially symmetric) magnetic spiral arms (both of which are well observed and documented) and predict reversing rotation measures in galaxy haloes (now observed in the CHANG-ES sample) as well as the fact that planar magnetic spirals are lifted into the galactic halo.

Normal Spiral Galaxies Really Do Have Hot Gas in Their Halos: Chandra Observations of NGC 4013 and NGC 4217.

NASA Astrophysics Data System (ADS)

Strickland, D. K.; Colbert, E. J. M.; Heckman, T. M.; Hoopes, C. G.; Howk, J. C.; Rand, R. J.

2004-08-01

Although soft X-ray emission from million degree plasma has long been observed in the halos of starburst galaxies known to have supernova-driven galactic superwinds, X-ray observations have generally failed to detect hot halos around normal spiral galaxies. Indeed, the Milky Way and NGC 891 have historically been the only genuinely "normal" spiral galaxies with unambiguous X-ray halo detections, until now. Here we report on deep observations of NGC 4013 and NGC 4217, two Milky-Way-mass spiral galaxies with star formation rates per unit area similar to the Milky Way and NGC 891, using the Chandra X-ray observatory. Preliminary investigation of the observations clearly show extra-planar diffuse X-ray emission extending several kpc into the halo of NGC 4013. We will present the results of these observations, compare them to the non-detections of hot gas around normal spirals, and relate them to galactic fountain and IGM accretion based models for hot halos. DKS acknowledges funding from NASA through the Smithsonian Astrophysical Observatory. grant G045095X.

Halo-shaped flowing atmospheric pressure afterglow: a heavenly design for simplified sample introduction and improved ionization in ambient mass spectrometry.

PubMed

Pfeuffer, Kevin P; Schaper, J Niklas; Shelley, Jacob T; Ray, Steven J; Chan, George C-Y; Bings, Nicolas H; Hieftje, Gary M

2013-08-06

The flowing atmospheric-pressure afterglow (FAPA) is a promising new source for atmospheric-pressure, ambient desorption/ionization mass spectrometry. However, problems exist with reproducible sample introduction into the FAPA source. To overcome this limitation, a new FAPA geometry has been developed in which concentric tubular electrodes are utilized to form a halo-shaped discharge; this geometry has been termed the halo-FAPA or h-FAPA. With this new geometry, it is still possible to achieve direct desorption and ionization from a surface; however, sample introduction through the inner capillary is also possible and improves interaction between the sample material (solution, vapor, or aerosol) and the plasma to promote desorption and ionization. The h-FAPA operates with a helium gas flow of 0.60 L/min outer, 0.30 L/min inner, and applied current of 30 mA at 200 V for 6 W of power. In addition, separation of the discharge proper and sample material prevents perturbations to the plasma. Optical-emission characterization and gas rotational temperatures reveal that the temperature of the discharge is not significantly affected (<3% change at 450 K) by water vapor during solution-aerosol sample introduction. The primary mass-spectral background species are protonated water clusters, and the primary analyte ions are protonated molecular ions (M + H(+)). Flexibility of the new ambient sampling source is demonstrated by coupling it with a laser ablation unit, a concentric nebulizer, and a droplet-on-demand system for sample introduction. A novel arrangement is also presented in which the central channel of the h-FAPA is used as the inlet to a mass spectrometer.

Hot gas, cold gas and sub-haloes in a Lyman α blob at redshift 2.38

NASA Astrophysics Data System (ADS)

Francis, Paul. J.; Dopita, Michael A.; Colbert, James W.; Palunas, Povilas; Scarlata, Claudia; Teplitz, Harry; Williger, Gerard M.; Woodgate, Bruce E.

2013-01-01

We present integral field spectroscopy of a Lyman α blob at redshift 2.38, with a spectral resolution three times better than previous published work. As with previous observations, the blob has a chaotic velocity structure, much of which breaks up into multiple components. Our spectroscopy shows, however, that some of these multiple components are extremely narrow: they have velocity widths of less than 100 km s- 1. Combining these new data with previous observations, we argue that this Lyman α blob resides in a dark matter halo of around 1013 M⊙. At the centre of this halo are two compact red massive galaxies. They are surrounded by hot gas, probably a superwind from merger-induced nuclear starbursts. This hot gas has shut down star formation in the non-nuclear region of these galaxies, leading to their red-and-dead colours. A filament or lump of infalling cold gas is colliding with the hot gas phase and being shocked to high temperatures, while still around 30 kpc from the red galaxies. The shock region is self-absorbed in Lyman α but produces C iv emission. Further out still, the cold gas in a number of sub-haloes is being lit up, most likely by a combination of tidally triggered star formation, bow shocks as they plough through the hot halo medium, resonant scattering of Lyman α from the filament collision and tidal stripping of gas which enhances the Lyman α escape fraction. The observed Lyman α emission from the blob is dominated by the sum of the emission from these sub-haloes. On statistical grounds, we argue that Lyman α blobs are not greatly elongated in shape and that most are not powered by ionization or scattering from a central active galactic nucleus or starburst.

Disc-halo interactions in ΛCDM

NASA Astrophysics Data System (ADS)

Bauer, Jacob S.; Widrow, Lawrence M.; Erkal, Denis

2018-05-01

We present a new method for embedding a stellar disc in a cosmological dark matter halo and provide a worked example from a Λ cold dark matter zoom-in simulation. The disc is inserted into the halo at a redshift z = 3 as a zero-mass rigid body. Its mass and size are then increased adiabatically while its position, velocity, and orientation are determined from rigid-body dynamics. At z = 1, the rigid disc (RD) is replaced by an N-body disc whose particles sample a three-integral distribution function (DF). The simulation then proceeds to z = 0 with live disc (LD) and halo particles. By comparison, other methods assume one or more of the following: the centre of the RD during the growth phase is pinned to the minimum of the halo potential, the orientation of the RD is fixed, or the live N-body disc is constructed from a two rather than three-integral DF. In general, the presence of a disc makes the halo rounder, more centrally concentrated, and smoother, especially in the innermost regions. We find that methods in which the disc is pinned to the minimum of the halo potential tend to overestimate the amount of adiabatic contraction. Additionally, the effect of the disc on the subhalo distribution appears to be rather insensitive to the disc insertion method. The LD in our simulation develops a bar that is consistent with the bars seen in late-type spiral galaxies. In addition, particles from the disc are launched or `kicked up' to high galactic latitudes.

Reconstructing the Accretion History of the Galactic Stellar Halo from Chemical Abundance Ratio Distributions

NASA Astrophysics Data System (ADS)

Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

2015-03-01

Observational studies of halo stars during the past two decades have placed some limits on the quantity and nature of accreted dwarf galaxy contributions to the Milky Way (MW) stellar halo by typically utilizing stellar phase-space information to identify the most recent halo accretion events. In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from 11 “MW-like” halos to generate satellite template sets (STSs) of 2D CARDs of accreted dwarf satellites, which are composed of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ˜103-4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those 11 halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the STS used and the sample size. For certain STSs used we typically can identify the relative mass contributions of all accreted satellites to within a factor of two. We also find that this method is particularly sensitive to older accretion events involving low-luminosity dwarfs, e.g., ultra-faint dwarfs—precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ˜6-9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us to recover its accretion history—and the luminosity function of infalling dwarf galaxies—across cosmic time.

RECONSTRUCTING THE ACCRETION HISTORY OF THE GALACTIC STELLAR HALO FROM CHEMICAL ABUNDANCE RATIO DISTRIBUTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva

Observational studies of halo stars during the past two decades have placed some limits on the quantity and nature of accreted dwarf galaxy contributions to the Milky Way (MW) stellar halo by typically utilizing stellar phase-space information to identify the most recent halo accretion events. In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from 11 “MW-like” halos to generate satellite template sets (STSs) of 2D CARDs of accreted dwarf satellites, which are composed of accreted dwarfsmore » from various mass regimes and epochs of accretion. Next, we randomly drew samples of ∼10{sup 3–4} mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those 11 halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the STS used and the sample size. For certain STSs used we typically can identify the relative mass contributions of all accreted satellites to within a factor of two. We also find that this method is particularly sensitive to older accretion events involving low-luminosity dwarfs, e.g., ultra-faint dwarfs—precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ∼6–9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us to recover its accretion history—and the luminosity function of infalling dwarf galaxies—across cosmic time.« less

Galactic Forces Rule the Dynamics of Milky Way Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Hammer, Francois; Yang, Yanbin; Arenou, Frederic; Babusiaux, Carine; Wang, Jianling; Puech, Mathieu; Flores, Hector

2018-06-01

Dwarf galaxies populating the Galactic halo are assumed to host the largest fractions of dark matter, as calculated from their velocity dispersions. Their major axes are preferentially aligned with the Vast Polar Structure (VPOS) that is perpendicular to the Galactic disk, and we find their velocity gradients aligned as well. This finding results in a probability of random occurrence for the VPOS as low as ∼10‑5. It suggests that tidal forces exerted by the Milky Way are distorting dwarf galaxies. Here we demonstrate on the basis of the impulse approximation that the Galactic gravitational acceleration induces the dwarf line-of-sight velocity dispersion, which is also evidenced by strong dependences between both quantities. Since this result is valid for any dwarf mass value, it implies that dark matter estimates in Milky Way dwarfs cannot be deduced from the product of their radius to the square of their line-of-sight velocity dispersion. This questions the high dark matter fractions reported for these evanescent systems, and the universally adopted total-to-stellar mass relationship in the dwarf regime. It suggests that many dwarfs are at their first passage and are dissolving into the Galactic halo. This gives rise to a promising method to estimate the Milky Way total mass profile at large distances.

The Initial Conditions and Evolution of Isolated Galaxy Models: Effects of the Hot Gas Halo

NASA Astrophysics Data System (ADS)

Hwang, Jeong-Sun; Park, Changbom; Choi, Jun-Hwan

2013-02-01

We construct several Milky Way-like galaxy models containing a gas halo (as well as gaseous and stellar disks, a dark matter halo, and a stellar bulge) following either an isothermal or an NFW density profile with varying mass and initial spin. In addition, galactic winds associated with star formation are tested in some of the simulations. We evolve these isolated galaxy models using the GADGET-3 N-body/hydrodynamic simulation code, paying particular attention to the effects of the gaseous halo on the evolution. We find that the evolution of the models is strongly affected by the adopted gas halo component, particularly in the gas dissipation and the star formation activity in the disk. The model without a gas halo shows an increasing star formation rate (SFR) at the beginning of the simulation for some hundreds of millions of years and then a continuously decreasing rate to the end of the run at 3 Gyr. Whereas the SFRs in the models with a gas halo, depending on the density profile and the total mass of the gas halo, emerge to be either relatively flat throughout the simulations or increasing until the middle of the run (over a gigayear) and then decreasing to the end. The models with the more centrally concentrated NFW gas halo show overall higher SFRs than those with the isothermal gas halo of the equal mass. The gas accretion from the halo onto the disk also occurs more in the models with the NFW gas halo, however, this is shown to take place mostly in the inner part of the disk and not to contribute significantly to the star formation unless the gas halo has very high density at the central part. The rotation of a gas halo is found to make SFR lower in the model. The SFRs in the runs including galactic winds are found to be lower than those in the same runs but without winds. We conclude that the effects of a hot gaseous halo on the evolution of galaxies are generally too significant to be simply ignored. We also expect that more hydrodynamical processes in

The annihilation of galactic positrons

NASA Technical Reports Server (NTRS)

Bussard, R.; Rematy, R.

1978-01-01

The probabilities of various channels of galactic positron annihilation were evaluated and the spectrum of the resulting radiation was calculated. The narrow width (FWHM less than 3.2 keV) of the 0.511 MeV line observed from the galactic center implies that a large fraction of positrons should annihilate in a medium of temperature less than 100,000 K and ionization fraction greater than 0.05. HII regions at the galactic center could be possible sites of annihilation.

The slight spin of the old stellar halo

NASA Astrophysics Data System (ADS)

Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.; Gómez, Facundo A.; Grand, Robert J.; Marinacci, Federico; Pakmor, Rüdiger

2017-09-01

We combine Gaia data release 1 astrometry with Sloan Digital Sky Survey (SDSS) images taken some ˜10-15 years earlier, to measure proper motions of stars in the halo of our Galaxy. The SDSS-Gaia proper motions have typical statistical errors of 2 mas yr-1 down to r ˜ 20 mag, and are robust to variations with magnitude and colour. Armed with this exquisite set of halo proper motions, we identify RR Lyrae, blue horizontal branch (BHB), and K giant stars in the halo, and measure their net rotation with respect to the Galactic disc. We find evidence for a gently rotating prograde signal (〈Vϕ〉 ˜ 5-25 km s-1) in the halo stars, which shows little variation with Galactocentric radius out to 50 kpc. The average rotation signal for the three populations is 〈Vϕ〉 = 14 ± 2 ± 10 (syst.) km s-1. There is also tentative evidence for a kinematic correlation with metallicity, whereby the metal richer BHB and K giant stars have slightly stronger prograde rotation than the metal poorer stars. Using the Auriga simulation suite, we find that the old (T >10 Gyr) stars in the simulated haloes exhibit mild prograde rotation, with little dependence on radius or metallicity, in general agreement with the observations. The weak halo rotation suggests that the Milky Way has a minor in situ halo component, and has undergone a relatively quiet accretion history.

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and >3D< Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

NASA Astrophysics Data System (ADS)

Bergemann, Maria; Collet, Remo; Schönrich, Ralph; Andrae, Rene; Kovalev, Mikhail; Ruchti, Greg; Hansen, Camilla Juul; Magic, Zazralt

2017-09-01

From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged <3D> models. We show that compared to the <3D> NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best <3D> NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]-[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H] ˜ -1.6 dex, further than previously proven. The thick disk stars display a constant [Mg/Fe] ≈ 0.3 dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo.

Co-formation of the disc and the stellar halo

NASA Astrophysics Data System (ADS)

Belokurov, V.; Erkal, D.; Evans, N. W.; Koposov, S. E.; Deason, A. J.

2018-07-01

Using a large sample of main sequence stars with 7D measurements supplied by Gaia and SDSS, we study the kinematic properties of the local (within ˜10 kpc from the Sun) stellar halo. We demonstrate that the halo's velocity ellipsoid evolves strongly with metallicity. At the low-[Fe/H] end, the orbital anisotropy (the amount of motion in the radial direction compared with the tangential one) is mildly radial, with 0.2 <β< 0.4. For stars with [Fe/H] > -1.7, however, we measure extreme values of β˜ 0.9. Across the metallicity range considered, namely-3 < [Fe/H] < -1, the stellar halo's spin is minimal, at the level of 20< \\bar{v}_{θ }(kms^{-1}) < 30. Using a suite of cosmological zoom-in simulations of halo formation, we deduce that the observed acute anisotropy is inconsistent with the continuous accretion of dwarf satellites. Instead, we argue, the stellar debris in the inner halo was deposited in a major accretion event by a satellite with Mvir > 1010M⊙ around the epoch of the Galactic disc formation, between 8 and 11 Gyr ago. The radical halo anisotropy is the result of the dramatic radialization of the massive progenitor's orbit, amplified by the action of the growing disc.

Galactic cosmic ray composition

NASA Technical Reports Server (NTRS)

Meyer, J. P.

1986-01-01

An assessment is given of the galactic cosmic ray source (GCRS) elemental composition and its correlation with first ionization potential. The isotopic composition of heavy nuclei; spallation cross sections; energy spectra of primary nuclei; electrons; positrons; local galactic reference abundances; comparison of solar energetic particles and solar coronal compositions; the hydrogen; lead; nitrogen; helium; and germanium deficiency problems; and the excess of elements are among the topics covered.

Cumulative Neutrino and Gamma-Ray Backgrounds from Halo and Galaxy Mergers

NASA Astrophysics Data System (ADS)

Yuan, Chengchao; Mészáros, Peter; Murase, Kohta; Jeong, Donghui

2018-04-01

The merger of dark matter halos and the gaseous structures embedded in them, such as protogalaxies, galaxies, and groups and clusters of galaxies, results in strong shocks that are capable of accelerating cosmic rays (CRs) to ≳10 PeV. These shocks will produce high-energy neutrinos and γ-rays through inelastic pp collisions. In this work, we study the contributions of these halo mergers to the diffuse neutrino flux and to the nonblazar portion of the extragalactic γ-ray background. We formulate the redshift dependence of the shock velocity, galactic radius, halo gas content, and galactic/intergalactic magnetic fields over the dark matter halo distribution up to a redshift z = 10. We find that high-redshift mergers contribute a significant amount of the CR luminosity density, and the resulting neutrino spectra could explain a large part of the observed diffuse neutrino flux above 0.1 PeV up to several PeV. We also show that our model can somewhat alleviate tensions with the extragalactic γ-ray background. First, since a larger fraction of the CR luminosity density comes from high redshifts, the accompanying γ-rays are more strongly suppressed through γγ annihilations with the cosmic microwave background and the extragalactic background light. Second, mildly radiative-cooled shocks may lead to a harder CR spectrum with spectral indices of 1.5 ≲ s ≲ 2.0. Our study suggests that halo mergers, a fraction of which may also induce starbursts in the merged galaxies, can be promising neutrino emitters without violating the existing Fermi γ-ray constraints on the nonblazar component of the extragalactic γ-ray background.

Present-day Galaxy Evolution through Baryon Flows in the Circumgalactic Medium of the Galactic-Magellanic System

NASA Astrophysics Data System (ADS)

Barger, Kathleen Ann

Galaxy evolution is governed by an intricate ballet of gas flows. To sustain star formation over many billions of years, more gas must inflow than outflow. Although numerous gas clouds surround the Milky Way, their attributes, origins, destinations, and responses to their surroundings need thorough investigation on an individual basis to realize how the entire population affects Galactic evolution. This dissertation hones in on two circumgalactic gas structures near the Milky Way: Complex A and the Magellanic Bridge. Complex A is an elongated gas structure that is traversing the hot Halo of the Milky Way, plummeting towards the Galaxy's disk. The Magellanic Bridge is a bridge of gas and stars that connects the Magellanic Clouds, created by galaxy interactions. In this thesis, I present the results of the highest sensitivity and kinematically resolved Halpha emission-line survey of Complex A and Halpha, [S II], and [N II] surveys of the Magellanic Bridge using the Wisconsin Halpha Mapper to explore their properties, surroundings, origins, and fates to unravel how circumgalactic structures influence galaxy evolution. I find that the observational properties of Complex A closely match with radiative transfer model predictions of a cloud ionized by the Milky Way and extragalactic background, implying a 5% escape fraction of ionizing photons from the Galactic disk. The multiline observations and modeling place the cloud's metallicity below solar. These results combined with other studies suggests the cloud has an intergalactic medium origin. I find that the global distribution of the warm ionized gas traces the neutral gas in the Magellanic Bridge. These observations place the ionized gas mass between (0.7 -- 1.6) x 108 solar masses, implying an ionization fraction of 25 -- 33% and a 5% maximum escape fraction of ionizing photons from the Magellanic Clouds. The line ratios reveal that the physical state of the the SMC-Tail and the LMC-Bridge interface regions differ

Halo-independence with quantified maximum entropy at DAMA/LIBRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fowlie, Andrew, E-mail: andrew.j.fowlie@googlemail.com

2017-10-01

Using the DAMA/LIBRA anomaly as an example, we formalise the notion of halo-independence in the context of Bayesian statistics and quantified maximum entropy. We consider an infinite set of possible profiles, weighted by an entropic prior and constrained by a likelihood describing noisy measurements of modulated moments by DAMA/LIBRA. Assuming an isotropic dark matter (DM) profile in the galactic rest frame, we find the most plausible DM profiles and predictions for unmodulated signal rates at DAMA/LIBRA. The entropic prior contains an a priori unknown regularisation factor, β, that describes the strength of our conviction that the profile is approximately Maxwellian.more » By varying β, we smoothly interpolate between a halo-independent and a halo-dependent analysis, thus exploring the impact of prior information about the DM profile.« less

White dwarfs in the building blocks of the Galactic spheroid

NASA Astrophysics Data System (ADS)

van Oirschot, Pim; Nelemans, Gijs; Starkenburg, Else; Toonen, Silvia; Helmi, Amina; Zwart, Simon Portegies

2017-11-01

Aims: The Galactic halo likely grew over time in part by assembling smaller galaxies, the so-called building blocks (BBs). We investigate if the properties of these BBs are reflected in the halo white dwarf (WD) population in the solar neighbourhood. Furthermore, we compute the halo WD luminosity functions (WDLFs for four major BBs of five cosmologically motivated stellar haloes). We compare the sum of these to the observed WDLF of the Galactic halo, derived from selected halo WDs in the SuperCOSMOS Sky Survey, aiming to investigate if they match better than the WDLFs predicted by simpler models. Methods: We couple the SeBa binary population synthesis model to the Munich-Groningen semi-analytic galaxy formation model applied to the high-resolution Aquarius dark matter simulations. Although the semi-analytic model assumes an instantaneous recycling approximation, we model the evolution of zero-age main sequence stars to WDs, taking age and metallicity variations of the population into account. To be consistent with the observed stellar halo mass density in the solar neighbourhood (ρ0), we simulate the mass in WDs corresponding to this density, assuming a Chabrier initial mass function (IMF) and a binary fraction of 50%. We also normalize our WDLFs to ρ0. Results: Although the majority of halo stars are old and metal-poor and therefore the WDs in the different BBs have similar properties (including present-day luminosity), we find in our models that the WDs originating from BBs that have young and/or metal-rich stars can be distinguished from WDs that were born in other BBs. In practice, however, it will be hard to prove that these WDs really originate from different BBs, as the variations in the halo WD population due to binary WD mergers result in similar effects. The five joined stellar halo WD populations that we modelled result in WDLFs that are very similar to each other. We find that simple models with a Kroupa or Salpeter IMF fit the observed luminosity

Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor.

PubMed

Frebel, Anna; Kirby, Evan N; Simon, Joshua D

2010-03-04

Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. On the basis of the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. Verification of the iron-deficiency, however, and measurements of additional elements, such as the alpha-element Mg, are necessary to demonstrate that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming its iron abundance of less than 1/4,000th that of the Sun, and showing that the overall abundance pattern follows that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.

Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars

NASA Astrophysics Data System (ADS)

Reggiani, Henrique; Meléndez, Jorge; Kobayashi, Chiaki; Karakas, Amanda; Placco, Vinicius

2017-12-01

Context. The chemical abundances of metal-poor halo stars are important to understanding key aspects of Galactic formation and evolution. Aims: We aim to constrain Galactic chemical evolution with precise chemical abundances of metal-poor stars (-2.8 ≤ [Fe/H] ≤ -1.5). Methods: Using high resolution and high S/N UVES spectra of 23 stars and employing the differential analysis technique we estimated stellar parameters and obtained precise LTE chemical abundances. Results: We present the abundances of Li, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Zn, Sr, Y, Zr, and Ba. The differential technique allowed us to obtain an unprecedented low level of scatter in our analysis, with standard deviations as low as 0.05 dex, and mean errors as low as 0.05 dex for [X/Fe]. Conclusions: By expanding our metallicity range with precise abundances from other works, we were able to precisely constrain Galactic chemical evolution models in a wide metallicity range (-3.6 ≤ [Fe/H] ≤ -0.4). The agreements and discrepancies found are key for further improvement of both models and observations. We also show that the LTE analysis of Cr II is a much more reliable source of abundance for chromium, as Cr I has important NLTE effects. These effects can be clearly seen when we compare the observed abundances of Cr I and Cr II with GCE models. While Cr I has a clear disagreement between model and observations, Cr II is very well modeled. We confirm tight increasing trends of Co and Zn toward lower metallicities, and a tight flat evolution of Ni relative to Fe. Our results strongly suggest inhomogeneous enrichment from hypernovae. Our precise stellar parameters results in a low star-to-star scatter (0.04 dex) in the Li abundances of our sample, with a mean value about 0.4 dex lower than the prediction from standard Big Bang nucleosynthesis; we also study the relation between lithium depletion and stellar mass, but it is difficult to assess a correlation due to the limited mass range. We

Highly ionized atoms in cooling gas. [in model for cooling of hot Galactic corona

NASA Technical Reports Server (NTRS)

Edgar, Richard J.; Chevalier, Roger A.

1986-01-01

The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Bruna, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate.

The Suppression of Star Formation in Low-Mass Galaxies Caused by the Reionization of their Local Patch

NASA Astrophysics Data System (ADS)

Dawoodbhoy, Taha; Shapiro, Paul R.; Choi, Jun-Hwan; Ocvirk, Pierre; Gillet, Nicolas; Aubert, Dominique; Iliev, Ilian T.; Teyssier, Romain; Yepes, Gustavo; Sullivan, David; Knebe, Alexander; Gottloeber, Stefan; D'Aloisio, Anson; Park, Hyunbae; Hoffman, Yehuda; Stranex, Timothy

2017-01-01

The first stars and galaxies released enough ionizing radiation into the intergalactic medium (IGM) to ionize almost all the hydrogen atoms there by redshift z ~ 6. This process was "patchy" --- ionized zones grew in size over time until they overlapped to finish reionization.The photoheating associated with reionization caused a negative feedback on the galactic sources of reionization that suppressed star formation in low-mass galactic halos, especially those below 109 M⊙. To establish the causal connection between reionization and this suppression, we analyze the results of CoDa ("Cosmic Dawn"), the first fully-coupled radiation-hydrodynamical simulation of reionization and galaxy formation in the Local Universe, in a volume large enough to model reionization globally but with enough resolving power to follow all the atomic-cooling galactic halos in that volume. A 90 Mpc box was simulated from a constrained realization of primordial fluctuations, chosen to reproduce present-day features of the Local Group, including the Milky Way and M31, and the local universe beyond, including the Virgo cluster, with 40963 N-body particles for the dark matter and 40963 cells for the atomic gas and ionizing radiation. We use these results to show that the star formation rate in haloes below 109 M⊙ in different patches of the universe declined when each patch was reionized. Star formation in much more massive haloes continued, however. As a result, the earliest patches to develop structure and reionize ultimately produced more stars than they needed to reionize themselves, exporting their starlight to help reionize the regions that developed structure late.

The Suppression of Star Formation in Low-Mass Galaxies Caused by the Reionization of their Local Patch

NASA Astrophysics Data System (ADS)

Dawoodbhoy, Taha; Shapiro, Paul R.; Choi, Jun-Hwan; Ocvirk, Pierre; Gillet, Nicolas; Aubert, Dominique; Iliev, Ilian T.; Teyssier, Romain; Yepes, Gustavo; Sullivan, David; Knebe, Alexander; Gottloeber, Stefan; D'Aloisio, Anson; Park, Hyunbae; Hoffman, Yehuda; Stranex, Timothy

2017-06-01

The first stars and galaxies released enough ionizing radiation into the intergalactic medium (IGM) to ionize almost all the hydrogen atoms there by redshift z ~ 6. This process was "patchy" --- ionized zones grew in size over time until they overlapped to finish reionization. The photoheating associated with reionization caused a negative feedback on the galactic sources of reionization that suppressed star formation in low-mass galactic halos, especially those below 109 M⊙. To establish the causal connection between reionization and this suppression, we analyze the results of CoDa ("Cosmic Dawn"), the first fully-coupled radiation-hydrodynamical simulation of reionization and galaxy formation in the Local Universe, in a volume large enough to model reionization globally but with enough resolving power to follow all the atomic-cooling galactic halos in that volume. A 90 Mpc box was simulated from a constrained realization of primordial fluctuations, chosen to reproduce present-day features of the Local Group, including the Milky Way and M31, and the local universe beyond, including the Virgo cluster, with 40963 N-body particles for the dark matter and 40963 cells for the atomic gas and ionizing radiation. We use these results to show that the star formation rate in haloes below 109 M⊙ in different patches of the universe declined when each patch was reionized. Star formation in much more massive haloes continued, however. As a result, the earliest patches to develop structure and reionize ultimately produced more stars than they needed to reionize themselves, exporting their starlight to help reionize the regions that developed structure late.

FERMI BUBBLES AND BUBBLE-LIKE EMISSION FROM THE GALACTIC PLANE

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Boer, Wim; Weber, Markus, E-mail: wim.de.boer@kit.edu, E-mail: markus.weber2@kit.edu

2014-10-10

The diffuse gamma-ray sky revealed ''bubbles'' of emission above and below the Galactic plane, symmetric around the center of the Milky Way, with a height of 10 kpc in both directions. At present, there is no convincing explanation for the origin. To understand the role of the Galactic center, one has to study the bubble spectrum inside the disk, a region that has been excluded from previous analyses because of the large foreground. From a novel template fit, which allows a simultaneous determination of the signal and foreground in any direction, we find that bubble-like emission is not only found inmore » the halo, but in the Galactic plane as well, with a width in latitude coinciding with the molecular clouds. The longitude distribution has a width corresponding to the Galactic bar with an additional contribution from the Scutum-Centaurus arm. The energy spectrum of the bubbles coincides with the predicted contribution from CRs trapped in sources (SCRs). Also, the energetics fits well. Hence, we conclude that the bubble-like emission has a hadronic origin that arises from SCRs, and the bubbles in the halo arise from hadronic interactions in advected gas. Evidence for advection is provided by the ROSAT X-rays of hot gas in the bubble region.« less

The star formation history in the Andromeda halo

NASA Astrophysics Data System (ADS)

Brown, Thomas M.

I present the preliminary results of a program to measure the star formation history in the halo of the Andromeda galaxy. Using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, we obtained the deepest optical images of the sky to date, in a field on the southeast minor axis of Andromeda, 51' (11 kpc) from the nucleus. The resulting color-magnitude diagram (CMD) contains approximately 300,000 stars and extends more than 1.5 mag below the main sequence turnoff, with 50% completeness at V = 30.7 mag. We interpret this CMD using comparisons to ACS observations of five Galactic globular clusters through the same filters, and through χ2-fitting to a finely-spaced grid of calibrated stellar population models. We find evidence for a major (~30%) intermediate-age (6-8 Gyr) metal-rich ([Fe/H])>-0.5) population in the Andromeda halo, along with a significant old metal-poor population akin to that in the Milky Way halo. The large spread in ages suggests that the Andromeda halo formed as a result of a more violent merging history than that in our own Milky Way.

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

NASA Technical Reports Server (NTRS)

Zhang, Ming

2005-01-01

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.

Extent of warm haloes around medium-redshift galaxies

NASA Technical Reports Server (NTRS)

Burbidge, E. M.; Barlow, T. A.; Cohen, R. D.; Junkkarinen, V. T.; Womble, D. S.

1989-01-01

The properties of low-to-medium ionization gaseous haloes around galaxies are briefly reviewed. New observations concerning such haloes are presented. For the galaxy-QSO pair in the field of the radio source 3C303, the higher-redshift QSO has been found to show Mg II absorption at the lower redshift of the faint nearby galaxy. Secondly, new data are presented on one of the galaxies in the environment of the well-known BL Lac object AO 0235 + 164.

Convergence properties of halo merger trees; halo and substructure merger rates across cosmic history

NASA Astrophysics Data System (ADS)

Poole, Gregory B.; Mutch, Simon J.; Croton, Darren J.; Wyithe, Stuart

2017-12-01

We introduce GBPTREES: an algorithm for constructing merger trees from cosmological simulations, designed to identify and correct for pathological cases introduced by errors or ambiguities in the halo finding process. GBPTREES is built upon a halo matching method utilizing pseudo-radial moments constructed from radially sorted particle ID lists (no other information is required) and a scheme for classifying merger tree pathologies from networks of matches made to-and-from haloes across snapshots ranging forward-and-backward in time. Focusing on SUBFIND catalogues for this work, a sweep of parameters influencing our merger tree construction yields the optimal snapshot cadence and scanning range required for converged results. Pathologies proliferate when snapshots are spaced by ≲0.128 dynamical times; conveniently similar to that needed for convergence of semi-analytical modelling, as established by Benson et al. Total merger counts are converged at the level of ∼5 per cent for friends-of-friends (FoF) haloes of size np ≳ 75 across a factor of 512 in mass resolution, but substructure rates converge more slowly with mass resolution, reaching convergence of ∼10 per cent for np ≳ 100 and particle mass mp ≲ 109 M⊙. We present analytic fits to FoF and substructure merger rates across nearly all observed galactic history (z ≤ 8.5). While we find good agreement with the results presented by Fakhouri et al. for FoF haloes, a slightly flatter dependence on merger ratio and increased major merger rates are found, reducing previously reported discrepancies with extended Press-Schechter estimates. When appropriately defined, substructure merger rates show a similar mass ratio dependence as FoF rates, but with stronger mass and redshift dependencies for their normalization.

The Halo Occupation Distribution of obscured quasars: revisiting the unification model

NASA Astrophysics Data System (ADS)

Mitra, Kaustav; Chatterjee, Suchetana; DiPompeo, Michael A.; Myers, Adam D.; Zheng, Zheng

2018-06-01

We model the projected angular two-point correlation function (2PCF) of obscured and unobscured quasars selected using the Wide-field Infrared Survey Explorer (WISE), at a median redshift of z ˜ 1 using a five parameter Halo Occupation Distribution (HOD) parametrization, derived from a cosmological hydrodynamic simulation by Chatterjee et al. The HOD parametrization was previously used to model the 2PCF of optically selected quasars and X-ray bright active galactic nuclei (AGNs) at z ˜ 1. The current work shows that a single HOD parametrization can be used to model the population of different kinds of AGN in dark matter haloes suggesting the universality of the relationship between AGN and their host dark matter haloes. Our results show that the median halo mass of central quasar hosts increases from optically selected (4.1^{+0.3}_{-0.4} × 10^{12} h^{-1} M_{⊙}) and infra-red (IR) bright unobscured populations (6.3^{+6.2}_{-2.3} × 10^{12} h^{-1} M_{⊙}) to obscured quasars (10.0^{+2.6}_{-3.7} × 10^{12} h^{-1} M_{⊙}), signifying an increase in the degree of clustering. The projected satellite fractions also increase from optically bright to obscured quasars and tend to disfavour a simple `orientation only' theory of active galactic nuclei unification. Our results also show that future measurements of the small-scale clustering of obscured quasars can constrain current theories of galaxy evolution where quasars evolve from an IR-bright obscured phase to the optically bright unobscured phase.

Highly ionized gas absorption in the disk and halo toward HD 167756 at 3.5 kilometers per second resolution

NASA Technical Reports Server (NTRS)

Savage, Blair D.; Sembach, Kenneth R.; Cardelli, Jason A.

1994-01-01

High-resolution spectra of interstellar Si IV, C IV, and N V absorption lines along the 4 kpc path to the inner Galaxy star HD 167756 at z = -0.85 kpc are presented. The spectra were obtained with the echelle mode of Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) and have signal-to-noise ratios ranging from 23 to 38. The high resolution of the measurements full width at half maximum (FWHM = 3.5 km/s) results in fully resolved line profiles for the highly ionized gas absorption. The measurements provide information on the column density per unit velocity, N(v), as a function of velocity for Si IV, C IV, and N V. The C IV and N V profiles extend from -70 to +70 km/s, while the Si IV profiles extend from -40 to +70 km/s. The integrated logarithmic column densities are long N(Si IV) = 13.09 +/- 0.02, log N(C IV) = 13.83 +/- 0.02, and log N(N V) = 13.56 +/- 0.03. The N V profile is broad, asymmetric, and featureless, while the Si IV profile contains narrow absorption components near V(sub LSR) = -19, 0, +20, and +52 km/s with Doppler spread parameters, b about = 10-12 km/s. The C IV profile contains both broad and narrow structure. The high ion feature near +52 km/s is also detected in the low-ionization lines of Ca II, O I, Si II, and Fe II. The other narrow Si IV and C IV components occur within several km/s of components seen in low-ionization species. The sight line contains at least two types of highly ionized gas. One type gives rise to a broad N V profile, and the other results in the more structured Si IV profile. The C IV profile contains contributions from both types of highly ionized gas. The broad but asymmetric N V profile is well represented by a large Galactic scale height gas which is participating in Galactic rotation and has a combination of thermal and turbulent broadening with b(sub tot) about = 42 km/s. The C IV to N V abundance ratio of 1.0 +/- 0.3 for the gas implies T about 1.6 x 10(exp 5) K or about 8 x 10

Gaia reveals a metal-rich in-situ component of the local stellar halo

NASA Astrophysics Data System (ADS)

Bonaca, Ana; Conroy, Charlie; Wetzel, Andrew; Hopkins, Philip; Keres, Dusan

2018-01-01

We use the first Gaia data release, combined with RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within ~3 kpc from the Sun. We identify halo stars kinematically, as moving with a relative speed of at least 220 km/s with respect to the local standard of rest. These stars are in general more metal-poor than the disk, but surprisingly, half of our halo sample is comprised of stars with [Fe/H]>-1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the isotropic orbital distribution of the more metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, while lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the Solar neighborhood in fact formed in situ within the Galactic disk rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.

Gaia Reveals a Metal-rich, in situ Component of the Local Stellar Halo

NASA Astrophysics Data System (ADS)

Bonaca, Ana; Conroy, Charlie; Wetzel, Andrew; Hopkins, Philip F.; Kereš, Dušan

2017-08-01

We use the first Gaia data release, combined with the RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within ≲ 3 kpc from the Sun. We identify halo stars kinematically as moving at a relative speed of at least 220 km s-1 with respect to the local standard of rest. These stars are generally less metal-rich than the disk, but surprisingly, half of our halo sample is comprised of stars with [{Fe}/{{H}}]> -1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the intrinsically isotropic orbital distribution of the metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, whereas lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the solar neighborhood actually formed in situ within the Galactic disk, rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.

Halo-shaped Flowing Atmospheric Pressure Afterglow – a Heavenly New Design for Simplified Sample Introduction and Improved Ionization in Ambient Mass Spectrometry

PubMed Central

Pfeuffer, Kevin P.; Schaper, J. Niklas; Shelley, Jacob T.; Ray, Steven J.; Chan, George C.-Y.; Bings, Nicolas H.; Hieftje, Gary M.

