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Sample records for galactic stellar halo

  1. 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

  2. The Dual Origin of Galactic Stellar Halos

    NASA Astrophysics Data System (ADS)

    Zolotov, Adi

    2011-01-01

    Accreted stellar halos are a natural consequence of galaxy formation in a Lambda-CDM Universe, and contain unique fossil records of hierarchical galaxy formation. The properties of local Milky Way halo stars, however, suggest that the Galaxy's halo is composed of at least two distinct stellar populations, each exhibiting different spatial distributions, orbits, and metallicities. This observed dichotomy is the result of the assembly history of the halo, which likely formed through a process more complex than pure hierarchical accretions. In this talk I will describe the formation of stellar halos surrounding Milky Way-massed disk galaxies simulated using high-resolution cosmological Smooth Particle Hydrodynamics + N-Body simulations. We find that two competing physical processes - accretion of dwarf galaxies and in situ star formation - contribute to the formation of every stellar halo. While the outer regions (r > 20 kpc) of the halos were assembled solely through the accretion and disruption of satellites, in situ star formation supplements accretion in the formation of inner halos. The relative contribution of each stellar population to a halo is shown to be a function of a galaxy's merging 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 population of such stars. We show how the chemical abundance trends ([Fe/H] vs. [alpha/Fe]) of accreted and in situ stars diverge at the high [Fe/H] end of the metallicity distribution function, and discuss how such trends can be used to study and identify the observable imprints of the Milky Way's formation history.

  3. The Stellar Density Profile of the Distant Galactic Halo

    NASA Astrophysics Data System (ADS)

    Slater, Colin T.; Nidever, David L.; Munn, Jeffrey A.; Bell, Eric F.; Majewski, Steven R.

    2016-12-01

    We use extensive gravity-sensitive DDO 51 photometry over 5100 square degrees, combined with Sloan Digital Sky Survey broadband photometry, to select a catalog of ˜4000 giant stars covering a large fraction of the high Galactic latitude sky and reaching out to ˜80 kpc in the Galactic halo. This sample of bright and unbiased tracers enables us to measure the radial profile and 3D structure of the stellar halo to large distances, which had previously only been measured with sparse tracers or small samples. Using population synthesis models to reproduce the observed giant star luminosity function, we find that the halo maintains a {r}-3.5 profile from 30 to 80 kpc with no signs of a truncation or sharp break over this range. The radial profile measurement is largely insensitive to individual halo substructure components, but we find that attempting to measure the shape of the halo is overwhelmed by the Sagittarius stream such that no elliposidal shape is a satisfactory description in this region. These measurements allow us to begin placing the Milky Way in context with the growing sample of external galaxies where similar halo profile measurements are available, with the goal of further linking the properties of stellar halos to the accretion histories that formed them.

  4. Formation of the Galactic Stellar Halo. I. Structure and Kinematics

    NASA Astrophysics Data System (ADS)

    Bekki, Kenji; Chiba, Masashi

    2001-09-01

    We perform numerical simulations for the formation of the Galactic stellar halo, based on the currently favored cold dark matter theory of galaxy formation. Our numerical models, taking into account both dynamical and chemical evolution processes in a consistent manner, are aimed at explaining the observed structure and kinematics of the stellar halo in the context of hierarchical galaxy formation. The main results of the present simulations are summarized as follows: (1) Basic physical processes involved in the formation of the stellar halo, composed of metal-deficient stars with [Fe/H]<=-1.0, are described by both dissipative and dissipationless merging of subgalactic clumps and their resultant tidal disruption in the course of gravitational contraction of the Galaxy at high redshift (z>1). (2) The simulated halo has a density profile similar to the observed power-law form of ρ(r)~r-3.5 and also has a metallicity distribution similar to the observations. The halo shows virtually no radial gradient for stellar ages and only a small gradient for metallicities. (3) The dual nature of the halo, i.e., its inner flattened and outer spherical density distribution, is reproduced, at least qualitatively, by the present model. The outer spherical halo is formed via essentially dissipationless merging of small subgalactic clumps, whereas the inner flattened one is formed via three different mechanisms, i.e., dissipative merging between larger, more massive clumps, adiabatic contraction due to the growing Galactic disk, and gaseous accretion onto the equatorial plane. (4) For the simulated metal-poor stars with [Fe/H]<=-1.0, there is no strong correlation between metal abundances and orbital eccentricities, in good agreement with the recent observations. Moreover, the observed fraction of the low-eccentricity stars is reproduced correctly for [Fe/H]<=-1.6 and approximately for the intermediate-abundance range of -1.6<[Fe/H]<=-1.0. (5) The mean rotational velocity of the

  5. 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

    the process of dissolving into the Galactic halo or a faint, dark matter-dominated stellar system. Based on data 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 NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

  6. The Stellar Metallicity Distribution of the Galactic Halo Based on SCUSS and SDSS Data

    NASA Astrophysics Data System (ADS)

    Zuo, Wenbo; Du, Cuihua; Jing, Yingjie; Gu, Jiayin; Newberg, Heidi Jo; Wu, Zhenyu; Ma, Jun; Zhou, Xu

    2017-05-01

    Based on the Sloan Digital Sky Survey and South Galactic Cap u-band Sky Survey (SCUSS), we simulate the photometric metallicity distribution functions (MDFs) of stars in the Galactic halo. The photometric metallicity of stars was estimated by a new Monte-Carlo method. Due to the use of a more reliable metallicity calibration method and more accurate u-band deep measurements from SCUSS, we can obtain more accurate MDFs of a large sample of distant stars in the Galactic halo. In this study, we select 78,092 F/G main-sequence turnoff stars (MSTO) in the south Galactic cap, with 0.2 < (g - r)0 < 0.4, as tracers of the stellar MDFs in the Galactic halo. The sample stars are divided into two height intervals above the Galactic plane: -8 < z < -4 kpc and -12 < z < -8 kpc. The MDFs of selected stars in each interval are well fit by a three-Gaussian model, with peaks at [Fe/H] ≈ -0.63, -1.45, and -2.0. The two metal-poor components correspond to the inner halo and outer halo, respectively. The fraction of the metal-rich component, which may be contributed by the substructure (such as Sagittarius stream or other streams) is about 10%. With limited kinematic estimation, we find the correlations between metallicity and kinematics. Our results provide additional supporting evidence of duality of the Galactic halo.

  7. 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).

  8. 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.

  9. 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

  10. Did globular clusters contribute to the stellar population of the Galactic halo?

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne; Krause, Martin

    2016-08-01

    The origin of Galactic halo stars and the contribution of globular clusters (GC) to this stellar population have long been (and still are) debated. The discovery of multiple stellar populations with peculiar chemical properties in GCs both in the Milky Way and in Local Group galaxies recently brought a renewal on these questions. Indeed most of the scenarios that compete to reproduce the present-day GC characteristics call for fast expulsion of both gas and low-mass stars from these clusters in their early infancy. In this framework, the initial masses of GCs could have been 8 to 25 times higher than their present-day stellar mass, and they could have contributed to 5 to 20 % of the low-mass stars in the Galactic halo. Here we revisit these conclusions, which are in tension with observations of dwarf galaxies and of young massive star clusters in the Local Group. We come back in particular on the paradigm of gas expulsion from massive star clusters, and propose an alternative interpretation of the GC abundance properties. We conclude by proposing a major revision of the current concepts regarding the role massive star clusters play in the assembly of galactic haloes.

  11. THE STELLAR METALLICITY DISTRIBUTION FUNCTION OF THE GALACTIC HALO FROM SDSS PHOTOMETRY

    SciTech Connect

    An, Deokkeun; Beers, Timothy C.; Johnson, Jennifer A.; Pinsonneault, Marc H.; Lee, Young Sun; Bovy, Jo; Ivezic, Zeljko; Carollo, Daniela; Newby, Matthew

    2013-01-20

    We explore the stellar metallicity distribution function of the Galactic halo based on SDSS ugriz photometry. A set of stellar isochrones is calibrated using observations of several star clusters and validated by comparisons with medium-resolution spectroscopic values over a wide range of metal abundance. We estimate distances and metallicities for individual main-sequence stars in the multiply scanned SDSS Stripe 82, at heliocentric distances in the range 5-8 kpc and |b| > 35 Degree-Sign , and find that the in situ photometric metallicity distribution has a shape that matches that of the kinematically selected local halo stars from Ryan and Norris. We also examine independent kinematic information from proper-motion measurements for high Galactic latitude stars in our sample. We find that stars with retrograde rotation in the rest frame of the Galaxy are generally more metal poor than those exhibiting prograde rotation, which is consistent with earlier arguments by Carollo et al. that the halo system comprises at least two spatially overlapping components with differing metallicity, kinematics, and spatial distributions. The observed photometric metallicity distribution and that of Ryan and Norris can be described by a simple chemical evolution model by Hartwick (or by a single Gaussian distribution); however, the suggestive metallicity-kinematic correlation contradicts the basic assumption in this model that the Milky Way halo consists primarily of a single stellar population. When the observed metallicity distribution is deconvolved using two Gaussian components with peaks at [Fe/H] Almost-Equal-To -1.7 and -2.3, the metal-poor component accounts for {approx}20%-35% of the entire halo population in this distance range.

  12. Beryllium in the Galactic halo - Surface abundances from standard, diffusive, and rotational stellar evolution, and implications

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Pinsonneault, Marc H.

    1990-01-01

    The recently observed upper limits to the beryllium abundances in population II stars are much lower than population I detections. This difference reflects an intrinsic difference in the initial abundances and is not caused by different degrees of depletion driven by stellar evolution processes from similar initial abundances. Evolutionary sequences of models from the early premain sequence to beyond the turnoff that correspond to halo dwarfs with Fe/H abundances of -1.3, -2.3, and -3.3 are constructed, and standard, diffusive, and rotational mechanisms are used to estimate a maximal possible beryllium depletion. Halo star models in the T(eff) range 6000 to 5000 K might be rotationally depleted by a factor of 1.5-2, and the total depletion should be no more than (conservatively) a factor of 3. Implications for cosmology, cosmic-ray theory, and Galactic chemical evolution are discussed.

  13. Hot subdwarf stars in the Galactic halo Tracers of prominent events in late stellar evolution

    NASA Astrophysics Data System (ADS)

    Geier, Stephan; Kupfer, Thomas; Schaffenroth, Veronika; Heber, Ulrich

    2016-08-01

    Hot subdwarf stars (sdO/Bs) are the stripped cores of red giants located at the bluest extension of the horizontal branch. They constitute the dominant population of UV-bright stars in old stellar environments and are most likely formed by binary interactions. We perform the first systematic, spectroscopic analysis of a sample of those stars in the Galactic halo based on data from SDSS. In the course of this project we discovered 177 close binary candidates. A significant fraction of the sdB binaries turned out to have close substellar companions, which shows that brown dwarfs and planets can significantly influence late stellar evolution. Close hot subdwarf binaries with massive white dwarf companions on the other hand are good candidates for the progenitors of type Ia supernovae. We discovered a hypervelocity star, which not only turned out to be the fastest unbound star known in our Galaxy, but also the surviving companion of such a supernova explosion.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Bekki, Kenji; Chiba, Masashi

    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 [Fe/H]<=-1.0, that there is no strong correlation between metal abundances and orbital eccentricities, in good agreement with the observations. Moreover, the observed fraction of the low-eccentricity stars is reproduced correctly for [Fe/H]<=-1.6 and approximately for the intermediate abundance range of -1.6<[Fe/H]<=-1.0. We show that this successful reproduction of the kinematics of the Galactic halo is a natural consequence of the hierarchical evolution of the subgalactic clumps seeded from the cold dark matter density fluctuations.

  16. ASSEMBLY OF THE OUTER GALACTIC STELLAR HALO IN THE HIERARCHICAL MODEL

    SciTech Connect

    Murante, Giuseppe; Curir, Anna; Poglio, Eva; Villalobos, Alvaro E-mail: curir@oato.inaf.i E-mail: villalobos@oats.inaf.i

    2010-06-20

    We provide a set of numerical N-body simulations for studying the formation of the outer Milky Ways' stellar halo through accretion events. After simulating minor mergers of prograde and retrograde orbiting satellite halos with a dark matter main halo, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions where a retrograde signal in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the Milky Way stellar halo. Our results show that, for satellites more massive than {approx}1/40 of the main halo, the dynamical friction has a fundamental role in assembling the final velocity distributions resulting from different orbits and that retrograde satellites moving on low-inclination orbits deposit more stars in the outer halo regions and therefore can produce the counter-rotating behavior observed in the outer Milky Way halo.

  17. DETECTING TRIAXIALITY IN THE GALACTIC DARK MATTER HALO THROUGH STELLAR KINEMATICS

    SciTech Connect

    Rojas-Nino, Armando; Valenzuela, Octavio; Pichardo, Barbara; Aguilar, Luis A. E-mail: barbara@astro.unam.mx

    2012-10-01

    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 would be the smoking gun for the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.

  18. Simultaneous orbit fitting of stellar streams: Constraining the galactic dark matter halo

    NASA Astrophysics Data System (ADS)

    Willett, Benjamin Arthur

    2010-12-01

    The Milky Way Galaxy serves as a laboratory for testing models of galaxy formation. Discovering the nature of dark matter is often cited as the second most important problem in astrophysics, preceded only by dark energy. Mapping the structure and dynamics of the Milky Way Galaxy can tell us how galaxies form, and place constraints on the properties of dark matter. We can map the distribution of dark matter in the Milky Way using tidal streams, collections of stars that have been gravitationally stripped from satellite dwarf galaxies and globular clusters. By knowing the positions and velocities of these stars, and assuming they came from a compact source, we can follow them back in time and constrain the shape of the Milky Way dark matter halo. This Thesis presents a method that allows us to constrain the parameters of a static Galactic gravitational potential using the data from any number of tidal debris streams. The method is tested on simulated tidal streams, and successfully recovers the original model parameters in most cases. The importance of simultaneously fitting the measured rotation curve of the Milky Way is explored, and the strengths and weaknesses of the algorithm are discussed. The orbit fitting algorithm is applied independently to the Stream of Grillmair and Dionatos (GD-1), the Orphan Stream, and the Cetus Polar Stream (CPS). We show that no known globular cluster or dwarf galaxy in the Milky Way has kinematics consistent with being the progenitor of the GD-1 stream. The Orphan Stream constrains the Milky Way dark matter halo as having a mass at the low end of previous measurements, giving a best fit halo speed of vhalo = 73 +/- 24 km s-1, compared to typical values of vhalo ≈ 115 km s -1. A lower halo speed implies a less massive halo. The GD-1 and Orphan streams are then fit simultaneously with the Sagittarius Dwarf Tidal Stream (Sgr), within a triaxial dark matter halo. Results for restricted triaxial cases are shown to be consistent with

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

    SciTech Connect

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

    2015-03-20

    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 ∼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.

  20. 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.

  1. 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.

  2. 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.

  3. Origins of Stellar Halos

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn V.

    2016-08-01

    This contribution reviews ideas about the origins of stellar halos. It includes discussion of the theoretical understanding of and observational evidence for stellar populations formed ``in situ'' (meaning formed in orbits close to their current ones), ``kicked-out'' (meaning formed in the inner galaxy in orbits unlike their current ones) and ``accreted'' (meaning formed in a dark matter halo other than the one they currently occupy). At this point there is general agreement that a significant fraction of any stellar halo population is likely ``accreted''. There is modest evidence for the presence of a ``kicked-out'' population around both the Milky Way and M31. Our theoretical understanding of and the observational evidence for an ``in situ'' population are less clear.

  4. STELLAR ARCHAEOLOGY IN THE GALACTIC HALO WITH THE ULTRA-FAINT DWARFS. VI. URSA MAJOR II

    SciTech Connect

    Dall'Ora, M.; Ripepi, Vincenzo; Marconi, Marcella; Musella, Ilaria E-mail: ripepi@na.astro.it E-mail: ilaria@na.astro.it; and others

    2012-06-10

    We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf satellite Ursa Major II (UMa II), spanning the magnitude range from V {approx} 15 to V {approx} 23.5 mag and extending over an 18 Multiplication-Sign 18 arcmin{sup 2} area centered on the Galaxy. Our photometry goes down to about 2 mag below the Galaxy's main-sequence turnoff that we detected at V {approx} 21.5 mag. We have discovered a bona fide RR Lyrae variable star in UMa II, which we use to estimate a conservative dereddened distance modulus for the galaxy of (m - M){sub 0} = 17.70 {+-} 0.04 {+-} 0.12 mag, where the first error accounts for the uncertainties of the calibrated photometry, and the second reflects our lack of information on the metallicity of the star. The corresponding distance to UMa II is 34.7{sup +0.6}{sub -0.7}({sup +2.0}{sub -1.9}) kpc. Our photometry shows evidence of a spread in the Galaxy's subgiant branch, compatible with a spread in metal abundance in the range between Z = 0.0001 and Z = 0.001. Based on our estimate of the distance, a comparison of the fiducial lines of the Galactic globular clusters M68 and M5 ([Fe/H] = -2.27 {+-} 0.04 dex and -1.33 {+-} 0.02 dex, respectively), with the position on the CMD of spectroscopically confirmed Galaxy members, may suggest the existence of stellar populations of different metal abundance/age in the central region of UMa II.

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

    SciTech Connect

    Rojas-Niño, Armando; Pichardo, Barbara; Valenzuela, Octavio; Martínez-Medina, Luis A. E-mail: octavio@astro.unam.mx

    2015-05-20

    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 of 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.

  6. STELLAR ARCHEOLOGY IN THE GALACTIC HALO WITH ULTRA-FAINT DWARFS. VII. HERCULES

    SciTech Connect

    Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella E-mail: ripepi@na.astro.it; and others

    2012-09-10

    We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, (P{sub ab}) = 0.68 days ({sigma} = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 {+-} 0.15 dex, E(B - V) = 0.09 {+-} 0.02 mag, and (m - M){sub 0} = 20.6 {+-} 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V {approx} 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' Multiplication-Sign 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68.

  7. PyMGC3: Finding stellar streams in the Galactic Halo using a family of Great Circle Cell counts methods

    NASA Astrophysics Data System (ADS)

    Mateu, C.

    2014-11-01

    PyMGC3 is a Python toolkit to apply the Modified Great Circle Cell Counts (mGC3) method to search for tidal streams in the Galactic Halo. The code computes pole count maps using the full mGC3/nGC3/GC3 family of methods. The original GC3 method (Johnston et al., 1996) uses positional information to search for 'great-circle-cell structures'; mGC3 makes use of full 6D data and nGC3 uses positional and proper motion data.

  8. "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)

  9. "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)

  10. Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey

    SciTech Connect

    Miceli, A; Rest, A; Stubbs, C W; Hawley, S L; Cook, K H; Magnier, E A; Krisciunas, K; Bowell, E; Koehn, B

    2007-02-23

    We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg{sup 2} and span distances ranging from 3-30kpc from the Galactic Center. Object selection is based on phased, photometric data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of these RR Lyrae stars resemble Oosterhoff type I, but there is a significant fraction (26%) which have longer periods and appear to be Oosterhoff type II. We find that the radial distributions of these two populations have significantly different profiles ({rho}{sub OoI} {approx} R{sup -2.26{+-}0.07} and {rho}{sub OoII} {approx} R{sup -2.88{+-}0.11}). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.

  11. Galactic Halos of Hydrogen

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This image shows two companion galaxies, NGC 4625 (top) and NGC 4618 (bottom), and their surrounding cocoons of cool hydrogen gas (purple). The huge set of spiral arms on NGC 4625 (blue) was discovered by the ultraviolet eyes of NASA's Galaxy Evolution Explorer. Though these arms are nearly invisible when viewed in optical light, they glow brightly in ultraviolet. This is because they are bustling with hot, newborn stars that radiate primarily ultraviolet light.

    The vibrant spiral arms are also quite lengthy, stretching out to a distance four times the size of the galaxy's core. They are part of the largest ultraviolet galactic disk discovered so far.

    Astronomers do not know why NGC 4625 grew arms while NGC 4618 did not. The purple nebulosity shown here illustrates that hydrogen gas - an ingredient of star formation - is diffusely distributed around both galaxies. This means that other unknown factors led to the development of the arms of NGC 4625.

    Located 31 million light-years away in the constellation Canes Venatici, NGC 4625 is the closest galaxy ever seen with such a young halo of arms. It is slightly smaller than our Milky Way, both in size and mass. However, the fact that this galaxy's disk is forming stars very actively suggests that it might evolve into a more massive and mature galaxy resembling our own.

    The image is composed of ultraviolet, visible-light and radio data, from the Galaxy Evolution Explorer, the California Institute of Technology's Digitized Sky Survey, and the Westerbork Synthesis Radio Telescope, the Netherlands, respectively. Near-ultraviolet light is colored green; far-ultraviolet light is colored blue; and optical light is colored red. Radio emissions are colored purple.

  12. GALACTIC WARPS IN TRIAXIAL HALOS

    SciTech Connect

    Jeon, Myoungwon; Kim, Sungsoo S.; Ann, Hong Bae E-mail: sungsoo.kim@khu.ac.kr

    2009-05-10

    We study the behavior of galactic disks in triaxial halos both numerically and analytically to see if warps can be excited and sustained in triaxial potentials. We consider the following two scenarios: (1) galactic disks that are initially tilted relative to the equatorial plane of the halo (for a pedagogical purpose), and (2) tilted infall of dark matter relative to the equatorial plane of the disk and the halo. With numerical simulations of 100,000 disk particles in a fixed halo potential, we find that in triaxial halos, warps can be excited and sustained just as in spherical or axisymmetric halos but they show some oscillatory behavior and even can be transformed to a polar-ring system if the halo has a prolate-like triaxiality. The nonaxisymmetric component of the halo causes the disk to nutate, and the differential nutation between the inner and outer parts of the disk generally makes the magnitude of the warp slightly diminish and fluctuate. We also find that warps are relatively weaker in oblate and oblate-like triaxial halos, and since these halos are the halo configurations of disk galaxies inferred by cosmological simulations, our results are consistent with the fact that most of the observed warps are quite weak. We derive approximate formulae for the torques exerted on the disk by the triaxial halo and the dark matter torus, and with these formulae we successfully describe the behavior of the disks in our simulations. The techniques used in deriving these formulae could be applied for realistic halos with more complex structures.

  13. 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

  14. Stellar halos: a rosetta stone for galaxy formation and cosmology

    NASA Astrophysics Data System (ADS)

    Inglis Read, Justin

    2015-08-01

    Stellar halos make up about a percent of the total stellar mass in galaxies. Yet their old age and long phase mixing times make them living fossil records of galactic history. In this talk, I review the latest simulations of structure formation in our standard Lambda Cold Dark Matter cosmology. I discuss the latest predictions for stellar halos and the relationship between the stellar halo light and the underlying dark matter. Finally, I discuss how these simulations compare to observations of the Milky Way and Andromeda and, ultimately, what this means for our cosmological model and the formation history of the Galaxy.

  15. Stellar populations of stellar halos: Results from the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Cook, B. A.; Conroy, C.; Pillepich, A.; Hernquist, L.

    2016-08-01

    The influence of both major and minor mergers is expected to significantly affect gradients of stellar ages and metallicities in the outskirts of galaxies. Measurements of observed gradients are beginning to reach large radii in galaxies, but a theoretical framework for connecting the findings to a picture of galactic build-up is still in its infancy. We analyze stellar populations of a statistically representative sample of quiescent galaxies over a wide mass range from the Illustris simulation. We measure metallicity and age profiles in the stellar halos of quiescent Illustris galaxies ranging in stellar mass from 1010 to 1012 M ⊙, accounting for observational projection and luminosity-weighting effects. We find wide variance in stellar population gradients between galaxies of similar mass, with typical gradients agreeing with observed galaxies. We show that, at fixed mass, the fraction of stars born in-situ within galaxies is correlated with the metallicity gradient in the halo, confirming that stellar halos contain unique information about the build-up and merger histories of galaxies.

  16. 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.

  17. New views of the distant stellar halo

    NASA Astrophysics Data System (ADS)

    Sanderson, Robyn E.; Secunda, Amy; Johnston, Kathryn V.; Bochanski, John J.

    2017-10-01

    Currently, only a small number of Milky Way (MW) stars are known to exist beyond 100 kpc from the Galactic Centre. Though the distribution of these stars in the outer halo is believed to be sparse, they can provide evidence of more recent accretion events than in the inner halo and help map out the MW's dark matter halo to its virial radius. We have re-examined the outermost regions of 11 existing stellar halo models with two synthetic surveys: one mimicking present-day searches for distant M giants and another mimicking RR Lyra (RRL) projections for the Large Synoptic Survey Telescope (LSST). Our models suggest that colour and proper motion cuts currently used to select M giant candidates for follow-up successfully remove nearly all self-contamination from foreground halo dwarf stars and are useful for focusing observations on distant M giants, of which there are thousands to tens of thousands beyond 100 kpc in our models. We likewise expect that LSST will identify comparable numbers of RRLe at these distances. We demonstrate that several observable properties of both tracers, such as proximity of neighbouring stars, proper motions and distances (for RRLe), could help us separate different accreted dwarf galaxies from one another in the distant MW halo. We also discuss prospects for using ratios of M giants to RRLe as a proxy for accretion time, which in the future could provide new constraints on the recent accretion history of our Galaxy.

  18. The Galactic stellar disc

    NASA Astrophysics Data System (ADS)

    Feltzing, S.; Bensby, T.

    2008-12-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Also based on observations collected at the Nordic Optical Telescope on La Palma, Spain, and at the European Southern Observatories on La Silla and Paranal, Chile, Proposals no. 65.L-0019(B), 67.B-0108(B), 69.B-0277.

  19. A Speeding Binary in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    The recent discovery of a hyper-velocity binary star system in the halo of the Milky Way poses a mystery: how was this system accelerated to its high speed?Accelerating StarsUnlike the uniform motion in the Galactic disk, stars in the Milky Ways halo exhibit a huge diversity of orbits that are usually tilted relative to the disk and have a variety of speeds. One type of halo star, so-called hyper-velocity stars, travel with speeds that can approach the escape velocity of the Galaxy.How do these hyper-velocity stars come about? Assuming they form in the Galactic disk, there are multiple proposed scenarios through which they could be accelerated and injected into the halo, such as:Ejection after a close encounter with the supermassive black hole at the Galactic centerEjection due to a nearby supernova explosionEjection as the result of a dynamical interaction in a dense stellar population.Further observations of hyper-velocity stars are necessary to identify the mechanism responsible for their acceleration.J1211s SurpriseModels of J1211s orbit show it did not originate from the Galactic center (black dot). The solar symbol shows the position of the Sun and the star shows the current position of J1211. The bottom two panels show two depictions(x-y plane and r-z plane) of estimated orbits of J1211 over the past 10 Gyr. [Nmeth et al. 2016]To this end, a team of scientists led by Pter Nmeth (Friedrich Alexander University, Erlangen-Nrnberg) recently studied the candidate halo hyper-velocity star SDSS J121150.27+143716.2. The scientists obtained spectroscopy of J1211 using spectrographs at the Keck Telescope in Hawaii and ESOs Very Large Telescope in Chile. To their surprise, they discovered the signature of a companion in the spectra: J1211 is actually a binary!Nmeth and collaborators found that J1211, located roughly 18,000 light-years away, is moving at a rapid ~570 km/s relative to the galactic rest frame. The binary system consists of a hot (30,600 K) subdwarf and a

  20. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

    2011-03-01

    Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars

  1. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

    1994-08-01

    Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars

  2. Accretion in the galactic halo

    NASA Astrophysics Data System (ADS)

    Stephens, Alex Courtney

    2000-10-01

    The Milky Way disk is enveloped in a diffuse, dynamically-hot collection of stars and star clusters collectively known as the ``stellar halo''. Photometric and chemical analyses suggest that these stars are ancient fossils of the galaxy formation epoch. Yet, little is known about the origin of this trace population. Is this system merely a vestige of the initial burst of star formation within the decoupled proto-Galaxy, or is it the detritus of cannibalized satellite galaxies? In an attempt to unravel the history of the Milky Way's stellar halo, I performed a detailed spectroscopic analysis of 55 metal-poor stars possessing ``extreme'' kinematic properties. It is thought that stars on orbits that either penetrate the remote halo or exhibit large retrograde velocities could have been associated with assimilated (or ``accreted'') dwarf galaxies. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the α-elements (O, Mg, Si, Ca, Ti) with respect to iron, a consequence of sporadic bursts of star formation within the diminutive galaxies. Abundances for a select group of light metals (Li, Na, Mg, Si, Ca, Ti), iron-peak nuclides (Cr, Fe, Ni), and neutron-capture elements (Y, Ba) were calculated using line-strengths measured from high-resolution, high signal-to-noise spectral observations collected with the Keck I 10-m and KPNO 4-m telescopes. The abundances extracted from the spectra reveal: (1)The vast majority of outer halo stars possess supersolar [α/Fe] > 0.0) ratios. (2)The [α/Fe] ratio appears to decrease with increasing metallicity. (3)The outer halo stars have lower ratios of [α/Fe] than inner halo stars at a given metallicity. (4)At the largest metallicities, there is a large spread in the observed [α/Fe] ratios. (5)[α/Fe] anti-correlates with RAPO. (6)Only one star (BD+80° 245) exhibits the peculiar abundances expected of an assimilated star. The general conclusion extracted from these data is that the

  3. Clouds Dominate the Galactic Halo

    NASA Astrophysics Data System (ADS)

    2003-01-01

    Using the exquisite sensitivity of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomer Jay Lockman of the National Radio Astronomy Observatory (NRAO) in Green Bank, W. Va., has produced the best cross-section ever of the Milky Way Galaxy's diffuse halo of hydrogen gas. This image confirms the presence of discrete hydrogen clouds in the halo, and could help astronomers understand the origin and evolution of the rarefied atmosphere that surrounds our Galaxy. Lockman presented his findings at the American Astronomical Society meeting in Seattle, WA. Hydrogen Clouds Graphic Artist's Rendering of the Milky Way (background) with insert showing GBT image of cross-section of neutral atomic Hydrogen Credit: Kirk Woellert/National Science Foundation Patricia Smiley, NRAO. "The first observations with the Green Bank Telescope suggested that the hydrogen in the lower halo, the transition zone between the Milky Way and intergalactic space, is very clumpy," said Lockman. "The latest data confirm these results and show that instead of trailing away smoothly from the Galactic plane, a significant fraction of the hydrogen gas in the halo is concentrated in discrete clouds. There are even some filaments." Beyond the star-filled disk of the Milky Way, there exists an extensive yet diffuse halo of hydrogen gas. For years, astronomers have speculated about the origin and structure of this gas. "Even the existence of neutral hydrogen in the halo has been somewhat of a puzzle," Lockman remarked. "Unlike the Earth's atmosphere, which is hot enough to hold itself up against the force of gravity, the hydrogen in the halo is too cool to support itself against the gravitational pull of the Milky Way." Lockman points out that some additional factor has to be involved to get neutral hydrogen to such large distances from the Galactic plane. "This force could be cosmic rays, a supersonic wind, the blast waves from supernovae, or something we have not thought of

  4. Mapping Dark Matter Halos with Stellar Kinematics

    NASA Astrophysics Data System (ADS)

    Murphy, Jeremy; Gebhardt, K.; Greene, J. E.; Graves, G.

    2013-07-01

    Galaxies of all sizes form and evolve in the centers of dark matter halos. As these halos constitute the large majority of the total mass of a galaxy, dark matter certainly plays a central role in the galaxy's formation and evolution. Yet despite our understanding of the importance of dark matter, observations of the extent and shape of dark matter halos have been slow in coming. The paucity of data is particularly acute in elliptical galaxies. Happily, concerted effort over the past several years by a number of groups has been shedding light on the dark matter halos around galaxies over a wide range in mass. The development of new instrumentation and large surveys, coupled with the tantalizing evidence for a direct detection of dark matter from the AMS experiment, has brought on a golden age in the study of galactic scale dark matter halos. I report on results using extended stellar kinematics from integrated light to dynamically model massive elliptical galaxies in the local universe. I use the integral field power of the Mitchell Spectrograph to explore the kinematics of stars to large radii (R > 2.5 r_e). Once the line-of-sight stellar kinematics are measured, I employ orbit-based, axisymmetric dynamical modeling to explore a range of dark matter halo parameterizations. Globular cluster kinematics at even larger radii are used to further constrain the dynamical models. The dynamical models also return information on the anisotropy of the stars which help to further illuminate the primary formation mechanisms of the galaxy. Specifically, I will show dynamical modeling results for the first and second rank galaxies in the Virgo Cluster, M49 and M87. Although similar in total luminosity and ellipticity, these two galaxies show evidence for different dark matter halo shapes, baryon to dark matter fractions, and stellar anisotropy profiles. Moreover, the stellar velocity dispersion at large radii in M87 is significantly higher than the globular clusters at the same

  5. The Anemic Stellar Halo of M101

    NASA Astrophysics Data System (ADS)

    Holwerda, Benne

    2014-10-01

    Models of galaxy formation in a cosmological context predict that massive disk galaxies should have richly-structured extended stellar halos, containing ~10% of a galaxy's stars, originating in large part from the tidal disruption of dwarf galaxies. Observations of a number of nearby disk galaxies have generally agreed with these expectations. Recent new observations in integrated light with a novel array of low scattered-light telephoto lenses have failed to convincingly detect a stellar halo in the nearby massive face-on disk galaxy M101 (van Dokkum et al. 2014). They argue that any halo has to have <0.3% of the mass of the galaxy. This halo would be the least massive of any massive disk galaxy in the local Universe (by factors of several) -- such a halo is not predicted or naturally interpreted by the models, and would present a critical challenge to the picture of ubiquitous stellar halos formed from the debris of disrupting dwarf galaxies.We propose to resolve the stellar populations of this uniquely anemic stellar halo for 6 orbits with HST (ACS and WFC3), allowing us to reach surface brightness limits sufficient to clearly detect and characterize M101's stellar halo if it carries more than 0.1% of M101's mass. With resolved stellar populations, we can use the gradient of stellar populations as a function of radius to separate stellar halo from disk, which is impossible using integrated light observations. The resolved stellar populations will reveal the halo mass to much greater accuracy, measure the halo radial profile, constrain any halo lopsidedness, estimate the halo's stellar metallicity, and permit an analysis of outer disk stellar populations.

  6. SUBSTRUCTURE IN THE STELLAR HALOS OF THE AQUARIUS SIMULATIONS

    SciTech Connect

    Helmi, Amina; Cooper, A. P.; Cole, S.; Frenk, C. S.; White, S. D. M.; Navarro, J. F.

    2011-05-20

    We characterize the substructure in the simulated stellar halos of Cooper et al. which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius project. These stellar halos exhibit a wealth of tidal features: broad overdensities and very narrow faint streams akin to those observed around the Milky Way. The substructures are distributed anisotropically on the sky, a characteristic that should become apparent in the next generation of photometric surveys. The normalized RMS of the density of stars on the sky appears to be systematically larger for our halos compared with the value estimated for the Milky Way from main-sequence turnoff stars in the Sloan Digital Sky Survey. We show that this is likely to be due in part to contamination by faint QSOs and redder main-sequence stars, and might suggest that {approx}10% of the Milky Way halo stars have formed in situ.

  7. Modelling galactic conformity with the colour-halo age relation in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Bray, Aaron D.; Pillepich, Annalisa; Sales, Laura V.; Zhu, Emily; Genel, Shy; Rodriguez-Gomez, Vicente; Torrey, Paul; Nelson, Dylan; Vogelsberger, Mark; Springel, Volker; Eisenstein, Daniel J.; Hernquist, Lars

    2016-01-01

    Comparisons between observational surveys and galaxy formation models find that dark matter haloes' mass can largely explain their galaxies' stellar mass. However, it remains uncertain whether additional environmental variables, known as assembly bias, are necessary to explain other galaxy properties. We use the Illustris simulation to investigate the role of assembly bias in producing galactic conformity by considering 18 000 galaxies with Mstellar > 2 × 109 M⊙. We find a significant signal of galactic conformity: out to distances of about 10 Mpc, the mean red fraction of galaxies around redder galaxies is higher than around bluer galaxies at fixed stellar mass. Dark matter haloes exhibit an analogous conformity signal, in which the fraction of haloes formed at earlier times (old haloes) is higher around old haloes than around younger ones at fixed halo mass. A plausible interpretation of galactic conformity is the combination of the halo conformity signal with the galaxy colour-halo age relation: at fixed stellar mass, particularly towards the low-mass end, Illustris' galaxy colours correlate with halo age, with the reddest galaxies (often satellites) preferentially found in the oldest haloes. We explain the galactic conformity effect with a simple semi-empirical model, assigning stellar mass via halo mass (abundance matching) and galaxy colour via halo age (age matching). Regarding comparison to observations, we conclude that the adopted selection/isolation criteria, projection effects, and stacking techniques can have a significant impact on the measured amplitude of the conformity signal.

  8. Stellar and Galactic Astrophysics with SIM

    NASA Astrophysics Data System (ADS)

    Gould, A.

    2001-05-01

    SIM will revolutionize stellar and Galactic astrophysics by tackling new questions that could never previously be addressed and making order of magnitude improvements in key parameters. SIM will measure R0 and Theta0 to <2 will enable precise measurements of the Milky Way mass and rotation curve. It will probe the Galactic 3-D mass distribution by 2 independent methods. By calibrating the RR Lyrae MV-[Fe/H] relation as well as obtaining direct distances to clusters and halo field objects, SIM will precisely date halo and globular-cluster formation as a function of metallicity. SIM will obtain 1 measurements for 200 stars of all types ranging from brown dwarfs (BD) to O stars from a broad range of metallicities, including both binaries and single stars, and it will yield precision measurements of white dwarf (WD) and black hole (BH) remnants as well. SIM microlensing will take an unbiased census of all objects in the Galactic bulge, both dark (BD WD NS BH) and luminous, and will resolve the nature of the dark-halo (MACHO) candidates currently being detected toward the LMC.

  9. Dark matter particles in the galactic halo

    SciTech Connect

    Bernabei, R. Belli, P.; Montecchia, F.; Nozzoli, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Prosperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, J. M.; Sheng, X. D.; Ye, Z. P.

    2009-12-15

    Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

  10. Two stellar components in the halo of the Milky Way.

    PubMed

    Carollo, Daniela; Beers, Timothy C; Lee, Young Sun; Chiba, Masashi; Norris, John E; Wilhelm, Ronald; Sivarani, Thirupathi; Marsteller, Brian; Munn, Jeffrey A; Bailer-Jones, Coryn A L; Fiorentin, Paola Re; York, Donald G

    2007-12-13

    The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components--an inner and an outer halo--that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.

  11. Resolved Stellar Halos of M87 and NGC 5128: Metallicities from the Red-Giant Branch

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.

    2016-08-01

    We have searched halo fields of two giant elliptical galaxies: M87, using HST images at 10 kpc from the galactic center, and NGC 5128 (Cen A), using VIMOS VLT images at 65 kpc from the center and archival HST data from 8 to 38 kpc from the center. We have resolved thousands of red-giant-branch (RGB) stars in these stellar halo fields using V and I filters, and, in addition, measured the metallicity using stellar isochrones. The metallicity distribution function (MDF) of the inner stellar halo of M87 is similar to that of NGC 5128's stellar halo.

  12. MODIFIED GRAVITY SPINS UP GALACTIC HALOS

    SciTech Connect

    Lee, Jounghun; Zhao, Gong-Bo; Li, Baojiu; Koyama, Kazuya

    2013-01-20

    We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.

  13. QUANTIFYING KINEMATIC SUBSTRUCTURE IN THE MILKY WAY'S STELLAR HALO

    SciTech Connect

    Xue Xiangxiang; Zhao Gang; Luo Ali; Rix, Hans-Walter; Bell, Eric F.; Koposov, Sergey E.; Kang, Xi; Liu, Chao; Yanny, Brian; Beers, Timothy C.; Lee, Young Sun; Bullock, James S.; Johnston, Kathryn V.; Morrison, Heather; Rockosi, Constance

    2011-09-01

    We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative 'close pair distribution' as a statistic in the four-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that are close in position on the sky tend to have more similar distances and radial velocities compared to a random sampling of these overall distributions. We make analogous mock observations of 11 numerical halo formation simulations, in which the stellar halo is entirely composed of disrupted satellite debris, and find a level of substructure comparable to that seen in the actually observed BHB star sample. This result quantitatively confirms the hierarchical build-up of the stellar halo through a signature in phase (position-velocity) space. In detail, the structure present in the BHB stars is somewhat less prominent than that seen in most simulated halos, quite possibly because BHB stars represent an older sub-population. BHB stars located beyond 20 kpc from the Galactic center exhibit stronger substructure than at r{sub gc} < 20 kpc.

  14. Population Gradients in Stellar Halos from GHOSTS

    NASA Astrophysics Data System (ADS)

    Bailin, Jeremy; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Ghosts Survey

    2015-01-01

    We report on recent results from the Galaxy Halos, Outer disks, Substructure, Thick disks, and Star clusters (GHOSTS) survey, an HST ACS+WFC3 imaging survey to study stellar populations in and around 16 nearby spiral galaxies. By using HST resolution to resolve the stellar halos into individual red giant branch (RGB) stars, we are able to detect distinct stellar populations at several points throughout the halo of the half dozen massive highly-inclined galaxies in the sample. In approximately half of these galaxies, we detect a gradient in the color of the RGB; which we interpret as a metallicity gradient. Stellar halo formation models predict a wide variety of metallicity gradients: those in which the halos are dominated by stars formed in situ predict stronger gradients than we observe, while accretion-dominated halo models predict weaker or nonexistent gradients. Our measurements therefore provide a useful discriminator between stellar halo models, and at first look appear most consistent with the accretion-based model of Cooper et al. (2010).

  15. Static galactic halo and galactic wind

    NASA Technical Reports Server (NTRS)

    Ko, Chung-Ming

    1993-01-01

    Although the exact state of the interstellar medium (ISM) in our Galaxy (other galaxies as well) is not clear at all, the 'common consensus' is that a rough pressure balance (or equipartition of energy) exists between different components and phases: cold, warm, hot phases of the ISM, magnetic field, cosmic rays, etc. If the halo of a galaxy is taken to be an extension of the ISM, then its structure is influenced by various ISM components. A 'complete' description of the halo is evidently very complicated. This paper gives a brief account on cosmic ray halo, which emphasizes the role played by cosmic rays. The interaction between cosmic rays and thermal plasma is facilitated by magnetic field. The cosmic rays are scattered by hydromagnetic waves (e.g., Alfven waves) which in turn can be generated by cosmic ray streaming instability. This constitutes a self-consistent picture. Since we are interested in the structure of the halo, we adopted a hydrodynamic model in which the cosmic rays and waves are described by their pressures. In general there are two classes of halos: static and dynamic.

  16. The Information Content of Stellar Halos: Stellar Population Gradients and Accretion Histories in Early-type Illustris Galaxies

    NASA Astrophysics Data System (ADS)

    Cook, B. A.; Conroy, C.; Pillepich, A.; Rodriguez-Gomez, V.; Hernquist, L.

    2016-12-01

    Long dynamical timescales in the outskirts of galaxies preserve the information content of their accretion histories, for example in the form of stellar population gradients. We present a detailed analysis of the stellar halo properties of a statistically representative sample of early-type galaxies from the Illustris simulation, and show that stellar population gradients at large radii can indeed be used to infer basic properties of galactic accretion histories. We measure metallicity, age, and surface-brightness profiles in quiescent Illustris galaxies ranging from {M}\\star = 1010-2 × 1012 {M}⊙ and show that they are in reasonable agreement with observations. At fixed mass, galaxies that accreted little of their stellar halo material tend to have steeper metallicity and surface-brightness profiles, between 2-4 effective radii ({R}e), than those with larger accreted fractions. Profiles of metallicity and surface-brightness in the stellar halo typically flatten from z = 1 to the present. This suggests that the accretion of stars into the stellar halo tends to flatten metallicity and surface-brightness profiles, a picture which is supported by the tight correlation between the two gradients in the stellar halo. We find no statistical evidence of additional information content related to accretion histories in stellar halo metallicity profiles, beyond what is contained in surface-brightness profiles. Age gradients in the stellar halo do not appear to be sensitive to galactic accretion histories, and none of the stellar population gradients studied are strongly correlated with the mean merger mass-ratio. Our findings relate specifically to regions of the stellar halo within 4 {R}e, but suggest that future observations that reach large radii outside galaxies (including to 10 {R}e and beyond) will have the best potential to constrain galactic accretion histories.

  17. Studying stellar halos with future facilities

    NASA Astrophysics Data System (ADS)

    Greggio, Laura; Falomo, Renato; Uslenghi, Michela

    2016-08-01

    Stellar halos around galaxies retain fundamental evidence of the processes which lead to their build up. Sophisticated models of galaxy formation in a cosmological context yield quantitative predictions about various observable characteristics, including the amount of substructure, the slope of radial mass profiles and three dimensional shapes, and the properties of the stellar populations in the halos. The comparison of such models with the observations provides constraints on the general picture of galaxy formation in the hierarchical Universe, as well as on the physical processes taking place in the halos formation. With the current observing facilities, stellar halos can be effectively probed only for a limited number of nearby galaxies. In this paper we illustrate the progress that we expect in this field with the future ground based large aperture telescopes (E-ELT) and with space based facilities as JWST.

  18. THE DUAL ORIGIN OF STELLAR HALOS

    SciTech Connect

    Zolotov, Adi; Hogg, David W.; Willman, Beth; Brooks, Alyson M.; Brook, Chris B.; Stinson, Greg E-mail: bwillman@haverford.edu

    2009-09-10

    We investigate the formation of the stellar halos of four simulated disk galaxies using high-resolution, cosmological SPH + N-body simulations. These simulations include a self-consistent treatment of all the major physical processes involved in galaxy formation. The simulated galaxies presented here each have a total mass of {approx}10{sup 12} M{sub sun}, but span a range of merger histories. These simulations allow us to study the competing importance of in situ star formation (stars formed in the primary galaxy) and accretion of stars from subhalos in the building of stellar halos in a {lambda}CDM universe. All four simulated galaxies are surrounded by a stellar halo, whose inner regions (r < 20 kpc) contain both accreted stars, and an in situ stellar population. The outer regions of the galaxies' halos were assembled through pure accretion and disruption of satellites. Most of the in situ halo stars formed at high redshift out of smoothly accreted cold gas in the inner 1 kpc of the galaxies' potential wells, possibly as part of their primordial disks. These stars were displaced from their central locations into the halos through a succession of major mergers. We find that the two galaxies with recently quiescent merger histories have a higher fraction of in situ stars ({approx}20%-50%) in their inner halos than the two galaxies with many recent mergers ({approx}5%-10% in situ fraction). Observational studies concentrating on stellar populations in the inner halo of the Milky Way will be the most affected by the presence of in situ stars with halo kinematics, as we find that their existence in the inner few tens of kpc is a generic feature of galaxy formation.

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

    NASA Astrophysics Data System (ADS)

    Lee, Young Sun; Beers, Timothy C.; Kim, Young Kwang; Placco, Vinicius; Yoon, Jinmi; Carollo, Daniela; Masseron, Thomas; Jung, Jaehun

    2017-02-01

    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] = -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.

  20. SECULAR DAMPING OF STELLAR BARS IN SPINNING DARK MATTER HALOS

    SciTech Connect

    Long, Stacy; Shlosman, Isaac; Heller, Clayton

    2014-03-01

    We demonstrate using numerical simulations of isolated galaxies that growth of stellar bars in spinning dark matter halos is heavily suppressed in the secular phase of evolution. In a representative set of models, we show that for values of the cosmological spin parameter λ ≳ 0.03, bar growth (in strength and size) becomes increasingly quenched. Furthermore, the slowdown of the bar pattern speed weakens considerably with increasing λ until it ceases completely. The terminal structure of the bars is affected as well, including extent and shape of their boxy/peanut bulges. The essence of this effect lies in the modified angular momentum exchange between the disk and the halo facilitated by the bar. For the first time we have demonstrated that a dark matter halo can emit and not purely absorb angular momentum. Although the halo as a whole is not found to emit, the net transfer of angular momentum from the disk to the halo is significantly reduced or completely eliminated. The paradigm shift implies that the accepted view that disks serve as sources of angular momentum and halos serve as sinks must be revised. Halos with λ ≳ 0.03 are expected to form a substantial fraction, based on the lognormal distribution of λ. The dependence of secular bar evolution on halo spin, therefore, implies profound corollaries for the cosmological evolution of galactic disks.

  1. Systematic Problems With Stellar Halo Modelling

    NASA Astrophysics Data System (ADS)

    Bailin, Jeremy

    2012-05-01

    Stellar halos contain a small fraction of the stellar mass of a galaxy. The dynamic range required to model the substructure within this small component while simultaneously modeling the main galaxy is currently unobtainable, which has lead to the prevalence of stellar halo models that tag stellar content onto dark matter particles in pure dark matter simulations, making it computationally feasible (e.g. Bullock & Johnston 2005; Cooper et al. 2010). Using paired simulations with identical initial conditions, we estimate the magnitude of the systematic effects these simplifications have on the structure of the halos. We find that (1) "painting" and (2) neglecting baryonic processes each introduce factor-of-several changes to the amount of substructure predicted. We therefore urge caution when interpreting differences between models and observations that are at this level.

  2. Parametrizing the stellar haloes of galaxies

    NASA Astrophysics Data System (ADS)

    D'Souza, Richard; Kauffman, Guinevere; Wang, Jing; Vegetti, Simona

    2014-09-01

    We study the stellar haloes of galaxies out to 70-100 kpc as a function of stellar mass and galaxy type by stacking aligned r- and g-band images from a sample of 45 508 galaxies from Sloan Digital Sky Survey Data Release 9 in the redshift range 0.06 ≤ z ≤ 0.1 and in the mass range 1010.0 M⊙ < M* < 1011.4 M⊙. We derive surface brightness profiles to a depth of almost μr ˜ 32 mag arcsec-2. We find that the ellipticity of the stellar halo is a function of galaxy stellar mass and that the haloes of high-concentration galaxies are more elliptical than those of low-concentration galaxies. Where the g - r colour of the stellar halo can be measured, we find that the stellar light is always bluer than in the main galaxy. The colour of the stellar halo is redder for more massive galaxies. We further demonstrate that the full two-dimensional surface intensity distribution of our galaxy stacks can only be fit through multicomponent Sérsic models. Using the fraction of light in the outer component of the models as a proxy for the fraction of accreted stellar light, we show that this fraction is a function of stellar mass and galaxy type. The fraction of accreted stellar light rises from 30 to 70 per cent and from 2 to 25 per cent for high- and low-concentration galaxies, respectively, over the mass range 1010.0-1011.4 M⊙.

  3. Probing the galactic halo with ROSAT

    NASA Technical Reports Server (NTRS)

    Burrows, David N.; Mendenhall, J. A.

    1992-01-01

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

  4. Probing the galactic halo with ROSAT

    NASA Technical Reports Server (NTRS)

    Burrows, D. N.; Mendenhall, J. A.

    1993-01-01

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

  5. A Search for Moving Groups in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Aguilar, L. A.; Hoogerwerf, R.

    The idea that the Galactic Halo has been formed largely by the accretion and tidal disruption of satellite systems has been gaining strength. The discovery of a retrograde rotating stellar group (Majewski et al., 1992), patchiness in the kinematics of halo stars (Majewski et al., 1996), the realization that most of the Milky Way satellites lie near two great circles in the sky (Lynden-Bell, 1976) and the discovery of an elongated dwarf galaxy in Sagittarius (Ibata et al., 1994), all add credence to this idea. Theoretically, the apparent fragility of galactic disks (Toth & Ostriker, 1992) no longer seems to be a problem for accretion (Velazquez & White, 1997). The tidal ``streamers'' from tidal disruption seem to be long lived (Barnes 1996) and can be exploited to devise algorithms to search for them in galactic surveys (Johnston et al., 1996). The phase space portrait of the halo, far from being a smooth distribution, should consist of a patchy aggregation of tidally disrupted systems that have been phase mixed over wide swaths in the sky, but which retain kinematic memory of their existence as a coherent entity. The challenges to discover these moving groups in the halo are enormous due to the distances involved and the fact that they can span large angles in the sky. The availability of astrometric databases of unprecedent accuracies (HIPPARCOS) and plans for follow up (GAIA), offer an opportunity to search for these moving groups. Together with these databases, new search techniques must be devised (Chen etal. 1997, Hoogerwerf & Aguilar, 1997).