2013-01-01

The flowing atmospheric pressure afterglow (FAPA) is a promising new source for atmospheric pressure, ambient desorption/ionization mass spectrometry. However, problems exist with reproducible sample introduction into the FAPA source. To overcome this limitation, a new FAPA geometry has been developed in which concentric tubular electrodes are utilized to form a halo-shaped discharge; this geometry has been termed the halo-FAPA or h-FAPA. With this new geometry, it is still possible to achieve direct desorption and ionization from a surface; however, sample introduction through the inner capillary is also possible and improves interaction between the sample material (solution, vapor, or aerosol) and the plasma to promote desorption and ionization. The h-FAPA operates with a helium gas flow of 0.60 L/min outer, 0.30 L/min inner, applied current of 30 mA at 200 V for 6 watts of power. In addition, separation of the discharge proper and sample material prevents perturbations to the plasma. Optical-emission characterization and gas rotational temperatures reveal that the temperature of the discharge is not significantly affected (< 3% change at 450K) by water vapor during solution-aerosol sample introduction. The primary mass-spectral background species are protonated water clusters, and the primary analyte ions are protonated molecular ions (M+H+). Flexibility of the new ambient sampling source is demonstrated by coupling it with a laser ablation unit, a concentric nebulizer and a droplet-on-demand system for sample introduction. A novel arrangement is also presented in which the central channel of the h-FAPA is used as the inlet to a mass spectrometer. PMID:23808829

Evidence for halo kinematics among cool carbon-rich dwarfs

NASA Astrophysics Data System (ADS)

Farihi, J.; Arendt, A. R.; Machado, H. S.; Whitehouse, L. J.

2018-07-01

This paper reports preliminary, yet compelling, kinematical inferences for N≳ 600 carbon-rich dwarf stars that demonstrate around 30-60 per cent are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogues based on Gaia DR1 astrometry to generate estimates of their 3D space velocities. The fraction of stars with halo-like kinematics is roughly 30 per cent for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disc, but close to 60 per cent of the sample lies below an old, metal-poor disc isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundance and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favours low-mass stars as in the Galactic disc, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

Evidence for halo kinematics among cool carbon-rich dwarfs

NASA Astrophysics Data System (ADS)

Farihi, J.; Arendt, A. R.; Machado, H. S.; Whitehouse, L. J.

2018-04-01

This paper reports preliminary yet compelling kinematical inferences for N ≳ 600 carbon-rich dwarf stars that demonstrate around 30% to 60% are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogs based on Gaia DR1 astrometry to generate estimates of their 3-D space velocities. The fraction of stars with halo-like kinematics is roughly 30% for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disk, but close to 60% of the sample lie below an old, metal-poor disk isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundances, and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favors low-mass stars as in the Galactic disk, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

Wide-Field Imaging of Galactic Halos with a Near-Infrared Rocket-Borne Telescope

NASA Technical Reports Server (NTRS)

Lange, Andrew E.

2000-01-01

We successfully completed both of the proposed flights by May of 1998, on schedule and on budget. In both flights the instrument worked flawlessly, achieving sensitivities slightly better than the specification (1 nW/sq m sr per pixel). The payload was recovered with only minor damage after both flights. The results from the first flight, which targeted the nearby edge-on spiral NCG 4565, have been published. Analysis of the data failed to detect any significant emission, from the halo around the galaxy, and set a very stringent 2 sigma lower limit on the M/L ratio of the halo of greater than 260 in solar units. The results from the second flight, which targeted the infamous NGC 5907, have taken longer to analyze because of an offset in the absolute pointing of the payload which broke the symmetry of the scan pattern about the galaxy, thus complicating the analysis, After careful analysis, Caltech graduate student, Sarah Yost, has recovered the full sensitivity of the experiment, setting a 2 sigma lower limit on the M/L ratio of the halo of greater than 280 in solar units. This result rules out the hypothesis that a significant portion of the halo around NGC 5907 is composed of low-mass stars, as previous observations had suggested. NITE probes directly the halo at 10 to 30 kpc from the disk, a region far too dim for other experiments. Our conclusion is that observations of a significant IR signature associated with the halo at less than approximately 5kpc radius where contaminated by tidally disrupted disk population of stars. In order to test the idea that we could study faint surface-brightness fluctuations in the diffuse background using NITE, we have analyzed the data from the 1997 flight which targeted NCG 4565 (this target is in a region of lower stellar confusion than is NGC 5907). We have detected a significant correlation in the noise at zero-lag, with an amplitude that corresponds to brightness fluctuations of 3.04 plus or minus 0.16 nW/sq m sr. This

THE MAGELLANIC STREAM: BREAK-UP AND ACCRETION ONTO THE HOT GALACTIC CORONA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tepper-García, Thor; Bland-Hawthorn, Joss; Sutherland, Ralph S.

The Magellanic H i Stream (≈2 × 10{sup 9} M{sub ⊙} [d/55 kpc]{sup 2}) encircling the Galaxy at a distance d is arguably the most important tracer of what happens to gas accreting onto a disk galaxy. Recent observations reveal that the Stream’s mass is in fact dominated (3:1) by its ionized component. Here we revisit the origin of the mysterious Hα recombination emission observed along much of its length that is overly bright (∼150–200 mR) for the known Galactic ultraviolet (UV) background (≈20–40 mR [d/55 kpc]{sup −2}). In an earlier model, we proposed that a slow shock cascade wasmore » operating along the Stream due to its interaction with the extended Galactic hot corona. We find that for a smooth coronal density profile, this model can explain the bright Hα emission if the coronal density satisfies 2 × 10{sup −4} < (n/cm{sup −3}) < 4 × 10{sup −4} at d = 55 kpc. But in view of updated parameters for the Galactic halo and mounting evidence that most of the Stream must lie far beyond the Magellanic Clouds (d > 55 kpc), we revisit the shock cascade model in detail. At lower densities, the H i gas is broken down by the shock cascade but mostly mixes with the hot corona without significant recombination. At higher densities, the hot coronal mass (including the other baryonic components) exceeds the baryon budget of the Galaxy. If the Hα emission arises from the shock cascade, the upper limit on the smooth coronal density constrains the Stream’s mean distance to ≲75 kpc. If, as some models indicate, the Stream is even further out, either the shock cascade is operating in a regime where the corona is substantially mass-loaded with recent gas debris, or an entirely different ionization mechanism is responsible.« less

Galaxy mergers moulding the circum-galactic medium - I. The impact of a major merger

NASA Astrophysics Data System (ADS)

Hani, Maan H.; Sparre, Martin; Ellison, Sara L.; Torrey, Paul; Vogelsberger, Mark

2018-03-01

Galaxies are surrounded by sizeable gas reservoirs which host a significant amount of metals: the circum-galactic medium (CGM). The CGM acts as a mediator between the galaxy and the extragalactic medium. However, our understanding of how galaxy mergers, a major evolutionary transformation, impact the CGM remains deficient. We present a theoretical study of the effect of galaxy mergers on the CGM. We use hydrodynamical cosmological zoom-in simulations of a major merger selected from the Illustris project such that the z = 0 descendant has a halo mass and stellar mass comparable to the Milky Way. To study the CGM we then re-simulated this system at a 40 times better mass resolution, and included detailed post-processing ionization modelling. Our work demonstrates the effect the merger has on the characteristic size of the CGM, its metallicity, and the predicted covering fraction of various commonly observed gas-phase species, such as H I, C IV, and O VI. We show that merger-induced outflows can increase the CGM metallicity by 0.2-0.3 dex within 0.5 Gyr post-merger. These effects last up to 6 Gyr post-merger. While the merger increases the total metal covering fractions by factors of 2-3, the covering fractions of commonly observed UV ions decrease due to the hard ionizing radiation from the active galactic nucleus, which we model explicitly. Our study of the single simulated major merger presented in this work demonstrates the significant impact that a galaxy interaction can have on the size, metallicity, and observed column densities of the CGM.

The masses and metallicities of stellar haloes reflect galactic merger histories

NASA Astrophysics Data System (ADS)

D'Souza, Richard; Bell, Eric F.

2018-03-01

There is increasing observational and theoretical evidence for a correlation between the metallicity and the mass of the stellar halo for galaxies with Milky Way-like stellar masses. Using the Illustris cosmological hydrodynamical simulations, we find that this relationship arises because a single massive progenitor contributes the bulk of the mass to the accreted stellar component as well as sets its metallicity. Moreover, in the Illustris simulations, this relationship extends over 3 orders of magnitude in accreted stellar mass for central galaxies. We show that for Milky Way-like mass galaxies, the scatter in accreted metallicity at a fixed accreted stellar mass encodes information about the stellar mass of the dominant accreted progenitor, while the radial density and metallicity gradients of the accreted stellar component encodes information about the time of accretion of the dominant progenitor. We demonstrate that for Milky Way-like mass galaxies, the Illustris simulations predict that the metallicity and the stellar mass of the total accreted stellar component can be reconstructed from aperture measurements of the stellar halo along the minor axis of edge-on disc galaxies. These correlations highlight the potential for observational studies of stellar haloes to quantify our understanding of the most dominant events in the growth history of galaxies. We explore the implications of our model for our understanding of the accretion histories of the Milky Way, M31, and NGC 5128. In particular, a relatively late and massive accretion is favoured for M31; additionally, we provide a first estimate of the accreted stellar mass for NGC 5128.

The Galactic Center S-stars and the Hypervelocity Stars in the Galactic Halo: Two Faces of the Tidal Breakup of Stellar Binaries by the Central Massive Black Hole?

NASA Astrophysics Data System (ADS)

Zhang, Fupeng; Lu, Youjun; Yu, Qingjuan

2013-05-01

In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the Galactic center (GC) S-stars, under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up dynamical evolution. We find that many statistical properties of the detected HVSs and GC S-stars could be reproduced under some binary injecting models, and their number ratio can be reproduced if the stellar initial mass function is top-heavy (e.g., with slope ~ - 1.6). The total number of the captured companions is ~50 that have masses in the range ~3-7 M ⊙ and semimajor axes <~ 4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis ~300-1500 AU and a pericenter distance ~10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a close star would offer an important test to general relativity. The majority of the surviving ejected companions of the GC S-stars are expected to be located at Galactocentric distances <~ 20 kpc, and have heliocentric radial velocities ~ - 500-1500 km s-1 and proper motions up to ~5-20 mas yr-1. Future detection of these HVSs may provide evidence for the tidal breakup formation mechanism of the GC S-stars.

Tully-Fisher relation, galactic rotation curves and dissipative mirror dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foot, R., E-mail: rfoot@unimelb.edu.au

2014-12-01

If dark matter is dissipative then the distribution of dark matter within galactic halos can be governed by dissipation, heating and hydrostatic equilibrium. Previous work has shown that a specific model, in the framework of mirror dark matter, can explain several empirical galactic scaling relations. It is shown here that this dynamical halo model implies a quasi-isothermal dark matter density, ρ(r) ≅ ρ{sub 0}r{sub 0}{sup 2}/(r{sup 2}+r{sub 0}{sup 2}), where the core radius, r{sub 0}, scales with disk scale length, r{sub D}, via r{sub 0}/kpc ≈ 1.4(r{sub D}/kpc). Additionally, the product ρ{sub 0}r{sub 0} is roughly constant, i.e. independent ofmore » galaxy size (the constant is set by the parameters of the model). The derived dark matter density profile implies that the galactic rotation velocity satisfies the Tully-Fisher relation, L{sub B}∝v{sup 3}{sub max}, where v{sub max} is the maximal rotational velocity. Examples of rotation curves resulting from this dynamics are given.« less

Extended Galactic emission at l=312°: a comparison of mid-infrared and radio continuum (843 MHz) images

NASA Astrophysics Data System (ADS)

Cohen, Martin; Green, Anne J.

2001-08-01

We report on the comparison of images of a region of the Galactic plane (centred on l=312°) as seen by the Midcourse Space Experiment (MSX) at 8.3μm and by the Molonglo Observatory Synthesis Telescope (MOST) at 843MHz in the radio continuum. We note that the survey from each telescope is without peer and occupies a niche in panoramic coverage with high spatial resolution. Using independent classification of sources in the selected region, a detailed comparison of the two surveys was made. The aim of the project was to seek global characteristics for different types of source, with a view to establishing predictive criteria for identification and hence emission mechanisms. Several strong trends were found. There is a complete absence in this field of any detected MSX counterparts to non-thermal radio sources. Almost every Hii region in the radio image has its MSX counterpart, in the form of a polycyclic aromatic hydrocarbon halo in the neutral zone surrounding the ionized gas. Both surveys show large-scale `braided' filamentary structures, extending over 1°, which appear to be produced by thermal processes. These filaments may be structures in the warm ionized phase of the interstellar medium or extended haloes around Hii regions. The comparisons in this paper were made using both preliminary MSX 8.3-μm results with 46-arcsec resolution and final MSX images with the intrinsic 20-arcsec resolution of the instruments.

A galactic chimney in the Perseus arm of the Milky Way.

PubMed

Normandeau, M; Taylor, A R; Dewdney, P E

1996-04-25

Galaxies are surrounded by large haloes of hot gas which must be replenished as the gas cools. This has led to the concept of galactic 'chimneys'--cavities in the interstellar medium, created by multiple supernova explosions, that can act as conduits for the efficient transport of hot gas from a galaxy's disk to its halo. Here we present a high-resolution map of atomic hydrogen in the Perseus arm of our galaxy, which shows clear evidence for the existence of such a chimney. This chimney appears to have been formed by the energetic winds from a cluster of young massive stars, and may currently have reached the stage of bowing out into the halo.

What is the Milky Way outer halo made of?

NASA Astrophysics Data System (ADS)

Jablonka, Pascale; Battaglia, G.

2018-06-01

In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in-situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this talk I will focus on the outer regions of the Milky Way stellar halo, and present results from a program aimed at determining chemical abundances of halo stars with large present-day Galactocentric distances, $>$15 kpc. The data-set consists of high resolution spectra for 28 red giant branch stars covering a wide metallicity range.We show that the ratio of $\\alpha$-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H]$\\gtrsim -1.5$ when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples.

Reconstructing the Accretion History of the Galactic Halo Using Stellar Chemical Abundance Ratio Distributions

NASA Astrophysics Data System (ADS)

Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

2016-08-01

In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven ``MW-like'' halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~ 103-4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs - precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~ 6-9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD-generating dwarf models) to recover the luminosity function of infalling dwarf galaxies - and the detailed accretion history of the halo - across cosmic time.

Reconstructing the Accretion History of the Galactic Halo Using Stellar Chemical Abundance Ratio Distributions

NASA Astrophysics Data System (ADS)

Lee, Duane Morris; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

2015-08-01

In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven ``MW-like'' halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~103-4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs --- precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~6-9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD-generating dwarf models) to recover the luminosity function of infalling dwarf galaxies --- and the detailed accretion history of the halo --- across cosmic time.

Population studies. 12: The duality of the galactic halo

NASA Astrophysics Data System (ADS)

Norris, John E.

1994-08-01

Consideration of the abundance distribution and the complicated dependence of kinematics on abundance in high-proper-motion samples of main-sequence stars, together with the velocities of non-kinematically selected objects in the direction of the Galactic poles, leads to the conjectures (1) that for (Fe/H) less than -1.0, two distinct components are present in the samples, each of which spans the range -3.0 less than or equal (Fe/H) less than or equal -1.0, (2) that one of the components has the properties of the accretion process postulated for the formation of the halo by Searle & Zinn (1978) and amplified by Rodgers & Paltoglou (1984), van den Bergh (1993), and Zinn (1993), and (3) that the second component encompasses at high abundance ((Fe/H) greater than -1.5) the disklike entity variously referred to as the thick disk, the metal-weak thick disk, the extended disk, and Intermediate Population II, together with, at lower abundances, material which has an abundance distribution similar to that of the so-called Best Accretion Model of Lynden-Bell and kinematics which have a very hot spheroidal signature sigmaU = sigmaV = sigmaW approximately 130 km/s and low systemic rotation Vrot at the lowest values ((Fe/H) approximately -2.0 to -3.0). The second component has many of the properties espoused by Eggen, Lynden-Bell, & Sandage (1962) in the context of the contraction of the proto-Galaxy. Monte Carlo simulations are presented which demonstrate that, within the framework of these conjectures and the rather large uncertainties associated with the second component, it is possible to explain fully the basic features of the abundance distribution and kinematics of the high-proper-motion samples. The crux of the issue is that such a model can explain the observed relative constancy of sigmaU and Vrot for (Fe/H) less than or equal -1.5, together with the constancy of sigmaV and the steady increase of sigmaW from 50 to 120 km/s as (Fe/H) decreases from -1.0 to -2.5. It is

The bulge-halo conspiracy in massive elliptical galaxies: implications for the stellar initial mass function and halo response to baryonic processes

NASA Astrophysics Data System (ADS)

Dutton, Aaron A.; Treu, Tommaso

2014-03-01

Recent studies have shown that massive elliptical galaxies have total mass density profiles within an effective radius that can be approximated as ρ_tot∝ r^{-γ^', with mean slope <γ'> = 2.08 ± 0.03 and scatter σ _{γ ^' } }=0.16± 0.02. The small scatter of the slope (known as the bulge-halo conspiracy) is not generic in Λ cold dark matter (ΛCDM) based models and therefore contains information about the galaxy formation process. We compute the distribution of γ' for ΛCDM-based models that reproduce the observed correlations between stellar mass, velocity dispersion, and effective radius of early-type galaxies in the Sloan Digital Sky Survey. The models have a range of stellar initial mass functions (IMFs) and dark halo responses to galaxy formation. The observed distribution of γ' is well reproduced by a model with cosmologically motivated but uncontracted dark matter haloes, and a Salpeter-type IMF. Other models are on average ruled out by the data, even though they may happen in individual cases. Models with adiabatic halo contraction (and lighter IMFs) predict too small values of γ'. Models with halo expansion, or mass-follows-light predict too high values of γ'. Our study shows that the non-homologous structure of massive early-type galaxies can be precisely reproduced by ΛCDM models if the IMF is not universal and if mechanisms, such as feedback from active galactic nuclei, or dynamical friction, effectively on average counterbalance the contraction of the halo expected as a result of baryonic cooling.

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

NASA Technical Reports Server (NTRS)

Vaughan, S.; Willingale, R.; OBrien, P. T.; Osborne, J. P.; Reeves, J. N.; Levan, A. J.; Watson, M. G.; Tedds, J. A.; Watson, D.; Santos-Lleo, M.

2003-01-01

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.

Dark halos formed via dissipationless collapse. I - Shapes and alignment of angular momentum

NASA Astrophysics Data System (ADS)

Warren, Michael S.; Quinn, Peter J.; Salmon, John K.; Zurek, Wojciech H.

1992-11-01

We use N-body simulations on highly parallel supercomputers to study the structure of Galactic dark matter halos. The systems form by gravitational collapse from scale-free and more general Gaussian initial density perturbations in an expanding 400 Mpc-cubed spherical slice of an Einstein-deSitter universe. We analyze the structure and kinematics of about 100 of the largest relaxed halos in each of 10 separate simulations. A typical halo is a triaxial spheroid which tends to be more often prolate than oblate. These shapes are maintained by anisotropic velocity dispersion rather than by angular momentum. Nevertheless, there is a significant tendency for the total angular momentum vector to be aligned with the minor axis of the density distribution.

On the possibility that ultra-light boson haloes host and form supermassive black holes

NASA Astrophysics Data System (ADS)

Avilez, Ana A.; Bernal, Tula; Padilla, Luis E.; Matos, Tonatiuh

2018-07-01

Several observations suggest the existence of supermassive black holes (SMBH) at the centres of galaxies. However, the mechanism under which these objects form remains non-completely understood. In this work, we review an alternative mechanism of formation of galactic SMBHs from the collapse of a fraction of a dark matter (DM) halo made of an ultra-light scalar field (SF) whose critical mass of collapse is ˜1013 M⊙. Once the BH is formed, a long-living quasi-resonant SF configuration survives and plays the role of a central fraction of the galactic DM halo. In this work, we construct a model with an ultra-light SF configuration laying in a Schwarzschild space-time to describe the centre of the DM halo hosting an SMBH in equilibrium, in the limit where self-gravitating effects can be neglected. We compute the induced stellar velocity dispersion in order to investigate the influence of the BH on to the velocity field of visible matter at the central galactic regions. We fit the empirical correlation between stellar velocity dispersions and masses of SMBHs considering two instances: the idealized case of DM-dominated (DMD) systems, where the gravitational influence of baryons is neglected, and cases of real luminous galaxies (LGAL). In the DMD case, we found it is possible to reproduce the observed stellar velocity dispersions at the effective radius of systems hosting SMBHs of at most 108 M⊙. In the LGAL case, we found that the baryons are crucial to reproduce the observed velocity dispersion.

A window on first-stars models from studies of dwarf galaxies and galactic halo stars

NASA Astrophysics Data System (ADS)

Venkatesan, Aparna

2018-06-01

Dwarf galaxies dominate the local universe by number and are predicted to be even more dominant at early times, with many having large star formation rates per unit mass. The cosmological role of dwarf galaxies in the metal enrichment and the reionization of the universe is an important but unresolved problem at present. Nearby low-mass galaxies are much more accessible observationally for detailed study and may be local analogs of the types of galaxies that hosted the first-light sources relevant for reionization. I will share recent results on UV studies of the escaping radiation from nearby low-mass starforming galaxies, as well as the tantalizing similarities in element abundance patterns between local dwarf galaxies and the latest data compilations on extremely metal-poor stars in galactic halos. I will highlight trends of interest in a variety of individual elements at values of [Fe/H] between -7 and -3, including alpha-elements, elements originating mostly in intermediate-mass stars, lithium, titanium, and r-process elements. These trends constrain not only models of the first stars and their supernovae, but provide a window into the physical conditions in early galaxies and when metal-free star formation may have ceased in the early universe.This work was supported by the University of San Francisco Faculty Development Fund, and NSF grant AST-1637339. We thank the Aspen Center for Physics, where some of this work was conducted, and which is supported by National Science Foundation grant PHY-1607611.

Analysis Of Ultra Compact Ionized Hydrogen Regions Within The Northern Half Of The Galactic Disk

NASA Astrophysics Data System (ADS)

Bruce, John

2011-01-01

From a catalog of 199 candidate ultra compact (UC) HII regions 123 sources included in the the intersection of the GLIMPSE (8 μm),Cornish (6 cm), and Bolocam ( 1.1 mm) galactic plane surveys (BGPS) were analyzed. The sources were sorted based on 6 cm morphology and coincidence with 8 μm bubbles. The 1.1 mm flux attributes were measured and calculations were performed to determine the ionized hydrogen contributions to the 1.1 mm flux. The category averages and frequencies were obtained as well. Significant differences in HII percentages were present among the morphology groups but ranged widely, without apparent distinction, between the bubble forming and triggered source categories.

Metal flows of the circumgalactic medium, and the metal budget in galactic haloes

NASA Astrophysics Data System (ADS)

Muratov, Alexander L.; Kereš, Dušan; Faucher-Giguère, Claude-André; Hopkins, Philip F.; Ma, Xiangcheng; Anglés-Alcázar, Daniel; Chan, T. K.; Torrey, Paul; Hafen, Zachary H.; Quataert, Eliot; Murray, Norman

2017-07-01

We present an analysis of the flow of metals through the circumgalactic medium (CGM) in the Feedback in Realistic Environments (FIRE) simulations of galaxy formation, ranging from isolated dwarfs to L* galaxies. We find that nearly all metals produced in high-redshift galaxies are carried out in winds that reach 0.25Rvir. When measured at 0.25Rvir the metallicity of outflows is slightly higher than the interstellar medium (ISM) metallicity. Many metals thus reside in the CGM. Cooling and recycling from this reservoir determine the metal budget in the ISM. The outflowing metal flux decreases by a factor of ˜2-5 between 0.25Rvir and Rvir. Furthermore, outflow metallicity is typically lower at Rvir owing to dilution of the remaining outflow by metal-poor material swept up from the CGM. The inflow metallicity at Rvir is generally low, but outflow and inflow metallicities are similar in the inner halo. At low redshift, massive galaxies no longer generate outflows that reach the CGM, causing a divergence in CGM and ISM metallicity. Dwarf galaxies continue to generate outflows, although they preferentially retain metal ejecta. In all but the least massive galaxy considered, a majority of the metals are within the halo at z = 0. We measure the fraction of metals in CGM, ISM and stars, and quantify the thermal state of CGM metals in each halo. The total amount of metals in the low-redshift CGM of two simulated L* galaxies is consistent with estimates from the Cosmic Origin Spectrograph haloes survey, while for the other two it appears to be lower.

Determination of the Point-Spread Function for the FERMI Large Area Telescope from On-Orbit Data and Limits on Pair Halos of Active Galactic Nuclei

DOE PAGES

Ackermann, M.; Ajello, M.; Allafort, A.; ...

2013-02-15

We present the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from ≈20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of γ rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broadermore » than the pre-launch PSF. We checked for dependence of the PSF on the class of γ-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. Finally, we found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347–121.« less

Ionized Gas in the Halos of Edge-on Starburst Galaxies: Evidence for Supernova-driven Superwinds

NASA Astrophysics Data System (ADS)

Lehnert, Matthew D.; Heckman, Timothy M.

1996-05-01

Supernova-driven galactic winds ("superwinds") have been invoked to explain many aspects of galaxy formation and evolution. Such winds should arise when the supernova rate is high enough to create a cavity of very hot shock-heated gas within a galaxy. This gas can then expand outward as a high-speed wind that can accelerate and heat ambient interstellar or circum-galactic gas causing it to emit optical line radiation and/or thermal X-rays. Theory suggests that such winds should be common in starburst galaxies and that the nature of the winds should depend on the star formation rate and distribution. In order to systematize our observational understanding of superwinds (determine their incidence rate and the dependence of their properties on the star formation that drives them) and to make quantitative comparisons with the theory of superwinds, we have analyzed data from an optical spectroscopic and narrow-band imaging survey of an infrared flux-limited (S_60 microns_ >= 5.4 Jy) sample of about 50 IR-warm (S_60 microns_/S_100 microns_ > 0.4), starburst galaxies whose stellar disks are viewed nearly edge-on (b/a ~> 2). This sample contains galaxies with infrared luminosities from ~10^10^-10^12^ L_sun_ and allows us to determine the properties of superwinds over a wide range of star formation rates. We have found that extraplanar emission-line gas is a very common feature of these edge-on, IR-bright galaxies and the properties of the extended emission-line gas are qualitatively and quantitatively consistent with the superwind theory. We can summarize these properties as morphological, ionization, dynamical, and physical. 1. Morphological properties.-Extraplanar filamentary and shell-like emission-line morphologies on scales of hundreds of parsecs to 10 kpc are common, there is a general "excess" of line emission along the minor axis, the minor axis emission-line "excess" correlates with "IR activity," and the minor axis emission-line "excess" also correlates with the

Search for dark matter annihilation in the Galactic Center with IceCube-79

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aartsen, M. G.; Abraham, K.; Ackermann, M.

The Milky Way is expected to be embedded in a halo of dark matter particles, with the highest density in the central region, and decreasing density with the halo-centric radius. Dark matter might be indirectly detectable at Earth through a flux of stable particles generated in dark matter annihilations and peaked in the direction of the Galactic Center. We present a search for an excess flux of muon (anti-) neutrinos from dark matter annihilation in the Galactic Center using the cubic-kilometer-sized IceCube neutrino detector at the South Pole. There, the Galactic Center is always seen above the horizon. Thus, newmore » and dedicated veto techniques against atmospheric muons are required to make the southern hemisphere accessible for IceCube. We used 319.7 live-days of data from IceCube operating in its 79-string configuration during 2010 and 2011. Here, no neutrino excess was found and the final result is compatible with the background. We present upper limits on the self-annihilation cross-section, Av>, for WIMP masses ranging from 30 GeV up to 10 TeV, assuming cuspy (NFW) and flat-cored (Burkert) dark matter halo profiles, reaching down to ≃4•10 –24 cm 3 s –1, and ≃2.6•10 –23 cm 3 s –1 for the ν ν¯ channel, respectively.« less

Search for dark matter annihilation in the Galactic Center with IceCube-79

DOE PAGES

Aartsen, M. G.; Abraham, K.; Ackermann, M.; ...

2015-10-15

The Milky Way is expected to be embedded in a halo of dark matter particles, with the highest density in the central region, and decreasing density with the halo-centric radius. Dark matter might be indirectly detectable at Earth through a flux of stable particles generated in dark matter annihilations and peaked in the direction of the Galactic Center. We present a search for an excess flux of muon (anti-) neutrinos from dark matter annihilation in the Galactic Center using the cubic-kilometer-sized IceCube neutrino detector at the South Pole. There, the Galactic Center is always seen above the horizon. Thus, newmore » and dedicated veto techniques against atmospheric muons are required to make the southern hemisphere accessible for IceCube. We used 319.7 live-days of data from IceCube operating in its 79-string configuration during 2010 and 2011. Here, no neutrino excess was found and the final result is compatible with the background. We present upper limits on the self-annihilation cross-section, Av>, for WIMP masses ranging from 30 GeV up to 10 TeV, assuming cuspy (NFW) and flat-cored (Burkert) dark matter halo profiles, reaching down to ≃4•10 –24 cm 3 s –1, and ≃2.6•10 –23 cm 3 s –1 for the ν ν¯ channel, respectively.« less

On the contribution of active galactic nuclei to the high-redshift metagalactic ionizing background

NASA Astrophysics Data System (ADS)

D'Aloisio, Anson; Upton Sanderbeck, Phoebe R.; McQuinn, Matthew; Trac, Hy; Shapiro, Paul R.

2017-07-01

Motivated by the claimed detection of a large population of faint active galactic nuclei (AGNs) at high redshift, recent studies have proposed models in which AGNs contribute significantly to the z > 4 H I ionizing background. In some models, AGNs are even the chief sources of reionization. If proved true, these models would make necessary a complete revision to the standard view that galaxies dominated the high-redshift ionizing background. It has been suggested that AGN-dominated models can better account for two recent observations that appear to be in conflict with the standard view: (1) large opacity variations in the z ˜ 5.5 H I Ly α forest, and (2) slow evolution in the mean opacity of the He II Ly α forest. Large spatial fluctuations in the ionizing background from the brightness and rarity of AGNs may account for the former, while the earlier onset of He II reionization in these models may account for the latter. Here we show that models in which AGN emissions source ≳50 per cent of the ionizing background generally provide a better fit to the observed H I Ly α forest opacity variations compared to standard galaxy-dominated models. However, we argue that these AGN-dominated models are in tension with constraints on the thermal history of the intergalactic medium (IGM). Under standard assumptions about the spectra of AGNs, we show that the earlier onset of He II reionization heats up the IGM well above recent temperature measurements. We further argue that the slower evolution of the mean opacity of the He II Ly α forest relative to simulations may reflect deficiencies in current simulations rather than favour AGN-dominated models as has been suggested.

The abundance, distribution, and physical nature of highly ionized oxygen O VI, O VII, and O VIII in IllustrisTNG

NASA Astrophysics Data System (ADS)

Nelson, Dylan; Kauffmann, Guinevere; Pillepich, Annalisa; Genel, Shy; Springel, Volker; Pakmor, Rüdiger; Hernquist, Lars; Weinberger, Rainer; Torrey, Paul; Vogelsberger, Mark; Marinacci, Federico

2018-06-01

We explore the abundance, spatial distribution, and physical properties of the O VI, O VII, and O VIII ions of oxygen in circumgalactic and intergalactic media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume cosmological magnetohydrodynamical simulations. Modelling the ionization states of simulated oxygen, we find good agreement with observations of the low-redshift O VI column density distribution function (CDDF), and present its evolution for all three ions from z = 0 to z = 4. Producing mock quasar absorption line spectral surveys, we show that the IllustrisTNG simulations are fully consistent with constraints on the O VI content of the CGM from COS-haloes and other low-redshift observations, producing columns as high as observed. We measure the total amount of mass and average column densities of each ion using hundreds of thousands of simulated galaxies spanning 10^{11} < {M}_halo/ M⊙<1015 corresponding to 109 < M⋆/ M⊙<1012 in stellar mass. Stacked radial profiles of O VI are computed in 3D number density and 2D projected column density, decomposing into 1-halo and 2-halo terms. Relating halo O VI to properties of the central galaxy, we find a correlation between the (g - r) colour of a galaxy and the total amount of O VI in its CGM. In comparison to the COS-Haloes finding, this leads to a dichotomy of columns around star-forming versus passive galaxies at fixed stellar (or halo) mass. We demonstrate that this correlation is a direct result of black hole feedback associated with quenching and represents a causal consequence of galactic-scale baryonic feedback impacting the physical state of the circumgalactic medium.

Kinematics of metal-poor giants in an inner-halo field, with implications for disk formation

NASA Technical Reports Server (NTRS)

Morrison, Heather L.

1993-01-01

A sample of approximately 100 predominantly metal-weak giants, identified in a high-latitude field towards the galactic center using an automated objective-prism survey technique, is presented. Abundances and radial velocities have been measured for these giants, whose distances from the Sun range from 1 to 18 kpc. While the extremely metal-weak stars in the field have halo kinematics, the majority of the stars with intermediate abundance have thick disk kinematics, despite the fact that their average distance from the galactic plane is 3 kpc. The most satisfactory explanation for this effect is that the inner halo is moderately flattened, and the metal-weak stars of the thick disk have a scale height of about 2 kpc. It is suggested that the thick disk may have formed in a dissipational collapse, rather than in a separate event such as the accretion of a small satellite galaxy.

The COS-AGN survey: Revealing the nature of circum-galactic gas around hosts of active galactic nuclei

NASA Astrophysics Data System (ADS)

Berg, Trystyn A. M.; Ellison, Sara L.; Tumlinson, Jason; Oppenheimer, Benjamin D.; Horton, Ryan; Bordoloi, Rongmon; Schaye, Joop

2018-04-01

Active galactic nuclei (AGN) are thought to play a critical role in shaping galaxies, but their effect on the circumgalactic medium (CGM) is not well studied. We present results from the COS-AGN survey: 19 quasar sightlines that probe the CGM of 20 optically-selected AGN host galaxies with impact parameters 80 <ρimp<300 kpc. Absorption lines from a variety of species are measured and compared to a stellar mass and impact parameter matched sample of sightlines through non-AGN galaxies. Amongst the observed species in the COS-AGN sample (Lyα, Cii , Siii , Siiii , Civ , Siiv , Nv ), only Lyα shows a high covering fraction (94^{+6}_{-23}% for rest-frame equivalent widths EW≥124 mÅ) whilst many of the metal ions are not detected in individual sightlines. A sightline-by-sightline comparison between COS-AGN and the control sample yields no significant difference in EW distribution. However, stacked spectra of the COS-AGN and control samples show significant (>3σ) enhancements in the EW of both Siiii And Lyα at impact parameters >164 kpc by a factor of +0.45 ± 0.05 dex and >+0.75 dex respectively. The lack of detections of both high-ionization species near the AGN and strong kinematic offsets between the absorption systemic galaxy redshifts indicates that neither the AGN's ionization nor its outflows are the origin of these differences. Instead, we suggest the observed differences could result from either AGN hosts residing in haloes with intrinsically distinct gas properties, or that their CGM has been affected by a previous event, such as a starburst, which may also have fuelled the nuclear activity.

DETECTING TRIAXIALITY IN THE GALACTIC DARK MATTER HALO THROUGH STELLAR KINEMATICS. II. DEPENDENCE ON NATURE DARK MATTER AND GRAVITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rojas-Niño, Armando; Pichardo, Barbara; Valenzuela, Octavio

Recent studies have presented evidence that the Milky Way global potential may be non-spherical. In this case, the assembling process of the Galaxy may have left long-lasting stellar halo kinematic fossils due to the shape of the dark matter halo, potentially originated by orbital resonances. We further investigate such a possibility, now considering potential models further away from ΛCDM halos, like scalar field dark matter halos and Modified Newtonian Dynamics (MOND), and including several other factors that may mimic the emergence and permanence of kinematic groups, such as a spherical and triaxial halo with an embedded disk potential. We find that regardless ofmore » the density profile (DM nature), kinematic groups only appear in the presence of a triaxial halo potential. For the case of a MOND-like gravity theory no kinematic structure is present. We conclude that the detection of these kinematic stellar groups could confirm the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.« less

A DIRECT MEASUREMENT OF THE BARYONIC MASS FUNCTION OF GALAXIES AND IMPLICATIONS FOR THE GALACTIC BARYON FRACTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Papastergis, Emmanouil; Huang, Shan; Giovanelli, Riccardo

We use both an H I-selected and an optically selected galaxy sample to directly measure the abundance of galaxies as a function of their 'baryonic' mass (stars + atomic gas). Stellar masses are calculated based on optical data from the Sloan Digital Sky Survey and atomic gas masses are calculated using atomic hydrogen (H I) emission line data from the Arecibo Legacy Fast ALFA survey. By using the technique of abundance matching, we combine the measured baryonic function of galaxies with the dark matter halo mass function in a {Lambda}CDM universe, in order to determine the galactic baryon fraction asmore » a function of host halo mass. We find that the baryon fraction of low-mass halos is much smaller than the cosmic value, even when atomic gas is taken into account. We find that the galactic baryon deficit increases monotonically with decreasing halo mass, in contrast with previous studies which suggested an approximately constant baryon fraction at the low-mass end. We argue that the observed baryon fractions of low-mass halos cannot be explained by reionization heating alone, and that additional feedback mechanisms (e.g., supernova blowout) must be invoked. However, the outflow rates needed to reproduce our result are not easily accommodated in the standard picture of galaxy formation in a {Lambda}CDM universe.« less

The Crossroads between the Galactic Disk and Interstellar Space, Ablaze in 3/4 keV Light

NASA Astrophysics Data System (ADS)

Shelton, Robin L.

2016-04-01

The halo is the crossroads between the Galactic disk and intergalactic space. This region is inhabited by hot gas that has risen from the disk, gas heated in situ, and hot material that has fallen in from intergalactic space. Owing to high spectral resolution observations made by by XMM-Newton, Suzaku, and Chandra of the hot plasma's 3/4 keV emission and absorption, increasingly sophisticated and CPU intensive computer modeling, and an awareness that charge exchange can contaminate 3/4 keV observations, we are now better able to understand the hot halo gas than ever before.Spectral analyses indicate that the 3/4 keV emission comes from T ~ 2.2 million Kelvin gas. Although observations suggest that the gas may be convectively unstable and the spectra's temperature is similar to that predicted by recent sophisticated models of the galactic fountain, the observed emission measure is significantly brighter than that predicted by fountain models. This brightness disparity presents us with another type of crossroads: should we continue down the road of adding physics to already sophisticated modeling or should we seek out other sources? In this presentation, I will discuss the galactic fountain crossroads, note the latitudinal and longitudinal distribution of the hot halo gas, provide an update on charge exchange, and explain how shadowing observations have helped to fine tune our understanding of the hot gas.

The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

NASA Astrophysics Data System (ADS)

Dauphas, Nicolas

2005-06-01

Some heavy elements (with atomic number A > 69) are produced by the `rapid' (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from ~0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely . This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way ( in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution.

On the relevance of chaos for halo stars in the solar neighbourhood II

NASA Astrophysics Data System (ADS)

Maffione, Nicolas P.; Gómez, Facundo A.; Cincotta, Pablo M.; Giordano, Claudia M.; Grand, Robert J. J.; Marinacci, Federico; Pakmor, Rüdiger; Simpson, Christine M.; Springel, Volker; Frenk, Carlos S.

2018-05-01

In a previous paper based on dark matter only simulations we show that, in the approximation of an analytic and static potential describing the strongly triaxial and cuspy shape of Milky Way-sized haloes, diffusion due to chaotic mixing in the neighbourhood of the Sun does not efficiently erase phase space signatures of past accretion events. In this second paper we further explore the effect of chaotic mixing using multicomponent Galactic potential models and solar neighbourhood-like volumes extracted from fully cosmological hydrodynamic simulations, thus naturally accounting for the gravitational potential associated with baryonic components, such as the bulge and disc. Despite the strong change in the global Galactic potentials with respect to those obtained in dark matter only simulations, our results confirm that a large fraction of halo particles evolving on chaotic orbits exhibit their chaotic behaviour after periods of time significantly larger than a Hubble time. In addition, significant diffusion in phase space is not observed on those particles that do exhibit chaotic behaviour within a Hubble time.

The formation of low-ionization emission in the halo of NGC 891

NASA Technical Reports Server (NTRS)

Sokolowski, James; Bland-Hawthorn, Jonathan

1993-01-01

Imaging and Spectroscopic study first revealed the presence of a diffuse ionized medium (DIM), having unusual excitation, pervading the lower halo of the edge-on spiral galaxy NGC 891. Emission from this DIM is strongest northeast of the nucleus, at radii between 2 and 8 kpc (hereafter region 1). The (N2)(lambda)6583/H(alpha) and (S2)(lambda) (lambda)6716,6731/H(alpha) ratios increase dramatically with z in region 1, from 0.6 and 0.5 respectively at z is approximately equal to 500 pc to 1.1 and 1.0 at z is approximately equal to 1 kpc, while nondetections of (O1)(lambda)6300 and (O3)(lambda)5007 emission yield upper limits of (O1)(lambda)6300/H(alpha) less than or equal to 0.05 and (O3)(lambda)5007/H(alpha) less than or equal to 0.15 for z less than 1 kpc. Previous photoionization models, using the radiation field from disk O and B stars, have been successful in reproducing the elevated (N2)(lambda)6583/H(alpha) and (S2)(lambda)(lambda)6716.6731/H(alpha) ratios observed. However, these radiation bounded models also produce significant (O3)(lambda)5007 emission, in conflict with the observed upper limit. Here, we report the results of new, matter bounded models for the photoionization of the DIM in region 1 of NGC 891.

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

PubMed

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G; Serenelli, Aldo M; Sheffield, Allyson; Li, Ting S; Casagrande, Luca; Johnston, Kathryn V; Laporte, Chervin F P; Price-Whelan, Adrian M; Schönrich, Ralph; Gould, Andrew

2018-03-15

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

Constraining the Galactic structure parameters with the XSTPS-GAC and SDSS photometric surveys

NASA Astrophysics Data System (ADS)

Chen, B.-Q.; Liu, X.-W.; Yuan, H.-B.; Robin, A. C.; Huang, Y.; Xiang, M.-S.; Wang, C.; Ren, J.-J.; Tian, Z.-J.; Zhang, H.-W.

2017-01-01

Photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) and the Sloan Digital Sky Survey (SDSS) are used to derive the global structure parameters of the smooth components of the Milky Way. The data, which cover nearly 11 000 deg2 sky area and the full range of Galactic latitude, allow us to construct a globally representative Galactic model. The number density distribution of Galactic halo stars is fitted with an oblate spheroid that decays by power law. The best fitting yields an axis ratio and a power-law index κ = 0.65 and p = 2.79, respectively. The r-band differential star counts of three dwarf samples are then fitted with a Galactic model. The best-fitting model yielded by a Markov Chain Monte Carlo analysis has thin and thick disc scale heights and lengths of H1 = 322 pc and L1 = 2343 pc, H2 = 794 pc and L2 = 3638 pc, a local thick-to-thin disc density ratio of f2 = 11 per cent, and a local density ratio of the oblate halo to the thin disc of fh = 0.16 per cent. The measured star count distribution, which is in good agreement with the above model for most of the sky area, shows a number of statistically significant large-scale overdensities, including some of the previously known substructures, such as the Virgo overdensity and the so-called `north near structure', and a new feature between 150° < l < 240° and -1° < b < -5°, at an estimated distance between 1.0 and 1.5 kpc. The Galactic North-South asymmetry in the anticentre is even stronger than previously thought.

Shining a light on galactic outflows: photoionized outflows

NASA Astrophysics Data System (ADS)

Chisholm, John; Tremonti, Christy A.; Leitherer, Claus; Chen, Yanmei; Wofford, Aida

2016-04-01

We study the ionization structure of galactic outflows in 37 nearby, star-forming galaxies with the Cosmic Origins Spectrograph on the Hubble Space Telescope. We use the O I, Si II, Si III, and Si IV ultraviolet absorption lines to characterize the different ionization states of outflowing gas. We measure the equivalent widths, line widths, and outflow velocities of the four transitions, and find shallow scaling relations between them and galactic stellar mass and star formation rate. Regardless of the ionization potential, lines of similar strength have similar velocities and line widths, indicating that the four transitions can be modelled as a comoving phase. The Si equivalent width ratios (e.g. Si IV/Si II) have low dispersion, and little variation with stellar mass; while ratios with O I and Si vary by a factor of 2 for a given stellar mass. Photoionization models reproduce these equivalent width ratios, while shock models under predict the relative amount of high ionization gas. The photoionization models constrain the ionization parameter (U) between -2.25 < log (U) < -1.5, and require that the outflow metallicities are greater than 0.5 Z⊙. We derive ionization fractions for the transitions, and show that the range of ionization parameters and stellar metallicities leads to a factor of 1.15-10 variation in the ionization fractions. Historically, mass outflow rates are calculated by converting a column density measurement from a single metal ion into a total hydrogen column density using an ionization fraction, thus mass outflow rates are sensitive to the assumed ionization structure of the outflow.

Orbits of Selected Globular Clusters in the Galactic Bulge

NASA Astrophysics Data System (ADS)

Pérez-Villegas, A.; Rossi, L.; Ortolani, S.; Casotto, S.; Barbuy, B.; Bica, E.

2018-05-01

We present orbit analysis for a sample of eight inner bulge globular clusters, together with one reference halo object. We used proper motion values derived from long time base CCD data. Orbits are integrated in both an axisymmetric model and a model including the Galactic bar potential. The inclusion of the bar proved to be essential for the description of the dynamical behaviour of the clusters. We use the Monte Carlo scheme to construct the initial conditions for each cluster, taking into account the uncertainties in the kinematical data and distances. The sample clusters show typically maximum height to the Galactic plane below 1.5 kpc, and develop rather eccentric orbits. Seven of the bulge sample clusters share the orbital properties of the bar/bulge, having perigalactic and apogalatic distances, and maximum vertical excursion from the Galactic plane inside the bar region. NGC 6540 instead shows a completely different orbital behaviour, having a dynamical signature of the thick disc. Both prograde and prograde-retrograde orbits with respect to the direction of the Galactic rotation were revealed, which might characterise a chaotic behaviour.

Cosmological simulations of decaying dark matter: implications for small-scale structure of dark matter haloes

NASA Astrophysics Data System (ADS)

Wang, Mei-Yu; Peter, Annika H. G.; Strigari, Louis E.; Zentner, Andrew R.; Arant, Bryan; Garrison-Kimmel, Shea; Rocha, Miguel

2014-11-01

We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable dark matter particle and a non-interacting light particle with decay lifetime comparable to the Hubble time. We study the effects of the recoil kick velocity (Vk) received by the stable dark matter on the structures of dark matter haloes ranging from galaxy-cluster to Milky Way-mass scales. For Milky Way-mass haloes, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. In general, haloes with circular velocities comparable to the magnitude of kick velocity are most strongly affected by decays. We show that models with lifetimes Γ-1 ˜ H_0^{-1} and recoil speeds Vk ˜ 20-40 km s-1 can significantly reduce both the abundance of Galactic subhaloes and their internal densities. We find that decaying dark matter models that do not violate current astrophysical constraints can significantly mitigate both the `missing satellites problem' and the more recent `too big to fail problem'. These decaying models predict significant time evolution of haloes, and this implies that at high redshifts decaying models exhibit the similar sequence of structure formation as cold dark matter. Thus, decaying dark matter models are significantly less constrained by high-redshift phenomena than warm dark matter models. We conclude that models of decaying dark matter make predictions that are relevant for the interpretation of small galaxies observations in the Local Group and can be tested as well as by forthcoming large-scale surveys.

Pulsar TeV Halos Explain the Diffuse TeV Excess Observed by Milagro.

PubMed

Linden, Tim; Buckman, Benjamin J

2018-03-23

Milagro observations have found bright, diffuse TeV emission concentrated along the galactic plane of the Milky Way. The intensity and spectrum of this emission is difficult to explain with current models of hadronic γ-ray production, and has been named the "TeV excess." We show that TeV emission from pulsars naturally explains this excess. Recent observations have detected "TeV halos" surrounding pulsars that are either nearby or particularly luminous. Extrapolating this emission to the full population of Milky Way pulsars indicates that the ensemble of "subthreshold" sources necessarily produces bright TeV emission diffusively along the Milky Way plane. Models indicate that the TeV halo γ-ray flux exceeds that from hadronic γ rays above an energy of ∼500  GeV. Moreover, the spectrum and intensity of TeV halo emission naturally matches the TeV excess. Finally, we show that upcoming HAWC observations will resolve a significant fraction of the TeV excess into individual TeV halos, conclusively confirming, or ruling out, this model.

Exploring the making of a galactic wind in the starbursting dwarf irregular galaxy IC 10 with LOFAR

NASA Astrophysics Data System (ADS)

Heesen, V.; Rafferty, D. A.; Horneffer, A.; Beck, R.; Basu, A.; Westcott, J.; Hindson, L.; Brinks, E.; ChyŻy, K. T.; Scaife, A. M. M.; Brüggen, M.; Heald, G.; Fletcher, A.; Horellou, C.; Tabatabaei, F. S.; Paladino, R.; Nikiel-Wroczyński, B.; Hoeft, M.; Dettmar, R.-J.

2018-05-01

Low-mass galaxies are subject to strong galactic outflows, in which cosmic rays may play an important role; they can be best traced with low-frequency radio continuum observations, which are less affected by spectral ageing. We present a study of the nearby starburst dwarf irregular galaxy IC 10 using observations at 140 MHz with the Low-Frequency Array (LOFAR), at 1580 MHz with the Very Large Array (VLA), and at 6200 MHz with the VLA and the 100-m Effelsberg telescope. We find that IC 10 has a low-frequency radio halo, which manifests itself as a second component (thick disc) in the minor axis profiles of the non-thermal radio continuum emission at 140 and 1580 MHz. These profiles are then fitted with 1D cosmic ray transport models for pure diffusion and advection. We find that a diffusion model fits best, with a diffusion coefficient of D = (0.4-0.8) × 1026(E/GeV)0.5 cm2 s-1, which is at least an order of magnitude smaller than estimates both from anisotropic diffusion and the diffusion length. In contrast, advection models, which cannot be ruled out due to the mild inclination, while providing poorer fits, result in advection speeds close to the escape velocity of ≈ 50 km s- 1, as expected for a cosmic ray-driven wind. Our favoured model with an accelerating wind provides a self-consistent solution, where the magnetic field is in energy equipartition with both the warm neutral and warm ionized medium with an important contribution from cosmic rays. Consequently, cosmic rays can play a vital role for the launching of galactic winds in the disc-halo interface.

Single cell HaloChip assay on paper for point-of-care diagnosis.

PubMed

Ma, Liyuan; Qiao, Yong; Jones, Ross; Singh, Narendra; Su, Ming

2016-11-01

This article describes a paper-based low cost single cell HaloChip assay that can be used to assess drug- and radiation-induced DNA damage at point-of-care. Printing ink on paper effectively blocks fluorescence of paper materials, provides high affinity to charged polyelectrolytes, and prevents penetration of water in paper. After exposure to drug or ionizing radiation, cells are patterned on paper to create discrete and ordered single cell arrays, embedded inside an agarose gel, lysed with alkaline solution to allow damaged DNA fragments to diffuse out of nucleus cores, and form diffusing halos in the gel matrix. After staining DNA with a fluorescent dye, characteristic halos formed around cells, and the level of DNA damage can be quantified by determining sizes of halos and nucleus with an image processing program based on MATLAB. With its low fabrication cost and easy operation, this HaloChip on paper platform will be attractive to rapidly and accurately determine DNA damage for point-of-care evaluation of drug efficacy and radiation condition. Graphical Abstract Single cell HaloChip on paper.

Milky Way mass and potential recovery using tidal streams in a realistic halo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bonaca, Ana; Geha, Marla; Küpper, Andreas H. W.

2014-11-01

We present a new method for determining the Galactic gravitational potential based on forward modeling of tidal stellar streams. We use this method to test the performance of smooth and static analytic potentials in representing realistic dark matter halos, which have substructure and are continually evolving by accretion. Our FAST-FORWARD method uses a Markov Chain Monte Carlo algorithm to compare, in six-dimensional phase space, an 'observed' stream to models created in trial analytic potentials. We analyze a large sample of streams that evolved in the Via Lactea II (VL2) simulation, which represents a realistic Galactic halo potential. The recovered potentialmore » parameters are in agreement with the best fit to the global, present-day VL2 potential. However, merely assuming an analytic potential limits the dark matter halo mass measurement to an accuracy of 5%-20%, depending on the choice of analytic parameterization. Collectively, the mass estimates using streams from our sample reach this fundamental limit, but individually they can be highly biased. Individual streams can both under- and overestimate the mass, and the bias is progressively worse for those with smaller perigalacticons, motivating the search for tidal streams at galactocentric distances larger than 70 kpc. We estimate that the assumption of a static and smooth dark matter potential in modeling of the GD-1- and Pal5-like streams introduces an error of up to 50% in the Milky Way mass estimates.« less

Formation and evolution of substructures in tidal tails: spherical dark matter haloes

NASA Astrophysics Data System (ADS)

Reinoso, B.; Fellhauer, M.; Véjar, R.

2018-05-01

Recently a theory about the formation of overdensities of stars along tidal tails of globular clusters has been presented. This theory predicts the position and the time of the formation of such overdensities and was successfully tested with N-body simulations of globular clusters in a point-mass galactic potential. In this work, we present a comparison between this theory and our simulations using a dwarf galaxy orbiting two differently shaped dark matter haloes to study the effects of a cored and a cuspy halo on the formation and the evolution of tidal tails. We find no difference using a cuspy or a cored halo, however, we find an intriguing asymmetry between the leading arm and the trailing arm of the tidal tails. The trailing arm grows faster than the leading arm. This asymmetry is seen in the distance to the first overdensity and its size as well. We establish a relation between the distance to the first overdensity and the size of this overdensity.

Ionized Absorbers in Active Galactic Nuclei and Very Steap Soft X-Ray Quasars

NASA Technical Reports Server (NTRS)

Fiore, Fabrizio; White, Nicholas (Technical Monitor)

2000-01-01

Steep soft X-ray (0.1-2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2-10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026. Both objects show similar variations (factor of approximately 2 in 10 ks), despite a factor of approximately 10 difference in the 0.5-10 keV luminosity (7.3 x 10(exp 43) erg/s for PG 1244 + 026 and 6.4 x 10(exp 44) erg/s for NAB 0205 + 024, assuming isotropic emission, H(sub 0) = 50.0 and q(sub 0) = 0.0). The X-ray continuum of the two quasars flattens by 0.5-1 going from the 0.1-2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei. PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centered at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3-0.6 c).

Large-scale structure after COBE: Peculiar velocities and correlations of cold dark matter halos

NASA Technical Reports Server (NTRS)

Zurek, Wojciech H.; Quinn, Peter J.; Salmon, John K.; Warren, Michael S.

1994-01-01

Large N-body simulations on parallel supercomputers allow one to simultaneously investigate large-scale structure and the formation of galactic halos with unprecedented resolution. Our study shows that the masses as well as the spatial distribution of halos on scales of tens of megaparsecs in a cold dark matter (CDM) universe with the spectrum normalized to the anisotropies detected by Cosmic Background Explorer (COBE) is compatible with the observations. We also show that the average value of the relative pairwise velocity dispersion sigma(sub v) - used as a principal argument against COBE-normalized CDM models-is significantly lower for halos than for individual particles. When the observational methods of extracting sigma(sub v) are applied to the redshift catalogs obtained from the numerical experiments, estimates differ significantly between different observation-sized samples and overlap observational estimates obtained following the same procedure.

Constraining the galaxy-halo connection over the last 13.3 Gyr: star formation histories, galaxy mergers and structural properties

NASA Astrophysics Data System (ADS)

Rodríguez-Puebla, Aldo; Primack, Joel R.; Avila-Reese, Vladimir; Faber, S. M.

2017-09-01

We present new determinations of the stellar-to-halo mass relation (SHMR) at z = 0-10 that match the evolution of the galaxy stellar mass function, the star formation rate (SFR)-M* relation and the cosmic SFR. We utilize a compilation of 40 observational studies from the literature and correct them for potential biases. Using our robust determinations of halo mass assembly and the SHMR, we infer star formation histories, merger rates and structural properties for average galaxies, combining star-forming and quenched galaxies. Our main findings are as follows: (1) The halo mass M50 above which 50 per cent of galaxies are quenched coincides with sSFR/sMAR ˜ 1, where sSFR is the specific SFR and sMAR is the specific halo mass accretion rate. (2) M50 increases with redshift, presumably due to cold streams being more efficient at high redshifts, while virial shocks and active galactic nucleus feedback become more relevant at lower redshifts. (3) The ratio sSFR/sMAR has a peak value, which occurs around {M_vir}˜ 2× 10^{11} M_{⊙}. (4) The stellar mass density within 1 kpc, Σ1, is a good indicator of the galactic global sSFR. (5) Galaxies are statistically quenched after they reach a maximum in Σ1, consistent with theoretical expectations of the gas compaction model; this maximum depends on redshift. (6) In-situ star formation is responsible for most galactic stellar mass growth, especially for lower mass galaxies. (7) Galaxies grow inside-out. The marked change in the slope of the size-mass relation when galaxies became quenched, from d log {R_eff}/d log {M_*}˜ 0.35 to ˜2.5, could be the result of dry minor mergers.

Exploring Halo Substructure with Giant Stars. XV. Discovery of a Connection between the Monoceros Ring and the Triangulum–Andromeda Overdensity?

DOE PAGES

Li, Ting S.; Sheffield, Allyson A.; Johnston, Kathryn V.; ...

2017-07-24

Thanks to modern sky surveys, over twenty stellar streams and overdensity structures have been discovered in the halo of the Milky Way. Here, in this paper, we present an analysis of spectroscopic observations of individual stars from one such structure, "A13", first identified as an overdensity using the M giant catalog from the Two Micron All-Sky Survey. Our spectroscopic observations show that stars identified with A13 have a velocity dispersion ofmore » $$\\lesssim$$ 40 $$\\mathrm{km~s^{-1}}$$, implying that it is a genuine coherent structure rather than a chance super-position of random halo stars. From its position on the sky, distance ($$\\sim$$15 kpc heliocentric), and kinematical properties, A13 is likely to be an extension of another low Galactic latitude substructure -- the Galactic Anticenter Stellar Structure (also known as the Monoceros Ring) -- towards smaller Galactic longitude and farther distance. Furthermore, the kinematics of A13 also connect it with another structure in the southern Galactic hemisphere -- the Triangulum-Andromeda overdensity. Finally, we discuss these three connected structures within the context of a previously proposed scenario that one or all of these features originate from the disk of the Milky Way.« less

Exploring Halo Substructure with Giant Stars. XV. Discovery of a Connection between the Monoceros Ring and the Triangulum–Andromeda Overdensity?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Ting S.; Sheffield, Allyson A.; Johnston, Kathryn V.

Thanks to modern sky surveys, over twenty stellar streams and overdensity structures have been discovered in the halo of the Milky Way. Here, in this paper, we present an analysis of spectroscopic observations of individual stars from one such structure, "A13", first identified as an overdensity using the M giant catalog from the Two Micron All-Sky Survey. Our spectroscopic observations show that stars identified with A13 have a velocity dispersion ofmore » $$\\lesssim$$ 40 $$\\mathrm{km~s^{-1}}$$, implying that it is a genuine coherent structure rather than a chance super-position of random halo stars. From its position on the sky, distance ($$\\sim$$15 kpc heliocentric), and kinematical properties, A13 is likely to be an extension of another low Galactic latitude substructure -- the Galactic Anticenter Stellar Structure (also known as the Monoceros Ring) -- towards smaller Galactic longitude and farther distance. Furthermore, the kinematics of A13 also connect it with another structure in the southern Galactic hemisphere -- the Triangulum-Andromeda overdensity. Finally, we discuss these three connected structures within the context of a previously proposed scenario that one or all of these features originate from the disk of the Milky Way.« less

A Fundamental Test for Galaxy Formation Models: Matching the Lyman-α Absorption Profiles of Galactic Halos Over Three Decades in Distance

NASA Astrophysics Data System (ADS)

Sorini, Daniele; Oñorbe, José; Hennawi, Joseph F.; Lukić, Zarija

2018-06-01

Galaxy formation depends critically on the physical state of gas in the circumgalactic medium (CGM) and its interface with the intergalactic medium (IGM), determined by the complex interplay between inflow from the IGM and outflows from supernovae and/or AGN feedback. The average Lyα absorption profile around galactic halos represents a powerful tool to probe their gaseous environments. We compare predictions from Illustris and Nyx hydrodynamical simulations with the observed absorption around foreground quasars, damped Lyα systems, and Lyman-break galaxies. We show how large-scale BOSS and small-scale quasar pair measurements can be combined to precisely constrain the absorption profile over three decades in transverse distance 20 {kpc}≲ b≲ 20 {Mpc}. Far from galaxies, ≳ 2 {Mpc}, the simulations converge to the same profile and provide a reasonable match to the observations. This asymptotic agreement arises because the ΛCDM model successfully describes the ambient IGM and represents a critical advantage of studying the mean absorption profile. However, significant differences between the simulations, and between simulations and observations, are present on scales 20 {kpc}≲ b≲ 2 {Mpc}, illustrating the challenges of accurately modeling and resolving galaxy formation physics. It is noteworthy that these differences are observed as far out as ∼ 2 {Mpc}, indicating that the “sphere of influence” of galaxies could extend to approximately ∼7 times the halo virial radius. Current observations are very precise on these scales and can thus strongly discriminate between different galaxy formation models. We demonstrate that the Lyα absorption profile is primarily sensitive to the underlying temperature–density relationship of diffuse gas around galaxies, and argue that it thus provides a fundamental test of galaxy formation models.

Pushing the boundaries: probing the halo of the Milky Way beyond 100 kpc with RR Lyrae

NASA Astrophysics Data System (ADS)

Carlin, Jeffrey L.; Medina, Gustavo; Munoz, Ricardo R.; Vivas, Anna Katherina; Willman, Beth

2018-01-01

Stars in the outermost halo of the Milky Way are vital tracers of the mass of our Galaxy. Furthermore, beyond ~100 kpc from the Galactic center, most (or perhaps all) of the stars are likely to be in faint dwarf galaxies or tidal debris from recently accreted dwarfs, making the outer reaches of the Galaxy important for understanding the Milky Way’s accretion history. However, confirmed stars are scarce at these distances because they are difficult to securely identify among the more numerous foreground stars. Pulsating variables such as RR Lyrae are ideal probes of the distant halo because they are readily identified in time-series data, are intrinsically bright and thus can be seen at large distances, and follow well-known period-luminosity relations that enable precise distance measurements. We present results from our program to find RR Lyrae using deep DECam time series data (from the HiTS supernova survey as well as our own observing program) covering ~300 square degrees. Our sample of distant RR Lyrae more than doubles the number of known Milky Way stars beyond distances of ~150 kpc. Among these, we find two distinct groups of two and three stars that are members of the Leo IV and Leo V ultra-faint dwarf galaxies, located at distances of ~145 kpc and ~175 kpc, respectively. We derive the stellar density as a function of Galactocentric radius, extending to more than 250 kpc from the Galactic center. This sample of RR Lyrae provides a set of important probes of the mass of the Milky Way and the accretion origin of the outer Galactic halo.

OT1_mputman_1: ASCII: All Sky observations of Galactic CII

NASA Astrophysics Data System (ADS)

Putman, M.

2010-07-01

The Milky Way and other galaxies require a significant source of ongoing star formation fuel to explain their star formation histories. A new ubiquitous population of discrete, cold clouds have recently been discovered at the disk-halo interface of our Galaxy that could potentially provide this source of fuel. We propose to observe a small sample of these disk-halo clouds with HIFI to determine if the level of [CII] emission detected suggests they represent the cooling of warm clouds at the interface between the star forming disk and halo. These cooling clouds are predicted by simulations of warm clouds moving into the disk-halo interface region. We target 5 clouds in this proposal for which we have high resolution HI maps and can observe the densest core of the cloud. The results of our observations will also be used to interpret the surprisingly high detections of [CII] for low HI column density clouds in the Galactic Plane by the GOT C+ Key Program by extending the clouds probed to high latitude environments.

Detection of possible intervening Mg X associated with A hot gaseous galaxy halo

NASA Astrophysics Data System (ADS)

Qu, Zhijie; Bregman, Joel N.

2017-08-01

Galaxies may store a significant fraction of baryonic material in their hot halos, which can be traced by high ionization absorption systems in spectra of background QSOs. A hot halo of an L* galaxy has a virial temperature ~ 10^6 K, corresponding to the peak ionization fraction for Mg X. We discovered a Mg X absorption system, in the sightline towards LBQS 1435-0134, which also contains Ne VIII, Ne VI, O VI, Ne V, O V, Ne IV, O IV, N IV, O III, and H I. Further modeling shows that the highest ionization state ions, Mg X and Ne VIII, cannot be produced by the photoionization model. A collisional ionization model can reproduce the observations, and all of the ions can be accommodated in a three- temperature plasma or one gas with a power-law temperature distribution, dN / dT = 10^(4.4 +- 2.2 - [Z/X]) T^(1.55 +- 0.41) (for 10^(4.39 +- 0.13) K < T < 10^(6.04+-0.05) K). In the power-law temperature model, the total hydrogen column density is 8.2 * 10^19(0.3 Zsun/Z), and most of the gaseous mass is in the hot phase with the postive power index. The modeling results show that the gas is consistent with a hot volume-filled gaseous galaxy halo (N(H) <~ 10^20 cm^-2 and T ~ 10^6 K), which contains a baryonic mass that may be comparable or greater than the stellar mass (~10^11Msun assuming n200).

The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars.

PubMed

Dauphas, Nicolas

2005-06-30

Some heavy elements (with atomic number A > 69) are produced by the 'rapid' (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from approximately 0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely (0.57(+0.037)(-0.031). This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way (14.5(+2.8)(-2.2)Gyr in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution.

EGRET excess of diffuse galactic gamma rays as tracer of dark matter

NASA Astrophysics Data System (ADS)

de Boer, W.; Sander, C.; Zhukov, V.; Gladyshev, A. V.; Kazakov, D. I.

2005-12-01

The public data from the EGRET space telescope on diffuse Galactic gamma rays in the energy range from 0.1 to 10 GeV are reanalyzed with the purpose of searching for signals of Dark Matter annihilation (DMA). The analysis confirms the previously observed excess for energies above 1 GeV in comparison with the expectations from conventional Galactic models. In addition, the excess was found to show all the key features of a signal from Dark Matter Annihilation (DMA): a) the excess is observable in all sky directions and has the same shape everywhere, thus pointing to a common source; b) the shape corresponds to the expected spectrum of the annihilation of non-relativistic massive particles into - among others - neutral π0 mesons, which decay into photons. From the energy spectrum of the excess we deduce a WIMP mass between 50 and 100 GeV, while from the intensity of the excess in all sky directions the shape of the halo could be reconstructed. The DM halo is consistent with an almost spherical isothermal profile with substructure in the Galactic plane in the form of toroidal rings at 4 and 14 kpc from the center. These rings lead to a peculiar shape of the rotation curve, in agreement with the data, which proves that the EGRET excess traces the Dark Matter.

Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gondolo, Paolo; Scopel, Stefano, E-mail: paolo.gondolo@utah.edu, E-mail: scopel@sogang.ac.kr

2017-09-01

We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame from which the unmodulated signal descends. Then we describe a mathematically-sound profile likelihood analysis in which the likelihood is profiled over a continuum of nuisance parameters (namely, the WIMP velocity distribution). As a first application of the method, which is very general and valid for any class of velocity distributions, we restrict the analysismore » to velocity distributions that are isotropic in the Galactic frame. In this way we obtain halo-independent maximum-likelihood estimates and confidence intervals for the DAMA unmodulated signal. We find that the estimated unmodulated signal is in line with expectations for a WIMP-induced modulation and is compatible with the DAMA background+signal rate. Specifically, for the isotropic case we find that the modulated amplitude ranges between a few percent and about 25% of the unmodulated amplitude, depending on the WIMP mass.« less

Metals in the circumgalactic medium are out of ionization equilibrium due to fluctuating active galactic nuclei

NASA Astrophysics Data System (ADS)

Segers, Marijke C.; Oppenheimer, Benjamin D.; Schaye, Joop; Richings, Alexander J.

2017-10-01

We study the effect of a fluctuating active galactic nucleus (AGN) on the abundance of circumgalactic O VI in galaxies selected from the Evolution and Assembly of GaLaxies and their Environments simulations. We follow the time-variable O VI abundance in post-processing around four galaxies - two at z = 0.1 with stellar masses of M* ˜ 1010 M⊙ and M* ˜ 1011 M⊙, and two at z = 3 with similar stellar masses - out to impact parameters of twice their virial radii, implementing a fluctuating central source of ionizing radiation. Due to delayed recombination, the AGN leave significant 'AGN proximity zone fossils' around all four galaxies, where O VI and other metal ions are out of ionization equilibrium for several megayears after the AGN fade. The column density of O VI is typically enhanced by ≈0.3-1.0 dex at impact parameters within 0.3Rvir, and by ≈0.06-0.2 dex at 2Rvir, thereby also enhancing the covering fraction of O VI above a given column density threshold. The fossil effect tends to increase with increasing AGN luminosity, and towards shorter AGN lifetimes and larger AGN duty cycle fractions. In the limit of short AGN lifetimes, the effect converges to that of a continuous AGN with a luminosity of (fduty/100 per cent) times the AGN luminosity. We also find significant fossil effects for other metal ions, where low-ionization state ions are decreased (Si IV, C IV at z = 3) and high-ionization state ions are increased (C IV at z = 0.1, Ne viii, Mg x). Using observationally motivated AGN parameters, we predict AGN proximity zone fossils to be ubiquitous around M* ˜ 1010-11 M⊙ galaxies, and to affect observations of metals in the circumgalactic medium at both low and high redshifts.

The disk-halo connection and the nature of the interstellar medium

NASA Technical Reports Server (NTRS)

Norman, Colin A.; Ikeuchi, Satoru

1988-01-01

Some results on the nature of the interstellar medium that are specifically concerned with the disk-halo interaction are discussed. Over the last five years or so it has become clear that the supernovae rate in our Galaxy is spatially clumped and the consequences of such clumping are superbubbles and supershells fed by tens or hundreds of supernovae per shell. These objects evolve and expand rapidly and soon break out of the disk of the Galaxy, feeding the halo with very significant mass, energy, and momentum. As cooling occurs, gas will rain down onto the disk of the Galaxy completing the cycle. The basic flow of physical quantities from disk to halo and vice versa are discussed. Some of the many implications are noted including aspects of dynamo theory, quasar absorption lines, the theory of galactic coronae, and the nature of the x ray background. The essential difference here with the McKee-Ostriker (1977) theory is that the filling factor of the hot gas in the disk is significantly less than unity.

DO NOT FORGET THE FOREST FOR THE TREES: THE STELLAR-MASS HALO-MASS RELATION IN DIFFERENT ENVIRONMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tonnesen, Stephanie; Cen, Renyue, E-mail: stonnes@gmail.com, E-mail: cen@astro.princeton.edu

2015-10-20

The connection between dark matter halos and galactic baryons is often not well constrained nor well resolved in cosmological hydrodynamical simulations. Thus, halo occupation distribution models that assign galaxies to halos based on halo mass are frequently used to interpret clustering observations, even though it is well known that the assembly history of dark matter halos is related to their clustering. In this paper we use high-resolution hydrodynamical cosmological simulations to compare the halo and stellar mass growth of galaxies in a large-scale overdensity to those in a large-scale underdensity (on scales of about 20 Mpc). The simulation reproduces assemblymore » bias, in which halos have earlier formation times in overdense environments than in underdense regions. We find that the ratio of stellar mass to halo mass is larger in overdense regions in central galaxies residing in halos with masses between 10{sup 11} and 10{sup 12.9} M{sub ⊙}. When we force the local density (within 2 Mpc) at z = 0 to be the same for galaxies in the large-scale over- and underdensities, we find the same results. We posit that this difference can be explained by a combination of earlier formation times, more interactions at early times with neighbors, and more filaments feeding galaxies in overdense regions. This result puts the standard practice of assigning stellar mass to halos based only on their mass, rather than considering their larger environment, into question.« less

Can thermal instabilities drive galactic precipitation and explain observed circumgalactic structure?

NASA Astrophysics Data System (ADS)

Silvia, Devin

2015-10-01

Understanding the complex nature of the circumgalactic medium (CGM) has been a target of numerous research efforts, both observationally and theoretically. While significant progress has been made in probing the structure and thermodynamic state of the CGM through the detection of metal line absorption systems using the Hubble Space Telescope (HST), a complete picture of the physical mechanisms that produce the observed properties does not yet exist. Recent theoretical work has suggested that a delicate balance between radiative cooling and thermal feedback detemines whether or not the CGM is capable of sustaining a stable, multiphase medium that would allow cool clouds to precipitate out of the galactic halo. This new theoretical framework may provide the explanation for many observational results. In this project, we will detemine whether or not this elegant and simple precipitation model can be supported by physics-rich numerical simulations of isolated galaxies. We will use our simulations to gain a deeper understanding of the precipitation model and explore the ionization and temperature stucture of the CGM. Our analysis will include the comparison of realistic synthetic spectra to those produced by HST, using the newly-developed Trident software package.

Multifrequency observations of the radio continuum emission from NGC 253. 1: Magnetic fields and rotation measures in the bar and halo

NASA Astrophysics Data System (ADS)

Beck, R.; Carilli, C. L.; Holdaway, M. A.; Klein, U.

1994-12-01

Radio continuum observations of the spiral galaxy NGC 253 with the Effelsberg and Very Large Array (VLA) telescopes reveal polarized emission from the bar and halo regions. Within the bar Faraday depolarization is strong at 1.5 and 5 GHz, due to ionized gas with ne approximately equal 0.1 - 3/cu cm which is mixed with turbulent magnetic fields of approximately equal 17 microG estimated strength. Even at 10 GHz the degree of polarization in the bar is low (only approximately equal 5% east and approximately equal 2% west of the nucleus) due to beam depolarization by unresolved tangled fields. In contrast, the magnetic fields in the halo are highly uniform, as indicated by fractional polarizations up to 40% at 10 GHz. Faraday depolarization in the halo at 1.5 GHz calls for a warm, clumpy gas component with ne approximately equal 0.02/cu cm and approximately equal 6 microG turbulent fields. We detected Faraday rotation in the bar, with rotation measures absolute value of RM approximately equal 100 rad/sq m (between 10 and 5 GHz) having different signs east and west of the nucleus. Below 5 GHz Faraday rotation is strongly reduced by the limited transparency for polarized emission in the bar. Faraday rotation in the halo in two regions at approximately 5 kpc above and below the plane with RM approximately equal -7 rad/sq m between 10 and 1.5 GHz can be ascribed to hot gas with mean value of ne approximately equal 0.002/cu cm and uniform fields along the line of sight of mean value of Bu parallel approximately equal -2 microG. The magnetic field structure in the bar and halo of NGC 253 is best described by the quadrupole-type dynamo mode SO, with a ring-like field in the bar and a field mainly parallel to the plane in a co-rotating halo. A major perturbation occurs in the east where the field is perpendicular to the plane and follows a 'spur'. The galactic wind is suppressed by the dominating plane-parallel field, except along the spur.