  6. New detections of embedded clusters in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Camargo, D.; Bica, E.; Bonatto, C.

    2016-09-01

    Context. Until recently it was thought that high Galactic latitude clouds were a non-star-forming ensemble. However, in a previous study we reported the discovery of two embedded clusters (ECs) far away from the Galactic plane (~ 5 kpc). In our recent star cluster catalogue we provided additional high and intermediate latitude cluster candidates. Aims: This work aims to clarify whether our previous detection of star clusters far away from the disc represents just an episodic event or whether star cluster formation is currently a systematic phenomenon in the Galactic halo. We analyse the nature of four clusters found in our recent catalogue and report the discovery of three new ECs each with an unusually high latitude and distance from the Galactic disc midplane. Methods: The analysis is based on 2MASS and WISE colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). The CMDs are built by applying a field-star decontamination procedure, which uncovers the cluster's intrinsic CMD morphology. Results: All of these clusters are younger than 5 Myr. The high-latitude ECs C 932, C 934, and C 939 appear to be related to a cloud complex about 5 kpc below the Galactic disc, under the Local arm. The other clusters are above the disc, C 1074 and C 1100 with a vertical distance of ~3 kpc, C 1099 with ~ 2 kpc, and C 1101 with ~1.8 kpc. Conclusions: According to the derived parameters ECs located below and above the disc occur, which gives evidence of widespread star cluster formation throughout the Galactic halo. This study therefore represents a paradigm shift, by demonstrating that a sterile halo must now be understood as a host for ongoing star formation. The origin and fate of these ECs remain open. There are two possibilities for their origin, Galactic fountains or infall. The discovery of ECs far from the disc suggests that the Galactic halo is more actively forming stars than previously thought. Furthermore, since most ECs do not survive the infant

  7. Stellar halos around Local Group galaxies

    NASA Astrophysics Data System (ADS)

    McConnachie, Alan W.

    2016-08-01

    The Local Group is now home to 102 known galaxies and candidates, with many new faint galaxies continuing to be discovered. The total stellar mass range spanned by this population covers a factor of close to a billion, from the faintest systems with stellar masses of order a few thousand to the Milky Way and Andromeda, with stellar masses of order 1011 M ⊙. Here, I discuss the evidence for stellar halos surrounding Local Group galaxies spanning from dwarf scales (with the case of the Andromeda II dwarf spheroidal), though to intermediate mass systems (M33) and finishing with M31. Evidence of extended stellar populations and merging is seen across the luminosity function, indicating that the processes that lead to halo formation are common at all mass scales.

  8. 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.

  9. Stability of BEC galactic dark matter halos

    NASA Astrophysics Data System (ADS)

    Guzmán, F. S.; Lora-Clavijo, F. D.; González-Avilés, J. J.; Rivera-Paleo, F. J.

    2013-09-01

    In this paper we show that spherically symmetric BEC dark matter halos, with the sin r/r density profile, that accurately fit galactic rotation curves and represent a potential solution to the cusp-core problem are unstable. We do this by introducing back the density profiles into the fully time-dependent Gross-Pitaevskii-Poisson system of equations. Using numerical methods to track the evolution of the system, we found that these galactic halos lose mass at an approximate rate of half of its mass in a time scale of dozens of Myr. We consider this time scale is enough as to consider these halos are unstable and unlikely to be formed. We provide some arguments to show that this behavior is general and discuss some other drawbacks of the model that restrict its viability.

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

    SciTech Connect

    Janesh, William; Morrison, Heather L.; Ma, Zhibo; Harding, Paul; Rockosi, Constance; Xue, Xiang Xiang; Rix, Hans-Walter; Beers, Timothy C.; Johnson, Jennifer; Lee, Young Sun; Schneider, Donald P.

    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 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.

  11. The SEGUE K Giant Survey. III. Quantifying Galactic Halo Substructure

    NASA Astrophysics Data System (ADS)

    Janesh, William; Morrison, Heather L.; Ma, Zhibo; Rockosi, Constance; Starkenburg, Else; Xue, Xiang Xiang; Rix, Hans-Walter; Harding, Paul; Beers, Timothy C.; Johnson, Jennifer; Lee, Young Sun; Schneider, Donald P.

    2016-01-01

    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 5-125 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 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.

  12. Analysis of HST/COS spectra of the bare C-O stellar core H1504+65 and a high-velocity twin in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Werner, K.; Rauch, T.

    2015-12-01

    H1504+65 is an extremely hot white dwarf (effective temperature Teff = 200 000 K) with a carbon-oxygen dominated atmosphere devoid of hydrogen and helium. This atmospheric composition was hitherto unique among hot white dwarfs (WDs), and it could be related to recently detected cooler WDs with C or O dominated spectra. The origin of the H and He deficiency in H1504+65 is unclear. To further assess this problem, we performed ultraviolet spectroscopy with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST). In accordance with previous far-ultraviolet spectroscopy performed with the Far Ultraviolet Spectroscopic Explorer, the most prominent lines stem from C iv, O v-vi, and Ne vi-viii. Archival HST/COS spectra are utilized to prove that the supersoft X-ray source RX J0439.8-6809 is, considering the exotic composition, a twin of H1504+65 that is even hotter (Teff = 250 000 K). In contrast to earlier claims, we find that the star is not located in the Large Magellanic Cloud but a foreground object in the Galactic halo at a distance of 9.2 kpc, 5.6 kpc below the Galactic plane, receding with vrad = +220 km s-1. Based on observations 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 NAS5-26666.

  13. Galactic stellar populations with APOGEE and Kepler

    NASA Astrophysics Data System (ADS)

    Johnson, J. A.; APOKASC Collaboration

    2016-09-01

    Understanding the history of baryons is key to understanding galaxy formation, as galaxies with very similar stellar mass and/or dark matter halo mass can have markedly different morphologies in their stellar light. Stars are a useful way to study this history, because properties such as their composition, age, and orbital motion can map galaxy formation and evolution. Lightcurves from the Kepler mission, both original and extended, provide asteroseismic parameters, such as Δ ν and ν_max, and rotation periods. The high-resolution near-infrared APOGEE spectroscopic survey is observing an extensive sample of red giants and cool dwarfs in both the Kepler and K2 fields to provide composition and effective temperature measurements. These spectroscopic and seismic parameters can be combined to yield ages, important for dissecting the history of the Milky Way. Results based on this combination have already been published in the first APOKASC catalog. Among the interesting results about stellar populations so far are the presence of a large metallicity spread in the young secondary red clump population at the solar circle, the identification of young, yet α-rich stars, and the detection of a field blue straggler descendant. The K2 fields along the ecliptic will extend the possibilities of these techniques to new lines of sight in the Galaxy and provide a much more representative sample of Galactic populations with seismic and spectroscopic information.

  14. Globular Cluster Contributions to the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Martell, Sarah; Grebel, Eva; Lai, David

    2010-08-01

    The goal of this project is to confirm chemically that globular clusters are the source of as much as half the population of the Galactic halo. Using moderate-resolution spectroscopy from the SEGUE survey, we have identified a previously unknown population of halo field giants with distinctly strong CN features. CN variations are typically only observed in globular clusters, so these stars are interpreted as immigrants to the halo that originally formed in globular clusters. In one night of Keck/HIRES time, we will obtain high-quality, high- resolution spectra for five such stars, and determine abundances of O, Na, Mg, Al, alpha, iron-peak and neutron-capture elements. With this information we can state clearly whether these unusual CN-strong halo stars carry the full abundance pattern seen in CN-strong globular cluster stars, with depleted C, O, and Mg and enhanced N, Na, and Al. This type of coarse ``chemical tagging'' will allow a clearer division of the Galactic halo into contributions from globular clusters and from dwarf galaxies, and will place constraints on theoretical models of globular cluster formation and evolution.

  15. 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.

  16. Neutron stars and white dwarfs in galactic halos?

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  17. Stellar halo hierarchical density structure identification using (F)OPTICS

    NASA Astrophysics Data System (ADS)

    Sans Fuentes, S. A.; De Ridder, J.; Debosscher, J.

    2017-03-01

    Context. The stellar halo holds some of the best preserved fossils of Galactic formation history that can be detected as overdensities. The detection and analysis of merger by-products within the halo enables the reconstruction of the accretion history of the Milky Way. Upcoming large-scale all-sky surveys such as Gaia and The Large Synoptic Survey Telescope (LSST) will provide a huge and rich data set, which at the same time poses challenges for automated halo debris detection. Aims: We investigate the overdensity detection algorithm Ordering Points To Identify the Clustering Structure (OPTICS) as a method to identify tidal debris in the Galactic halo with large-scale surveys, as well as the variant FOPTICS which is capable of handling data sets with multi-dimensional uncertainty ellipsoids. Methods: We applied OPTICS to the a simulated Galactic stellar Halo to assess the detection performance. Additionally, we tested the performance of FOPTICS is tested by introducing uncertainty ellipsoids to the 6D phase space of two test cases. We present the Jaccard index as an alternative way to test the stability of halo debris overdensity detections without the need for a local background density estimate. Results: We optimized the OPTICS overdensity detection algorithm so that it has a slightly superlinear run-time complexity, making the method suitable for large-scale surveys. Our test on a mock galactic halo in 6D phase space shows an excellent capability to not only detect the compact dense clusters, but also the larger streams that cover a significant part of the sky. The output of OPTICS, the so-called 2D reachability diagram, proved to be a very useful tool to grasp the size, density, and substructure of the overdensities without needing to resort to complex projections of the 6D phase space. Using FOPTICS, we show the effects of introducing uncertainty ellipsoids in the 6D phase space on the retrieved tidal streams, and how the detectability of a cluster depends on

  18. RADIAL VELOCITIES OF GALACTIC HALO STARS IN VIRGO

    SciTech Connect

    Brink, Thomas G.; Mateo, Mario; Martinez-Delgado, David E-mail: mmateo@umich.ed

    2010-11-15

    We present multi-slit radial velocity measurements for 111 stars in the direction of the Virgo Stellar Stream (VSS). The stars were photometrically selected to be probable main-sequence stars in the Galactic halo. When compared with the radial velocity distribution expected for the halo of the Milky Way, as well as the distribution seen in a control field, we observe a significant excess of negative velocity stars in the field, which can likely be attributed to the presence of a stellar stream. This kinematic excess peaks at a Galactic standard of rest radial velocity of -75 km s{sup -1}. A rough distance estimate suggests that this feature extends from {approx}15 kpc out to, and possibly beyond, the {approx}30 kpc limit of the study. The mean velocity of these stars is incompatible with those of the VSS itself (V{sub gsr} {approx} 130 km s{sup -1}), which we weakly detect, but it is consistent with radial velocity measurements of nearby 2MASS M-giants and SDSS+SEGUE K/M-giants and blue horizontal branch stars that constitute the leading tidal tail of the Sagittarius dwarf spheroidal galaxy. Some oblate models for the shape of the Milky Way's dark matter halo predict that the leading arm of the Sagittarius Stream should pass through this volume, and have highly negative (V{sub gsr} {approx}< -200 km s{sup -1}) radial velocities, as it descends down from the northern Galactic hemisphere toward the Galactic plane. The kinematic feature observed in this study, if it is in fact Sagittarius debris, is not consistent with these predictions, and instead, like other leading stream radial velocity measurements, is consistent with a recently published triaxial halo model, or, if axisymmetry is imposed, favors a prolate shape for the Galactic halo potential. However, a rough distance estimate to the observed kinematic feature places it somewhat closer (D {approx} 15-30 kpc) than the Sagittarius models predict (D {approx} 35-45 kpc).

  19. Galactic evolution. II - Disk galaxies with massive halos

    NASA Technical Reports Server (NTRS)

    Ostriker, J. P.; Thuan, T. X.

    1975-01-01

    Models of galactic evolution are computed in which matter shed by dying halo stars accumulates in a smaller, more rapidly rotating disk. The models are simpler and more successful than one-zone (pure disk) models in that (1) the observed absence of low-metal-abundance low-mass dwarfs is expected, not anomalous and (2) the relative birthrate function (or IMF) need not be a strongly variable function of time in agreement with recent interpretations of observed stellar populations and neutral hydrogen in our own and other galaxies. Even a simple 'Salpeter' IMF for both disk and halo will produce an acceptable model. The model with a halo 'Salpeter' IMF, roughly one-quarter of the mass in the secondary disk, and approximately half the metals produced in the halo seems most compatible with observations of the metal abundance in low-mass stars, the deuterium abundance, halo planetary nebulae, and light from Population II stars, as well as with arguments on the stability of the disk.

  20. Structure of the Galactic Halo Towards the North Galactic Pole

    NASA Astrophysics Data System (ADS)

    Kinman, T. D.; Bragaglia, A.; Cacciari, C.; Buzzoni, A.; Spagna, A.

    2005-01-01

    We have used RR Lyrae and Blue HB stars as tracers of the old Galactic halo, in order to study the halo structure and the galactic rotation as a function of height above the plane. Our sample includes 40 RR Lyrae and 80 BHB stars that are about 2 to 15 kpc above the plane, in a roughly 250 deg2 area around the North Galactic Pole (NGP). We use proper motions (derived from the GSCII data base) and radial velocities to determine the rotation of the halo. From the whole sample the motion appears to be significantly more retrograde than the samples in the solar neighbourhood, confirming Majewski (1992) results and our own preliminary results based on 1/3 the present sample (Kinman et al. 2003; Spagna et al. 2003). However, the better statistics have now revealed the likely existence of two components, whose characteristics need an accurate analysis of systematic errors on the proper motions in order to be assessed in detail.

  1. The WFIRST view of the distant stellar halo

    NASA Astrophysics Data System (ADS)

    Secunda, Amy; Sanderson, Robyn Ellyn; Johnston, Kathryn V.; Sharma, Sanjib

    2017-01-01

    Only a handful of Milky Way (MW) stars are now known to exist beyond 100 kpc from the Galactic center. Though the distribution of these stars is believed to be sparse, they can be a valuable source of information on the accretion history of the galaxy, providing evidence of more recent accretion events than the inner halo, while kinematic data for these distant stars can help map out the MW’s dark matter halo all the way to the virial radius. Currently, searches for distant M giants are opening this window into the distant galaxy for the first time; in the future, WFIRST’s High-Latitude Survey (HLS) offers the prospect of extending proper motion measurements to the edge of the MW virial radius over several thousand square degrees of sky. RR Lyrae identified by LSST in the HLS field will have accurate distances as well, offering the tantalizing prospect of complete six-dimensional phase space coordinates for these tracers at large distances. Using synthetic surveys of cosmological mock stellar halos, we explore how WFIRST will shed new light on the contents of the distant stellar halo.

  2. Haloes light and dark: dynamical models of the stellar halo and constraints on the mass of the Galaxy

    NASA Astrophysics Data System (ADS)

    Williams, A. A.; Evans, N. W.

    2015-11-01

    We develop a flexible set of action-based distribution functions (DFs) for stellar haloes. The DFs have five free parameters, controlling the inner and outer density slope, break radius, flattening, and anisotropy, respectively. The DFs generate flattened stellar haloes with a rapidly varying logarithmic slope in density, as well as a spherically aligned velocity ellipsoid with a long axis that points towards the Galactic Centre - all attributes possessed by the stellar halo of the Milky Way. We use our action-based DF to model the blue horizontal branch stars extracted from the Sloan Digital Sky Survey as stellar halo tracers in a spherical Galactic potential. As the selection function is hard to model, we fix the density law from earlier studies and solve for the anisotropy and gravitational potential parameters. Our best-fitting model has a velocity anisotropy that becomes more radially anisotropic on moving outwards. It changes from β ≈ 0.4 at Galactocentric radius of 15 kpc to ≈0.7 at 60 kpc. This is a gentler increase than is typically found in simulations of stellar haloes built from the multiple accretion of smaller systems. We find the potential corresponds to an almost flat rotation curve with amplitude of ≈200 km s-1 at these distances. This implies an enclosed mass of ≈4.5 × 1011 M⊙ within a spherical shell of radius 50 kpc.

  3. The angular momentum distribution in galactic halos

    NASA Astrophysics Data System (ADS)

    Quinn, P. J.; Zurek, W. H.

    1988-08-01

    N-body simulations are used to model the formation of individual galactic halos from scale-free density perturbations in universes dominated by cold, nondissipative dark matter. In well-mixed halos, the angular momentum distribution is shown to have a systematic behavior with power law index n corresponding to that found for circular rotation curves. For a given n, the distribution of angular momentum has the same trend with radius and energy as that implied for a halo in which all the matter has its maximum possible angular momentum. Dynamical mixing during the relaxation of the halo redistributes both angular momentum and binding energy in an orderly manner. The organized nature of the collapse means that relaxation is not completely violent and that the secondary infall paradigm, in its simplest form, needs to be modified to include the organizing effects of dynamical friction. It is shown that the Mestel hypothesis is not consistent with the final collapsed state of halos, but may be applicable to the collapse of the disks of spirals.

  4. Cool Carbon Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Gigoyan, K. S.

    2016-06-01

    In this paper we report current status of search and study for Faint High Latitude Carbon Stars (FHLCs). Data for more than 1800 spectroscopically confirmed FHLCs are known, which are found thanks to objective prism surveys and photometric selections. More than half of the detected objects belongs to group of dwarf Carbon (dC) stars. Many-sided investigations based on modern astrophysical databases are necessary to study the space distribution of different groups of the FHLC stars and their possible origin in the Halo of our Galaxy. We report about the selection of FHLCs by the spectroscopic surveys: First Byurakan Survey (FBS), Hamburg/ESO Survey (HES), LAMOST Pilot Survey and SDSS, as well as by photometric selection: APM Survey for Cool Carbon Stars in the Galactic Halo, SDSS and 2MASS JHK colours.

  5. Stellar discs in Aquarius dark matter haloes

    NASA Astrophysics Data System (ADS)

    DeBuhr, Jackson; Ma, Chung-Pei; White, Simon D. M.

    2012-10-01

    We investigate the gravitational interactions between live stellar discs and their dark matter haloes, using Λ cold dark matter haloes similar in mass to that of the Milky Way taken from the Aquarius Project. We introduce the stellar discs by first allowing the haloes to respond to the influence of a growing rigid disc potential from z = 1.3 to 1.0. The rigid potential is then replaced with star particles which evolve self-consistently with the dark matter particles until z = 0.0. Regardless of the initial orientation of the disc, the inner parts of the haloes contract and change from prolate to oblate as the disc grows to its full size. When the disc's normal is initially aligned with the major axis of the halo at z = 1.3, the length of the major axis contracts and becomes the minor axis by z = 1.0. Six out of the eight discs in our main set of simulations form bars, and five of the six bars experience a buckling instability that results in a sudden jump in the vertical stellar velocity dispersion and an accompanying drop in the m = 2 Fourier amplitude of the disc surface density. The bars are not destroyed by the buckling but continue to grow until the present day. Bars are largely absent when the disc mass is reduced by a factor of 2 or more; the relative disc-to-halo mass is therefore a primary factor in bar formation and evolution. A subset of the discs is warped at the outskirts and contains prominent non-coplanar material with a ring-like structure. Many discs reorient by large angles between z = 1 and 0, following a coherent reorientation of their inner haloes. Larger reorientations produce more strongly warped discs, suggesting a tight link between the two phenomena. The origins of bars and warps appear independent: some discs with strong bars show little disturbances at the outskirts, while the discs with the weakest bars show severe warps.

  6. Stellar Streams in the Andromeda Halo

    NASA Astrophysics Data System (ADS)

    Fardal, Mark A.; PAndAS Collaboration

    2011-05-01

    The PAndAS survey detects RGB and AGB stars in our neighbor galaxy M31, out to 150 kpc from the galaxy center with an extension to M33. Maps of this survey display a spectacular collection of stellar streams extending tens to hundreds of kpc in length. Many of these streams overlap with each other or with M31's central regions, making it difficult to disentangle the different streams. I discuss what is currently known about the nature, origin, significance, and eventual fate of these stellar streams. Photometric observations from the PAndAS survey and follow-up work constrain the metallicity, age, luminosity, and stellar mass of the stellar population. I discuss scenarios for how some of these streams formed, while for others their origin remains a mystery. I present observationally constrained numerical simulations for the formation of some of the streams. The streams also are probes of the mass profile and lumpiness of M31's dark matter halo. Spectroscopic samples are used to constrain M31's halo mass at large radius.

  7. Inhomogeneous chemical enrichment in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kobayashi, Chiaki

    2016-08-01

    In a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M ⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.

  8. 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.

  9. Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Mackey, A. D.; Gilmore, G. F.

    2004-12-01

    /disc clusters, and ~15-17 per cent of objects with structures typical of external clusters. Taken together our results fully support the accretion hypothesis. We conclude that all 30 young halo clusters and 15-17 per cent of the old halo clusters (10-12 objects) are of external origin. Based on cluster number counts, we estimate that the Galaxy may have experienced approximately seven merger events with cluster-bearing dwarf-spheroidal-type galaxies during its lifetime, building up ~45-50 per cent of the mass of the Galactic stellar halo. Finally, we identify a number of old halo objects which have properties characteristic of accreted clusters. Several of the clusters associated with the recently proposed dwarf galaxy in Canis Major fall into this category.

  10. Diverse stellar haloes in nearby Milky Way mass disc galaxies

    NASA Astrophysics Data System (ADS)

    Harmsen, Benjamin; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Bailin, Jeremy; Radburn-Smith, David J.; Holwerda, Benne W.

    2017-04-01

    We have examined the resolved stellar populations at large galactocentric distances along the minor axis (from 10 kpc up to between 40 and 75 kpc), with limited major axis coverage, of six nearby highly inclined Milky Way (MW) mass disc galaxies using Hubble Space Telescope data from the Galaxy haloes, Outer discs, Substructure, Thick discs, and Star clusters (GHOSTS) survey. We select red giant branch stars to derive stellar halo density profiles. The projected minor axis density profiles can be approximated by power laws with projected slopes of -2 to -3.7 and a diversity of stellar halo masses of 1-6 × 109 M⊙, or 2-14 per cent of the total galaxy stellar masses. The typical intrinsic scatter around a smooth power-law fit is 0.05-0.1 dex owing to substructure. By comparing the minor and major axis profiles, we infer projected axis ratios c/a at ∼25 kpc between 0.4and0.75. The GHOSTS stellar haloes are diverse, lying between the extremes charted out by the (rather atypical) haloes of the MW and M31. We find a strong correlation between the stellar halo metallicities and the stellar halo masses. We compare our results with cosmological models, finding good agreement between our observations and accretion-only models where the stellar haloes are formed by the disruption of dwarf satellites. In particular, the strong observed correlation between stellar halo metallicity and mass is naturally reproduced. Low-resolution hydrodynamical models have unrealistically high stellar halo masses. Current high-resolution hydrodynamical models appear to predict stellar halo masses somewhat higher than observed but with reasonable metallicities, metallicity gradients, and density profiles.

  11. Inhomogeneous chemical enrichment in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kobayashi, Chiaki

    2015-08-01

    In a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances is originated from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relations. This means that the most metal poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant blanch stars or neutron star mergers can contribute the abundance patterns of extremely metal-poor stars, which are in good agreement with observations.

  12. Particle Dark Matter in the galactic halo

    NASA Astrophysics Data System (ADS)

    Bernabei, R.; Belli, P.; D'Angelo, S.; di Marco, A.; Montecchia, F.; D'Angelo, A.; Incicchitti, A.; Cappella, F.; Caracciolo, V.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, X. H.; Sheng, X. D.; Wang, R. G.; Ye, Z. P.

    2015-10-01

    The DAMA/LIBRA-phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton × yr, corresponding to 14 annual cycles) give evidence at 9.3σ C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(Tl) target. Results and comparisons will be shortly recalled. Recent analyses on possible diurnal effects and on the Earth shadowing effect (the latter holds only for some DM candidates) will be mentioned. The analysis of the time distribution of the low-energy single-hit events in DAMA/LIBRA-phase1 is reported for the first time. Finally, some perspectives of the presently running DAMA/LIBRA-phase2 will be mentioned.

  13. Experimental searches for galactic halo axions.

    PubMed

    van Bibber, Karl A; Kinion, S Darin

    2003-11-15

    A very light axion would be copiously produced during the Big Bang as a zero-temperature Bose gas, and it would possess vanishingly small couplings to matter and radiation. It thus represents an ideal cold dark matter candidate. Galactic halo axions may be detected by their resonant conversion to microwave photons in a high-Q cavity permeated by a strong magnetic field. A large-scale search for the axion is ongoing in the US with sufficient sensitivity to see axions of plausible model couplings. Dramatic breakthroughs in the development of near-quantum limited superconducting quantum interference device amplifiers promise to improve the sensitivity of the experiment by a factor of 30 in the near future. In Japan, a group has been developing a Rydberg atom single-quantum detector as an alternative to linear amplifiers for a microwave-cavity axion experiment. Should the axion be discovered, the predicted fine structure in the axion signal would be rich in information about the history of galactic formation.

  14. The Stellar Halos of Massive Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Greene, Jenny E.; Murphy, Jeremy D.; Comerford, Julia M.; Gebhardt, Karl; Adams, Joshua J.

    2012-05-01

    We use the Mitchell Spectrograph (formerly VIRUS-P) on the McDonald Observatory 2.7 m Harlan J. Smith Telescope to search for the chemical signatures of massive elliptical galaxy assembly. The Mitchell Spectrograph is an integral-field spectrograph with a uniquely wide field of view (107'' × 107''), allowing us to achieve remarkably high signal-to-noise ratios of ~20-70 pixel-1 in radial bins of 2-2.5 times the effective radii of the eight galaxies in our sample. Focusing on a sample of massive elliptical galaxies with stellar velocity dispersions σ* > 150 km s-1, we study the radial dependence in the equivalent widths (EW) of key metal absorption lines. By twice the effective radius, the Mgb EWs have dropped by ~50%, and only a weak correlation between σ* and Mgb EW remains. The Mgb EWs at large radii are comparable to those seen in the centers of elliptical galaxies that are ~ an order of magnitude less massive. We find that the well-known metallicity gradients often observed within an effective radius continue smoothly to 2.5 Re , while the abundance ratio gradients remain flat. Much like the halo of the Milky Way, the stellar halos of our galaxies have low metallicities and high α-abundance ratios, as expected for very old stars formed in small stellar systems. Our observations support a picture in which the outer parts of massive elliptical galaxies are built by the accretion of much smaller systems whose star formation history was truncated at early times.

  15. THE STELLAR HALOS OF MASSIVE ELLIPTICAL GALAXIES

    SciTech Connect

    Greene, Jenny E.; Murphy, Jeremy D.; Comerford, Julia M.; Gebhardt, Karl; Adams, Joshua J.

    2012-05-01

    We use the Mitchell Spectrograph (formerly VIRUS-P) on the McDonald Observatory 2.7 m Harlan J. Smith Telescope to search for the chemical signatures of massive elliptical galaxy assembly. The Mitchell Spectrograph is an integral-field spectrograph with a uniquely wide field of view (107'' Multiplication-Sign 107''), allowing us to achieve remarkably high signal-to-noise ratios of {approx}20-70 pixel{sup -1} in radial bins of 2-2.5 times the effective radii of the eight galaxies in our sample. Focusing on a sample of massive elliptical galaxies with stellar velocity dispersions {sigma}{sub *} > 150 km s{sup -1}, we study the radial dependence in the equivalent widths (EW) of key metal absorption lines. By twice the effective radius, the Mgb EWs have dropped by {approx}50%, and only a weak correlation between {sigma}{sub *} and Mgb EW remains. The Mgb EWs at large radii are comparable to those seen in the centers of elliptical galaxies that are {approx} an order of magnitude less massive. We find that the well-known metallicity gradients often observed within an effective radius continue smoothly to 2.5 R{sub e} , while the abundance ratio gradients remain flat. Much like the halo of the Milky Way, the stellar halos of our galaxies have low metallicities and high {alpha}-abundance ratios, as expected for very old stars formed in small stellar systems. Our observations support a picture in which the outer parts of massive elliptical galaxies are built by the accretion of much smaller systems whose star formation history was truncated at early times.

  16. Resolved Stellar Halos of M87 and NGC 5128

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.; Harris, William; Flynn, Chris; Blakeslee, John P.; Valtonen, Mauri

    2015-08-01

    We search halo fields of two giant elliptical galaxies: M87, using HST images at 10 kpc from the center, and NGC 5128 (Cen A), using VIMOS VLT images at 65 kpc from the center and archival HST data from 8 to 38 kpc from the center. We resolve thousands of red-giant-branch stars in these stellar halo fields using V and I filters, and, in addition, measure the metallicity using stellar isochrones. In Cen A, we find that the density of metal-rich and metal-poor halo stars falls off with the same slope in the de Vaucouleurs' law profile, from the inner halo of 8 kpc out to 70 kpc, with no sign of a transition to dominance by metal-poor stars. We also find that the metallicity distribution of the inner stellar halo of M87 is most similar to that of NGC 5128's inner stellar halo.

  17. The Stellar Kinematics of Galactic Disks

    NASA Astrophysics Data System (ADS)

    Bottema, R.

    1993-08-01

    Stellar velocity dispersion measurements of a sample of 12 galactic disks are summarized. The observed radial functionality is parameterized such that one dispersion value is assigned to each galaxy. Comparison of the galaxy dispersion with absolute magnitude and maximum rotation reveals that the dispersion is larger for the more massive systems; the relation between dispersion and intrinsic brightness of the old disk population appears to be linear. Combination of the data for face-on and inclined systems makes the conclusion plausible that the ratio between vertical and radial dispersion in external systems equals 0.6, as for the solar neighbourhood. From the vertical disk dispersion the maximum rotation of a disk can be calculated once the ratio of scalelength to scaleheight (h/z_0_) is known. This ratio is derived as a function of disk brightness from the observed dispersion, for a simple one colour, one mass-to-light ratio disk model. It appears to be rather constant, possibly increasing towards the fainter systems. Then, for realistic h/z_0_ values, the stellar velocity dispersions only allow the disk to have maximum rotation of on average 63% of the observed maximum rotation. The disk is then still dominant in the central parts of the galaxy but generally the maximum disk hypothesis predicting a maximum disk rotation of 85-90% of the observed, does not apply. Exploring the consequences for the Tully-Fisher relation, it is found that the relation for disks only must be positioned at lower rotational velocities than what is observed. A dark halo and bulge must supply the additional rotation. A relation is calculated between Toomre's Q parameter and the mass-to- light ratio for a disk. When this relation is projected onto the observed velocity dispersion - maximum rotational velocity data it is found that the same M/L ratio for galactic disks implies that the Q value is also equal for all disks, and vice versa. A universal Q value can indeed be expected when a

  18. Stellar haloes in Milky Way mass galaxies: from the inner to the outer haloes

    NASA Astrophysics Data System (ADS)

    Tissera, Patricia B.; Beers, Timothy C.; Carollo, Daniela; Scannapieco, Cecilia

    2014-04-01

    We present a comprehensive study of the chemical properties of the stellar haloes of Milky Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ˜15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighbourhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01] dex kpc-1. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies.

  19. Joint constraints on the Galactic dark matter halo and Galactic Centre from hypervelocity stars

    NASA Astrophysics Data System (ADS)

    Rossi, Elena M.; Marchetti, T.; Cacciato, M.; Kuiack, M.; Sari, R.

    2017-05-01

    The mass assembly history of the Milky Way can inform both theory of galaxy formation and the underlying cosmological model. Thus, observational constraints on the properties of both its baryonic and dark matter contents are sought. Here, we show that hypervelocity stars (HVSs) can in principle provide such constraints. We model the observed velocity distribution of HVSs, produced by tidal break-up of stellar binaries caused by Sgr A*. Considering a Galactic Centre (GC) binary population consistent with that inferred in more observationally accessible regions, a fit to current HVS data with significance level >5 per cent can only be obtained if the escape velocity from the GC to 50 kpc is VG ≲ 850 km s-1, regardless of the enclosed mass distribution. When a Navarro, Frenk and White matter density profile for the dark matter halo is assumed, haloes with VG ≲ 850 km s-1 are in agreement with predictions in the Λ cold dark matter model and a subset of models around M200 ˜ 0.5-1.5 × 1012 M⊙ and rs ≲ 35 kpc can also reproduce Galactic circular velocity data. HVS data alone cannot currently exclude potentials with VG > 850 km s-1. Finally, specific constraints on the halo mass from HVS data are highly dependent on the assumed baryonic mass potentials. This first attempt to simultaneously constrain GC and dark halo properties is primarily hampered by the paucity and quality of data. It nevertheless demonstrates the potential of our method, that may be fully realized with the ESA Gaia mission.

  20. Highly ionized gas in the Galactic halo

    NASA Technical Reports Server (NTRS)

    Shull, J. Michael; Slavin, Jonathan D.

    1994-01-01

    We reexamine the values of electron density n(sub e) and gas pressure P/k in the interstellar medium (ISM) of the Galactic halo, as inferred from C IV emission and absorption lines and using current C IV atomic data. In a homogeneous model with 4.7 less than or equal to log T less than or equal to 5.3, the data are consistent with 0.01 less than or equal to n(sub e) less than or equal to 0.02/cu cm and 2200 less than or equal to P/k less than or equal to 3700/cu cm K, a factor of 2-3 higher than advocated by Martin & Bowyer (1990) and comparable to the thermal pressure in the disk. If some of the C IV absorption arises from nonemitting, photoionized gas, then the inferred density and pressure will increase accordingly. The volume filling factor for homogeneous models ranges from 0.5% to 5%. Because of the constraints arising from filling factor and radiated power, most of the C IV must arise from gas near the peak of the cooling curve, at log t less than or equal to 5.6. We relate both emission-line and absorption-line observations to recent models in which turbulent mixing layers and isobarically cooling supernova remnants (SNRs) provide significant amounts of halo gas at approximately 10(exp 5.3) K and process 20-40 solar mass/yr with a power of approximately 10(exp 41) ergs/sec. Since the observed C IV and N V absorption scale heights have been reported to differ, at 4.9 kpc and 1.6 kpc, respectively, we examine inhomogeneous models with different exponential scale heights of T, P, and SN energy input. The ISM may change its character with distance above the Galactic plane, as superbubbles and mixing layers dominate over isolated SNRs as the source of the C IV. For appropiate scale heights, the midplane pressure is twice the homogeneous values quoted above. The O IV lambda 1034 diffuse emission line, which can be used as a temperature diagnostic of the hot gas, is predicted to be comparable in strength to that of C IV lambda 1549 (approximately 6000 photons

  1. MAPPING THE STELLAR STRUCTURE OF THE MILKY WAY THICK DISK AND HALO USING SEGUE PHOTOMETRY

    SciTech Connect

    De Jong, Jelte T. A.; Rix, Hans-Walter; Martin, Nicolas F.; Yanny, Brian; Dolphin, Andrew E.; Beers, Timothy C.

    2010-05-01

    We map the stellar structure of the Galactic thick disk and halo by applying color-magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1 kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75 {+-} 0.07 kpc and 4.1 {+-} 0.4 kpc, respectively. We find a stellar halo flattening within {approx}25 kpc of c/a = 0.88 {+-} 0.03 and a power-law index of 2.75 {+-} 0.07 (for 7 kpc {approx_lt}R{sub GC} {approx_lt} 30 kpc). The model fits yield thick-disk and stellar halo densities at the solar location of {rho}{sub thick,sun} = 10{sup -2.3{+-}0.1} M{sub sun} pc{sup -3} and {rho}{sub halo,sun} = 10{sup -4.20{+-}0.05} M{sub sun} pc{sup -3}, averaging over any substructures. Our analysis provides the first clear in situ evidence for a radial metallicity gradient in the Milky Way's stellar halo: within R {approx_lt} 15 kpc the stellar halo has a mean metallicity of [Fe/H] {approx_equal} -1.6, which shifts to [Fe/H] {approx_equal} -2.2 at larger radii, in line with the two-component halo deduced by Carollo et al. from a local kinematic analysis. Subtraction of the best-fit smooth and symmetric model from the overall density maps reveals a wealth of substructures at all latitudes, some attributable to known streams and overdensities, and some

  2. The warp of the Galactic stellar disk detected in IRAS source counts

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Sosin, Craig

    1989-01-01

    About 90,000 IRAS point sources have been used as disk tracers in order to explore the possibility of warp in the Galactic stellar disk. The results imply that the Galactic stellar disk is warped at large radii in a way similar to the H-I layer, and that the warp is an important characteristic of the Galaxy as a whole. It is suggested that the warp may be a long-lasting phenomenon, possibly caused by asymmetries of the mass distribution in the outer regions of the Galactic dark halo.

  3. Black holes in binary stellar systems and galactic nuclei

    NASA Astrophysics Data System (ADS)

    Cherepashchuk, A. M.

    2014-04-01

    In the last 40 years, following pioneering papers by Ya B Zeldovich and E E Salpeter, in which a powerful energy release from nonspherical accretion of matter onto a black hole (BH) was predicted, many observational studies of black holes in the Universe have been carried out. To date, the masses of several dozen stellar-mass black holes (M_BH = (4{-}20) M_\\odot) in X-ray binary systems and of several hundred supermassive black holes (M_BH = (10^{6}{-}10^{10}) M_\\odot) in galactic nuclei have been measured. The estimated radii of these massive and compact objects do not exceed several gravitational radii. For about ten stellar-mass black holes and several dozen supermassive black holes, the values of the dimensionless angular momentum a_* have been estimated, which, in agreement with theoretical predictions, do not exceed the limiting value a_* = 0.998. A new field of astrophysics, so-called black hole demography, which studies the birth and growth of black holes and their evolutionary connection to other objects in the Universe, namely stars, galaxies, etc., is rapidly developing. In addition to supermassive black holes, massive stellar clusters are observed in galactic nuclei, and their evolution is distinct from that of supermassive black holes. The evolutionary relations between supermassive black holes in galactic centers and spheroidal stellar components (bulges) of galaxies, as well as dark-matter galactic haloes are brought out. The launch into Earth's orbit of the space radio interferometer RadioAstron opened up the real possibility of finally proving that numerous discovered massive and highly compact objects with properties very similar to those of black holes make up real black holes in the sense of Albert Einstein's General Relativity. Similar proofs of the existence of black holes in the Universe can be obtained by intercontinental radio interferometry at short wavelengths \\lambda \\lesssim 1 mm (the international program, Event Horizon Telescope).

  4. The Dragonfly Nearby Galaxies Survey: A Census of the Stellar Halos of Nearby Luminous Galaxies

    NASA Astrophysics Data System (ADS)

    Merritt, Allison T.

    2017-01-01

    The Dragonfly Telephoto Array, comprised of 48 individual Canon telephoto lenses operating together as a single telescope, is an innovative approach to low surface brightness imaging and the study of galactic stellar halos in particular. Sub-nanometer coatings on each optical element reduce scattered light from nearby bright stars and compact galaxy centers - typically a key obstacle for integrated light observations - by an order of magnitude, and Dragonfly's large field of view (2x2.6 degrees for a single frame) provides a large-scale view of stellar halos free from substructure biases. Using extremely deep (>30 mag/arcsec^2) optical imaging in g and r bands from the Dragonfly Nearby Galaxies Survey (DNGS), we have characterized the stellar halos of a sample of ~20 nearby luminous galaxies. I will present measurements of the stellar halo mass fractions of these galaxies as a function of stellar mass, morphology, and environment, and discuss the scatter in halo fractions in the context of the galaxies' individual accretion histories.

  5. THE FRACTION OF GLOBULAR CLUSTER SECOND-GENERATION STARS IN THE GALACTIC HALO

    SciTech Connect

    Vesperini, Enrico; McMillan, Stephen L. W.; D'Antona, Francesca; D'Ercole, Annibale

    2010-08-01

    Many observational studies have revealed the presence of multiple stellar generations in Galactic globular clusters. These studies suggest that second-generation stars make up a significant fraction of the current mass of globular clusters, with the second-generation mass fraction ranging from {approx}50% to 80% in individual clusters. In this Letter, we carry out hydrodynamical simulations to explore the dependence of the mass of second-generation stars on the initial mass and structural parameters and stellar initial mass function (IMF) of the parent cluster. We then use the results of these simulations to estimate the fraction f{sub SG,H} of the mass of the Galactic stellar halo composed of second-generation stars that originated in globular clusters. We study the dependence of f{sub SG,H} on the parameters of the IMF of the Galactic globular cluster system. For a broad range of initial conditions, we find that the fraction of mass of the Galactic stellar halo in second-generation stars is always small, f{sub SG,H} < 4%-6% for a Kroupa-1993 IMF and f{sub SG,H} < 7%-9% for a Kroupa-2001 IMF.

  6. The Milky Way, the Galactic Halo, and the Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin

    2016-08-01

    The Milky Way, ``our'' Galaxy, is currently the subject of intense study with many ground-based surveys, in anticipation of upcoming results from the Gaia mission. From this work we have been learning about the full three-dimensional structure of the Galactic box/peanut bulge, the distribution of stars in the bar and disk, and the many streams and substructures in the Galactic halo. The data indicate that a large fraction of the Galactic halo has been accreted from outside. Similarly, in many external galaxy halos there is now evidence for tidal streams and accretion of satellites. To study these features requires exquisite, deep photometry and spectroscopy. These observations illustrate how galaxy halos are still growing, and sometimes can be used to ``time'' the accretion events. In comparison with cosmological simulations, the structure of galaxy halos gives us a vivid illustration of the hierarchical nature of our Universe.

  7. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2017-08-01

    Observations of the nearby universe fail to locate about half of the normal matter (baryons) observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We describe the current status of HaloSat.

  8. Stellar Bar Evolution in Cuspy and Flat-cored Triaxial CDM Halos

    NASA Astrophysics Data System (ADS)

    Berentzen, Ingo; Shlosman, Isaac; Jogee, Shardha

    2006-02-01

    We analyze the formation and evolution of stellar bars in galactic disks embedded in mildly triaxial cold dark matter (CDM) halos that have density distributions ranging from large flat cores to cuspy profiles. We have applied tailored numerical simulations of analytical and live halos that include the feedback from disk/bar system onto the halo in order to test and extend earlier work by El-Zant and Shlosman. The latter employed the method of Liapunov exponents to analyze the fate of bars in analytical asymmetric halos. We find the following: (1) The bar growth is very similar in all rigid axisymmetric and triaxial halos. (2) Bars in live models experience vertical buckling instability and the formation of a pseudobulge with a boxy/peanut shape, while bars in rigid halos do not buckle. (3) In live axisymmetric halos, the bar strength varies by a factor of <~2, in growth or decay, during the secular evolution following the buckling. The bar pattern speed evolution (i.e., deceleration) anticorrelates with the halo core size. In such halos, the bar strength is larger for smaller disk-to-halo mass ratios (D/H) within disk radii, the bar size correlates with the halo core sizes, and the bar pattern speeds correlate with the halo central mass concentration. In contrast, bars embedded in live triaxial halos have a starkly different fate: they dissolve on a timescale of ~1.5-5 Gyr due to the onset of chaos over continuous zones, sometimes leaving behind a weak oval distortion. The onset of chaos is related to the halo triaxiality, the fast-rotating bar, and the halo cuspiness. Before the bar dissolves, the region outside it develops strong spiral structures, especially in the live triaxial halos. (4) More angular momentum is absorbed (fractionally) by the triaxial halos than in the axisymmetric models. The disk-halo angular momentum exchange is mediated by the lower resonances in the latter models. (5) Cuspy halos are more susceptible than flat-core halos to having their

  9. New cluster members and halo stars of the Galactic globular cluster NGC 1851

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar evolutionary sequences, light and heavy element abundance variations and indications of a surrounding stellar halo. We present the first results of a spectroscopic study of red giant stars within and outside of the tidal radius of this cluster. Our results identify nine probable new cluster members (inside the tidal radius) with heliocentric radial velocities consistent with that of NGC 1851. We also identify, based on their radial velocities, four probable extratidal cluster halo stars at distances up to ˜3.1 times the tidal radius, which are supportive of previous findings that NGC 1851 is surrounded by an extended stellar halo. Proper motions were available for 12 of these 13 stars and all are consistent with that of NGC 1851. Apart from the cluster members and cluster halo stars, our observed radial velocity distribution agrees with the expected distribution from a Besançon disc/N-body stellar halo Milky Way model generated by the GALAXIA code, suggesting that no other structures at different radial velocities are present in our field. The metallicities of these stars are estimated using equivalent width measurements of the near-infrared calcium triplet absorption lines and are found, within the limitations of this method, to be consistent with that of NGC 1851. In addition we recover 110 red giant cluster members from previous studies based on their radial velocities and identify three stars with unusually high radial velocities.

  10. Stellar-to-halo mass relation of cluster galaxies

    DOE PAGES

    Niemiec, Anna; Jullo, Eric; Limousin, Marceau; ...

    2017-07-04

    In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can bemore » used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science veri cation archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we nd a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we nd that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this nding as further evidence for tidal stripping of dark matter haloes in high density environments.« less

  11. Stellar-to-halo mass relation of cluster galaxies

    NASA Astrophysics Data System (ADS)

    Niemiec, Anna; Jullo, Eric; Limousin, Marceau; Giocoli, Carlo; Erben, Thomas; Hildebrant, Hendrik; Kneib, Jean-Paul; Leauthaud, Alexie; Makler, Martin; Moraes, Bruno; Pereira, Maria E. S.; Shan, Huanyuan; Rozo, Eduardo; Rykoff, Eli; Van Waerbeke, Ludovic

    2017-10-01

    In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: Assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can be used as a proxy of the infall mass. We study the stellar-to-halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the Dark Energy Survey (DES) science verification archive, the Canada-France-Hawaii Lensing Survey (CFHTLenS) and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we find a stellar-to- halo mass relation in good agreement with the theoretical expectations from Moster et al. for central galaxies. In the centre of the cluster, we find that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this finding as further evidence for tidal stripping of dark matter haloes in high-density environments.

  12. The stellar halo in the inner Milky Way: predicted shape and kinematics

    NASA Astrophysics Data System (ADS)

    Pérez-Villegas, Angeles; Portail, Matthieu; Gerhard, Ortwin

    2017-01-01

    We have used N-body simulations for the Milky Way to investigate the kinematic and structural properties of the old metal-poor stellar halo in the barred inner region of the Galaxy. We find that the extrapolation of the density distribution for bulge RR Lyrae stars, ρ ˜ r-3, approximately matches the number density of RR Lyrae in the nearby stellar halo. We follow the evolution of such a tracer population through the formation and evolution of the bar and box/peanut bulge in the N-body model. We find that its density distribution changes from oblate to triaxial, and that it acquires slow rotation in agreement with recent measurements. The maximum radial velocity is ˜15-25 km s-1 at |l| = 10°-30°, and the velocity dispersion is ˜120 km s-1. Even though the simulated metal-poor halo in the bulge has a barred shape, just 12 per cent of the orbits follow the bar, and it does not trace the peanut/X structure. With these properties, the RR Lyrae population in the Galactic bulge is consistent with being the inward extension of the Galactic metal-poor stellar halo.

  13. STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Beky, Bence; Kocsis, Bence E-mail: bkocsis@cfa.harvard.edu

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10{sup 6} solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or {approx}10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  14. STELLAR ENCOUNTER RATE IN GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Bahramian, Arash; Heinke, Craig O.; Sivakoff, Gregory R.; Gladstone, Jeanette C.

    2013-04-01

    The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates ({Gamma}) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed 'King-model' profiles for all clusters. By deprojecting cluster surface brightness profiles to estimate luminosity density profiles, we treat 'King-model' and 'core-collapsed' clusters in the same way. In addition, we use Monte Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on {Gamma}, producing the first catalog of globular cluster stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and {gamma}-ray luminosity) we find both clear correlations and some differences with published results.

  15. Mixing between high velocity clouds and the galactic halo

    SciTech Connect

    Gritton, Jeffrey A.; Shelton, Robin L.; Kwak, Kyujin E-mail: rls@physast.uga.edu

    2014-11-01

    In the Galactic halo, metal-bearing Galactic halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before the clouds completely dissipate and long before they slow to the velocity of the Galactic material. In order to make quantitative estimates of the mixing efficiency and resulting metal enrichment of HVCs, we made detailed two- and three-dimensional simulations of cloud-interstellar medium interactions. Our simulations track the hydrodynamics and time-dependent ionization levels. They assume that the cloud originally has a warm temperature and extremely low metallicity while the surrounding medium has a high temperature, low density, and substantial metallicity, but our simulations can be generalized to other choices of initial metallicities. In our simulations, mixing between cloud and halo gas noticeably raises the metallicity of the high velocity material. We present plots of the mixing efficiency and metal enrichment as a function of time.

  16. The elusive stellar halo of the Triangulum galaxy

    NASA Astrophysics Data System (ADS)

    McMonigal, B.; Lewis, G. F.; Brewer, B. J.; Irwin, M. J.; Martin, N. F.; McConnachie, A. W.; Ibata, R. A.; Ferguson, A. M. N.; Mackey, A. D.; Chapman, S. C.

    2016-10-01

    The stellar haloes of large galaxies represent a vital probe of the processes of galaxy evolution. They are the remnants of the initial bouts of star formation during the collapse of the protogalactic cloud, coupled with imprint of ancient and ongoing accretion events. Previously, we have reported the tentative detection of a possible, faint, extended stellar halo in the Local Group spiral, the Triangulum galaxy (M33). However, the presence of substructure surrounding M33 made interpretation of this feature difficult. Here, we employ the final data set from the Pan-Andromeda Archaeological Survey, combined with an improved calibration and a newly derived contamination model for the region to revisit this claim. With an array of new fitting algorithms, fully accounting for contamination and the substantial substructure beyond the prominent stellar disc in M33, we reanalyse the surrounds to separate the signal of the stellar halo and the outer halo substructure. Using more robust search algorithms, we do not detect a large-scale smooth stellar halo and place a limit on the maximum surface brightness of such a feature of μV = 35.5 mag arcsec-2, or a total halo luminosity of L < 106 L⊙.

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

    SciTech Connect

    Tonnesen, Stephanie; Cen, Renyue 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 assembly 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.

  18. THE GROWTH OF GALAXY STELLAR MASS WITHIN DARK MATTER HALOS

    SciTech Connect

    Zehavi, Idit; Patiri, Santiago; Zheng Zheng

    2012-02-20

    We study the evolution of stellar mass in galaxies as a function of host halo mass, using the 'MPA' and 'Durham' semi-analytic models, implemented on the Millennium Run simulation. For both models, the stellar mass of the central galaxies increases rapidly with halo mass at the low-mass end and more slowly in halos of larger masses at the three redshifts probed (z {approx} 0, 1, 2). About 45% of the stellar mass in central galaxies in present-day halos less massive than {approx}10{sup 12} h{sup -1} M{sub Sun} is already in place at z {approx} 1, and this fraction increases to {approx}65% for more massive halos. The baryon conversion efficiency into stars has a peaked distribution with halo mass, and the peak location shifts toward lower mass from z {approx} 1 to z {approx} 0. The stellar mass in low-mass halos grows mostly by star formation since z {approx} 1, while in high-mass halos most of the stellar mass is assembled by mergers, reminiscent of 'downsizing'. We compare our findings to empirical results from the Sloan Digital Sky Survey and DEEP2 surveys utilizing galaxy clustering measurements to study galaxy evolution. The theoretical predictions are in qualitative agreement with these phenomenological results, but there are large discrepancies. The most significant one concerns the number of stars already in place in the progenitor galaxies at z {approx} 1, which is about a factor of two larger in both semi-analytic models. We demonstrate that methods studying galaxy evolution from the galaxy-halo connection are powerful in constraining theoretical models and can guide future efforts of modeling galaxy evolution. Conversely, semi-analytic models serve an important role in improving such methods.

  19. Feedback and the formation of dwarf galaxy stellar haloes

    NASA Astrophysics Data System (ADS)

    Stinson, G. S.; Dalcanton, J. J.; Quinn, T.; Gogarten, S. M.; Kaufmann, T.; Wadsley, J.