Shrinking galaxy disks with fountain-driven accretion from the halo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmegreen, Bruce G.; Struck, Curtis; Hunter, Deidre A., E-mail: bge@watson.ibm.com, E-mail: curt@iastate.edu, E-mail: dah@lowell.edu

2014-12-01

Star formation in most galaxies requires cosmic gas accretion because the gas consumption time is short compared to the Hubble time. This accretion presumably comes from a combination of infalling satellite debris, cold flows, and condensation of hot halo gas at the cool disk interface, perhaps aided by a galactic fountain. In general, the accretion will have a different specific angular momentum than the part of the disk that receives it, even if the gas comes from the nearby halo. The gas disk then expands or shrinks over time. Here we show that condensation of halo gas at a ratemore » proportional to the star formation rate in the fountain model will preserve an initial shape, such as an exponential, with a shrinking scale length, leaving behind a stellar disk with a slightly steeper profile of younger stars near the center. This process is slow for most galaxies, producing imperceptible radial speeds, and it may be dominated by other torques, but it could be important for blue compact dwarfs, which tend to have large, irregular gas reservoirs and steep blue profiles in their inner stellar disks.« less

The Galactic HII Region Luminosity Function at Infrared and Radio Wavelengths

NASA Astrophysics Data System (ADS)

Mascoop, Joshua; Anderson, Loren; Sandor Makai, Zoltan; Armentrout, William Paul

2018-01-01

HII regions are the clearest indicators of ongoing high-mass star formation. The HII region luminosity function (LF) therefore probes present global star formation properties, and its shape has been related to HII region properties and galaxy Hubble types. Most HII region LF studies to date have been conducted in external galaxies; due to observational difficulties, there have been relatively few studies of the Milky Way HII region LF. Using ~600 HII regions from the WISE Catalog of Galactic HII Regions, we examine the Galactic LF in the first quadrant. Our high-resolution view of Galactic star formation regions allows us to separate nearby sources, and our sample is complete for all HII regions ionized by single O9.5 stars.We analyze the Galactic LF at six infrared wavelengths - where the emission is due to dust - and also at 20 cm, where the emission is from ionized gas. All LFs have a similar shape, showing that infrared LFs can be used in place of ionized gas tracers. All LFs can be described by a single power law with an index of approximately -2, in agreement with previous studes. We find no compelling evidence of a break or "knee" in the LF. Moreover, we see no significant variation in the form of the LF as a function of heliocentric distance, HII region size, or Galactocentric radius.

The Exceptional Soft X-Ray Halo of the Galaxy Merger NGC 6240

NASA Astrophysics Data System (ADS)

Nardini, E.; Wang, Junfeng; Fabbiano, G.; Elvis, M.; Pellegrini, S.; Risaliti, G.; Karovska, M.; Zezas, A.

2013-03-01

We report on a recent ~150 ks long Chandra observation of the ultraluminous infrared galaxy merger NGC 6240, which allows a detailed investigation of the diffuse galactic halo. Extended soft X-ray emission is detected at the 3σ confidence level over a diamond-shaped region with projected physical size of ~110 × 80 kpc, and a single-component thermal model provides a reasonably good fit to the observed X-ray spectrum. The hot gas has a temperature of ~7.5 million K, an estimated density of 2.5 × 10-3 cm-3, and a total mass of ~1010 M ⊙, resulting in an intrinsic 0.4-2.5 keV luminosity of 4 × 1041 erg s-1. The average temperature of 0.65 keV is quite high to be obviously related to either the binding energy in the dark-matter gravitational potential of the system or the energy dissipation and shocks following the galactic collision, yet the spatially resolved spectral analysis reveals limited variations across the halo. The relative abundance of the main α-elements with respect to iron is several times the solar value, and nearly constant as well, implying a uniform enrichment by type II supernovae out to the largest scales. Taken as a whole, the observational evidence is not compatible with a superwind originated by a recent, nuclear starburst, but rather hints at widespread, enhanced star formation proceeding at a steady rate over the entire dynamical timescale (~200 Myr). The preferred scenario is that of a starburst-processed gas component gently expanding into, and mixing with, a pre-existing halo medium of lower metallicity (Z ~ 0.1 solar) and temperature (kT ~ 0.25 keV). This picture cannot be probed more extensively with the present data, and the ultimate fate of the diffuse, hot gas remains uncertain. Under some favorable conditions, at least a fraction of it might be retained after the merger completion, and evolve into the hot halo of a young elliptical galaxy.

The Excursion Set Theory of Halo Mass Functions, Halo Clustering, and Halo Growth

NASA Astrophysics Data System (ADS)

Zentner, Andrew R.

I review the excursion set theory with particular attention toward applications to cold dark matter halo formation and growth, halo abundance, and halo clustering. After a brief introduction to notation and conventions, I begin by recounting the heuristic argument leading to the mass function of bound objects given by Press and Schechter. I then review the more formal derivation of the Press-Schechter halo mass function that makes use of excursion sets of the density field. The excursion set formalism is powerful and can be applied to numerous other problems. I review the excursion set formalism for describing both halo clustering and bias and the properties of void regions. As one of the most enduring legacies of the excursion set approach and one of its most common applications, I spend considerable time reviewing the excursion set theory of halo growth. This section of the review culminates with the description of two Monte Carlo methods for generating ensembles of halo mass accretion histories. In the last section, I emphasize that the standard excursion set approach is the result of several simplifying assumptions. Dropping these assumptions can lead to more faithful predictions and open excursion set theory to new applications. One such assumption is that the height of the barriers that define collapsed objects is a constant function of scale. I illustrate the implementation of the excursion set approach for barriers of arbitrary shape. One such application is the now well-known improvement of the excursion set mass function derived from the "moving" barrier for ellipsoidal collapse. I also emphasize that the statement that halo accretion histories are independent of halo environment in the excursion set approach is not a general prediction of the theory. It is a simplifying assumption. I review the method for constructing correlated random walks of the density field in the more general case. I construct a simple toy model to illustrate that excursion set

Special Features of Galactic Dynamics

NASA Astrophysics Data System (ADS)

Efthymiopoulos, Christos; Voglis, Nikos; Kalapotharakos, Constantinos

This is an introductory article to some basic notions and currently open problems of galactic dynamics. The focus is on topics mostly relevant to the so-called `new methods' of celestial mechanics or Hamiltonian dynamics, as applied to the ellipsoidal components of galaxies, i.e., to the elliptical galaxies and to the dark halos and bulges of disk galaxies. Traditional topics such as Jeans theorem, the role of a `third integral' of motion, Nekhoroshev theory, violent relaxation, and the statistical mechanics of collisionless stellar systems are first discussed. The emphasis is on modern extrapolations of these old topics. Recent results from orbital and global dynamical studies of galaxies are then shortly reviewed. The role of various families of orbits in supporting self-consistency, as well as the role of chaos in galaxies, are stressed. A description is then given of the main numerical techniques of integration of the N-body problem in the framework of stellar dynamics and of the results obtained via N-Body experiments. A final topic is the secular evolution and self-organization of galactic systems.

Modelling of Lyman-alpha emitting galaxies and ionized bubbles at the epoch of reionization

NASA Astrophysics Data System (ADS)

Yajima, Hidenobu; Sugimura, Kazuyuki; Hasegawa, Kenji

2018-07-01

Understanding {Ly{α}} emitting galaxies (LAEs) can be a key to reveal cosmic reionization and galaxy formation in the early Universe. Based on halo merger trees and {Ly{α}} radiation transfer calculations, we model redshift evolution of LAEs and their observational properties at z ≥ 6. We consider ionized bubbles associated with individual LAEs and IGM (integer-galactic medium) transmission of {Ly{α}} photons. We find that {Ly{α}} luminosity tightly correlates with halo mass and stellar mass, while the relation with star formation rate has a large dispersion. Comparing our models with the observed luminosity function by Konno et al., we suggest that LAEs at z ˜ 7 have galactic wind of V_out ≳ 100 km s^{-1} and H I column density of N_HI ≳ 10^{20} cm^{-2}. Number density of bright LAEs rapidly decreases as redshift increases, due to both lower star formation rate and smaller H II bubbles. Our model predicts future wide deep surveys with next-generation telescopes, such as James Webb Space Telescope, European Extremely Large Telescope, and Thirty Metre Telescope, can detect LAEs at z ˜ 10 with a number density of n_LAE ˜ {a few } × 10^{-6} Mpc^{-3} for the flux sensitivity of 10^{-18} erg cm^{-2} s^{-1}. When giant H II bubbles are formed by clustering LAEs, the number density of observable LAEs can increase by a factor of few. By combining these surveys with future 21-cm observations, it could be possible to detect both LAEs with L_{Lyα }≳ 10^{42} erg s^{-1} and their associated giant H II bubbles with the size {≳ } 250 kpc at z ˜ 10.

The MUSE Hubble Ultra Deep Field Survey. VIII. Extended Lyman-α haloes around high-z star-forming galaxies

NASA Astrophysics Data System (ADS)

Leclercq, Floriane; Bacon, Roland; Wisotzki, Lutz; Mitchell, Peter; Garel, Thibault; Verhamme, Anne; Blaizot, Jérémy; Hashimoto, Takuya; Herenz, Edmund Christian; Conseil, Simon; Cantalupo, Sebastiano; Inami, Hanae; Contini, Thierry; Richard, Johan; Maseda, Michael; Schaye, Joop; Marino, Raffaella Anna; Akhlaghi, Mohammad; Brinchmann, Jarle; Carollo, Marcella

2017-11-01

We report the detection of extended Lyα haloes around 145 individual star-forming galaxies at redshifts 3 ≤ z ≤ 6 in the Hubble Ultra Deep Field observed with the Multi-Unit Spectroscopic Explorer (MUSE) at ESO-VLT. Our sample consists of continuum-faint (- 15 ≥ MUV ≥ -22) Lyα emitters (LAEs). Using a 2D, two-component (continuum-like and halo) decomposition of Lyα emission assuming circular exponential distributions, we measure scale lengths and luminosities of Lyα haloes. We find that 80% of our objects having reliable Lyα halo measurements show Lyα emission that is significantly more extended than the UV continuum detected by HST (by a factor ≈4 to >20). The median exponential scale length of the Lyα haloes in our sample is ≈4.5 kpc with a few haloes exceeding 10 kpc. By comparing the maximal detected extent of the Lyα emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Lyα emission of our selected sample of Lyα emitters probes a significant portion of the cold circum-galactic medium of these galaxies (>50% in average). This result therefore shows that there must be significant HI reservoirs in the circum-galactic medium and reinforces the idea that Lyα haloes are ubiquitous around high-redshift Lyα emitting galaxies. Our characterization of the Lyα haloes indicates that the majority of the Lyα flux comes from the halo (≈65%) and that their scale lengths seem to be linked to the UV properties of the galaxies (sizes and magnitudes). We do not observe a significant Lyα halo size evolution with redshift, although our sample for z> 5 is very small. We also explore the diversity of the Lyα line profiles in our sample and we find that the Lyα lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km s-1. While the FWHM does not seem to be correlated to the Lyα scale length, most compact Lyα haloes and those that are not detected with high significance tend

The impact of feedback and the hot halo on the rates of gas accretion on to galaxies

NASA Astrophysics Data System (ADS)

Correa, Camila A.; Schaye, Joop; van de Voort, Freeke; Duffy, Alan R.; Wyithe, J. Stuart B.

2018-07-01

We investigate the physics that drives the gas accretion rates on to galaxies at the centres of dark matter haloes using the EAGLE suite of hydrodynamical cosmological simulations. We find that at redshifts z ≤ 2, the accretion rate on to the galaxy increases with halo mass in the halo mass range 1010-1011.7 M⊙, flattens between the halo masses 1011.7 and 1012.7 M⊙, and increases again for higher mass haloes. However, the galaxy gas accretion does not flatten at intermediate halo masses when active galactic nucleus (AGN) feedback is switched off. To better understand these trends, we develop a physically motivated semi-analytic model of galaxy gas accretion. We show that the flattening is produced by the rate of gas cooling from the hot halo. The ratio of the cooling radius and the virial radius does not decrease continuously with increasing halo mass as generally thought. While it decreases up to ˜1013 M⊙ haloes, it increases for higher halo masses, causing an upturn in the galaxy gas accretion rate. This may indicate that in high-mass haloes, AGN feedback is not sufficiently efficient. When there is no AGN feedback, the density of the hot halo is higher, the ratio of the cooling and virial radii does not decrease as much, and the cooling rate is higher. Changes in the efficiency of stellar feedback can also increase or decrease the accretion rates on to galaxies. The trends can plausibly be explained by the re-accretion of gas ejected by progenitor galaxies and by the suppression of black hole growth, and hence AGN feedback, by stellar feedback.

Mapping stellar content to dark matter haloes - III. Environmental dependence and conformity of galaxy colours

NASA Astrophysics Data System (ADS)

Zu, Ying; Mandelbaum, Rachel

2018-05-01

Recent studies suggest that the quenching properties of galaxies are correlated over several megaparsecs. The large-scale `galactic conformity' phenomenon around central galaxies has been regarded as a potential signature of `galaxy assembly bias' or `pre-heating', both of which interpret conformity as a result of direct environmental effects acting on galaxy formation. Building on the iHOD halo quenching framework developed in Zu and Mandelbaum, we discover that our fiducial halo mass quenching model, without any galaxy assembly bias, can successfully explain the overall environmental dependence and the conformity of galaxy colours in Sloan Digital Sky Survey, as measured by the mark correlation functions of galaxy colours and the red galaxy fractions around isolated primaries, respectively. Our fiducial iHOD halo quenching mock also correctly predicts the differences in the spatial clustering and galaxy-galaxy lensing signals between the more versus less red galaxy subsamples, split by the red-sequence ridge line at fixed stellar mass. Meanwhile, models that tie galaxy colours fully or partially to halo assembly bias have difficulties in matching all these observables simultaneously. Therefore, we demonstrate that the observed environmental dependence of galaxy colours can be naturally explained by the combination of (1) halo quenching and (2) the variation of halo mass function with environment - an indirect environmental effect mediated by two separate physical processes.

Search for γ -Ray Line Signals from Dark Matter Annihilations in the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

NASA Astrophysics Data System (ADS)

Abdallah, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Angüner, E. O.; Arakawa, M.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Becker Tjus, J.; Berge, D.; Bernhard, S.; Bernlöhr, K.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bonnefoy, S.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Büchele, M.; Bulik, T.; Capasso, M.; Caroff, S.; Carosi, A.; Carr, J.; Casanova, S.; Cerruti, M.; Chakraborty, N.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Colafrancesco, S.; Condon, B.; Conrad, J.; Davids, I. D.; Decock, J.; Deil, C.; Devin, J.; deWilt, P.; Dirson, L.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O'C.; Dutson, K.; Dyks, J.; Edwards, T.; Egberts, K.; Eger, P.; Emery, G.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gallant, Y. A.; Garrigoux, T.; Gaté, F.; Giavitto, G.; Giebels, B.; Glawion, D.; Glicenstein, J. F.; Gottschall, D.; Grondin, M.-H.; Hahn, J.; Haupt, M.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holch, T. L.; Holler, M.; Horns, D.; Ivascenko, A.; Iwasaki, H.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katsuragawa, M.; Katz, U.; Kerszberg, D.; Khangulyan, D.; Khélifi, B.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Liu, R.; Lohse, T.; Lorentz, M.; López-Coto, R.; Lypova, I.; Malyshev, D.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Mohrmann, L.; Morâ, K.; Moulin, E.; Murach, T.; Nakashima, S.; de Naurois, M.; Ndiyavala, H.; Niederwanger, F.; Niemiec, J.; Oakes, L.; O'Brien, P.; Odaka, H.; Ohm, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Pekeur, N. W.; Pelletier, G.; Perennes, C.; Petrucci, P.-O.; Peyaud, B.; Piel, Q.; Pita, S.; Poireau, V.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Rauth, R.; Reimer, A.; Reimer, O.; Renaud, M.; de los Reyes, R.; Rieger, F.; Rinchiuso, L.; Romoli, C.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Saito, S.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schandri, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seglar-Arroyo, M.; Settimo, M.; Seyffert, A. S.; Shafi, N.; Shilon, I.; Shiningayamwe, K.; Simoni, R.; Sol, H.; Spanier, F.; Spir-Jacob, M.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steppa, C.; Sushch, I.; Takahashi, T.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tibaldo, L.; Tiziani, D.; Tluczykont, M.; Trichard, C.; Tsirou, M.; Tsuji, N.; Tuffs, R.; Uchiyama, Y.; van der Walt, J.; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zaborov, D.; Zacharias, M.; Zanin, R.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Zorn, J.; Żywucka, N.; H. E. S. S. Collaboration

2018-05-01

Spectral lines are among the most powerful signatures for dark matter (DM) annihilation searches in very-high-energy γ rays. The central region of the Milky Way halo is one of the most promising targets given its large amount of DM and proximity to Earth. We report on a search for a monoenergetic spectral line from self-annihilations of DM particles in the energy range from 300 GeV to 70 TeV using a two-dimensional maximum likelihood method taking advantage of both the spectral and spatial features of the signal versus background. The analysis makes use of Galactic center observations accumulated over ten years (2004-2014) with the H.E.S.S. array of ground-based Cherenkov telescopes. No significant γ -ray excess above the background is found. We derive upper limits on the annihilation cross section ⟨σ v ⟩ for monoenergetic DM lines at the level of 4 ×10-28 cm3 s-1 at 1 TeV, assuming an Einasto DM profile for the Milky Way halo. For a DM mass of 1 TeV, they improve over the previous ones by a factor of 6. The present constraints are the strongest obtained so far for DM particles in the mass range 300 GeV-70 TeV. Ground-based γ -ray observations have reached sufficient sensitivity to explore relevant velocity-averaged cross sections for DM annihilation into two γ -ray photons at the level expected from the thermal relic density for TeV DM particles.

Search for γ-Ray Line Signals from Dark Matter Annihilations in the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

PubMed

Abdallah, H; Abramowski, A; Aharonian, F; Ait Benkhali, F; Angüner, E O; Arakawa, M; Arrieta, M; Aubert, P; Backes, M; Balzer, A; Barnard, M; Becherini, Y; Becker Tjus, J; Berge, D; Bernhard, S; Bernlöhr, K; Blackwell, R; Böttcher, M; Boisson, C; Bolmont, J; Bonnefoy, S; Bordas, P; Bregeon, J; Brun, F; Brun, P; Bryan, M; Büchele, M; Bulik, T; Capasso, M; Caroff, S; Carosi, A; Carr, J; Casanova, S; Cerruti, M; Chakraborty, N; Chaves, R C G; Chen, A; Chevalier, J; Colafrancesco, S; Condon, B; Conrad, J; Davids, I D; Decock, J; Deil, C; Devin, J; deWilt, P; Dirson, L; Djannati-Ataï, A; Domainko, W; Donath, A; Drury, L O'C; Dutson, K; Dyks, J; Edwards, T; Egberts, K; Eger, P; Emery, G; Ernenwein, J-P; Eschbach, S; Farnier, C; Fegan, S; Fernandes, M V; Fiasson, A; Fontaine, G; Förster, A; Funk, S; Füßling, M; Gabici, S; Gallant, Y A; Garrigoux, T; Gaté, F; Giavitto, G; Giebels, B; Glawion, D; Glicenstein, J F; Gottschall, D; Grondin, M-H; Hahn, J; Haupt, M; Hawkes, J; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hofmann, W; Hoischen, C; Holch, T L; Holler, M; Horns, D; Ivascenko, A; Iwasaki, H; Jacholkowska, A; Jamrozy, M; Janiak, M; Jankowsky, D; Jankowsky, F; Jingo, M; Jouvin, L; Jung-Richardt, I; Kastendieck, M A; Katarzyński, K; Katsuragawa, M; Katz, U; Kerszberg, D; Khangulyan, D; Khélifi, B; King, J; Klepser, S; Klochkov, D; Kluźniak, W; Komin, Nu; Kosack, K; Krakau, S; Kraus, M; Krüger, P P; Laffon, H; Lamanna, G; Lau, J; Lees, J-P; Lefaucheur, J; Lemière, A; Lemoine-Goumard, M; Lenain, J-P; Leser, E; Liu, R; Lohse, T; Lorentz, M; López-Coto, R; Lypova, I; Malyshev, D; Marandon, V; Marcowith, A; Mariaud, C; Marx, R; Maurin, G; Maxted, N; Mayer, M; Meintjes, P J; Meyer, M; Mitchell, A M W; Moderski, R; Mohamed, M; Mohrmann, L; Morå, K; Moulin, E; Murach, T; Nakashima, S; de Naurois, M; Ndiyavala, H; Niederwanger, F; Niemiec, J; Oakes, L; O'Brien, P; Odaka, H; Ohm, S; Ostrowski, M; Oya, I; Padovani, M; Panter, M; Parsons, R D; Pekeur, N W; Pelletier, G; Perennes, C; Petrucci, P-O; Peyaud, B; Piel, Q; Pita, S; Poireau, V; Poon, H; Prokhorov, D; Prokoph, H; Pühlhofer, G; Punch, M; Quirrenbach, A; Raab, S; Rauth, R; Reimer, A; Reimer, O; Renaud, M; de Los Reyes, R; Rieger, F; Rinchiuso, L; Romoli, C; Rowell, G; Rudak, B; Rulten, C B; Sahakian, V; Saito, S; Sanchez, D A; Santangelo, A; Sasaki, M; Schandri, M; Schlickeiser, R; Schüssler, F; Schulz, A; Schwanke, U; Schwemmer, S; Seglar-Arroyo, M; Settimo, M; Seyffert, A S; Shafi, N; Shilon, I; Shiningayamwe, K; Simoni, R; Sol, H; Spanier, F; Spir-Jacob, M; Stawarz, Ł; Steenkamp, R; Stegmann, C; Steppa, C; Sushch, I; Takahashi, T; Tavernet, J-P; Tavernier, T; Taylor, A M; Terrier, R; Tibaldo, L; Tiziani, D; Tluczykont, M; Trichard, C; Tsirou, M; Tsuji, N; Tuffs, R; Uchiyama, Y; van der Walt, J; van Eldik, C; van Rensburg, C; van Soelen, B; Vasileiadis, G; Veh, J; Venter, C; Viana, A; Vincent, P; Vink, J; Voisin, F; Völk, H J; Vuillaume, T; Wadiasingh, Z; Wagner, S J; Wagner, P; Wagner, R M; White, R; Wierzcholska, A; Willmann, P; Wörnlein, A; Wouters, D; Yang, R; Zaborov, D; Zacharias, M; Zanin, R; Zdziarski, A A; Zech, A; Zefi, F; Ziegler, A; Zorn, J; Żywucka, N

2018-05-18

Spectral lines are among the most powerful signatures for dark matter (DM) annihilation searches in very-high-energy γ rays. The central region of the Milky Way halo is one of the most promising targets given its large amount of DM and proximity to Earth. We report on a search for a monoenergetic spectral line from self-annihilations of DM particles in the energy range from 300 GeV to 70 TeV using a two-dimensional maximum likelihood method taking advantage of both the spectral and spatial features of the signal versus background. The analysis makes use of Galactic center observations accumulated over ten years (2004-2014) with the H.E.S.S. array of ground-based Cherenkov telescopes. No significant γ-ray excess above the background is found. We derive upper limits on the annihilation cross section ⟨σv⟩ for monoenergetic DM lines at the level of 4×10^{-28}  cm^{3} s^{-1} at 1 TeV, assuming an Einasto DM profile for the Milky Way halo. For a DM mass of 1 TeV, they improve over the previous ones by a factor of 6. The present constraints are the strongest obtained so far for DM particles in the mass range 300 GeV-70 TeV. Ground-based γ-ray observations have reached sufficient sensitivity to explore relevant velocity-averaged cross sections for DM annihilation into two γ-ray photons at the level expected from the thermal relic density for TeV DM particles.

Pal 12 - A metal-rich globular cluster in the outer halo

NASA Technical Reports Server (NTRS)

Cohen, J. G.; Frogel, J. A.; Persson, S. E.; Zinn, R.

1980-01-01

New optical and infrared observations of several stars in the distant globular cluster Pal 12 show that they have CO strengths and heavy element abundances only slightly less than in M 71, one of the more metal-rich globular clusters. Pal 12 thus has a metal abundance near the high end of the range over which globular clusters exist and lies in the outer galactic halo. Its red horizontal branch is not anomalous in view of the abundance that has been found.

Galactic center gamma-ray excess from dark matter annihilation: is there a black hole spike?

PubMed

Fields, Brian D; Shapiro, Stuart L; Shelton, Jessie

2014-10-10

If the supermassive black hole Sgr A* at the center of the Milky Way grew adiabatically from an initial seed embedded in a Navarro-Frenk-White dark matter (DM) halo, then the DM profile near the hole has steepened into a spike. We calculate the dramatic enhancement to the gamma-ray flux from the Galactic center (GC) from such a spike if the 1-3 GeV excess observed in Fermi data is due to DM annihilations. We find that for the parameter values favored in recent fits, the point-source-like flux from the spike is 35 times greater than the flux from the inner 1° of the halo, far exceeding all Fermi point source detections near the GC. We consider the dependence of the spike signal on astrophysical and particle parameters and conclude that if the GC excess is due to DM, then a canonical adiabatic spike is disfavored by the data. We discuss alternative Galactic histories that predict different spike signals, including (i) the nonadiabatic growth of the black hole, possibly associated with halo and/or black hole mergers, (ii) gravitational interaction of DM with baryons in the dense core, such as heating by stars, or (iii) DM self-interactions. We emphasize that the spike signal is sensitive to a different combination of particle parameters than the halo signal and that the inclusion of a spike component to any DM signal in future analyses would provide novel information about both the history of the GC and the particle physics of DM annihilations.

Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

DOE PAGES

Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

2017-12-01

Secondary halo bias, commonly known as ‘assembly bias’, is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalomore » properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. Lastly, this results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.« less

Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

NASA Astrophysics Data System (ADS)

Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

2018-03-01

Secondary halo bias, commonly known as `assembly bias', is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalo properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. This results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.

Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

Secondary halo bias, commonly known as ‘assembly bias’, is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalomore » properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. Lastly, this results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.« less

Constraints on the Galactic Halo Dark Matter from Fermi-LAT Diffuse Measurements

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.;

Constraints on the Galactic Halo Dark Matter From FERMI-LAT Diffuse Measurements

DOE PAGES

Ackermann, M.; Ajello, M.; Atwood, W. B.; ...

2012-11-28

For this study, we have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e +/e – produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limitsmore » is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. In conclusion, the resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.« less

IUE observations of blue halo high luminosity stars

NASA Technical Reports Server (NTRS)

Hack, M.; Franco, M. L.; Stalio, R.

1981-01-01

Two high luminosity population II blue stars of high galactic latitude, BD+33 deg 2642 and HD 137569 were observed at high resolution. The stellar spectra show the effect of mass loss in BD+33 deg 2642 and abnormally weak metallic lines in HD 137569. The interstellar lines in the direction of BD+33 deg 2642, which lies at a height z greater than or equal to 6.2 kpc from the galactic plane, are split into two components. No high ionization stages are found at the low velocity component; nor can they be detected in the higher velocity clouds because of mixing with the corresponding stellar/circumstellar lines.

Suzaku and XMM-Newton observations of the North Polar Spur: Charge exchange or ISM absorption?

NASA Astrophysics Data System (ADS)

Gu, Liyi; Mao, Junjie; Costantini, Elisa; Kaastra, Jelle

2016-10-01

By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we discovered that the spectra are inconsistent with the traditional model consisting of pure thermal emission and neutral absorption. The most prominent discrepancies are the enhanced O vii and Ne ix forbidden-to-resonance ratios, and a high O viii Lyβ line relative to other Lyman series. A collisionally ionized absorption model can naturally explain both features, while a charge exchange component can only account for the former. By including the additional ionized absorption, the plasma in the North Polar Spur can be described by a single-phase collisional ionization equilibrium (CIE) component with a temperature of 0.25 keV, and nitrogen, oxygen, neon, magnesium, and iron abundances of 0.4-0.8 solar. The abundance pattern of the North Polar Spur is well in line with those of the Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous studies can be migrated to the large transmission of the O viii Lyα line. The ionized absorber is characterized by a balance temperature of 0.17-0.20 keV and a column density of 3-5 × 1019 cm-2. Based on the derived abundances and absorption, we speculate that the North Polar Spur is a structure in the Galactic halo, so that the emission is mostly absorbed by the Galactic interstellar medium in the line of sight.

Group quenching and galactic conformity at low redshift

NASA Astrophysics Data System (ADS)

Treyer, M.; Kraljic, K.; Arnouts, S.; de la Torre, S.; Pichon, C.; Dubois, Y.; Vibert, D.; Milliard, B.; Laigle, C.; Seibert, M.; Brown, M. J. I.; Grootes, M. W.; Wright, A. H.; Liske, J.; Lara-Lopez, M. A.; Bland-Hawthorn, J.

2018-06-01

We quantify the quenching impact of the group environment using the spectroscopic survey Galaxy and Mass Assembly to z ˜ 0.2. The fraction of red (quiescent) galaxies, whether in groups or isolated, increases with both stellar mass and large-scale (5 Mpc) density. At fixed stellar mass, the red fraction is on average higher for satellites of red centrals than of blue (star-forming) centrals, a galactic conformity effect that increases with density. Most of the signal originates from groups that have the highest stellar mass, reside in the densest environments, and have massive, red only centrals. Assuming a colour-dependent halo-to-stellar-mass ratio, whereby red central galaxies inhabit significantly more massive haloes than blue ones of the same stellar mass, two regimes emerge more distinctly: at log (Mhalo/M⊙) ≲ 13, central quenching is still ongoing, conformity is no longer existent, and satellites and group centrals exhibit the same quenching excess over field galaxies at all mass and density, in agreement with the concept of `group quenching'; at log (Mh/M⊙) ≳ 13, a cut-off that sets apart massive (log (M⋆/M⊙) > 11), fully quenched group centrals, conformity is meaningless, and satellites undergo significantly more quenching than their counterparts in smaller haloes. The latter effect strongly increases with density, giving rise to the density-dependent conformity signal when both regimes are mixed. The star formation of blue satellites in massive haloes is also suppressed compared to blue field galaxies, while blue group centrals and the majority of blue satellites, which reside in low-mass haloes, show no deviation from the colour-stellar mass relation of blue field galaxies.

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

DOE PAGES

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; ...

2018-02-26

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 couldmore » 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.« less

Changing Amplitudes: Detecting RR Lyrae Light Curve Shape Variations in the Galactic Disk and Inner Halo

NASA Astrophysics Data System (ADS)

De Lee, Nathan M.; Kinemuchi, K.; Pepper, J.; Rodriguez, J. E.

2014-01-01

In this poster we will discuss our ongoing program to use extant light curves from the Kilodegree Extremely Little Telescope (KELT) survey to find and characterize RR Lyrae (RRL) stars in the disk and inner halo of the Milky Way. RRL stars are of particular interest because they are standard candles and can be used to map out structure in the galaxy. The periods and shape of RRL light curves also contain information about their Oosterhoff type, which can probe galactic formation history, and metallicity respectively. Although there have been several large photometric surveys for RR Lyrae in the nearby galaxy (OGLE, NSVS, ASAS, and MACHO to name a few), they have each been limited in either sky coverage or number of epochs. The KELT survey represents a new generation of surveys that has many epochs over a large portion of the sky. KELT samples 60% of the sky in both northern and southern hemispheres, and has a long-time-baseline of 4-8 years with a very high cadence rate of less than 20 minutes. This translates into 4,000 to 9,000 epochs per light curve with completeness out to 3 kpc from the Sun. Recent results from both Kepler and ground based surveys results suggest that as many as 50% of RR Lyrae stars show long-term modulation of their light curve shapes (Blazhko effect). These stars combined with RRL stars that pulsate in more than one mode give a sample of objects that the KELT survey is uniquely suited to explore. This poster concentrates on a pilot project to examine RRL stars in a limited number of KELT fields. In particular, we focus on, detecting RR Lyrae, developing a light curve shape-metallicity relationship in the KELT band-pass, and some initial characterization of RRL with either amplitude-modulated or period-modulated light curves.

High-velocity gas toward the LMC resides in the Milky Way halo

NASA Astrophysics Data System (ADS)

Richter, P.; de Boer, K. S.; Werner, K.; Rauch, T.

2015-12-01

Aims: To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud, (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d = 9.2+4.1-7.2 kpc distance. Methods: We study the velocity-component structure of low and intermediate metal ions (C ii, Si ii, Si iii) in the spectrum of RX J0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST), and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the nearby LMC star Sk -69 59 and with H i 21 cm data from the Leiden-Argentina-Bonn (LAB) survey. Results: Metal absorption toward RX J0439.8-6809 is unambiguously detected in three different velocity components near vLSR = 0, + 60, and + 150 km s-1. The presence of absorption proves that all three gas components are situated in front of the star, thus located in the disk and inner halo of the Milky Way. For the high-velocity cloud (HVC) at vLSR = + 150 km s-1, we derive an oxygen abundance of [O/H] =-0.63 (~0.2 solar) from the neighboring Sk -69 59 sight line, in accordance with previous abundance measurements for this HVC. From the observed kinematics we infer that the HVC hardly participates in the Galactic rotation. Conclusions: Our study shows that the HVC toward the LMC represents a Milky Way halo cloud that traces low column density gas with relatively low metallicity. We rule out scenarios in which the HVC represents material close to the LMC that stems from a LMC outflow.

THE DEARTH OF NEUTRAL HYDROGEN IN GALACTIC DWARF SPHEROIDAL GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spekkens, Kristine; Urbancic, Natasha; Mason, Brian S.

We present new upper limits on the neutral hydrogen (H I) content within the stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with the Green Bank Telescope (GBT) as well as Arecibo L-band Fast ALFA survey and Galactic All-Sky Survey data. All of the limits M{sub H} {sub I}{sup lim} are more stringent than previously reported values, and those from the GBT improve upon constraints in the literature by a median factor of 23. Normalizing by V-band luminosity L{sub V} and dynamical mass M {sub dyn}, we find M{sub H} {sub I}{sup lim}/L{sub V}∼10{supmore » −3} M{sub ⊙}/L{sub ⊙} and M{sub H} {sub I}{sup lim}/M{sub dyn}∼5×10{sup −5}, irrespective of location in the Galactic halo. Comparing these relative H I contents to those of the Local Group and nearby neighbor dwarfs compiled by McConnachie, we find that the Galactic dSphs are extremely gas-poor. Our H I upper limits therefore provide the clearest picture yet of the environmental dependence of the H I content in Local Volume dwarfs. If ram pressure stripping explains the dearth of H I in these systems, then orbits in a relatively massive Milky Way are favored for the outer halo dSph Leo I, while Leo II and Canes Venatici I have had a pericentric passage in the past. For Draco and Ursa Minor, the interstellar medium mass that should accumulate through stellar mass loss in between pericentric passages exceeds M{sub H} {sub I}{sup lim} by a factor of ∼30. In Ursa Minor, this implies that either this material is not in the atomic phase, or that another mechanism clears the recycled gas on shorter timescales.« less

Galactic cosmic ray antiprotons and supersymmetry

NASA Technical Reports Server (NTRS)

Stecker, F. W.; Walsh, T.; Rudaz, S.

1985-01-01

The physics of the annihilation of photinos is considered as a function of mass in detail, in order to obtain the energy spectra of the cosmic ray antiprotons produced under the assumption that photinos make up the missing mass in the galactic halo. The modulated spectrum is at 1 a.w. with the cosmic ray antiprotons data. A very intriguing fit is obtained to all of the present antiprotons up to 13.4 GeV data for similar to 15 GeV. A cutoff is predicted in the antiprotons spectrum at E = photino mass above which only a small flux from secondary production should remain.

Evolution of heavy-element abundances in the Galactic halo and disk

NASA Technical Reports Server (NTRS)

Mathews, G. J.; Cowan, J. J.; Schramm, D. N.

1988-01-01

The constraints on the universal energy density and cosmological constant from cosmochronological ages and the Hubble age are reviewed. Observational evidence for the galactic chemical evolution of the heavy-element chronometers is descirbed in the context of numerical models. The viability of the recently discovered Th/Nd stellar chronometer is discussed, along with the suggestion that high r-process abundances in metal-poor stars may have resulted from a primordial r-process, as may be required by some inhomogeneous cosmologies.

Density diagnostics of ionized outflows in active galactic nuclei. X-ray and UV absorption lines from metastable levels in Be-like to C-like ions

NASA Astrophysics Data System (ADS)

Mao, Junjie; Kaastra, J. S.; Mehdipour, M.; Raassen, A. J. J.; Gu, Liyi; Miller, J. M.

2017-11-01

Context. Ionized outflows in active galactic nuclei (AGNs) are thought to influence their nuclear and local galactic environment. However, the distance of the outflows with respect to the central engine is poorly constrained, which limits our understanding of their kinetic power as a cosmic feedback channel. Therefore, the impact of AGN outflows on their host galaxies is uncertain. However, when the density of the outflows is known, their distance can be immediately obtained from their modeled ionization parameters. Aims: We perform a theoretical study of density diagnostics of ionized outflows using absorption lines from metastable levels in Be-like to C-like cosmic abundant ions. Methods: With the new self-consistent PhotoIONization (PION) model in the SPEX code, we are able to calculate detailed level populations, including the ground and metastable levels. This enables us to determine under what physical conditions the metastable levels are significantly populated. We then identify characteristic lines from these metastable levels in the 1-2000 Å wavelength range. Results: In the broad density range of nH ∈ (106, 1020) m-3, the metastable levels 2s2p (3P0-2) in Be-like ions can be significantly populated. For B-like ions, merely the first excited level 2s22p (2P3/2) can be used as a density probe. For C-like ions, the first two excited levels 2s22p2 (3P1 and 3P2) are better density probes than the next two excited levels 2s22p2 (1S0 and 1D2). Different ions in the same isoelectronic sequence cover not only a wide range of ionization parameters, but also a wide range of density values. On the other hand, within the same isonuclear sequence, those less ionized ions probe lower density and smaller ionization parameters. Finally, we reanalyzed the high-resolution grating spectra of NGC 5548 observed with Chandra in January 2002 using a set of PION components to account for the ionized outflow. We derive lower (or upper) limits of plasma density in five out of

Beta Dips in the Gaia Era: Simulation Predictions of the Galactic Velocity Anisotropy Parameter (β) for Stellar Halos

NASA Astrophysics Data System (ADS)

Loebman, Sarah R.; Valluri, Monica; Hattori, Kohei; Debattista, Victor P.; Bell, Eric F.; Stinson, Greg; Christensen, Charlotte R.; Brooks, Alyson; Quinn, Thomas R.; Governato, Fabio

2018-02-01

The velocity anisotropy parameter, β, is a measure of the kinematic state of orbits in the stellar halo, which holds promise for constraining the merger history of the Milky Way (MW). We determine global trends for β as a function of radius from three suites of simulations, including accretion-only and cosmological hydrodynamic simulations. We find that the two types of simulations are consistent and predict strong radial anisotropy (< β > ∼ 0.7) for Galactocentric radii greater than 10 kpc. Previous observations of β for the MW’s stellar halo claim a detection of an isotropic or tangential “dip” at r ∼ 20 kpc. Using the N-body+SPH simulations, we investigate the temporal persistence, population origin, and severity of “dips” in β. We find that dips in the in situ stellar halo are long-lived, while dips in the accreted stellar halo are short-lived and tied to the recent accretion of satellite material. We also find that a major merger as early as z ∼ 1 can result in a present-day low (isotropic to tangential) value of β over a broad range of radii and angles. While all of these mechanisms are plausible drivers for the β dip observed in the MW, each mechanism in the simulations has a unique metallicity signature associated with it, implying that future spectroscopic surveys could distinguish between them. Since an accurate knowledge of β(r) is required for measuring the mass of the MW halo, we note that significant transient dips in β could cause an overestimate of the halo’s mass when using spherical Jeans equation modeling.