    2009-05-01

    Stellar population studies show that low-mass galaxies in all environments exhibit stellar haloes that are older and more spherically distributed than the main body of the galaxy. In some cases, there is a significant intermediate age component that extends beyond the young disc. We examine a suite of Smoothed Particle Hydrodynamic simulations and find that elevated early star formation activity combined with supernova feedback can produce an extended stellar distribution that resembles these haloes for model galaxies ranging from v200 = 15 to 35 km s-1, without the need for accretion of subhaloes.

  20. The gamma-ray-flux PDF from galactic halo substructure

    SciTech Connect

    Lee, Samuel K.; Ando, Shin'ichiro; Kamionkowski, Marc E-mail: ando@tapir.caltech.edu

    2009-07-01

    One of the targets of the recently launched Fermi Gamma-ray Space Telescope is a diffuse gamma-ray background from dark-matter annihilation or decay in the Galactic halo. N-body simulations and theoretical arguments suggest that the dark matter in the Galactic halo may be clumped into substructure, rather than smoothly distributed. Here we propose the gamma-ray-flux probability distribution function (PDF) as a probe of substructure in the Galactic halo. We calculate this PDF for a phenomenological model of halo substructure and determine the regions of the substructure parameter space in which the PDF may be distinguished from the PDF for a smooth distribution of dark matter. In principle, the PDF allows a statistical detection of substructure, even if individual halos cannot be detected. It may also allow detection of substructure on the smallest microhalo mass scales, ∼ M{sub ⊕}, for weakly-interacting massive particles (WIMPs). Furthermore, it may also provide a method to measure the substructure mass function. However, an analysis that assumes a typical halo substructure model and a conservative estimate of the diffuse background suggests that the substructure PDF may not be detectable in the lifespan of Fermi in the specific case that the WIMP is a neutralino. Nevertheless, for a large range of substructure, WIMP annihilation, and diffuse background models, PDF analysis may provide a clear signature of substructure.

  1. 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.

  2. Compact binary mergers as the origin of r-process elements in the Galactic halo

    SciTech Connect

    Ishimaru, Yuhri; Wanajo, Shinya; Prantzos, Nikos

    2014-05-02

    Compact binary mergers (of double neutron star and black hole-neutron star systems) are suggested to be the major site of the r-process elements in the Galaxy by recent hydrodynamical and nucleosynthesis studies. It has been pointed out, however, that estimated long lifetimes of compact binaries are in conflict with the presence of r-process-enhanced stars at the metallicity [Fe/H] ∼ −3. To resolve this problem, we examine the role of compact binary mergers in the early Galactic chemical evolution on the assumption that our Galactic halo was formed from merging sub-halos. The chemical evolutions are modeled for sub-halos with their total stellar masses between 10{sup 4}M{sub ⊙} and 2 × 10{sup 8}M{sub ⊙}. The lifetimes of compact binaries are assumed to be 100 Myr (95%) and 1 Myr (5%) according to recent binary population synthesis studies. We find that the r-process abundances (relative to iron; [r/Fe]) start increasing at [Fe/H] ≤ −3 if the star formation rates are smaller for less massive sub-halos. Our models also suggest that the star-to-star scatter of [r/Fe]'s observed in Galactic halo stars can be interpreted as a consequence of greater gas outflow rates for less massive sub-halos. In addition, the sub-solar [r/Fe]'s (observed as [Ba/Fe] ∼ −1.5 for [Fe/H] < −3) are explained by the contribution from the short-lived (∼ 1 Myr) binaries. Our result indicates, therefore, that compact binary mergers can be potentially the origin of the r-process elements throughout the Galactic history.

  3. HaloSat- A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    We propose to develop, build, and fly HaloSat, a CubeSat capable of measuring the oxygen line emission from the hot Galactic halo. A dedicated CubeSat enables an instrument design and observing strategy to maximize the halo signal while minimizing foregrounds from solar wind charge exchange interactions within the solar system. We will use HaloSat to map the distribution of hot gas in the Milky Way and determine whether it fills an extended, and thus massive halo, or whether the halo is compact, and thus does not contribute significantly to the total mass of the Milky Way. HaloSat can be accomplished at modest cost using a CubeSat, a novel platform for space astrophysics missions. We will use a commercially available CubeSat bus and commercially available X-ray detectors to reduce development risk and minimize overall mission cost. HaloSat builds on the initiatives of GSFC/Wallops Flight Facility (WFF) in the development of CubeSats for low cost access to space and relies on the technical expertise of WFF personnel for spacecraft and mission design and operations. The team, from University of Iowa (UI), GSFC, Johns Hopkins, and CNRS (France), contains experts in X-ray detector development and data analysis and the astrophysics of hot plasmas and Galactic structure. The UI team will include a number of junior researchers (undergraduates, graduate students, and a postdoc) and help train them for future leadership roles on NASA space flight missions.

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

    SciTech Connect

    De Propris, Roberto; Harrison, Craig D.; Mares, Peter J.

    2010-08-20

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

  5. High-velocity pulsars in the galactic halo.

    PubMed

    Eichler, D; Silk, J

    1992-08-14

    It is proposed that high-velocity pulsars are produced in extended galactic halos, and possibly in extragalactic space, from primordial (population III) stars. Such a population of neutron stars could provide an explanation for the gamma-ray bursters and would then accommodate the possibility that most bursters are not in the visible parts of galaxies.

  6. Creating mock catalogues of stellar haloes from cosmological simulations

    NASA Astrophysics Data System (ADS)

    Lowing, Ben; Wang, Wenting; Cooper, Andrew; Kennedy, Rachel; Helly, John; Cole, Shaun; Frenk, Carlos

    2015-01-01

    We present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmological simulations and show how the catalogues can be used to test and interpret observational data. The catalogues are constructed from a combination of methods. A semi-analytic galaxy formation model is used to calculate the star formation history in haloes in an N-body simulation and dark matter particles are tagged with this stellar mass. The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained. A set of catalogues based on the Λ cold dark matter Aquarius simulations of Milky Way mass haloes have been created and made publicly available on a website. Two example applications are discussed that demonstrate the power and flexibility of the mock catalogues. We show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. We also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stellar populations, allow streams to be easily identified.

  7. Lithium in halo stars from standard stellar evolution

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Demarque, Pierre; Kawaler, Steven D.

    1990-01-01

    A grid has been constructed of theoretical evolution sequences of models for low-metallicity stars from the premain-sequence to the giant branch phases. The grid is used to study the history of surface Li abundance during standard stellar evolution. The Li-7 observations of halo stars by Spite and Spite (1982) and subsequent observations are synthesized to separate the halo stars by age. The theory of surface Li abundance is illustrated by following the evolution of a reference halo star model from the contracting fully convective premain sequence to the giant branch phase. The theoretical models are compared with observed Li abundances. The results show that the halo star lithium abundances can be explained in the context of standard stellar evolution theory using completely standard assumptions and physics.

  8. Lithium in halo stars from standard stellar evolution

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Demarque, Pierre; Kawaler, Steven D.

    1990-01-01

    A grid has been constructed of theoretical evolution sequences of models for low-metallicity stars from the premain-sequence to the giant branch phases. The grid is used to study the history of surface Li abundance during standard stellar evolution. The Li-7 observations of halo stars by Spite and Spite (1982) and subsequent observations are synthesized to separate the halo stars by age. The theory of surface Li abundance is illustrated by following the evolution of a reference halo star model from the contracting fully convective premain sequence to the giant branch phase. The theoretical models are compared with observed Li abundances. The results show that the halo star lithium abundances can be explained in the context of standard stellar evolution theory using completely standard assumptions and physics.

  9. WEIGHING THE GALACTIC DARK MATTER HALO: A LOWER MASS LIMIT FROM THE FASTEST HALO STAR KNOWN

    SciTech Connect

    Przybilla, Norbert; Tillich, Alfred; Heber, Ulrich; Scholz, Ralf-Dieter

    2010-07-20

    The mass of the Galactic dark matter halo is under vivid discussion. A recent study by Xue et al. revised the Galactic halo mass downward by a factor of {approx}2 relative to previous work, based on the line-of-sight velocity distribution of {approx}2400 blue horizontal-branch (BHB) halo stars. The observations were interpreted with a statistical approach using cosmological galaxy formation simulations, as only four of the six-dimensional phase-space coordinates were determined. Here we concentrate on a close investigation of the stars with the highest negative radial velocity from that sample. For one star, SDSSJ153935.67+023909.8 (J1539+0239 for short), we succeed in measuring a significant proper motion, i.e., full phase-space information is obtained. We confirm the star to be a Population II BHB star from an independent quantitative analysis of the Sloan Digital Sky Survey (SDSS) spectrum-providing the first non-LTE (NLTE) study of any halo BHB star-and reconstruct its three-dimensional trajectory in the Galactic potential. J1539+0239 turns out to be the fastest halo star known to date, with a Galactic rest-frame velocity of 694{sup +300}{sub -221} km s{sup -1} (full uncertainty range from Monte Carlo error propagation) at its current position. The extreme kinematics of the star allows a significant lower limit to be put on the halo mass in order to keep it bound, of M {sub halo} {>=} 1.7{sup +2.3}{sub -1.1} x 10{sup 12} M{sub sun}. We conclude that the Xue et al. results tend to underestimate the true halo mass as their most likely mass value is consistent with our analysis only at a level of 4%. However, our result confirms other studies that make use of the full phase-space information.

  10. 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).

  11. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2017-01-01

    Observations of the nearby universe fail to locate about half of the baryons observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We will describe the HaloSat mission concept, progress towards its implementation, and plans for archiving and distribution of the data.

  12. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2016-04-01

    Observations of the nearby universe fail to locate about half of the normal matter (baryons) observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We will describe the HaloSat mission concept, progress towards its implementation, and plans for archiving and distribution of the data.

  13. 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.

  14. Mapping the Galactic Halo. I. The ``Spaghetti'' Survey

    NASA Astrophysics Data System (ADS)

    Morrison, Heather L.; Mateo, Mario; Olszewski, Edward W.; Harding, Paul; Dohm-Palmer, R. C.; Freeman, Kenneth C.; Norris, John E.; Morita, Miwa

    2000-05-01

    We describe a major survey of the Milky Way halo designed to test for kinematic substructure caused by destruction of accreted satellites. We use the Washington photometric system to identify halo stars efficiently for spectroscopic follow-up. Tracers include halo giants (detectable out to more than 100 kpc), blue horizontal-branch (BHB) stars, halo stars near the main-sequence turnoff, and the ``blue metal-poor stars'' of Preston, Beers, & Shectman. We demonstrate the success of our survey by showing spectra of stars we have identified in all these categories, including giants as distant as 75 kpc. We discuss the problem of identifying the most distant halo giants. In particular, extremely metal-poor halo K dwarfs are present in approximately equal numbers to the distant giants for V>18, and we show that our method will distinguish reliably between these two groups of metal-poor stars. We plan to survey 100 deg2 at high Galactic latitude and expect to increase the numbers of known halo giants, BHB stars, and turnoff stars by more than an order of magnitude. In addition to the strong test that this large sample will provide for the question, Was the Milky Way halo accreted from satellite galaxies? we will improve the accuracy of mass measurements of the Milky Way beyond 50 kpc via the kinematics of the many distant giants and BHB stars we find. We show that one of our first data sets constrains the halo density law over Galactocentric radii of 5-20 kpc and z-heights of 2-15 kpc. The data support a flattened power-law halo with b/a of 0.6 and exponent -3.0. More complex models with a varying axial ratio may be needed with a larger data set.

  15. The halo+cluster system of the Galactic globular cluster NGC 1851

    NASA Astrophysics Data System (ADS)

    Marino, A. F.; Milone, A. P.; Yong, D.; Dotter, A.; Da Costa, G.; Asplund, M.; Jerjen, H.; Mackey, D.; Norris, J.; Cassisi, S.; Sbordone, L.; Stetson, P. B.; Weiss, A.; Aparicio, A.; Bedin, L. R.; Lind, K.; Monelli, M.; Piotto, G.; Angeloni, R.; Buonanno, R.

    2014-08-01

    NGC 1851 is surrounded by a stellar component that extends more than 10 times beyond the tidal radius. Although the nature of this stellar structure is not known, it has been suggested to be a sparse halo of stars or associated with a stellar stream. We analyse the nature of this intriguing stellar component surrounding NGC 1851 by investigating its radial velocities and chemical composition, in particular in comparison with those of the central cluster analysed in a homogeneous manner. In total we observed 23 stars in the halo with radial velocities consistent with NGC 1851, and for 15 of them we infer [Fe/H] abundances. Our results show that (i) stars dynamically linked to NGC 1851 are present at least up to ˜2.5 tidal radii, supporting the presence of a halo of stars surrounding the cluster; (ii) apart from the NGC 1851 radial velocity-like stars, our observed velocity distribution agrees with that expected from Galactic models, suggesting that no other substructure (such as a stream) at different radial velocities is present in our field; (iii) the chemical abundances for the s-process elements Sr and Ba are consistent with the s-normal stars observed in NGC 1851; (iv) all halo stars have metallicities, and abundances for the other studied elements Ca, Mg and Cr, consistent with those exhibited by the cluster. The complexity of the whole NGC 1851 cluster+halo system may agree with the scenario of a tidally disrupted dwarf galaxy in which NGC 1851 was originally embedded.

  16. A general relativistic approach to the Navarro Frenk White galactic halos

    NASA Astrophysics Data System (ADS)

    Matos, Tonatiuh; Núñez, Darío; Sussman, Roberto A.

    2004-11-01

    Although galactic dark matter halos are basically Newtonian structures, the study of their interplay with large-scale cosmic evolution and with relativistic effects, such as gravitational lenses, quintessence sources or gravitational waves, makes it necessary to obtain adequate relativistic descriptions for these self-gravitating systems. With this purpose in mind, we construct a post-Newtonian fluid framework for the 'Navarro Frenk White' (NFW) models of galactic halos that follow from N-body numerical simulations. Since these simulations are unable to resolve regions very near the halo centre, the extrapolation of the fitting formula leads to a spherically averaged 'universal' density profile that diverges at the origin. We remove this inconvenient feature by replacing a small central region of the NFW halo with an interior Schwarzschild solution with constant density, continuously matched to the remaining NFW spacetime. A model of a single halo, as an isolated object with finite mass, follows by smoothly matching the NFW spacetime to a Schwarzschild vacuum exterior along the virial radius, the physical 'cut-off' customarily imposed, as the mass associated with NFW profiles diverges asymptotically. Numerical simulations assume weakly interacting collisionless particles, hence we suggest that NFW halos approximately satisfy an 'ideal gas' type of equation of state, where mass-density is the dominant rest-mass contribution to matter-energy, with the internal energy contribution associated with an anisotropic kinetic pressure. We show that, outside the central core, this pressure and the mass density roughly satisfy a polytropic relation. Since stellar polytropes are the equilibrium configurations in Tsallis' non-extensive formalism of statistical mechanics, we argue that NFW halos might provide a rough empirical estimate of the free parameter q of Tsallis' formalism.

  17. Does SEGUE/SDSS indicate a dual galactic halo?

    SciTech Connect

    Schönrich, Ralph; Asplund, Martin; Casagrande, Luca

    2014-05-01

    We re-examine recent claims of observational evidence for a dual Galactic halo in SEGUE/SDSS data, and trace them back to improper error treatment and neglect of selection effects. In particular, the detection of a vertical abundance gradient in the halo can be explained as a metallicity bias in distance. A similar bias and the impact of disk contamination affect the sample of blue horizontal branch stars. These examples highlight why non-volume complete samples require forward modeling from theoretical models or extensive bias-corrections. We also show how observational uncertainties produce the specific non-Gaussianity in the observed azimuthal velocity distribution of halo stars, which can be erroneously identified as two Gaussian components. A single kinematic component yields an excellent fit to the observed data, when we model the measurement process including distance uncertainties. Furthermore, we show that sample differences in proper motion space are the direct consequence of kinematic cuts and are enhanced when distance estimates are less accurate. Thus, their presence is neither proof of a separate population nor a measure of reliability for the applied distances. We conclude that currently there is no evidence from SEGUE/SDSS that would favor a dual Galactic halo over a single halo that is full of substructure.

  18. 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.

  19. Simulating the carbon footprint of galactic haloes

    NASA Astrophysics Data System (ADS)

    Bird, Simeon; Rubin, Kate H. R.; Suresh, Joshua; Hernquist, Lars

    2016-10-01

    We compare simulations, including the Illustris simulations, to observations of C IV and C II absorption at z = 2-4. These are the C IV column density distribution function in the column density range 1012-1015 cm-2, the C IV equivalent width distribution at 0.1-2 Å, and the covering fractions and equivalent widths of C IV1548 Å and C II 1337 Å around damped Lyman α systems (DLAs). In the context of the feedback models that we investigate, all C IV observations favour the use of more energetic wind models, which are better able to enrich the gas surrounding haloes. We propose two ways to achieve this: an increased wind velocity and an increase in wind thermal energy. However, even our most energetic wind models do not produce enough absorbers with C IV equivalent width >0.6 Å, which in our simulations are associated with the most massive haloes. All simulations are in reasonable agreement with the C II covering fraction and equivalent widths around damped Lyman α absorbers, although there is a moderate deficit in one bin 10-100 kpc from the DLA. Finally, we show that the C IV in our simulations is predominantly photoionized.

  20. Stellar Feedback and Hot Gaseous Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Wang, Q. Daniel

    I will review our recent work on galactic diffuse hot gas as a tracer of stellar feedback and its relationship to the formation and evolution of galaxies, concentrating on ones that show no ongoing starburst or AGN. I will first summarize relevant observations to highlight various clues that these observations offer to the understanding of the feedback. I will then present our hydrodynamic simulations of hot gas structure and evolution, including the feedback from galactic stellar bulges. These simulations show that the feedback can play an essential role in shaping the galactic gaseous structure and evolution and may provide a solution to several long-standing problems in understanding various galaxies, including the so-called missing stellar feedback and over-cooling problems.

  1. 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.

  2. Characterizing the X-Ray Spectrum of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The goal of this project is to determine the spectrum of the Galactic halo's soft X-ray emission. These photons are emitted by hot, diffuse gas hundreds to thousands of parsecs from the Galactic plane. Thus, the emission is weak, can be confused with locally produced photons, and must be distinguished from noise. My co-I has made significant progress on determining the background. I have been working on a complementary aspect of the project: computer simulations of the hot gas in the local and distant regions.

  3. Characterizing the X-Ray Spectrum of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The goal of this project is to determine the spectrum of the Galactic halo's soft X-ray emission. These photons are emitted by hot, diffuse gas hundreds to thousands of parsecs from the Galactic plane. Thus, the emission is weak, can be confused with locally produced photons, and must be distinguished from noise. My co-I has made significant progress on determining the background. I have been working on a complementary aspect of the project: computer simulations of the hot gas in the local and distant regions.

  4. What to expect from dynamical modelling of galactic haloes

    NASA Astrophysics Data System (ADS)

    Wang, Wenting; Han, Jiaxin; Cole, Shaun; Frenk, Carlos; Sawala, Till

    2017-09-01

    Many dynamical models of the Milky Way halo require assumptions that the distribution function of a tracer population should be independent of time (i.e. a steady-state distribution function) and that the underlying potential is spherical. We study the limitations of such modelling by applying a general dynamical model with minimal assumptions to a large sample of galactic haloes from cosmological N-body and hydrodynamical simulations. Using dark matter particles as dynamical tracers, we find that the systematic uncertainties in the measured mass and concentration parameters typically have an amplitude of 25-40 per cent. When stars are used as tracers, however, the systematic uncertainties can be as large as a factor of 2-3. The systematic uncertainties are not reduced by increasing the tracer sample size and vary stochastically from halo to halo. These systematic uncertainties are mostly driven by underestimated statistical noise caused by correlated phase-space structures that violate the steady-state assumption. The number of independent phase-space structures inferred from the uncertainty level sets a limiting sample size beyond which a further increase no longer significantly improves the accuracy of dynamical inferences. The systematic uncertainty level is determined by the halo merger history, the shape and environment of the halo. Our conclusions apply generally to any spherical steady-state model.

  5. Stellar Spirals in Triaxial Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Hu, Shaoran; Sijacki, Debora

    2017-03-01

    Two-armed grand-design spirals may form if the shape of its dark matter halo changes abruptly enough. The feasibility of such a mechanism is tested in realistic simulations. The interplay of such externally-driven spirals and self-induced transient spirals is then studied. Subhaloes are also found to lead to transient grand-design spiral structures when they impact the disk.

  6. The accreted stellar halo as a window on halo assembly in L* galaxies

    NASA Astrophysics Data System (ADS)

    Amorisco, Nicola C.

    2017-07-01

    Theory and observations agree that the accreted stellar haloes (ASHs) of Milky Way-like galaxies display significant scatter. I take advantage of this stochasticity to invert the link between halo assembly history (HAH) and ASH, using mock ASHs corresponding to 750 ΛCDM HAHs, sharing a final virial mass of Mh(z = 0) = 1012.25M⊙. Hosts with poor/rich ASHs assemble following orthogonal growth-patterns. Hosts with rich ASHs experience accretion events (AEs) with high virial mass ratios (HVMRs, Ms/Mh ≳ 0.1) at 0.5 ≲ zinfall ≲ 1.5, in a phase of fast growth. This maximizes the accreted stellar mass under the condition these satellites are disrupted by z = 0. At similar times, hosts with poor ASHs grow slowly through minor mergers, with only very recent HVMR AEs: this results in a globally more abundant satellite population and in distinctive surviving massive satellites (stellar mass log Ms, */M⊙ ≳ 9). Several properties of the Milky Way are in agreement with the predictions of this framework for hosts with poor, concentrated ASHs, including: (i) the recent infall of Sagittarius and Magellanic Clouds, (ii) the likely higher-than-average concentration of its dark halo and (iii) the signatures of fast chemical enrichment of a sizable fraction of its halo stellar populations.

  7. 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.

  8. The FUSE Survey of 0 VI in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Jenkins, E. B.; Moos, H. W.; Shull, J. M.

    2003-01-01

    This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

  9. The FUSE Survey of 0 VI in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Jenkins, E. B.; Moos, H. W.; Shull, J. M.

    2003-01-01

    This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

  10. 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.

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

    SciTech Connect

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

    2014-05-20

    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 {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.

  12. 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.

  13. Globular clusters, satellite galaxies and stellar haloes from early dark matter peaks

    NASA Astrophysics Data System (ADS)

    Moore, Ben; Diemand, Juerg; Madau, Piero; Zemp, Marcel; Stadel, Joachim

    2006-05-01

    The Milky Way contains several distinct old stellar components that provide a fossil record of its formation. We can understand their spatial distribution and kinematics in a hierarchical formation scenario by associating the protogalactic fragments envisaged by Searle & Zinn (1978) with the rare peaks able to cool gas in the cold dark matter density field collapsing at redshift z > 10. We use hierarchical structure formation simulations to explore the kinematics and spatial distribution of these early star-forming structures in galaxy haloes today. Most of the protogalaxies rapidly merge, their stellar contents and dark matter becoming smoothly distributed and forming the inner Galactic halo. The metal-poor globular clusters and old halo stars become tracers of this early evolutionary phase, centrally biased and naturally reproducing the observed steep fall off with radius. The most outlying peaks fall in late and survive to the present day as satellite galaxies. The observed radial velocity dispersion profile and the local radial velocity anisotropy of Milky Way halo stars are successfully reproduced in this model. If this epoch of structure formation coincides with a suppression of further cooling into lower sigma peaks then we can reproduce the rarity, kinematics and spatial distribution of satellite galaxies as suggested by Bullock, Kravtsov & Weinberg (2000). Reionization at z= 12 +/- 2 provides a natural solution to the missing satellites problem. Measuring the distribution of globular clusters and halo light on scales from galaxies to clusters could be used to constrain global versus local reionization models. If reionization occurs contemporary, our model predicts a constant frequency of blue globulars relative to the host halo mass, except for dwarf galaxies where the average relative frequencies become smaller.

  14. The ionization conditions in the Milky Way halo - Infalling gas toward the North Galactic Pole

    NASA Technical Reports Server (NTRS)

    Danly, Laura

    1992-01-01

    Observations of gas in the Milky Way halo are studied with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown that indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Understanding the nature of Milky Way halo gas plays a critical role in interpreting QSO absorption lines in the investigation of galaxies at high redshift.

  15. The ionization conditions in the Milky Way halo - Infalling gas toward the North Galactic Pole

    NASA Technical Reports Server (NTRS)

    Danly, Laura

    1992-01-01

    Observations of gas in the Milky Way halo are studied with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown that indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Understanding the nature of Milky Way halo gas plays a critical role in interpreting QSO absorption lines in the investigation of galaxies at high redshift.

  16. Galaxy Evolution: Effects of Stellar Feedback on the Halo Formation

    NASA Astrophysics Data System (ADS)

    Myers, J. M.; Hartmann, D. H.; The, L.-S.

    2003-05-01

    Recent reviews of Milky Way globular cluster formation indicate three groups associated with the formation of the bulge, disk and halo, and one group associated with accretion processes (van den Bergh 2000). Malinie et al. (1991) showed that the metallicity distribution of the halo globular clusters can be reproduced in the ELS scenario if the initial density profile is nonuniform and kinetic feedback from supernovae is taken into account. Their simulations were performed in 1D and did not include dark matter. In this study, using an N-body/SPH simulation, we attempt to explain the effect of stellar feedback on the formation and distribution of the halo globular clusters. We present 3D simulations of a rotating homogeneous collapse including dark matter, cooling gas, and stars. Three formulations of supernova feedback are considered.

  17. THE HERCULES SATELLITE: A STELLAR STREAM IN THE MILKY WAY HALO?

    SciTech Connect

    Martin, Nicolas F.; Jin, Shoko E-mail: shoko@ari.uni-heidelberg.d

    2010-10-01

    We investigate the possibility that the recently discovered Hercules Milky Way (MW) satellite is in fact a stellar stream in formation, thereby explaining its very elongated shape with an axis ratio of 3:1. Under the assumption that Hercules is a stellar stream and that its stars are flowing along the orbit of its progenitor, we find an orbit that would have recently brought the system close enough to the MW to induce its disruption and transformation from a bound dwarf galaxy into a stellar stream. The application of simple analytical techniques to the tentative radial velocity gradient observed in the satellite provides tight constraints on the tangential velocity of the system (v{sub t} = -16{sup +6}{sub -22} km s{sup -1} in the Galactic standard of rest). Combined with its large receding velocity, the determined tangential velocity yields an orbit with a small pericentric distance (R{sub peri} = 6{sup +9}{sub -2} kpc). Tidal disruption is therefore a valid scenario for explaining the extreme shape of Hercules. The increase in the mean flattening of dwarf galaxies as one considers fainter systems could therefore be the impact of a few of these satellites not being bound stellar systems dominated by dark matter but, in fact, stellar streams in formation, shedding their stars in the MW's stellar halo.

  18. Evidence for recent star formation in the galactic halo

    NASA Astrophysics Data System (ADS)

    Keenan, F. P.

    1986-09-01

    Observational data for PHL 346 obtained with the 2.5 m Issac Newton telescope on August 1985 are studied. Measured stellar Stromgren colors, hydrogen-line profiles, and helium and metal-line equivalent widths are compared with those predicted by local thermodynamic equilibrium model-atmosphere calculations. Effective temperature, surface gravity, microturbulent velocity, and helium and metal abundances for the star are derived. A mass of 13 + or - 2 solar masses, a lifetime of 11 x 10 to the 6th yr, a distance from the galactic plane of 8.7 + or - 1.5 kpc, and a velocity in the z direction of +56 + or - 10 km/s are calculated for the star. The data reveal that the star was not ejected from the galactic plane, but that it formed out of galactic fountain gas at about 6 kpc from the disc.

  19. Coupling Semi-Analytic Models and N-Body Simulations: A New Way of Making Galaxies and Stellar Halos

    NASA Astrophysics Data System (ADS)

    McCord, Krista

    Stellar halos give insight into the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites via their different stellar populations. An algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. CoSANG (Coupling Semi-Analytic/N-body Galaxies) is a new computational method that we are developing which couples pure dark matter N-body simulations with a semi-analytic galaxy formation model. At each timestep, results from the N-body simulation feed into the semi-analytic code, whose results feed back into the N-body code making the evolution of the dark matter and baryonic matter dependent on one another. CoSANG will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection. In this dissertation, I will describe the new simulation code CoSANG. The results from the extensive testing phase on CoSANG will be presented which indicate CoSANG is properly simulating feedback from galaxies within a dark matter halo. I used this validated code to analyze a CoSANG zoom simulation of a 1012M solar masses dark matter halo. Results showed a flatter inner halo near the disk and a more spherical outer halo which is expected when a galaxy exists at the center of a dark matter halo. A comparison is made with a simulation run with the same initial conditions, but with the baryonic component simulated using a hydrodynamic algorithm. The semi-analytic model predicted galaxy types better than the hydrodynamic simulation leading to the conclusion that the CoSANG halo is more accurate. I also present a dark matter direct detection analysis on the CoSANG zoom halo to measure the dark matter velocity distributions and modulation amplitudes

  20. TESTING GALAXY FORMATION MODELS WITH THE GHOSTS SURVEY: THE COLOR PROFILE OF M81's STELLAR HALO

    SciTech Connect

    Monachesi, Antonela; Bell, Eric F.; Bailin, Jeremy; Radburn-Smith, David J.; Dalcanton, Julianne J.; Vlajic, Marija; De Jong, Roelof S.; Streich, David; Holwerda, Benne W.

    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-dominated 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.

  1. Characterizing the high-velocity stars of RAVE: the discovery of a metal-rich halo star born in the Galactic disc

    NASA Astrophysics Data System (ADS)

    Hawkins, K.; Kordopatis, G.; Gilmore, G.; Masseron, T.; Wyse, R. F. G.; Ruchti, G.; Bienaymé, O.; Bland-Hawthorn, J.; Boeche, C.; Freeman, K.; Gibson, B. K.; Grebel, E. K.; Helmi, A.; Kunder, A.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W. A.; Scholz, R. D.; Seabroke, G.; Siebert, A.; Steinmetz, M.; Watson, F.; Zwitter, T.

    2015-02-01

    We aim to characterize high-velocity (HiVel) stars in the solar vicinity both chemically and kinematically using the fourth data release of the RAdial Velocity Experiment (RAVE). We used a sample of 57 HiVel stars with Galactic rest-frame velocities larger than 275 km s-1. With 6D position and velocity information, we integrated the orbits of the HiVel stars and found that, on average, they reach out to 13 kpc from the Galactic plane and have relatively eccentric orbits consistent with the Galactic halo. Using the stellar parameters and [α/Fe] estimates from RAVE, we found the metallicity distribution of the HiVel stars peak at [M/H] = -1.2 dex and is chemically consistent with the inner halo. There are a few notable exceptions that include a hypervelocity star candidate, an extremely HiVel bound halo star, and one star that is kinematically consistent with the halo but chemically consistent with the disc. High-resolution spectra were obtained for the metal-rich HiVel star candidate and the second highest velocity star in the sample. Using these high-resolution data, we report the discovery of a metal-rich halo star that has likely been dynamically ejected into the halo from the Galactic thick disc. This discovery could aid in explaining the assembly of the most metal-rich component of the Galactic halo.

  2. WEAK GALACTIC HALO-DWARF SPHEROIDAL CONNECTION FROM RR LYRAE STARS

    SciTech Connect

    Fiorentino, Giuliana; Bono, Giuseppe; Monelli, Matteo; Gallart, Carme; Martínez-Vásquez, Clara E.; Tolstoy, Eline; Salaris, Maurizio; Bernard, Edouard J.

    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 Sagittarius 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.

  3. NGC 5694: another foster son of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Mucciarelli, A.; Bellazzini, M.; Catelan, M.; Dalessandro, E.; Amigo, P.; Correnti, M.; Cortés, C.; D'Orazi, V.

    2013-11-01

    We present the results of the analysis of high-resolution spectra obtained with UVES-FLAMES at the Very Large Telescope for six red giant branch stars in the outer-halo metal-poor ([Fe/H] I = -1.98 and [Fe/H] II = -1.83) Galactic globular cluster NGC 5694, which has been suggested as a possible incomer by Lee et al. based on the anomalous chemical composition of a single cluster giant. We obtain accurate abundances for a large number of elements and we find that (a)the six target stars have the same chemical composition within the uncertainties, except for Na and Al; (b) the average cluster abundance of α elements (with the only exception of Si) is nearly solar, at odds with typical halo stars and globular clusters of similar metallicity; (c) Y, Ba, La and Eu abundances are also significantly lower than in Galactic field stars and star clusters of similar metallicity. Hence, we confirm the Lee et al. classification of NGC 5694 as a cluster of extragalactic origin. We provide the first insight on the Na-O and Mg-Al anticorrelations in this cluster: all the considered stars have very similar abundance ratios for these elements, except one that has significantly lower [Na/Fe] and [Al/Fe] ratios, suggesting that some degree of early self-enrichment has occurred also in this cluster.

  4. Interaction of Cosmic Rays with Cold Clouds in Galactic Halos

    NASA Astrophysics Data System (ADS)

    Wiener, Joshua; Peng Oh, S.; Zweibel, Ellen G.

    2017-01-01

    We investigate the effects of cosmic ray (CR) dynamics on cold, dense clouds embedded in a hot, tenuous galactic halo. If the magnetic field does not increase too much inside the cloud, the local reduction in Alfvén speed imposes a bottleneck on CRs streaming out from the star-forming galactic disk. The bottleneck flattens the upstream CR gradient in the hot gas, implying that multi-phase structure could have global effects on CR driven winds. A large CR pressure gradient can also develop on the outward-facing edge of the cloud. This pressure gradient has two independent effects. The CRs push the cloud upward, imparting it with momentum. On smaller scales, the CRs pressurize cold gas in the fronts, reducing its density, consistent with the low densities of cold gas inferred in recent COS observations of local L★ galaxies. They also heat the material at the cloud edge, broadening the cloud-halo interface and causing an observable change in interface ionic abundances. Due to the much weaker temperature dependence of cosmic ray heating relative to thermal conductive heating, CR mediated fronts have a higher ratio of low to high ions compared to conduction fronts, in better agreement with observations. We investigate these effects separately using 1D simulations and analytic techniques.

  5. Interaction of cosmic rays with cold clouds in galactic haloes

    NASA Astrophysics Data System (ADS)

    Wiener, Joshua; Oh, S. Peng; Zweibel, Ellen G.

    2017-05-01

    We investigate the effects of cosmic ray (CR) dynamics on cold, dense clouds embedded in a hot, tenuous galactic halo. If the magnetic field does not increase too much inside the cloud, the local reduction in Alfvén speed imposes a bottleneck on CRs streaming out from the star-forming galactic disc. The bottleneck flattens the upstream CR gradient in the hot gas, implying that multiphase structure could have global effects on CR-driven winds. A large CR pressure gradient can also develop on the outward-facing edge of the cloud. This pressure gradient has two independent effects. The CRs push the cloud upwards, imparting it with momentum. On smaller scales, the CRs pressurize cold gas in the fronts, reducing its density, consistent with the low densities of cold gas inferred in recent Cosmic Origins Spectrograph (COS) observations of local L* galaxies. They also heat the material at the cloud edge, broadening the cloud-halo interface and causing an observable change in interface ionic abundances. Due to the much weaker temperature dependence of CR heating relative to thermal-conductive heating, CR mediated fronts have a higher ratio of low-to-high ions compared to conduction fronts, in better agreement with observations. We investigate these effects separately using 1D simulations and analytic techniques.

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

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Jones, F. C.

    1977-01-01

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

  7. Joint constraints on the Galactic dark matter halo and GC from hypervelocity stars

    NASA Astrophysics Data System (ADS)

    Rossi, Elena M.; Marchetti, T.; Cacciato, M.; Kuiack, M.; Sari, R.

    2017-01-01

    The mass assembly history of the Milky Way can inform both theory of galaxy formation and the underlying cosmological model. Thus, observational constraints on the properties of both its baryonic and dark matter contents are sought. Here we show that hypervelocity stars (HVSs) can in principle provide such constraints. We model the observed velocity distribution of HVSs, produced by tidal break-up of stellar binaries caused by Sgr A*. Considering a Galactic Centre (GC) binary population consistent with that inferred in more observationally accessible regions, a fit to current HVS data with significance level >5% can only be obtained if the escape velocity from the GC to 50 kpc is V_G ≲ 850 km s-1, regardless of the enclosed mass distribution. When a NFW matter density profile for the dark matter halo is assumed, haloes with V_G ≲ 850 km s-1are in agreement with predictions in the ΛCDM model and that a subset of models around M200 ˜ 0.5 - 1.5 × 1012M⊙ and r_s ≲ 35 kpc can also reproduce Galactic circular velocity data. HVS data alone cannot currently exclude potentials with VG > 850 km s-1. Finally, specific constraints on the halo mass from HVS data are highly dependent on the assumed baryonic mass potentials. This first attempt to simultaneously constrain GC and dark halo properties is primarily hampered by the paucity and quality of data. It nevertheless demonstrates the potential of our method, that may be fully realised with the ESA Gaia mission.

  8. 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 (-160stellar isochrones to an object's location in a (B-I, I) color-magnitude diagram. The [Fe/H] distribution of M31 halo 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

  9. Self-Conistent Dynamical Modeling of the Milky Way Halo with Stellar Orbits

    NASA Astrophysics Data System (ADS)

    Valluri, Monica

    Despite significant advances in understanding our Galaxy in the context of LCDM, important questions remain unanswered. LCDM predicts that dark matter halos are triaxial overall, but oblate in regions where baryons dominate. However recent measurements of the shape of the Milky Way (MW) dark matter (DM) halo find it to be very triaxial with a shape and orientation that are significantly at odds with theoretical predictions. The European Space Agency s Gaia satellite will soon map the entire MW giving us six phase-space coordinates, ages and abundances for hundreds of thousands of stars. The PI and a postdoc will build a novel code (based on the Schwarzschild orbit superposition method and orbital frequency mapping), to determine the global shape of the Milky Way's dark matter halo using field stars from Gaia. Our technique will simultaneously yield the self-consistent phase-space distribution function of the stellar halo in the inner 20-30 kpc region. Detailed analysis of correlations between the chemical abundances, ages and orbits of halo stars in this distribution function will enable us to extract clues to the formation history of the MW that are encoded in orbital properties of halo stars. Our technique is unique since we will use independent sets of observational constraints, at small and large radii, to measure the radial variation in halo shape, in conjunction with a strategy tailored to modeling discrete stellar datasets. We will perform end-to-end tests of our new code with mock catalogs generated from state-of-the art cosmological simulations of MW like disk galaxies. Our team has the ideal combination of expertise in dynamical modeling, observations, simulations, and Gaia data analysis and processing necessary to achieve our goals. PI Valluri has significant prior experience with Schwarzschild modeling and the analysis of phase-space distribution functions of simulated halos, Co-I Loebman recently published the first measurement of the shape of the DM

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

    SciTech Connect

    Bubar, Eric J.; Mamajek, Eric E.; Jensen, Eric L. N.; Walter, Frederick M.

    2011-04-15

    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 similar 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.

  11. Weak Galactic halo-Fornax dSph connection from RR Lyrae stars

    NASA Astrophysics Data System (ADS)

    Fiorentino, G.; Monelli, M.; Stetson, P. B.; Bono, G.; Gallart, C.; Martínez-Vázquez, C. E.; Bernard, E. J.; Massari, D.; Braga, V. F.; Dall'Ora, M.

    2017-03-01

    Aims: For the first time accurate pulsation properties of the ancient variable stars of the Fornax dwarf spheroidal galaxy (dSph) are discussed in the broad context of galaxy formation and evolution. Methods: Homogeneous multi-band BVI optical photometry of spanning twenty years has allowed us to identify and characterize more than 1400 RR Lyrae stars (RRLs) in this galaxy. Results: Roughly 70% are new discoveries. We investigate the period-amplitude distribution and find that Fornax shows a lack of high amplitude (AV ⪆ 0.75 mag) short period fundamental-mode RRLs (P ≲ 0.48 d, HASPs). These objects occur in stellar populations more metal-rich than [Fe/H] -1.5 and they are common in the Galactic halo (hereafter Halo) and in globulars. This evidence suggests that old Fornax stars (older than 10 Gyr) are relatively metal poor. A detailed statistical analysis of the role of the present-day Fornax dSph in reproducing the Halo period distribution shows that it can only account for up to 20% of the Halo when combined with RRLs in massive dwarf galaxies (Sagittarius dSph, Large Magellanic Cloud). This finding indicates that Fornax-like systems played a smaller role than massive dwarfs in building up the Halo. Conclusions: We also discuss the occurrence of HASPs in connection with the luminosity and the early chemical composition of nearby dwarf galaxies. We find that, independently of their individual star formation histories, bright (MV ≲ -13.5 mag) galaxies have HASPs, whereas faint ones (MV ⪆ -11 mag) do not. Interestingly enough, Fornax belongs to a luminosity range (-11 < MV ≲ -13.5 mag) in which the occurrence of HASPs appears to be correlated with the early star formation and chemical enrichment of the host galaxy.

  12. Large-scale gas dynamical processes affecting the origin and evolution of gaseous galactic halos

    NASA Technical Reports Server (NTRS)

    Shapiro, Paul R.

    1991-01-01

    Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions ad superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.

  13. 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.

  14. An origin for multiphase gas in galactic winds and haloes

    NASA Astrophysics Data System (ADS)

    Thompson, Todd A.; Quataert, Eliot; Zhang, Dong; Weinberg, David H.

    2016-01-01

    The physical origin of high-velocity cool gas seen in galactic winds remains unknown. Following work by B. Wang, we argue that radiative cooling in initially hot thermally-driven outflows can produce fast neutral atomic and photoionized cool gas. The inevitability of adiabatic cooling from the flow's initial 107-108 K temperature and the shape of the cooling function for T ≲ 107 K imply that outflows with hot gas mass-loss rate relative to star formation rate of β =dot{M}_hot/dot{M}_star ≳ 0.5 cool radiatively on scales ranging from the size of the energy injection region to tens of kpc. We highlight the β and star formation rate surface density dependence of the column density, emission measure, radiative efficiency, and velocity. At rcool, the gas produces X-ray and then UV/optical line emission with a total power bounded by ˜10-2 L⋆ if the flow is powered by steady-state star formation with luminosity L⋆. The wind is thermally unstable at rcool, potentially leading to a multiphase medium. Cooled winds decelerate significantly in the extended gravitational potential of galaxies. The cool gas precipitated from hot outflows may explain its prevalence in galactic haloes. We forward a picture of winds whereby cool clouds are initially accelerated by the ram pressure of the hot flow, but are rapidly shredded by hydrodynamical instabilities, thereby increasing β, seeding radiative and thermal instability, and cool gas rebirth. If the cooled wind shocks as it sweeps up the circumgalactic medium, its cooling time is short, thus depositing cool gas far out into the halo. Finally, conduction can dominate energy transport in low-β hot winds, leading to flatter temperature profiles than otherwise expected, potentially consistent with X-ray observations of some starbursts.

  15. SMASH: Spitzer Merger History and Shape of the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn; Scowcroft, Vicky; Madore, Barry; Freedman, Wendy; Scowcroft, Victoria; Clementini, Gisella; Cioni, Maria-Rosa; van der Marel, Roeland; Udalski, Andrzej; Pietrzynski, Grzegorz; Soszynski, Igor; Nidever, David; Kallivayalil, Nitya; Besla, Gurtina; Majewski, Steve; Monson, Andy; Seibert, Mark; Smith, Horace; Preston, George; Kollmeier, Juna; Bono, Giuseppe; Marengo, Massimo; Persson, Eric; Law, David; Grillmair, Carl; Cohen, Judy; Sesar, Branimir; Price-Whelan, Adrian; Fabrizio, Michele

    2013-10-01

    The existence of a period-luminosity relation for RR Lyrae variables as measured at IRAC mid-infrared wavelengths allows Spitzer to estimate distances to individual stars with 2% errors. The SMASH program will exploit this unprecedented opportunity to precisely map structures throughout the halo of our Galaxy. SMASH will construct the first 3-D map of one of the larger satellites of the Milky Way (Sagittarius), it will determine precise distances to four more satellites (Ursa Minor, Carina, Sculptor & Bootes) and make the only measurements of stars in tidal streams accurate enough to determine their individual positions within the debris. This proposal describes some of the ground-breaking science enabled by this program, from increased accuracy in determining the orbits of satellite galaxies, to revolutionary constraints on the mass, shape and orientation of our Milky Way's dark matter halo. The foundational importance of these data sets cannot be overstated. These Milky Way structures lie far beyond the reach of any current or proposed future direct parallax measurements. Moreover, the combination of the SMASH results with proper motions from ESA's upcoming astrometric mission, Gaia, can effectively stretch Gaia's horizon for full 6D phase-space maps of our Galaxy by nearly four orders of magnitude in volume! These data and the resulting distance measurements will become Spitzer's legacy to the Galactic Astronomy community for years to come.

  16. IDENTIFYING CONTRIBUTIONS TO THE STELLAR HALO FROM ACCRETED, KICKED-OUT, AND IN SITU POPULATIONS

    SciTech Connect

    Sheffield, Allyson A.; Johnston, Kathryn V.; Majewski, Steven R. E-mail: kvj@astro.columbia.edu; and others

    2012-12-20

    We present a medium-resolution spectroscopic survey of late-type giant stars at mid-Galactic latitudes of (30 Degree-Sign < |b| < 60 Degree-Sign ), designed to probe the properties of this population to distances of {approx}9 kpc. Because M giants are generally metal-rich and we have limited contamination from thin disk stars by the latitude selection, most of the stars in the survey are expected to be members of the thick disk (([Fe/H]) {approx} -0.6) with some contribution from the metal-rich component of the nearby halo. Here we report first results for 1799 stars. The distribution of radial velocity (RV) as a function of l for these stars shows (1) the expected thick disk population and (2) local metal-rich halo stars moving at high speeds relative to the disk, which in some cases form distinct sequences in RV-l space. High-resolution echelle spectra taken for 34 of these ''RV outliers'' reveal the following patterns across the [Ti/Fe]-[Fe/H] plane: 17 of the stars have abundances reminiscent of the populations present in dwarf satellites of the Milky Way, 8 have abundances coincident with those of the Galactic disk and a more metal-rich halo, and 9 of the stars fall on the locus defined by the majority of stars in the halo. The chemical abundance trends of the RV outliers suggest that this sample consists predominantly of stars accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV outlier sample may have been formed in the inner Galaxy and subsequently kicked to higher eccentricity orbits, but the sample is not large enough to distinguish conclusively between this interpretation and the alternative that these stars represent the tail of the velocity distribution of the thick disk. Our data do not rule out the possibility that a minority of the sample could have formed from gas in situ on their current orbits. These results are consistent with scenarios where the stellar halo, at least as probed by M giants, arises from multiple

  17. 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.

  18. Probing the Canis Major stellar over-density as due to the Galactic warp

    NASA Astrophysics Data System (ADS)

    Momany, Y.; Zaggia, S. R.; Bonifacio, P.; Piotto, G.; De Angeli, F.; Bedin, L. R.; Carraro, G.

    2004-07-01

    Proper-motion, star counts and photometric catalog simulations are used to explain the detected stellar over-density in the region of Canis Major, claimed to be the core of a disrupted dwarf galaxy (CMa, Martin et al. \\cite{martin04}, MNRAS, 348, 12; Bellazzini et al. \\cite{luna04}, [arXiv:astro-ph/0311119]), as due to the Galactic warp and flare in the external disk. We compare the kinematics of CMa M-giant selected sample with surrounding Galactic disk stars in the UCAC2 catalog and find no peculiar proper motion signature: CMa stars mimic thick disk kinematics. Moreover, when taking into account the Galactic warp and flare of the disk, 2MASS star count profiles reproduce the CMa stellar over-density. This star count analysis is confirmed by direct comparison with synthetic color-magnitude diagrams simulated with the Besançon models (Robin et al. \\cite{robin03}, A&A, 409, 523) that include the warp and flare of the disk. The presented evidence casts doubt on the identification of the CMa over-density as the core of a disrupted Milky Way satellite. This however does not make clear the origin of over-densities responsible for the ring structure in the anticenter direction of the Galactic halo (Newberg et al. \\cite{newberg02}, ApJ, 569, 245; Yanny et al. 2003, ApJ, 588, 824).

  19. On the shoulders of giants: properties of the stellar halo and the Milky Way mass distribution

    SciTech Connect

    Kafle, Prajwal Raj; Sharma, Sanjib; Lewis, Geraint F.; Bland-Hawthorn, Joss

    2014-10-10

    Halo stars orbit within the potential of the Milky Way, and hence their kinematics can be used to understand the underlying mass distribution. However, the inferred mass distribution depends sensitively on assumptions made on the density and the velocity anisotropy profiles of the tracer population. Also, there is a degeneracy between the parameters of the halo and those of the disk or bulge. Most previous attempts that use halo stars have made arbitrary assumptions about these. In this paper, we decompose the Galaxy into three major components—a bulge, a Miyamoto-Nagai disk, and a Navarro-Frenk-White dark matter halo - and then model the kinematic data of the halo blue horizontal branch and K-giant stars from the Sloan Extension for Galactic Understanding and Exploration. Additionally, we use the gas terminal velocity curve and the Sgr A* proper motion. With the distance of the Sun from the center of the Galaxy R {sub ☉} = 8.5 kpc, our kinematic analysis reveals that the density of the stellar halo has a break at 17.2{sub −1.0}{sup +1.1} kpc and an exponential cutoff in the outer parts starting at 97.7{sub −15.8}{sup +15.6} kpc. Also, we find that the tracer velocity anisotropy is radially biased with β {sub s} = 0.4 ± 0.2 in the outer halo. We measure halo virial mass M {sub vir} to be 0.80{sub −0.16}{sup +0.31}×10{sup 12} M{sub ⊙}, concentration c to be 21.1{sub −8.3}{sup +14.8}, disk mass to be 0.95{sub −0.30}{sup +0.24}×10{sup 11} M{sub ⊙}, disk scale length to be 4.9{sub −0.4}{sup +0.4} kpc, and bulge mass to be 0.91{sub −0.38}{sup +0.31}×10{sup 10} M{sub ⊙}. The halo mass is found to be small, and this has important consequences. The giant stars reveal that the outermost halo stars have low velocity dispersion, but interestingly this suggests a truncation of the stellar halo density rather than a small overall mass of the Galaxy. Our estimates of local escape velocity v{sub esc}=550.9{sub −22.1}{sup +32.4} km s{sup −1} and

  20. Production and Recycling of Carbon in the Early Galactic Halo

    NASA Astrophysics Data System (ADS)

    Andersen, Johannes; Thidemann Hansen, Terese; Nordström, Birgitta

    2015-08-01

    Extremely metal-poor (EMP) stars - [Fe/H] below ~ -3 - are fossil records of the conditions in the early halo. High-resolution 8m-class spectroscopy has shown that the detailed abundance pattern of EMP giant stars is surprisingly uniform and essentially Solar (e.g. Bonifacio+ 2012), apart from the usual α-enhancement in the halo. In the simplest picture, iron is a proxy for both overall metallicity and time, so the EMP stars should form before the oldest and most metal-poor Galactic globular clusters, notably at the lowest metallicities ([Fe/H] ≲ -3.5).It is thus striking that 20-40% of the EMP giants are strongly enhanced in carbon - the CEMP stars (Lucatello+ 2006). This is conventionally ascribed to mass transfer from a former AGB binary companion, and from a limited compilation of data, Lucatello+ (2005) concluded that most or all CEMP stars are indeed binaries, similar to the classical Ba and CH stars (e.g. Jorissen+ 1998). However, most of the sample was of the inner-halo CEMP-s variety (C and s-process elements both enhanced), while CEMP-no stars dominate the outer halo (Carollo+ 2014). Our precise radial velocity monitoring for CEMP stars over 8 years shed light on this issue.Our data suggest a normal binary frequency for the CEMP-no stars; i.e. the C was not produced in a binary companion, but in sites at interstellar distances, e.g. ‘faint’ SNe, and imprinted on the natal clouds of the low-mass stars we observe. This has immediate implications for the formation of dust in primitive, high-redshift galaxies (Watson+ 2015) and the origin of C-enhanced DLAs (Cooke+ 2011, 2012). The CEMP-s binary orbits are also revealing, with periods up to several decades and generally low amplitudes and eccentricities, suggesting that EMP AGB stars have very large radii, facilitating extensive mass loss. More work on faint SNe and EMP AGB envelopes is needed!