Life in the Outer Limits: Insight into Hierarchical Merging from the Outermost Structure of the Andromeda Stellar Halo

NASA Astrophysics Data System (ADS)

Beaton, Rachael; Majewski, S. R.; Patterson, R. J.; Guhathakurta, P.; Gilbert, K.; Kalirai, J. S.; Tollerud, E. J.; SPLASH Team

2014-01-01

Owing to their large dynamical timescales, the stellar haloes of Milky Way (MW) sized galaxies represent ideal environments to test modern theories of galaxy formation in the Lambda-CDM paradigm. Only in stellar haloes can the remnants of hierarchical accretion be preserved over long timescales as in-tact dwarf satellites or as tidal debris and can be easily distinguished from the underlying smooth structure. Stellar haloes, however, remain some of the most difficult galactic structures to constrain due to their large angular extent and extremely low surface brightness. Thus, the basic properties of stellar haloes -- the overall stellar distribution, substructure fraction, global kinematics and detailed stellar content -- remained relatively unconstrained. In this thesis, we present several projects designed to understand the current structure and the the formation of the Andromeda (M31) stellar halo, the only stellar halo -- besides our own -- that is within reach of current ground based facilities on the large scale required to constrain the basic properties of stellar haloes. First, we describe a seven season imaging campaign comprising the backbone of the Spectroscopic and Photometric Landscape of the Andromeda Stellar Halo (SPLASH) program. This survey is unique in its application of the Washington + DDO51 filter system to select individual M31 RGB stars without spectroscopic follow up. Second, we use the SPLASH photometric survey to identify sample of halo stars at projected radii of 120 kpc, for which we have obtained spectroscopic follow-up. Third, we add this large radius sample to the existing spectroscopic results from SPLASH, and use this unique sample to explore the stellar kinematics of the halo at large radii with full azimuthal coverage. Lastly, we preview on-going work to constrain the formation of the Andromeda stellar halo, using both in-tact satellites and resolved M31 halo members as tracers of its accretion history.

Haloes gone MAD: The Halo-Finder Comparison Project

NASA Astrophysics Data System (ADS)

Knebe, Alexander; Knollmann, Steffen R.; Muldrew, Stuart I.; Pearce, Frazer R.; Aragon-Calvo, Miguel Angel; Ascasibar, Yago; Behroozi, Peter S.; Ceverino, Daniel; Colombi, Stephane; Diemand, Juerg; Dolag, Klaus; Falck, Bridget L.; Fasel, Patricia; Gardner, Jeff; Gottlöber, Stefan; Hsu, Chung-Hsing; Iannuzzi, Francesca; Klypin, Anatoly; Lukić, Zarija; Maciejewski, Michal; McBride, Cameron; Neyrinck, Mark C.; Planelles, Susana; Potter, Doug; Quilis, Vicent; Rasera, Yann; Read, Justin I.; Ricker, Paul M.; Roy, Fabrice; Springel, Volker; Stadel, Joachim; Stinson, Greg; Sutter, P. M.; Turchaninov, Victor; Tweed, Dylan; Yepes, Gustavo; Zemp, Marcel

2011-08-01

We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends, spherical-overdensity and phase-space-based algorithms. We further introduce a robust (and publicly available) suite of test scenarios that allow halo finder developers to compare the performance of their codes against those presented here. This set includes mock haloes containing various levels and distributions of substructure at a range of resolutions as well as a cosmological simulation of the large-scale structure of the universe. All the halo-finding codes tested could successfully recover the spatial location of our mock haloes. They further returned lists of particles (potentially) belonging to the object that led to coinciding values for the maximum of the circular velocity profile and the radius where it is reached. All the finders based in configuration space struggled to recover substructure that was located close to the centre of the host halo, and the radial dependence of the mass recovered varies from finder to finder. Those finders based in phase space could resolve central substructure although they found difficulties in accurately recovering its properties. Through a resolution study we found that most of the finders could not reliably recover substructure containing fewer than 30-40 particles. However, also here the phase-space finders excelled by resolving substructure down to 10-20 particles. By comparing the halo finders using a high-resolution cosmological volume, we found that they agree remarkably well on fundamental properties of astrophysical significance (e.g. mass, position, velocity and peak of the rotation curve). We further suggest to utilize the peak of the rotation curve, vmax, as a proxy for mass, given the arbitrariness in defining a proper halo edge. Airport code for Madrid, Spain

Galactic Disk Winds Driven by Cosmic Ray Pressure

NASA Astrophysics Data System (ADS)

Mao, S. Alwin; Ostriker, Eve C.

2018-02-01

Cosmic ray pressure gradients transfer energy and momentum to extraplanar gas in disk galaxies, potentially driving significant mass loss as galactic winds. This may be particularly important for launching high-velocity outflows of “cool” (T ≲ 104 K) gas. We study cosmic ray-driven disk winds using a simplified semi-analytic model assuming streamlines follow the large-scale gravitational potential gradient. We consider scaled Milky Way–like potentials including a disk, bulge, and halo with a range of halo velocities V H = 50–300 km s-1 and streamline footpoints with radii in the disk R 0 = 1–16 kpc at a height of 1 kpc. Our solutions cover a wide range of footpoint gas velocity u 0, magnetic–to–cosmic ray pressure ratio, gas–to–cosmic ray pressure ratio, and angular momentum. Cosmic ray streaming at the Alfvén speed enables the effective sound speed C eff to increase from the footpoint to a critical point where C eff,c = u c ∼ V H; this differs from thermal winds, in which C eff decreases outward. The critical point is typically at a height of 1–6 kpc from the disk, increasing with V H, and the asymptotic wind velocity exceeds the escape speed of the halo. Mass-loss rates are insensitive to the footpoint values of the magnetic field and angular momentum. In addition to numerical parameter space exploration, we develop and compare to analytic scaling relations. We show that winds have mass-loss rates per unit area up to \\dot{Σ}∼ Π0VH-5/3u02/3, where Π0 is the footpoint cosmic ray pressure and u 0 is set by the upwelling of galactic fountains. The predicted wind mass-loss rate exceeds the star formation rate for V H ≲ 200 km s-1 and u 0 = 50 km s-1, a typical fountain velocity.

Detecting dark matter with imploding pulsars in the galactic center.

PubMed

Bramante, Joseph; Linden, Tim

2014-11-07

The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.

The PAndAS Field of Streams: Stellar Structures in the Milky Way Halo toward Andromeda and Triangulum

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael; Collins, Michelle L. M.; Fardal, Mark A.; Irwin, Michael J.; Lewis, Geraint F.; McConnachie, Alan W.; Babul, Arif; Bate, Nicholas F.; Chapman, Scott C.; Conn, Anthony R.; Crnojević, Denija; Ferguson, Annette M. N.; Mackey, A. Dougal; Navarro, Julio F.; Peñarrubia, Jorge; Tanvir, Nial T.; Valls-Gabaud, David

2014-05-01

We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ~5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ~17 kpc. With a surface brightness of Σ V ~ 32-32.5 mag arcsec-2, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s-1 at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.

The PAndAS field of streams: Stellar structures in the milky way halo toward Andromeda and Triangulum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael

We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ∼5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ∼17more » kpc. With a surface brightness of Σ {sub V} ∼ 32-32.5 mag arcsec{sup –2}, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s{sup –1} at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.« less

Shining a light on star formation driven outflows: the physical conditions within galactic outflows

NASA Astrophysics Data System (ADS)

Chisholm, John P.; Tremonti, Christina A.; Leitherer, Claus; Wofford, Aida; Chen, Yanmei

2016-01-01

Stellar feedback drives energy and momentum into the surrounding gas, which drives gas and metals out of galaxies through a galactic outflow. Unfortunately, galactic outflows are difficult to observe and characterize because they are extremely diffuse, and contain gas at many different temperatures. Here we present results from a sample of 37 nearby (z < 0.27) star forming galaxies observed in the ultraviolet with the Cosmic Origins Spectrograph on the Hubble Space Telescope. The sample covers over three decades in stellar mass and star formation rate, probing different morphologies such as dwarf irregulars and high-mass merging systems. Using four different UV absorption lines (O I, Si II, Si III and Si IV) that trace a wide range of temperatures (ionization potentials between 13.6 eV and 45 eV), we find shallow correlations between the outflow velocity or the equivalent width of absorption lines with stellar mass or star formation rate. Absorption lines probing different temperature phases have similar centroid velocities and line widths, indicating that they are comoving. Using the equivalent width ratios of the four different transitions, we find the ratios to be consistent with photo-ionized outflows, with moderately strong ionization parameters. By constraining the ionization mechanism we model the ionization fractions for each transition, but find the ionization fractions depend crucially on input model parameters. The shallow velocity scalings imply that low-mass galaxies launch outflows capable of escaping their galactic potential, while higher mass galaxies retain all of their gas, unless they undergo a merger.

Finding Distant Galactic HII Regions

NASA Astrophysics Data System (ADS)

Anderson, L. D.; Armentrout, W. P.; Johnstone, B. M.; Bania, T. M.; Balser, Dana S.; Wenger, Trey V.; Cunningham, V.

2015-12-01

The WISE Catalog of Galactic H ii Regions contains ˜2000 H ii region candidates lacking ionized gas spectroscopic observations. All candidates have the characteristic H ii region mid-infrared morphology of WISE 12 μ {{m}} emission surrounding 22 μ {{m}} emission, and additionally have detected radio continuum emission. We here report Green Bank Telescope hydrogen radio recombination line and radio continuum detections in the X-band (9 GHz; 3 cm) of 302 WISE H ii region candidates (out of 324 targets observed) in the zone 225^\\circ ≥slant {\\ell }≥slant -20^\\circ , | {\\text{}}b| ≤slant 6^\\circ . Here we extend the sky coverage of our H ii region Discovery Survey, which now contains nearly 800 H ii regions distributed across the entire northern sky. We provide LSR velocities for the 302 detections and kinematic distances for 131 of these. Of the 302 new detections, 5 have ({\\ell },{\\text{}}b,v) coordinates consistent with the Outer Scutum-Centaurus Arm (OSC), the most distant molecular spiral arm of the Milky Way. Due to the Galactic warp, these nebulae are found at Galactic latitudes >1° in the first Galactic quadrant, and therefore were missed in previous surveys of the Galactic plane. One additional region has a longitude and velocity consistent with the OSC but lies at a negative Galactic latitude (G039.183-01.422 -54.9 {km} {{{s}}}-1). With Heliocentric distances >22 kpc and Galactocentric distances >16 kpc, the OSC H ii regions are the most distant known in the Galaxy. We detect an additional three H ii regions near {\\ell }≃ 150^\\circ whose LSR velocities place them at Galactocentric radii >19 kpc. If their distances are correct, these nebulae may represent the limit to Galactic massive star formation.

Halo Nuclei

NASA Astrophysics Data System (ADS)

Al-Khalili, Jim

2017-10-01

While neutron halos were discovered 30 years ago, this is the first book written on the subject of this exotic form of nuclei that typically contain many more neutrons than stable isotopes of those elements. It provides an introductory description of the halo and outlines the discovery and evidence for its existence. It also discusses different theoretical models of the halo's structure as well as models and techniques in reaction theory that have allowed us to study the halo. This is written at the graduate student (starting at PhD) level. The author of the book, Jim Al-Khalili, is a theoretician who published some of the key papers on the structure of the halo in the mid and late 90s and was the first to determine its true size. This monograph is based on review articles he has written on the mathematical models used to determine the halo structure and the reactions used to model that structure.

Results from the MACHO Galactic Pixel Lensing Search

NASA Astrophysics Data System (ADS)

Drake, Andrew J.; Minniti, Dante; Alcock, Charles; Allsman, Robyn A.; Alves, David; Axelrod, Tim S.; Becker, Andrew C.; Bennett, David; Cook, Kem H.; Freeman, Ken C.; Griest, Kim; Lehner, Matt; Marshall, Stuart; Peterson, Bruce; Pratt, Mark; Quinn, Peter; Rodgers, Alex; Stubbs, Chris; Sutherland, Will; Tomaney, Austin; Vandehei, Thor; Welch, Doug L.

The MACHO, EROS, OGLE and AGAPE collaborations have been studying nature of the galactic halo for a number of years using microlensing events. The MACHO group undertakes observations of the LMC, SMC and Galactic Bulge monitoring the light curves of millions of stars to detect microlensing. Most of these fields are crowded to the extent that all the monitored stars are blended. Such crowding makes the performance of accurate photometry difficult. We apply the new technique of Difference Image Analysis (DIA) on archival data to improve the photometry and increase both the detection sensitivity and effective search area. The application of this technique also allows us to detect so called `pixel lensing' events. These are microlensing events where the source star is only detectable during lensing. The detection of these events will allow us to make a large increase in the number of detected microlensing events. We present a light curve demonstrating the detection of a pixel lensing event with this technique.

Dark-Matter Halos of Tenuous Galaxies

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-03-01

A series of recent deep-imaging surveys has revealed dozens of lurking ultra-diffuse galaxies (UDGs) in nearby galaxy clusters. A new study provides key information to help us understand the origins of these faint giants.What are UDGs?There are three main possibilities for how UDGs galaxies with the sizes of giants, but luminosities no brighter than those of dwarfs formed:They are tidal dwarfs, created in galactic collisions when streams of matter were pulled away from the parent galaxies and halos to form dwarfs.They are descended from normal galaxies and were then altered by tidal interactions with the galaxy cluster.They are ancient remnant systems large galaxies whose gas was swept away, putting an early halt to star formation. The gas removal did not, however, affect their large dark matter halos, which permitted them to survive in the cluster environment.The key to differentiating between these options is to obtain mass measurements for the UDGs how large are their dark matter halos? In a recent study led by Michael Beasley (Institute of Astrophysics of the Canary Islands, University of La Laguna), a team of astronomers has determined a clever approach for measuring these galaxies masses: examine their globular clusters.Masses from Globular ClustersVCC 1287s mass measurements put it outside of the usual halo-mass vs. stellar-mass relationships for nearby galaxies: it has a significantly higher halo mass than is normal, given its stellar mass. [Adapted from Beasley et al. 2016]Beasley and collaborators selected one UDG, VCC 1287, from the Virgo galaxy cluster, and they obtained spectra of the globular clusters around it using the OSIRIS spectrograph on the Great Canary Telescope. They then determined VCC 1287s total halo mass in two ways: first by using the dynamics of the globular clusters, and then by relying on a relation between total globular cluster mass and halo mass.The two masses they found are in good agreement with each other; both are around 80

The great galactic centre mystery

NASA Technical Reports Server (NTRS)

Riegler, G. R.

1982-01-01

Gamma-ray observations of the center of the Galaxy show a varying positron-electron annihilation radiation emission, while at radio wavelengths a non-thermal compact source surrounded by ionized gas moving at high velocities can be seen. Line emission maps for atomic and ionized hydrogen and molecular gas suggest gas expulsion and a massive collapsed object. IR observations show that ionized gas in the central few parsecs of the Galactic center is concentrated in at least 14 small clouds. Charge-coupled device images show a pair of faint, very red sources within a few arc seconds of IRS 16 and the compact non-thermal radio source. The positron-electron annihilation line emission implies an annihilation rate of 10 to the 43rd per sec, compared with an observed luminosity at IR wavelengths of 10 to the 40 erg per sec. Some models are briefly discussed.

Annihilation physics of exotic galactic dark matter particles

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1990-01-01

Various theoretical arguments make exotic heavy neutral weakly interacting fermions, particularly those predicted by supersymmetry theory, attractive candidates for making up the large amount of unseen gravitating mass in galactic halos. Such particles can annihilate with each other, producing secondary particles of cosmic-ray energies, among which are antiprotons, positrons, neutrinos, and gamma-rays. Spectra and fluxes of these annihilation products can be calculated, partly by making use of positron electron collider data and quantum chromodynamic models of particle production derived therefrom. These spectra may provide detectable signatures of exotic particle remnants of the big bang.

The Lyman-alpha glow of gas falling into the dark matter halo of a z = 3 galaxy.

PubMed

Weidinger, Michael; Møller, Palle; Fynbo, Johan Peter Uldall

2004-08-26

Quasars are the visible signatures of gas falling into the deep potential well of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards their centres. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-alpha line of hydrogen, effectively imaging the DM halo. Here we present a Lyalpha image of a DM halo at redshift z = 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM haloes; we infer a mass of (2 - 7) x 10(12) solar masses (M(\\circ)) for the halo.

The metal-poor stellar halo in RAVE-TGAS and its implications for the velocity distribution of dark matter

NASA Astrophysics Data System (ADS)

Herzog-Arbeitman, Jonah; Lisanti, Mariangela; Necib, Lina

2018-04-01

The local velocity distribution of dark matter plays an integral role in interpreting the results from direct detection experiments. We previously showed that metal-poor halo stars serve as excellent tracers of the virialized dark matter velocity distribution using a high-resolution hydrodynamic simulation of a Milky Way-like halo. In this paper, we take advantage of the first Gaia data release, coupled with spectroscopic measurements from the RAdial Velocity Experiment (RAVE), to study the kinematics of stars belonging to the metal-poor halo within an average distance of ~5 kpc of the Sun. We study stars with iron abundances [Fe/H] < ‑1.5 and ‑1.8 that are located more than 1.5 kpc from the Galactic plane. Using a Gaussian mixture model analysis, we identify the stars that belong to the halo population, as well as some kinematic outliers. We find that both metallicity samples have similar velocity distributions for the halo component, within uncertainties. Assuming that the stellar halo velocities adequately trace the virialized dark matter, we study the implications for direct detection experiments. The Standard Halo Model, which is typically assumed for dark matter, is discrepant with the empirical distribution by ~6σ, predicts fewer high-speed particles, and is anisotropic. As a result, the Standard Halo Model overpredicts the nuclear scattering rate for dark matter masses below ~10 GeV. The kinematic outliers that we identify may potentially be correlated with dark matter substructure, though further study is needed to establish this correspondence.

Sub-MeV bosonic dark matter, misalignment mechanism, and galactic dark matter halo luminosities

NASA Astrophysics Data System (ADS)

Yang, Qiaoli; Di, Haoran

2017-04-01

We explore a scenario that dark matter is a boson condensate created by the misalignment mechanism, in which a spin 0 boson (an axionlike particle) and a spin 1 boson (the dark photon) are considered, respectively. We find that although the sub-MeV dark matter boson is extremely stable, the huge number of dark matter particles in a galaxy halo makes the decaying signal detectable. A galaxy halo is a large structure bounded by gravity with a typical ˜1 012 solar mass, and the majority of its components are made of dark matter. For the axionlike particle case, it decays via ϕ →γ γ , therefore the photon spectrum is monochromatic. For the dark photon case, it is a three body decay A'→γ γ γ . However, we find that the photon spectrum is heavily peaked at M /2 and thus can facilitate observation. We also suggest a physical explanation for the three body decay spectrum by comparing the physics in the decay of orthopositronium. In addition, for both cases, the decaying photon flux can be measured for some regions of parameter space using current technologies.

To the Galactic Virial Radius with Hyper Suprime-Cam

NASA Astrophysics Data System (ADS)

Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.

2018-01-01

We exploit the exquisite, deep Hyper Suprime-Cam (HSC) imaging data to probe the Galactic halo out to 200 kpc. Using the ∼100 square degree, multiband photometry of the first HSC Wide survey data release, we identify blue horizontal branch (BHB) stars beyond 50 kpc in the halo. The presence of the Sagittarius (Sgr) stream in the HSC fields produces a notable excess of stars at the apocenter of the leading arm (∼50–60 kpc). For fields excluding Sgr, the BHB counts are consistent with a continuation of a ‑4 power law from the inner halo. However, we find that the majority of the non-Sgr BHB stars beyond 50 kpc reside in one 27 square degree HSC field called “VVDS.” Curiously, this field is located close to the Magellanic plane, and we hypothesize that the excess of stars between 50 and 200 kpc could be associated with distant Magellanic debris. Indeed, without the VVDS, there are very few BHBs in the remaining portions of the Galaxy probed by the HSC. Accordingly, this scarcity of tracers is consistent with a significant decline in stellar density beyond 50 kpc, with a power law of ‑4 or steeper.

Massive stellar content of some Galactic supershells

NASA Astrophysics Data System (ADS)

Kaltcheva, Nadejda; Golev, Valeri

2015-08-01

The giant Galactic H II regions provide a unique opportunity to study the OB-star influence on the surrounding interstellar matter. In this contribution, several multi-wavelength surveys (Wisconsin H-α Mapper Northern Sky Survey, Southern H-α Sky Survey Atlas, MSX Mid-IR Galactic Plane Survey, WISE All-Sky Data Release, CO survey of the Milky Way, and the Southern Galactic Plane HI Survey) are combined with available intermediate-band uvbyβ photometry to attempt a precise spatial correlation between the OB-stars and the neutral and ionized material. Our study is focused on the H I supershell GSH 305+01-24 in Centaurus, the Car OB2 supershell, the Cygnus star-forming complex and the GSH 224-01+24 shell toward the GMN 39/Seagull nebula region. We refine the massive stellar content of these star-forming fields and study the energetics of its interaction with the shells’ material.

The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs

NASA Astrophysics Data System (ADS)

Kilic, Mukremin; Munn, Jeffrey A.; Harris, Hugh C.; von Hippel, Ted; Liebert, James W.; Williams, Kurtis A.; Jeffery, Elizabeth; DeGennaro, Steven

2017-03-01

We present a detailed analysis of the white dwarf luminosity functions derived from the local 40 pc sample and the deep proper motion catalog of Munn et al. Many previous studies have ignored the contribution of thick disk white dwarfs to the Galactic disk luminosity function, which results in an erroneous age measurement. We demonstrate that the ratio of thick/thin disk white dwarfs is roughly 20% in the local sample. Simultaneously fitting for both disk components, we derive ages of 6.8-7.0 Gyr for the thin disk and 8.7 ± 0.1 Gyr for the thick disk from the local 40 pc sample. Similarly, we derive ages of 7.4-8.2 Gyr for the thin disk and 9.5-9.9 Gyr for the thick disk from the deep proper motion catalog, which shows no evidence of a deviation from a constant star formation rate in the past 2.5 Gyr. We constrain the time difference between the onset of star formation in the thin disk and the thick disk to be {1.6}-0.4+0.3 Gyr. The faint end of the luminosity function for the halo white dwarfs is less constrained, resulting in an age estimate of {12.5}-3.4+1.4 Gyr for the Galactic inner halo. This is the first time that ages for all three major components of the Galaxy have been obtained from a sample of field white dwarfs that is large enough to contain significant numbers of disk and halo objects. The resultant ages agree reasonably well with the age estimates for the oldest open and globular clusters.

Nearby stars of the Galactic disk and halo. III.

NASA Astrophysics Data System (ADS)

Fuhrmann, K.

2004-01-01

High-resolution spectroscopic observations of about 150 nearby stars or star systems are presented and discussed. The study of these and another 100 objects of the previous papers of this series implies that the Galaxy became reality 13 or 14 Gyr ago with the implementation of a massive, rotationally-supported population of thick-disk stars. The very high star formation rate in that phase gave rise to a rapid metal enrichment and an expulsion of gas in supernovae-driven Galactic winds, but was followed by a star formation gap for no less than three billion years at the Sun's galactocentric distance. In a second phase, then, the thin disk - our ``familiar Milky Way'' - came on stage. Nowadays it traces the bright side of the Galaxy, but it is also embedded in a huge coffin of dead thick-disk stars that account for a large amount of baryonic dark matter. As opposed to this, cold-dark-matter-dominated cosmologies that suggest a more gradual hierarchical buildup through mergers of minor structures, though popular, are a poor description for the Milky Way Galaxy - and by inference many other spirals as well - if, as the sample implies, the fossil records of its long-lived stars do not stick to this paradigm. Apart from this general picture that emerges with reference to the entire sample stars, a good deal of the present work is however also concerned with detailed discussions of many individual objects. Among the most interesting we mention the blue straggler or merger candidates HD 165401 and HD 137763/HD 137778, the likely accretion of a giant planet or brown dwarf on 59 Vir in its recent history, and HD 63433 that proves to be a young solar analog at \\tau˜200 Myr. Likewise, the secondary to HR 4867, formerly suspected non-single from the Hipparcos astrometry, is directly detectable in the high-resolution spectroscopic tracings, whereas the visual binary \\chi Cet is instead at least triple, and presumably even quadruple. With respect to the nearby young stars a

Quasars in the Galactic Anti-Center Area from LAMOST DR3

NASA Astrophysics Data System (ADS)

Huo, Zhi-Ying; Liu, Xiao-Wei; Shi, Jian-Rong; Xiang, Mao-Sheng; Huang, Yang; Yuan, Hai-Bo; Zhang, Jian-Nan; Zhang, Wei; Wang, Jian-Ling; Wu, Yu-Zhong; Cao, Zi-Huang; Zhang, Yong; Hou, Yong-Hui; Wang, Yue-Fei

2017-03-01

We present a sample of quasars discovered in an area near the Galactic Anti-Center covering 150^\\circ ≤ l≤ 210^\\circ and | b| ≤ 30^\\circ , based on LAMOST Data Release 3 (DR3). This sample contains 151 spectroscopically confirmed quasars. Among them 80 are newly discovered with LAMOST. All these quasars are very bright, with i magnitudes peaking around 17.5 mag. All the new quasars were discovered serendipitously from objects that were originally targeted with LAMOST as stars having bluer colors, except for a few candidates targeted as variable, young stellar objects. This bright quasar sample at low Galactic latitudes will help fill the gap in the spatial distribution of known quasars near the Galactic disk that are used to construct an astrometric reference frame for the purpose of accurate proper motion measurements that can be applied to, for example, Gaia. They are also excellent tracers to probe the kinematics and chemistry of the interstellar medium in the Milky Way disk and halo via absorption line spectroscopy.

Search for Dark Matter Annihilations towards the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

NASA Astrophysics Data System (ADS)

Abdallah, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Angüner, E.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Becker Tjus, J.; Berge, D.; Bernhard, S.; Bernlöhr, K.; Birsin, E.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Bulik, T.; Capasso, M.; Carr, J.; Casanova, S.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Chrétien, M.; Colafrancesco, S.; Cologna, G.; Condon, B.; Conrad, J.; Couturier, C.; Cui, Y.; Davids, I. D.; Degrange, B.; Deil, C.; deWilt, P.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O'C.; Dubus, G.; Dutson, K.; Dyks, J.; Dyrda, M.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Grudzińska, M.; Hadasch, D.; Hahn, J.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hillert, A.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jogler, T.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kerszberg, D.; Khélifi, B.; Kieffer, M.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krayzel, F.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lefranc, V.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Lohse, T.; Lorentz, M.; Lui, R.; Lypova, I.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Menzler, U.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Morâ, K.; Moulin, E.; Murach, T.; de Naurois, M.; Niederwanger, F.; Niemiec, J.; Oakes, L.; Odaka, H.; Ohm, S.; Öttl, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Paz Arribas, M.; Pekeur, N. W.; Pelletier, G.; Petrucci, P.-O.; Peyaud, B.; Pita, S.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reimer, A.; Reimer, O.; Renaud, M.; de los Reyes, R.; Rieger, F.; Romoli, C.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seyffert, A. S.; Shafi, N.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spieß, F.; Stawarz, L.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tluczykont, M.; Trichard, C.; Tuffs, R.; van der Walt, J.; van Eldik, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Żywucka, N.; H. E. S. S. Collaboration

2016-09-01

The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using γ -ray observations towards the inner 300 pc of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10 years (2004-2014), and does not show any significant γ -ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section ⟨σ v ⟩. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach ⟨σ v ⟩ values of 6 ×10-26 cm3 s-1 in the W+W- channel for a DM particle mass of 1.5 TeV, and 2 ×10-26 cm3 s-1 in the τ+τ- channel for a 1 TeV mass. For the first time, ground-based γ -ray observations have reached sufficient sensitivity to probe ⟨σ v ⟩ values expected from the thermal relic density for TeV DM particles.

Searching for planetary nebulae at the Galactic halo via J-PAS and J-PLUS

NASA Astrophysics Data System (ADS)

Goncalves, Denise R.; Aparício-Villegas, Teresa; Akras, Stavros; Borges Fernandes, Marcelo; J-PAS Collaboration

2015-08-01

The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is a narrow-band imaging, very wide field cosmological survey to be carried out from a dedicated 2.5m telescope and a 4.7 sq.deg camera with 1.2Gpix. It will last 5 years and will observe 8500 sq.deg of Northern sky to a 5-σ magnitude depth for point sources, equivalent to i ~23.3 over an aperture of 2 arcsec2. The J-PAS filter system consists of 54 contiguous narrow band filters of 145-Å FWHM, from 3,500 to 10,000Å. Two broad-band filters will be added at the extremes, UV and IR, plus 3 SDSS g, r, and i filters. The Javalambre Photometric Local Universe Survye (J-PLUS) will be an auxiliary survey ofJ-PAS (mainly for calibration) with a dedicated 0.80m telescope. J-PLUS comprises 12 filters, including g, r, i and z SDSS ones. Though about 2,500 planetary nebulae (PNe, confirmed spectroscopically) are known in the Galaxy, only 14 objects have been convincingly identified as halo PNe. They were classified as such from their location, kinematics and chemistry. Halo PNe are able to reveal precious information for the study of low- and intermediate-mass star evolution and the early chemical conditions of the Galaxy. The characteristic low continuum and intense line emissions of PNe make them good objects to be searched by J-PAS, and even by J-PLUS. For instance, the halo PNe BoBn 1, DdDm 1 and PS 1, located somewhere between 11 and 24 kpc from the Sun, have B magnitudes of 16, 14 and 13.4, respectively. Such values are easily encompassed by J-PAS/J-PLUS, given the typical limit magnitude of the survey. Though covering a significantly smaller sky area, data from the ALHAMBRA survey were used to test our J-PAS/J-PLUS strategy to search for PNe. Our first results will be shown in this poster.

The Lack of Influence of Metallicity on Cooling and Collapse of Ionized Gas in Small Protogalactic Halos

NASA Astrophysics Data System (ADS)

Jappsen, A.-K.; Glover, S. C. O.; Klessen, R. S.; Mac Low, M.-M.

2005-12-01

We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos. We use three-dimensional, smoothed particle hydrodynamics simulations, run with the publicly available parallel code GADGET (Springel et al. 2001). We implement a sink particle algorithm. This allows us to safely represent gas that has collapsed beyond the resolution limit without causing numerical errors within the resolved regions of the simulation. We also include the necessary framework for following the non-equilibrium chemistry of H2 in the protogalactic gas, and a treatment of radiative heating and cooling. Our initial conditions represent protogalaxies forming within a fossil H ii region---a previously ionized H ii region that has not yet had time to cool and recombine. Prior to cosmological reionization, such regions should be relatively common, since the characteristic lifetimes of the likely ionizing sources are significantly shorter than a Hubble time. We show that in these regions, H2 is the dominant and most effective coolant, even in the presence of small amounts of metals. It is the amount of H2 which forms that controls whether or not the gas can collapse and form stars. For metallicities Z ≤ 10-3 Z⊙, we find that metal line cooling alters the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm-3 and temperatures above 2000 K. However, at higher densities and lower temperatures, metal line cooling does become rather more important, and will affect the ability of the gas to fragment. We also show that an external ultraviolet background delays or suppresses the cooling and collapse of the gas regardless of whether or not it is metal-enriched. RSK and A-KJ acknowledge support from the Emmy Noether Program of the Deutsche Forschungsgemeinschaft (grant no. KL1358/1). M-MML acknowledges support from NSF grants AST99-85392 and AST03-07854, and NASA grant NAG5

FERMI-LAT OBSERVATIONS OF HIGH- AND INTERMEDIATE-VELOCITY CLOUDS: TRACING COSMIC RAYS IN THE HALO OF THE MILKY WAY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tibaldo, L.; Digel, S. W.; Franckowiak, A.

2015-07-10

It is widely accepted that cosmic rays (CRs) up to at least PeV energies are Galactic in origin. Accelerated particles are injected into the interstellar medium where they propagate to the farthest reaches of the Milky Way, including a surrounding halo. The composition of CRs coming to the solar system can be measured directly and has been used to infer the details of CR propagation that are extrapolated to the whole Galaxy. In contrast, indirect methods, such as observations of γ-ray emission from CR interactions with interstellar gas, have been employed to directly probe the CR densities in distant locationsmore » throughout the Galactic plane. In this article we use 73 months of data from the Fermi Large Area Telescope in the energy range between 300 MeV and 10 GeV to search for γ-ray emission produced by CR interactions in several high- and intermediate-velocity clouds (IVCs) located at up to ∼7 kpc above the Galactic plane. We achieve the first detection of IVCs in γ rays and set upper limits on the emission from the remaining targets, thereby tracing the distribution of CR nuclei in the halo for the first time. We find that the γ-ray emissivity per H atom decreases with increasing distance from the plane at 97.5% confidence level. This corroborates the notion that CRs at the relevant energies originate in the Galactic disk. The emissivity of the upper intermediate-velocity Arch hints at a 50% decline of CR densities within 2 kpc from the plane. We compare our results to predictions of CR propagation models.« less

Fermi-Lat observations of high-and intermediate-velocity clouds: tracing cosmic rays in the halo of the Milky Way

DOE PAGES

Tibaldo, L.; Digel, S. W.; Casandjian, J. M.; ...

2015-07-09

It is widely accepted that cosmic rays (CRs) up to at least PeV energies are Galactic in origin. Accelerated particles are injected into the interstellar medium where they propagate to the farthest reaches of the Milky Way, including a surrounding halo. The composition of CRs coming to the solar system can be measured directly and has been used to infer the details of CR propagation that are extrapolated to the whole Galaxy. In contrast, indirect methods, such as observations of γ-ray emission from CR interactions with interstellar gas, have been employed to directly probe the CR densities in distant locationsmore » throughout the Galactic plane. In this article we use 73 months of data from the Fermi Large Area Telescope in the energy range between 300 MeV and 10 GeV to search for γ-ray emission produced by CR interactions in several high- and intermediate-velocity clouds (IVCs) located at up to ~7 kpc above the Galactic plane. We achieve the first detection of IVCs in γ rays and set upper limits on the emission from the remaining targets, thereby tracing the distribution of CR nuclei in the halo for the first time. Here, we find that the γ-ray emissivity per H atom decreases with increasing distance from the plane at 97.5% confidence level. This corroborates the notion that CRs at the relevant energies originate in the Galactic disk. The emissivity of the upper intermediate-velocity Arch hints at a 50% decline of CR densities within 2 kpc from the plane. Finally, we compare our results to predictions of CR propagation models.« less

Halo assembly bias and the tidal anisotropy of the local halo environment

NASA Astrophysics Data System (ADS)

Paranjape, Aseem; Hahn, Oliver; Sheth, Ravi K.

2018-05-01

We study the role of the local tidal environment in determining the assembly bias of dark matter haloes. Previous results suggest that the anisotropy of a halo's environment (i.e. whether it lies in a filament or in a more isotropic region) can play a significant role in determining the eventual mass and age of the halo. We statistically isolate this effect, using correlations between the large-scale and small-scale environments of simulated haloes at z = 0 with masses between 1011.6 ≲ (m/h-1 M⊙) ≲ 1014.9. We probe the large-scale environment, using a novel halo-by-halo estimator of linear bias. For the small-scale environment, we identify a variable αR that captures the tidal anisotropy in a region of radius R = 4R200b around the halo and correlates strongly with halo bias at fixed mass. Segregating haloes by αR reveals two distinct populations. Haloes in highly isotropic local environments (αR ≲ 0.2) behave as expected from the simplest, spherically averaged analytical models of structure formation, showing a negative correlation between their concentration and large-scale bias at all masses. In contrast, haloes in anisotropic, filament-like environments (αR ≳ 0.5) tend to show a positive correlation between bias and concentration at any mass. Our multiscale analysis cleanly demonstrates how the overall assembly bias trend across halo mass emerges as an average over these different halo populations, and provides valuable insights towards building analytical models that correctly incorporate assembly bias. We also discuss potential implications for the nature and detectability of galaxy assembly bias.

Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

NASA Astrophysics Data System (ADS)

Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

2014-02-01

The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

GBT CHANG-ES: Enhancing Radio Halos in Edge-on Galaxies Through Short-Spacing Corrections

NASA Astrophysics Data System (ADS)

Trent Braun, Timothy; Kepley, Amanda; Rand, Richard J.; Mason, Brian Scott; CHANG-ES

2018-01-01

We present L- and C-band continuum Stokes I data from the Green Bank Telescope (GBT) of 35 edge-on spiral galaxies that are part of the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES). CHANG-ES is an Expanded Very Large Array (EVLA) large program to measure radio continuum emission from the halos of 35 edge-on spiral galaxies in order to address a wide variety of science goals, including constraining the structure of magnetic fields, understanding the origins of radio halos, and probing both cosmic ray transport and cosmic ray driven winds. These goals can be reached by studying radio halo scale heights, spectral index variations with height, and the distribution of intensity and position angle of polarized emission. In particular, we are interested in modeling non-thermal presssure gradients in the gaseous halos of nearby galaxies to predict how they contribute to the decrease in the rotation of extraplanar gas with increasing height off of the galactic midplanes (lagging halos). Ultimately, the study of lagging halos will help us probe the efficacy of gas cycling between the disk and the halo in nearby galaxies. Crucial to this and the rest of the CHANG-ES analysis is the combination of the VLA data (B,C,D configurations in L-band and C,D configurations in C-band) with the GBT data in order to fill in the missing short-spacings in the u-v plane, which increases our sensitivity to large-scale emission and allows us to recover the total flux density. We present preliminary results from two methods of combining single-dish and interferometic data, namely the use of GBT data cubes as a model for the CASA task tclean and combining the Fourier transforms of the images as weighted sums in the u-v plane (feathering). Lastly, we detail our new data reduction pipeline for our wideband GBT continuum data, with an emphasis on the application of a least-squares basket-weaving technique used to remove striping image artifacts that notoriously plague single

The Cycles of Gaseous Baryons between the Disk and Halo

NASA Astrophysics Data System (ADS)

Zheng, Yong

2018-01-01

The disks of galaxies closely interact with the circumgalactic medium (CGM) through the disk-halo (D/H) interface. The disks grow by inflows from the CGM, while the CGM is enriched, stirred, and heated by outflows from the disks. Recent years have seen great breakthroughs in observations of inflows and outflows at the D/H interface; however, inflow detections are still rare and the structure of the D/H interface is unclear. My thesis work includes searching for inflows and studying the multiphase gas at the D/H interface, and building my expertise in both UV spectroscopy and HI 21cm observations.I will first show HST/COS observations of gas inflows detected in Si IV absorption lines at M33’s D/H interface (Zheng et al. 2017a); this is among the first to unambiguously reveal the existence of disk-wide galactic inflows. The detection of Si IV-bearing inflows indicates that baryons are efficiently recycled between the disk and halo, mostly consistent with a galactic fountain scenario. Then I will present a 3-dimensional kinematic model of the Milky Way (MW)’s D/H interface. I will show that beyond the MW’s D/H interface, there is a significant amount of baryons in the MW’s CGM moving at low velocities (|vlsr|<100 km/s; Zheng et al. 2015, Zheng et al. 2017c). Current MW’s CGM mass estimates suffer from an inside-out observational bias: local observers miss more than half of the gas mass in the MW’s CGM that is blocked out in high-velocity focused studies.

The Origin and Survival of Cold Gas in Hot Halos

NASA Astrophysics Data System (ADS)

Oh, Siang Peng

gas is expelled from the galaxy disk in large-scale outflows, or 2) that it is produced in-situ by thermal instability. In both cases, we focus on observational tests of our model, and on methods to incorporate our results into future cosmological simulations via a sub-grid model. Additional science results will include understanding the unexplained entrainment of cold gas in galactic winds, as well as understanding the surprisingly strong magnetic fields seen in galaxy halos at low redshift, which likely dominate over thermal pressure in halo gas. To our knowledge, no models currently exist for either of these results. The work outlined in this proposal focuses on recent observations which cannot yet be reproduced in cosmological simulations. As part of our proposed work, we will produce a sub-grid model for unresolved cold clouds in hydrodynamics, and will determine the resolution needed to reproduce these effects in future cosmological simulations. Our work is timely and represents the necessary next step in advancing our theories of the CGM.

Benchmark of 3D halo neutral simulation in TRANSP and FIDASIM and application to projected neutral-beam-heated NSTX-U plasmas

NASA Astrophysics Data System (ADS)

Liu, D.; Medley, S. S.; Gorelenkova, M. V.; Heidbrink, W. W.; Stagner, L.

2014-10-01

A cloud of halo neutrals is created in the vicinity of beam footprint during the neutral beam injection and the halo neutral density can be comparable with beam neutral density. Proper modeling of halo neutrals is critical to correctly interpret neutral particle analyzers (NPA) and fast ion D-alpha (FIDA) signals since these signals strongly depend on local beam and halo neutral density. A 3D halo neutral model has been recently developed and implemented inside TRANSP code. The 3D halo neutral code uses a ``beam-in-a-box'' model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components produce thermal halo neutrals that are tracked through successive halo neutral generations until an ionization event occurs or a descendant halo exits the box. A benchmark between 3D halo neural model in TRANSP and in FIDA/NPA synthetic diagnostic code FIDASIM is carried out. Detailed comparison of halo neutral density profiles from two codes will be shown. The NPA and FIDA simulations with and without 3D halos are applied to projections of plasma performance for the National Spherical Tours eXperiment-Upgrade (NSTX-U) and the effects of halo neutral density on NPA and FIDA signal amplitude and profile will be presented. Work supported by US DOE.

Elusive active galactic nuclei

NASA Astrophysics Data System (ADS)

Maiolino, R.; Comastri, A.; Gilli, R.; Nagar, N. M.; Bianchi, S.; Böker, T.; Colbert, E.; Krabbe, A.; Marconi, A.; Matt, G.; Salvati, M.

2003-10-01

A fraction of active galactic nuclei do not show the classical Seyfert-type signatures in their optical spectra, i.e. they are optically `elusive'. X-ray observations are an optimal tool to identify this class of objects. We combine new Chandra observations with archival X-ray data in order to obtain a first estimate of the fraction of elusive active galactic nuclei (AGN) in local galaxies and to constrain their nature. Our results suggest that elusive AGN have a local density comparable to or even higher than optically classified Seyfert nuclei. Most elusive AGN are heavily absorbed in the X-rays, with gas column densities exceeding 1024 cm-2, suggesting that their peculiar nature is associated with obscuration. It is likely that in elusive AGN the nuclear UV source is completely embedded and the ionizing photons cannot escape, which prevents the formation of a classical narrow-line region. Elusive AGN may contribute significantly to the 30-keV bump of the X-ray background.

Sturm und Drang: The turbulent, magnetic tempest in the Galactic center

NASA Astrophysics Data System (ADS)

Lacki, Brian C.

2014-05-01

The Galactic center central molecular zone (GCCMZ) bears similarities with extragalactic starburst regions, including a high supernova (SN) rate density. As in other starbursts like M82, the frequent SNe can heat the ISM until it is filled with a hot (˜ 4 × 107 K) superwind. Furthermore, the random forcing from SNe stirs up the wind, powering Mach 1 turbulence. I argue that a turbulent dynamo explains the strong magnetic fields in starbursts, and I predict an average B ˜70 μG in the GCCMZ. I demonstrate how the SN driving of the ISM leads to equipartition between various pressure components in the ISM. The SN-heated wind escapes the center, but I show that it may be stopped in the Galactic halo. I propose that the Fermi bubbles are the wind's termination shock.

Tidal breakup of triple stars in the Galactic Centre

NASA Astrophysics Data System (ADS)

Fragione, Giacomo; Gualandris, Alessia

2018-04-01

The last decade has seen the detection of fast moving stars in the Galactic halo, the so-called hypervelocity stars (HVSs). While the bulk of this population is likely the result of a close encounter between a stellar binary and the supermassive black hole (MBH) in the Galactic Centre (GC), other mechanims may contribute fast stars to the sample. Few observed HVSs show apparent ages, which are shorter than the flight time from the GC, thereby making the binary disruption scenario unlikely. These stars may be the result of the breakup of a stellar triple in the GC, which led to the ejection of a hypervelocity binary (HVB). If such binary evolves into a blue straggler star due to internal processes after ejection, a rejuvenation is possible that make the star appear younger once detected in the halo. A triple disruption may also be responsible for the presence of HVBs, of which one candidate has now been observed. We present a numerical study of triple disruptions by the MBH in the GC and find that the most likely outcomes are the production of single HVSs and single/binary stars bound to the MBH, while the production of HVBs has a probability ≲ 1 per cent regardless of the initial parameters. Assuming a triple fraction of ≈ 10 per cent results in an ejection rate of ≲ 1 Gyr - 1, insufficient to explain the sample of HVSs with lifetimes shorter than their flight time. We conclude that alternative mechanisms are responsible for the origin of such objects and HVBs in general.

CO-ORBITING PLANES OF SUB-HALOS ARE SIMILARLY UNLIKELY AROUND PAIRED AND ISOLATED HOSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pawlowski, Marcel S.; McGaugh, Stacy S., E-mail: marcel.pawlowski@case.edu

2014-07-01

Sub-halos in dark-matter-based cosmological simulations tend to be distributed approximately isotropically around their host. The existence of highly flattened, co-orbiting planes of satellite galaxies has therefore been identified as a possible problem for these cosmological models, but so far studies have not considered the hosts' environments. That satellite planes are now known around both major galaxies in the Local Group raises the question whether they are more likely to be found around paired hosts. In a first attempt to investigate this possibility, we focus on the flattening and orbital coherence of the 11 brightest satellite galaxies of the vast polarmore » structure (VPOS) around the Milky Way (MW). We search for VPOS analogs in the ''Exploring the Local Volume in Simulations'' suite of cosmological simulations, which consist of 24 paired and 24 isolated host halos. We do not find significant differences between the properties of sub-halo distributions around paired and isolated hosts. The observed flattening and the observed orbital alignment are each reproduced by only 0.2%-2% of paired and isolated systems incorporating the obscuration of satellites by randomly oriented galactic disks. Only 1 of all 4800 analyzed realizations (0.02%) reproduces both parameters simultaneously, but the average orbital pole of this sub-halo system does not align as well with the normal to the plane fit as observed. That the MW is part of a galaxy pair thus does not help to explain the existence of the VPOS if the satellite galaxies are identified with sub-halos found in dissipationless simulations.« less

The halo Boltzmann equation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biagetti, Matteo; Desjacques, Vincent; Kehagias, Alex

2016-04-01

Dark matter halos are the building blocks of the universe as they host galaxies and clusters. The knowledge of the clustering properties of halos is therefore essential for the understanding of the galaxy statistical properties. We derive an effective halo Boltzmann equation which can be used to describe the halo clustering statistics. In particular, we show how the halo Boltzmann equation encodes a statistically biased gravitational force which generates a bias in the peculiar velocities of virialized halos with respect to the underlying dark matter, as recently observed in N-body simulations.

The ellipticity of galaxy cluster haloes from satellite galaxies and weak lensing

NASA Astrophysics Data System (ADS)

Shin, Tae-hyeon; Clampitt, Joseph; Jain, Bhuvnesh; Bernstein, Gary; Neil, Andrew; Rozo, Eduardo; Rykoff, Eli

2018-04-01

We study the ellipticity of galaxy cluster haloes as characterized by the distribution of cluster galaxies and as measured with weak lensing. We use Monte Carlo simulations of elliptical cluster density profiles to estimate and correct for Poisson noise bias, edge bias and projection effects. We apply our methodology to 10 428 Sloan Digital Sky Survey clusters identified by the redMaPPer algorithm with richness above 20. We find a mean ellipticity =0.271 ± 0.002 (stat) ±0.031 (sys) corresponding to an axis ratio = 0.573 ± 0.002 (stat) ±0.039 (sys). We compare this ellipticity of the satellites to the halo shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016). We find a best-fitting axis ratio of 0.56 ± 0.09 (stat) ±0.03 (sys), consistent with the ellipticity of the satellite distribution. Thus, cluster galaxies trace the shape of the dark matter halo to within our estimated uncertainties. Finally, we restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements, we infer a misalignment angle with an root-mean-square of 30° ± 10° when stacking on the central galaxy. We discuss applications of halo shape measurements to test the effects of the baryonic gas and active galactic nucleus feedback, as well as dark matter and gravity. The major improvements in signal-to-noise ratio expected with the ongoing Dark Energy Survey and future surveys from Large Synoptic Survey Telescope, Euclid, and Wide Field Infrared Survey Telescope will make halo shapes a useful probe of these effects.

Influence of Dust Loading on Atmospheric Ionizing Radiation on Mars

NASA Technical Reports Server (NTRS)

Norman, Ryan B.; Gronoff, Guillaume; Mertens, Christopher J.

2014-01-01

Measuring the radiation environment at the surface of Mars is the primary goal of the Radiation Assessment Detector on the NASA Mars Science Laboratory's Curiosity rover. One of the conditions that Curiosity will likely encounter is a dust storm. The objective of this paper is to compute the cosmic ray ionization in different conditions, including dust storms, as these various conditions are likely to be encountered by Curiosity at some point. In the present work, the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety model, recently modified for Mars, was used along with the Badhwar & O'Neill 2010 galactic cosmic ray model. In addition to galactic cosmic rays, five different solar energetic particle event spectra were considered. For all input radiation environments, radiation dose throughout the atmosphere and at the surface was investigated as a function of atmospheric dust loading. It is demonstrated that for galactic cosmic rays, the ionization depends strongly on the atmosphere profile. Moreover, it is shown that solar energetic particle events strongly increase the ionization throughout the atmosphere, including ground level, and can account for the radio blackout conditions observed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on the Mars Express spacecraft. These results demonstrate that the cosmic rays' influence on the Martian surface chemistry is strongly dependent on solar and atmospheric conditions that should be taken into account for future studies.

Globular Cluster Orbits from HST Proper Motions: Constraining the Formation and Mass of the Milky Way Halo

NASA Astrophysics Data System (ADS)

Sohn, S. Tony; Van Der Marel, Roeland P.; Deason, Alis J.; Bellini, Andrea; Besla, Gurtina; Watkins, Laura

2016-06-01

The globular cluster (GC) system of the Milky Way (MW) provides important information on the MW's present structure and past evolution. GCs in the halo are particularly useful tracers; because of their long dynamical timescales, their orbits retain imprints of their origin or accretion history. Full 3D motions are required to calculate past orbits. While most GCs have known line of sight velocities, accurate proper motion (PM) measurements are currently available for only a few halo GCs. Our goal is to create the first high-quality PM database for halo GCs. We have identified suitable 1st-epoch data in the HST Archive for 20 halo GCs at 10-100 kpc from the Galactic Center. We are in the process of obtaining the necessary 2nd-epoch data to determine absolute PMs of the target GCs through our HST program GO-14235. We will use the same advanced astrometric techniques that allowed us to measure the PMs of M31 and Leo I. Previous studies of the halo GC system based on e.g., stellar populations, metallicities, RR Lyrae properties, and structural properties have revealed a dichotomy between old and young halo GCs. This may reflect distinct formation scenarios (in situ vs. accreted). Orbit calculations based on our PMs will directly test this. The PMs will also yield the best handle yet on the velocity anisotropy profile of any tracer population in the halo. This will resolve the mass-anisotropy degeneracy to provide an improved estimate of the MW mass, which is at present poorly known. In summary, our project will deliver the first accurate PMs for halo GCs, and will significantly increase our understanding of the formation, evolution, and mass of the MW.

Stellar haloes in massive early-type galaxies

NASA Astrophysics Data System (ADS)

Buitrago, F.

2017-03-01

The Hubble Ultra Deep Field (HUDF) opens up an unique window to witness galaxy assembly at all cosmic distances. Thanks to its extraordinary depth, it is a privileged tool to beat the cosmological dimming, which affects any extragalactic observations and has a very strong dependence with redshift (1 +z)^4. In particular, massive (M_{stellar}>5 × 10^{10} M_⊙) Early Type Galaxies (ETGs) are the most interesting candidates for these studies, as they must grow in an inside-out fashion developing an extended stellar envelope/halo that accounts for their remarkable size evolution (˜5 times larger in the nearby Universe than at z=2-3). To this end we have analysed the 6 most massive ETGs at z <1 in the HUDF12. Because of the careful data reduction and the exhaustive treatment of the Point Spread Function (PSF), we are able to trace the galaxy surface brightness profiles up to the same levels as in the local Universe but this time at = 0.65 (31 mag arcsec^{-2} in all 8 HST bands, ˜ 29 mag arcsec^{-2} restframe or beyond 25 effective radii). This fact enables us to investigate the galactic outskirts or stellar haloes at a previously unexplored era, characterising their light and mass profiles, colors and for the first time the amount of mass in ongoing mergers.

Exploring the Dust Content of Galactic Winds with MIPS

NASA Astrophysics Data System (ADS)

Martin, Crystal; Engelbracht, Charles; Gordon, Karl

2005-06-01

This program explores the dust content of galactic winds. Nearly half of all stars in the universe probably form in a starburst event, where high concentrations of supernova explosions drive galactic-scale gaseous outflows. In nearby starburst galaxies, winds have been mapped at radio, optical, and X-ray frequencies revealing bipolar lobes of hot gas laced with cooler filaments bubbling out of the host galaxy. Most of the outflowing material is entrained interstellar gas, so it will remain quite dusty unless the grains are destroyed. Dusty winds have significant implications for the circulation of heavy elements in galaxies, the dust content of the intergalactic medium, and the acceleration of gaseous outflows. GALEX images of scattered ultraviolet light from galactic winds now provide compelling evidence for the survival of some grains. MIPS photometry of starburst winds at 24, 70, and 160 microns can, in principle, measure the dust temperature providing accurate estimates of the amount of dust (e.g. Engelbracht et al. 2004). To date, however, most MIPS observations of starburst galaxies are far too shallow to detect thermal emission from halo dust. The requested observations would provide the most sensitive observations currently possible for a sample of starburst galaxies, selected to span the full range of starburst luminosity and spatial geometry in the local universe.

Scaling Relations of Starburst-driven Galactic Winds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanner, Ryan; Cecil, Gerald; Heitsch, Fabian, E-mail: rytanner@augusta.edu

2017-07-10

Using synthetic absorption lines generated from 3D hydrodynamical simulations, we explore how the velocity of a starburst-driven galactic wind correlates with the star formation rate (SFR) and SFR density. We find strong correlations for neutral and low ionized gas, but no correlation for highly ionized gas. The correlations for neutral and low ionized gas only hold for SFRs below a critical limit set by the mass loading of the starburst, above which point the scaling relations flatten abruptly. Below this point the scaling relations depend on the temperature regime being probed by the absorption line, not on the mass loading.more » The exact scaling relation depends on whether the maximum or mean velocity of the absorption line is used. We find that the outflow velocity of neutral gas can be up to five times lower than the average velocity of ionized gas, with the velocity difference increasing for higher ionization states. Furthermore, the velocity difference depends on both the SFR and mass loading of the starburst. Thus, absorption lines of neutral or low ionized gas cannot easily be used as a proxy for the outflow velocity of the hot gas.« less

Testing Intermittence of the Galactic Star Formation History along with the Infall Model

NASA Astrophysics Data System (ADS)

Takeuchi, Tsutomu T.; Hirashita, Hiroyuki

2000-09-01

We analyze the star formation history (SFH) of the Galactic disk by using an infall model. Based on the observed SFH of the Galactic disk, we first determine the timescale of the gas infall into the Galactic disk (tin) and that of the gas consumption to form stars (tsf). Since each of the two timescales does not prove to be determined independently from the SFH, we first fix tsf. Then, tin is determined so that we minimize χ2. Consequently, we choose three parameter sets: [tsf (Gyr),tin (Gyr)]=(6.0, 23), (11, 12), and (15, 9.0), where we set the Galactic age as 15 Gyr. All of the three cases predict almost identical star formation history. Next, we test the intermittence (or variability) of the star formation rate (SFR) along with the smooth SFH suggested from the infall model. The large value of the χ2 statistic supports the violent time variation of the SFH. If we interpret the observed SFH with smooth and variable components, the amplitude of the variable component is comparable to the smooth component. Thus, intermittent SFH of the Galactic disk is strongly suggested. We also examined the metallicity distribution of G dwarfs. We found that the true parameter set lies between [tsf (Gyr),tin (Gyr)]=(6, 23) and (11, 12), though we need a more sophisticated model including the process of metal enrichment within the Galactic halo.

Earth-mass dark-matter haloes as the first structures in the early Universe.

PubMed

Diemand, J; Moore, B; Stadel, J

2005-01-27

The Universe was nearly smooth and homogeneous before a redshift of z = 100, about 20 million years after the Big Bang. After this epoch, the tiny fluctuations imprinted upon the matter distribution during the initial expansion began to collapse because of gravity. The properties of these fluctuations depend on the unknown nature of dark matter, the determination of which is one of the biggest challenges in present-day science. Here we report supercomputer simulations of the concordance cosmological model, which assumes neutralino dark matter (at present the preferred candidate), and find that the first objects to form are numerous Earth-mass dark-matter haloes about as large as the Solar System. They are stable against gravitational disruption, even within the central regions of the Milky Way. We expect over 10(15) to survive within the Galactic halo, with one passing through the Solar System every few thousand years. The nearest structures should be among the brightest sources of gamma-rays (from particle-particle annihilation).

In silico studies to explore the mutagenic ability of 5-halo/oxy/li-oxy-uracil bases with guanine of DNA base pairs.

PubMed

Jana, Kalyanashis; Ganguly, Bishwajit

2014-10-16

DNA nucleobases are reactive in nature and undergo modifications by deamination, oxidation, alkylation, or hydrolysis processes. Many such modified bases are susceptible to mutagenesis when formed in cellular DNA. The mutagenesis can occur by mispairing with DNA nucleobases by a DNA polymerase during replication. We have performed a study of mispairing of DNA bases with unnatural bases computationally. 5-Halo uracils have been studied as mispairs in mutagenesis; however, the reports on their different forms are scarce in the literature. The stability of mispairs with keto form, enol form, and ionized form of 5-halo-uracil has been computed with the M06-2X/6-31+G** level of theory. The enol form of 5-halo-uracil showed remarkable stability toward DNA mispair compared to the corresponding keto and ionized forms. (F)U-G mispair showed the highest stability in the series and (Halo)(U(enol/ionized)-G mispair interactions energies are more stable than the natural G-C basepair of DNA. To enhance the stability of DNA mispairs, we have introduced the hydroxyl group in the place of halogen atoms, which provides additional hydrogen-bonding interactions in the system while forming the 5-membered ring. The study has been further extended with lithiated 5-hydroxymethyl-uracil to stabilize the DNA mispair. (CH2OLi)U(ionized)-G mispair has shown the highest stability (ΔG = -32.4 kcal/mol) with multi O-Li interactions. AIM (atoms in molecules) and EDA (energy decomposition analysis) analysis has been performed to examine the nature of noncovalent interactions in such mispairs. EDA analysis has shown that electrostatic energy mainly contributes toward the interaction energy of mispairs. The higher stability achieved in these studied mispairs can play a pivotal role in the mutagenesis and can help to attain the mutation for many desired biological processes.

Mapping Milky Way Halo Structure with Blue Horizontal Branch Stars

NASA Astrophysics Data System (ADS)

Martin, Charles; Newberg, Heidi Jo; Carlin, Jeffrey L.

2017-01-01

The use of blue horizontal brach (BHB) and red giant branch stars as tracers of stellar debris streams is a common practice and has been useful in the confirmation of kinematic properties of previously identified streams. This work explores less common ways of untangling the velocity signatures of streams traveling radially to our line of sight, and to peer toward the higher density region of the Galactic Center using data from the Sloan Digital Sky Survey (SDSS). Using spectra of BHB stars, we are able to kinematically distinguish moving groups in the Milky Way halo. The results of this thesis advance our knowledge of the following stellar halo substructures: the Pisces Stellar Stream, the Hercules-Aquila Cloud, the Hercules Halo Stream, and the Hermus Stream. A study of red giant stars led to the kinematic discovery of the Pisces Stellar Stream. Red giant stars were also examined to determine that the previously identified velocity signature that was suggested for the Hercules-Aquila Cloud was due to disk star contamination and errors in preliminary SDSS velocities. The Hercules Halo Stream is a previously unidentified structure that could be related to the Hercules-Aquila Cloud, and was discovered as a velocity excess of SDSS BHB stars. We identify a group of 10 stars with similar velocities that are spatially coincident with the Hermus Stream. An orbit is fit to the Hermus Stream that rules out a connection with the Phoenix Stream.This work was supported by NSF grants AST 09-37523, 14-09421, 16-15688, the NASA/NY Space Grant fellowship, and contributions made by The Marvin Clan, Babette Josephs, Manit Limlamai, and the 2015 Crowd Funding Campaign to Support Milky Way Research.

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

NASA Astrophysics Data System (ADS)

Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; Serenelli, Aldo M.; Sheffield, Allyson; Li, Ting S.; Casagrande, Luca; Johnston, Kathryn V.; Laporte, Chervin F. P.; Price-Whelan, Adrian M.; Schönrich, Ralph; Gould, Andrew

2018-03-01

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo—the faint, roughly spherical component of the Galaxy—reveals rich ‘fossil’ evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane—locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

Moving-mesh cosmology: characteristics of galaxies and haloes

NASA Astrophysics Data System (ADS)

Kereš, Dušan; Vogelsberger, Mark; Sijacki, Debora; Springel, Volker; Hernquist, Lars

2012-09-01

of massive galaxies in AREPO also slightly increase the baryon content within the virial radius of massive haloes. We show that these differences persist as a function of numerical resolution. While both codes agree to acceptable accuracy on a number of baryonic properties of cosmic structures, our results thus clearly demonstrate that galaxy formation simulations greatly benefit from the use of more accurate hydrodynamical techniques such as AREPO and call into question the reliability of galaxy formation studies in a cosmological context using traditional standard formulations of SPH, such as the one implemented in GADGET. Our new moving-mesh simulations demonstrate that a population of extended gaseous discs of galaxies in large volume cosmological simulations can be formed even without energetic feedback in the form of galactic winds, although such outflows appear required to obtain realistic stellar masses.

Active galactic nucleus outflows in galaxy discs

NASA Astrophysics Data System (ADS)

Hartwig, Tilman; Volonteri, Marta; Dashyan, Gohar

2018-05-01

Galactic outflows, driven by active galactic nuclei (AGNs), play a crucial role in galaxy formation and in the self-regulated growth of supermassive black holes (BHs). AGN feedback couples to and affects gas, rather than stars, and in many, if not most, gas-rich galaxies cold gas is rotationally supported and settles in a disc. We present a 2D analytical model for AGN-driven outflows in a gaseous disc and demonstrate the main improvements, compared to existing 1D solutions. We find significant differences for the outflow dynamics and wind efficiency. The outflow is energy-driven due to inefficient cooling up to a certain AGN luminosity (˜1043 erg s-1 in our fiducial model), above which the outflow remains momentum-driven in the disc up to galactic scales. We reproduce results of 3D simulations that gas is preferentially ejected perpendicular to the disc and find that the fraction of ejected interstellar medium is lower than in 1D models. The recovery time of gas in the disc, defined as the free-fall time from the radius to which the AGN pushes the ISM at most, is remarkably short, of the order 1 Myr. This indicates that AGN-driven winds cannot suppress BH growth for long. Without the inclusion of supernova feedback, we find a scaling of the BH mass with the halo velocity dispersion of MBH ∝ σ4.8.

Herschel Galactic Plane Survey of [NII] Fine Structure Emission

NASA Astrophysics Data System (ADS)

Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.; Pineda, Jorge L.

2015-12-01

We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10-8-10-7 Wm-2 sr-1 level over the range -60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointing is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10-50 cm-3 with an average value of 29 cm-3 and N+ column densities 1016-1017 cm-2. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.

2MASS J06562998+3002455: Not a Cool White Dwarf Candidate, but a Population II Halo Star

NASA Astrophysics Data System (ADS)

de la Fuente Marcos, Raúl; de la Fuente Marcos, Carlos

2018-06-01

2MASS J06562998+3002455 or PSS 309-6 is a high proper-motion star that was discovered during a survey with the 2.1 m telescope at Kitt Peak National Observatory. Here, we reevaluate the status of this interesting star using Gaia DR2. Our results strongly suggest that PSS 309-6 could be a Population II star as the value of its V component is close to -220 km/s, which is typical for halo stars in the immediate solar neighborhood. Kapteyn's star is the nearest known halo star and PSS 309-6 exhibits similar kinematic and photometric signatures. Its properties also resemble those of 2MASS J15484023-3544254, which was once thought to be the nearest cool white dwarf but was later reclassified as K-type subdwarf. Although it is virtually certain that PSS 309-6 is not a nearby white dwarf but a more distant Population II subdwarf, further spectroscopic information, including radial velocity measurements, is necessary to fully characterize this probable member of the Galactic halo.

On the stability of satellite planes - I. Effects of mass, velocity, halo shape and alignment

NASA Astrophysics Data System (ADS)

Fernando, Nuwanthika; Arias, Veronica; Guglielmo, Magda; Lewis, Geraint F.; Ibata, Rodrigo A.; Power, Chris

2017-02-01

The recently discovered vast thin plane of dwarf satellites orbiting the Andromeda Galaxy (M31) adds to the mystery of the small-scale distribution of the Local Group's galaxy population. Such well-defined planar structures are apparently rare occurrences in cold dark matter cosmological simulations, and we lack a coherent explanation of their formation and existence. In this paper, we explore the long-term survivability of thin planes of dwarfs in galactic haloes, focusing, in particular, on systems mimicking the observed Andromeda distribution. The key results show that, in general, planes of dwarf galaxies are fragile, sensitive to the shape of the dark matter halo and other perturbing effects. In fact, long-lived planes of satellites only exist in polar orbits in spherical dark matter haloes, presenting a challenge to the observed Andromeda plane that is significantly tilted with respect to the optical disc. Our conclusion is that, in the standard cosmological models, planes of satellites are generally short lived, and hence we must be located at a relatively special time in the evolution of the Andromeda Plane, lucky enough to see its coherent pattern.

The Age of the Inner Halo Globular Cluster NGC 6652

NASA Technical Reports Server (NTRS)

Chaboyer, Brian; Sarajedini, Ata; Armandroff, Taft E.

2000-01-01

Hubble Space Telescope (HST) (V,I) photometry has been obtained for the inner halo globular cluster NGC 6652. The photometry reaches approximately 4 mag below the turn-off and includes a well populated horizontal branch (HB). This cluster is located close to the Galactic center at RGC approximately equal to 2.0 kpc with a reddening of E(V-I) = 0.15 +/- 0.02 and has a metallicity of [Fe/H] approximately equal to -0.85. Based upon DELTA V (sup SGB) (sub HB), NGC 6652 is 11.7 plus or minus 1.6 Gyr old. Using A HB precise differential ages for 47 Tuc (a thick disk globular), M107 and NGC 1851 (both halo clusters) were obtained. NGC 6652 appears to be the same age as 47 Tuc and NGC 1851 (within +/- 1.2 Gyr), while there is a slight suggestion that M107 is older than NGC 6652 by 2.3 +/- 1.5 Gyr. As this is a less than 2 sigma result, this issue needs to be investigated further before a definitive statement regarding the relative age of M107 and NGC 6652 may be made.

A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE

NASA Astrophysics Data System (ADS)

Helmi, Amina; Veljanoski, Jovan; Breddels, Maarten A.; Tian, Hao; Sales, Laura V.

2017-02-01

Context. The hierarchical structure formation model predicts that stellar halos should form, at least partly, via mergers. If this was a predominant formation channel for the Milky Way's halo, imprints of this merger history in the form of moving groups or streams should also exist in the vicinity of the Sun. Aims: We study the kinematics of halo stars in the Solar neighbourhood using the very recent first data release from the Gaia mission, and in particular the TGAS dataset, in combination with data from the RAVE survey. Our aim is to determine the amount of substructure present in the phase-space distribution of halo stars that could be linked to merger debris. Methods: To characterise kinematic substructure, we measured the velocity correlation function in our sample of halo (low-metallicity) stars. We also studied the distribution of these stars in the space of energy and two components of the angular momentum, in what we call "integrals of motion" space. Results: The velocity correlation function reveals substructure in the form of an excess of pairs of stars with similar velocities, well above that expected for a smooth distribution. Comparison to cosmological simulations of the formation of stellar halos indicates that the levels found are consistent with the Galactic halo having been built solely via accretion. Similarly, the distribution of stars in the space of integrals of motion is highly complex. A strikingly high fraction (from 58% up to more than 73%) of the stars that are somewhat less bound than the Sun are on (highly) retrograde orbits. A simple comparison to Milky Way-mass galaxies in cosmological hydrodynamical simulations suggests that less than 1% have such prominently retrograde outer halos. We also identify several other statistically significant structures in integrals of motion space that could potentially be related to merger events.

Halo vest instrumentation

NASA Astrophysics Data System (ADS)

Huston, Dryver R.; Krag, Martin

1996-05-01

The halo vest is a head and neck immobilization system that is often used on patients that are recovering from cervical trauma or surgery. The halo vest system consists of a rigid halo that is firmly attached to the skull, an upright support structure for stabilization and immobilization, and a torso-enveloping vest. The main purpose of this study was to measure the forces that are carried by the halo-vest structure as the subject undergoes various activities of daily living and external loading for different vest designs. A tethered strain gage load cell based instrumentation system was used to take these load measurements on ten different subjects. Three different halo-vest systems were evaluated. The primary difference between the vests was the amount of torso coverage and the use of shoulder straps. The loads were measured, analyzed and used to compare the vests and to create a model of halo-vest-neck mechanics. Future applications of this technology to standalone data logging, pin-load measuring and biofeedback applications are discussed.

What the Milky Way's dwarfs tell us about the Galactic Center extended gamma-ray excess

NASA Astrophysics Data System (ADS)

Keeley, Ryan E.; Abazajian, Kevork N.; Kwa, Anna; Rodd, Nicholas L.; Safdi, Benjamin R.

2018-05-01

The Milky Way's Galactic Center harbors a gamma-ray excess that is a candidate signal of annihilating dark matter. Dwarf galaxies remain predominantly dark in their expected commensurate emission. In this work we quantify the degree of consistency between these two observations through a joint likelihood analysis. In doing so we incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center extended gamma-ray excess (GCE) detected by the Fermi Gamma-Ray Space Telescope. The preferred range of annihilation rates and masses expands when including these unknowns. Even so, using two recent determinations of the Milky Way halo's local density leaves the GCE preferred region of single-channel dark matter annihilation models to be in strong tension with annihilation searches in combined dwarf galaxy analyses. A third, higher Milky Way density determination, alleviates this tension. Our joint likelihood analysis allows us to quantify this inconsistency. We provide a set of tools for testing dark matter annihilation models' consistency within this combined data set. As an example, we test a representative inverse Compton sourced self-interacting dark matter model, which is consistent with both the GCE and dwarfs.

Results from the Splash Survey: Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo

NASA Astrophysics Data System (ADS)

Guhathakurta, Puragra; SPLASH Collaboration

2009-01-01

Detailed studies of nearby galaxies provide vital clues about their formation and evolutionary history. This "fossil record" approach is complementary to direct look-back studies of distant galaxies. Our Galaxy and the Andromeda spiral galaxy (M31) have long been cornerstones in the former category. M31 provides an external perspective on a large galaxy similar to our own and yet is close enough to allow detailed studies of individual stars. In my talk, I will present results from the SPLASH collaboration: Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo. The collective data set from this large international team includes thousands of Keck/DEIMOS spectra of individual red giant branch stars, ground-based deep wide-field imaging and photometry with KPNO/Mosaic, CFHT/MegaCam, and Subaru/Suprime-Cam, and ultra-deep pencil-beam probes with HST/ACS imaging reaching below the main-sequence turnoff. Our recent discovery of an extended stellar halo in M31 (R > 150 kpc) shows that most previous studies of its spheroid have been sampling its inner bulge-like spheroidal component, not its halo. In my talk I will touch upon several related topics related to the general theme of hierarchical galaxy formation including: M31's global structure and subcomponents (halo, bulge/central bar, and disk), stellar dynamics, statistical properties of substructure, detailed chemical abundance measurements, detailed forensic reconstruction of recent collision events, dwarf satellites as tracers and building blocks of larger galaxies, and empirical constraints on the tangential motion of the M31 system. I will also discuss recent results on the chemical abundance of the lowest luminosity Galactic satellites (recently discovered by SDSS) and implications for the formation of the Milky Way halo. This research was supported by funds from the National Science Foundation, NASA, and the Institute for Geophysics and Planetary Physics.

Rate for annihilation of galactic dark matter into two photons

NASA Technical Reports Server (NTRS)

Giudice, Gian F.; Griest, Kim

1989-01-01

A calculation of the cross section for neutralino-neutralino annihilation into two photons is performed and applied to dark matter in the galactic halo to find the counting rate in a large gamma ray detector such as EGRET (Energetic Gamma Ray Experiment Telescope) or ASTROGAM. Combining constraints from particle accelerators with the requirement that the neutralinos make up the dark matter, it is found that rates of over a few dozen events per year are unlikely. The assumptions that go into these conclusions are listed. Other particle dark matter candidates which could give larger and perhaps observable signals are suggested.

Implementation of a 3D halo neutral model in the TRANSP code and application to projected NSTX-U plasmas

NASA Astrophysics Data System (ADS)

Medley, S. S.; Liu, D.; Gorelenkova, M. V.; Heidbrink, W. W.; Stagner, L.

2016-02-01

A 3D halo neutral code developed at the Princeton Plasma Physics Laboratory and implemented for analysis using the TRANSP code is applied to projected National Spherical Torus eXperiment-Upgrade (NSTX-U plasmas). The legacy TRANSP code did not handle halo neutrals properly since they were distributed over the plasma volume rather than remaining in the vicinity of the neutral beam footprint as is actually the case. The 3D halo neutral code uses a ‘beam-in-a-box’ model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components produce first generation halo neutrals that are tracked through successive generations until an ionization event occurs or the descendant halos exit the box. The 3D halo neutral model and neutral particle analyzer (NPA) simulator in the TRANSP code have been benchmarked with the Fast-Ion D-Alpha simulation (FIDAsim) code, which provides Monte Carlo simulations of beam neutral injection, attenuation, halo generation, halo spatial diffusion, and photoemission processes. When using the same atomic physics database, TRANSP and FIDAsim simulations achieve excellent agreement on the spatial profile and magnitude of beam and halo neutral densities and the NPA energy spectrum. The simulations show that the halo neutral density can be comparable to the beam neutral density. These halo neutrals can double the NPA flux, but they have minor effects on the NPA energy spectrum shape. The TRANSP and FIDAsim simulations also suggest that the magnitudes of beam and halo neutral densities are relatively sensitive to the choice of the atomic physics databases.