  1. Coupling Semi-Analytic Models and N-Body Simulations: A New Way of Making Galaxies and Stellar Halos

    NASA Astrophysics Data System (ADS)

    McCord, Krista M.; Bailin, Jeremy; Croton, Darren; Valluri, Monica

    2015-01-01

    Stellar halos give insight to the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites by looking at the different stellar populations. An algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. Currently being developed is CoSANG (Coupled Semi-Analytic/N-body Galaxies), a new computational method that will couple pure dark matter N-body simulations with a semi-analytic model. At each timestep, results from the N-body simulation will feed into the semi-analytic code, whose results will feed back into the N-body code making the evolution of the dark matter and baryonic matter dependent on one another. CoSANG will require much less computing power than hydrodynamical simulations, and will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection.

  2. Formation of a Giant Galactic Gaseous Halo: Metal-Absorption Lines and High-Velocity Clouds

    NASA Astrophysics Data System (ADS)

    Li, Fan

    1992-04-01

    A Galactic gaseous halo formed through the interstellar disk-halo connection is simulated by means of a two-dimensional axisymmetric hydrodynamic code based upon the chimney model of the interstellar medium, a new version of the galactic fountain. Galactic rotation, heating processes by diffuse UV flux, and radiative cooling processes are taken into account. The resulting gaseous halo can be divided into three categories, i.e., wind-type halo, bound-type halo, and cooled-type halo. In this way, we try to reproduce the column densities of C IV, N V, O VI, and Si IV in the observed absorption lines of halo stars. Assuming that the radiatively cooled halo gas condenses into clouds due to thermal instabilities, we can calculate their distribution and ballistic motions in the Galactic gravitational field. These correspond to the high- and intermediate-velocity clouds observed at high Galactic latitudes. We find that a cooled-type halo with a gas temperature between 5 X 10^5 and 10^6 K and a density between 10^-3 and 10^-2 cm^-3 at the disk-halo interface can reproduce the observational facts about our Galaxy. Supposing that the metal-absorption-line systems of QSOs arise from the halos of intervening galaxies formed by similar processes, we calculate features of the Ca II, Mg II, C IV, and Si IV absorption lines in various stages of galactic evolution. We conclude that C IV systems which are greater than 50 kpc in size correspond to the wind-type halo. On the other hand, Mg II and Ca II systems can only be detected in a very restricted region ( Metaxa, SMALL FAINT CLUSTERS IN THE LMC This is a short review of the main results of my Ph.D. thesis concerning some important problems on the dynamical properties of the LMC star clusters. The topic of this thesis was to find and study the dynamical paramters (tidal radius r_t core radius r_c concentration parameters log (r_t/r_c), and total mass M) for a large sample of small LMC clusters and to define their location in the

  3. F Turnoff Distribution in the Galactic Halo Using Globular Clusters as Proxies

    NASA Astrophysics Data System (ADS)

    Newby, Matthew; Newberg, H. J.; Simones, J.; Monaco, M.; Cole, N.

    2012-01-01

    F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful, luminous, and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey (SDSS). We describe the absolute magnitude distribution of color-selected F turnoff stars, as measured from SDSS data, for eleven globular clusters in the Milky Way halo. We find that the absolute magnitude distribution of turnoff stars is intrinsically the same for all clusters studied, and is well fit by two half Gaussian functions, centered at μ = 4.18, with a bright-side σ = 0.36, and with a faint-side σ = 0.76. However, the color errors and detection efficiencies cause the observed σ of the faint-side Gaussian to change with magnitude due to contamination from redder main sequence stars (40% at 21st magnitude). We present a function that will correct for this magnitude-dependent change in selected stellar populations, when calculating stellar density from color-selected turnoff stars. We also present a consistent set of distances, ages and metallicities for eleven clusters in the SDSS Data Release 7. We calculate a linear correction function to Padova isochrones so that they are consistent with SDSS globular cluster data from previous papers. We show that our cluster population falls along the theoretical Age-Metallicity Relationship (AMR), and further find that isochrones for stellar populations on the AMR have very similar turnoffs; increasing metallicity and decreasing age conspire to produce similar turnoff magnitudes and colors for all old clusters that lie on the AMR. This research was supported by NSF grant AST 10-09670 and the NASA/NY Space Grant.

  4. Transonic galactic outflows in a dark matter halo with a central black hole

    NASA Astrophysics Data System (ADS)

    Igarashi, Asuka; Mori, Masao; Nitta, Shin-Ya

    We study fundamental properties of transonic galactic outflows in the gravitational potential of a cold dark matter halo (DMH) with a central super-massive black hole (SMBH) assuming an isothermal, steady and spherically symmetric state. Transonic solutions of galactic outflows are classified according to their topological features. As result, we find two types of transonic solutions distinguished by a magnitude relationship between the gravity of DMH and that of SMBH. The loci of transonic points for two types are different; one transonic point is formed at a central region (< 0.01kpc) and another is at a very distant region (> 100kpc). Also, mass fluxes and outflow velocities are different for two solutions. Thus, these solutions may differently influence the evolution of galaxies and the release of metals into the intergalactic space. Furthermore, we apply our model to the Sombrero galaxy. In this galaxy, the wide-spread hot gas is detected as the trace of galactic outflows while the star-formation rate is low, and the observed gas density distribution is similar to the hydrostatic state (Li et al. 2011). To solve this discrepancy, we propose a solution that this galaxy has a slowly accelerating outflow; the transonic point forms in a very distant region (~ 120 kpc) and the wide subsonic region spreads across the stellar distribution. Thus, the gas density distribution in the observed region is similar to the hydrostatic state. Such slowly accelerating outflows are different from high-velocity outflows conventionally studied (Igarashi et al. 2014). However, this isothermal model requires an unrealistically large mass flux. Then, we apply the polytropic model to this galaxy incorporating mass flux supplied by stellar components. We find that it can reproduce the observed gas density and the temperature distributions with the realistic mass flux. Thus, our polytropic model successfully demonstrates the existence of the slowly accelerating outflow in the Sombrero

  5. Rotational signature of the Milky Way stellar halo

    NASA Astrophysics Data System (ADS)

    Fermani, Francesco; Schönrich, Ralph

    2013-07-01

    We measure the rotation of the Milky Way stellar halo on two samples of blue horizontal branch (BHB) field halo stars from the Sloan Digital Sky Survey (SDSS) with four different methods. The two samples comprise 1582 and 2563 stars, respectively, and reach out to ˜50 kpc in galactocentric distance. Two of the methods to measure rotation rely exclusively on line-of-sight (l.o.s.) velocities, namely the popular double power-law model and a direct estimate of the de-projected l.o.s. velocity. The other two techniques use the full 3D motions: the radial velocity based rotation estimator of Schönrich et al. and a simple 3D azimuthal velocity mean. In this context we (a) critique the popular model and (b) assess the reliability of the estimators. All four methods agree on a weakly prograde or non-rotating halo. Further, we observe no duality in the rotation of sub-samples with different metallicities or at different radii. We trace the rotation gradient across metallicity measured by Deason et al. on a similar sample of BHB stars back to the inclusion of regions in the apparent magnitude-surface gravity plane known to be contaminated. In the spectroscopically selected sample of Xue et al., we flag ˜500 hot metal-poor stars for their peculiar kinematics w.r.t. to both their cooler metal-poor counterparts and the metal-rich stars in the same sample. They show a seemingly retrograde behaviour in l.o.s. velocities, which is not confirmed by the 3D estimators. Their anomalous vertical motion hints at either a pipeline problem or a stream-like component rather than a smooth retrograde population.

  6. Stellar Mass Versus Stellar Velocity Dispersion: Which is Better for Linking Galaxies to Their Dark Matter Halos?

    NASA Astrophysics Data System (ADS)

    Li, Cheng; Wang, Lixin; Jing, Y. P.

    2013-01-01

    It was recently suggested that compared to its stellar mass (M *), the central stellar velocity dispersion (σ*) of a galaxy might be a better indicator for its host dark matter halo mass. Here we test this hypothesis by estimating the dark matter halo mass for central galaxies in groups as a function of M * and σ*. For this we have estimated the redshift-space cross-correlation function (CCF) between the central galaxies at given M * and σ* and a reference galaxy sample, from which we determine both the projected CCF, wp (rp ), and the velocity dispersion profile. A halo mass is then obtained from the average velocity dispersion within the virial radius. At fixed M *, we find very weak or no correlation between halo mass and σ*. In contrast, strong mass dependence is clearly seen even when σ* is limited to a narrow range. Our results thus firmly demonstrate that the stellar mass of central galaxies is still a good (if not the best) indicator for dark matter halo mass, better than the stellar velocity dispersion. The dependence of galaxy clustering on σ* at fixed M *, as recently discovered by Wake et al., may be attributed to satellite galaxies, for which the tidal stripping occurring within halos has stronger effect on stellar mass than on central stellar velocity dispersion.

  7. Mapping stellar content to dark matter haloes - II. Halo mass is the main driver of galaxy quenching

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2016-04-01

    We develop a simple yet comprehensive method to distinguish the underlying drivers of galaxy quenching, using the clustering and galaxy-galaxy lensing of red and blue galaxies in Sloan Digital Sky Survey. Building on the iHOD framework developed by Zu & Mandelbaum, we consider two quenching scenarios: (1) a `halo' quenching model in which halo mass is the sole driver for turning off star formation in both centrals and satellites; and (2) a `hybrid' quenching model in which the quenched fraction of galaxies depends on their stellar mass, while the satellite quenching has an extra dependence on halo mass. The two best-fitting models describe the red galaxy clustering and lensing equally well, but halo quenching provides significantly better fits to the blue galaxies above 1011 h-2 M⊙. The halo quenching model also correctly predicts the average halo mass of the red and blue centrals, showing excellent agreement with the direct weak lensing measurements of locally brightest galaxies. Models in which quenching is not tied to halo mass, including an age-matching model in which galaxy colour depends on halo age at fixed M*, fail to reproduce the observed halo mass for massive blue centrals. We find similar critical halo masses responsible for the quenching of centrals and satellites (˜1.5 × 1012 h-1 M⊙), hinting at a uniform quenching mechanism for both, e.g. the virial shock heating of infalling gas. The success of the iHOD halo quenching model provides strong evidence that the physical mechanism that quenches star formation in galaxies is tied principally to the masses of their dark matter haloes rather than the properties of their stellar components.

  8. HaloSat: A CubeSat to Map the Distribution of Baryonic Matter in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Miles, Drew M.

    2016-04-01

    Approximately half of predicted baryonic matter in the Milky Way remains unidentified. One possible explanation for the location of this missing matter is in an extended Galactic halo. HaloSat is a CubeSat that aims to constrain the mass and distribution of the halo’s baryonic matter by obtaining an all-sky map of O VII and O VIII emission in the hot gas associated with the halo of the Milky Way. HaloSat offers an improvement in the quality of measurements of oxygen line emission over existing X-ray observatories and an observation plan dedicated to mapping the hot gas in the Galactic halo. In addition to the missing baryon problem, HaloSat will assign a portion of its observations to the solar wind charge exchange (SWCX) in order to calibrate models of SCWX emission. We present here the current status of HaloSat and the progression of instrument development in anticipation of a 2018 launch.

  9. THE STELLAR-TO-HALO MASS RELATION FOR LOCAL GROUP GALAXIES

    SciTech Connect

    Brook, C. B.; Cintio, A. Di; Knebe, A.; Yepes, G.; Gottlöber, S.; Hoffman, Y.; Garrison-Kimmel, S.

    2014-03-20

    We contend that a single power-law halo mass distribution is appropriate for direct matching to the stellar masses of observed Local Group dwarf galaxies, allowing the determination of the slope of the stellar mass-halo mass relation for low-mass galaxies. Errors in halo masses are well defined as the Poisson noise of simulated Local Group realizations, which we determine using local volume simulations. For the stellar mass range 10{sup 7} M {sub ☉}stellar mass-halo mass relation follows a power law with slope of 3.1, significantly steeper than most values in the literature. This steep relation between stellar and halo masses would indicate that Local Group dwarf galaxies are hosted by dark matter halos with a small range of mass. Our methodology is robust down to the stellar mass to which the census of observed Local Group galaxies is complete, but the significant uncertainty in the currently measured slope of the stellar-to-halo mass relation will decrease dramatically if the Local Group completeness limit was 10{sup 6.5} M {sub ☉} or below, highlighting the importance of pushing such limit to lower masses and larger volumes.

  10. Neutron-Capture Elements in Low Metallicity Stars within the Inner Galactic Halo

    NASA Astrophysics Data System (ADS)

    Jumper, Kenneth A.; Burris, Debra L.

    2017-01-01

    The inner galactic halo is home to some of the oldest and low metallicity stars known. These stars are local enough to observe heavy element synthesis in the oldest stars in our galaxy. The purpose of this research is to analyze the distributions of neutron capture elements in low metallicity stars to help us understand the nature of first stars, which are responsible for the chemical enrichment of our galaxy, and consequently get man closer to an answer to some of the most fundamental questions about the universe.. The researchers will analyze and measure the stellar abundances of metal poor stars using MOOG’s spectral synthesis. Heavy element formation is connected to stellar evolution, thus by observing the chronometric ages of the distributions of Thorium/Europium, one can determine the age of the oldest stars. Analyzing the distribution of Uranium and Thorium as chronometers can set a lower limit on the age of the Universe. The chemical composition in our oldest observable stars resemble that of the earliest stars. This demonstrates that these stars were not synthesized internally but a result of previous deaths of stars generations before. This in turn provides useful information about the first star’s formation, evolution and nucleosynthesis of stars, and the arrangement of the structure of the early Universe. The most r-process rich halo stars abundances are consistent with a scaled solar system r-process abundance distribution. Also, there is symmetry in the rare earth elements in the stars within the Galactic halo. However the lighter n-capture abundances don’t conform to the solar pattern. This suggests the possibility of multiple synthesis mechanisms for the n capture elements. The combinations could include the main r-process, V-P process (core collapsed super- novae), charged particle reactions with Beta delayed fission, and the weak r-process. The weak r-process is sometimes called the incomplete r-process does not have enough neutrons to

  11. Planetary geology, stellar evolution and galactic cosmology

    NASA Technical Reports Server (NTRS)

    1972-01-01

    Field studies of selected basalt flows in the Snake River Plain, Idaho, were made for comparative lunar and Mars geological investigations. Studies of basalt lava tubes were also initiated in Washington, Oregon, Hawaii, and northern California. The main effort in the stellar evolution research is toward the development of a computer code to calculate hydrodynamic flow coupled with radiative energy transport. Estimates of the rotation effects on a collapsing cloud indicate that the total angular momentum is the critical parameter. The study of Paschen and Balmer alpha lines of positronium atoms in the center of a galaxy is mentioned.

  12. Analytical galactic models with mild stellar cusps

    NASA Astrophysics Data System (ADS)

    Rindler-Daller, T.

    2009-06-01

    In the past two decades, it has been established by high-resolution observations of early-type galaxies that their nuclear surface brightness and corresponding stellar mass densities are characterized by cusps. In this paper, we present a new spherical analytical model family describing mild cuspy centres. We study isotropic and anisotropic models of Osipkov-Merritt type. It is shown that the associated distribution functions and intrinsic velocity dispersions can be represented analytically in a unified way in terms of hypergeometric series, allowing thus a straightforward comparison of these important global quantities for galaxies having underlying mass densities which may differ significantly in their degree of central cuspiness or radial falloff.

  13. 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

  14. Architecture of the Andromeda galaxy: a quantitative analysis of clustering in the inner stellar halo

    NASA Astrophysics Data System (ADS)

    Kafle, P. R.; Sharma, S.; Robotham, A. S. G.; Lewis, G. F.; Driver, S. P.

    2017-02-01

    We present a quantitative measurement of the amount of clustering present in the inner ˜30 kpc of the stellar halo of the Andromeda galaxy (M31). For this we analyse the angular positions and radial velocities of the carefully selected planetary nebulae in the M31 stellar halo. We study the cumulative distribution of pairwise distances in angular position and line-of-sight velocity space, and find that the M31 stellar halo contains substantially more stars in the form of close pairs as compared to that of a featureless smooth halo. In comparison to a smoothed/scrambled distribution, we estimate that the clustering excess in the M31 inner halo is roughly 40 per cent at maximum and on average ˜20 per cent. Importantly, comparing against the 11 stellar halo models of Bullock & Johnston, which were simulated within the context of the ΛCDM (Λ cold dark matter) cosmological paradigm, we find that the amount of substructures in the M31 stellar halo closely resembles that of a typical ΛCDM halo.

  15. The large-scale structure of the halo of the Andromeda galaxy. I. Global stellar density, morphology and metallicity properties

    SciTech Connect

    Ibata, Rodrigo A.; Martin, Nicolas F.; Lewis, Geraint F.; McConnachie, Alan W.; Irwin, Michael J.; Ferguson, Annette M. N.; Bernard, Edouard J.; Peñarrubia, Jorge; Babul, Arif; Navarro, Julio; Chapman, Scott C.; Collins, Michelle; Fardal, Mark; Mackey, A. D.; Rich, R. Michael; Tanvir, Nial; Widrow, Lawrence

    2014-01-10

    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 with 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 importance as

  16. The Large-scale Structure of the Halo of the Andromeda Galaxy. I. Global Stellar Density, Morphology and Metallicity Properties

    NASA Astrophysics Data System (ADS)

    Ibata, Rodrigo A.; Lewis, Geraint F.; McConnachie, Alan W.; Martin, Nicolas F.; Irwin, Michael J.; Ferguson, Annette M. N.; Babul, Arif; Bernard, Edouard J.; Chapman, Scott C.; Collins, Michelle; Fardal, Mark; Mackey, A. D.; Navarro, Julio; Peñarrubia, Jorge; Rich, R. Michael; Tanvir, Nial; Widrow, Lawrence

    2014-01-01

    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}] \\lt -1.7}) are distributed approximately spherically (slightly prolate with ellipticity c/a = 1.09 ± 0.03), with only a relatively small fraction residing in discernible stream-like structures (f 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 stream becoming as high as 86% for [{Fe/H] \\gt -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 × 1010 M ⊙, while that of the smooth component is ~3 × 109 M ⊙. Extrapolating into the inner galaxy, the total stellar mass of the smooth halo is plausibly ~8 × 109 M ⊙. We detect a substantial metallicity gradient, which declines from lang[Fe/H]rang = -0.7 at R = 30 kpc to lang[Fe/H]rang = -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 importance as they provide a prototype template that

  17. Global properties of M31's stellar halo from the splash survey. II. Metallicity profile

    SciTech Connect

    Gilbert, Karoline M.; Kalirai, Jason S.; Guhathakurta, Puragra; Geha, Marla C.; Tollerud, Erik J.; Kirby, Evan N.; Bullock, James S.; Tanaka, Mikito; Chiba, Masashi

    2014-12-01

    We present the metallicity distribution of red giant branch (RGB) stars in M31's stellar halo, derived from photometric metallicity estimates for over 1500 spectroscopically confirmed RGB halo stars. The stellar sample comes from 38 halo fields observed with the Keck/DEIMOS spectrograph, ranging from 9 to 175 kpc in projected distance from M31's center, and includes 52 confirmed M31 halo stars beyond 100 kpc. While a wide range of metallicities is seen throughout the halo, the metal-rich peak of the metallicity distribution function becomes significantly less prominent with increasing radius. The metallicity profile of M31's stellar halo shows a continuous gradient from 9 to ∼100 kpc, with a magnitude of ∼ – 0.01 dex kpc{sup –1}. The stellar velocity distributions in each field are used to identify stars that are likely associated with tidal debris features. The removal of tidal debris features does not significantly alter the metallicity gradient in M31's halo: a gradient is maintained in fields spanning 10-90 kpc. We analyze the halo metallicity profile, as well as the relative metallicities of stars associated with tidal debris features and the underlying halo population, in the context of current simulations of stellar halo formation. We argue that the large-scale gradient in M31's halo implies M31 accreted at least one relatively massive progenitor in the past, while the field to field variation seen in the metallicity profile indicates that multiple smaller progenitors are likely to have contributed substantially to M31's outer halo.

  18. PRIMUS: One- and Two-halo Galactic Conformity at 0.2 < z < 1

    NASA Astrophysics Data System (ADS)

    Berti, Angela M.; Coil, Alison L.; Behroozi, Peter S.; Eisenstein, Daniel J.; Bray, Aaron D.; Cool, Richard J.; Moustakas, John

    2017-01-01

    We test for galactic conformity at 0.2< z< 1.0 to a projected distance of 5 Mpc using spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS). Our sample consists of ∼60,000 galaxies in five separate fields covering a total of ∼5.5 square degrees, which allows us to account for cosmic variance. We identify star-forming and quiescent “isolated primary” (i.e., central) galaxies using isolation criteria and cuts in specific star formation rate. We match the redshift and stellar mass distributions of these samples to control for correlations between quiescent fraction and redshift and stellar mass. We detect a significant (>3σ) one-halo conformity signal, or an excess of star-forming neighbors around star-forming central galaxies, of ∼5% on scales of 0–1 Mpc and a 2.5σ two-halo signal of ∼1% on scales of 1–3 Mpc. These signals are weaker than those detected in the Sloan Digital Sky Survey and are consistent with galactic conformity being the result of large-scale tidal fields and reflecting assembly bias. We also measure the star-forming fraction of central galaxies at fixed stellar mass as a function of large-scale environment and find that central galaxies are more likely to be quenched in overdense environments, independent of stellar mass. However, we find that environment does not affect the star formation efficiency of central galaxies, as long as they are forming stars. We test for redshift and stellar mass dependence of the conformity signal within our sample and show that large volumes and multiple fields are required at intermediate redshift to adequately account for cosmic variance.

  19. Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations with explicit stellar feedback

    NASA Astrophysics Data System (ADS)

    Muratov, Alexander L.; Kereš, Dušan; Faucher-Giguère, Claude-André; Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

    2015-12-01

    We present an analysis of the galaxy-scale gaseous outflows from the Feedback in Realistic Environments (FIRE) simulations. This suite of hydrodynamic cosmological zoom simulations resolves formation of star-forming giant molecular clouds to z = 0, and features an explicit stellar feedback model on small scales. Our simulations reveal that high-redshift galaxies undergo bursts of star formation followed by powerful gusts of galactic outflows that eject much of the interstellar medium and temporarily suppress star formation. At low redshift, however, sufficiently massive galaxies corresponding to L* progenitors develop stable discs and switch into a continuous and quiescent mode of star formation that does not drive outflows far into the halo. Mass-loading factors for winds in L* progenitors are η ≈ 10 at high redshift, but decrease to η ≪ 1 at low redshift. Although lower values of η are expected as haloes grow in mass over time, we show that the strong suppression of outflows with decreasing redshift cannot be explained by mass evolution alone. Circumgalactic outflow velocities are variable and broadly distributed, but typically range between one and three times the circular velocity of the halo. Much of the ejected material builds a reservoir of enriched gas within the circumgalactic medium, some of which could be later recycled to fuel further star formation. However, a fraction of the gas that leaves the virial radius through galactic winds is never regained, causing most haloes with mass Mh ≤ 1012 M⊙ to be deficient in baryons compared to the cosmic mean by z = 0.

  20. The cold veil of the Milky Way stellar halo

    NASA Astrophysics Data System (ADS)

    Deason, A. J.; Belokurov, V.; Evans, N. W.; Koposov, S. E.; Cooke, R. J.; Peñarrubia, J.; Laporte, C. F. P.; Fellhauer, M.; Walker, M. G.; Olszewski, E. W.

    2012-10-01

    We build a sample of distant (D > 80 kpc) stellar halo stars with measured radial velocities. Faint (20 < g < 22) candidate blue horizontal branch (BHB) stars were selected using the deep, but wide, multi-epoch Sloan Digital Sky Survey photometry. Follow-up spectroscopy for these A-type stars was performed using the Very Large Telescope (VLT) FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument. We classify stars according to their Balmer line profiles, and find that seven are bona fide BHB stars and 31 are blue stragglers (BS). Owing to the magnitude range of our sample, even the intrinsically fainter BS stars can reach out to D ˜ 90 kpc. We complement this sample of A-type stars with intrinsically brighter, intermediate-age, asymptotic giant branch stars. A set of four distant cool carbon stars is compiled from the literature and we perform spectroscopic follow-up on a further four N-type carbon stars using the William Herschel Telescope (WHT) Intermediate dispersion Spectrograph and Imaging System (ISIS) instrument. Altogether, this provides us with the largest sample to date of individual star tracers out to r ˜ 150 kpc. We find that the radial velocity dispersion of these tracers falls rapidly at large distances and is surprisingly cold (σr ≈ 50-60 km s-1) between 100 and 150 kpc. Relating the measured radial velocities to the mass of the Milky Way requires knowledge of the (unknown) tracer density profile and anisotropy at these distances. Nonetheless, by assuming the stellar halo stars between 50 and 150 kpc have a moderate density fall-off (with power-law slope α < 5) and are on radial orbits (σt2/σr2<1), we infer that the mass within 150 kpc is less than 1012 M⊙ and suggest it probably lies in the range (5-10) × 1011 M⊙. We discuss the implications of such a low mass for the Milky Way. Based on observations made with European Southern Observatory Telescopes at the La Silla Paranal Observatory under programme ID 085.B-0567(A) and

  1. Contributions to the accreted stellar halo: an atlas of stellar deposition

    NASA Astrophysics Data System (ADS)

    Amorisco, N. C.

    2017-01-01

    The accreted component of stellar haloes is composed of the contributions of several satellites, falling on to their host with their different masses, at different times, on different orbits. This work uses a suite of idealized, collisionless N-body simulations of minor mergers and a particle-tagging technique to understand how these different ingredients shape each contribution to the accreted halo, in both density and kinematics. I find that more massive satellites deposit their stars deeper into the gravitational potential of the host, with a clear segregation enforced by dynamical friction. Earlier accretion events contribute more to the inner regions of the halo; more concentrated subhaloes sink deeper through increased dynamical friction. The orbital circularity of the progenitor at infall is only important for low-mass satellites: dynamical friction efficiently radializes the most massive minor mergers erasing the imprint of the infall orbit for satellite-to-host virial mass ratios ≳ 1/20. The kinematics of the stars contributed by each satellite is also ordered with satellite mass: low-mass satellites contribute fast-moving populations, in both ordered rotation and radial velocity dispersion. In turn, contributions by massive satellites have lower velocity dispersion and lose their angular momentum to dynamical friction, resulting in a strong radial anisotropy.

  2. Blue horizontal branch field stars in the galactic halo - Observations versus kinematic models

    NASA Astrophysics Data System (ADS)

    Sommer-Larsen, Jesper; Christensen, Per Rex

    1989-07-01

    A sample of 185 blue horizontal branch field (BHBF) stars situated in four fields in the galactic halo at galactocentric distances r of less than 40 kpc has been analyzed. The BHBF stars are found to constitute a well mixed system. The Sommer-Larsen (1986, 1987) model is shown to provide a better fit to the kinematical data in all four fields than either the White (1985, 1988) or Ratnatunga and Freeman (1985, 1989) models. A formation scenario for the galactic halo which includes the effects of gas dynamical processes is proposed to account for the feature of the Sommer-Larsen model that the velocity distribution of halo stars is radially anisotropic in the inner halo, but tangentially anisotropic in the outer parts of the halo.

  3. Are ancient dwarf satellites the building blocks of the Galactic halo?

    NASA Astrophysics Data System (ADS)

    Spitoni, E.; Vincenzo, F.; Matteucci, F.; Romano, D.

    2016-05-01

    According to the current cosmological cold dark matter paradigm, the Galactic halo could have been the result of the assemblage of smaller structures. Here we explore the hypothesis that the classical and ultra-faint dwarf spheroidal satellites of the Milky Way have been the building blocks of the Galactic halo by comparing their [α/Fe] and [Ba/Fe] versus [Fe/H] patterns with the ones observed in Galactic halo stars. The α elements deviate substantially from the observed abundances in the Galactic halo stars for [Fe/H] values larger than -2 dex, while they overlap for lower metallicities. On the other hand, for the [Ba/Fe] ratio, the discrepancy is extended at all [Fe/H] values, suggesting that the majority of stars in the halo are likely to have been formed in situ. Therefore, we suggest that [Ba/Fe] ratios are a better diagnostic than [α/Fe] ratios. Moreover, for the first time we consider the effects of an enriched infall of gas with the same chemical abundances as the matter ejected and/or stripped from dwarf satellites of the Milky Way on the chemical evolution of the Galactic halo. We find that the resulting chemical abundances of the halo stars depend on the assumed infall time-scale, and the presence of a threshold in the gas for star formation. In particular, in models with an infall time-scale for the halo around 0.8 Gyr coupled with a threshold in the surface gas density for the star formation (4 M⊙ pc-2), and the enriched infall from dwarf spheroidal satellites, the first halo stars formed show [Fe/H]>-2.4 dex. In this case, to explain [α/Fe] data for stars with [Fe/H]<-2.4 dex, we need stars formed in dSph systems.

  4. Runaway Stars in the Galactic Halo: Their Origin and Kinematics

    NASA Astrophysics Data System (ADS)

    Duarte de Vasconcelos Silva, Manuel

    2012-03-01

    Star formation in the Milky Way is confined to star-forming regions (OB associ- ation, HII regions, and open clusters) in the Galactic plane. It is usually assumed that these regions are found preferably along spiral arms, as is observed in other spiral galaxies. However, young early-type stars are often found at high Galactic latitudes, far away from their birthplaces in the Galactic disc. These stars are called runaway stars, and it is believed that they were ejected from their birth- places early in their lifetimes by one of two mechanisms: ejection from a binary system following the destruction of the massive companion in a supernova type II event (the binary ejection mechanism), or ejection from a dense cluster following a close gravitational encounter between two close binaries (the dynamical ejection mechanism). The aims of our study were: to improve the current understanding of the nature of high Galactic latitude runaway stars, in particular by investigating whether the theoretical ejection mechanisms could explain the more extreme cases; to show the feasibility of using high Galactic latitude stars as tracers of the spiral arms. The main technique used in this investigation was the tracing of stellar orbits back in time, given their present positions and velocities in 3D space. This technique allowed the determination of the ejection velocities, flight times and birthplaces of a sample of runaway stars. In order to obtain reasonable velocity estimates several recent catalogues of proper motion data were used. We found that the evolutionary ages of the vast majority of runaway stars is consistent with the disc ejection scenario. However, we identified three outliers which would need flight times much larger then their estimated ages in order to reach their present positions in the sky. Moreover, the ejection velocity distribution appears to be bimodal, showing evidence for two populations of runaway stars: a "low" velocity population (89 per cent of the

  5. A Galactic-Scale Origin for Stellar Clustering

    NASA Astrophysics Data System (ADS)

    Kruijssen, J. M. Diederik

    We recently presented a model for the cluster formation efficiency (CFE), i.e. the fraction of star formation occurring in bound stellar clusters. It utilizes the idea that the formation of stars and stellar clusters occurs across a continuous spectrum of ISM densities. Bound stellar clusters naturally arise from the high-density end of this density spectrum. Due to short free-fall times, these high-density regions can achieve high star formation efficiencies (SFEs) and can be unaffected by gas expulsion. Lower-density regions remain gas-rich and substructured, and are unbound upon gas expulsion. The model enables the CFE to be calculated using galactic-scale observables. I present a brief summary of the model physics, assumptions and caveats, and show that it agrees well with observations. Fortran and IDL routines for calculating the CFE are publicly available at http://www.mpa-garching.mpg.de/cfe.

  6. CALET's sensitivity to Dark Matter annihilation in the galactic halo

    SciTech Connect

    Motz, H.; Asaoka, Y.; Torii, S.; Bhattacharyya, S. E-mail: yoichi.asaoka@aoni.waseda.jp E-mail: saptashwab@ruri.waseda.jp

    2015-12-01

    CALET (Calorimetric Electron Telescope), installed on the ISS in August 2015, directly measures the electron+positron cosmic rays flux up to 20 TeV. With its proton rejection capability of 1 : 10{sup 5} and an aperture of 1200 cm{sup 2·} sr, it will provide good statistics even well above one TeV, while also featuring an energy resolution of 2%, which allows it to detect fine structures in the spectrum. Such structures may originate from Dark Matter annihilation or decay, making indirect Dark Matter search one of CALET's main science objectives among others such as identification of signatures from nearby supernova remnants, study of the heavy nuclei spectra and gamma astronomy. The latest results from AMS-02 on positron fraction and total electron+positron flux can be fitted with a parametrization including a single pulsar as an extra power law source with exponential cut-off, which emits an equal amount of electrons and positrons. This single pulsar scenario for the positron excess is extrapolated into the TeV region and the expected CALET data for this case are simulated. Based on this prediction for CALET data, the sensitivity of CALET to Dark Matter annihilation in the galactic halo has been calculated. It is shown that CALET could significantly improve the limits compared to current data, especially for those Dark Matter candidates that feature a large fraction of annihilation directly into e{sup +} + e{sup −}, such as the LKP (Lightest Kaluza-Klein particle)

  7. HUBBLE'S SEARCH FOR FAINT FIELD STARS IN GALACTIC HALO

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Left A NASA Hubble Space Telescope image of a randomly selected area of sky taken to search for faint red stars that might constitute dark matter in our Milky Way Galaxy. (Dark matter is material of an unknown type that makes up most of the mass of our galaxy). If the dark matter in our Galaxy was made of faint red stars -- as many scientists have previously conjectured -- then about 38 such stars should have been visible in this HST image. The simulated stars (diamond-shaped symbols), based on theoretical calculations, illustrate what scientists would have seen if the dark matter were locked-up in faint red stars. These surprising results rule out dim stars as an explanation for dark matter in our Galaxy. Right The unmodified HST image shows the region is actually so devoid of stars that far more distant background galaxies can easily be seen. The field is in the constellation Eridanus, far outside the plane of our Milky Way Galaxy. This region was chosen to highlight stars in the galactic halo, where dark matter exists, and to avoid the contribution of faint stars in the plane of the Galaxy. Technical Information: The image was constructed from seven exposures totaling almost three hours of searching by HST. The field shown is about 1.5 arc-minutes across. The image was taken in near-infrared light (814 nm) with the Wide Field Planetary Camera 2, on Feb 8, 1994. This observation is part of the HST parallel observing program. Credit: J Bahcall, Institute for Advance Study, Princeton and NASA

  8. HUBBLE'S SEARCH FOR FAINT FIELD STARS IN GALACTIC HALO

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Left A NASA Hubble Space Telescope image of a randomly selected area of sky taken to search for faint red stars that might constitute dark matter in our Milky Way Galaxy. (Dark matter is material of an unknown type that makes up most of the mass of our galaxy). If the dark matter in our Galaxy was made of faint red stars -- as many scientists have previously conjectured -- then about 38 such stars should have been visible in this HST image. The simulated stars (diamond-shaped symbols), based on theoretical calculations, illustrate what scientists would have seen if the dark matter were locked-up in faint red stars. These surprising results rule out dim stars as an explanation for dark matter in our Galaxy. Right The unmodified HST image shows the region is actually so devoid of stars that far more distant background galaxies can easily be seen. The field is in the constellation Eridanus, far outside the plane of our Milky Way Galaxy. This region was chosen to highlight stars in the galactic halo, where dark matter exists, and to avoid the contribution of faint stars in the plane of the Galaxy. Technical Information: The image was constructed from seven exposures totaling almost three hours of searching by HST. The field shown is about 1.5 arc-minutes across. The image was taken in near-infrared light (814 nm) with the Wide Field Planetary Camera 2, on Feb 8, 1994. This observation is part of the HST parallel observing program. Credit: J Bahcall, Institute for Advance Study, Princeton and NASA

  9. The 6dF Galaxy Survey: dependence of halo occupation on stellar mass

    NASA Astrophysics Data System (ADS)

    Beutler, Florian; Blake, Chris; Colless, Matthew; Jones, D. Heath; Staveley-Smith, Lister; Campbell, Lachlan; Parker, Quentin; Saunders, Will; Watson, Fred

    2013-03-01

    In this paper we study the stellar mass dependence of galaxy clustering in the 6dF Galaxy Survey (6dFGS). The near-infrared selection of 6dFGS allows more reliable stellar mass estimates compared to optical bands used in other galaxy surveys. Using the halo occupation distribution model, we investigate the trend of dark matter halo mass and satellite fraction with stellar mass by measuring the projected correlation function, wp(rp). We find that the typical halo mass (M1) as well as the satellite power-law index (α) increases with stellar mass. This indicates (1) that galaxies with higher stellar mass sit in more massive dark matter haloes and (2) that these more massive dark matter haloes accumulate satellites faster with growing mass compared to haloes occupied by low stellar mass galaxies. Furthermore, we find a relation between M1 and the minimum dark matter halo mass (Mmin) of M1 ≈ 22 Mmin, in agreement with similar findings for Sloan Digital Sky Survey galaxies. The satellite fraction of 6dFGS galaxies declines with increasing stellar mass from 21 per cent at Mstellar = 2.6 × 1010 h-2 M⊙ to 12 per cent at Mstellar = 5.4 × 1010 h-2 M⊙ indicating that high stellar mass galaxies are more likely to be central galaxies. We compare our results to two different semi-analytic models derived from the Millennium Simulation, finding some disagreement. Our results can be used for placing new constraints on semi-analytic models in the future, particularly the behaviour of luminous red satellites. Finally, we compare our results to studies of halo occupation using galaxy-galaxy weak lensing. We find good overall agreement, representing a valuable cross-check for these two different tools of studying the matter distribution in the Universe.

  10. Photometric Stellar Variability in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Rafelski, M.; Ghez, A. M.; Hornstein, S. D.; Lu, J. R.; Morris, M.

    2006-12-01

    We report the results of a diffraction-limited, photometric variability study of the central 5'' × 5'' of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W.M. Keck I 10 m telescope. Within our limiting magnitude of mK < 16 for maps made from a single night of data, we find a minimum of 25 variable stars out of 131 monitored stars. Among 46 stars brighter than mK < 14 which have roughly uniform photometric uncertainties, there are 16 variable stars. This suggests a minimum variable star frequency of 34%. We see no evidence of fares or dimming of the 7 stars that have known 3-dimensional orbits in our study, which greatly limits the possibility of a cold, geometrically-thin, inactive accretion disk around the supermassive black hole, Sgr A*. While large populations of binaries have been posited to exist in this region both to explain the presence of young stars in the vicinity of a black hole and because of the high stellar densities, only one eclipsing binary is identiffed. The only periodic source in our sample is the previously identiffed variable IRS 16SW (P = 19.448 ± 0.002 days). In contrast to recent results, our data show an asymmetric phased light curve with a much steeper fall-time than rise-time. IRS 29N shows variability on time scales of approx 5 years and has a known spectral type of WC9. This variation is likely due to episodic dust production, which may suggest that this source is a binary star system. Only 2 of the LBV candidates in our sample (16NW, 16SW) show variability and none of the 4 show the characteristic large increase or decrease in luminosity. However, our time baseline is too short to rule them out as LBVs. Our study has shown that photometric variability provides a useful handle on the unusual massive star population surrounding our Galaxy's supermassive black hole and its local environment.

  11. The kinematic footprints of five stellar streams in Andromeda's halo

    NASA Astrophysics Data System (ADS)

    Chapman, S. C.; Ibata, R.; Irwin, M.; Koch, A.; Letarte, B.; Martin, N.; Collins, M.; Lewis, G. F.; McConnachie, A.; Peñarrubia, J.; Rich, R. M.; Trethewey, D.; Ferguson, A.; Huxor, A.; Tanvir, N.

    2008-11-01

    We present a spectroscopic analysis of five stellar streams (`A', `B', `Cr', `Cp' and `D') as well as the extended star cluster, EC4, which lies within Stream`C', all discovered in the halo of M31 from our Canada-France-Hawaii Telescope/MegaCam survey. These spectroscopic results were initially serendipitous, making use of our existing observations from the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams that account for ~70 per cent of the M31 halo stars in the targeted fields. Subsequent spectroscopy was then procured in Stream`C' and Stream`D' to trace the velocity gradient along the streams. Nine metal-rich ([Fe/H] ~ -0.7) stars at vhel = -349.5kms-1,σv,corr ~ 5.1 +/- 2.5km s-1 are proposed as a serendipitous detection of Stream`Cr', with follow-up kinematic identification at a further point along the stream. Seven metal-poor ([Fe/H] ~-1.3) stars confined to a narrow, 15 km s-1 velocity bin centred at vhel = -285.6, σv,corr = 4.3+1.7-1.4 km s-1 represent a kinematic detection of Stream`Cp', again with follow-up kinematic identification further along the stream. For the cluster EC4, candidate member stars with average [Fe/H] ~-1.4, are found at vhel = -282 suggesting it could be related to Stream`Cp'. No similarly obvious cold kinematic candidate is found for Stream`D', although candidates are proposed in both of two spectroscopic pointings along the stream (both at ~ -400km s-1). Spectroscopy near the edge of Stream`B' suggests a likely kinematic detection at vhel ~ -330, σv,corr ~ 6.9km s-1, while a candidate kinematic detection of Stream`A' is found (plausibly associated to M33 rather than M31) with vhel ~ -170, σv,corr = 12.5km s-1. The low dispersion of the streams in kinematics, physical thickness and metallicity makes it hard to reconcile with a scenario whereby these stream structures as an ensemble are related to the giant southern stream. We conclude that the M31 stellar

  12. A `Universal' Density Profile for the Outer Stellar Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Remus, Rhea-Silvia; Burkert, Andreas; Dolag, Klaus

    2017-03-01

    The outer stellar halos of galaxies contain vital information about the formation history of galaxies, since the relaxation timescales in the outskirts are long enough to keep the memory, while the information about individual formation events in the central parts has long been lost due to mixing, star formation and relaxation. To unveil some of the information encoded in these faint outer halo regions, we study the stellar outskirts of galaxies selected from a fully hydrodynamical high-resolution cosmological simulation, called Magneticum. We find that the density profiles of the outer stellar halos of galaxies over a broad mass range can be well described by an Einasto profile. For a fixed total mass range, the free parameters of the Einasto fits are closely correlated. Galaxies which had more (dry) merger events tend to have lesser curved outer stellar halos, however, we find no indication that the amount of curvature is correlated with galaxy morphology. The Einasto-like shape of the outer stellar halo densities can also explain the observed differences between the Milky Way and Andromeda outer stellar halos.

  13. The Correlation between Halo Mass and Stellar Mass for the Most Massive Galaxies in the Universe

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.; Brownstein, Joel R.; Guo, Hong; Leauthaud, Alexie; Maraston, Claudia; Masters, Karen; Montero-Dorta, Antonio D.; Thomas, Daniel; Tojeiro, Rita; Weiner, Benjamin; Zehavi, Idit; Olmstead, Matthew D.

    2017-04-01

    We present measurements of the clustering of galaxies as a function of their stellar mass in the Baryon Oscillation Spectroscopic Survey. We compare the clustering of samples using 12 different methods for estimating stellar mass, isolating the method that has the smallest scatter at fixed halo mass. In this test, the stellar mass estimate with the smallest errors yields the highest amplitude of clustering at fixed number density. We find that the PCA stellar masses of Chen et al. clearly have the tightest correlation with halo mass. The PCA masses use the full galaxy spectrum, differentiating them from other estimates that only use optical photometric information. Using the PCA masses, we measure the large-scale bias as a function of {M}* for galaxies with {log}{M}* ≥slant 11.4, correcting for incompleteness at the low-mass end of our measurements. Using the abundance matching ansatz to connect dark matter halo mass to stellar mass, we construct theoretical models of b({M}* ) that match the same stellar mass function but have different amounts of scatter in stellar mass at fixed halo mass, {σ }{logM* }. Using this approach, we find {σ }{logM* }={0.18}-0.02+0.01. This value includes both intrinsic scatter as well as random errors in the stellar masses. To partially remove the latter, we use repeated spectra to estimate statistical errors on the stellar masses, yielding an upper limit to the intrinsic scatter of 0.16 dex.

  14. The impact of stellar feedback on hot gas in galaxy haloes: the Sunyaev-Zel'dovich effect and soft X-ray emission

    NASA Astrophysics Data System (ADS)

    van de Voort, Freeke; Quataert, Eliot; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Feldmann, Robert; Kereš, Dušan; Chan, T. K.; Hafen, Zachary

    2016-12-01

    The thermal Sunyaev-Zel'dovich (SZ) effect and soft X-ray emission are routinely observed around massive galaxies and in galaxy groups and clusters. We study these observational diagnostics of galaxy haloes for a suite of cosmological `zoom-in' simulations from the `Feedback In Realistic Environments' project, which spans a large range in halo mass (1010-13 M⊙). We explore the effect of stellar feedback on the hot gas observables. The properties of our simulated groups, such as baryon fractions, SZ flux, and X-ray luminosities (LX), are broadly consistent with existing observations, even though feedback from active galactic nuclei is not included. We make predictions for future observations of lower mass objects for both SZ and diffuse X-ray measurements, finding that they are not just scaled-down versions of massive galaxies, but more strongly affected by galactic winds driven by star formation. Low-mass haloes (≲1011 M⊙) retain a low fraction of their baryons, which results in a strong suppression of the SZ signal. Our simulations therefore predict a scaling with halo mass that is steeper than self-similar for haloes less massive than 1013 M⊙. For halo masses ≲1012 M⊙, LX is time variable and correlated primarily with the star formation rate (SFR). For these objects, the diffuse X-ray emission is powered mostly by galactic winds and the gas dominating the X-ray emission is flowing out with radial velocities close to the halo's circular velocity. For halo masses ≳1013 M⊙, on the other hand, LX is much less variable and not correlated with the SFR, because the emission originates from the quasi-hydrostatic, virialized halo gas.

  15. The Magellanic Analog Dwarf Companions and Stellar Halos (MADCASH) Survey: Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

    NASA Astrophysics Data System (ADS)

    Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Peter, Annika; Price, Paul A.; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

    2017-01-01

    We discuss the first results of our observational program to comprehensively map nearly the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. These will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. We will detail our discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

  16. Detecting the Disruption of Dark-Matter Halos with Stellar Streams.

    PubMed

    Bovy, Jo

    2016-03-25

    Narrow stellar streams in the Milky Way halo are uniquely sensitive to dark-matter subhalos, but many of these subhalos may be tidally disrupted. I calculate the interaction between stellar and dark-matter streams using analytical and N-body calculations, showing that disrupting objects can be detected as low-concentration subhalos. Through this effect, we can constrain the lumpiness of the halo as well as the orbit and present position of individual dark-matter streams. This will have profound implications for the formation of halos and for direct- and indirect-detection dark-matter searches.

  17. Impact of galactic and intergalactic dust on the stellar EBL

    NASA Astrophysics Data System (ADS)

    Vavryčuk, V.

    2016-06-01

    Current theories assume that the low intensity of the stellar extragalactic background light (stellar EBL) is caused by finite age of the Universe because the finite-age factor limits the number of photons that have been pumped into the space by galaxies and thus the sky is dark in the night. We oppose this opinion and show that two main factors are responsible for the extremely low intensity of the observed stellar EBL. The first factor is a low mean surface brightness of galaxies, which causes a low luminosity density in the local Universe. The second factor is light extinction due to absorption by galactic and intergalactic dust. Dust produces a partial opacity of galaxies and of the Universe. The galactic opacity reduces the intensity of light from more distant background galaxies obscured by foreground galaxies. The inclination-averaged values of the effective extinction AV for light passing through a galaxy is about 0.2 mag. This causes that distant background galaxies become apparently faint and do not contribute to the EBL significantly. In addition, light of distant galaxies is dimmed due to absorption by intergalactic dust. Even a minute intergalactic opacity of 1 × 10^{-2} mag per Gpc is high enough to produce significant effects on the EBL. As a consequence, the EBL is comparable with or lower than the mean surface brightness of galaxies. Comparing both extinction effects, the impact of the intergalactic opacity on the EBL is more significant than the obscuration of distant galaxies by partially opaque foreground galaxies by factor of 10 or more. The absorbed starlight heats up the galactic and intergalactic dust and is further re-radiated at IR, FIR and micro-wave spectrum. Assuming static infinite universe with no galactic or intergalactic dust, the stellar EBL should be as high as the surface brightness of stars. However, if dust is considered, the predicted stellar EBL is about 290 nW m^{-2} sr^{-1}, which is only 5 times higher than the observed

  18. Clump formation through colliding stellar winds in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Calderón, Diego

    2016-07-01

    The gas cloud G2 is currently being tidally disrupted by the Galactic Center super-massive black hole, Sgr A*. The region around the black hole is populated by ˜30 Wolf-Rayet stars, which produce strong outflows. Following an analytical approach, we explore the possibility that gas clumps, such as G2, originate from the collision of identical stellar winds via the Non-Linear Thin Shell Instability. We have found that the collision of relatively slow (<750 km s^{-1}) and strong (˜10^{-5} M_{⊙} yr^{-1}) stellar winds from stars at short separations (<2000 AU) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their orbits are not common in the Galactic Centre, however close binaries, such as IRS 16SW, are promising clump sources (see Calderón et al. 2016). We also present the first results of 2D models of colliding wind systems using the hydrodynamics adaptive mesh refinement code RAMSES, aiming to obtain a clump mass function, and the rate of clump formation and ejection to the ISM. We study the effect of parameters such as wind properties, stellar separation and orbital motion, in order to understand how likely the formation of G2 is in this context.

  19. STELLAR POPULATIONS IN THE OUTER HALO OF THE MASSIVE ELLIPTICAL M49

    SciTech Connect

    Mihos, J. Christopher; Harding, Paul; Rudick, Craig S.; Feldmeier, John J. E-mail: paul.harding@case.edu E-mail: jjfeldmeier@ysu.edu

    2013-02-20

    We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our data trace M49's stellar halo out to {approx}100 kpc (7r{sub e}), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B - V {approx} 0.7); if this is purely a metallicity effect, it argues for extremely metal-poor stellar populations with [Fe/H] < -1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxy's surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49's outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49's halo. Thus the extremely metal-poor nature of M49's extended halo provides some tension against current models for elliptical galaxy formation.

  20. Broken and Unbroken: The Milky Way and M31 Stellar Halos

    NASA Astrophysics Data System (ADS)

    Deason, A. J.; Belokurov, V.; Evans, N. W.; Johnston, K. V.

    2013-02-01

    We use the Bullock & Johnston suite of simulations to study the density profiles of L*-type galaxy stellar halos. Observations of the Milky Way and M31 stellar halos show contrasting results: the Milky Way has a "broken" profile, where the density falls off more rapidly beyond ~25 kpc, while M31 has a smooth profile out to 100 kpc with no obvious break. Simulated stellar halos, built solely by the accretion of dwarf galaxies, also exhibit this behavior: some halos have breaks, while others do not. The presence or absence of a break in the stellar halo profile can be related to the accretion history of the galaxy. We find that a break radius is strongly related to the buildup of stars at apocenters. We relate these findings to observations, and find that the "break" in the Milky Way density profile is likely associated with a relatively early (~6-9 Gyr ago) and massive accretion event. In contrast, the absence of a break in the M31 stellar halo profile suggests that its accreted satellites have a wide range of apocenters. Hence, it is likely that M31 has had a much more prolonged accretion history than the Milky Way.

  1. BROKEN AND UNBROKEN: THE MILKY WAY AND M31 STELLAR HALOS

    SciTech Connect

    Deason, A. J.; Belokurov, V.; Evans, N. W.; Johnston, K. V.

    2013-02-15

    We use the Bullock and Johnston suite of simulations to study the density profiles of L*-type galaxy stellar halos. Observations of the Milky Way and M31 stellar halos show contrasting results: the Milky Way has a 'broken' profile, where the density falls off more rapidly beyond {approx}25 kpc, while M31 has a smooth profile out to 100 kpc with no obvious break. Simulated stellar halos, built solely by the accretion of dwarf galaxies, also exhibit this behavior: some halos have breaks, while others do not. The presence or absence of a break in the stellar halo profile can be related to the accretion history of the galaxy. We find that a break radius is strongly related to the buildup of stars at apocenters. We relate these findings to observations, and find that the 'break' in the Milky Way density profile is likely associated with a relatively early ({approx}6-9 Gyr ago) and massive accretion event. In contrast, the absence of a break in the M31 stellar halo profile suggests that its accreted satellites have a wide range of apocenters. Hence, it is likely that M31 has had a much more prolonged accretion history than the Milky Way.

  2. Testing galaxy formation models with the GHOSTS survey: The stellar halo of M81

    NASA Astrophysics Data System (ADS)

    Monachesi, A.; Bell, E.; Radburn-Smith, D.; Vlajić, M.; de Jong, R.; Bailin, J.; Dalcanton, J.; Holwerda, B.; Streich, D.

    2015-03-01

    The GHOSTS survey is the largest study to date of the resolved stellar populations in the outskirts of disk galaxies (Radburn-Smith et al. 2011). The sample currently consists of 16 nearby disk galaxies, whose outer disks and halos are imaged with the Hubble Space Telescope (HST). I will present new results obtained from the study of 19 GHOSTS fields in M81's outermost part. The observed fields probe the stellar halo of M81 out to projected distances of ~50 kpc, an unprecedented distance for halo studies outside the Local Group. The 50% completeness levels of the color magnitude diagrams are typically at 2.5 mag below the tip of the red giant branch. When considering only fields located at galactocentric radius R > 15 kpc, we detect no color gradient in the stellar halo of M81. We compare these results with model predictions for the colors of stellar halos formed purely via accretion of satellite galaxies (Bullock & Johnston 2005). 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 (see Fig. 1).

  3. The halo-to-stellar mass ratio in the S4G

    NASA Astrophysics Data System (ADS)

    Díaz-García, Simón; Salo, Heikki; Laurikainen, Eija

    2017-03-01

    We use 3.6 μm photometry for 1154 disk galaxies (i < 65°) in the S4G (Sheth et al. 2010). We obtain the average stellar component of the circular velocity (V disk) and the mean (dark matter) halo-to-stellar mass ratio (M halo/M *) inside the optical radius (R opt) in bins of total stellar mass (M *, from Muñoz-Mateos et al. 2015), providing observational constraints for galaxy formation models to be tested against. We find the M halo/M * - M * relation in good agreement with the best-fit model at z ~ 0 in ΛCDM cosmological simulations (e.g. Moster 2010), assuming that the dark matter halo within R opt comprises a constant fraction (~ 4%) of its total mass.

  4. Characterization of Stellar Sub-Structure in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Kunder, Andrea; De Propris, Roberto; Rich, R. Michael; Koch, Andreas; Johnson, Christian I.

    2014-02-01

    We have discovered a group of 7 bulge giants with radial velocities of +300 km/s in a two degree field toward the Galactic bulge at (l,b)=(-6,-8). They are separated from the highest velocity bulge members by ~100 km/s. Recently, ARGOS reported a group of 4 kinematically distinct metal-poor bulge stars in their bulge fields at l=-20. Coincidentally, these stars have radial velocities of +300 km/sec. Given the scarcity of stars with velocities of +300 km/s in the bulge, these stellar features are likely related and part of a large independent stream or moving group in the inner Galaxy. We propose to search for connecting stars that link these two features and trace the extent of this newly discovered stream and understand their stellar system of origin, via their chemical composition.

  5. Highly-Ionized Gas in the Galactic Halo: A FUSE Survey of O 6 Absorption toward 22 Halo Stars

    NASA Astrophysics Data System (ADS)

    Zsargo, J.; Sembach, K. R.; Howk, J. C.; Savage, B. D.

    2002-12-01

    Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of 22 Galactic halo stars are studied to determine the amount of O 6 in the Galactic halo between ~0.3 and ~10 kpc from the Galactic mid-plane. Strong O 6 λ 1031.93 absorption was detected toward 21 stars, and a reliable 3 σ upper limit was obtained toward HD 97991. The weaker member of the O 6 doublet at 1037.62 Å could be studied toward only six stars. The observed columns are reasonably consistent with a patchy exponential O 6 distribution with a mid-plane density of 1.7x10-8 cm-3 and scale height between 2.3 and 4 kpc. We do not see clear signs of strong high-velocity components in O 6 absorption along the Galactic sight lines, which indicates the general absence of high velocity O 6 within 2-5 kpc of the Galactic mid-plane. The correlation between the H 1 and O 6 intermediate velocity absorption is also poor. The O 6 velocity dispersions are much larger than the value of ~18 km/s expected from thermal broadening for gas at T ~ 3x105 K, the temperature at which O 6 is expected to reach its peak abundance in collisional ionization equilibrium. Turbulence, inflow, and outflow must have an effect on the shape of the O 6 profiles. Kinematical comparisons of O 6 with Ar 1 reveal that 9 of 21 sight lines are closely aligned in LSR velocity (|Δ VLSR| <=5 km/s ), while 8 of 21 exhibit significant velocity differences (|Δ VLSR| >= 15 km/s ). This dual behavior may indicate the presence of two different types of O 6-bearing environments toward the Galactic sight lines. Comparison of O 6 with other highly-ionized species suggests that the high ions are produced primarily by cooling hot gas in the Galactic fountain flow, and that turbulent mixing also has a significant contribution. The role of turbulent mixing is most important toward sight lines that sample supernova remnants like Loop I and IV. We are also able to show that the O 6 enhancement toward the Galactic center region that was observed in the FUSE

  6. Sc and neutron-capture abundances in Galactic low- and high-α field halo stars

    NASA Astrophysics Data System (ADS)

    Fishlock, C. K.; Yong, D.; Karakas, A. I.; Alves-Brito, A.; Meléndez, J.; Nissen, P. E.; Kobayashi, C.; Casey, A. R.

    2017-01-01

    We determine relative abundance ratios for the neutron-capture elements Zr, La, Ce, Nd, and Eu for a sample of 27 Galactic dwarf stars with -1.5 < [Fe/H] <-0.8. We also measure the iron-peak element Sc. These stars separate into three populations (low- and high-α halo and thick-disc stars) based on the [α/Fe] abundance ratio and their kinematics as discovered by Nissen & Schuster. We find differences between the low- and high-α groups in the abundance ratios of [Sc/Fe], [Zr/Fe], [La/Zr], [Y/Eu], and [Ba/Eu] when including Y and Ba from Nissen & Schuster. For all ratios except [La/Zr], the low-α stars have a lower abundance compared to the high-α stars. The low-α stars display the same abundance patterns of high [Ba/Y] and low [Y/Eu] as observed in present-day dwarf spheroidal galaxies, although with smaller abundance differences, when compared to the high-α stars. These distinct chemical patterns have been attributed to differences in the star formation rate between the two populations and the contribution of low-metallicity, low-mass asymptotic giant branch (AGB) stars to the low-α population. By comparing the low-α population with AGB stellar models, we place constraints on the mass range of the AGB stars.

  7. Studies of the Hot Gas in the Galactic halo and Local Bubble

    NASA Technical Reports Server (NTRS)

    Shelton, Robin L.

    2003-01-01

    This paper presents a report on the progress made on Studies of the Hot Gas in the Galactic halo and Local Bubble at Johns Hopkins University. The broad goals of this project are to determine the physical conditions and history of the hot phase of the Galaxy's interstellar medium. Such gas resides in the Galactic halo, the Local Bubble surrounding the solar neighborhood, other bubbles, and supernova remnants. A better understanding of the hot gas and the processes occurring within it requires several types of work, including ultraviolet and X-ray data analyses and computer modeling.

  8. Exploring the Hot Galactic Halo Using Shadows of High Latitude Clouds

    NASA Technical Reports Server (NTRS)

    Juda, M.; Petre, Robert (Technical Monitor)

    2001-01-01

    The objective of this proposal was to measure variations in the 1/4 keV emission from the galactic halo, using ROSAT (x-ray astronomy satellite) Position Sensitive Proportional Counters (PSPC) observations toward known enhancements in the absorbing column density along the line-of-sight out of the Galaxy. Target directions were selected to have a low total hydrogen column density but to also show significant gradients in the amount of absorbing material, as traced by Infrared Astronomical Satellite (IRAS) 100 micron emission, on angular scales that would be contained within the PSPC field of view. In addition, we restricted the galactic latitude of the target directions to be greater than 60 degrees or less than -60 degrees in order to enable a cleaner separation of Galactic halo emission from that of the Galactic disk. The observations would also provide a measurement of the brightness of the emission from the Local Bubble.

  9. Galactic rotation and solar motion from stellar kinematics

    NASA Astrophysics Data System (ADS)

    Schönrich, Ralph

    2012-11-01

    I present three methods to determine the distance to the Galactic Centre R0, the solar azimuthal velocity in the Galactic rest frame Vg, ⊙ and hence the local circular speed Vc at R0. These simple, model-independent strategies reduce the set of assumptions to near-axisymmetry of the disc and are designed for kinematically hot stars, which are less affected by spiral arms and other effects. The first two methods use the position-dependent rotational streaming in the heliocentric radial velocities (U). The resulting rotation estimate θ from U velocities does not depend on Vg, ⊙. The first approach compares this with rotation from the Galactic azimuthal velocities to constrain Vg, ⊙ at an assumed R0. Both Vg, ⊙ and R0 can be determined using the proper motion of Sgr A* as a second constraint. The second strategy makes use of θ being roughly proportional to R0. Therefore a wrong R0 can be detected by an unphysical trend of Vg, ⊙ with the intrinsic rotation of different populations. From these two strategies I estimate R0 = (8.27 ± 0.29) kpc and Vg, ⊙ = (250 ± 9) km s-1 for a stellar sample from Sloan Extension for Galactic Understanding and Exploration, or, respectively, Vc = (238 ± 9) km s-1. The result is consistent with the third estimator, where I use the angle of the mean motion of stars, which should follow the geometry of the Galactic disc. This method also gives the solar radial motion with high accuracy. The rotation effect on U velocities must not be neglected when measuring the solar radial velocity U⊙. It biases U⊙ in any extended sample that is lop-sided in position angle α by of the order of 10 km s-1. Combining different methods I find U⊙ ˜ 14 km s-1, moderately higher than previous results from the Geneva-Copenhagen Survey.

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

    SciTech Connect

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

    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 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.

  11. Testing galaxy quenching theories with scatter in the stellar-to-halo mass relation

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.

    2017-05-01

    We use the scatter in the stellar-to-halo mass relation to constrain galaxy evolution models. If the efficiency of converting accreted baryons into stars varies with time, haloes of the same present-day mass but different formation histories will have different z = 0 galaxy stellar mass. This is one of the sources of scatter in stellar mass at fixed halo mass, σlog M*. For massive haloes that undergo rapid quenching of star formation at z ˜ 2, different mechanisms that trigger this quenching yield different values of σlog M*. We use this framework to test various models in which quenching begins after a galaxy crosses a threshold in one of the following physical quantities: redshift, halo mass, stellar mass and stellar-to-halo mass ratio. Our model is highly idealized, with other sources of scatter likely to arise as more physics is included. Thus, our test is whether a model can produce scatter lower than observational bounds, leaving room for other sources. Recent measurements find σlog M* = 0.16 dex for 1011 M⊙ galaxies. Under the assumption that the threshold is constant with time, such a low value of σlog M* rules out all of these models with the exception of quenching by a stellar mass threshold. Most physical quantities, such as metallicity, will increase scatter if they are uncorrelated with halo formation history. Thus, to decrease the scatter of a given model, galaxy properties would correlate tightly with formation history, creating testable predictions for their clustering. Understanding why σlog M* is so small may be key to understanding the physics of galaxy formation.

  12. Formation and Assembly History of Stellar Components in Galaxies as a Function of Stellar and Halo Mass

    NASA Astrophysics Data System (ADS)

    Lee, Jaehyun; Yi, Sukyoung K.

    2017-02-01

    Galaxy mass assembly is an end product of structure formation in the ΛCDM cosmology. As an extension of Lee & Yi, we investigate the assembly history of stellar components in galaxies as a function of halo environments and stellar mass using semi-analytic approaches. In our fiducial model, halo mass intrinsically determines the formation and assembly of the stellar mass. Overall, the ex situ fraction slowly increases in central galaxies with increasing halo mass but sharply increases for {log}{M}* /{M}ȯ ≳ 11. A similar trend is also found in satellite galaxies, which implies that mergers are essential to build stellar masses above {log}{M}* /{M}ȯ ∼ 11. We also examine the time evolution of the contribution of mass growth channels. Mergers become the primary channel in the mass growth of central galaxies when their host halo mass begins to exceed {log}{M}200/{M}ȯ ∼ 13. However, satellite galaxies seldom reach the merger-dominant phase despite their reduced star-formation activities due to environmental effects.

  13. Systematic problems with using dark matter simulations to model stellar halos

    SciTech Connect

    Bailin, Jeremy; Bell, Eric F.; Valluri, Monica; Stinson, Greg S.; Debattista, Victor P.; Couchman, H. M. P.; Wadsley, James

    2014-03-10

    The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be 'painted' onto dark matter (DM) particles in progenitor satellites; (2) pure DM simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted DM particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure DM simulation that does not form a baryonic disk. We find that the 'painting' simplification reduces the halo concentration and internal structure, predominantly because painted DM particles have different kinematics from star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure DM simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on DM-only simulations when such differences are less than an order of magnitude.

  14. Clump formation through colliding stellar winds in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Calderón, D.; Ballone, A.; Cuadra, J.; Schartmann, M.; Burkert, A.; Gillessen, S.

    2016-02-01

    The gas cloud G2 is currently being tidally disrupted by the Galactic Centre supermassive black hole, Sgr A*. The region around the black hole is populated by ˜30 Wolf-Rayet stars, which produce strong outflows. We explore the possibility that gas clumps, such as G2, originate from the collision of stellar winds via the non-linear thin shell instability. Following an analytical approach, we study the thermal evolution of slabs formed in the symmetric collision of winds, evaluating whether instabilities occur, and estimating possible clump masses. We find that the collision of relatively slow (≲750 km s-1) and strong (˜10-5 M⊙ yr-1) stellar winds from stars at short separations (<10 mpc) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their known orbits are not common in the Galactic Centre, making this process a possible but unlikely origin for G2. We also discuss clump formation in close binaries such as IRS 16SW and in asymmetric encounters as promising alternatives that deserve further numerical study.

  15. Environment effects on galactical and extra-galactical stellar systems: a numerical and observational study.

    NASA Astrophysics Data System (ADS)

    Leon, S.

    1998-09-01

    This thesis work is dealing in a first part with the influence of our Galaxy on its globular cluster population. First we simulated the gravitational shocks felt by a globular cluster during the crossing of the galactic plane (<>). We adapted a code from F. Leeuwin which is devoted to probe very weak perturbations on a stellar system at the equilibrium. It has been possible to describe the transient effects of the disk shocking on the globular cluster structure. It appears that the adiabatic component of the stellar system, defined by Weinberg (1994a), contributes to an important part for the heating of the cluster during the crossing. Some observational tests are proposed to measure these disk shocking effects on the globular cluster. We observed 6 globular clusters in the CO(1 to 0) transition at 115 GHz with the IRAM 30-m telescope (Granada) : it is shown that the disk crossing and the hot gaseous halo are very efficient in the stripping of the molecular gas in the globular clusters, released by the mass loss of the giant stars. The internal dynamics of globular clusters and the influence of the Galaxy lead to a mass loss in these stellar systems varying with time. We performed N-body simulations to study this mass loss in the galactic potential well and enlight various physical processes (rotation, gravitational shocks, mass segregation). A program of wide field study has been conducted on 20 globular clusters from photographic films and plates digitalized at the <> (CAI). In order to detect the tidal tails of globular cluster, we used a star-counting technique from a source-extracted catalogue. These stars are selected in the color-magnitude diagram. A wavelet transform is then applied on the star-count because it is particularly suited for different scale structure analysis. It has been found around the clusters large tidal structures revealing their dynamical story in the Galaxy. In one case (NGC 5139) it has been

  16. CLUMPY STREAMS FROM CLUMPY HALOS: DETECTING MISSING SATELLITES WITH COLD STELLAR STRUCTURES

    SciTech Connect

    Yoon, Joo Heon; Johnston, Kathryn V.; Hogg, David W.

    2011-04-10

    Dynamically cold stellar streams are ideal probes of the gravitational field of the Milky Way. This paper re-examines the question of how such streams might be used to test for the presence of {sup m}issing satellites{sup -}the many thousands of dark-matter subhalos with masses 10{sup 5}-10{sup 7} M{sub sun} which are seen to orbit within Galactic-scale dark-matter halos in simulations of structure formation in {Lambda}CDM cosmologies. Analytical estimates of the frequency and energy scales of stream encounters indicate that these missing satellites should have a negligible effect on hot debris structures, such as the tails from the Sagittarius dwarf galaxy. However, long cold streams, such as the structure known as GD1 or those from the globular cluster Palomar 5 (Pal 5), are expected to suffer many tens of direct impacts from missing satellites during their lifetimes. Numerical experiments confirm that these impacts create gaps in the debris' orbital energy distribution, which will evolve into degree- and sub-degree-scale fluctuations in surface density over the age of the debris. Maps of Pal 5's own stream contain surface density fluctuations on these scales. The presence and frequency of these inhomogeneities suggests the existence of a population of missing satellites in numbers predicted in the standard {Lambda}CDM cosmologies.

  17. Assembly history of subhalo populations in galactic and cluster sized dark haloes

    NASA Astrophysics Data System (ADS)

    Xie, Lizhi; Gao, Liang

    2015-12-01

    We make use of two suits of ultrahigh resolution N-body simulations of individual dark matter haloes from the Phoenix and the Aquarius Projects to investigate systematics of assembly history of subhaloes in dark matter haloes differing by a factor of 1000 in the halo mass. We have found that real progenitors which built up present-day subhalo population are relatively more abundant for high-mass haloes, in contrast to previous studies claiming a universal form independent of the host halo mass. That is mainly because of repeated counting of the `re-accreted' (progenitors passed through and were later re-accreted to the host more than once) and inclusion of the `ejected' progenitor population (progenitors were accreted to the host in the past but no longer members at present day) in previous studies. The typical accretion time for all progenitors vary strongly with the host halo mass, which is typical about z ˜ 5 for the galactic Aquarius and about z ˜ 3 for the cluster sized Phoenix haloes. Once these progenitors start to orbit their parent haloes, they rapidly lose their original mass but not their identifiers, more than 55 (50) per cent of them survive to present day for the Phoenix (Aquarius) haloes. At given redshift, survival fraction of the accreted subhalo is independent of the parent halo mass, whilst the mass-loss of the subhalo is more efficient in high-mass haloes. These systematics results in similarity and difference in the subhalo population in dark matter haloes of different masses at present day.

  18. Kinematics of the Old Stellar Population at the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Trippe, S.; Gillessen, S.; Gerhard, O. E.; Bartko, H.; Fritz, T. K.; Eisenhauer, F.; Ott, T.; Dodds-Eden, K.; Genzel, R.; Maness, H. L.; Martins, F.

    2011-05-01

    We discuss the kinematic properties of the old, (several Gyrs) late-type CO-absorption star population among the Galactic centre (GC) cluster stars. This cluster is composed of a central supermassive black hole (Sgr A*) and a self-gravitating system of stars. Understanding its kinematics thus offers the opportunity to understand the dynamical interaction between a central point mass and the surrounding stars in general, especially in view of understanding other galactic nuclei. We applied AO-assisted, near-infrared imaging and integral-field spectroscopy using the instruments NAOS/CONICA and SINFONI at the VLT. We obtained proper motions for 5445 stars and 3D velocities for 664 stars. We detect for the first time significant cluster rotation in the sense of the general Galactic rotation in proper motions. Out of the 3D velocity dispersion, we derive an improved statistical parallax for the GC of R0 = 8.07 ± 0.32stat ± 0.13sys kpc. The distribution of 3D stellar speeds can be approximated by local Maxwellian distributions. Kinematic modelling provides deprojected 3D kinematic parameters, including the mass profile of the cluster. Overall, the GC late-type cluster is described well as a uniform, isotropic, rotating, dynamically relaxed system. The results presented at this conference have been published in Trippe et al. (2008).

  19. A relationship between halo mass, cooling, active galactic nuclei heating and the co-evolution of massive black holes

    NASA Astrophysics Data System (ADS)

    Main, R. A.; McNamara, B. R.; Nulsen, P. E. J.; Russell, H. R.; Vantyghem, A. N.

    2017-02-01

    We derive X-ray mass, luminosity, and temperature profiles for 45 galaxy clusters to explore relationships between halo mass, active galactic nuclei (AGN) feedback, and central cooling time. We find that radio-mechanical feedback power (referred to here as `AGN power') in central cluster galaxies correlates with halo mass as Pmech ∝ M1.55 ± 0.26, but only in haloes with central atmospheric cooling times shorter than 1 Gyr. The trend of AGN power with halo mass is consistent with the scaling expected from a self-regulating AGN feedback loop, as well as with galaxy and central black hole co-evolution along the MBH-σ relation. AGN power in clusters with central atmospheric cooling times longer than ˜1 Gyr typically lies two orders of magnitude below those with shorter central cooling times. Galaxies centred in clusters with long central cooling times nevertheless experience ongoing and occasionally powerful AGN outbursts. We further investigate the impact of feedback on cluster scaling relations. We find L-T and M-T relations in clusters with direct evidence of feedback which are steeper than self-similar, but not atypical compared to previous studies of the full cluster population. While the gas mass rises, the stellar mass remains nearly constant with rising total mass, consistent with earlier studies. This trend is found regardless of central cooling time, implying tight regulation of star formation in central galaxies as their haloes grew, and long-term balance between AGN heating and atmospheric cooling. Our scaling relations are presented in forms that can be incorporated easily into galaxy evolution models.

  20. Kinematics of the Stellar Halo and the Mass Distribution of the Milky Way Using Blue Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; Bland-Hawthorn, Joss

    2012-12-01

    Here, we present a kinematic study of the Galactic halo out to a radius of ~60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates (σ r , σθ, σphi) and the anisotropy profile (β). The radial velocity dispersion profile (σ r ) is measured out to a galactocentric radius of r ~ 60 kpc, but due to the lack of proper-motion information, σθ, σphi, and β could only be derived directly out to r ~ 25 kpc. From a starting value of β ≈ 0.5 in the inner parts (9 < r/kpc < 12), the profile falls sharply in the range r ≈ 13-18 kpc, with a minimum value of β = -1.2 at r = 17 kpc, rising sharply at larger radius. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of β ≈ 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (v circ) of the Galaxy out to r ~ 25 kpc. The mass of the Galaxy within r <~ 25 kpc is determined to be 2.1 × 1011 M ⊙, and with a three-component fit to v circ(r), we determine the virial mass of the Milky Way dark matter halo to be M vir = 0.9+0.4 -0.3 × 1012 M ⊙ (R vir = 249+34 -31 kpc).

  1. 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.

  2. IC 1257: A New Globular Cluster in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Harris, W. E.; Phelps, R. L.; Madore, B. F.; Pevunova, O.; Skiff, B. A.; Crute, C.; Wilson, B.

    1996-01-01

    New CCD photometry of the faint, compact star cluster IC 1257 (L = 17? = +/- 15?obtained with the Palomar 5m telescope, reveals that it is a highly reddened globular cluster well beyond the Galactic center.

  3. IC 1257: A New Globular Cluster in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Harris, W. E.; Phelps, R. L.; Madore, B. F.; Pevunova, O.; Skiff, B. A.; Crute, C.; Wilson, B.

    1996-01-01

    New CCD photometry of the faint, compact star cluster IC 1257 (L = 17? = +/- 15?obtained with the Palomar 5m telescope, reveals that it is a highly reddened globular cluster well beyond the Galactic center.

  4. GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. I. SURFACE BRIGHTNESS PROFILE

    SciTech Connect

    Gilbert, Karoline M.; Guhathakurta, Puragra; Bullock, James; Tollerud, Erik J.; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Tanaka, Mikito; Chiba, Masashi

    2012-11-20

    We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 {+-} 0.2 and extends to a projected distance of at least {approx}175 kpc ({approx}2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects.

  5. 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.

  6. Stellar disc truncations and extended haloes in face-on spiral galaxies

    NASA Astrophysics Data System (ADS)

    Peters, S. P. C.; van der Kruit, P. C.; Knapen, J. H.; Trujillo, I.; Fliri, J.; Cisternas, M.; Kelvin, L. S.

    2017-09-01

    We use data from the IAC Stripe82 Legacy Project to study the surface photometry of 22 nearby, face-on to moderately inclined spiral galaxies. The reprocessed and combined Stripe 82 g',r' and i' images allow us to probe the galaxy down to 29-30 r'-magnitudes arcsec-2 and thus reach into the very faint outskirts of the galaxies. Truncations are found in three galaxies. An additional 15 galaxies are found to have an apparent extended stellar halo. Simulations show that the scattering of light from the inner galaxy by the point spread function (PSF) can produce faint structures resembling haloes, but this effect is insufficient to fully explain the observed haloes. The presence of these haloes and of truncations is mutually exclusive, and we argue that the presence of a stellar halo and/or light scattered by the PSF can hide truncations. Furthermore, we find that the onset of the stellar halo and the truncations scales tightly with galaxy size. Interestingly, the fraction of light does not correlate with dynamic mass. Nineteen galaxies are found to have breaks in their profiles, the radius of which also correlates with galaxy size.

  7. Hierarchical Galaxy Growth and Scatter in the Stellar Mass-Halo Mass Relation

    NASA Astrophysics Data System (ADS)

    Gu, Meng; Conroy, Charlie; Behroozi, Peter

    2016-12-01

    The relation between galaxies and dark matter halos reflects the combined effects of many distinct physical processes. Observations indicate that the z = 0 stellar mass-halo mass (SMHM) relation has remarkably small scatter in stellar mass at fixed halo mass (≲0.2 dex), with little dependence on halo mass. We investigate the origins of this scatter by combining N-body simulations with observational constraints on the SMHM relation. We find that at the group and cluster scale ({M}{vir}\\gt {10}14 {M}⊙ ) the scatter due purely to hierarchical assembly is ≈ 0.16 dex, which is comparable to recent direct observational estimates. At lower masses, mass buildup since z≈ 2 is driven largely by in situ growth. We include a model for the in situ buildup of stellar mass and find that an intrinsic scatter in this growth channel of 0.2 dex produces a relation between scatter and halo mass that is consistent with observations from {10}12 {M}⊙ \\lt {M}{vir}\\lt {10}14.75 {M}⊙ . The approximately constant scatter across a wide range of halo masses at z = 0 thus appears to be a coincidence, as it is determined largely by in situ growth at low masses and by hierarchical assembly at high masses. These results indicate that the scatter in the SMHM relation can provide unique insight into the regularity of the galaxy formation process.

  8. 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.

  9. 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.

  10. The Dark Matter Halo Profile Of NGC 2976 Via Stellar Kinematics

    NASA Astrophysics Data System (ADS)

    Adams, Joshua J.; Gebhardt, K.; Hill, G. J.; van den Bosch, R. C. E.; Blanc, G. A.

    2011-01-01

    The observations of kinematics in low surface brightness (LSB) and dwarf late type galaxies have stubbornly resisted giving clear evidence for the cuspy Navarro-Frenk-White (NFW) dark matter (DM) halo profiles that simulations with ΛCDM inputs predict. Instead, most LSBs and late type dwarfs suggest cored DM halos or the observations are not yet constraining enough to rule out cusps. One viable theory to explain cored DM halos relies on the gravitational perturbation of a growing baryonic disk that is then rapidly removed causing the halo to expand to a cored equilibrium. Weakly self-interacting dark matter has also been invoked to explain cored DM halos. This problem may loom large over small galaxy formation and growth. However, different measurements can be taken to further test the apparent problem. Most previous data have relied on HI or Hα as kinematic tracers. A small number of works have studied the problem with longslit stellar kinematics. Ideally, the advantages of 2D spectroscopic coverage and a collisionless kinematic tracer would be combined. So far, NGC 2976 has made one of the cleanest cases for a cored DM halo via integral field spectroscopy in Hα. We here report on observations of NGC 2976 with the large field-of-view fiber-fed Visible Integral field Replicable Unit Spectrograph Prototype (VIRUS-P) at R=3200 to concurrently measure the gaseous and stellar kinematics and probe the DM halo. We find that the gas and stellar kinematics disagree both in the magnitude of their second velocity moments and their detailed profiles. We unexpectedly find emission features in one of NGC 2976's two large star-forming regions which may be indicative of carbon-rich Wolf-Rayet stars. A putative bar further complicates the use of gaseous tracers. We solve the Jeans equations with stellar kinematics to reevaluate the DM profile in this exemplar galaxy of the core-cusp problem.

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

    SciTech Connect

    Xue, Xiang-Xiang; Rix, Hans-Walter; Ma, Zhibo; Morrison, Heather L.; Harding, Paul; Beers, Timothy C.; Ivans, Inese I.; Jacobson, Heather R.; Johnson, Jennifer; Lee, Young Sun; Lucatello, Sara; Rockosi, Constance M.; Yanny, Brian; Zhao, Gang; Allende Prieto, Carlos

    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, 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.

  12. Stellar contributions to the hard X-ray galactic ridge

    NASA Technical Reports Server (NTRS)

    Worrall, S. M.; Marshall, F. E.

    1982-01-01

    The number density of serendipitous sources in galactic plane Einstein Observatory IPC fields are compared with predictions based on the intensity of the HEAO-1 A2 unresolved hrd X-ray galactic ridge emission. It is concluded that theoretically predicted X-ray source populations of luminosity 8 x 10 to the 32nd power to 3 x 10 to the 34th power ergs s have 2 KeV to 10 KeV local surface densities of less than approximately .0008 L(32) pc/2 and are unlikely to be the dominant contributors to the hard X-ray ridge. An estimate for Be/neutron star binary systems, such as X Persei, gives a 2 keV to 10 keV local surface density of approximately 26 x 10 to the -5 power L(32) pc/2. Stellar systems of low luminosity, are more likely contributors. Both RS CVn and cataclysmic variable systems contribute 43% + or - 18% of the ridge. A more sensitive measurement of the ridge's hard X-ray spectrum should reveal Fe-line emission. We speculate that dM stars are further major contributors.

  13. Searching for Stellar Sub-Structure in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Hsyu, Tiffany; Johnson, C. I.; Kunder, A.; Rich, R. M.; de Propris, R.; Koch, A.

    2014-01-01

    We have discovered a group of 7 bulge giants with radial velocities of +300 km/s in a two degree field toward the Galactic bulge at (l,b) = (-6,-8). They are separated from the highest velocity bulge members by ~100 km/s. Recently, ARGOS reported a group of 4 kinematically distinct metal-poor bulge stars in their l = -20 fields. Coincidentally, these stars have radial velocities of +300 km/s. Given the scarcity of stars with velocities of +300 km/s in the Bulge, these stellar features may be related and part of a large independent stream or moving group in the inner Galaxy. We present preliminary results of high-resolution spectroscopy of 4 BRAVA stars with 300 km/s at (l, b) = (-6°,-8°) and 2 RAVE stars with 300 km/s at (l, b) = (-12°,-15°), taken with the MIKE spectrograph on the 6.5m Magellan telescope. The detailed abundance signatures provide an understanding as to the extent of this 300 km/s stellar system and a discussion on this potential newly discovered bulge stream.

  14. Polytropic transonic galactic outflows in a dark matter halo with a central black hole

    NASA Astrophysics Data System (ADS)

    Igarashi, Asuka; Mori, Masao; Nitta, Shin-ya

    2017-09-01

    Polytropic transonic solutions of spherically symmetric and steady galactic winds in the gravitational potential of a dark matter halo (DMH) with a supermassive black hole (SMBH) are studied. The solutions are classified in terms of their topological features, and the gravitational potential of the SMBH adds a new branch to the transonic solutions generated by the gravity of the DMH. The topological types of the transonic solutions depend on the mass distribution, the amount of supplied energy, the polytropic index γ and the slope α of the DMH mass distribution. When α becomes larger than a critical value αc, the transonic solution types change dramatically. Further, our model predicts that it is possible for a slowly accelerating outflow to exist, even in quiescent galaxies with small γ. This slowly accelerating outflow differs from those considered in many of the previous studies focusing on supersonic outflows in active star-forming galaxies. In addition, our model indicates that outflows in active star-forming galaxies have only one transonic point in the inner region (∼0.01 kpc). The locus of this transonic point does not strongly depend on γ. We apply the polytropic model incorporating mass flux supplied by stellar components to the Sombrero galaxy, and conclude that it can reproduce the observed gas density and the temperature distribution well. This result differs significantly from the isothermal model, which requires an unrealistically large mass flux. Thus, we conclude that the polytropic model is more realistic than the isothermal model, and that the Sombrero galaxy can have a slowly accelerating outflow.

  15. Measuring the Shape and Orientation of the Galactic Dark-Matter Halo using Hypervelocity Stars

    NASA Astrophysics Data System (ADS)

    Gnedin, Oleg

    2009-07-01

    We propose to obtain high-resolution images of five hypervelocity stars in the Galactic halo in order to establish the first-epoch astrometric frame for them, as a part of a long-term program to measure precise proper motions. The origin of these recently discovered stars, all with positive radial velocities above 540 km/s, is consistent only with being ejected from the deep potential well of the massive black hole at the Galactic center. The deviations of their space motions from purely radial trajectories probe the departures from spherical symmetry of the Galactic potential, mainly due to the triaxiality of the dark-matter halo. Reconstructing the full three-dimensional space motion of the hypervelocity stars, through astrometric proper motions, provides a unique opportunity to measure the shape and orientation of the dark halo. The hypervelocity stars allow measurement of the potential up to 75 kpc from the center, independently of and at larger distances than are afforded by tidal streams of satellite galaxies such as the Sagittarius dSph galaxy. HVS3 may be associated with the LMC, rather then the Galactic center, and would therefore present a case for a supermassive black hole at the center of the LMC. We request one orbit with ACS/WFC for each of the five hypervelocity stars to establish their current positions relative to background galaxies. We will request a repeated observation of these stars in Cycle 17, which will conclusively measure the astrometric proper motions.

  16. Measuring the Shape and Orientation of the Galactic Dark-Matter Halo using Hypervelocity Stars

    NASA Astrophysics Data System (ADS)

    Gnedin, Oleg

    2006-07-01

    We propose to obtain high-resolution images of five hypervelocity stars in the Galactic halo in order to establish the first-epoch astrometric frame for them, as a part of a long-term program to measure precise proper motions. The origin of these recently discovered stars, all with positive radial velocities above 540 km/s, is consistent only with being ejected from the deep potential well of the massive black hole at the Galactic center. The deviations of their space motions from purely radial trajectories probe the departures from spherical symmetry of the Galactic potential, mainly due to the triaxiality of the dark-matter halo. Reconstructing the full three-dimensional space motion of the hypervelocity stars, through astrometric proper motions, provides a unique opportunity to measure the shape and orientation of the dark halo. The hypervelocity stars allow measurement of the potential up to 75 kpc from the center, independently of and at larger distances than are afforded by tidal streams of satellite galaxies such as the Sagittarius dSph galaxy. HVS3 may be associated with the LMC, rather then the Galactic center, and would therefore present a case for a supermassive black hole at the center of the LMC. We request one orbit with ACS/WFC for each of the five hypervelocity stars to establish their current positions relative to background galaxies. We will request a repeated observation of these stars in Cycle 17, which will conclusively measure the astrometric proper motions.

  17. Tracing the stellar halo of an early type galaxy out to 25 effective radii

    NASA Astrophysics Data System (ADS)

    Rejkuba, Marina

    2016-08-01

    We have used ACS and WFC3 cameras on board HST to resolve stars in the halo of NGC 5128 out to 140 kpc (25 effective radii, R eff) along the major axis and 70 kpc (13 R eff) along the minor axis. This dataset provides an unprecedented radial coverage of stellar halo properties in any galaxy. Color-magnitude diagrams clearly reveal the presence of the red giant branch stars belonging to the halo of NGC 5128 even in the most distant fields. The V-I colors of the red giants enable us to measure the metallicity distribution in each field and so map the metallicity gradient over the sampled area. The stellar metallicity follows a shallow gradient and even out at 140 kpc (25 R eff) its median value does not go below [M/H]~-1 dex. We observe significant field-to-field metallicity and stellar density variations. The star counts are higher along the major axis when compared to minor axis field located 90 kpc from the galaxy centre, indicating flattening in the outer halo. These observational results provide new important constraints for the assembly history of the halo and the formation of this gE galaxy.

  18. Touching the void: A striking drop in stellar halo density beyond 50 kpc

    SciTech Connect

    Deason, A. J.; Rockosi, C. M.; Belokurov, V.; Koposov, S. E.

    2014-05-20

    We use A-type stars selected from Sloan Digital Sky Survey data release 9 photometry to measure the outer slope of the Milky Way stellar halo density profile beyond 50 kpc. A likelihood-based analysis is employed that models the ugr photometry distribution of blue horizontal branch and blue straggler stars. In the magnitude range 18.5 < g < 20.5, these stellar populations span a heliocentric distance range of: 10 ≲ D {sub BS}/kpc ≲ 75, 40 ≲ D {sub BHB}/kpc ≲ 100. Contributions from contaminants, such as QSOs, and the effect of photometric uncertainties, are also included in our modeling procedure. We find evidence for a very steep outer halo profile, with power-law index α ∼ 6 beyond Galactocentric radii r = 50 kpc, and even steeper slopes favored (α ∼ 6-10) at larger radii. This result holds true when stars belonging to known overdensities, such as the Sagittarius stream, are included or excluded. We show that, by comparison to numerical simulations, stellar halos with shallower slopes at large distances tend to have more recent accretion activity. Thus, it is likely that the Milky Way has undergone a relatively quiet accretion history over the past several gigayears. Our measurement of the outer stellar halo profile may have important implications for dynamical mass models of the Milky Way, where the tracer density profile is strongly degenerate with total mass estimates.

  19. Modelling the Formation of HI Clouds in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    de Avillez, M. A.; Mac Low, M.-M.

    2001-05-01

    Large scale modelling of the cycle of gas between the disk and the halo has been carried out with a 3D adaptive mesh refinement code. The model includes a gravitational field provided by the stars in the disk, an ideal-gas equation of state, and an approximation for the cooling curve, assuming collisional ionization equilibrium. Supernovae are set up at the beginning of their Sedov phases at a rate compatible with observations. Sixty percent of the SNe are set up within associations and the rest are set up at random sites. After a transient startup period of roughly 200 Myr, dynamical balance between upward and downward flowing gas is reached. Gas at the disk-halo interface (z ~ 1.5 kpc) flows into the halo in a turbulent convective flow at a rate of ~ 6 Msun yr-1, forming a large scale fountain. Ascending gas cools into clouds, with a large range of velocities, which we identify with observed H i clouds. These in turn rain down upon the disk. The descending clouds interact with the thick gas disk and eventually impact onto the thin disk leading to its deformation and disruption. The sizes of the clouds vary from a few pc to several tens of pc and their distribution in the halo varies with z. Intermediate velocity clouds (IVCs) are mainly distributed between z=0.8 and 4.2 kpc, whereas a large fraction of high velocity clouds (HVCs) are found at greater heights. On average 55-60% of the clouds have negative velocities. During a period of 50 Myr, approximately 18% of the total number of clouds have velocities between -90 and -160 km/s, whereas only ~ 3% of the clouds have vz<-160 km/s. The bulk of the HI clouds detected in the simulations have intermediate positive (40 to 90 km/s) and negative (-40 to -90 km/s) velocities. The former constitutes ~20% and the latter constitutes 25-27% of the total number of HI clouds detected. Most of the clouds show a multiphase structure with a core of cold gas, having temperatures of some 103 K, embedded in a warmer phase. M

  20. CHARACTERIZING THE CHEMISTRY OF THE MILKY WAY STELLAR HALO: DETAILED CHEMICAL ANALYSIS OF A METAL-POOR STELLAR STREAM ,

    SciTech Connect

    Roederer, Ian U.; Sneden, Christopher; Thompson, Ian B.; Preston, George W.; Shectman, Stephen A.

    2010-03-10

    We present the results of a detailed abundance analysis of one of the confirmed building blocks of the Milky Way stellar halo, a kinematically coherent metal-poor stellar stream. We have obtained high-resolution and high signal-to-noise spectra of 12 probable stream members using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the 2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have derived abundances or upper limits for 51 species of 46 elements in each of these stars. The stream members show a range of metallicity (-3.4 < [Fe/H] <-1.5) but are otherwise chemically homogeneous, with the same star-to-star dispersion in [X/Fe] as the rest of the halo. This implies that, in principle, a significant fraction of the Milky Way stellar halo could have formed from accreted systems like the stream. The stream stars show minimal evolution in the alpha or Fe-group elements over the range of metallicity. This stream is enriched with material produced by the main and weak components of the rapid neutron-capture process and shows no evidence for enrichment by the slow neutron-capture process.

  1. Ages and abundances of local galactic stellar populations

    NASA Astrophysics Data System (ADS)

    Feuillet, Diane Karen

    2016-08-01

    The chemical compositions of stellar atmospheres reflect the interstellar gas from which they formed, each one containing a snapshot of the Milky Way Galaxy's chemical evolution. By comparing abundances of stars across the disk of our Galaxy, we can explore how different parts of the Galaxy were enriched, where star formation proceeded most rapidly, and whether there has been significant mixing of stars and gas through the disk. In general, older stars formed from material that had fewer metals and younger stars formed after more metals had been deposited into the interstellar medium. However, the relative dating of stars based on metallicity cannot easily be mapped to an absolute age, and the local age metallicity relation cannot be used in different Galactic locations. The rate of metal enrichment depends strongly on the star formation rate. To use the full power of studying stellar atmosphere compositions across the Galaxy, we also need to determine absolute stellar ages. In this dissertation, I examine the ages and chemical abundances of stars in the solar neighborhood with the goal of extending this analysis to the larger APOGEE sample, which spans the full Milky Way disk. Through an independent analysis of optical spectra of APOGEE stars, I validate the individual chemical abundances measured by the near-infrared spectroscopic survey. The main stellar targets of APOGEE are red giant stars, for which the atmospheric parameters are degenerate with age. I develop a method of constraining the age distribution of a sample of giants, and determining individual ages to 0.1 dex, using a sample of local red giant stars with well measured distance. For the solar neighborhood, I find that the mean age of the sample is closely correlated with the abundance of a-elements in the stars, even at young ages. Using a sample of local subgiant stars, for which ages can be more precisely measured, I confirm this result for the solar neighborhood. I conclude that the method

  2. Halo K-Giant Stars from LAMOST: Kinematics and Galactic Mass Estimate

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.

    2017-03-01

    We analyze line-of-sight velocities of over 3000 halo K-giant stars from the second data release of the spectral survey LAMOST (Zhao et al. 2012). We find a nearly constant velocity dispersion profile, with no large dips or peaks, in a Galactocentric radial range of 10-30 kpc, in accord with earlier analyses (Battaglia et al. 2005, 2006; Xue et al. 2008, 2014) (see Fig. 1). Previous studies of halo star radial velocity dispersions in a reference frame centered on the Galactic Center have detected dips within this radial range (Sommer-Larsen et al. 1994; Kafle et al. 2012, 2014). We use the stars to make estimates of the enclosed mass out to 40 kpc from the Galactic Center using the method of Evans et al. (2011). Tens of thousands of such stars are expected to become available to this analysis by the end of the five-year survey.

  3. 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.

  4. NIHAO VII: predictions for the galactic baryon budget in dwarf to Milky Way mass haloes

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Dutton, Aaron A.; Stinson, Gregory S.; Macciò, Andrea V.; Gutcke, Thales; Kang, Xi

    2017-04-01

    We use the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) galaxy formation simulations to make predictions for the baryonic budget in present day galaxies ranging from dwarf (M200 ˜ 1010 M⊙) to Milky Way (M200 ˜ 1012 M⊙) masses. The sample is made of 88 independent high-resolution cosmological zoom-in simulations. NIHAO galaxies reproduce key properties of observed galaxies, such as the stellar mass versus halo mass and cold gas versus stellar mass relations. Thus they make plausible predictions for the baryon budget. We present the mass fractions of stars, cold gas (T < 104 K), cool gas (104 < T < 105 K), warm-hot gas (105 < T < 5 × 106 K) and hot gas (T > 5 × 106 K), inside the virial radius, R200. Compared to the predicted baryon mass, using the dark halo mass and the universal baryon fraction, fb ≡ Ωb/Ωm = 0.15, we find that all of our haloes are missing baryons. The missing mass has been relocated past 2 virial radii, and cool gas dominates the corona at low mass (M200 ≲ 3 × 1011 M⊙) while the warm-hot gas dominates at high mass (M200 ≳ 3 × 1011 M⊙). Haloes of mass M200 ˜ 1010 M⊙ are missing ˜90 per cent of their baryons. More massive haloes (M200 ˜ 1012 M⊙) retain a higher fraction of their baryons, with ˜30 per cent missing, consistent with recent observational estimates. Moreover, these more massive haloes reproduce the observed fraction of cold, warm-hot and hot gases. The fraction of cool gas we predict (0.11 ± 0.06) is significantly lower than the observation from COS-Halos (0.3-0.47), but agrees with the alternative analysis of Stern et al. (2016).

  5. NIHAO VII: Predictions for the galactic baryon budget in dwarf to Milky Way mass haloes

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Dutton, Aaron A.; Stinson, Gregory S.; Macciò, Andrea V.; Gutcke, Thales; Kang, Xi

    2017-01-01

    We use the NIHAO galaxy formation simulations to make predictions for the baryonic budget in present day galaxies ranging from dwarf (M_{200} ˜ 10^{10} M_{⊙}) to Milky Way (M_{200} ˜ 10^{12} M_{⊙}) masses. The sample is made of 88 independent high resolution cosmological zoom-in simulations. NIHAO galaxies reproduce key properties of observed galaxies, such as the stellar mass vs halo mass and cold gas vs stellar mass relations. Thus they make plausible predictions for the baryon budget. We present the mass fractions of stars, cold gas (T < 104K), cool gas (104 < T < 105K), warm-hot gas (105 < T < 5 × 106K), and hot gas (T>5 × 106K), inside the virial radius, R200. Compared to the predicted baryon mass, using the dark halo mass and the universal baryon fraction, fb ≡ Ωb/Ωm = 0.15, we find that all of our haloes are missing baryons. The missing mass has been relocated past 2 virial radii, and cool gas dominates the corona at low mass (M_{200} ≲ 3 × 10^{11} M_{⊙}) while the warm-hot gas dominates at high mass (M_{200} ≳ 3 × 10^{11} M_{⊙}). Haloes of mass M_{200} ˜ 10^{10}M_{⊙} are missing ˜90% of their baryons. More massive haloes (M_{200} ˜ 10^{12}M_{⊙}) retain a higher fraction of their baryons, with ˜30% missing, consistent with recent observational estimates. Moreover, these more massive haloes reproduce the observed fraction of cold, warm-hot and hot gas. The fraction of cool gas we predict (0.11 ± 0.06) is significantly lower than the observation from COS-HALOs (0.3-0.47), but agrees with the alternative analysis of Stern et al. (2016).

  6. Using chemical tagging to redefine the interface of the Galactic disc and halo

    NASA Astrophysics Data System (ADS)

    Hawkins, K.; Jofré, P.; Masseron, T.; Gilmore, G.

    2015-10-01

    We present a chemical abundance distribution study in 14 α, odd-Z, even-Z, light, and Fe-peak elements of approximately 3200 intermediate-metallicity giant stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The main aim of our analysis is to explore the Galactic disc-halo transition region within -1.20 < [Fe/H] < -0.55 as a means to study chemical difference (and similarities) between these components. In this paper, we show that there is an α-poor and α-rich sequence within both the metal-poor and intermediate-metallicity regions. Using the Galactic rest-frame radial velocity and spatial positions, we further separate our sample into the canonical Galactic components. We then studied the abundances ratios of Mg, Ti, Si, Ca, O, S, Al, C+N, Na, Ni, Mn, V, and K for each of the components and found the following: (1) the α-poor halo subgroup is chemically distinct in the α-elements, particularly O, Mg, S, Al, C+N, and Ni, from the α-rich halo, consistent with the literature confirming the existence of an α-poor accreted halo population; (2) the canonical thick disc and halo are not chemically distinct in all elements indicating a smooth transition between the thick disc and halo; (3) a subsample of the α-poor stars at metallicities as low as [Fe/H] ˜ -0.85 dex are chemically and dynamically consistent with the thin disc indicating that the thin disc may extend to lower metallicities than previously thought; and (4) the locations of the most metal-poor thin disc stars are consistent with a negative radial metallicity gradient. Finally, we used our analysis to suggest a new set of chemical abundance planes ([α/Fe], [C+N/Fe], [Al/Fe], and [Mg/Mn]) that may be able to chemically label the Galactic components in a clean and efficient way independent of kinematics.

  7. Soft X-Ray Observations of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Shelton, Robin; Kuntz, K. D.

    2003-01-01

    In this project, my co-I (K.D. Kuntz) and I plan to extract the soft X-ray spectrum emitted by the hot gas along a high latitude line of sight. We plan to subtract off the local component (garnered from other observations) in order to isolate the halo component. We then plan to combine this spectral information with the ultraviolet resonance line emission produced by slightly cooler gas along the line of sight and use the two observations as a constraint on models. My co-I, K.D., Kuntz has been working on the determination of the instrumental background. I have not yet drawn any of the funds for this project. I have just moved from J h s Hopkins University to the University of Georgia and anticipate finishing the project while at the University of Georgia.

  8. Soft X-Ray Observations of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Shelton, Robin; Kuntz, K. D.

    2003-01-01

    In this project, my co-I (K.D. Kuntz) and I plan to extract the soft X-ray spectrum emitted by the hot gas along a high latitude line of sight. We plan to subtract off the local component (garnered from other observations) in order to isolate the halo component. We then plan to combine this spectral information with the ultraviolet resonance line emission produced by slightly cooler gas along the line of sight and use the two observations as a constraint on models. My co-I, K.D., Kuntz has been working on the determination of the instrumental background. I have not yet drawn any of the funds for this project. I have just moved from J h s Hopkins University to the University of Georgia and anticipate finishing the project while at the University of Georgia.

  9. Expanding hydrodynamical jets crossing a galactic halo/intergalactic medium interface

    NASA Technical Reports Server (NTRS)

    Wiita, Paul J.; Rosen, Alexander; Norman, Michael L.

    1990-01-01

    Parameters within ranges that are plausible for radio sources are presently used to perform two-dimensional hydrodynamical calculations of axisymmetric, initially conical, jets whose initial propagation is through isothermal galactic halos with power-law density distributions; these emerge across a pressure-matched interface into a hotter, but less dense medium whose parameters are typical of an intracluster or intergalactic gas. Upon crossing this interface, the jets accelerate and focused toward cylindrical shapes having long, narrow cocoons.

  10. The Stellar Population Structure of the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Bovy, Jo; Rix, Hans-Walter; Schlafly, Edward F.; Nidever, David L.; Holtzman, Jon A.; Shetrone, Matthew; Beers, Timothy C.