Implementation of a 3D halo neutral model in the TRANSP code and application to projected NSTX-U plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medley, S. S.; Liu, D.; Gorelenkova, M. V.

2016-01-12

A 3D halo neutral code developed at the Princeton Plasma Physics Laboratory and implemented for analysis using the TRANSP code is applied to projected National Spherical Torus eXperiment-Upgrade (NSTX-U plasmas). The legacy TRANSP code did not handle halo neutrals properly since they were distributed over the plasma volume rather than remaining in the vicinity of the neutral beam footprint as is actually the case. The 3D halo neutral code uses a 'beam-in-a-box' model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components producemore » first generation halo neutrals that are tracked through successive generations until an ionization event occurs or the descendant halos exit the box. The 3D halo neutral model and neutral particle analyzer (NPA) simulator in the TRANSP code have been benchmarked with the Fast-Ion D-Alpha simulation (FIDAsim) code, which provides Monte Carlo simulations of beam neutral injection, attenuation, halo generation, halo spatial diffusion, and photoemission processes. When using the same atomic physics database, TRANSP and FIDAsim simulations achieve excellent agreement on the spatial profile and magnitude of beam and halo neutral densities and the NPA energy spectrum. The simulations show that the halo neutral density can be comparable to the beam neutral density. These halo neutrals can double the NPA flux, but they have minor effects on the NPA energy spectrum shape. The TRANSP and FIDAsim simulations also suggest that the magnitudes of beam and halo neutral densities are relatively sensitive to the choice of the atomic physics databases.« less

Role of Turbulent Damping in Cosmic Ray Galactic Winds

NASA Astrophysics Data System (ADS)

Holguin, Francisco; Ruszkowski, Mateusz; Lazarian, Alex; Yang, H. Y. Karen

2018-06-01

Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, pushing and redistributing material throughout the interstellar medium (ISM) and galactic halo. A detailed understanding of the exact physical mechanisms responsible for these winds is lacking. Non-thermal feedback from galactic cosmic rays (CR), high-energy charged particles accelerated in supernovae and young stars, can impact the efficiency in accelerating the wind. In the self-confinement model, CR stream along magnetic field lines at the Alfven speed due to scattering off self-excited Aflv{é}n waves. However, magneto-hydrodynamic (MHD) turbulence stirred up by stellar feedback dissipates these confining waves, allowing CR to be super Aflvenic. Previous simulations relying on a simplified model of transport have shown that super-Alfv{é}nic streaming of CRs can launch a stronger wind. We perform three-dimensional MHD simulations of a section of a galactic disk, including CR streaming dependent on the local environment, using a realistic model of turbulent dissipation of Alfven waves presented in Lazarian (2016). In this implementation, the CR streaming speed can be super Alfv{é}nic depending on local conditions. We compare results for Alfv{é}nic and locally determined streaming, and find that gas/CR distributions and instantaneous mass loading factor of the wind are different depending on the level of turbulence.Lazarian, A. “Damping of Alfven waves by turbulence and its consequences: from cosmic-ray streaming to launching winds.” ApJ. Vol. 833, Num. 2. (2016).

Galaxy and Mass Assembly (GAMA): halo formation times and halo assembly bias on the cosmic web

NASA Astrophysics Data System (ADS)

Tojeiro, Rita; Eardley, Elizabeth; Peacock, John A.; Norberg, Peder; Alpaslan, Mehmet; Driver, Simon P.; Henriques, Bruno; Hopkins, Andrew M.; Kafle, Prajwal R.; Robotham, Aaron S. G.; Thomas, Peter; Tonini, Chiara; Wild, Vivienne

2017-09-01

We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying Galaxy and Mass Assembly (GAMA) galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with GE is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.

EFFECTS OF HOT HALO GAS ON STAR FORMATION AND MASS TRANSFER DURING DISTANT GALAXY–GALAXY ENCOUNTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Jeong-Sun; Park, Changbom, E-mail: jshwang@kias.re.kr, E-mail: cbp@kias.re.kr

2015-06-01

We use N-body/smoothed particle hydrodynamics simulations of encounters between an early-type galaxy (ETG) and a late-type galaxy (LTG) to study the effects of hot halo gas on the evolution for a case with the mass ratio of the ETG to LTG of 2:1 and the closest approach distance of ∼100 kpc. We find that the dynamics of the cold disk gas in the tidal bridge and the amount of the newly formed stars depend strongly on the existence of a gas halo. In the run of interacting galaxies not having a hot gas halo, the gas and stars accreted into themore » ETG do not include newly formed stars. However, in the run using the ETG with a gas halo and the LTG without a gas halo, a shock forms along the disk gas tidal bridge and induces star formation near the closest approach. The shock front is parallel to a channel along which the cold gas flows toward the center of the ETG. As a result, the ETG can accrete star-forming cold gas and newly born stars at and near its center. When both galaxies have hot gas halos, a shock is formed between the two gas halos somewhat before the closest approach. The shock hinders the growth of the cold gas bridge to the ETG and also ionizes it. Only some of the disk stars transfer through the stellar bridge. We conclude that the hot halo gas can give significant hydrodynamic effects during distant encounters.« less

Vertical Shear of the Galactic Interstellar Medium

NASA Technical Reports Server (NTRS)

Benjamin, Robert A.

2000-01-01

The detection of UV absorption, 21 cm, H alpha and other diffuse optical emission lines from gas up to ten kiloparsecs above the plane of the Milky Way and other galaxies provides the first, opportunity to probe the rotational properties of the ionized "atmospheres" of galaxies. This rotation has implications for our understanding of the Galactic gravitational potential, angular momentum transport in the Galactic disk, and the maintenance of a Galactic dynamo. The available evidence indicates that gas rotates nearly cylindrically up to a few kiloparsecs. This is in contrast to the expectation that there should be a significant gradient in rotation speed as a function of height assuming a reasonable mass model for the Galaxy. For example, for a vertical cut at galactocentric radius R = 5 kpc in NGC 891 by Rand, the rotation speed is observed to drop by approximately 30 kilometers per second from z = 1 to 5 kpc and is expected to drop by 80 kilometers per second. Magnetic tension forces may resolve this discrepancy. Other possibilities will be examined in the near future.

Metallicity and Kinematics of M31's Outer Stellar Halo from a Keck Spectroscopic Survey

NASA Astrophysics Data System (ADS)

Reitzel, David B.; Guhathakurta, Puragra

2002-07-01

We present first results from a spectroscopic survey designed to examine the metallicity and kinematics of individual red giant branch stars in the outer halo of the Andromeda spiral galaxy (M31). This study is based on multislit spectroscopy with the Keck II 10 m telescope and Low Resolution Imaging Spectrograph of the Ca II near-infrared triplet in 99 M31 halo candidates in a field at R=19 kpc on the southeast minor axis with brightnesses from 20halo red giants from foreground Milky Way dwarf stars, faint compact background galaxies, and M31 disk giants. The observed distribution of radial velocities is well fitted by an equal mix of foreground Milky Way dwarf stars, drawn from a standard Galactic model and with velocities v<~0 km s-1, and M31 halo giants represented by a Gaussian of width σM31v~150 km s-1 centered on its systemic velocity of vM31sys~-300 km s-1. A secure sample of 29 M31 red giant stars is identified on the basis of radial velocity (v<-220 km s-1) and, in the case of four intermediate-velocity stars (-160halo giants has an rms spread of at least 0.6 dex and spans the >~2 dex range over which the abundance measurement methods are calibrated. The mean/median metallicity of the M31 halo is about <[Fe/H]>=-1.9 to -1.1 dex (depending on the details of metallicity calibration and sample selection) and possibly higher: the high-metallicity end of the distribution is poorly constrained by our data since the selection function for the secure M31 sample excludes over 80% of the giants in solar/supersolar metallicity range. Possible reasons are

The Formation of Galactic Bulges

NASA Astrophysics Data System (ADS)

Carollo, C. Marcella; Ferguson, Henry C.; Wyse, Rosemary F. G.

2000-03-01

Part I. Introduction: What are galactic bulges?; Part II. The Epoch of Bulge Formation: Origin of bulges; Deep sub-mm surveys: High-z ULIRGs and the formation of spheroids; Ages and metallicities for stars in the galactic bulge; Integrated stellar populations of bulges: First results; HST-NICMOS observations of galactic bulges: Ages and dust; Inside-out bulge formation and the origin of the Hubble sequence; Part III. The Timescales of Bulge Formation: Constraints on the bulge formation timescale from stellar populations; Bulge building with mergers and winds; Role of winds, starbursts, and activity in bulge formation; Dynamical timescales of bulge formation; Part IV. Physical Processes in Bulge Formation: the role of bars for secular bulge formation; Bars and boxy/peanut-shaped bulges: an observational point of view; Boxy- and peanut-shaped bulges; A new class of bulges; The role of secondary bars in bulge formation; Radial transport of molecular gas to the nuclei of spiral galaxies; Dynamical evolution of bulge shapes; Two-component stellar systems: Phase-space constraints; Central NGC 2146 - a firehose-type bending instability?; Bulge formation: the role of the multi-phase ISM; Global evolution of a self-gravitating multi-phase ISM in the central kpc region of galaxies; Part V. Bulge Phenomenology: Bulge-disk decomposition of spiral galaxies in the near-infrared; The triaxial bulge of NGC 1371; The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672; The kinematics and the origin of the ionized gas in NGC 4036; Optically thin thermal plasma in the galactic bulge; X-ray properties of bulges; The host galaxies of radio-loud AGN; The centers of radio-loud early-type galaxies with HST; Central UV spikes in two galactic spheroids; Conference summary: where do we stand?

First direct comparison of high and low ionization line kinematics in active galactic nuclei

NASA Technical Reports Server (NTRS)

Sulentic, J. W.; Marziani, P.; Dultzin-Hacyan, D.; Calvani, M.; Moles, M.

1995-01-01

We present first results of a comparison of emission line shift properties for the high (HILs) and low (LILs) ionization lines in 43 low-reshift quasars. We identify a core sample of C IV lambda 1549 and hydrogen beta profiles with a wide distribution of red- and blueshifts (less than or equal to +/- 1000 km/sec). We also identify two tails in this distribution: one with large hydrogen beta redshifts (greater than or equal to 2000 km/sec) and another with large C IV blueshifts (greater than or equal to 1500 km/sec). The tails are mutually exclusive. All objects with extreme hydrogen beta redshift are radio loud, and all objects with extreme C IV blueshift are radio quiet. The core samples of smaller shifts can be most simply divided into: (1) hydrogen beta - a redshifted radio-loud population (related to the tail) and a radio-quiet population with mean shift near zero, and (2) C IV - a blueshifted radio-quiet population (related to the tail) and a radio-loud population with mean shift near zero. The results suggest fundamentally different kinematics for the HILs and LILs. They also suggest very different kinematics for radio-loud and radio-quiet active galactic nuclei. They also favor a predominance of radial motion in a large fraction of the sample.

On The Evidence For Large-Scale Galactic Conformity In The Local Universe

NASA Astrophysics Data System (ADS)

Sin, Larry P. T.; Lilly, Simon J.; Henriques, Bruno M. B.

2017-10-01

We re-examine the observational evidence for large-scale (4 Mpc) galactic conformity in the local Universe, as presented in Kauffmann et al. We show that a number of methodological features of their analysis act to produce a misleadingly high amplitude of the conformity signal. These include a weighting in favour of central galaxies in very high density regions, the likely misclassification of satellite galaxies as centrals in the same high-density regions and the use of medians to characterize bimodal distributions. We show that the large-scale conformity signal in Kauffmann et al. clearly originates from a very small number of central galaxies in the vicinity of just a few very massive clusters, whose effect is strongly amplified by the methodological issues that we have identified. Some of these 'centrals' are likely misclassified satellites, but some may be genuine centrals showing a real conformity effect. Regardless, this analysis suggests that conformity on 4 Mpc scales is best viewed as a relatively short-range effect (at the virial radius) associated with these very large neighbouring haloes, rather than a very long-range effect (at tens of virial radii) associated with the relatively low-mass haloes that host the nominal central galaxies in the analysis. A mock catalogue constructed from a recent semi-analytic model shows very similar conformity effects to the data when analysed in the same way, suggesting that there is no need to introduce new physical processes to explain galactic conformity on 4 Mpc scales.

TESTING GALAXY FORMATION MODELS WITH THE GHOSTS SURVEY: THE COLOR PROFILE OF M81's STELLAR HALO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monachesi, Antonela; Bell, Eric F.; Bailin, Jeremy

2013-04-01

We study the properties of the stellar populations in M81's outermost part, which hereafter we will call the stellar halo, using Hubble Space Telescope (HST) Advanced Camera for Surveys observations of 19 fields from the GHOSTS survey. The observed fields probe the stellar halo out to a projected distance of {approx}50 kpc from the galactic center. Each field was observed in both F606W and F814W filters. The 50% completeness levels of the color-magnitude diagrams (CMDs) are typically at 2 mag below the tip of the red giant branch (TRGB). Fields at distances closer than 15 kpc show evidence of disk-dominatedmore » populations whereas fields at larger distances are mostly populated by halo stars. The red giant branch (RGB) of the M81's halo CMDs is well matched with isochrones of {approx}10 Gyr and metallicities [Fe/H] {approx} - 1.2 dex, suggesting that the dominant stellar population of M81's halo has a similar age and metallicity. The halo of M81 is characterized by a color distribution of width {approx}0.4 mag and an approximately constant median value of (F606W - F814W) {approx}1 mag measured using stars within the magnitude range 23.7 {approx}< F814W {approx}< 25.5. When considering only fields located at galactocentric radius R > 15 kpc, we detect no color gradient in the stellar halo of M81. We place a limit of 0.03 {+-} 0.11 mag difference between the median color of RGB M81 halo stars at {approx}15 and at 50 kpc, corresponding to a metallicity difference of 0.08 {+-} 0.35 dex over that radial range for an assumed constant age of 10 Gyr. We compare these results with model predictions for the colors of stellar halos formed purely via accretion of satellite galaxies. When we analyze the cosmologically motivated models in the same way as the HST data, we find that they predict no color gradient for the stellar halos, in good agreement with the observations.« less

HALOE Science Investigation

NASA Technical Reports Server (NTRS)

Benner, D. Chris

1998-01-01

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.

TWO DISTANT HALO VELOCITY GROUPS DISCOVERED BY THE PALOMAR TRANSIENT FACTORY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sesar, Branimir; Cohen, Judith G.; Levitan, David

2012-08-20

We report the discovery of two new halo velocity groups (Cancer groups A and B) traced by eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R.A. {approx} 129 Degree-Sign , decl. {approx} 20 Degree-Sign (l {approx} 205 Degree-Sign , b {approx} 32 Degree-Sign ). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1 m Hale telescope and W. M. Keck Observatory 10 m Keck I telescope indicatemore » that the two groups are moving away from the Galaxy at v-bar{sub gsr}{sup A} = 78.0{+-}5.6 km s{sup -1} (Cancer group A) and v-bar{sub gsr}{sup B} = 16.3{+-}7.1 km s{sup -1} (Cancer group B). The groups have velocity dispersions of {sigma}{sub v{sub g{sub s{sub r}{sup A}}}} = 12.4{+-}5.0 km s{sup -1} and {sigma}B{sub v{sub g{sub s{sub r}{sup B}}}} =14.9{+-}6.2 km s{sup -1} and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of [Fe/H]{sup A} = -1.6 dex and [Fe/H]{sup B} = -2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of {approx}0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with velocities consistent with those of the Cancer groups have been observed {approx}25 Degree-Sign east, suggesting possible extension of the groups in that direction.« less

CONNECTING ANGULAR MOMENTUM AND GALACTIC DYNAMICS: THE COMPLEX INTERPLAY BETWEEN SPIN, MASS, AND MORPHOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teklu, Adelheid F.; Remus, Rhea-Silvia; Dolag, Klaus

The evolution and distribution of the angular momentum of dark matter (DM) halos have been discussed in several studies over the past decades. In particular, the idea arose that angular momentum conservation should allow us to infer the total angular momentum of the entire DM halo from measuring the angular momentum of the baryonic component, which is populating the center of the halo, especially for disk galaxies. To test this idea and to understand the connection between the angular momentum of the DM halo and its galaxy, we use a state-of-the-art, hydrodynamical cosmological simulation taken from the set of Magneticummore » Pathfinder simulations. Thanks to the inclusion of the relevant physical processes, the improved underlying numerical methods, and high spatial resolution, we successfully produce populations of spheroidal and disk galaxies self-consistently. Thus, we are able to study the dependence of galactic properties on their morphology. We find that (1) the specific angular momentum of stars in disk and spheroidal galaxies as a function of their stellar mass compares well with observational results; (2) the specific angular momentum of the stars in disk galaxies is slightly smaller compared to the specific angular momentum of the cold gas, in good agreement with observations; (3) simulations including the baryonic component show a dichotomy in the specific stellar angular momentum distribution when splitting the galaxies according to their morphological type (this dichotomy can also be seen in the spin parameter, where disk galaxies populate halos with slightly larger spin compared to spheroidal galaxies); (4) disk galaxies preferentially populate halos in which the angular momentum vector of the DM component in the central part shows a better alignment to the angular momentum vector of the entire halo; and (5) the specific angular momentum of the cold gas in disk galaxies is approximately 40% smaller than the specific angular momentum of the total

SDSS IV MaNGA—Rotation Velocity Lags in the Extraplanar Ionized Gas from MaNGA Observations of Edge-on Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bizyaev, D.; Pan, K.; Brinkmann, J.

2017-04-20

We present a study of the kinematics of the extraplanar ionized gas around several dozen galaxies observed by the Mapping of Nearby Galaxies at the Apache Point Observatory (MaNGA) survey. We considered a sample of 67 edge-on galaxies out of more than 1400 extragalactic targets observed by MaNGA, in which we found 25 galaxies (or 37%) with regular lagging of the rotation curve at large distances from the galactic midplane. We model the observed H α emission velocity fields in the galaxies, taking projection effects and a simple model for the dust extinction into account. We show that the verticalmore » lag of the rotation curve is necessary in the modeling, and estimate the lag amplitude in the galaxies. We find no correlation between the lag and the star formation rate in the galaxies. At the same time, we report a correlation between the lag and the galactic stellar mass, central stellar velocity dispersion, and axial ratio of the light distribution. These correlations suggest a possible higher ratio of infalling-to-local gas in early-type disk galaxies or a connection between lags and the possible presence of hot gaseous halos, which may be more prevalent in more massive galaxies. These results again demonstrate that observations of extraplanar gas can serve as a potential probe for accretion of gas.« less

SDSS IV MaNGA—Rotation Velocity Lags in the Extraplanar Ionized Gas from MaNGA Observations of Edge-on Galaxies

NASA Astrophysics Data System (ADS)

Bizyaev, D.; Walterbos, R. A. M.; Yoachim, P.; Riffel, R. A.; Fernández-Trincado, J. G.; Pan, K.; Diamond-Stanic, A. M.; Jones, A.; Thomas, D.; Cleary, J.; Brinkmann, J.

2017-04-01

We present a study of the kinematics of the extraplanar ionized gas around several dozen galaxies observed by the Mapping of Nearby Galaxies at the Apache Point Observatory (MaNGA) survey. We considered a sample of 67 edge-on galaxies out of more than 1400 extragalactic targets observed by MaNGA, in which we found 25 galaxies (or 37%) with regular lagging of the rotation curve at large distances from the galactic midplane. We model the observed Hα emission velocity fields in the galaxies, taking projection effects and a simple model for the dust extinction into account. We show that the vertical lag of the rotation curve is necessary in the modeling, and estimate the lag amplitude in the galaxies. We find no correlation between the lag and the star formation rate in the galaxies. At the same time, we report a correlation between the lag and the galactic stellar mass, central stellar velocity dispersion, and axial ratio of the light distribution. These correlations suggest a possible higher ratio of infalling-to-local gas in early-type disk galaxies or a connection between lags and the possible presence of hot gaseous halos, which may be more prevalent in more massive galaxies. These results again demonstrate that observations of extraplanar gas can serve as a potential probe for accretion of gas.

CEMP Stars in the Halo and Their Origin in Ultra-Faint Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Beers, Timothy C.

2018-06-01

The very metal-poor (VMP; [Fe/H] < –2.0) and extremely metal-poor (EMP; [Fe/H] < –3.0) stars provide a direct view of Galactic chemical and dynamical evolution; detailed spectroscopic studies of these objects are the best way to identify and distinguish between various scenarios for the enrichment of early star-forming gas clouds soon after the Big Bang. It has been recognized that a large fraction of VMP (15-20%) and EMP stars (30-40%) possess significant over-abundances of carbon relative to iron, [C/Fe] > +0.7. This fraction rises to at least 80% for stars with [Fe/H] < –4.0. Recent studies show that the majority of CEMP stars with [Fe/H] < –3.0 belong to the CEMP-no sub-class, characterized by the lack of strong enhancements in the neutron-capture elements (e.g., [Ba/Fe] < 0.0). The CEMP-no abundance signature is commonly observed among stars ultra-faint dwarf spheroidal galaxies such as SEGUE-1. In addition, kinematic studies of CEMP-no stars strongly suggest an association with the outer-halo population of the Galaxy, which was likely formed from the accretion of low-mass mini-halos. These observations, and other lines of evidence, indicate that the CEMP-no stars of the Milky Way were born in low-mass dwarf galaxies, and later subsumed into the halo.

Statistical Aspects of X-Class Halo and Non-Halo Events, 1996-2014

NASA Technical Reports Server (NTRS)

Wilson, Robert M.

2016-01-01

Of the 166 X-class events that occurred during the interval 1996-2014, 80 had associations with halo events, 68 had no associations with halo events, and 18 occurred during LASCO (Large Angle and Spectrometric COronagraph) data gaps. Both the duration and location of the X-class halo events proved to be statistically important parameters with respect to the geo-effectiveness of the events. Forty-four of the 80 X-class halo events occurred within 45 degrees of the Sun's central meridian and 47 of the 80 had duration greater than or equal to 30 minutes, whereas only 28 of the 68 X-class non-halo events occurred within 45 degrees of the Sun's central meridian (2 events have unknown location) and 22 of the 68 had duration greater than or equal to 30 minutes. Ignoring the 4 largest X-class flares greater than or equal to X4.0 during the LASCO data gaps, 17 of the remaining 20 were associated with halo events, and 14 of the 17 had at least one geo-magnetically disturbed day (Ap (i.e. NOAA's Ap* (ApStar)index: the major magnetic storms going back to 1932) greater than or equal to 25 nanotesias) within 1-5 days following the X-class halo event. Based on the hourly Dst (Disturbance storm time) index, the most geo-effective X-class halo event during the interval 1996-2014 was that of an X1.7 flare that occurred on 2001 March 29 at 0957, having an hourly Disturbance storm time minimum equal to minus 387 nanotesias. On average, the X-class halo events (80 events) were found to have a mean duration (42 minutes) slightly longer than the mean duration (29 minutes) of the X-class non-halo events (68 events) with the difference in the means being statistically important at the 1 percent level of significance.

Galactic fly-bys: New source of lithium production

NASA Astrophysics Data System (ADS)

Prodanović, Tijana; Bogdanović, Tamara; Urošević, Dejan

2013-05-01

Observations of low-metallicity halo stars have revealed a puzzling result: the abundance of Li7 in these stars is at least three times lower than their predicted primordial abundance. It is unclear whether the cause of this disagreement is a lack of understanding of lithium destruction mechanisms in stars or the non-standard physics behind the big bang nucleosynthesis (BBN). Uncertainties related to the destruction of lithium in stars can be circumvented if lithium abundance is measured in the “pristine” gas of the low metallicity systems. The first measurement in one such system, the small magellanic cloud (SMC), was found to be at the level of the pure expected primordial value, but is on the other hand, just barely consistent with the expected galactic abundance for the system at the SMC metallicity, where important lithium quantity was also produced in interactions of galactic cosmic rays and presents an addition to the already present primordial abundance. Because of the importance of the SMC lithium measurement for the resolution of the lithium problem, we here draw attention to the possibility of another post-BBN production channel of lithium, which could present an important addition to the observed SMC lithium abundance. Besides standard galactic cosmic rays, additional post-BBN production of lithium might come from cosmic rays accelerated in galaxy-galaxy interactions. This might be important for a system such is the SMC, which has experienced galaxy harassment in its history. Within a simplified but illustrative framework we demonstrate that large-scale tidal shocks from a few galactic fly-bys can possibly produce lithium in amounts comparable to those expected from the interactions of galactic cosmic-rays produced in supernovae over the entire history of a system. In case of the SMC, we find that only two such fly-bys could possibly account for as much lithium as the standard, galactic cosmic ray production channel. However, adding any a new

Deep photometry of two accreted families of globular clusters in the remote M31 halo

NASA Astrophysics Data System (ADS)

Mackey, Dougal

2013-10-01

Globular clusters {GCs} are fossil relics from which we can obtain critical insights into the merger and accretion events that underlie hierarchical galaxy assembly. As part of the major Pan-Andromeda Archaeological Survey {PAndAS} we have discovered two groups of GCs that closely trace narrow stellar debris streams in the M31 halo. These clearly represent two distinct accreted families of GCs - the only known examples apart from the few Galactic GCs arriving with the Sagittarius dwarf. We propose to obtain deep ACS imaging of 14 GCs spanning these two accreted families, allowing us to measure the constituent stellar populations, line-of-sight distance, and structural parameters of each object. We will, for the first time, quantify the typical properties of accreted GCs in the M31 halo as well as the degree of variation amongst them, and how closely they correspond to the suspected accreted GC population in the Milky Way. Combined with new radial velocity measurements for the GCs, our proposed observations will allow us to trace the 3D orbits of the two streams within the M31 halo, and thus break the main degeneracies that plague numerical models designed to probe the gravitational potential and distribution of dark mass.

The role of self-interacting right-handed neutrinos in galactic structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Argüelles, C.R.; Rueda, J.A.; Ruffini, R.

2016-04-01

It has been shown previously that the DM in galactic halos can be explained by a self-gravitating system of massive keV fermions ('inos') in thermodynamic equilibrium, and predicted the existence of a denser quantum core of inos towards the center of galaxies. In this article we show that the inclusion of self-interactions among the inos, modeled within a relativistic mean-field-theory approach, allows the quantum core to become massive and compact enough to explain the dynamics of the S-cluster stars closest to the Milky Way's galactic center. The application of this model to other galaxies such as large elliptical harboring massivemore » central dark objects of ∼ 10{sup 9} M {sub ⊙} is also investigated. We identify these interacting inos with sterile right-handed neutrinos pertaining to minimal extensions of the Standard Model, and calculate the corresponding total cross-section σ within an electroweak-like formalism to be compared with other observationally inferred cross-section estimates. The coincidence of an ino mass range of few tens of keV derived here only from the galactic structure, with the range obtained independently from other astrophysical and cosmological constraints, points towards an important role of the right-handed neutrinos in the cosmic structure.« less

Cosmic web type dependence of halo clustering

NASA Astrophysics Data System (ADS)

Fisher, J. D.; Faltenbacher, A.

2018-01-01

We use the Millennium Simulation to show that halo clustering varies significantly with cosmic web type. Haloes are classified as node, filament, sheet and void haloes based on the eigenvalue decomposition of the velocity shear tensor. The velocity field is sampled by the peculiar velocities of a fixed number of neighbouring haloes, and spatial derivatives are computed using a kernel borrowed from smoothed particle hydrodynamics. The classification scheme is used to examine the clustering of haloes as a function of web type for haloes with masses larger than 1011 h- 1 M⊙. We find that node haloes show positive bias, filament haloes show negligible bias and void and sheet haloes are antibiased independent of halo mass. Our findings suggest that the mass dependence of halo clustering is rooted in the composition of web types as a function of halo mass. The substantial fraction of node-type haloes for halo masses ≳ 2 × 1013 h- 1 M⊙ leads to positive bias. Filament-type haloes prevail at intermediate masses, 1012-1013 h- 1 M⊙, resulting in unbiased clustering. The large contribution of sheet-type haloes at low halo masses ≲ 1012 h- 1 M⊙ generates antibiasing.

The ellipticity of galaxy cluster haloes from satellite galaxies and weak lensing

DOE PAGES

Shin, Tae-hyeon; Clampitt, Joseph; Jain, Bhuvnesh; ...

2018-01-04

Here, we study the ellipticity of galaxy cluster haloes as characterized by the distribution of cluster galaxies and as measured with weak lensing. We use Monte Carlo simulations of elliptical cluster density profiles to estimate and correct for Poisson noise bias, edge bias and projection effects. We apply our methodology to 10 428 Sloan Digital Sky Survey clusters identified by the redMaPPer algorithm with richness above 20. We find a mean ellipticity =0.271 ± 0.002 (stat) ±0.031 (sys) corresponding to an axis ratio = 0.573 ± 0.002 (stat) ±0.039 (sys). We compare this ellipticity of the satellites to the halomore » shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016). We find a best-fitting axis ratio of 0.56 ± 0.09 (stat) ±0.03 (sys), consistent with the ellipticity of the satellite distribution. Thus, cluster galaxies trace the shape of the dark matter halo to within our estimated uncertainties. Finally, we restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements, we infer a misalignment angle with an root-mean-square of 30° ± 10° when stacking on the central galaxy. We discuss applications of halo shape measurements to test the effects of the baryonic gas and active galactic nucleus feedback, as well as dark matter and gravity. The major improvements in signal-to-noise ratio expected with the ongoing Dark Energy Survey and future surveys from Large Synoptic Survey Telescope, Euclid, and Wide Field Infrared Survey Telescope will make halo shapes a useful probe of these effects.« less

The ellipticity of galaxy cluster haloes from satellite galaxies and weak lensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Tae-hyeon; Clampitt, Joseph; Jain, Bhuvnesh

Here, we study the ellipticity of galaxy cluster haloes as characterized by the distribution of cluster galaxies and as measured with weak lensing. We use Monte Carlo simulations of elliptical cluster density profiles to estimate and correct for Poisson noise bias, edge bias and projection effects. We apply our methodology to 10 428 Sloan Digital Sky Survey clusters identified by the redMaPPer algorithm with richness above 20. We find a mean ellipticity =0.271 ± 0.002 (stat) ±0.031 (sys) corresponding to an axis ratio = 0.573 ± 0.002 (stat) ±0.039 (sys). We compare this ellipticity of the satellites to the halomore » shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016). We find a best-fitting axis ratio of 0.56 ± 0.09 (stat) ±0.03 (sys), consistent with the ellipticity of the satellite distribution. Thus, cluster galaxies trace the shape of the dark matter halo to within our estimated uncertainties. Finally, we restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements, we infer a misalignment angle with an root-mean-square of 30° ± 10° when stacking on the central galaxy. We discuss applications of halo shape measurements to test the effects of the baryonic gas and active galactic nucleus feedback, as well as dark matter and gravity. The major improvements in signal-to-noise ratio expected with the ongoing Dark Energy Survey and future surveys from Large Synoptic Survey Telescope, Euclid, and Wide Field Infrared Survey Telescope will make halo shapes a useful probe of these effects.« less

The Galactic thick disc density profile traced with RR Lyrae stars

NASA Astrophysics Data System (ADS)

Mateu, Cecilia; Vivas, A. Katherina

2018-05-01

We used a combination of public RR Lyrae star catalogs and a Bayesian methodology to derive robust structural parameters of the inner halo (<25 kpc) and thick disc of the Milky Way. RR Lyrae stars are an unequivocal tracer of old metal-poor populations, for which accurate distances and extinctions can be individually estimated and so, are a reliable independent means of tracing the population of the old high-[α/Fe] disc usually associated to the thick disc. In particular, the chosen RR Lyrae sample spans regions at low galactic latitude toward the anti-center direction, allowing to probe the outermost parts of the disc. Our results favour a thick disc with short scale height and short scale length, h_z=0.65_{-0.05}^{+0.09} kpc, h_R=2.1_{-0.25}^{+0.82} kpc, for a model in which the inner halo has a constant flattening of q=0.90_{-0.03}^{+0.05} and a power law index of n=-2.78_{-0.05}^{+0.05}. Similar short scales for the thick disc are also found when considering an inner halo with flattening dependent on radius. We also explored a model in which the thick disc has a flare and, although this is only mildly constrained with our data, a flare onset in the inner ˜11 kpc is highly disfavoured.

THE CLUSTERING OF ALFALFA GALAXIES: DEPENDENCE ON H I MASS, RELATIONSHIP WITH OPTICAL SAMPLES, AND CLUES OF HOST HALO PROPERTIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Papastergis, Emmanouil; Giovanelli, Riccardo; Haynes, Martha P.

We use a sample of ≈6000 galaxies detected by the Arecibo Legacy Fast ALFA (ALFALFA) 21 cm survey to measure the clustering properties of H I-selected galaxies. We find no convincing evidence for a dependence of clustering on galactic atomic hydrogen (H I) mass, over the range M{sub H{sub I}} ≈ 10{sup 8.5}-10{sup 10.5} M{sub ☉}. We show that previously reported results of weaker clustering for low H I mass galaxies are probably due to finite-volume effects. In addition, we compare the clustering of ALFALFA galaxies with optically selected samples drawn from the Sloan Digital Sky Survey (SDSS). We findmore » that H I-selected galaxies cluster more weakly than even relatively optically faint galaxies, when no color selection is applied. Conversely, when SDSS galaxies are split based on their color, we find that the correlation function of blue optical galaxies is practically indistinguishable from that of H I-selected galaxies. At the same time, SDSS galaxies with red colors are found to cluster significantly more than H I-selected galaxies, a fact that is evident in both the projected as well as the full two-dimensional correlation function. A cross-correlation analysis further reveals that gas-rich galaxies 'avoid' being located within ≈3 Mpc of optical galaxies with red colors. Next, we consider the clustering properties of halo samples selected from the Bolshoi ΛCDM simulation. A comparison with the clustering of ALFALFA galaxies suggests that galactic H I mass is not tightly related to host halo mass and that a sizable fraction of subhalos do not host H I galaxies. Lastly, we find that we can recover fairly well the correlation function of H I galaxies by just excluding halos with low spin parameter. This finding lends support to the hypothesis that halo spin plays a key role in determining the gas content of galaxies.« less

The role of environment in the observed Fundamental Plane of radio Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Shabala, Stanislav S.

2018-05-01

The optical Fundamental Plane of black hole activity relates radio continuum luminosity of Active Galactic Nuclei to [O III] luminosity and black hole mass. We examine the environments of low redshift (z < 0.2) radio-selected AGN, quantified through galaxy clustering, and find that halo mass provides similar mass scalings to black hole mass in the Fundamental Plane relations. AGN properties are strongly environment-dependent: massive haloes are more likely to host radiatively inefficient (low-excitation) radio AGN, as well as a higher fraction of radio luminous, extended sources. These AGN populations have different radio - optical luminosity scaling relations, and the observed mass scalings in the parent AGN sample are built up by combining populations preferentially residing in different environments. Accounting for environment-driven selection effects, the optical Fundamental Plane of supermassive black holes is likely to be mass-independent, as predicted by models.

HERSCHEL GALACTIC PLANE SURVEY OF [N ii] FINE STRUCTURE EMISSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldsmith, Paul F.; Yıldız, Umut A.; Langer, William D.

2015-12-01

We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N ii]) at 122 and 205 μm. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10{sup −8}–10{sup −7} Wm{sup −2} sr{sup −1} level over the range –60° ≤ l ≤ 60°. The rms of the intensity among the 25 PACS spaxels of a given pointingmore » is typically less than one third of the mean intensity, showing that the emission is extended. [N ii] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10–50 cm{sup −3} with an average value of 29 cm{sup −3} and N{sup +} column densities 10{sup 16}–10{sup 17} cm{sup −2}. [N ii] emission is highly correlated with that of [C ii], and we calculate that between 1/3 and 1/2 of the [C ii] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N ii] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N ii] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H ii regions, and low-filling factor high-density fluctuations of the WIM.« less

Galactic conformity and central/satellite quenching, from the satellite profiles of M* galaxies at 0.4 < z < 1.9 in the UKIDSS UDS

NASA Astrophysics Data System (ADS)

Hartley, W. G.; Conselice, C. J.; Mortlock, A.; Foucaud, S.; Simpson, C.

2015-08-01

We explore the redshift evolution of a curious correlation between the star formation properties of central galaxies and their satellites (`galactic conformity') at intermediate to high redshift (0.4 < z < 1.9). Using an extremely deep near-infrared survey, we study the distribution and properties of satellite galaxies with stellar masses, log(M*/M⊙) > 9.7, around central galaxies at the characteristic Schechter function mass, M ˜ M*. We fit the radial profiles of satellite number densities with simple power laws, finding slopes in the range -1.1 to -1.4 for mass-selected satellites, and -1.3 to -1.6 for passive satellites. We confirm the tendency for passive satellites to be preferentially located around passive central galaxies at 3σ significance and show that it exists to at least z ˜ 2. Meanwhile, the quenched fraction of satellites around star-forming galaxies is consistent with field galaxies of equal stellar masses. We find no convincing evidence for a redshift-dependent evolution of these trends. One simple interpretation of these results is that only passive central galaxies occupy an environment that is capable of independently shutting off star formation in satellite galaxies. By examining the satellites of higher stellar mass star-forming galaxies (log(M*/M⊙) > 11), we conclude that the origin of galactic conformity is unlikely to be exclusively due to the host dark matter halo mass. A halo-mass-independent correlation could be established by either formation bias or a more physical connection between central and satellite star formation histories. For the latter, we argue that a star formation (or active galactic nucleus) related outburst event from the central galaxy could establish a hot halo environment which is then capable of quenching both central and satellite galaxies.