    2016-05-01

    The spatial structure of stellar populations with different chemical abundances in the Milky Way (MW) contains a wealth of information on Galactic evolution over cosmic time. We use data on 14,699 red-clump stars from the APOGEE survey, covering 4 {kpc}≲ R≲ 15 {kpc}, to determine the structure of mono-abundance populations (MAPs)—stars in narrow bins in [α /{Fe}] and [{Fe}/{{H}}]—accounting for the complex effects of the APOGEE selection function and the spatially variable dust obscuration. We determine that all MAPs with enhanced [α /{Fe}] are centrally concentrated and are well-described as exponentials with a scale length of 2.2+/- 0.2 {kpc} over the whole radial range of the disk. We discover that the surface-density profiles of low-[α /{Fe}] MAPs are complex: they do not monotonically decrease outwards, but rather display a peak radius ranging from ≈ 5 to ≈ 13 {kpc} at low [{Fe}/{{H}}]. The extensive radial coverage of the data allows us to measure radial trends in the thickness of each MAP. While high-[α /{Fe}] MAPs have constant scale heights, low-[α /{Fe}] MAPs flare. We confirm, now with high-precision abundances, previous results that each MAP contains only a single vertical scale height and that low-[{Fe}/{{H}}], low-[α /{Fe}] and high-[{Fe}/{{H}}], high-[α /{Fe}] MAPs have intermediate ({h}Z≈ 300{--}600 {pc}) scale heights that smoothly bridge the traditional thin- and thick-disk divide. That the high-[α /{Fe}], thick disk components do not flare is strong evidence against their thickness being caused by radial migration. The correspondence between the radial structure and chemical-enrichment age of stellar populations is clear confirmation of the inside-out growth of galactic disks. The details of these relations will constrain the variety of physical conditions under which stars form throughout the MW disk.

  11. 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.

  12. 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.

  13. INTERACTION BETWEEN DARK MATTER SUB-HALOS AND A GALACTIC GASEOUS DISK

    SciTech Connect

    Kannan, Rahul; Maccio, Andrea V.; Walter, Fabian; Pasquali, Anna; Moster, Benjamin P.

    2012-02-10

    We investigate the idea that the interaction of dark matter (DM) sub-halos with the gaseous disks of galaxies can be the origin for the observed holes and shells found in their neutral hydrogen (H I) distributions. We use high-resolution hydrodynamic simulations to show that pure DM sub-halos impacting a galactic disk are not able to produce holes; on the contrary, they result in high-density regions in the disk. However, sub-halos containing a small amount of gas (a few percent of the total DM mass of the sub-halo) are able to displace the gas in the disk and form holes and shells. The sizes and lifetimes of these holes depend on the sub-halo gas mass, density, and impact velocity. A DM sub-halo, of mass 10{sup 8} M{sub Sun} and a gas mass fraction of {approx}3%, is able to create a kiloparsec-scale hole with a lifetime similar to those observed in nearby galaxies. We also register an increase in the star formation rate at the rim of the hole, again in agreement with observations. Even though the properties of these simulated structures resemble those found in observations, we find that the number of predicted holes (based on mass and orbital distributions of DM halos derived from cosmological N-body simulations) falls short compared to the observations. Only a handful of holes are produced per gigayear. This leads us to conclude that DM halo impact is not the major channel through which these holes are formed.

  14. Surface density of dark matter haloes on galactic and cluster scales

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.; Cardone, V. F.; Belvedere, G.

    2013-02-01

    In this paper, we analysed the correlation between the central surface density and the halo core radius of galaxies, and cluster of galaxies dark matter (DM) haloes, in the framework of the secondary infall model. We used Del Popolo secondary infall model taking into account ordered and random angular momentum, dynamical friction and DM adiabatic contraction to calculate the density profile of haloes, and then these profiles are used to determine the surface density of DM haloes. The main result is that r* (the halo characteristic radius) is not a universal quantity as claimed by Donato et al. and Gentile et al. On the contrary, we find a correlation with the halo mass M200 in agreement with Cardone & Tortora, Boyarsky et al. and Napolitano, Romanowsky & Tortora, but with a significantly smaller scatter, namely 0.16 ± 0.05. We also consider the baryon column density finding this latter being indeed a constant for low-mass systems, such as dwarfs, but correlating with mass with a slope of α = 0.18 ± 0.05. In the case of the surface density of DM for a system composed only of DM, as in dissipationless simulations, we get α = 0.20 ± 0.05. These results leave little room for the recently claimed universality of (dark and stellar) column density.

  15. Magnetized High Velocity Clouds in the Galactic Halo: A New Distance Constraint

    NASA Astrophysics Data System (ADS)

    Grønnow, Asger; Tepper-García, Thor; Bland-Hawthorn, Joss; McClure-Griffiths, N. M.

    2017-08-01

    High velocity gas that does not conform to Galactic rotation is observed throughout the Galaxy’s halo. One component of this gas, H i high velocity clouds (HVCs), have attracted attention since their discovery in the 1960s and remain controversial in terms of their origins, largely due to the lack of reliable distance estimates. The recent discovery of enhanced magnetic fields toward HVCs has encouraged us to explore their connection to cloud evolution, kinematics, and survival as they fall through the magnetized Galactic halo. For a reasonable model of the halo magnetic field, most infalling clouds see transverse rather than radial field lines. We find that significant compression (and thereby amplification) of the ambient magnetic field occurs in front of the cloud and in the tail of material stripped from the cloud. The compressed transverse field attenuates hydrodynamical instabilities. This delays cloud destruction, though not indefinitely. The observed {\\boldsymbol{B}} field compression is related to the cloud’s distance from the Galactic plane. As a result, the observed rotation measure provides useful distance information on a cloud’s location.

  16. Measuring the Stellar Halo Velocity Anisotropy With 3D Kinematics

    NASA Astrophysics Data System (ADS)

    Cunningham, Emily C.; Deason, Alis J.; Guhathakurta, Puragra; Rockosi, Constance M.; van der Marel, Roeland P.; Sohn, S. Tony

    2016-08-01

    We present the first measurement of the anisotropy parameter β using 3D kinematic information outside of the solar neighborhood. Our sample consists of 13 Milky Way halo stars with measured proper motions and radial velocities in the line of sight of M31. Proper motions were measured using deep, multi-epoch HST imaging, and radial velocities were measured from Keck II/DEIMOS spectra. We measure β = -0.3-0.9 +0.4, which is consistent with isotropy, and inconsistent with measurements in the solar neighborhood. We suggest that this may be the kinematic signature of a relatively early, massive accretion event, or perhaps several such events.

  17. 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

  18. 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

  19. At a Crossroads: Stellar Streams in the South Galactic Cap

    NASA Astrophysics Data System (ADS)

    Grillmair, Carl J.

    2017-10-01

    We examine the distribution of old, metal-poor stars in a portion of the recently released PanSTARRs survey. We find an interesting confluence of four new cold stellar stream candidates that appear to converge on or pass near the south Galactic pole. The stream candidates, which we designate as Murrumbidgee, Molonglo, Orinoco, and Kwando, lie at a distance of ≈ 20 {kpc} and range in length from 13^\\circ to 95^\\circ , or about 5 to 33 kpc. The stream candidates are between 100 and 300 pc in width and are estimated to contain between 3000 and 8000 stars each, suggesting progenitors similar to modern day globular clusters. The trajectories of the streams imply orbits that range from hyperbolic to nearly circular. The Molonglo stream is nearly parallel to, at the same distance as, and offset by only 2\\buildrel{\\circ}\\over{.} 5 from the previously discovered ATLAS stream, suggesting a possible common origin. Orinoco and Kwando also have similarly shaped, moderately eccentric, obliquely viewed orbits that suggest distinct progenitors within a common, larger parent body.

  20. Galactic flows and the formation of stellar clusters

    NASA Astrophysics Data System (ADS)

    Smilgys, Romas; Bonnell, Ian A.

    2017-03-01

    We investigate the formation of stellar clusters from a Galactic scale SPH simulation. The simulation traces star formation over a 5.6 Myr timescale, with local gravitational instabilities resulting in ~ 105 solar masses of star formation in the form of sink particles. We investigate the time evolution of the physical properties of the forming clusters including their half-mass radii, their energies and the depletion time of the gas. Star formation is driven by the large scale flows which compress the gas to higher densities where self gravity takes over and collapse occurs. We show that the more massive clusters (up to ~ 2 × 104 solar masses) gather their material from of order 10 pc due to these large scale motions associated with the spiral arm passage and shock. The bulk of the gas becomes gravitationally bound near 1-2 Myr before sink formation, and in the absence of feedback, significant accretion ongoing on longer timescales. We trace the hierarchical merging process of cluster formation which naturally results in age spreads of order the crossing time of the original region which provides the gas reservoir for the cluster.

  1. Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile

    NASA Astrophysics Data System (ADS)

    Gilbert, Karoline M.; Guhathakurta, Puragra; Beaton, Rachael L.; Bullock, James; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J.; Tollerud, Erik J.; Tanaka, Mikito; Chiba, Masashi

    2012-11-01

    We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 ± 0.2 and extends to a projected distance of at least ~175 kpc (~2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California

  2. Optical Galactic Spiral Patterns as the Gas Response to a Rotating 2-Armed Stellar Spiral

    NASA Astrophysics Data System (ADS)

    Martos, Marco; Yáñez, Miguel

    2005-09-01

    We report ongoing simulations of the gas response to a rigidly rotating spiral pattern in the non-self-gravitating hydrodynamic regime using the ZEUS code in a Galactic disk model. The disk model is a bidimensional projection of a 3D mass distribution representing the known axisymmetric Galactic components including a massive dark matter halo, and a spiral 2-armed pattern modelled following the locus and pitch angle of K-band observations in our Galaxy. We find that the isothermal gaseous response is a sensitive function of the pattern rotation speed Ωp. The same behavior was found in previous work for the dynamical self-consistency of the stellar orbital structure, for this model of the Milky Way. Here we studied the response as a function of Ωp and the pattern termination placed at different galactocentric radii R (12 kpc, corotation, and the 4:1 resonance) to test known theoretical predictions for the extent of spiral arms according to their strength. Our results suggest that the Milky Way is a weak spiral, with its gaseous pattern ending at corotation; however, there are as well indications of an abrupt fall off in density along the spiral, in agreement with infrared data analysis. The spiral mass, hence the forcing, was also varied within plausible values for a Sb galaxy. The response to the 2-armed stellar pattern is a 4-armed gaseous pattern for Ωp of 20 km s-1 kpc-1. Values close to this optimal Galactic (dynamically self-consistent) rotation speed present similar bifurcations of the arms. Except possibly for very high forcing, low rotation speeds of 10 km s-1 kpc-1 or so lead to a gas response that only mimics the imposed 2-armed pattern and there are no arm bifurcations. For values of Ωp higher than 20 km s-1 kpc-1, a complex multi-arm response is produced. While most cases explored rapidly reach steady state (in timescales of the order 300 Myr or less) and maintained it to elapsed times of the order 3 Gyr, the high spiral mass case at that elapsed

  3. The lithium content of the galactic halo stars

    NASA Astrophysics Data System (ADS)

    Charbonnel, C.; Primas, F.

    Thanks to the accurate determination of the baryon density of the Universe by the recent cosmic microwave background experiments, updated predictions of the standard model of Big Bang nucleosynthesis yield the initial abundances of the primordial light elements with an unprecedented precision (Bennet et al. 2003; Spergel et al. 2003; Coc et al. 2004; Cyburt 2004; Serpico et al. 2004). In the case of ^7Li, the CMB+SBBN value is significantly higher than the generally reported abundances for Pop II stars along the Spite plateau. Here, we report on the very recent results we obtained by revisiting a large sample of literature Li data in halo stars that we assembled following some strict criteria on the quality of the original analyses published from the early 90 s onwards. We put a strong emphasis on the temperature scale and reddening issues, and on the determination of the evolutionary status of each of our sample stars. Using our “best" (i.e. most consistent) set of temperatures we discuss the resulting mean Li value along the plateau for the dwarf stars on one hand and for the turnoff and subgiant stars on the other hand.

  4. 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.

  5. Nearby stars of the Galactic disc and halo - V

    NASA Astrophysics Data System (ADS)

    Fuhrmann, Klaus

    2011-07-01

    This fifth in a series of papers finishes the model atmosphere analyses of an unbiased, volume-complete sample of more than 300 nearby solar-type stars. The sample first disintegrates into thick-disc and thin-disc stars on account of their different distributions in the [Mg/H]-[Fe/Mg] chemical abundance plane. Detailed stellar age-datings of the locally few, but very relevant, subgiants show this map to be the sequel of a major star formation gap and hence the legacy for the two stellar populations. Among the stars of the thin disc the subgiant 70 Vir with τ= 8.1 ± 0.6 Gyr remains the best case to constrain the age of this comparatively young population. Uncertainties for the existing thick-disc subgiants are about twice as much, but they consistently promote ages of 12-13 Gyr. The unbiased thin-disc metallicity distribution functions of magnesium and iron average at <[Mg/H]>=-0.009 ± 0.012 dex and <[Fe/H]>=-0.034 ± 0.015 dex, thereby demonstrating that the Sun is a typical thin-disc star in terms of these two elements. The small but likewise unbiased sample of thick-disc stars leads to <[Mg/H]>=-0.207 ± 0.049 dex and <[Fe/H]>=-0.584 ± 0.057 dex, which implies that about two-thirds of the α-element magnesium was already synthesized in the early Milky Way. Similarly, the age-metallicity relations for the thin disc result in Δ[Mg/H]=+0.006 dex Gyr-1 and Δ[Fe/H]=+0.017 dex Gyr-1 and lead to the conclusion that a similar percentage of iron was synthesized before the birth of the thin disc. In comparison with the considerable metallicity dispersions σ[Mg/H]= 0.151 dex and σ[Fe/H]= 0.191 dex for the stars of the thin disc, this immediately explains the coexistence of old, metal rich as well as young, fairly metal poor stars within this stellar population. The stellar multiplicities of the solar-type thin-disc stars show a minority of less than 47 per cent to be single and at least 15 per cent to belong to triple and higher level systems. More concisely, in

  6. Two Stellar Components in the Halo of the Milky Way

    DTIC Science & Technology

    2007-12-13

    Centre, based on much smaller samples of globular clusters2,10 and stars6–9,13,14 than we consider here. The 15 Z (k p c) 10 5 0 –5 –10 –15 0 5 10 R (kpc...Data Release 512) spectrophotometric and telluric calibration stars in the Z– R plane is shown, where Z is the derived distance from the Galactic plane in...the vertical direction and R is the derived distance from the centre of the Galaxy projected onto this plane. The dashed blue line represents the

  7. A STATISTICAL ANALYSIS OF THE LATE-TYPE STELLAR CONTENT IN THE ANDROMEDA HALO

    SciTech Connect

    Koch, Andreas; Rich, R. Michael E-mail: rmr@astro.ucla.ed

    2010-06-15

    We present a statistical characterization of the carbon-star to M-giant (C/M) ratio in the halo of M31. Based on the application of pseudo-filter bandpasses to our Keck/DEIMOS spectra, we measure the 81 - 77 color index of 1288 stars in the giant stellar stream and in halo fields out to large distances. From this well-established narrow-band system, supplemented by V - I colors, we find only a low number (five in total) of C-star candidates. The resulting low C/M ratio of 10% is consistent with the values in the M31 disk and inner halo from the literature. Although our analysis is challenged by small number statistics and our sample selection, there is an indication that the oxygen-rich M-giants occur in similar number throughout the entire halo. We also find no difference in the C-star population of the halo fields compared to the giant stream. The very low C/M ratio is at odds with the observed low metallicities and the presence of intermediate-age stars at large radii. Our observed absence of a substantial carbon-star population in these regions indicates that the (outer) M31 halo cannot be dominated by the debris of disk-like or Small-Magellanic-Cloud-type galaxies, but rather resemble the dwarf elliptical NGC 147.

  8. Stellar orbital properties as diagnostics of the origin of the stellar halo

    NASA Astrophysics Data System (ADS)

    Valluri, Monica; Loebman, Sarah R.; Bailin, Jeremy; Clarke, Adam; Debattista, Victor P.; Stinson, Greg

    2016-08-01

    We examine metallicities, ages and orbital properties of halo stars in a Milky-Way like disk galaxy formed in the cosmological hydrodynamical MaGICC simulations. Halo stars were either accreted from satellites or they formed in situ in the disk or bulge of the galaxy and were then kicked up into the halo (``in situ/kicked-up'' stars). Regardless of where they formed both types show surprisingly similar orbital properties: the majority of both types are on short-axis tubes with the same sense of rotation as the disk - implying that a large fraction of satellites are accreted onto the halo with the same sense of angular momentum as the disk.

  9. Neutrino propagation in the Galactic dark matter halo

    NASA Astrophysics Data System (ADS)

    de Salas, P. F.; Lineros, R. A.; Tórtola, M.

    2016-12-01

    Neutrino oscillations are a widely observed and well-established phenomenon. It is also well known that deviations with respect to flavor conversion probabilities in vacuum arise due to neutrino interactions with matter. In this work, we analyze the impact of new interactions between neutrinos and the dark matter present in the Milky Way on the neutrino oscillation pattern. The dark matter-neutrino interaction is modeled by using an effective coupling proportional to the Fermi constant GF with no further restrictions on its flavor structure. For the galactic dark matter profile we consider a homogeneous distribution as well as several density profiles, estimating in all cases the size of the interaction required to get an observable effect at different neutrino energies. Our discussion is mainly focused in the PeV neutrino energy range, to be explored in observatories like IceCube and KM3NeT. The obtained results may be interpreted in terms of a light O (sub -eV - keV ) or weakly interacting massive particlelike dark matter particle or as a new interaction with a mediator of O (sub -eV - keV ) mass.

  10. A New Model for Chemical Evolution of the Galactic Halo: Formulation and Applications

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Takuji; Shigeyama, Toshikazu; Yoshii, Yuzuru

    A model for Galactic chemical evolution, driven by supernova-induced star formation, is formulated and used to examine the nature of the Galactic halo at early epochs. In this model, new stars are formed following each supernova event, thus their abundance pattern is determined by the combination of heavy elements ejected from the supernova itself and those elements which are already present in the interstellar gas swept up by the supernova remnant. The end result is a prediction of large scatter in the abundance ratios among low-metallicity stars, reflecting a different nucleosynthesis yield for each Type II supernova (SN II) with a different progenitor mass. Formation of new stars is terminated when supernova remnants sweep up too little gas to form shells. We show from calculations based on the above scenario that (i) the observed [Fe/H] distribution for the Galactic halo field stars can be reproduced without effectively decreasing the heavy-element yields from SNe II by some manipulation required by previous models (e.g., via mass lass from the early Galaxy, or later mixing with "pristine" hydrogen clouds), (ii) the large observed scatter in the abundante ratio [Eu/Fe] for the most metal-poor stars can also be reproduced, and (iii) the frequency distribution of stars in the [Eu/Fe]-[Fe/H] plane can be predicted. Our model suggests that the probability of identifying essentially metal-free stars (Population III) in the local halo is around one in 103-4, provided that star formation in the halo is confined to individual gas clouds with mass of 10 ^{6-7} M_⊙ and that the initial mass function of metal-free stars is not significantly different from the Salpeter mass function.

  11. White Dwarfs:. Contributors and Tracers of the Galactic Dark-Matter Halo

    NASA Astrophysics Data System (ADS)

    Koopmans, L. V. E.; Blandford, R. D.

    2002-03-01

    We examine the claim by Oppenheimer et al. (2001) that the local halo density of white dwarfs is an order of magnitude higher than previously thought. As it stands, the observational data support the presence of a kinematically distinct population of halo white dwarfs at the >99% confidence level. A maximum-likelihood analysis gives a radial velocity dispersion of σ hU = 150+80-40\\ km s-1 and an asymmetric drift of ν ha = 176+102-80\\ km s-1, for a Schwarzschild velocity distribution function with σU:σV:σW = 1:2/3:1/2. Halo white dwarfs have a local number density of 1.1+2.1-0.7 × 10-4\\ pc-3, which amounts to 0.8+1.6-0.5 per cent of the nominal local dark-matter halo density and is 5.0+9.5-3.2 times (90% C.L.) higher and thus only marginally in agreement with previous estimates. We discuss several direct consequences of this white-dwarf population (e.g. microlensing) and postulate a potential mechanism to eject young white dwarfs from the disc to the halo, through the orbital instabilities in triple or multiple stellar systems.

  12. STELLAR MASS-GAP AS A PROBE OF HALO ASSEMBLY HISTORY AND CONCENTRATION: YOUTH HIDDEN AMONG OLD FOSSILS

    SciTech Connect

    Deason, A. J.; Conroy, C.; Wetzel, A. R.; Tinker, J. L.

    2013-11-10

    We investigate the use of the halo mass-gap statistic—defined as the logarithmic difference in mass between the host halo and its most massive satellite subhalo—as a probe of halo age and concentration. A cosmological N-body simulation is used to study N ∼ 25, 000 group/cluster-sized halos in the mass range 10{sup 12.5} < M{sub halo}/M{sub ☉} < 10{sup 14.5}. In agreement with previous work, we find that halo mass-gap is related to halo formation time and concentration. On average, older and more highly concentrated halos have larger halo mass-gaps, and this trend is stronger than the mass-concentration relation over a similar dynamic range. However, there is a large amount of scatter owing to the transitory nature of the satellite subhalo population, which limits the use of the halo mass-gap statistic on an object-by-object basis. For example, we find that 20% of very large halo mass-gap systems (akin to {sup f}ossil groups{sup )} are young and have likely experienced a recent merger between a massive satellite subhalo and the central subhalo. We relate halo mass-gap to the observable stellar mass-gap via abundance matching. Using a galaxy group catalog constructed from the Sloan Digital Sky Survey Data Release 7, we find that the star formation and structural properties of galaxies at fixed mass show no trend with stellar mass-gap. This is despite a variation in halo age of ≈2.5 Gyr over ≈1.2 dex in stellar mass-gap. Thus, we find no evidence to suggest that the halo formation history significantly affects galaxy properties.

  13. The origin of scatter in the stellar mass-halo mass relation of central galaxies in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Matthee, Jorryt; Schaye, Joop; Crain, Robert A.; Schaller, Matthieu; Bower, Richard; Theuns, Tom

    2017-02-01

    We use the hydrodynamical EAGLE simulation to study the magnitude and origin of the scatter in the stellar mass-halo mass relation for central galaxies. We separate cause and effect by correlating stellar masses in the baryonic simulation with halo properties in a matched dark matter only (DMO) simulation. The scatter in stellar mass increases with redshift and decreases with halo mass. At z = 0.1, it declines from 0.25 dex at M200, DMO ≈ 1011 M⊙ to 0.12 dex at M200, DMO ≈ 1013 M⊙, but the trend is weak above 1012 M⊙. For M200, DMO < 1012.5 M⊙ up to 0.04 dex of the scatter is due to scatter in the halo concentration. At fixed halo mass, a larger stellar mass corresponds to a more concentrated halo. This is likely because higher concentrations imply earlier formation times and hence more time for accretion and star formation, and/or because feedback is less efficient in haloes with higher binding energies. The maximum circular velocity, Vmax, DMO, and binding energy are therefore more fundamental properties than halo mass, meaning that they are more accurate predictors of stellar mass, and we provide fitting formulae for their relations with stellar mass. However, concentration alone cannot explain the total scatter in the M_star - M_{200, DMO} relation, and it does not explain the scatter in Mstar-Vmax, DMO. Halo spin, sphericity, triaxiality, substructure and environment are also not responsible for the remaining scatter, which thus could be due to more complex halo properties or non-linear/stochastic baryonic effects.

  14. Resolving the extended stellar haloes of nearby galaxies: the wide-field PISCeS survey

    NASA Astrophysics Data System (ADS)

    Crnojevic, Denija; Sand, David J.; Caldwell, Nelson; Guhathakurta, Puragra; McLeod, Brian A.; Seth, Anil; Simon, Joshua D.; Strader, Jay; Toloba, Elisa

    2015-08-01

    I will present results from the wide-field Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS): we investigate the resolved stellar haloes of two nearby galaxies (the spiral NGC253 and the elliptical Centaurus A, D~3.7 Mpc) out to a galactocentric radius of 150 kpc with Magellan/Megacam. The survey led to the discovery of ~20 faint satellites and stunning streams/substructures in two environments substantially different from the Local Group, i.e. the loose Sculptor group of galaxies and the Centaurus A group dominated by an elliptical. These discoveries clearly testify the past and ongoing accretion processes shaping the haloes of these nearby galaxies, and provide the first complete census of their satellite systems down to an unprecedented M_V<-8. This effectively enables the first direct comparison of external galaxies' resolved haloes to the PAndAS survey. The detailed characterization of the stellar content, shape and gradients in the extended haloes of NGC253, Centaurus A and in their satellites represent crucial constraints to theoretical models of galaxy formation and evolution.

  15. Determining the Galactic Halo's Emission Measure from UV and X-Ray Observations

    NASA Astrophysics Data System (ADS)

    Lei, Shijun; Shelton, Robin L.; Henley, David B.

    2009-07-01

    We analyze a pair of Suzaku shadowing observations in order to determine the X-ray spectrum of the Galaxy's gaseous halo. Our data consist of an observation toward an absorbing filament in the southern Galactic hemisphere and an observation toward an unobscured region adjacent to the filament. We simultaneously fit the spectra with models having halo, local, and extragalactic components. The intrinsic intensities of the halo O VII triplet and O VIII Ly α emission lines are 9.98+1.10 -1.99 LU (line unit; photons cm-2 s-1 sr-1) and 2.66+0.37 -0.30 LU, respectively. These results imply the existence of hot gas with a temperature of ~106.0 K to ~107.0 K in the Galactic halo. Meanwhile, FUSE O VI observations for the same directions and SPEAR C IV observations for a nearby direction indicate the existence of hot halo gas at temperatures of ~105.0 K to ~106.0 K. This collection of data implies that the hot gas in the Galactic halo is not isothermal, but its temperature spans a relatively wide range from ~105.0 K to ~107.0 K. We therefore construct a differential emission measure (DEM) model for the halo's hot gas, consisting of two components. In each, dEM/dlog T is assumed to follow a power-law function of the temperature and the gas is assumed to be in collisional ionizational equilibrium. The low-temperature component (LTC) of the broken power-law DEM model covers the temperature range of 104.80-106.02 K with a slope of 0.30 and the high-temperature component (HTC) covers the temperature range of 106.02-107.02 K with a slope of -2.21. We compare our observations with predictions from models for hot gas in the halo. The observed spatial distribution of gas with temperatures in the range of our HTC is smoother than that of the LTC. We thus suggest that two types of sources contribute to our broken power-law model. We find that a simple model in which hot gas accretes onto the Galactic halo and cools radiatively cannot explain both the observed UV and X-ray portions of

  16. Galactic halo origin of the neutrinos detected by IceCube

    NASA Astrophysics Data System (ADS)

    Taylor, Andrew M.; Gabici, Stefano; Aharonian, Felix

    2014-05-01

    Recent IceCube results suggest that the first detection of very high energy astrophysical neutrinos have been accomplished. We consider these results at face value in a Galactic origin context. Emission scenarios from both the Fermi bubble and broader halo region are considered. We motivate that such an intensity of diffuse neutrino emission could be Galactic in origin if it is produced from an outflow into the halo region. This scenario requires cosmic ray transport within the outflow environment to be different to that inferred locally within the disk and that activity in the central part of the Galaxy accelerates cosmic rays to trans-"knee" energies before they escape into an outflow. The presence of a large reservoir of gas in a very extended halo around the Galaxy, recently inferred from x-ray observations, implies that the relatively modest acceleration power of 1039 erg s-1 in PeV energy cosmic rays may be sufficient to explain the observed neutrino flux. Such a luminosity is compatible with that required to explain the observed intensity of cosmic rays around the knee.

  17. A hierarchical model for the ages of Galactic halo white dwarfs

    NASA Astrophysics Data System (ADS)

    Si, Shijing; van Dyk, David A.; von Hippel, Ted; Robinson, Elliot; Webster, Aaron; Stenning, David

    2017-07-01

    In astrophysics, we often aim to estimate one or more parameters for each member object in a population and study the distribution of the fitted parameters across the population. In this paper, we develop novel methods that allow us to take advantage of existing software designed for such case-by-case analyses to simultaneously fit parameters of both the individual objects and the parameters that quantify their distribution across the population. Our methods are based on Bayesian hierarchical modelling that is known to produce parameter estimators for the individual objects that are on average closer to their true values than estimators based on case-by-case analyses. We verify this in the context of estimating ages of Galactic halo white dwarfs (WDs) via a series of simulation studies. Finally, we deploy our new techniques on optical and near-infrared photometry of 10 candidate halo WDs to obtain estimates of their ages along with an estimate of the mean age of Galactic halo WDs of 12.11_{-0.86}^{+0.85} Gyr. Although this sample is small, our technique lays the ground work for large-scale studies using data from the Gaia mission.

  18. An Update on Monitoring Stellar Orbits in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Gillessen, S.; Plewa, P. M.; Eisenhauer, F.; Sari, R.; Waisberg, I.; Habibi, M.; Pfuhl, O.; George, E.; Dexter, J.; von Fellenberg, S.; Ott, T.; Genzel, R.

    2017-03-01

    Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center, we present an update of the main results from this unique data set: a measurement of mass and distance to Sgr A*. Our progress is not only due to the eight-year increase in time base, but also to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to Sgr A* the statistical errors of 0.13× {10}6 {M}⊙ and 0.12 kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, the star S1 also yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M=4.28+/- 0.10{| }{stat.}+/- 0.21{| }{sys}× {10}6 {M}⊙ and {R}0=8.32+/- 0.07{| }{stat.}+/- 0.14{| }{sys} {kpc}. These numbers are in agreement with the recent determination of R 0 from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from Sgr A*, and of the radio source Sgr A* agree to within 1 mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars that we can explicitly show are members of the clockwise disk of young stars, and which have lower-eccentricity orbits.

  19. Connecting stellar mass and star-formation rate to dark matter halo mass out to z ˜ 2

    NASA Astrophysics Data System (ADS)

    Wang, L.; Farrah, D.; Oliver, S. J.; Amblard, A.; Béthermin, M.; Bock, J.; Conley, A.; Cooray, A.; Halpern, M.; Heinis, S.; Ibar, E.; Ilbert, O.; Ivison, R. J.; Marsden, G.; Roseboom, I. G.; Rowan-Robinson, M.; Schulz, B.; Smith, A. J.; Viero, M.; Zemcov, M.

    2013-05-01

    We have constructed an extended halo model (EHM) which relates the total stellar mass and star-formation rate (SFR) to halo mass (Mh). An empirical relation between the distribution functions of total stellar mass of galaxies and host halo mass, tuned to match the spatial density of galaxies over 0 < z < 2 and the clustering properties at z ˜ 0, is extended to include two different scenarios describing the variation of SFR on Mh. We also present new measurements of the redshift evolution of the average SFR for star-forming galaxies of different stellar masses up to z = 2, using data from the Herschel Multi-tiered Extragalactic Survey for infrared bright galaxies. Combining the EHM with the halo accretion histories from numerical simulations, we trace the stellar mass growth and star-formation history in haloes spanning a range of masses. We find that: (1) the intensity of the star-forming activity in haloes in the probed mass range has steadily decreased from z ˜ 2 to 0; (2) at a given epoch, haloes in the mass range between a few times 1011 M⊙ and a few times 1012 M⊙ are the most efficient at hosting star formation; (3) the peak of SFR density shifts to lower mass haloes over time; and (4) galaxies that are forming stars most actively at z ˜ 2 evolve into quiescent galaxies in today's group environments, strongly supporting previous claims that the most powerful starbursts at z ˜ 2 are progenitors of today's elliptical galaxies.

  20. Characterizing stellar halo populations II: the age gradient in blue horizontal-branch stars

    NASA Astrophysics Data System (ADS)

    Das, Payel; Williams, Angus; Binney, James

    2016-12-01

    The distribution of Milky Way halo blue horizontal-branch (BHB) stars is examined using action-based extended distribution functions (EDFs) that describe the locations of stars in phase space, metallicity, and age. The parameters of the EDFs are fitted using stars observed in the Sloan Extension for Galactic Understanding and Exploration-II (SEGUE-II) survey that traces the phase-space kinematics and chemistry out to ˜70 kpc. A maximum a posteriori probability (MAP) estimate method and a Markov Chain Monte Carlo method are applied, taking into account the selection function in positions, distance, and metallicity for the survey. The best-fitting EDF declines with actions less steeply at actions characteristic of the inner halo than at the larger actions characteristic of the outer halo, and older ages are found at smaller actions than at larger actions. In real space, the radial density profile steepens smoothly from -2 at ˜2 kpc to -4 in the outer halo, with an axis ratio ˜0.7 throughout. There is no indication for rotation in the BHBs, although this is highly uncertain. A moderate level of radial anisotropy is detected, with βs varying from isotropic to between ˜0.1 and ˜0.3 in the outer halo depending on latitude. The BHB data are consistent with an age gradient of -0.03 Gyr kpc-1, with some uncertainty in the distribution of the larger ages. These results are consistent with a scenario in which older, larger systems contribute to the inner halo, whilst the outer halo primarily comprises younger, smaller systems.

  1. 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

  2. Probing ionization conditions of Galactic halo gas using H-alpha observations of the Magellanic Stream

    NASA Astrophysics Data System (ADS)

    Barger, Kat; Madsen, Gregory J.; Fox, Andrew; Wakker, Bart P.; Bland-Hawthorn, Jonathan; Nidever, David L.; Lehner, Nicolas; Haffner, L. Matthew; Hill, Alex S.

    2017-01-01

    Galaxy interactions have greatly disturbed and redistributed the gas in the Magellanic System throughout the halos of the Milky Way. Using the Wisconsin H-alpha Mapper (WHAM) telescope, we have completed the highest sensitivity and kinematically resolved emission-line survey of the entire Magellanic Stream. These observations enable us to determine how the ionization conditions change over 100-degrees across the sky, including the region below the South Galactic Pole. We explore the sources of that ionization and find that photoionization from the Milky Way and Magellanic Clouds is insufficient to explain the observed H-alpha emission. We further investigate whether energetic processes associated with the Milky Way's center or interactions with the halo could provide the remaining ionization. The gas in the Magellanic Steam could supply enough gas to maintain or even boost the star formation in the Milky Way, but only if it can survive the journey to the Galaxy's disk.

  3. On the Stringent Constraint on Massive Dark Clusters in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Sánchez-Salcedo, F. J.

    1997-09-01

    This Letter revises the recent claims of a dynamical constraint on massive dark clusters from the Galactic globular cluster luminosity function (GCLF). We point out that this argument is invalid for two reasons. The first point is that with a proper sample of globular clusters, the GCLF presents a significant trend with Galactocentric position, and second, the disruption timescale of globular clusters by encounters with these massive objects depends strongly on many uncertain parameters. For the usual halo model of Cadwell & Ostriker, it may be smaller by only a factor of 2 for distant globular clusters. Therefore, the existence of massive dark clusters in the halo could be possible. This provides a scenario in which the formation of dark clusters and globular clusters may have a similar origin.

  4. Chemical Abundances of the Milky Way Thick Disk and Stellar Halo. II. Sodium, Iron-peak, and Neutron-capture Elements

    NASA Astrophysics Data System (ADS)

    Ishigaki, M. N.; Aoki, W.; Chiba, M.

    2013-07-01

    We present chemical abundance analyses of sodium, iron-peak, and neutron-capture elements for 97 kinematically selected thick disk, inner halo, and outer halo stars with metallicities -3.3 < [Fe/H] <-0.5. The main aim of this study is to examine chemical similarities and differences among metal-poor stars belonging to these old Galactic components as a clue to determine their early chemodynamical evolution. In our previous paper, we obtained abundances of α elements by performing a one-dimensional LTE abundance analysis based on the high-resolution (R ~ 50, 000) spectra obtained with the Subaru/HDS. In this paper, a similar analysis is performed to determine abundances of an additional 17 elements. We show that, in metallicities below [Fe/H] ~-2, the abundance ratios of many elements in the thick disk, inner halo, and outer halo subsamples are largely similar. In contrast, in higher metallicities ([Fe/H] gsim -1.5), differences in some of the abundance ratios among the three subsamples are identified. Specifically, the [Na/Fe], [Ni/Fe], [Cu/Fe], and [Zn/Fe] ratios in the inner and outer halo subsamples are found to be lower than those in the thick disk subsample. A modest abundance difference between the two halo subsamples in this metallicity range is also seen for the [Na/Fe] and [Zn/Fe] ratios. In contrast to that observed for [Mg/Fe] in our previous paper, [Eu/Fe] ratios are more enhanced in the two halo subsamples rather than in the thick disk subsample. The observed distinct chemical abundances of some elements between the thick disk and inner/outer halo subsamples with [Fe/H] >-1.5 support the hypothesis that these components formed through different mechanisms. In particular, our results favor the scenario that the inner and outer halo components formed through an assembly of multiple progenitor systems that experienced various degrees of chemical enrichments, while the thick disk formed through rapid star formation with an efficient mixing of chemical

  5. 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).

  6. Erratum: Evaporation, Tidal Disruption, and Orbital Decay of Star Clusters in a Galactic Halo

    NASA Astrophysics Data System (ADS)

    Capriotti, E. R.; Hawley, S. L.

    1997-07-01

    In § 2 of the recent paper ``Evaporation, Tidal Disruption, and Orbital Decay of Star Clusters in a Galactic Halo'' by E. R. Capriotti and S. L. Hawley (ApJ, 464, 765 [1996]), equation (1) contains a misprint. It should read rt=2r/3 [(Mc)/(AMH(r))]1/3/[1-r/(AMH(r)) (dMH(r))/dr]1/3 , (1)where the difference from the published version is that an A replaces the 3 in the denominator of the last term. The authors regret the error.

  7. A Rich Globular Cluster System in Dragonfly 17: Are Ultra-diffuse Galaxies Pure Stellar Halos?

    NASA Astrophysics Data System (ADS)

    Peng, Eric W.; Lim, Sungsoon

    2016-05-01

    Observations of nearby galaxy clusters at low surface brightness have identified galaxies with low luminosities, but sizes as large as L ⋆ galaxies, leading them to be dubbed “ultra-diffuse galaxies” (UDGs). The survival of UDGs in dense environments like the Coma cluster suggests that UDGs could reside in much more massive dark halos. We report the detection of a substantial population of globular clusters (GCs) around a Coma UDG, Dragonfly 17 (DF17). We find that DF17 has a high GC specific frequency of S N = 26 ± 13. The GC system is extended, with an effective radius of 12″ ± 2″, or 5.6 ± 0.9 kpc at Coma distance, 70% larger than the galaxy itself. We also estimate the mean of the GC luminosity function to infer a distance of {97}-14+17 Mpc, providing redshift-independent confirmation that one of these UDGs is in the Coma cluster. The presence of a rich GC system in DF17 indicates that, despite its low stellar density, star formation was intense enough to form many massive star clusters. If DF17's ratio of total GC mass to total halo mass is similar to those in other galaxies, then DF17 has an inferred total mass of ˜1011 M ⊙, only ˜10% the mass of the Milky Way, but extremely dominated by dark matter, with M/L V ≈ 1000. We suggest that UDGs like DF17 may be “pure stellar halos,” i.e., galaxies that formed their stellar halo components, but then suffered an early cessation in star formation that prevented the formation of any substantial central disk or bulge. Based on observations 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.

  8. The assembly of stellar haloes in massive Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Buitrago, F.

    2017-03-01

    Massive (Mstellar >= 5×1010 M⊙) Early-Type Galaxies (ETGs) must build an outer stellar envelope over cosmic time in order to account for their remarkable size evolution. This is similar to what occurs to nearby Late-Type Galaxies (LTGs), which create their stellar haloes out of the debris of lower mass systems. We analysed the outer parts of massive ETGs at z < 1 by exploiting the Hubble Ultra Deep Field imaging. These galaxies store 10-30% of their stellar mass at distances 10 < R/kpc < 50, in contrast to the low percentages (< 5%) found for LTGs. We find evidence for a progressive outskirt development with redshift driven solely via merging.

  9. RESOLVE and ECO: The Halo Mass-dependent Shape of Galaxy Stellar and Baryonic Mass Functions

    NASA Astrophysics Data System (ADS)

    Eckert, Kathleen D.; Kannappan, Sheila J.; Stark, David V.; Moffett, Amanda J.; Berlind, Andreas A.; Norris, Mark A.

    2016-06-01

    In this work, we present galaxy stellar and baryonic (stars plus cold gas) mass functions (SMF and BMF) and their halo mass dependence for two volume-limited data sets. The first, RESOLVE-B, coincides with the Stripe 82 footprint and is extremely complete down to baryonic mass M bary ˜ 109.1 M ⊙, probing the gas-rich dwarf regime below M bary ˜ 1010 M ⊙. The second, ECO, covers a ˜40× larger volume (containing RESOLVE-A) and is complete to M bary ˜ 109.4 M ⊙. To construct the SMF and BMF we implement a new “cross-bin sampling” technique with Monte Carlo sampling from the full likelihood distributions of stellar or baryonic mass. Our SMFs exhibit the “plateau” feature starting below M star ˜ 1010 M ⊙ that has been described in prior work. However, the BMF fills in this feature and rises as a straight power law below ˜1010 M ⊙, as gas-dominated galaxies become the majority of the population. Nonetheless, the low-mass slope of the BMF is not as steep as that of the theoretical dark matter halo MF. Moreover, we assign group halo masses by abundance matching, finding that the SMF and BMF, separated into four physically motivated halo mass regimes, reveal complex structure underlying the simple shape of the overall MFs. In particular, the satellite MFs are depressed below the central galaxy MF “humps” in groups with mass <1013.5 M ⊙ yet rise steeply in clusters. Our results suggest that satellite destruction and stripping are active from the point of nascent group formation. We show that the key role of groups in shaping MFs enables reconstruction of a given survey’s SMF or BMF based on its group halo mass distribution.

  10. Inflow of halo gas from the direction of the Galactic north pole

    NASA Technical Reports Server (NTRS)

    De Boer, K. S.; Savage, B. D.

    1984-01-01

    A far-UV echelle spectrum has been obtained of the UV-bright star vZ1128 in the globular cluster M3. This cluster lies in a direction 11 deg off the Galactic north pole at a distance of about 10 kpc. Only the usually strong interstellar lines are recognizable in the faint spectrum, and they show absorption at velocities from near +40 km/s to -100 km/s. Since in the direction observed the line-of-sight component of the Milky Way rotation is negligible, the detected velocities demonstrate for this direction the motion of gas from the Milky Way halo toward the disk. Gas returning to the disk in a galactic fountainlike flow may explain the observations.

  11. Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions

    NASA Astrophysics Data System (ADS)

    Dooley, Gregory A.; Peter, Annika H. G.; Vogelsberger, Mark; Zavala, Jesús; Frebel, Anna

    2016-09-01

    We investigate the effects of self-interacting dark matter (SIDM) on the tidal stripping and evaporation of satellite galaxies in a Milky Way-like host. We use a suite of five zoom-in, dark-matter-only simulations, two with velocity-independent SIDM cross-sections, two with velocity-dependent SIDM cross-sections, and one cold dark matter (CDM) simulation for comparison. After carefully assigning stellar mass to satellites at infall, we find that stars are stripped at a higher rate in SIDM than in CDM. In contrast, the total bound dark matter mass-loss rate is minimally affected, with subhalo evaporation having negligible effects on satellites for viable SIDM models. Centrally located stars in SIDM haloes disperse out to larger radii as cores grow. Consequently, the half-light radius of satellites increases, stars become more vulnerable to tidal stripping, and the stellar mass function is suppressed. We find that the ratio of core radius to tidal radius accurately predicts the relative strength of enhanced SIDM stellar stripping. Velocity-independent SIDM models show a modest increase in the stellar stripping effect with satellite mass, whereas velocity-dependent SIDM models show a large increase in this effect towards lower masses, making observations of ultrafaint dwarfs prime targets for distinguishing between and constraining SIDM models. Due to small cores in the largest satellites of velocity-dependent SIDM, no identifiable imprint is left on the all-sky properties of the stellar halo. While our results focus on SIDM, the main physical mechanism of enhanced tidal stripping of stars apply similarly to satellites with cores formed via other means.

  12. Emission from the Local Galactic Halo in the 1/4 keV Band

    NASA Astrophysics Data System (ADS)

    Juda, M.

    1994-12-01

    Pointed observations with the ROSAT PSPC toward clouds at high galactic latitude provide a unique opportunity to probe emission from the local galactic halo in the 1/4 keV band. I present data from five fields toward clouds at |b| > 60(deg) identified through their IRAS 100 microns emission, two in the north galactic hemisphere and three in the south. In four of the five fields significant shadows are detected (2 north, 2 south). The derivation of the brightness of the shadowed component depends strongly on the assumed location and amount of absorbing material. Scaling the IRAS 100 microns emission by 10(20) H atom cm(-2) /MJy sr(-1) and correcting for the difference from the observed average 21 cm derived column density, the implied brightness of the distant emitting component is the same for the two northern latitude fields at { ~ 1.2*E(-3) counts s(-1) arcmin(-2}) ; this brightness is lower than that seen in the direction of Draco (Burrows & Mendenhall 1991, Snowden et al. 1991) and higher than in Ursa Major (Snowden et al. 1994). The two southern fields also have the same derived distant brightness at nearly the same level as the northern fields, { ~ 1.0*E(-3) counts s(-1) arcmin(-2}) . Approximately 20% of this emission may be attributed to an extragalactic background (Hasinger et al. 1993). The remaining emission, { ~ 0.8*E(-3) counts s(-1) arcmin(-2}) , would be provided by the local galactic halo. If these x-rays arise from a collisionally excited plasma at a temperature of 10(6) K the required emission measure is { ~ 0.0033 cm(-6) pc}. Burrows & Mendenhall 1991, Nature, 351, 629. Hasinger et al. 1993, A&A, 275, 1. Snowden et al. 1991, Science, 252, 1529. Snowden et al. 1994, ApJ, 430, 601.

  13. Recent Results from SPLASH: Chemical Abundances and Kinematics of Andromeda's Stellar Halo

    NASA Astrophysics Data System (ADS)

    Gilbert, Karoline M.; Beaton, Rachael; Dorman, Claire

    2016-08-01

    Large scale surveys of Andromeda's resolved stellar populations have revolutionized our view of this galaxy over the past decade. The combination of large-scale, contiguous photometric surveys and pointed spectroscopic surveys has been particularly powerful for discovering substructure and disentangling the structural components of Andromeda. The SPLASH (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) survey consists of broad- and narrow-band imaging and spectroscopy of red giant branch stars in lines of sight ranging in distance from 2 kpc to more than 200 kpc from Andromeda's center. The SPLASH data reveal a power-law surface brightness profile extending to at least two-thirds of Andromeda's virial radius (Gilbert et al. 2012), a metallicity gradient extending to at least 100 kpc from Andromeda's center (Gilbert et al. 2014), and evidence of a significant population of heated disk stars in Andromeda's inner halo (Dorman et al. 2013). We are also using the velocity distribution of halo stars to measure the tangential motion of Andromeda (Beaton et al., in prep).

  14. Exploring the connection between stellar halo profiles and accretion histories in L * galaxies

    NASA Astrophysics Data System (ADS)

    Amorisco, Nicola C.

    2017-03-01

    I use a library of controlled minor merger N-body simulations, a particle tagging technique and Monte Carlo generated ΛCDM accretion histories to study the highly stochastic process of stellar deposition onto the accreted stellar halos (ASHs) of L * galaxies. I explore the main physical mechanisms that drive the connection between the accretion history and the density profile of the ASH. I find that: i) through dynamical friction, more massive satellites are more effective at delivering their stars deeper into the host; ii) as a consequence, ASHs feature a negative gradient between radius and the local mass-weighed virial satellite-to-host mass ratio; iii) in L * galaxies, most ASHs feature a density profile that steepens towards sharper logarithmic slopes at increasing radii, though with significant halo-to-halo scatter; iv) the ASHs with the largest total ex-situ mass are such because of the chance accretion of a small number of massive satellites (rather than of a large number of low-mass ones).

  15. Reliability of the Measured Velocity Anisotropy of the Milky Way Stellar Halo

    NASA Astrophysics Data System (ADS)

    Hattori, Kohei; Valluri, Monica; Loebman, Sarah R.; Bell, Eric F.

    2017-06-01

    Determining the velocity distribution of halo stars is essential for estimating the mass of the Milky Way and for inferring its formation history. Since the stellar halo is a dynamically hot system, the velocity distribution of halo stars is well described by the three-dimensional velocity dispersions ({σ }r,{σ }θ ,{σ }φ ) or by the velocity anisotropy parameter β =1-({σ }θ 2+{σ }φ 2)/(2{σ }r2). Direct measurements of ({σ }r,{σ }θ ,{σ }φ ) consistently suggest β = 0.5-0.7 for nearby halo stars. In contrast, the value of β at large Galactocentric radius r is still controversial, since reliable proper motion data are available for only a handful of stars. In the last decade, several authors have tried to estimate β for distant halo stars by fitting the observed line-of-sight velocities at each radius with simple velocity distribution models (local fitting methods). Some results of local fitting methods imply β < 0 at r≳ 20 {kpc}, which is inconsistent with recent predictions from cosmological simulations. Here we perform mock-catalog analyses to show that the estimates of β based on local fitting methods are reliable only at r≤slant 15 {kpc} with the current sample size (˜103 stars at a given radius). As r increases, the line-of-sight velocity (corrected for the solar reflex motion) becomes increasingly closer to the Galactocentric radial velocity, so it becomes increasingly more difficult to estimate the tangential velocity dispersion ({σ }θ ,{σ }φ ) from the line-of-sight velocity distribution. Our results suggest that the forthcoming Gaia data will be crucial for understanding the velocity distribution of halo stars at r≥slant 20 {kpc}.

  16. Identifying Galactic halo PN candidates in the imaging surveys: J-PLUS/S-PLUS and J-PAS

    NASA Astrophysics Data System (ADS)

    Gutiérrez-Soto, L.; Gonçalves, D. R.; Akras, S.; Cortesi, A.; Ederoclite, T.; Aparício-Villegas, T.; Borges-Fernandes, M.; Daflon, S.; Pereira, C. B.; Mendes de Oliveira, C.; Viironen, K.; J-PAS Collaboration

    2017-07-01

    Halo planetary nebulae (HPNe) are able to reveal important information about stellar and chemical evolution in galaxies. Their characteristic low continuum and strong emission lines make them good objects to be searched by multi-filter imaging surveys. Given that only 14 HPNe are known in the Galaxy, we are exploring colour-colour diagrams to search for these sources in Javalambre/Southern Photometric Local Universe Survey (J-PLUS/S-PLUS) and the Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS). They are narrow- and broad-band imaging cosmological surveys, with 12 and 54 filters, respectively. The J-PAS survey will be able to observe 85002 of Northern sky, it will detect sources up to magnitude mAB˜23. In the case of the J-PLUS survey the limit magnitudes is around mAB˜21.5. The S-PLUS survey will observe more than 60002 and it will map the Southern sky. Other optical emission lines sources, such as Galactic and extragalactic symbiotic stars (SySts), cataclysmic variables (CVs), QSOs at different redshifts, star-forming galaxies (SFGs), extragalactic H II regions and supernova remnants (SNR) can mimic PNe. Therefore, we explore different colour-colour diagrams in order to highlight those that can better identify HPN candidates, separating them from these other objects.

  17. Stellar envelopes of globular clusters embedded in dark mini-haloes

    NASA Astrophysics Data System (ADS)

    Peñarrubia, Jorge; Varri, Anna Lisa; Breen, Philip G.; Ferguson, Annette M. N.; Sánchez-Janssen, Rubén

    2017-10-01

    We show that hard encounters in the central regions of globular clusters embedded in dark matter (DM) haloes necessarily lead to the formation of gravitationally-bound stellar envelopes that extend far beyond the nominal tidal radius of the system. Using statistical arguments and numerical techniques we derive the equilibrium distribution function of stars ejected from the centre of a non-divergent spherical potential. Independently of the velocity distribution with which stars are ejected, GC envelopes have density profiles that approach asymptotically $\\rho\\sim r^{-4}$ at large distances and become isothermal towards the centre. Adding a DM halo component leaves two clear-cut observational signatures: (i) a flattening, or slightly increase of the projected velocity dispersion profile at large distances, and (ii) an outer surface density profile that is systematically shallower than in models with no dark matter.

  18. A Comprehensive Analysis of Uncertainties Affecting the Stellar Mass-Halo Mass Relation for 0

    SciTech Connect

    Behroozi, Peter S.; Conroy, Charlie; Wechsler, Risa H.

    2010-06-07

    We conduct a comprehensive analysis of the relationship between central galaxies and their host dark matter halos, as characterized by the stellar mass - halo mass (SM-HM) relation, with rigorous consideration of uncertainties. Our analysis focuses on results from the abundance matching technique, which assumes that every dark matter halo or subhalo above a specific mass threshold hosts one galaxy. We provide a robust estimate of the SM-HM relation for 0 < z < 1 and discuss the quantitative effects of uncertainties in observed galaxy stellar mass functions (GSMFs) (including stellar mass estimates and counting uncertainties), halo mass functions (including cosmology and uncertainties from substructure), and the abundance matching technique used to link galaxies to halos (including scatter in this connection). Our analysis results in a robust estimate of the SM-HM relation and its evolution from z=0 to z=4. The shape and evolution are well constrained for z < 1. The largest uncertainties at these redshifts are due to stellar mass estimates (0.25 dex uncertainty in normalization); however, failure to account for scatter in stellar masses at fixed halo mass can lead to errors of similar magnitude in the SM-HM relation for central galaxies in massive halos. We also investigate the SM-HM relation to z = 4, although the shape of the relation at higher redshifts remains fairly unconstrained when uncertainties are taken into account. We find that the integrated star formation at a given halo mass peaks at 10-20% of available baryons for all redshifts from 0 to 4. This peak occurs at a halo mass of 7 x 10{sup 11} M{sub {circle_dot}} at z = 0 and this mass increases by a factor of 5 to z = 4. At lower and higher masses, star formation is substantially less efficient, with stellar mass scaling as M{sub *} {approx} M{sub h}{sup 2.3} at low masses and M{sub *} {approx} M{sub h}{sup 0.29} at high masses. The typical stellar mass for halos with mass less than 10{sup 12} M

  19. High S/N Observations of Low-Ionization Gas Through the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Meyer, D. M.; Roth, K. C.; Savage, B. D.; Lu, L.

    1993-12-01

    Optical absorption-line studies of extragalactic objects can now provide a sensitive probe of low-ionization gas over the full extent of the Galactic halo. Such work is particularly pertinent to a better understanding of the distances, metallicities, and sky coverage of the high-velocity clouds (HVCs) primarily observed in H I 21 cm emission. We have recently obtained high S/N, high resolution (20 km s(-1) ) KPNO 4-m echelle observations of the Ca II absorption toward the QSO 1821+643, the Seyfert galaxy Mkn 231, and SN 1993J in the galaxy M81. We detect a weak (W_lambda ~30 m Angstroms) Ca II component at an LSR velocity of -140 km s(-1) toward 1821+643 that corresponds to the Outer Arm H I HVC Complex. In the case of Mkn 231, we find no evidence of high-velocity Ca II absorption despite the location of this sightline near H I HVC Complex C. Our Ca II observations toward SN 1993J are especially exceptional in quality (S/N~500) and reveal absorption due to the Galactic halo, the disk of M81, and intergalactic material in the M81 group. Although the M81 disk gas dominates the absorption in the velocity region encompassing HVC Complex C, we do find a high-velocity component at +228 km s(-1) in Ca II that has also been seen in Mg II absorption with HST (Bowen et al. 1994, Ap. J. (Letters), in press). Our echelle spectra of SN 1993J also reveal detections of other interstellar atoms and molecules such as Ti II, Ca I, and CH(+) \\@. The Ti II measurement is particularly interesting in that it represents the first detection of Ti II toward an extragalactic object and indicates a Ti II scale height of about 1200 pc which is somewhat less than expected from observations of Ti II toward halo stars.

  20. Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, B.

    2003-01-01

    The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory to study the X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in the existing experimental and theoretical data and are needed to explain all or part of the observed X-ray emission from the Galactic Ridge, solar and stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae.

  1. THE INTERGALACTIC STELLAR POPULATION FROM MERGERS OF ELLIPTICAL GALAXIES WITH DARK MATTER HALOS

    SciTech Connect

    Gonzalez-Garcia, A. Cesar; Stanghellini, Letizia; Manchado, Arturo

    2010-02-20

    We present simulations of dry-merger encounters between pairs of elliptical galaxies with dark matter halos. The aim of these simulations is to study the intergalactic (IG) stellar populations produced in both parabolic and hyperbolic encounters. We model progenitor galaxies with total-to-luminous mass ratios M{sub T} /M{sub L}= 3 and 11. The initial mass of the colliding galaxies are chosen so that M{sub 1}/M{sub 2} = 1 and 10. The model galaxies are populated by particles representing stars, as in Stanghellini et al., and dark matter. Merger remnants resulting from these encounters display a population of unbounded particles, both dark and luminous. The number of particles becoming unbounded depends on orbital configuration, with hyperbolic encounters producing a larger luminous intracluster population than parabolic encounters. Furthermore, in simulations with identical orbital parameters, a lower M{sub T} /M{sub L} of the colliding galaxies produces a larger fraction of unbounded luminous particles. For each modeled collision, the fraction of unbounded to initial stellar mass is the same in all mass bins considered, similarly to what we found previously by modeling encounters of galaxies without dark halos. The fraction of IG to total luminosity resulting from our simulations is {approx}4% and {approx}6% for dark-to-bright mass ratios of 10 and 2, respectively. These unbounded-to-total luminous fractions are down from the 17% that we had previously found in the case of no dark halos. Our results are in broad agreement with IG light observed in groups of galaxies, while the results of our previous models without dark halos better encompass observed intracluster populations. We suggest a possible formation scenario of IG stars.

  2. Tracing Galaxy Formation with Stellar Halos. II. Relating Substructure in Phase and Abundance Space to Accretion Histories

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn V.; Bullock, James S.; Sharma, Sanjib; Font, Andreea; Robertson, Brant E.; Leitner, Samuel N.

    2008-12-01

    This paper explores the mapping between the observable properties of a stellar halo in phase and abundance space and the parent galaxy's accretion history in terms of the characteristic epoch of accretion and mass and orbits of progenitor objects. The study utilizes a suite of 11 stellar halo models constructed within the context of a standard ΛCDM cosmology. The results demonstrate that coordinate-space studies are sensitive to the recent (0-8 Gyr ago) merger histories of galaxies (this timescale corresponds to the last few percent to tens of percent of mass accretion for a Milky Way-type galaxy). Specifically, the frequency, sky coverage, and fraction of stars in substructures in the stellar halo as a function of surface brightness are indicators of the importance of recent merging and of the luminosity function of infalling dwarfs. The morphology of features serves as a guide to the orbital distribution of those dwarfs. Constraints on the earlier merger history (>8 Gyr ago) can be gleaned from the abundance patterns in halo stars: within our models, dramatic differences in the dominant epoch of accretion or luminosity function of progenitor objects leave clear signatures in the [α/Fe] and [Fe/H] distributions of the stellar halo; halos dominated by very early accretion have higher average [α/Fe], while those dominated by high-luminosity satellites have higher [Fe/H]. This insight can be applied to reconstruct much about the merger histories of nearby galaxies from current and future data sets.

  3. THE STELLAR-TO-HALO MASS RELATION OF LOCAL GALAXIES SEGREGATES BY COLOR

    SciTech Connect

    Rodríguez-Puebla, Aldo; Yang, Xiaohu; Foucaud, Sebastien; Jing, Y. P.; Avila-Reese, Vladimir; Drory, Niv

    2015-02-01

    By means of a statistical approach that combines different semi-empirical methods of galaxy-halo connection, we derive the stellar-to-halo mass relations (SHMR) of local blue and red central galaxies. We also constrain the fraction of halos hosting blue/red central galaxies and the occupation statistics of blue and red satellites as a function of halo mass, M {sub h}. For the observational input we use the blue and red central/satellite galaxy stellar mass functions and two-point correlation functions in the stellar mass range of 9 < log(M {sub *}/M {sub ☉}) <12. We find that: (1) the SHMR of central galaxies is segregated by color, with blue centrals having a SHMR above that of red centrals; at log(M {sub h}/M {sub ☉}) ∼12, the M {sub *}-to-M {sub h} ratio of the blue centrals is ≈0.05, which is ∼1.7 times larger than the value of red centrals. (2) The constrained scatters around the SHMRs of red and blue centrals are ≈0.14 and ≈0.11 dex, respectively. The scatter of the average SHMR of all central galaxies changes from ∼0.20 dex to ∼0.14 dex in the 11.3 < log(M {sub h}/M {sub ☉}) <15 range. (3) The fraction of halos hosting blue centrals at M{sub h}=10{sup 11} M {sub ☉} is 87%, but at 2 × 10{sup 12} M {sub ☉} decays to ∼20%, approaching a few percent at higher masses. The characteristic mass at which this fraction is the same for blue and red galaxies is M{sub h}≈7×10{sup 11} M {sub ☉}. Our results suggest that the SHMR of central galaxies at large masses is shaped by mass quenching. At low masses processes that delay star formation without invoking too strong supernova-driven outflows could explain the high M {sub *}-to-M {sub h} ratios of blue centrals as compared to those of the scarce red centrals.

  4. Mapping stellar content to dark matter haloes using galaxy clustering and galaxy-galaxy lensing in the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2015-12-01

    The mapping between the distributions of the observed galaxy stellar mass and the underlying dark matter haloes provides the crucial link from theories of large-scale structure formation to interpreting the complex phenomena of galaxy formation and evolution. We develop a novel statistical method, based on the halo occupation distribution (HOD) model, to solve for this mapping by jointly fitting the galaxy clustering and the galaxy-galaxy lensing from the Sloan Digital Sky Survey (SDSS). The method, called the iHOD model, extracts maximum information from the survey by including ˜80 per cent more galaxies than the traditional HOD methods, accounting for the incompleteness of the stellar mass samples self-consistently. The derived stellar-to-halo mass relation (SHMR) explains the clustering and lensing of SDSS galaxies over four decades in stellar mass, while successfully predicting the observed stellar mass functions (SMFs). By modelling significantly more galaxies, the iHOD breaks the degeneracy between the logarithmic scatter in the stellar mass at fixed halo mass and the slope of the mean SHMR at high masses, without assuming a strong prior on the scatter and/or using the SMF as an input. We detect a decline of the scatter with halo mass, from 0.22_{-0.01}^{+0.02} dex below 1012 h-1 M⊙ to 0.18 ± 0.01 dex at 1014 h-1 M⊙. The model predicts a departure of satellite SMFs from the Schechter form in massive haloes and a linear scaling of satellite number with halo mass. The iHOD model can be easily applied to other spectroscopic data sets, greatly improving statistical constraints on the SHMR compared to traditional HOD methods within the same survey.

  5. Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

    NASA Technical Reports Server (NTRS)

    Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

    1975-01-01

    The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

  6. Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

    NASA Technical Reports Server (NTRS)

    Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

    1975-01-01

    The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

  7. HOT GAS IN THE GALACTIC THICK DISK AND HALO NEAR THE DRACO CLOUD

    SciTech Connect

    Shelton, R. L.; Henley, D. B.; Dixon, W. V. E-mail: dbh@physast.uga.ed

    2010-10-10

    This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of {approx}10{sup 5} to {approx}3 x 10{sup 6} K. We measured the O VI, O VII, and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p{sub th}/k = 6500{sup +2500}{sub -2600} K cm{sup -3}, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII intensities were compared with those predicted by theoretical models. Gas which was heated to 3 x 10{sup 6} K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 10{sup 5} K < T < 10{sup 6} K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.

  8. Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud

    NASA Astrophysics Data System (ADS)

    Shelton, R. L.; Henley, D. B.; Dixon, W. V.

    2010-10-01

    This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of ~105 to ~3 × 106 K. We measured the O VI, O VII, and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p th/k = 6500+2500 -2600 K cm-3, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII intensities were compared with those predicted by theoretical models. Gas which was heated to 3 × 106 K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 105 K < T < 106 K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.

  9. Searching for Gravitational Radiation from Binary Black Hole MACHOs in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Brown, Duncan A.

    2007-05-01

    The Laser Interferometer Gravitational Wave Observatory (LIGO) is one of a new generation of detectors of gravitational radiation. The existence of gravitational radiation was first predicted by Einstein in 1916, however gravitational waves have not yet been directly observed. One source of gravitation radiation is binary inspiral. Two compact bodies orbiting each other, such as a pair of black holes, lose energy to gravitational radiation. As the system loses energy the bodies spiral towards each other. This causes their orbital speed and the amount of gravitational radiation to increase, producing a characteristic ``chirp'' waveform in the LIGO sensitive band. In this thesis, matched filtering of LIGO science data is used to search for low mass binary systems in the halo of dark matter surrounding the Milky Way. Observations of gravitational microlensing events of stars in the Large Magellanic Cloud suggest that some fraction of the dark matter in the halo may be in the form of Massive Astrophysical Compact Halo Objects (MACHOs). It has been proposed that low mass black holes formed in the early universe may be a component of the MACHO population; some fraction of these black hole MACHOs will be in binary systems and detectable by LIGO. The inspiral from a MACHO binary composed of two 0.5 solar mass black holes enters the LIGO sensitive band around 40 Hz. The chirp signal increases in amplitude and frequency, sweeping through the sensitive band to 4400 Hz in 140 seconds. By using evidence from microlensing events and theoretical predictions of the population an upper limit is placed on the rate of black hole MACHO inspirals in the galactic halo.

  10. 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

  11. ARGOS - III. Stellar populations in the Galactic bulge of the Milky Way

    NASA Astrophysics Data System (ADS)

    Ness, M.; Freeman, K.; Athanassoula, E.; Wylie-de-Boer, E.; Bland-Hawthorn, J.; Asplund, M.; Lewis, G. F.; Yong, D.; Lane, R. R.; Kiss, L. L.

    2013-04-01

    We present the metallicity results from the ARGOS spectroscopic survey of the Galactic bulge. Our aim is to understand the formation of the Galactic bulge: did it form via mergers, as expected from Λ cold dark matter theory, or from disc instabilities, as suggested by its boxy/peanut shape, or both? Our stars are mostly red clump giants, which have a well-defined absolute magnitude from which distances can be determined. We have obtained spectra for 28 000 stars at a spectral resolution of R = 11 000. From these spectra, we have determined stellar parameters and distances to an accuracy of <1.5 kpc. The stars in the inner Galaxy span a large range in [Fe/H], -2.8 ≤ [Fe/H] ≤ +0.6. From the spatial distribution of the red clump stars as a function of [Fe/H], we propose that the stars with [Fe/H] > -0.5 are part of the boxy/peanut bar/bulge. We associate the lower metallicity stars ([Fe/H] < -0.5) with the thick disc, which may be puffed up in the inner region, and with the inner regions of the metal-weak thick disc and inner halo. For the bulge stars with [Fe/H] > -0.5, we find two discrete populations: (i) stars with [Fe/H] ≈ -0.25 which provide a roughly constant fraction of the stars in the latitude interval b = -5° to -10°, and (ii) a kinematically colder, more metal-rich population with mean [Fe/H] ≈ +0.15 which is more prominent closer to the plane. The changing ratio of these components with latitude appears as a vertical abundance gradient of the bulge. We attribute both of these bulge components to instability-driven bar/bulge formation from the thin disc. We associate the thicker component with the stars of the early less metal-rich thin disc, and associate the more metal-rich population concentrated to the plane with the colder more metal-rich stars of the early thin disc, similar to the colder and younger more metal-rich stars seen in the thin disc in the solar neighbourhood today. We do not exclude a weak underlying classical merger

  12. 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.

  13. 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.

  14. 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

  15. The Outer Halo -- Halo Origins and Mass of the Galaxy

    NASA Astrophysics Data System (ADS)

    Morrison, Heather; Arabadjis, John; Dohm-Palmer, Robbie; Freeman, Ken; Harding, Paul; Mateo, Mario; Norris, John; Olszewski, Ed; Sneden, Chris

    2000-02-01

    Through our detection of distant halo stars, we are now well placed to map the regions of the Galactic halo where previously only satellite galaxies and a few globular clusters were known. Mapping this region is crucial for answering questions like: How and over what timescales was the Milky Way's stellar halo assembled? What is the total mass and shape of its dark halo? The Sagittarius dwarf has demonstrated that at least some of the stellar halo was accreted. But, HOW MUCH of the halo was accreted? Our previous efforts have proven that the Washington photometric system, in conjuction with spectroscopy, is capable of efficiently and unambiguously identifying halo stars out to 100 kpc or more. We require followup spectroscopy to map velocity substructure, which is more likely visible in the outer halo because of the long dynamical timescales, and to identify the rare objects in the extreme outer halo which will constrain the shape and size of its dark halo. We are applying for 4m/RCSP time at both CTIO and KPNO to observe faint outer-halo giant and BHB candidates.

  16. Modeling the Gravitational Potential of a Cosmological Dark Matter Halo with Stellar Streams

    NASA Astrophysics Data System (ADS)

    Sanderson, Robyn E.; Hartke, Johanna; Helmi, Amina

    2017-02-01

    Stellar streams result from the tidal disruption of satellites and star clusters as they orbit a host galaxy, and can be very sensitive probes of the gravitational potential of the host system. We select and study narrow stellar streams formed in a Milky-Way-like dark matter halo of the Aquarius suite of cosmological simulations, to determine if these streams can be used to constrain the present day characteristic parameters of the halo’s gravitational potential. We find that orbits integrated in both spherical and triaxial static Navarro–Frenk–White potentials reproduce the locations and kinematics of the various streams reasonably well. To quantify this further, we determine the best-fit potential parameters by maximizing the amount of clustering of the stream stars in the space of their actions. We show that using our set of Aquarius streams, we recover a mass profile that is consistent with the spherically averaged dark matter profile of the host halo, although we ignored both triaxiality and time evolution in the fit. This gives us confidence that such methods can be applied to the many streams that will be discovered by the Gaia mission to determine the gravitational potential of our Galaxy.

  17. The Stellar Halos of Massive Elliptical Galaxies. III. Kinematics at Large Radius

    NASA Astrophysics Data System (ADS)

    Raskutti, Sudhir; Greene, Jenny E.; Murphy, Jeremy D.

    2014-05-01

    We present a two-dimensional kinematic analysis out to ~2-5 effective radii (Re ) of 33 massive elliptical galaxies with stellar velocity dispersions σ > 150 km s-1. Our observations were taken using the Mitchell Spectrograph (formerly VIRUS-P), a spectrograph with a large 107 × 107 arcsec2 field of view that allows us to construct robust, spatially resolved kinematic maps of V and σ for each galaxy extending to at least 2 Re . Using these maps, we study the radial dependence of the stellar angular momentum and other kinematic properties. We see the familiar division between slow and fast rotators persisting out to a large radius in our sample. Centrally slow rotating galaxies, which are almost universally characterized by some form of kinematic decoupling or misalignment, remain slowly rotating in their halos. The majority of fast-rotating galaxies show either increases in specific angular momentum outward or no change beyond Re . The generally triaxial nature of the slow rotators suggests that they formed through mergers, consistent with a "two-phase" picture of elliptical galaxy formation. However, we do not observe the sharp transitions in kinematics proposed in the literature as a signpost of moving from central dissipationally formed components to outer accretion-dominated halos.

  18. The stellar halos of massive elliptical galaxies. III. Kinematics at large radius

    SciTech Connect

    Raskutti, Sudhir; Greene, Jenny E.; Murphy, Jeremy D.

    2014-05-01

    We present a two-dimensional kinematic analysis out to ∼2-5 effective radii (R{sub e} ) of 33 massive elliptical galaxies with stellar velocity dispersions σ > 150 km s{sup –1}. Our observations were taken using the Mitchell Spectrograph (formerly VIRUS-P), a spectrograph with a large 107 × 107 arcsec{sup 2} field of view that allows us to construct robust, spatially resolved kinematic maps of V and σ for each galaxy extending to at least 2 R{sub e} . Using these maps, we study the radial dependence of the stellar angular momentum and other kinematic properties. We see the familiar division between slow and fast rotators persisting out to a large radius in our sample. Centrally slow rotating galaxies, which are almost universally characterized by some form of kinematic decoupling or misalignment, remain slowly rotating in their halos. The majority of fast-rotating galaxies show either increases in specific angular momentum outward or no change beyond R{sub e} . The generally triaxial nature of the slow rotators suggests that they formed through mergers, consistent with a 'two-phase' picture of elliptical galaxy formation. However, we do not observe the sharp transitions in kinematics proposed in the literature as a signpost of moving from central dissipationally formed components to outer accretion-dominated halos.

  19. Carbon star survey in the Local Group. VII. NGC 3109 a galaxy without a stellar halo

    NASA Astrophysics Data System (ADS)

    Demers, S.; Battinelli, P.; Letarte, B.

    2003-11-01

    We present a CFH12K wide field survey of the carbon star population in and around NGC 3109. Carbon stars, the brightest members of the intermediate-age population, were found nearly exclusively in and near the disk of NGC 3109, ruling out the existence of an extensive intermediate-age halo like the one found in NGC 6822. Over 400 carbon stars identified have = -4.71, confirming the nearly universality of mean magnitude of C star populations in Local Group galaxies. Star counts over the field reveal that NGC 3109 is a truncated disk shaped galaxy without an extensive stellar halo. The minor axis star counts reach the foreground density between 4' and 5', a distance that can be explained by an inclined disk rather than a spheroidal halo. We calculate a global C/M ratio of 1.75 +/- 0.20, a value expected for such a metal poor galaxy. The complete Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/795

  20. CHARACTERIZING THE FORMATION HISTORY OF MILKY WAY LIKE STELLAR HALOS WITH MODEL EMULATORS

    SciTech Connect

    Gomez, Facundo A.; O'Shea, Brian W.; Coleman-Smith, Christopher E.; Tumlinson, Jason; Wolpert, Robert L.

    2012-12-01

    We use the semi-analytic model ChemTreeN, coupled to cosmological N-body simulations, to explore how different galaxy formation histories can affect observational properties of Milky Way like galaxies' stellar halos and their satellite populations. Gaussian processes are used to generate model emulators that allow one to statistically estimate a desired set of model outputs at any location of a p-dimensional input parameter space. This enables one to explore the full input parameter space orders of magnitude faster than could be done otherwise. Using mock observational data sets generated by ChemTreeN itself, we show that it is possible to successfully recover the input parameter vectors used to generate the mock observables if the merger history of the host halo is known. However, our results indicate that for a given observational data set, the determination of 'best-fit' parameters is highly susceptible to the particular merger history of the host. Very different halo merger histories can reproduce the same observational data set, if the 'best-fit' parameters are allowed to vary from history to history. Thus, attempts to characterize the formation history of the Milky Way using these kind of techniques must be performed statistically, analyzing large samples of high-resolution N-body simulations.

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

    SciTech Connect

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

    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, and 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.

  2. Changes in interstellar atomic abundances from the galactic plane to the halo

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.

    1982-01-01

    A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron.

  3. Domain wall model in the galactic Bose-Einstein condensate halo

    SciTech Connect

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

    2013-05-01

    We assume that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [1], can present topological defects, namely domain walls, arising as the dark soliton solution for the Gross-Pitaevskii equation in a self-graviting potential. We investigate the influence that such substructures would have in the gravitational interactions within a galaxy. We find that, for the simple domain wall model proposed, the effects are too small to be identified, either by means of a local measurement of the gradient of the gravitational field or by analysing galaxy rotation curves. In the first case, the gradient of the gravitational field in the vicinity of the domain wall would be 10{sup −31} (m/s{sup 2})/m. In the second case, the ratio of the tangential velocity correction of a star due to the presence of the domain wall to the velocity in the spherical symmetric case would be 10{sup −8}.

  4. Light bending in the galactic halo by Rindler-Ishak method

    SciTech Connect

    Bhattacharya, Amrita; Nandi, Kamal K.; Isaev, Ruslan; Scalia, Massimo; Cattani, Carlo E-mail: subfear@gmail.com E-mail: ccattani@unisa.it

    2010-09-01

    After the work of Rindler and Ishak, it is now well established that the bending of light is influenced by the cosmological constant Λ appearing in the Schwarzschild-de Sitter spacetime. We show that their method, when applied to the exact Mannheim-Kazanas-de Sitter solution of the Weyl conformal gravity, nicely yields the expected answer together with several other physically interesting new terms. Apart from Λ, the solution is parametrized by a conformal parameter γ, which is known to play a dominant role in the galactic halo gravity. The application of the method yields exactly the same γ− correction to Schwarzschild bending as obtained by standard methods. Different cases are analyzed, which include some corrections to the special cases considered in the original paper by Rindler and Ishak.

  5. Particle Dark Matter in the galactic halo: results from DAMA/LIBRA

    SciTech Connect

    Bernabei, R.; Belli, P.; Nozzoli, F.; Montecchia, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Presperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, X. H.; Sheng, X. D.

    2010-02-10

    The DAMA/LIBRA experiment at the Gran Sasso National Laboratory of the I.N.F.N. has confirmed with higher sensitivity the model independent evidence for Dark Matter (DM) particles in the galactic halo obtained by the former DAMA/NaI experiment by investigating the DM annual modulation signature. Considering the data collected by DAMA/LIBRA together with the data collected by the former DAMA/NaI (cumulative exposure of 0.82 tonxyr) a confidence level of 8.2 sigma has been achieved. The experiment is in data taking; a first upgrading of the set-up has been carried out in Spetember 2008 and a second one--aiming to decrease the experimental energy threshold--is foreseen in September 2010.

  6. 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.

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

    SciTech Connect

    Faccioli, L.; Smith, M. C.; Yuan, H.-B.; Liu, X.-W.; Zhang, H.-H.; Zhao, H.-B.; Yao, J.-S. E-mail: msmith@shao.ac.cn

    2014-06-20

    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 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.

  8. Organized chaos: scatter in the relation between stellar mass and halo mass in small galaxies

    NASA Astrophysics Data System (ADS)

    Garrison-Kimmel, Shea; Bullock, James S.; Boylan-Kolchin, Michael; Bardwell, Emma

    2017-01-01

    We use Local Group galaxy counts together with the ELVIS N-body simulations to explore the relationship between the scatter and slope in the stellar mass versus halo mass relation at low masses, M⋆ ≃ 105-108 M⊙. Assuming models with lognormal scatter about a median relation of the form M_star ∝ M_halo^α, the preferred log-slope steepens from α ≃ 1.8 in the limit of zero scatter to α ≃ 2.6 in the case of 2 dex of scatter in M⋆ at fixed halo mass. We provide fitting functions for the best-fitting relations as a function of scatter, including cases where the relation becomes increasingly stochastic with decreasing mass. We show that if the scatter at fixed halo mass is large enough (≳ 1 dex) and if the median relation is steep enough (α ≳ 2), then the `too-big-to-fail' problem seen in the Local Group can be self-consistently eliminated in about ˜5-10 per cent of realizations. This scenario requires that the most massive subhaloes host unobservable ultra-faint dwarfs fairly often; we discuss potentially observable signatures of these systems. Finally, we compare our derived constraints to recent high-resolution simulations of dwarf galaxy formation in the literature. Though simulation-to-simulation scatter in M⋆ at fixed Mhalo is large among different authors (˜2 dex), individual codes produce relations with much less scatter and usually give relations that would overproduce local galaxy counts.

  9. HIERARCHICAL FORMATION OF THE GALACTIC HALO AND THE ORIGIN OF HYPER METAL-POOR STARS

    SciTech Connect

    Komiya, Yutaka; Habe, Asao; Suda, Takuma; Fujimoto, Masayuki Y.

    2009-05-01

    Extremely metal-poor (EMP) stars in the Galactic halo are unique probes into the early universe and the first stars. We construct a new program to calculate the formation history of EMP stars in the early universe with the chemical evolution, based on the merging history of the Galaxy. We show that the hierarchical structure formation model reproduces the observed metallicity distribution function and also the total number of observed EMP stars, when we take into account the high-mass initial mass function and the contribution of binaries, as proposed by Komiya et al. The low-mass survivors divide into two groups of those born before and after the mini-halos are polluted by their own first supernovae. The former has observational counterparts in the hyper metal-poor (HMP) stars below [Fe/H] < -4, while the latter represents the majority of EMP stars with {approx}<[Fe/H]> - 4. In this Letter, we focus on the origin of the extremely small iron abundances of HMP stars. We compute the change in the surface abundances of individual stars through the accretion of the metal-enriched interstellar gas along with the dynamical and chemical evolution of the Galaxy, to demonstrate that after-birth pollution of Population III stars is sufficiently effective to explain the observed abundances of HMP stars. Metal pre-enrichment by possible pair instability supernovae is also discussed, to derive constraints on their roles and on the formation of the first low-mass stars.

  10. The Galaxy-Halo Connection in High-redshift Universe: Details and Evolution of Stellar-to-halo Mass Ratios of Lyman Break Galaxies on CFHTLS Deep Fields

    NASA Astrophysics Data System (ADS)

    Ishikawa, Shogo; Kashikawa, Nobunari; Toshikawa, Jun; Tanaka, Masayuki; Hamana, Takashi; Niino, Yuu; Ichikawa, Kohei; Uchiyama, Hisakazu

    2017-05-01

    We present the results of clustering analyses of Lyman break galaxies (LBGs) at z˜ 3, 4, and 5 using the final data release of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). Deep- and wide-field images of the CFHTLS Deep Survey enable us to obtain sufficiently accurate two-point angular correlation functions to apply a halo occupation distribution analysis. The mean halo masses, calculated as < {M}h> ={10}11.7{--}{10}12.8 {h}-1 {M}⊙ , increase with the stellar-mass limit of LBGs. The threshold halo mass to have a central galaxy, {M}\\min , follows the same increasing trend as the low-z results, whereas the threshold halo mass to have a satellite galaxy, M 1, shows higher values at z=3{--}5 than z=0.5{--}1.5, over the entire stellar mass range. Satellite fractions of dropout galaxies, even at less massive halos, are found to drop sharply, from z = 2 down to less than 0.04, at z=3{--}5. These results suggest that satellite galaxies form inefficiently within dark halos at z=3{--}5, even for less massive satellites with {M}\\star < {10}10 {M}⊙ . We compute stellar-to-halo mass ratios (SHMRs) assuming a main sequence of galaxies, which is found to provide SHMRs consistent with those derived from a spectral energy distribution fitting method. The observed SHMRs are in good agreement with model predictions based on the abundance-matching method, within 1σ confidence intervals. We derive observationally, for the first time, {M}{{h}}{pivot}, which is the halo mass at a peak in the star-formation efficiency, at 3< z< 5, and it shows a small increasing trend with cosmic time at z> 3. In addition, {M}{{h}}{pivot} and its normalization are found to be almost unchanged during 0< z< 5. Our study provides observational evidence that galaxy formation is ubiquitously most efficient near a halo mass of {M}{{h}}˜ {10}12 {M}⊙ over cosmic time.

  11. ANISOTROPY AS A PROBE OF THE GALACTIC COSMIC-RAY PROPAGATION AND HALO MAGNETIC FIELD

    SciTech Connect

    Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo; Xue, Liang

    2012-05-01

    The anisotropy of cosmic rays (CRs) in the solar vicinity is generally attributed to CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two-dimensional large-scale CR anisotropy has been measured by many experiments in the TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large-scale anisotropy structures in such a wide energy range suggests that the anisotropy might be due to global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from the solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistency with the observed structure of the halo magnetic field.

  12. The Smith Cloud and its dark matter halo: survival of a Galactic disc passage

    NASA Astrophysics Data System (ADS)

    Nichols, Matthew; Mirabal, Nestor; Agertz, Oscar; Lockman, Felix J.; Bland-Hawthorn, Joss

    2014-08-01

    Under conservative assumptions about the Galaxy, the derived velocity of the Smith Cloud indicates that it will have undergone at least one passage of the Galactic disc. Using hydrodynamic simulations, we examine the present-day structure of the Smith Cloud and find that a dark matter supported cloud is able to reproduce the observed present-day neutral hydrogen mass, column density distribution and morphology. In this case, the dark matter halo becomes elongated owing to the tidal interaction with the Galactic disc. Clouds in models neglecting dark matter confinement are destroyed upon disc passage, unless the initial cloud mass is well in excess of what is observed today. We then determine integrated flux upper limits to the gamma-ray emission around such a hypothesized dark matter core in the Smith Cloud. No statistically significant core or extended gamma-ray emission are detected down to a 95 per cent confidence level upper limit of 1.4 × 10-10 ph cm-2 s-1 in the 1-300 GeV energy range. For the derived distance of 12.4 kpc, the Fermi upper limits set the first tentative constraints on the dark matter cross-sections annihilating into τ+τ- and bbar{b} for a high-velocity cloud.

  13. THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: CONFRONTING MODELS WITH XMM-NEWTON OBSERVATIONS

    SciTech Connect

    Henley, David B.; Shelton, Robin L.; Kwak, Kyujin; Joung, M. Ryan; Mac Low, Mordecai-Mark

    2010-11-01

    We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between l = 120{sup 0} and l = 240{sup 0}. These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a single-temperature plasma model. We find that the observed halo temperature is fairly constant across the sky ({approx}(1.8-2.4) x 10{sup 6} K), whereas the halo emission measure varies by an order of magnitude ({approx}0.0005-0.006 cm{sup -6} pc). When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in isolated extraplanar supernova (SN) remnants-this model predicts emission an order of magnitude too faint. A model of an SN-driven interstellar medium, including the flow of hot gas from the disk into the halo in a galactic fountain, gives good agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of {approx}2, but there are a several possible explanations for this discrepancy. We therefore conclude that a major (possibly dominant) contributor to the halo X-ray emission observed with XMM-Newton is a fountain of hot gas driven into the halo by disk SNe. However, we cannot rule out the possibility that the extended hot halo of accreted material predicted by disk galaxy formation models also contributes to the emission.

  14. Colliding galaxies: Global star formation and the creation of hot galactic halos

    NASA Astrophysics Data System (ADS)

    Hearn, Nathan Charles

    Galaxies are fundamental components of the structure of the universe, and mergers and collisions between galaxies are thought to have played an essential role in the formation of the galaxies that exist today. Collisions between galaxies of similar mass often trigger large amounts of star formation over short timescales. These collisions provide excellent laboratories for the study of collision-induced star formation and the production of hot halo material. In order to gain more insight into the processes involved in large-scale star formation, computer simulations of galaxy collisions have been compared with observations of real colliding systems exhibiting starburst activity. These comparisons show a correlation between star forming regions in the observed galaxies and regions of strong shocks and enhanced gas density that formed in the simulated systems. The evolution of structure in the simulations has been used in conjunction with observations taken at multiple wavelengths to determine the history of collision-induced star formation in these galaxies, and to calculate estimates on the timing and duration of the different star formation episodes. A number of galaxies have been found to possess extensive halos of hot gas enveloping, and sometimes extending well beyond, the visible galactic components; many of these systems have been involved in a recent collision or merger with a similarly-massive galaxy. The ram pressure and large-scale gravitational contraction that occur in the gaseous components of a colliding system can produce extensive regions of shock-heated gas; this hot material may serve to enrich an intergalactic or intracluster medium with heavy elements. I have written a new simulation code that incorporates thermal processes for the purpose of studying the role of shock heating and various cooling processes in the hot gas production mechanisms. It has been used to generate a model collision between two disk galaxies, which is compared with Arp 220

  15. Periastron shifts of stellar orbits near the Galactic Center

    NASA Astrophysics Data System (ADS)

    Rubilar, G. F.; Eckart, A.

    2001-07-01

    The presence of a 2.9+/-0.4 million solar mass object in the central stellar cluster of the Milky Way has recently been demonstrated via measurements of the stellar proper motions and radial velocities. This mass is located at the position of the compact radio source Sagittarius A* (Sgr A*) at a distance of Ro=8.0 kpc and is most likely present in the form of a massive black hole (BH). Some of the stars have a projected distance to Sgr A* of <=0.005 pc and have proper motion velocities of up to 1400 km s-1. Recent measurements indicate that their orbits show significant curvatures indicating that the stars indeed orbit the central compact object. Detailed measurements of the stellar orbits close to Sgr A* will allow us to precisely determine the distribution of this mass. With an increased point source sensitivity due to the combination of large telescope apertures, adaptive optics, and - in the very near future - NIR interferometry it is likely that stars with orbital time scales of the order of one year will be detected. Theses sources, however, will most likely not be on simple Keplerian orbits. The effects of measurable prograde relativistic and retrograde Newtonian periastron shifts will result in rosetta shaped orbits. A substantial Newtonian periastron rotation can already be expected if only a few percent of the central mass are extended. We discuss the conditions under which an extended mass can (over-) compensate the relativistic periastron shift. We also demonstrate that measuring a single periastron shift is not sufficient to determine the distribution of an extended mass component. A periastron shift will allow us to determine the inclination of the stellar orbits and to derive inclination corrected shift values. These have to be acquired for three stars on orbits with different energy or angular momentum in order to unambiguously solve for the compactness, extent and shape of any extended mass contribution.

  16. Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy

    NASA Astrophysics Data System (ADS)

    Foster, C.; Lux, H.; Romanowsky, A. J.; Martínez-Delgado, D.; Zibetti, S.; Arnold, J. A.; Brodie, J. P.; Ciardullo, R.; GaBany, R. J.; Merrifield, M. R.; Singh, N.; Strader, J.

    2014-08-01

    We study the dynamics of faint stellar substructures around the Umbrella Galaxy, NGC 4651, which hosts a dramatic system of streams and shells formed through the tidal disruption of a nucleated dwarf elliptical galaxy. We elucidate the basic characteristics of the system (colours, luminosities, stellar masses) using multiband Subaru/Suprime-Cam images. The implied stellar mass ratio of the ongoing merger event is ˜1:50. We identify candidate kinematic tracers (globular clusters, planetary nebulae, H II regions) and follow up a subset with Keck/DEIMOS (DEep Imaging Multi-object Spectrograph) spectroscopy to obtain velocities. We find that 15 of the tracers are likely associated with halo substructures, including the probable stream progenitor nucleus. These objects delineate a kinematically cold feature in position-velocity phase space. We model the stream using single test particle orbits, plus a rescaled pre-existing N-body simulation. We infer a very eccentric orbit with a period of ˜0.35 Gyr and turning points at ˜2-4 and ˜40 kpc, implying a recent passage of the satellite through the disc, which may have provoked the visible disturbances in the host galaxy. This work confirms that the kinematics of low surface brightness substructures can be recovered and modelled using discrete tracers - a breakthrough that opens up a fresh avenue for unravelling the detailed physics of minor merging.

  17. Searching for planetary nebulae at the Galactic halo via J-PAS

    NASA Astrophysics Data System (ADS)

    Gonçalves, Denise R.; Aparício-Villegas, T.; Akras, S.; Cortesi, A.; Borges-Fernandes, M.; Daflon, S.; Pereira, C. B.; Lorenz-Martins, S.; Marcolino, W.; Kanaan, A.; Viironen, K.; de Oliveira, C. Mendes; Molino, A.; Ederoclite, A.

    2016-08-01

    The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is a narrow-band imaging, very wide field cosmological survey. It will last 5 years and will observe 8500 sq. deg. of the sky. There will be 54 contiguous narrow-band filters of 145Å FWHM, from 3,500 to 10,000Å. Two broad-band filters will be added at the extremes, UV and IR, plus the 3-g, r, and i- SDSS filters. Thus, J-PAS can be an important tool to search for new planetary nebulae (PNe) at the halo, increasing their numbers, because only 14 of them have been convincingly identified in the literature. Halo PNe are able to reveal precious information for the study of stellar evolution and the early chemical conditions of the Galaxy. The characteristic low continuum and intense emission lines of PNe make them good objects to be searched by J-PAS. Though covering a significantly smaller sky area, data from the ALHAMBRA survey were used to test our J-PAS strategy to search for PNe. Our first results are shown in this contribution.

  18. Stellar mass to halo mass relation from galaxy clustering in VUDS: a high star formation efficiency at z ≃ 3

    NASA Astrophysics Data System (ADS)

    Durkalec, A.; Le Fèvre, O.; de la Torre, S.; Pollo, A.; Cassata, P.; Garilli, B.; Le Brun, V.; Lemaux, B. C.; Maccagni, D.; Pentericci, L.; Tasca, L. A. M.; Thomas, R.; Vanzella, E.; Zamorani, G.; Zucca, E.; Amorín, R.; Bardelli, S.; Cassarà, L. P.; Castellano, M.; Cimatti, A.; Cucciati, O.; Fontana, A.; Giavalisco, M.; Grazian, A.; Hathi, N. P.; Ilbert, O.; Paltani, S.; Ribeiro, B.; Schaerer, D.; Scodeggio, M.; Sommariva, V.; Talia, M.; Tresse, L.; Vergani, D.; Capak, P.; Charlot, S.; Contini, T.; Cuby, J. G.; Dunlop, J.; Fotopoulou, S.; Koekemoer, A.; López-Sanjuan, C.; Mellier, Y.; Pforr, J.; Salvato, M.; Scoville, N.; Taniguchi, Y.; Wang, P. W.

    2015-04-01

    The relation between the galaxy stellar mass M⋆ and the dark matter halo mass Mh gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We present measurements of the ratio of stellar mass to halo mass (SMHR) at redshifts 2 < z < 5, obtained from the VIMOS Ultra Deep Survey. We use halo occupation distribution (HOD) modelling of clustering measurements on ~3000 galaxies with spectroscopic redshifts to derive the dark matter halo mass Mh, and spectral energy density fitting over a large set of multi-wavelength data to derive the stellar mass M⋆ and compute the SMHR = M⋆/Mh. We find that the SMHR ranges from 1% to 2.5% for galaxies with M⋆ = 1.3 × 109 M⊙ to M⋆ = 7.4 × 109 M⊙ in DM halos with Mh = 1.3 × 1011 M⊙ to Mh = 3 × 1011 M⊙. We derive the integrated star formation efficiency (ISFE) of these galaxies and find that the star formation efficiency is a moderate 6-9% for lower mass galaxies, while it is relatively high at 16% for galaxies with the median stellar mass of the sample ~ 7 × 109 M⊙. The lower ISFE at lower masses may indicate that some efficient means of suppressing star formation is at work (like SNe feedback), while the high ISFE for the average galaxy at z ~ 3 indicates that these galaxies efficiently build up their stellar mass at a key epoch in the mass assembly process. Based on our results, we propose a possible scenario in which the average massive galaxy at z ~ 3 begins to experience truncation of its star formation within a few million years. Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Program 185.A-0791.

  19. 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

  20. AGE AND MASS SEGREGATION OF MULTIPLE STELLAR POPULATIONS IN GALACTIC NUCLEI AND THEIR OBSERVATIONAL SIGNATURES

    SciTech Connect

    Perets, Hagai B.; Mastrobuono-Battisti, Alessandra

    2014-04-01

    Nuclear stellar clusters (NSCs) are known to exist around massive black holes in galactic nuclei. They are thought to have formed through in situ star formation following gas inflow to the nucleus of the galaxy and/or through the infall of multiple stellar clusters. Here we study the latter, and explore the composite structure of the NSC and its relation to the various stellar populations originating from its progenitor infalling clusters. We use N-body simulations of cluster infalls and show that this scenario may produce observational signatures in the form of age segregation: the distribution of the stellar properties (e.g., stellar age and/or metallicity) in the NSCs reflects the infall history of the different clusters. The stellar populations of clusters, infalling at different times (dynamical ages), are differentially segregated in the NSC and are not fully mixed even after a few gigayears of evolution. Moreover, the radial properties of stellar populations in the progenitor cluster are mapped to their radial distribution in the final NSC, potentially leading to efficient mass segregation in NSCs, even those where relaxation times are longer than a Hubble time. Finally, the overall structures of the stellar populations present non-spherical configurations and show significant cluster to cluster population differences.

  1. Kinematic structure in the Galactic halo at the North Galactic Pole: RR Lyrae and blue horizontal branch stars show different kinematics

    NASA Astrophysics Data System (ADS)

    Kinman, T. D.; Cacciari, C.; Bragaglia, A.; Buzzoni, A.; Spagna, A.

    2007-03-01

    Radial velocities and proper motions (derived from the GSC-II data base) are given for 38 RR Lyrae (RRL) stars and 79 blue horizontal branch (BHB) stars in a ~200 deg2 area around the North Galactic Pole (NGP). Both heliocentric (UVW) and galactocentric (VR, Vφ, Vz) space motions are derived for these stars using a homogeneous distance scale consistent with (m - M)0 = 18.52 for the Large Magellanic Cloud (LMC). An analysis of the 26 RRL and 52 BHB stars whose height (Z) above the plane is less than 8 kpc shows that this halo sample is not homogeneous. Our BHB sample (like that of Sirko et al.) has a zero galactic rotation (Vφ) and roughly isotropic velocity dispersions. The RRL sample shows a definite retrograde rotation (Vφ = -95 +/- 29 kms-1) and non-isotropic velocity dispersions. The combined BHB and RRL sample has a retrograde galactic rotation (V) that is similar to that found by Majewski for his sample of subdwarfs in Selected Area (SA) 57. The velocity dispersion of the RRL stars that have a positive W motion is significantly smaller than the dispersion of those `streaming down' with a negative W. Also, the ratio of RRL to BHB stars is smaller for the sample that has positive W. Our halo sample occupies 10.4 kpc3 at a mean height of 5 kpc above the Galactic plane. In this volume, one component (rich in RRL stars) shows retrograde rotation and the streaming motion that we associate with the accretion process. The other component (traced by the BHB stars) shows essentially no rotation and less evidence of streaming. These two components have horizontal branch (HB) morphologies that suggest that they may be the field star equivalents of the young and old halo globular clusters, respectively. Clearly, it is quite desirable to use more than one tracer in any kinematic analysis of the halo.

  2. The extended stellar substructures of four metal-poor globular clusters in the galactic bulge

    NASA Astrophysics Data System (ADS)

    Chun, Sang-Hyun; Sohn, Young-Jong

    2015-08-01

    We investigated stellar spatial density distribution around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642 and NGC 6723) in order to find extended stellar substructures. Wide-field deep J, H, and K imaging data were taken using the WFCAM near-infrared array on United Kingdom Infrared Telescope (UKIRT). The contamination of field stars around clusters was minimised by applying a statistical weighted filtering algorithm for the stars on the color-magnitude diagram. In two-dimensional isodensity contour map, we find that all four of the globular clusters shows tidal stripping stellar features in the form of tidal tails (NGC 6266 and NGC 6723) or small density lobes/chunk (NGC 6642 and NGC 6723). The stellar substructures extend toward the Galactic centre or anticancer, and the proper motion direction of the clusters. The radial density profiles of the clusters also depart from theoretical King and Wilson models and show overdensity feature with a break in a slope of profile at the outer region of clusters. The observed results indicate that four globular clusters in the Galactic bulge have experienced strong tidal force or bulge/disk shock effect of the Galaxy. These observational results provide us further constraints to understand the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  3. Hercules and Wolf 630 stellar streams and galactic bar kinematics

    NASA Astrophysics Data System (ADS)

    Bobylev, V. V.; Bajkova, A. T.

    2016-04-01

    We have identified the four most significant features in the UV velocity distribution of solarneighborhood stars: H1, H2 in the Hercules stream and W1, W2 in the Wolf 630 stream. We have formulated the problemof determining several characteristics of the centralGalactic bar independently from each of the identified features by assuming that the Hercules and Wolf 630 streams are of a bar-induced dynamical nature. The problem has been solved by constructing 2: 1 resonant orbits in the rotating bar frame for each star in these streams. Analysis of the resonant orbits found has shown that the bar pattern speed is 45-55 km s-1 kpc-1, while the bar angle lies within the range 40°-60°. The results obtained are consistent with the view that the Hercules andWolf 630 streams could be formed by a long-term influence of the Galactic bar leading to a characteristic bimodal splitting of the UV velocity plane.

  4. COBE diffuse infrared background experiment observations of Galactic reddening and stellar populations

    NASA Technical Reports Server (NTRS)

    Arendt, R. G.; Berriman, G. B.; Boggess, N.; Dwek, E.; Hauser, M. G.; Kelsall, T.; Moseley, S. H.; Murdock, T. L.; Odegard, N.; Silverberg, R. F.

    1994-01-01

    This Letter describes the results of an initial study of Galactic extinction and the colors of Galactic stellar populations in the near-IR using the Diffuse Infrared Background Experiment (DIRBE) aboard the Cosmic Background Explorer (COBE) spacecraft. The near-IR reddening observed by DIRBE is consistent with the extinction law tabulated by Rieke & Lebofsky (1985). The distribution of dust and stars in most of the first and fourth quadrants of the Galactic plane (0 deg less than l less than 90 deg, and 270 deg less than l less than 360 deg, respectively) can be modeled as a stellar background source seen through up to approximately 4 mag of extinction at 1.25 micrometers. The unreddened near-IR colors of the Galactic disk are similar to those of late-K and M giants. The Galactic bulge exhibits slightly bluer colors in the 2.2-3.5 micrometers range, as noted by Terndrup et al. (1991). Star-forming regions exhibit colors that indicate the presence of a approximately 900 K continuum produced by hot dust or polycyclic aromatic hydrocarbons (PAHs) contributing at wavelengths as short as 3.5 micrometers.

  5. Multiple Stellar Populations in Galactic Globular Clusters: General Properties

    NASA Astrophysics Data System (ADS)

    Piotto, Giampaolo

    2015-08-01

    Globular clusters are the most ancient stellar systems for which we can have a reliable age estimate, and therefore bring information on star formation processes in the early Universe. The discovery that these objects host different, distinct populations of stars drastically changed our view on their origin and evolution. Some of the most plausible scenarios able to account for the photometric and chemical properties of multiple stellar populations in globular clusters necessarily imply that these objects must have been much more massive in the past. Whether globular clusters should be considered either as remnants of massive star clusters or nuclei of former dwarf galaxies (or both of them) is an open issue. Surely, we need to better know the chemical and kinematical properties of the different populations hosted by single clusters, and their relation with the cluster parameters, in order to shed light on this problem. Determination of the basic properties of stars hosted by (young ) massive clusters, nuclear clusters, and dwarf galaxies and a comparison with the parameters characterizing multiple stellar populations in globular cluster is a complementary approach that shall be pursued.For the first time, in my talk, I will discuss the results of a large, legacy multi-wavelength, astrometric and photometric survey based on ACS and WFC3/HST observations which include UV data. A census of the presence and frequency of multiple populations in almost half of the globular clusters of our Galaxy, their chemical tagging, radial distribution and kinematics will be presented. The relation between multiple population properties and cluster parameters will be illustrated. Consequences of these observational facts on different scenarios proposed for the formation and evolution of globular cluster stars will be critically discussed. Future perspectives towards our understanding if this complex phenomenon will be highlighted.

  6. Comparing semi-analytic particle tagging and hydrodynamical simulations of the Milky Way's stellar halo

    NASA Astrophysics Data System (ADS)

    Cooper, Andrew P.; Cole, Shaun; Frenk, Carlos S.; Le Bret, Theo; Pontzen, Andrew

    2017-08-01

    Particle tagging is an efficient, but approximate, technique for using cosmological N-body simulations to model the phase-space evolution of the stellar populations predicted, for example, by a semi-analytic model of galaxy formation. We test the technique developed by Cooper et al. (which we call stings here) by comparing particle tags with stars in a smooth particle hydrodynamic (SPH) simulation. We focus on the spherically averaged density profile of stars accreted from satellite galaxies in a Milky Way (MW)-like system. The stellar profile in the SPH simulation can be recovered accurately by tagging dark matter (DM) particles in the same simulation according to a prescription based on the rank order of particle binding energy. Applying the same prescription to an N-body version of this simulation produces a density profile differing from that of the SPH simulation by ≲10 per cent on average between 1 and 200 kpc. This confirms that particle tagging can provide a faithful and robust approximation to a self-consistent hydrodynamical simulation in this regime (in contradiction to previous claims in the literature). We find only one systematic effect, likely due to the collisionless approximation, namely that massive satellites in the SPH simulation are disrupted somewhat earlier than their collisionless counterparts. In most cases, this makes remarkably little difference to the spherically averaged distribution of their stellar debris. We conclude that, for galaxy formation models that do not predict strong baryonic effects on the present-day DM distribution of MW-like galaxies or their satellites, differences in stellar halo predictions associated with the treatment of star formation and feedback are much more important than those associated with the dynamical limitations of collisionless particle tagging.