An Investigation of the Ionization Structure of the Carina Spiral Arm with WHAM

NASA Astrophysics Data System (ADS)

Benjamin, Robert A.; Krishnarao, Dhanesh; Haffner, L. Matthew

2018-01-01

Recent investigations of the Sagittarius-Carina spiral arm with the Wisconsin H-alpha Mapper (Krishnarao et al 2017) show the presence of ionized gas stretching up to three kiloparsecs above and below the Carina section of this spiral arm. This arm segment, which wraps outside the solar circle in the fourth quadrant of the Galactic disk, seems to be unusual when compared to the other Milky Way spiral arms measured with WHAM. We review the status of what is known about the vertical ionization structure of the spiral arms of the Milky Way Galaxy and relate the properties of this spiral arm section to recent investigations of midplane HII regions and star formation in the Milky Way disk. We discuss potential implications of this star formation and ionization for our understanding of Milky Way Galactic structure.

Exploring the Milky Way halo with SDSS-II SN survey RR Lyrae stars

NASA Astrophysics Data System (ADS)

De Lee, Nathan

This thesis details the creation of a large catalog of RR Lyrae stars, their lightcurves, and their associated photometric and kinematic parameters. This catalog contains 421 RR Lyrae stars with 305 RRab and 116 RRc. Of these, 241 stars have stellar spectra taken with either the Blanco 4m RC spectrograph or the SDSS/SEGUE survey, and in some cases taken by both. From these spectra and photometric methods derived from them, an analysis is conducted of the RR lyrae's distribution, metallicity, kinematics, and photometric properties within the halo. All of these RR Lyrae originate from the SDSS-II Supernova Survey. The SDSS-II SN Survey covers a 2.5 degree equatorial stripe ranging from -60 to +60 degrees in RA. This corresponds to relatively high southern galactic latitudes in the anti-center direction. The full catalog ranges from g 0 magnitude 13 to 20 which covers a distance of 3 to 95 kpc from the sun. Using this sample, we explore the Oosterhoff dichotomy through the D log P method as a function of | Z | distance from the plane. This results in a clear division of the RRab stars into OoI and OoII groups at lower | Z |, but the population becomes dominated by OoI stars at higher | Z |. The idea of a dual halo is explored primarily in the context of radial velocity distributions as a function of | Z |. In particular, V gsr , the radial velocity in the galactic standard of rest, is used as a proxy for V [straight phi] , the cylindrical rotational velocity. This is then compared against a single halo model galaxy, which results in very similar V gsr histograms for both at low to medium | Z |. However, at high | Z | there is a clear separation into two distinct velocity groups for the data without a corresponding separation in the model, suggesting that at least a two-component model for the halo is necessary. The final part of the analysis involves [Fe/H] measurements from both spectra and photometric relations cut in both | Z | and radial velocity. In this case

Hot Gas Halos in Galaxies

NASA Astrophysics Data System (ADS)

Mulchaey, John

Most galaxy formation models predict that massive low-redshift disk galaxies are embedded in extended hot halos of externally accreted gas. Such gas appears necessary to maintain ongoing star formation in isolated spirals like the Milky Way. To explain the large population of red galaxies in rich groups and clusters, most galaxy evolution models assume that these hot gas halos are stripped completely when a galaxy enters a denser environment. This simple model has been remarkably successful at reproducing many observed properties of galaxies. Although theoretical arguments suggest hot gas halos are an important component in galaxies, we know very little about this gas from an observational standpoint. In fact, previous observations have failed to detect soft X-ray emission from such halos in disk galaxies. Furthermore, the assumption that hot gas halos are stripped completely when a galaxy enters a group or cluster has not been verified. We propose to combine proprietary and archival XMM-Newton observations of galaxies in the field, groups and clusters to study how hot gas halos are impacted by environment. Our proposed program has three components: 1) The deepest search to date for a hot gas halo in a quiescent spiral galaxy. A detection will confirm a basic tenet of disk galaxy formation models, whereas a non-detection will seriously challenge these models and impose new constraints on the growth mode and feedback history of disk galaxies. 2) A detailed study of the hot gas halos properties of field early-type galaxies. As environmental processes such as stripping are not expected to be important in the field, a study of hot gas halos in this environment will allow us to better understand how feedback and other internal processes impact hot gas halos. 3) A study of hot gas halos in the outskirts of groups and clusters. By comparing observations with our suite of simulations we can begin to understand what role the stripping of hot gas halos plays in galaxy

The QUEST RR Lyrae Survey. II. The Halo Overdensities in the First Catalog

NASA Astrophysics Data System (ADS)

Vivas, A. Katherina; Zinn, Robert

2006-08-01

The first catalog of the RR Lyrae stars (RRLSs) in the Galactic halo by the Quasar Equatorial Survey Team (QUEST) has been searched for significant overdensities that may be debris from disrupted dwarf galaxies or globular clusters. These RRLSs are contained in a band ~2.3d wide in declination that spans ~165° in right ascension and lie ~4 to ~60 kpc from the Sun. Away from the major overdensities, the distribution of these stars is adequately fitted by a smooth halo model, in which the flattening of the halo decreases with increasing galactocentric distance (as reported by Preston et al.). This model was used to estimate the ``background'' of RRLSs on which the halo overdensities are overlaid. A procedure was developed for recognizing groups of stars that constitute significant overdensities with respect to this background. To test this procedure, a Monte Carlo routine was used to make artificial RRLS surveys that follow the smooth halo model but with Poisson-distributed noise in the numbers of RRLSs and, within limits, random variations in the positions and magnitudes of the artificial stars. The 104 artificial surveys created by this routine were examined for significant groups in exactly the same way as the QUEST survey. These calculations provided estimates of the frequencies with which random fluctuations produce significant groups. In the QUEST survey there are six significant overdensities that contain six or more stars and several smaller ones. The small ones and possibly one or two of the larger ones may be artifacts of statistical fluctuations, and they need to be confirmed by measurements of radial velocity and/or proper motion. The most prominent groups are the northern stream from the Sagittarius dwarf spheroidal galaxy and a large group in Virgo, formerly known as the ``12.4 hr clump,'' which Duffau and coworkers have recently shown to contain a stellar stream (the Virgo stellar stream). Two other groups lie in the direction of the Monoceros stream

Under the sword of Damocles: plausible regeneration of dark matter cusps at the smallest galactic scales

NASA Astrophysics Data System (ADS)

Laporte, Chervin F. P.; Peñarrubia, Jorge

2015-04-01

We study the evolution of the dark matter (DM) halo profiles of dwarf galaxies driven by the accretion of DM substructures through controlled N-body experiments. Our initial conditions assume that early supernova feedback erases the primordial DM cusps of haloes with z = 0 masses of 109 - 1010 M⊙. The orbits and masses of the infalling substructures are borrowed from the Aquarius cosmological simulations. Our experiments show that a fraction of haloes that undergo 1:3 down to 1:30 mergers are susceptible to reform a DM cusp by z ≈ 0. Cusp regrowth is driven by the accretion of DM substructures that are dense enough to reach the central regions of the main halo before being tidally disrupted. The infall of substructures on the mean of the reported mass-concentration relation and a mass ratio above 1:6 systematically leads to cusp regrowth. Substructures with 1:6-1:8, and 1:8-1:30 only reform DM cusps if their densities are 1σ and 2σ above the mean, respectively. The merging time-scales of these dense, low-mass substructures is relatively long (5 - 11 Gyr), which may pose a time-scale problem for the longevity of DM cores in dwarfs galaxies and possibly explain the existence of dense dwarfs-like Draco. These results suggest that within cold dark matter a non-negligible level of scatter in the mass profiles of galactic haloes acted on by feedback is to be expected given the stochastic mass accretion histories of low-mass haloes and the diverse star formation histories observed in the Local Group dwarfs.

Millisecond Pulsars and the Galactic Center Excess

NASA Astrophysics Data System (ADS)

Gonthier, Peter L.; Koh, Yew-Meng; Kust Harding, Alice; Ferrara, Elizabeth C.

2017-08-01

Various groups including the Fermi team have confirmed the spectrum of the gamma- ray excess in the Galactic Center (GCE). While some authors interpret the GCE as evidence for the annihilation of dark matter (DM), others have pointed out that the GCE spectrum is nearly identical to the average spectrum of Fermi millisecond pul- sars (MSP). Assuming the Galactic Center (GC) is populated by a yet unobserved source of MSPs that has similar properties to that of MSPs in the Galactic Disk (GD), we present results of a population synthesis of MSPs from the GC. We establish parameters of various models implemented in the simulation code by matching characteristics of 54 detected Fermi MSPs in the first point source catalog and 92 detected radio MSPs in a select group of thirteen radio surveys and targeting a birth rate of 45 MSPs per mega-year. As a check of our simulation, we find excellent agreement with the estimated numbers of MSPs in eight globular clusters. In order to reproduce the gamma-ray spectrum of the GCE, we need to populate the GC with 10,000 MSPs having a Navarro-Frenk-White distribution suggested by the halo density of DM. It may be possible for Fermi to detect some of these MSPs in the near future; the simulation also predicts that many GC MSPs have radio fluxes S1400above 10 �μJy observable by future pointed radio observations. We express our gratitude for the generous support of the National Science Foundation (RUI: AST-1009731), Fermi Guest Investigator Program and the NASA Astrophysics Theory and Fundamental Program (NNX09AQ71G).

Modelling of Lyman-alpha emitting galaxies and ionized bubbles at the epoch of reionization

NASA Astrophysics Data System (ADS)

Yajima, Hidenobu; Sugimura, Kazuyuki; Hasegawa, Kenji

2018-04-01

Understanding {Ly{α }} emitting galaxies (LAEs) can be a key to reveal cosmic reionization and galaxy formation in the early Universe. Based on halo merger trees and {Ly{α }} radiation transfer calculations, we model redshift evolution of LAEs and their observational properties at z ≥ 6. We consider ionized bubbles associated with individual LAEs and IGM transmission of {Ly{α }} photons. We find that {Ly{α }} luminosity tightly correlates with halo mass and stellar mass, while the relation with star formation rate has a large dispersion. Comparing our models with the observed luminosity function by Konno et al., we suggest that LAEs at z ˜ 7 have galactic wind of V_out ≳ 100 km s^{-1} and HI column density of N_HI ≳ 10^{20} cm^{-2}. Number density of bright LAEs rapidly decreases as redshift increases, due to both lower star formation rate and smaller HII bubbles. Our model predicts future wide deep surveys with next generation telescopes, such as JWST, E-ELT and TMT, can detect LAEs at z ˜ 10 with a number density of n_LAE ˜ a few × 10^{-6} Mpc^{-3} for the flux sensitivity of 10^{-18} erg cm^{-2} s^{-1}. When giant HII bubbles are formed by clustering LAEs, the number density of observable LAEs can increase by a factor of few. By combining these surveys with future 21-cm observations, it could be possible to detect both LAEs with L_{Lyα }≳ 10^{42} erg s^{-1} and their associated giant HII bubbles with the size ≳ 250 kpc at z ˜ 10.

Spatial clustering of dark matter haloes: secondary bias, neighbour bias, and the influence of massive neighbours on halo properties

NASA Astrophysics Data System (ADS)

Salcedo, Andrés N.; Maller, Ariyeh H.; Berlind, Andreas A.; Sinha, Manodeep; McBride, Cameron K.; Behroozi, Peter S.; Wechsler, Risa H.; Weinberg, David H.

2018-04-01

We explore the phenomenon commonly known as halo assembly bias, whereby dark matter haloes of the same mass are found to be more or less clustered when a second halo property is considered, for haloes in the mass range 3.7 × 1011-5.0 × 1013 h-1 M⊙. Using the Large Suite of Dark Matter Simulations (LasDamas) we consider nine commonly used halo properties and find that a clustering bias exists if haloes are binned by mass or by any other halo property. This secondary bias implies that no single halo property encompasses all the spatial clustering information of the halo population. The mean values of some halo properties depend on their halo's distance to a more massive neighbour. Halo samples selected by having high values of one of these properties therefore inherit a neighbour bias such that they are much more likely to be close to a much more massive neighbour. This neighbour bias largely accounts for the secondary bias seen in haloes binned by mass and split by concentration or age. However, haloes binned by other mass-like properties still show a secondary bias even when the neighbour bias is removed. The secondary bias of haloes selected by their spin behaves differently than that for other halo properties, suggesting that the origin of the spin bias is different than of other secondary biases.

Galactic Cosmic Rays in the Outer Heliosphere

NASA Technical Reports Server (NTRS)

Florinski, V.; Washimi, H.; Pogorelov, N. V.; Adams, J. H.

2010-01-01

We report a next generation model of galactic cosmic ray (GCR) transport in the three dimensional heliosphere. Our model is based on an accurate three-dimensional representation of the heliospheric interface. This representation is obtained by taking into account the interaction between partially ionized, magnetized plasma flows of the solar wind and the local interstellar medium. Our model reveals that after entering the heliosphere GCRs are stored in the heliosheath for several years. The preferred GCR entry locations are near the nose of the heliopause and at high latitudes. Low-energy (hundreds of MeV) galactic ions observed in the heliosheath have spent, on average, a longer time in the solar wind than those observed in the inner heliosphere, which would explain their cooled-off spectra at these energies. We also discuss radial gradients in the heliosheath and the implications for future Voyager observations

Revealing the Cosmic Web-dependent Halo Bias

NASA Astrophysics Data System (ADS)

Yang, Xiaohu; Zhang, Youcai; Lu, Tianhuan; Wang, Huiyuan; Shi, Feng; Tweed, Dylan; Li, Shijie; Luo, Wentao; Lu, Yi; Yang, Lei

2017-10-01

Halo bias is the one of the key ingredients of the halo models. It was shown at a given redshift to be only dependent, to the first order, on the halo mass. In this study, four types of cosmic web environments—clusters, filaments, sheets, and voids—are defined within a state-of-the-art high-resolution N-body simulation. Within these environments, we use both halo-dark matter cross correlation and halo-halo autocorrelation functions to probe the clustering properties of halos. The nature of the halo bias differs strongly between the four different cosmic web environments described here. With respect to the overall population, halos in clusters have significantly lower biases in the {10}11.0˜ {10}13.5 {h}-1 {M}⊙ mass range. In other environments, however, halos show extremely enhanced biases up to a factor 10 in voids for halos of mass ˜ {10}12.0 {h}-1 {M}⊙ . Such a strong cosmic web environment dependence in the halo bias may play an important role in future cosmological and galaxy formation studies. Within this cosmic web framework, the age dependency of halo bias is found to be only significant in clusters and filaments for relatively small halos ≲ {10}12.5 {h}-1 {M}⊙ .

Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars

NASA Astrophysics Data System (ADS)

Chiba, Masashi; Beers, Timothy C.

2000-06-01

We present a detailed analysis of the space motions of 1203 solar-neighborhood stars with metal abundances [Fe/H]<=-0.6, on the basis of a catalog, of metal-poor stars selected without kinematic bias recently revised and supplemented by Beers et al. This sample, having available proper motions, radial velocities, and distance estimates for stars with a wide range of metal abundances, is by far the largest such catalog to be assembled to date. We show that the stars in our sample with [Fe/H]<=-2.2, which likely represent a ``pure'' halo component, are characterized by a radially elongated velocity ellipsoid (σU,σV,σW)=(141+/-11, 106+/-9, 94+/-8) km s-1 and small prograde rotation =30 to 50 km s-1, consistent with previous analysis of this sample by Beers and Sommer-Larsen based on radial velocity information alone. In contrast to the previous analysis, we find a decrease in with increasing distance from the Galactic plane for stars that are likely to be members of the halo population (Δ/Δ|Z|=-52+/-6 km s-1 kpc-1), which may represent the signature of a dissipatively formed flattened inner halo. Unlike essentially all previous kinematically selected catalogs, the metal-poor stars in our sample exhibit a diverse distribution of orbital eccentricities, e, with no apparent correlation between [Fe/H] and e. This demonstrates, clearly and convincingly, that the evidence offered in 1962 by Eggen, Lynden-Bell, & Sandage for a rapid collapse of the Galaxy, an apparent correlation between the orbital eccentricity of halo stars with metallicity, is basically the result of their proper-motion selection bias. However, even in our nonkinematically selected sample, we have identified a small concentration of high-e stars at [Fe/H]~-1.7, which may originate, in part, from infalling gas during the early formation of the Galaxy. We find no evidence for an additional thick disk component for stellar abundances [Fe/H]<=-2.2. The kinematics of the intermediate

IRAS and the Boston University Arecibo Galactic H I Survey: A catalog of cloud properties

NASA Technical Reports Server (NTRS)

Bania, Thomas M.

1992-01-01

The Infrared Astronomy Satellite (IRAS) Galactic Plane Surface Brightness Images were used to identify infrared emission associated with cool, diffuse H I clouds detected by the Boston University-Arecibo Galactic H I Survey. These clouds are associated with galactic star clusters, H II regions, and molecular clouds. Using emission-absorption experiments toward galactic H II regions, we determined the H I properties of cool H I clouds seen in absorption against the thermal continuum, including their kinematic distances. Correlations were then made between IRAS sources and these H II regions, thus some of the spatial confusion associated with the IRAS fields near the galactic plane was resolved since the distances to these sources was known. Because we can also correlate the BU-Arecibo clouds with existing CO surveys, these results will allow us to determine the intrinsic properties of the gas (neutral and ionized atomic as well as molecular) and dust for interstellar clouds in the inner galaxy. For the IRAS-identified H II region sample, we have established the far infrared (FIR) luminosities and galactic distribution of these sources.

Spatial clustering of dark matter haloes: secondary bias, neighbour bias, and the influence of massive neighbours on halo properties

DOE PAGES

Salcedo, Andres N.; Maller, Ariyeh H.; Berlind, Andreas A.; ...

2018-01-15

Here, we explore the phenomenon commonly known as halo assembly bias, whereby dark matter haloes of the same mass are found to be more or less clustered when a second halo property is considered, for haloes in the mass range 3.7 × 10 11–5.0 × 10 13 h –1 M ⊙. Using the Large Suite of Dark Matter Simulations (LasDamas) we consider nine commonly used halo properties and find that a clustering bias exists if haloes are binned by mass or by any other halo property. This secondary bias implies that no single halo property encompasses all the spatial clusteringmore » information of the halo population. The mean values of some halo properties depend on their halo's distance to a more massive neighbour. Halo samples selected by having high values of one of these properties therefore inherit a neighbour bias such that they are much more likely to be close to a much more massive neighbour. This neighbour bias largely accounts for the secondary bias seen in haloes binned by mass and split by concentration or age. However, haloes binned by other mass-like properties still show a secondary bias even when the neighbour bias is removed. The secondary bias of haloes selected by their spin behaves differently than that for other halo properties, suggesting that the origin of the spin bias is different than of other secondary biases.« less

Spatial clustering of dark matter haloes: secondary bias, neighbour bias, and the influence of massive neighbours on halo properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salcedo, Andres N.; Maller, Ariyeh H.; Berlind, Andreas A.

Here, we explore the phenomenon commonly known as halo assembly bias, whereby dark matter haloes of the same mass are found to be more or less clustered when a second halo property is considered, for haloes in the mass range 3.7 × 10 11–5.0 × 10 13 h –1 M ⊙. Using the Large Suite of Dark Matter Simulations (LasDamas) we consider nine commonly used halo properties and find that a clustering bias exists if haloes are binned by mass or by any other halo property. This secondary bias implies that no single halo property encompasses all the spatial clusteringmore » information of the halo population. The mean values of some halo properties depend on their halo's distance to a more massive neighbour. Halo samples selected by having high values of one of these properties therefore inherit a neighbour bias such that they are much more likely to be close to a much more massive neighbour. This neighbour bias largely accounts for the secondary bias seen in haloes binned by mass and split by concentration or age. However, haloes binned by other mass-like properties still show a secondary bias even when the neighbour bias is removed. The secondary bias of haloes selected by their spin behaves differently than that for other halo properties, suggesting that the origin of the spin bias is different than of other secondary biases.« less

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

NASA Technical Reports Server (NTRS)

Small, Ian; Blundell, Katherine M.; Lehmer, B. D.; Alexander, D. M.

2012-01-01

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

VizieR Online Data Catalog: Faint blue objects at high galactic latitude (Mitchell+, 2004)

NASA Astrophysics Data System (ADS)

Mitchell, K. J.; Usher, P. D.

2006-11-01

The US (UV-excess Starlike) survey has cataloged 3987 objects in 7 high Galactic latitude fields according to their optical colors, magnitudes, and morphologies using photographic techniques. This paper analyzes the effectiveness of the survey at producing finding lists for complete samples of hot stars and quasars that exhibit blue and/or ultraviolet excess (B-UVX) relative to the colors of halo F and G subdwarf stars. A table of 599 spectroscopic identifications summarizes the spectroscopic coverage of the US objects that has been accomplished to date. (6 data files).

Multiple ion species fluid modeling of sprite halos and the role of electron detachment from O- in their dynamics

NASA Astrophysics Data System (ADS)

Liu, N.

2011-12-01

Sprite halos are brief descending glows appearing at the lower ionosphere boundary, which follow impulsive cloud-to-ground lightning discharges [e.g., Barrington-Leigh et al., JGR, 106, 1741, 2001, Wescott et al., JGR, 106, 10467, 2001; Pasko, JGR, 115, A00E35, 2010]. They last for a few milliseconds, with horizontal extension of tens of kilometers and vertical thickness of several kilometers. According to global survey of the occurrence of transient luminous events by the ISUAL instruments on the FORMOSAT-2 satellite, on average sprite halos occur once every minute on Earth [Chen et al., JGR, 113, A08306, 2008]. It has been established that sprite halos are caused by electron heating, and molecule excitation and ionization in the lower ionosphere due to lightning quasi-electrostatic field [e.g., Pasko et al., JGR, 102, 4529, 1997; Barrington-Leigh et al., 2001; Pasko, 2010]. Past modeling work on sprite halos was conducted using either a two dimensional (2D) model of at most three charged species or a zero dimensional model of multiple ion species. In this talk, we report a modeling study of sprite halos using a recently developed 2D fluid model of multiple charged species. The model charged species include the ion species set used in [Lehtinen and Inan, GRL, 34, L08804, 2007] to study the dynamics of ionization perturbations produced by gigantic jets in the middle and upper atmosphere. In addition, another charged species, O-, is added to this set, because electron detachment of O- can proceed very fast under moderate electric field [Rayment and Moruzzi, Int. J. Mass Spectrom., 26, 321, 1978], requiring a separate treatment from the other light negative ions. The modeling results of a sprite halo driven by positive cloud-to-ground lightning indicate that the halo can descend to lower altitude with much higher electron density behind its front when the O- detachment process is included. Electron density ahead of the halo front is not significantly reduced from the

Sun-Earth L1 Region Halo-To-Halo Orbit and Halo-To-LisaJous Orbit Transfers

NASA Technical Reports Server (NTRS)

Roberts, Craig E.; DeFazio, Robert

2004-01-01

Practical techniques for designing transfer trajectories between Libration Point Orbits (LPOs) are presented. Motivation for development of these techniques was provided by a hardware contingency experienced by the Solar Heliospheric Observatory (SOHO), a joint mission of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) orbiting the L1 point of the Sun-Earth system. A potential solution to the problem involved a transfer from SOHO s periodic halo orbit to a new LPO of substantially different dimensions. Assuming the SOHO halo orbit as the departure orbit, several practical LPO transfer techniques were developed to obtain new Lissajous or periodic halo orbits that satisfy mission requirements and constraints. While not implemented for the SOHO mission, practical LPO transfer techniques were devised that are generally applicable to current and future LPO missions.

Effects of interstellar dust scattering on the X-ray eclipses of the LMXB AX J1745.6-2901 in the Galactic Centre

NASA Astrophysics Data System (ADS)

Jin, Chichuan; Ponti, Gabriele; Haberl, Frank; Smith, Randall; Valencic, Lynne

2018-07-01

AX J1745.6-2901 is an eclipsing low-mass X-ray binary in the Galactic Centre (GC). It shows significant X-ray excess emission during the eclipse phase, and its eclipse light curve shows an asymmetric shape. We use archival XMM-Newton and Chandra observations to study the origin of these peculiar X-ray eclipsing phenomena. We find that the shape of the observed X-ray eclipse light curves depends on both photon energy and the shape of the source extraction region, and also shows differences between the two instruments. By performing detailed simulations for the time-dependent X-ray dust-scattering halo, as well as directly modelling the observed eclipse and non-eclipse halo profiles of AX J1745.6-2901, we obtained solid evidence that its peculiar eclipse phenomena are indeed caused by the X-ray dust scattering in multiple foreground dust layers along the line of sight (LOS). The apparent dependence on the instruments is caused by different instrumental point spread functions. Our results can be used to assess the influence of dust-scattering in other eclipsing X-ray sources, and raise the importance of considering the timing effects of dust-scattering halo when studying the variability of other X-ray sources in the GC, such as Sgr A⋆. Moreover, our study of halo eclipse reinforces the existence of a dust layer local to AX J1745.6-2901 as reported by Jin et al. (2017), as well as identifying another dust layer within a few hundred parsecs to the Earth, containing up to several tens of percent LOS dust, which is likely to be associated with the molecular clouds in the Solar neighbourhood. The remaining LOS dust is likely to be associated with the molecular clouds located in the Galactic disc in-between.

Searching for Galactic hidden gas through interstellar scintillation: results from a test with the NTT-SOFI detector

NASA Astrophysics Data System (ADS)

Habibi, F.; Moniez, M.; Ansari, R.; Rahvar, S.

2011-01-01

Aims: Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected at a longer time scale when the light of remote stars crosses an interstellar molecular cloud, but it has never been observed at optical wavelength. In a favorable case, the light of a background star can be subject to stochastic fluctuations on the order of a few percent at a characteristic time scale of a few minutes. Our ultimate aim is to discover or exclude these scintillation effects to estimate the contribution of molecular hydrogen to the Galactic baryonic hidden mass. This feasibility study is a pathfinder toward an observational strategy to search for scintillation, probing the sensitivity of future surveys and estimating the background level. Methods: We searched for scintillation induced by molecular gas in visible dark nebulae as well as by hypothetical halo clumpuscules of cool molecular hydrogen (H2-He) during two nights. We took long series of 10 s infrared exposures with the ESO-NTT telescope toward stellar populations located behind visible nebulae and toward the Small Magellanic Cloud (SMC). We therefore searched for stars exhibiting stochastic flux variations similar to what is expected from the scintillation effect. According to our simulations of the scintillation process, this search should allow one to detect (stochastic) transverse gradients of column density in cool Galactic molecular clouds of order of ~ 3 × 10-5 g/cm2/10 000 km. Results: We found one light-curve that is compatible with a strong scintillation effect through a turbulent structure characterized by a diffusion radius Rdiff < 100 km in the B68 nebula. Complementary observations are needed to clarify the status of this candidate, and no firm conclusion can be established from this single observation. We can also infer limits on the existence of turbulent dense cores (of number density n > 109 cm-3) within the dark nebulae. Because no candidate is found toward the SMC, we

Evidence for the interaction of the IRS 16 wind with the ionized and molecular gas at the Galactic center

NASA Technical Reports Server (NTRS)

Yusef-Zadeh, Farhad; Wardle, Mark

1993-01-01

We present a number of high-resolution radio images showing evidence for the dynamical interaction of the outflow arising from the IRS 16 complex with the ionized gas associated with the Northern Arm of Sgr A West, and with the northwestern segment of the circumnuclear molecular disk which engulfs the inner few parsecs of the Galactic center. We suggest that the wind disturbs the dynamics of the Northern Arm within 0.1 pc of the center, is responsible for the waviness of the arm at larger distances, and is collimated by Sgr A West and the circumnuclear disk. The waviness is discussed in terms of the Rayleigh-Taylor instability induced by the ram pressure of the wind incident on the surface of the Northern Arm. Another consequence of this interaction is the strong mid-IR polarization of the Northern Arm in the vicinity of the IRS 16 complex which is explained as a result of the ram pressure of the wind compressing the gas and the magnetic field.

Diffuse gamma-ray emission from self-confined cosmic rays around Galactic sources

NASA Astrophysics Data System (ADS)

D'Angelo, Marta; Morlino, Giovanni; Amato, Elena; Blasi, Pasquale

2018-02-01

The propagation of particles accelerated at supernova remnant shocks and escaping the parent remnants is likely to proceed in a strongly non-linear regime, due to the efficient self-generation of Alfvén waves excited through streaming instability near the sources. Depending on the amount of neutral hydrogen present in the regions around the sites of supernova explosions, cosmic rays may accumulate an appreciable grammage in the same regions and get self-confined for non-negligible times, which in turn results in an enhanced rate of production of secondaries. Here we calculate the contribution to the diffuse gamma-ray background due to the overlap along lines of sight of several of these extended haloes as due to pion production induced by self-confined cosmic rays. We find that if the density of neutrals is low, the haloes can account for a substantial fraction of the diffuse emission observed by Fermi-Large Area Telescope (LAT), depending on the orientation of the line of sight with respect to the direction of the Galactic Centre.

Dependence of GAMA galaxy halo masses on the cosmic web environment from 100 deg2 of KiDS weak lensing data

NASA Astrophysics Data System (ADS)

Brouwer, Margot M.; Cacciato, Marcello; Dvornik, Andrej; Eardley, Lizzie; Heymans, Catherine; Hoekstra, Henk; Kuijken, Konrad; McNaught-Roberts, Tamsyn; Sifón, Cristóbal; Viola, Massimo; Alpaslan, Mehmet; Bilicki, Maciej; Bland-Hawthorn, Joss; Brough, Sarah; Choi, Ami; Driver, Simon P.; Erben, Thomas; Grado, Aniello; Hildebrandt, Hendrik; Holwerda, Benne W.; Hopkins, Andrew M.; de Jong, Jelte T. A.; Liske, Jochen; McFarland, John; Nakajima, Reiko; Napolitano, Nicola R.; Norberg, Peder; Peacock, John A.; Radovich, Mario; Robotham, Aaron S. G.; Schneider, Peter; Sikkema, Gert; van Uitert, Edo; Verdoes Kleijn, Gijs; Valentijn, Edwin A.

2016-11-01

Galaxies and their dark matter haloes are part of a complex network of mass structures, collectively called the cosmic web. Using the tidal tensor prescription these structures can be classified into four cosmic environments: voids, sheets, filaments and knots. As the cosmic web may influence the formation and evolution of dark matter haloes and the galaxies they host, we aim to study the effect of these cosmic environments on the average mass of galactic haloes. To this end we measure the galaxy-galaxy lensing profile of 91 195 galaxies, within 0.039 < z < 0.263, from the spectroscopic Galaxy And Mass Assembly survey, using {˜ }100 ° ^2 of overlapping data from the Kilo-Degree Survey. In each of the four cosmic environments we model the contributions from group centrals, satellites and neighbouring groups to the stacked galaxy-galaxy lensing profiles. After correcting the lens samples for differences in the stellar mass distribution, we find no dependence of the average halo mass of central galaxies on their cosmic environment. We do find a significant increase in the average contribution of neighbouring groups to the lensing profile in increasingly dense cosmic environments. We show, however, that the observed effect can be entirely attributed to the galaxy density at much smaller scales (within 4 h-1 Mpc), which is correlated with the density of the cosmic environments. Within our current uncertainties we find no direct dependence of galaxy halo mass on their cosmic environment.

TriAnd and its siblings: satellites of satellites in the Milky Way halo

NASA Astrophysics Data System (ADS)

Deason, A. J.; Belokurov, V.; Hamren, K. M.; Koposov, S. E.; Gilbert, K. M.; Beaton, R. L.; Dorman, C. E.; Guhathakurta, P.; Majewski, S. R.; Cunningham, E. C.

2014-11-01

We explore the Triangulum-Andromeda (TriAnd) overdensity in the SPLASH (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) and SEGUE (the Sloan Extension for Galactic Understanding and Exploration) spectroscopic surveys. Milky Way main-sequence turn-off stars in the SPLASH survey reveal that the TriAnd overdensity and the recently discovered Pan-Andromeda Archaeological Survey (PAndAS) stream share a common heliocentric distance (D ˜ 20 kpc), position on the sky, and line-of-sight velocity (VGSR ˜ 50 km s-1). Similarly, A-type, giant, and main-sequence turn-off stars selected from the SEGUE survey in the vicinity of the Segue 2 satellite show that TriAnd is prevalent in these fields, with a velocity and distance similar to Segue 2. The coincidence of the PAndAS stream and Segue 2 satellite in positional and velocity space to TriAnd suggests that these substructures are all associated, and may be a fossil record of group-infall on to the Milky Way halo. In this scenario, the Segue 2 satellite and PAndAS stream are `satellites of satellites', and the large, metal-rich TriAnd overdensity is the remains of the group central.

The large-scale structure of the halo of the Andromeda galaxy. I. Global stellar density, morphology and metallicity properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibata, Rodrigo A.; Martin, Nicolas F.; Lewis, Geraint F.

We present an analysis of the large-scale structure of the halo of the Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS), currently the most complete map of resolved stellar populations in any galactic halo. Despite the presence of copious substructures, the global halo populations follow closely power-law profiles that become steeper with increasing metallicity. We divide the sample into stream-like populations and a smooth halo component (defined as the population that cannot be resolved into spatially distinct substructures with PAndAS). Fitting a three-dimensional halo model reveals that the most metal-poor populations ([Fe/H]<−1.7) are distributed approximately spherically (slightly prolate withmore » ellipticity c/a = 1.09 ± 0.03), with only a relatively small fraction residing in discernible stream-like structures (f {sub stream} = 42%). The sphericity of the ancient smooth component strongly hints that the dark matter halo is also approximately spherical. More metal-rich populations contain higher fractions of stars in streams, with f {sub stream} becoming as high as 86% for [Fe/H]>−0.6. The space density of the smooth metal-poor component has a global power-law slope of γ = –3.08 ± 0.07, and a non-parametric fit shows that the slope remains nearly constant from 30 kpc to ∼300 kpc. The total stellar mass in the halo at distances beyond 2° is ∼1.1 × 10{sup 10} M {sub ☉}, while that of the smooth component is ∼3 × 10{sup 9} M {sub ☉}. Extrapolating into the inner galaxy, the total stellar mass of the smooth halo is plausibly ∼8 × 10{sup 9} M {sub ☉}. We detect a substantial metallicity gradient, which declines from ([Fe/H]) = –0.7 at R = 30 kpc to ([Fe/H]) = –1.5 at R = 150 kpc for the full sample, with the smooth halo being ∼0.2 dex more metal poor than the full sample at each radius. While qualitatively in line with expectations from cosmological simulations, these observations are of great

Probing Pre-galactic Metal Enrichment with High-redshift Gamma-Ray Bursts

NASA Astrophysics Data System (ADS)

Wang, F. Y.; Bromm, Volker; Greif, Thomas H.; Stacy, Athena; Dai, Z. G.; Loeb, Abraham; Cheng, K. S.

2012-11-01

We explore high-redshift gamma-ray bursts (GRBs) as promising tools to probe pre-galactic metal enrichment. We utilize the bright afterglow of a Population III (Pop III) GRB exploding in a primordial dwarf galaxy as a luminous background source, and calculate the strength of metal absorption lines that are imprinted by the first heavy elements in the intergalactic medium (IGM). To derive the GRB absorption line diagnostics, we use an existing highly resolved simulation of the formation of a first galaxy which is characterized by the onset of atomic hydrogen cooling in a halo with virial temperature >~ 104 K. We explore the unusual circumburst environment inside the systems that hosted Pop III stars, modeling the density evolution with the self-similar solution for a champagne flow. For minihalos close to the cooling threshold, the circumburst density is roughly proportional to (1 + z) with values of about a few cm-3. In more massive halos, corresponding to the first galaxies, the density may be larger, n >~ 100 cm-3. The resulting afterglow fluxes are weakly dependent on redshift at a fixed observed time, and may be detectable with the James Webb Space Telescope and Very Large Array in the near-IR and radio wavebands, respectively, out to redshift z >~ 20. We predict that the maximum of the afterglow emission shifts from near-IR to millimeter bands with peak fluxes from mJy to Jy at different observed times. The metal absorption line signature is expected to be detectable in the near future. GRBs are ideal tools for probing the metal enrichment in the early IGM, due to their high luminosities and featureless power-law spectra. The metals in the first galaxies produced by the first supernova (SN) explosions are likely to reside in low-ionization stages (C II, O I, Si II and Fe II). We show that, if the afterglow can be observed sufficiently early, analysis of the metal lines may distinguish whether the first heavy elements were produced in a pair

Probing Pre-Galactic Metal Enrichment with High-Redshift Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Wang, F. Y.; Bromm, Volker; Greif, Thomas H.; Stacy, Athena; Dai, Z. G.; Loeb, Abraham; Cheng, K. S.

2012-01-01

We explore high-redshift gamma-ray bursts (GRBs) as promising tools to probe pre-galactic metal enrichment. We utilize the bright afterglow of a Population III (Pop III) GRB exploding in a primordial dwarf galaxy as a luminous background source, and calculate the strength of metal absorption lines that are imprinted by the first heavy elements in the intergalactic medium (IGM). To derive the GRB absorption line diagnostics, we use an existing highly resolved simulation of the formation of a first galaxy which is characterized by the onset of atomic hydrogen cooling in a halo with virial temperature approximately greater than10(exp 4) K.We explore the unusual circumburst environment inside the systems that hosted Pop III stars, modeling the density evolution with the self-similar solution for a champagne flow. For minihalos close to the cooling threshold, the circumburst density is roughly proportional to (1 + z) with values of about a few cm(exp -3). In more massive halos, corresponding to the first galaxies, the density may be larger, n approximately greater than100 cm(exp -3). The resulting afterglow fluxes are weakly dependent on redshift at a fixed observed time, and may be detectable with the James Webb Space Telescope and Very Large Array in the near-IR and radio wavebands, respectively, out to redshift z approximately greater than 20. We predict that the maximum of the afterglow emission shifts from near-IR to millimeter bands with peak fluxes from mJy to Jy at different observed times. The metal absorption line signature is expected to be detectable in the near future. GRBs are ideal tools for probing the metal enrichment in the early IGM, due to their high luminosities and featureless power-law spectra. The metals in the first galaxies produced by the first supernova (SN) explosions are likely to reside in low-ionization stages (C II, O I, Si II and Fe II). We show that, if the afterglow can be observed sufficiently early, analysis of the metal lines may