  7. Phase-space model of a collisionless stellar cylinder embedded in a rotating halo

    NASA Astrophysics Data System (ADS)

    Kondratyev, B. P.; Kireeva, E. N.

    The phase-space model of a stellar cylindrical bar embedded in a rotating triaxial halo is constructed. The equations of motion of an individual star in the bar are derived and solved. The model has three integrals of motion and the condition of the cylinder boundary conservation is derived. The model is found to represent a four-dimensional ellipsoid in six-dimensional phase space. The phase-space distribution function of stars is derived, which depends on isolating integrals of motion. The centroid velocity field describes longitudinal shear averaged flows in the cylinder. Two non-zero components of the velocity dispersion tensor depend quadratically on coordinates and vanish at the surface of the cylindrical bar.

  8. A NEW MILKY WAY HALO STAR CLUSTER IN THE SOUTHERN GALACTIC SKY

    SciTech Connect

    Balbinot, E.; Santiago, B. X.; Da Costa, L.; Maia, M. A. G.; Rocha-Pinto, H. J.; Majewski, S. R.; Nidever, D.; Thomas, D.; Wechsler, R. H.; Yanny, B.

    2013-04-20

    We report on the discovery of a new Milky Way (MW) companion stellar system located at ({alpha}{sub J2000,}{delta}{sub J2000}) = (22{sup h}10{sup m}43{sup s}.15, 14 Degree-Sign 56 Prime 58 Double-Prime .8). The discovery was made using the eighth data release of SDSS after applying an automated method to search for overdensities in the Baryon Oscillation Spectroscopic Survey footprint. Follow-up observations were performed using Canada-France-Hawaii-Telescope/MegaCam, which reveal that this system is comprised of an old stellar population, located at a distance of 31.9{sup +1.0}{sub -1.6} kpc, with a half-light radius of r{sub h}= 7.24{sup +1.94}{sub -1.29} pc and a concentration parameter of c = log{sub 10}(r{sub t} /r{sub c} ) = 1.55. A systematic isochrone fit to its color-magnitude diagram resulted in log (age yr{sup -1}) = 10.07{sup +0.05}{sub -0.03} and [Fe/H] = -1.58{sup +0.08}{sub -0.13}. These quantities are typical of globular clusters in the MW halo. The newly found object is of low stellar mass, whose observed excess relative to the background is caused by 95 {+-} 6 stars. The direct integration of its background decontaminated luminosity function leads to an absolute magnitude of M{sub V} = -1.21 {+-} 0.66. The resulting surface brightness is {mu}{sub V} = 25.90 mag arcsec{sup -2}. Its position in the M{sub V} versus r{sub h} diagram lies close to AM4 and Koposov 1, which are identified as star clusters. The object is most likely a very faint star cluster-one of the faintest and lowest mass systems yet identified.

  9. A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

    NASA Technical Reports Server (NTRS)

    Burks, Geoffrey S.; Bartko, Frank; Shull, J. Michael; Stocke, John T.; Sachs, Elise R.; Burbidge, E. Margaret; Cohen, Ross D.; Junkkarinen, Vesa T.; Harms, Richard J.; Massa, Derck

    1994-01-01

    The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

  10. A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

    NASA Technical Reports Server (NTRS)

    Burks, Geoffrey S.; Bartko, Frank; Shull, J. Michael; Stocke, John T.; Sachs, Elise R.; Burbidge, E. Margaret; Cohen, Ross D.; Junkkarinen, Vesa T.; Harms, Richard J.; Massa, Derck

    1994-01-01

    The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

  11. Merging binaries in the Galactic Center: the eccentric Kozai-Lidov mechanism with stellar evolution

    NASA Astrophysics Data System (ADS)

    Stephan, Alexander P.; Naoz, Smadar; Ghez, Andrea M.; Witzel, Gunther; Sitarski, Breann N.; Do, Tuan; Kocsis, Bence

    2016-08-01

    Most, if not all, stars in the field are born in binary configurations or higher multiplicity systems. In dense stellar environment such as the Galactic Center (GC), many stars are expected to be in binary configurations as well. These binaries form hierarchical triple-body systems, with the massive black hole (MBH) as the third, distant object. The stellar binaries are expected to undergo large-amplitude eccentricity and inclination oscillations via the so-called `eccentric Kozai-Lidov' mechanism. These eccentricity excitations, combined with post-main-sequence stellar evolution, can drive the inner stellar binaries to merge. We study the mergers of stellar binaries in the inner 0.1 pc of the GC caused by gravitational perturbations due to the MBH. We run a large set of Monte Carlo simulations that include the secular evolution of the orbits, general relativistic precession, tides and post-main-sequence stellar evolution. We find that about 13 per cent of the initial binary population will have merged after a few Myr and about 29 per cent after a few Gyr. These expected merged systems represent a new class of objects at the GC, and we speculate that they are connected to G2-like objects and the young stellar population.

  12. Hypervelocity stars from young stellar clusters in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Fragione, G.; Capuzzo-Dolcetta, R.; Kroupa, P.

    2017-01-01

    The enormous velocities of the so called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of hypervelocity stars as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

  13. Hypervelocity stars from young stellar clusters in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Fragione, G.; Capuzzo-Dolcetta, R.; Kroupa, P.

    2017-05-01

    The enormous velocities of the so-called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of HVSs as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High-velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

  14. Dark halo response and the stellar initial mass function in early-type and late-type galaxies

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Conroy, Charlie; van den Bosch, Frank C.; Simard, Luc; Mendel, J. Trevor; Courteau, Stéphane; Dekel, Avishai; More, Surhud; Prada, Francisco

    2011-09-01

    We investigate the origin of the relations between stellar mass and optical circular velocity for early-type galaxies (ETGs) and late-type galaxies (LTGs) - the Faber-Jackson (FJ) and Tully-Fisher (TF) relations. We combine measurements of dark halo masses (from satellite kinematics and weak lensing), and the distribution of baryons in galaxies (from a new compilation of galaxy scaling relations), with constraints on dark halo structure from cosmological simulations. The principal unknowns are the halo response to galaxy formation and the stellar initial mass function (IMF). The slopes of the TF and FJ relations are naturally reproduced for a wide range of halo response and IMFs. However, models with a universal IMF and universal halo response cannot simultaneously reproduce the zero-points of both the TF and FJ relations. For a model with a universal Chabrier IMF, LTGs require halo expansion, while ETGs require halo contraction. A Salpeter IMF is permitted for high-mass (σ≳ 180 km s-1) ETGs, but is inconsistent for intermediate masses, unless Vcirc(Re)/σe≳ 1.6. If the IMF is universal and close to Chabrier, we speculate that the presence of a major merger may be responsible for the contraction in ETGs while clumpy accreting streams and/or feedback leads to expansion in LTGs. Alternatively, a recently proposed variation in the IMF disfavours halo contraction in both types of galaxies. Finally we show that our models naturally reproduce flat and featureless circular velocity profiles within the optical regions of galaxies without fine-tuning.

  15. A UNIFIED THEORY FOR THE EFFECTS OF STELLAR PERTURBATIONS AND GALACTIC TIDES ON OORT CLOUD COMETS

    SciTech Connect

    Collins, Benjamin F.; Sari, Re'em

    2010-11-15

    We examine the effects of passing field stars on the angular momentum of a nearly radial orbit of an Oort cloud comet bound to the Sun. We derive the probability density function of the change in angular momentum from one stellar encounter, assuming a uniform and isotropic field of perturbers. We show that the total angular momentum follows a Levy flight, and determine its distribution function. If there is an asymmetry in the directional distribution of perturber velocities, the marginal probability distribution of each component of the angular momentum vector can be different. The constant torque attributed to Galactic tides arises from a non-cancellation of perturbations with an impact parameter of order the semimajor axis of the comet. When the close encounters are rare, the angular momentum is best modeled by the stochastic growth of stellar encounters. If trajectories passing between the comet and the Sun occur frequently, the angular momentum exhibits the coherent growth attributed to the Galactic tides.

  16. The late-type stellar density profile in the Galactic Center: A statistical approach

    NASA Astrophysics Data System (ADS)

    Chappell, S. N.; Ghez, A. M.; Do, T.; Martinez, G. D.; Yelda, S.; Sitarski, B. N.; Lu, J. R.; Morris, M. R.

    2017-01-01

    The late-type stellar population in the Galactic Center was first predicted to reside in a dynamically relaxed cusp (power law slope ranging from 3/2 to 7/4). However, other works - which rely on models to correct for projection effects - have suggested a flat distribution instead. The need for this correction is due to the lack of information regarding the line-of-sight distances. With a two decade long baseline in astrometric measurements, we are now able to measure significant projected radial accelerations, six of which are newly reported here, which directly constrain line-of-sight distances. Here we present a statistical approach to take advantage of this information and more accurately constrain the shape of the radial density profile of the late-type stellar population in the Galactic Center.

  17. Galactic Bulge Giants: Probing Stellar and Galactic Evolution. 1. Catalogue of Spitzer IRAC and MIPS Sources (PREPRINT)

    NASA Technical Reports Server (NTRS)

    Uttenthaler, Stefan; Stute, Matthias; Sahai, Raghvendra; Blommaert, Joris A.; Schultheis, Mathias; Kraemer, Kathleen E.; Groenewegen, Martin A.; Price, Stephan D.

    2010-01-01

    Aims. We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods. To this end, we observed seven 15 15 arcmin2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.

  18. Galactic Bulge Giants: Probing Stellar and Galactic Evolution. 1. Catalogue of Spitzer IRAC and MIPS Sources (PREPRINT)

    NASA Technical Reports Server (NTRS)

    Uttenthaler, Stefan; Stute, Matthias; Sahai, Raghvendra; Blommaert, Joris A.; Schultheis, Mathias; Kraemer, Kathleen E.; Groenewegen, Martin A.; Price, Stephan D.

    2010-01-01

    Aims. We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods. To this end, we observed seven 15 15 arcmin2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.

  19. Gas motions within high-velocity cloud Complex A reveal that it is dissolving into the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Huey-You, Cannan; Barger, Kathleen; Nidever, David L.; Rueff, Katherine Meredith

    2017-01-01

    A massive gas cloud, known as Complex A, is headed towards our Galaxy. This high-velocity cloud is made up of 2 million solar masses of neutral and ionized hydrogen. This cloud is traveling through the Galactic halo, which causes a headwind that damages the cloud. Light escaping the Milky Way’s disk also hits the cloud and ionizes it. Using 21-cm radio observations from the Green Bank Telescope, we studied the motions of the gas. We found that diffuse gas is lagging behind the denser parts of the cloud. These motions suggest that gas is being stripped off the cloud and that it is dissolving into the Galactic halo. This disruptive process means that less gas will safely reach the disk of Milky Way and therefore the cloud will provide less gas for making future stars.

  20. THE STELLAR MASS–HALO MASS RELATION FOR LOW-MASS X-RAY GROUPS AT 0.5< z< 1 IN THE CDFS WITH CSI

    SciTech Connect

    Patel, Shannon G.; Kelson, Daniel D.; Williams, Rik J.; Mulchaey, John S.; Dressler, Alan; McCarthy, Patrick J.; Shectman, Stephen A.

    2015-01-30

    Since z∼1, the stellar mass density locked in low-mass groups and clusters has grown by a factor of ∼8. Here, we make the first statistical measurements of the stellar mass content of low-mass X-ray groups at 0.5stellar-to-halo mass scales for wide-field optical and infrared surveys. Groups are selected from combined Chandra and XMM-Newton X-ray observations in the Chandra Deep Field South. These ultra-deep observations allow us to identify bona fide low-mass groups at high redshift and enable measurements of their total halo masses. We compute aggregate stellar masses for these halos using galaxies from the Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Stars comprise ∼3%–4% of the total mass of group halos with masses 10{sup 12.8}halos at these redshifts, we find that the stellar-to-halo mass ratio decreases toward higher halo masses, consistent with other work in the local and high redshift universe. The observed scatter about the stellar–halo mass relation is σ∼0.25 dex, which is relatively small and suggests that total group stellar mass can serve as a rough proxy for halo mass. We find no evidence for any significant evolution in the stellar–halo mass relation since z≲1. Quantifying the stellar content in groups since this epoch is critical given that hierarchical assembly leads to such halos growing in number density and hosting increasing shares of quiescent galaxies.

  1. The cosmic assembly of stellar haloes in massive Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Buitrago, Fernando; Trujillo, Ignacio; Curtis-Lake, Emma; Montes, Mireia; Cooper, Andrew P.; Bruce, Victoria A.; Pérez-González, Pablo G.; Cirasuolo, Michele

    2017-01-01

    Using the exquisite depth of the Hubble Ultra Deep Field (HUDF12 programme) dataset, we explore the ongoing assembly of the outermost regions of the most massive galaxies (M_stellar≥5× 1010 M⊙) at z ≤ 1. The outskirts of massive objects, particularly Early-Types Galaxies (ETGs), are expected to suffer a dramatic transformation across cosmic time due to continuous accretion of small galaxies. HUDF imaging allows us to study this process at intermediate redshifts in 6 massive galaxies, exploring the individual surface brightness profiles out to ˜25 effective radii. We find that 5-20% of the total stellar mass for the galaxies in our sample is contained within 10 stellar mass stored in the outer envelopes/haloes of Massive Early-Type Galaxies increases with decreasing redshift, being 28.7% at = 0.1, 15.1% at = 0.65 and 3.5% at = 2. The fraction of mass in diffuse features linked with ongoing minor merger events is > 1-2%, very similar to predictions based on observed close pair counts. Therefore, the results for our small albeit meaningful sample suggest that the size and mass growth of the most massive galaxies have been solely driven by minor and major merging from z = 1 to today.

  2. An ancient F-type subdwarf from the halo crossing the Galactic plane

    NASA Astrophysics Data System (ADS)

    Scholz, R.-D.; Heber, U.; Heuser, C.; Ziegerer, E.; Geier, S.; Niederhofer, F.

    2015-02-01

    Aims: We selected the bluest object, WISE J0725-2351, from Luhman's new high proper motion (HPM) survey based on observations with the Wide-field Infrared Survey Explorer (WISE) for spectroscopic follow-up observations. Our aim was to unravel the nature of this relatively bright (V ~ 12, J ~ 11) HPM star (μ = 267 mas/yr). Methods: We obtained low- and medium-resolution spectra with the European Southern Observatory (ESO) New Technology Telescope (NTT)/EFOSC2 and Very Large Telescope (VLT)/X-Shooter instruments, investigated the radial velocity and performed a quantitative spectral analysis that allowed us to determine physical parameters. The fit of the spectral energy distribution based on the available photometry to low-metallicity model spectra and the similarity of our target to a metal-poor benchmark star (HD 84937) allowed us to estimate the distance and space velocity. Results: As in the case of HD 84937, we classified WISE J0725-2351 as sdF5: or a metal-poor turnoff star with [ Fe/H ] = -2.0 ± 0.2, Teff = 6250 ± 100 K, log g = 4.0 ± 0.2, and a possible age of about 12 Gyr. At an estimated distance of more than 400 pc, its proper motion translates to a tangential velocity of more than 500 km s-1. Together with its constant (on timescales of hours, days, and months) and large radial velocity (about +240 km s-1), the resulting Galactic restframe velocity is about 460 km s-1, implying a bound retrograde orbit for this extreme halo object that currently crosses the Galactic plane at high speed. Based on observations at the La Silla-Paranal Observatory of the European Southern Observatory for programmes 092.D-0040(A) and 093.D-0127(A).

  3. Gaps and length asymmetry in the stellar stream Palomar 5 as effects of Galactic bar rotation

    NASA Astrophysics Data System (ADS)

    Pearson, Sarah; Price-Whelan, Adrian M.; Johnston, Kathryn V.

    2017-09-01

    The stellar stream emerging from the globular cluster Palomar 5 (Pal 5) is one of the few Galactic streams that is clearly associated with its progenitor system. Recent optical photometric data show that Pal 5's leading arm appears truncated compared with the trailing arm, which is not expected from previous simulations. We demonstrate that inclusion of the rotating Galactic bar in the dynamical modelling of Pal 5 can reproduce the truncation. As the bar sweeps by, stream stars experience differences in net torques near their orbital pericentres. This leads to the formation of discontinuities in the energy distribution of stream members that in turn become apparent as ever-widening gaps in the stream's spatial density. We conclude that only streams orbiting far from the Galactic Centre or streams on retrograde orbits can be used to unambiguously constrain dark matter subhalo interactions. Additionally, we expect that the Pal 5 leading-arm debris should reappear south of the density truncation.

  4. Prospecting for Elements: Galactic Halo Planetary Nebulae Abundances and Virgo Spiral Galaxy Color Profiles

    NASA Astrophysics Data System (ADS)

    Howard, Joseph William

    Halo planetary nebulae. Using published spectral line data for nine halo planetary nebulae (HPNe), I have calculated photoionization models in an attempt to gain insight into the physical conditions and chemical abundances of these nebulae. The nine HPNE reported upon are K648, DdDm-1, NGC2242, NGC4361, PN243.8-37.1, PN006-41.9, M2-29, BB-1, and H4-1. The derived abundance ranges for the HPNe are: C 6.60-8.95, N 7.18-8.00, O 7.56-8.56, Ne 6.24-7.71, Ar 4.12-7.70, and S 4.90-7.00 (log(x) + 12). The temperature range for the central stars of these nebulae is 40,000 to 140,000K. Specifically, with a few exceptions, I find that all nine objects exhibit subsolar O/H; most show enhanced C/O and N/O, and a constant Ne/O ration. I also note the existence of comparatively larger abundance scatter in the HPNe as opposed to disk PNe, and suggest that this is consistent with the accretion model of halo formation formulated by Searle & Zinn. In addition, I test the effects on derived abundances and central star temperatures of a variety of model atmospheres as well as blackbodies for input ionizing spectra. I find that nebular line strengths are relatively insensitive to atmospheric details; thus blackbody spectra are suitable for central star continua. Near-infrared Virgo cluster spiral colors. Near-infrared (NIR) surface photometry in J (1.2μm), H (1.6μm) and K (2.2μm) have been obtained for a sample of Virgo cluster spirals; NGC4321, NGC4303, NGC4571, NGC4689, and NGC4254 which span a large range in HI deficiency. The spirals range from a normal gas content to a deficiency of a factor of 10 compared to normal galaxies. Using previous HII region abundance studies along with the NIR colors an attempt has been made to calibrate any correlation between the J-K index to the overall gas phase abundance gradients as a first step to probing the underlying stellar metallicity. Decomposition techniques have been used to produce estimates of spiral bulge/disk masses and luminosities

  5. Using Stellar Spectra to Constrain the Distribution of Galactic Dust

    NASA Astrophysics Data System (ADS)

    Jones, David; West, A. A.; Foster, J. B.

    2011-05-01

    We use stellar spectra from the Sloan Digital Sky Survey (SDSS) to create a high- latitude extinction map of the local Galaxy. Our technique compares spectra from SDSS stars in low-extinction lines of sight, as determined by Schlegel, Finkbeiner, & Davis, to other SDSS spectra in order to derive improved distance estimates and accurate line-of-sight extinctions. Unlike most previous studies, which have used a two-color method to determine extinction, we fit extinction curves to fluxes across a large spectral range. We apply this method to SDSS K dwarfs, nearby L dwarfs, and stars in the DR7 M dwarf sample. Our result is an extinction map that extends from tens of pc to several kpc away from the sun. We also use a similar technique to create a map of RV values within approximately 1 kpc of the sun, and find they are consistent with the widely accepted diffuse interstellar medium value of 3.1. Using our extinction data, we derive a dust scale height for the local galaxy of 119 ± 15 parsecs and find evidence for a local dust cavity.

  6. Li-7 abundances in halo stars: Testing stellar evolution models and the primordial Li-7 abundance

    NASA Technical Reports Server (NTRS)

    Chaboyer, Brian; Demarque, P.

    1994-01-01

    A large number of stellar evolution models with (Fe/H) = -2.3 and -3.3 have been calculated in order to determine the primordial Li-7 abundance and to test current stellar evolution models by a comparison to the extensive database of accurate Li abundances in extremely metal-poor halo stars observed by Thorburn (1994). Standard models with gray atmospheres do a very good job of fitting the observed Li abundances in stars hotter than approximately 5600 K. They predict a primordial. Li-7 abundance of log N(Li) = 2.24 +/- 0.03. Models which include microscopic diffusion predict a downward curvature in the Li-7 destruction isochrones at hot temperatures which is not present in the observations. Thus, the observations clearly rule out models which include uninhibited microscopic diffusion of Li-7 from the surface of the star. Rotational mixing inhibits the microscopic diffusion and the (Fe/H) = -2.28 stellar models which include both diffusion and rotational mixing provide an excellent match to the mean trend in T(sub eff) which is present in the observations. Both the plateau stars and the heavily depleted cool stars are well fit by these models. The rotational mixing leads to considerable Li-7 depletion in these models and the primordial Li-7 abundance inferred from these models is log N(Li) = 3.08 +/- 0.1. However, the (Fe/H) = -3.28 isochrones reveal problems with the combined models. These isochrones predict a trend of decreasing log N(Li) with increasing T(sub eff) which is not present in the observations. Possible causes for this discrepancy are discussed.

  7. Li-7 abundances in halo stars: Testing stellar evolution models and the primordial Li-7 abundance

    NASA Technical Reports Server (NTRS)

    Chaboyer, Brian; Demarque, P.

    1994-01-01

    A large number of stellar evolution models with (Fe/H) = -2.3 and -3.3 have been calculated in order to determine the primordial Li-7 abundance and to test current stellar evolution models by a comparison to the extensive database of accurate Li abundances in extremely metal-poor halo stars observed by Thorburn (1994). Standard models with gray atmospheres do a very good job of fitting the observed Li abundances in stars hotter than approximately 5600 K. They predict a primordial. Li-7 abundance of log N(Li) = 2.24 +/- 0.03. Models which include microscopic diffusion predict a downward curvature in the Li-7 destruction isochrones at hot temperatures which is not present in the observations. Thus, the observations clearly rule out models which include uninhibited microscopic diffusion of Li-7 from the surface of the star. Rotational mixing inhibits the microscopic diffusion and the (Fe/H) = -2.28 stellar models which include both diffusion and rotational mixing provide an excellent match to the mean trend in T(sub eff) which is present in the observations. Both the plateau stars and the heavily depleted cool stars are well fit by these models. The rotational mixing leads to considerable Li-7 depletion in these models and the primordial Li-7 abundance inferred from these models is log N(Li) = 3.08 +/- 0.1. However, the (Fe/H) = -3.28 isochrones reveal problems with the combined models. These isochrones predict a trend of decreasing log N(Li) with increasing T(sub eff) which is not present in the observations. Possible causes for this discrepancy are discussed.

  8. The complex stellar populations in the background of open clusters in the third Galactic quadrant

    NASA Astrophysics Data System (ADS)

    Carraro, Giovanni; Seleznev, Anton F.; Baume, Gustavo; Turner, David. G.

    2016-02-01

    Multicolour photometry of the stellar populations in five fields in the third Galactic quadrant centred on the clusters NGC 2215, NGC 2354, Haffner 22, Ruprecht 11, and ESO489 SC01 is interpreted in terms of a warped and flared Galactic disc, without resort to an external entity such as the popular Monoceros or Canis Major overdensities. Except for NGC 2215, the clusters are poorly or unstudied previously. The data generate basic parameters for each cluster, including the distribution of stars along the line of sight. We use star counts and photometric analysis, without recourse to Galactic-model-based predictions or interpretations, and confirms earlier results for NGC 2215 and NGC 2354. ESO489 SC01 is not a real cluster, while Haffner 22 is an overlooked cluster aged ˜2.5 Gyr. Conclusions for Ruprecht 11 are preliminary, evidence for a cluster being marginal. Fields surrounding the clusters show signatures of young and intermediate-age stellar populations. The young population background to NGC 2354 and Ruprecht 11 lies ˜8-9 kpc from the Sun and ˜1 kpc below the formal Galactic plane, tracing a portion of the Norma-Cygnus arm, challenging Galactic models that adopt a sharp cut-off of the disc 12-14 kpc from the Galactic Centre. The old population is metal-poor with an age of ˜2-3 Gyr, resembling star clusters like Tombaugh 2 or NGC 2158. It has a large colour spread and is difficult to locate precisely. Young and old populations follow a pattern that depends critically on the vertical location of the thin and/or thick disc, and whether or not a particular line of sight intersects one, both, or none.

  9. Discovery of a New, Polar-Orbiting Debris Stream in the Milky Way Stellar Halo

    SciTech Connect

    Newberg, Heidi Jo; Yanny, Brian; Willett, Benjamin A.; /Rensselaer Poly.

    2009-06-01

    We show that there is a low metallicity tidal stream that runs along l = 143{sup o} in the South Galactic Cap, about 34 kpc from the Sun, discovered from SEGUE stellar velocities. Since the most concentrated detections are in the Cetus constellation, and the orbital path is nearly polar, we name it the Cetus Polar Stream (CPS). Although it is spatially coincident with the Sgr dwarf trailing tidal tail at b = -70{sup o}, the metallicities ([Fe/H] = -2.1), ratio of blue straggler to blue horizontal branch stars, and velocities of the CPS stars differ from Sgr. Some CPS stars may contaminate previous samples of Sgr dwarf tidal debris. The unusual globular cluster NGC 5824 is located along an orbit fit to the CPS, with the correct radial velocity.

  10. DETECTION OF A DISTINCT METAL-POOR STELLAR HALO IN THE EARLY-TYPE GALAXY NGC 3115

    SciTech Connect

    Peacock, Mark B.; Strader, Jay; Romanowsky, Aaron J.; Brodie, Jean P.

    2015-02-10

    We present the resolved stellar populations in the inner and outer halo of the nearby lenticular galaxy NGC 3115. Using deep Hubble Space Telescope observations, we analyze stars 2 mag fainter than the tip of the red giant branch (TRGB). We study three fields along the minor axis of this galaxy, 19, 37, and 54 kpc from its center—corresponding to 7, 14, and 21 effective radii (r{sub e} ). Even at these large galactocentric distances, all of the fields are dominated by a relatively enriched population, with the main peak in the metallicity distribution decreasing with radius from [Z/H] ∼ –0.5 to –0.65. The fraction of metal-poor stars ([Z/H] < –0.95) increases from 17% at 16-37 kpc to 28% at ∼54 kpc. We observe a distinct low-metallicity population (peaked at [Z/H] ∼ –1.3 and with total mass 2 × 10{sup 10} M {sub ☉} ∼ 14% of the galaxy's stellar mass) and argue that this represents the detection of an underlying low-metallicity stellar halo. Such halos are generally predicted by galaxy formation theories and have been observed in several late-type galaxies, including the Milky Way and M31. The metallicity and spatial distribution of the stellar halo of NGC 3115 are consistent with the galaxy's globular cluster system, which has a similar low-metallicity population that becomes dominant at these large radii. This finding supports the use of globular clusters as bright chemodynamical tracers of galaxy halos. These data also allow us to make a precise measurement of the magnitude of the TRGB, from which we derive a distance modulus of NGC 3115 of 30.05 ± 0.05 ± 0.10{sub sys} (10.2 ± 0.2 ± 0.5{sub sys} Mpc)

  11. Quantitative chemical tagging, stellar ages and the chemo-dynamical evolution of the Galactic disc

    NASA Astrophysics Data System (ADS)

    Mitschang, A. W.; De Silva, G.; Zucker, D. B.; Anguiano, B.; Bensby, T.; Feltzing, S.

    2014-03-01

    The early science results from the new generation of high-resolution stellar spectroscopic surveys, such as Galactic Archaeology with HERMES (GALAH) and the Gaia European Southern Observatory survey (Gaia-ESO), will represent major milestones in the quest to chemically tag the Galaxy. Yet this technique to reconstruct dispersed coeval stellar groups has remained largely untested until recently. We build on previous work that developed an empirical chemical tagging probability function, which describes the likelihood that two field stars are conatal, that is, they were formed in the same cluster environment. In this work, we perform the first ever blind chemical tagging experiment, i.e. tagging stars with no known or otherwise discernible associations, on a sample of 714 disc field stars with a number of high-quality high-resolution homogeneous metal abundance measurements. We present evidence that chemical tagging of field stars does identify coeval groups of stars, yet these groups may not represent distinct formation sites, e.g. as in dissolved open clusters, as previously thought. Our results point to several important conclusions, among them that group finding will be limited strictly to chemical abundance space, e.g. stellar ages, kinematics, colours, temperature and surface gravity do not enhance the detectability of groups. We also demonstrate that in addition to its role in probing the chemical enrichment and kinematic history of the Galactic disc, chemical tagging represents a powerful new stellar age determination technique.

  12. The roles of stellar feedback and galactic environment in star-forming molecular clouds

    NASA Astrophysics Data System (ADS)

    Rey-Raposo, Ramon; Dobbs, Clare; Agertz, Oscar; Alig, Christian

    2017-01-01

    Feedback from massive stars is thought to play an important role in the evolution of molecular clouds. In this work, we analyse the effects of stellar winds and supernovae (SNe) in the evolution of two massive (˜106 M⊙) giant molecular clouds: one gravitationally bound collapsing cloud and one unbound cloud undergoing disruption by galactic shear. These two clouds have been extracted from a large-scale galaxy model and are re-simulated at a spatial resolution of ˜0.01 pc, including feedback from winds, SNe, and the combined effect of both. We find that stellar winds stop accretion of gas on to sink particles, and can also trigger star formation in the shells formed by the winds, although the overall effect is to reduce the global star formation rate of both clouds. Furthermore, we observe that winds tend to escape through the corridors of diffuse gas. The effect of SNe is not so prominent and the star formation rate is similar to models neglecting stellar feedback. We find that most of the energy injected by the SNe is radiated away, but overdense areas are created by multiple and concurrent SN events especially in the most virialized cloud. Our results suggest that the impact of stellar feedback is sensitive to the morphology of star-forming clouds, which is set by large-scale galactic flows, being of greater importance in clouds undergoing gravitational collapse.

  13. Stellar Populations And Galactic Outflows At z ˜ 3

    NASA Astrophysics Data System (ADS)

    McLinden, Emily; Rhoads, J. E.; Malhotra, S.; Finkelstein, S. L.; Hibon, P.; Richardson, M. L. A.

    2012-01-01

    We have measured a velocity offset between the Lyman-α emission line and the [OIII] nebular emission line in three spectroscopically confirmed z 3.1 Lyman-α emitting galaxies (LAEs). Such velocity offsets indicate the presence of powerful outflows in these galaxies. We made these measurements by combining near-infrared spectroscopy of the [OIII] line (from LBT/LUCIFER) with optical spectroscopy of the Lyman-α line (from MMT/Hectospec). We contend that tracing the kinematics of these galaxies is crucial for understanding how the prominent Ly-α emission from these galaxies is produced and how it escapes. LAEs are an exciting tool for studying the early universe, as Lyman-α emission is a prominent sign of young star forming galaxies at high redshift. It can be used to identify galaxy samples with characteristic continuum luminosities and stellar masses well below those typically obtained from Lyman break selection or other high-redshift galaxy search methods. To further understand what these young, low-mass objects tell us about galaxy formation, assembly, and evolution we have used our NIR spectroscopic data to demonstrate how the [OIII] emission line in the Ks filter alters SED fitting results of our z 3.1 LAEs. This information allows us to produce more accurate SED fits of those LAEs with NIR data, and predict [OIII] line fluxes in those LAEs that have yet to be observed in the NIR. Our SED fitting sample of 30 confirmed z 3.1 LAEs is one of the largest produced to date and provides a powerful look at accurate ages, masses, metallicities, dust characteristics and star formation histories of these early galaxies.

  14. The Relative Ages and Fractions of the Accreted and In Situ Populations in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Hawkins, K.; Jofré, P.; Masseron, T.

    2016-10-01

    The inner Galactic halo is thought to be formed by a combination of stars formed in situ and in dwarf galaxies that were accreted onto the Milky Way at later times. The two populations have been shown to be chemically distinct primarily in the α-elements such that the accreted population has lower [α/Fe] compared to the in situ stars at a constant metallicity. In this paper, we outline a powerful new spectral-indexing method to measure the [α/Fe] from low-resolution Sloan Digital Sky Survey spectra, and use the method in addition to turnoff temperature to study the relative age difference between, and age-metallicity relation of, the accreted and in situ populations. Our results indicate that at high metallicities the α-poor population is systematically younger than the α-rich population, but becomes coeval at low metallicities. Finally, we discuss the implication of this finding and potential applications for the new method.

  15. Dynamical evolution of the young stellar disc in the Galactic centre

    NASA Astrophysics Data System (ADS)

    Šubr, Ladislav; Haas, Jaroslav

    2012-07-01

    Origin of several hundreds of young stars in within the distance lesssim 1pc from the Galactic supermassive black hole still represents an open problem of contemporary astrophysics. In this contribution we further investigate the model which assumes their formation in situ via fragmentation of a self-gravitating gaseous disc. We show that currently observed configuration of the system of young stars can be obtained as an outcome of a dynamical evolution of a single, initially very thin stellar disc. Our model assumes the long-term evolution of the stellar disc to be determined by gravitational influence of a distant molecular torus (CND) and mutual resonances of stellar orbits within the disc.

  16. Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations

    NASA Astrophysics Data System (ADS)

    Crocker, Roland M.; Ruiter, Ashley J.; Seitenzahl, Ivo R.; Panther, Fiona H.; Sim, Stuart; Baumgardt, Holger; Möller, Anais; Nataf, David M.; Ferrario, Lilia; Eldridge, J. J.; White, Martin; Tucker, Brad E.; Aharonian, Felix

    2017-06-01

    Our Galaxy hosts the annihilation of a few 1043 low-energy positrons every second. Radioactive isotopes capable of supplying such positrons are synthesized in stars, stellar remnants and supernovae. For decades, however, there has been no positive identification of a main stellar positron source, leading to suggestions that many positrons originate from exotic sources like the Galaxy's central supermassive black hole or dark matter annihilation. Here we show that a single type of transient source, deriving from stellar populations of age 3-6 Gyr and yielding ∼0.03 M ⊙ of the positron emitter 44Ti, can simultaneously explain the strength and morphology of the Galactic positron annihilation signal and the Solar System abundance of the 44Ti decay product 44Ca. This transient is likely the merger of two low-mass white dwarfs, observed in external galaxies as the sub-luminous, thermonuclear supernova known as SN 1991bg-like.

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

    SciTech Connect

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

    2014-03-01

    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.

  18. A reservoir of ionized gas in the galactic halo to sustain star formation in the Milky Way.

    PubMed

    Lehner, Nicolas; Howk, J Christopher

    2011-11-18

    Without a source of new gas, our Galaxy would exhaust its supply of gas through the formation of stars. Ionized gas clouds observed at high velocity may be a reservoir of such gas, but their distances are key for placing them in the galactic halo and unraveling their role. We have used the Hubble Space Telescope to blindly search for ionized high-velocity clouds (iHVCs) in the foreground of galactic stars. We show that iHVCs with 90 ≤ |v(LSR)| ≲ 170 kilometers per second (where v(LSR) is the velocity in the local standard of rest frame) are within one galactic radius of the Sun and have enough mass to maintain star formation, whereas iHVCs with |v(LSR)| ≳ 170 kilometers per second are at larger distances. These may be the next wave of infalling material.

  19. Stellar Dynamics at the Galactic Center with a Thirty Meter Telescope

    NASA Astrophysics Data System (ADS)

    Weinberg, N. N.; Milosavljevic, M.

    2004-05-01

    We discuss physical experiments achievable via the infrared monitoring of stellar dynamics in the neighborhood of the massive black hole at the Galactic center with the proposed Thirty Meter Telescope (TMT). Given the likely observational capabilities of the TMT and present knowledge of the stellar environment at the Galactic Center, we construct plausible samples of stellar orbits around the black hole. Using the Markov Chain Monte Carlo method we evaluate the constraints such orbits place on the matter content within the dynamical sphere of influence of the black hole. We find that if the extended matter distribution enclosed by the orbits has a density greater than ˜ 108 M⊙ pc-3 it will produce measurable non-Keplerian effects. Thus, if the dark matter cusp at the Galactic Center matches the profiles expected in standard models of dark matter clustering, its influence will be detectable with the TMT. We also evaluate the constraint on the mass of the black hole, and the distance to the Galactic Center, and find that both can be measured to better than ˜ 0.1%. We discuss the significance of measuring the distance to within a few parsecs and the implications of the measurement for understanding the structure of the Galaxy. We demonstrate that relativistic effects, such as the prograde orbital precession, are also detectable with the TMT, though higher-order effects such as black hole spin-induced precession are not. Finally, we calculate the rate at which monitored stars undergo two-body encounters with background stars, resulting in detectable changes in orbital motions. Such encounters serve as a probe of the mass function of the background stars. We find that several such encounters are expected to be detected with the TMT over a ten year period.

  20. Internal Stellar Kinematics of M32 from the SPLASH Survey: Dark Halo Constraints

    NASA Astrophysics Data System (ADS)

    Howley, K. M.; Guhathakurta, P.; van der Marel, R.; Geha, M.; Kalirai, J.; Yniguez, B.; Kirby, E.; Cuillandre, J.-C.; Gilbert, K.

    2013-03-01

    As part of the SPLASH survey of the Andromeda (M31) system, we have obtained Keck/DEIMOS spectra of the compact elliptical (cE) satellite M32. This is the first resolved-star kinematical study of any cE galaxy. In contrast to most previous kinematical studies that extended out to r <~ 30'' ~ 1 r eff I ~ 100 pc, we measure the rotation curve and velocity dispersion profile out to r ~ 250'' and higher order Gauss-Hermite moments out to r ~ 70''. We achieve this by combining integrated-light spectroscopy at small radii (where crowding/blending are severe) with resolved stellar spectroscopy at larger radii, using spatial and kinematical information to account statistically for M31 contamination. The rotation curve and velocity dispersion profile extend well beyond the radius (r ~ 150'') where the isophotes are distorted. Unlike NGC 205, another close dwarf companion of M31, M32's kinematics appear regular and symmetric and do not show obvious sharp gradients across the region of isophotal elongation and twists. We interpret M31's kinematics using three-integral axisymmetric dynamical equilibrium models constructed using Schwarzschild's orbit superposition technique. Models with a constant mass-to-light ratio can fit the data remarkably well. However, since such a model requires an increasing tangential anisotropy with radius, invoking the presence of an extended dark halo may be more plausible. Such an extended dark halo is definitely required to bind a half-dozen fast-moving stars observed at the largest radii, but these stars may not be an equilibrium component of M32. Data 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 NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  1. INTERNAL STELLAR KINEMATICS OF M32 FROM THE SPLASH SURVEY: DARK HALO CONSTRAINTS

    SciTech Connect

    Howley, K. M.; Guhathakurta, P.; Geha, M.; Yniguez, B.; Kirby, E.; Cuillandre, J.-C.; Gilbert, K. E-mail: raja@ucolick.org E-mail: jkalirai@stsci.edu E-mail: byniguez@uci.edu E-mail: jcc@cfht.hawaii.edu

    2013-03-01

    As part of the SPLASH survey of the Andromeda (M31) system, we have obtained Keck/DEIMOS spectra of the compact elliptical (cE) satellite M32. This is the first resolved-star kinematical study of any cE galaxy. In contrast to most previous kinematical studies that extended out to r {approx}< 30'' {approx} 1 r {sup eff} {sub I} {approx} 100 pc, we measure the rotation curve and velocity dispersion profile out to r {approx} 250'' and higher order Gauss-Hermite moments out to r {approx} 70''. We achieve this by combining integrated-light spectroscopy at small radii (where crowding/blending are severe) with resolved stellar spectroscopy at larger radii, using spatial and kinematical information to account statistically for M31 contamination. The rotation curve and velocity dispersion profile extend well beyond the radius (r {approx} 150'') where the isophotes are distorted. Unlike NGC 205, another close dwarf companion of M31, M32's kinematics appear regular and symmetric and do not show obvious sharp gradients across the region of isophotal elongation and twists. We interpret M31's kinematics using three-integral axisymmetric dynamical equilibrium models constructed using Schwarzschild's orbit superposition technique. Models with a constant mass-to-light ratio can fit the data remarkably well. However, since such a model requires an increasing tangential anisotropy with radius, invoking the presence of an extended dark halo may be more plausible. Such an extended dark halo is definitely required to bind a half-dozen fast-moving stars observed at the largest radii, but these stars may not be an equilibrium component of M32.

  2. Three Dimensional Stellar Kinematics of the Galactic Bar and Disk: Where APOGEE Meets GLIMPSE

    NASA Astrophysics Data System (ADS)

    Benjamin, Robert; Babler, Brian; D'Onghia, Elena; Clarkson, Will; Churchwell, Ed; Kirkpatrick, Davy; Zasowski, Gail; Majewski, Steve

    2016-08-01

    We propose to use the Spitzer Space Telescope to re-image 53 square degrees (fourteen fields) of the inner Galactic plane (galactic longitudes \\|L\\|=6-45 degrees) that have also been targeted by the APOGEE/APOGEE-2 surveys-Sloan III and IV programs to obtain high resolution H band spectroscopy for hundreds of thousands of red giants. We will combine the proposed observations (198 hours) with the original GLIMPSE observations of the Galactic plane in 2004-2005 to measure the proper motions of sources along the Galactic plane over the past decade. When combined with the 43 square degrees of Priority 1 data being obtained for Cycle 12--which cover \\|L\\|< 5 degrees and \\|B\\|<2 degrees, plus Baade's window -we will have proper motion constraints for over 25 million sources. The combination of Spitzer proper motions for millions of sources and APOGEE radial velocities for thousands of sources will be used to constrain models of stellar kinematics for the Galactic bar(s) and disk. We will also use this data to test several bar formation models that have been developed to explain the mysterious 'high-velocity' Milky Way bar stars (Nidever et al 2012b), one of the first APOGEE discoveries. This program will be the most uniform and deep Galactic plane proper motion study as mid-infrared observations are minimally affected by extinction over most of the region we propose to cover. We also expect to be able to find at least 150 high proper motion stars which could be substellar objects and possible micro-lensing candidates against the crowded Galactic disk.

  3. Stellar populations in the Carina region. The Galactic plane at l = 291°

    NASA Astrophysics Data System (ADS)

    Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

    2016-08-01

    Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims: The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods: We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results: We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB - V ~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the

  4. 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.

  5. 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

  6. Core-halo age gradients and star formation in the Orion Nebula and NGS 2024 young stellar clusters

    SciTech Connect

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.

    2014-06-01

    We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, Age{sub JX} , derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024 cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on Age{sub JX} estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  7. Detection of lithium in the cool halo dwarfs Groombridge 1830 and HD 134439: Implications for internal stellar mixing and cosmology

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Ryan, Sean G.; Beers, Timothy C.; Thorburn, Julie A.

    1994-01-01

    Lithium abundances in halo stars, when interpreted correctly, hold the key to uncovering the primordial Li abundance Li(sub p). However, whereas standard stellar evolutionary models imply consistency in standard big bang nucleosynthesis (BBN), models with rotationally induced mixing imply a higher Li(sub p), possibly implying an inconsistency in standard BBN. We report here Li detections in two cool halo dwarfs, Gmb 1830 and HD 134439. These are the coolest and lowest Li detections in halo dwarfs to date, and are consistent with the metallicity dependence of Li depletion in published models. If the recent report of a beryllium deficiency in Gmb 1830 represents a real Be depletion, then the rotational models would be favored. We propose tests to reduce critical uncertainties.

  8. Detection of lithium in the cool halo dwarfs Groombridge 1830 and HD 134439: Implications for internal stellar mixing and cosmology

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Ryan, Sean G.; Beers, Timothy C.; Thorburn, Julie A.

    1994-01-01

    Lithium abundances in halo stars, when interpreted correctly, hold the key to uncovering the primordial Li abundance Li(sub p). However, whereas standard stellar evolutionary models imply consistency in standard big bang nucleosynthesis (BBN), models with rotationally induced mixing imply a higher Li(sub p), possibly implying an inconsistency in standard BBN. We report here Li detections in two cool halo dwarfs, Gmb 1830 and HD 134439. These are the coolest and lowest Li detections in halo dwarfs to date, and are consistent with the metallicity dependence of Li depletion in published models. If the recent report of a beryllium deficiency in Gmb 1830 represents a real Be depletion, then the rotational models would be favored. We propose tests to reduce critical uncertainties.

  9. Stellar binaries in galactic nuclei: tidally stimulated mergers followed by tidal disruptions

    NASA Astrophysics Data System (ADS)

    Bradnick, B.; Mandel, I.; Levin, Y.

    2017-08-01

    We investigate interactions of stellar binaries in galactic nuclear clusters with a massive black hole (MBH). We consider binaries on highly eccentric orbits around the MBH that change due to random gravitational interactions with other stars in the nuclear stellar cluster. The pericentres of the orbits perform a random walk, and we consider cases where this random walk slowly brings the binary to the Hills tidal separation radius (the so-called empty loss-cone regime). However, we find that in a majority of cases, the expected separation does not occur and instead the members of the binary merge together. This happens because the binary's eccentricity is excited by tidal interactions with the MBH, and the relative excursions of the internal eccentricity of the binary far exceed those in its internal semimajor axis. This frequently reduces the pericentre separation to values below typical stellar diameters, which induces a significant fraction of such binaries to merge (≳75 per cent in our set of numerical experiments). Stellar tides do not appreciably change the total rate of mergers but circularize binaries, leading to a significant fraction of low-eccentricity, low-impact-velocity mergers. Some of the stellar merger products will then be tidally disrupted by the MBH within ∼106 yr. If the merger strongly enhances the magnetic field of the merger product, this process could explain observations of prompt relativistic jet formation in some tidal disruption events.

  10. Stellar Dynamics at the Galactic Center with an Extremely Large Telescope

    NASA Astrophysics Data System (ADS)

    Weinberg, Nevin N.; Milosavljević, Miloš; Ghez, Andrea M.

    2005-04-01

    We discuss physical experiments achievable via the monitoring of stellar dynamics near the massive black hole at the Galactic center with a diffraction-limited, next-generation, extremely large telescope (ELT). Given the likely observational capabilities of an ELT and what is currently known about the stellar environment at the Galactic center, we synthesize plausible samples of stellar orbits around the black hole. We use the Markov Chain Monte Carlo method to evaluate the constraints that the monitoring of these orbits will place on the matter content within the dynamical sphere of influence of the black hole. We express our results as functions of the number N of stars with detectable orbital motions and the astrometric precision δθ and spectroscopic precision δv at which the stellar proper motions and radial velocities are monitored. Our results are easily scaled to different telescope sizes and precisions. For N=100, δθ=0.5mas, and δv=10kms-1 (a conservative estimate of the capabilities of a 30 m telescope) we find that if the extended matter distribution enclosed by the orbits at 0.01 pc has a mass greater than ~103 Msolar, it will produce measurable deviations from Keplerian motion. Thus, if the concentration of dark matter at the Galactic center matches theoretical predictions, its influence on the orbits will be detectable. We also estimate the constraints that will be placed on the mass of the black hole and on the distance to the Galactic center and find that both will be measured to better than ~0.1%. We discuss the significance of knowing the distance to within a few parsecs and the importance of this parameter for understanding the structure of the Galaxy. We demonstrate that the lowest order relativistic effects, such as the prograde precession, will be detectable if δθ<~0.5mas. Barring the favorable discovery of a star on a highly compact, eccentric orbit, the higher order effects, including the frame dragging due to the spin of the black

  11. The cosmic assembly of stellar haloes in massive early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Buitrago, Fernando; Trujillo, Ignacio; Curtis-Lake, Emma; Montes, Mireia; Cooper, Andrew P.; Bruce, Victoria A.; Pérez-González, Pablo G.; Cirasuolo, Michele

    2017-04-01

    Using the exquisite depth of the Hubble Ultra Deep Field (HUDF12 programme) data set, we explore the ongoing assembly of the outermost regions of the most massive galaxies (Mstellar ≥ 5× 1010 M⊙) at z ≤ 1. The outskirts of massive objects, particularly early-type Galaxies (ETGs), are expected to suffer a dramatic transformation across cosmic time due to continuous accretion of small galaxies. HUDF imaging allows us to study this process at intermediate redshifts in six massive galaxies, exploring the individual surface brightness profiles out to ˜25 effective radii. We find that 5-20 per cent of the total stellar mass for the galaxies in our sample is contained within 10 < R < 50 kpc. These values are in close agreement with numerical simulations, and higher than those reported for local late-type galaxies (≲5 per cent). The fraction of stellar mass stored in the outer envelopes/haloes of massive ETGs increases with decreasing redshift, being 28.7 per cent at = 0.1, 15.1 per cent at = 0.65 and 3.5 per cent at = 2. The fraction of mass in diffuse features linked with ongoing minor merger events is >1-2 per cent, very similar to predictions based on observed close pair counts. Therefore, the results for our small albeit meaningful sample suggest that the size and mass growth of the most massive galaxies have been solely driven by minor and major merging from z = 1 to today.

  12. The Shape of the Inner Milky Way Halo from Observations of the Pal 5 and GD--1 Stellar Streams

    NASA Astrophysics Data System (ADS)

    Bovy, Jo; Bahmanyar, Anita; Fritz, Tobias K.; Kallivayalil, Nitya

    2016-12-01

    We constrain the shape of the Milky Way’s halo by dynamical modeling of the observed phase-space tracks of the Pal 5 and GD-1 tidal streams. We find that the only information about the potential gleaned from the tracks of these streams are precise measurements of the shape of the gravitational potential—the ratio of vertical to radial acceleration—at the location of the streams, with weaker constraints on the radial and vertical accelerations separately. The latter will improve significantly with precise proper-motion measurements from Gaia. We measure that the overall potential flattening is 0.95 ± 0.04 at the location of GD-1 ([R,Z]≈ [12.5,6.7] {kpc}) and 0.94 ± 0.05 at the position of Pal 5 ([R,Z]≈ [8.4,16.8] {kpc}). Combined with constraints on the force field near the Galactic disk, we determine that the axis ratio of the dark-matter halo’s density distribution is 1.05 ± 0.14 within the inner 20 kpc, with a hint that the halo becomes more flattened near the edge of this volume. The halo mass within 20 {kpc} is (1.1+/- 0.1)× {10}11 {M}⊙ . A dark-matter halo this close to spherical is in tension with the predictions from numerical simulations of the formation of dark-matter halos.

  13. The stellar-to-halo mass relation of GAMA galaxies from 100 deg2 of KiDS weak lensing data

    NASA Astrophysics Data System (ADS)

    van Uitert, Edo; Cacciato, Marcello; Hoekstra, Henk; Brouwer, Margot; Sifón, Cristóbal; Viola, Massimo; Baldry, Ivan; Bland-Hawthorn, Joss; Brough, Sarah; Brown, M. J. I.; Choi, Ami; Driver, Simon P.; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Joachimi, Benjamin; Kuijken, Konrad; Liske, Jochen; Loveday, Jon; McFarland, John; Miller, Lance; Nakajima, Reiko; Peacock, John; Radovich, Mario; Robotham, A. S. G.; Schneider, Peter; Sikkema, Gert; Taylor, Edward N.; Verdoes Kleijn, Gijs

    2016-07-01

    We study the stellar-to-halo mass relation of central galaxies in the range 9.7 < log 10(M*/h- 2 M⊙) < 11.7 and z < 0.4, obtained from a combined analysis of the Kilo Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. We use ˜100 deg2 of KiDS data to study the lensing signal around galaxies for which spectroscopic redshifts and stellar masses were determined by GAMA. We show that lensing alone results in poor constraints on the stellar-to-halo mass relation due to a degeneracy between the satellite fraction and the halo mass, which is lifted when we simultaneously fit the stellar mass function. At M* > 5 × 1010 h- 2 M⊙, the stellar mass increases with halo mass as {˜ }M_h^{0.25}. The ratio of dark matter to stellar mass has a minimum at a halo mass of 8 × 1011 h-1 M⊙ with a value of M_h/M_{*}=56_{-10}^{+16} [h]. We also use the GAMA group catalogue to select centrals and satellites in groups with five or more members, which trace regions in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. We find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, we find that the stellar-to-halo mass relation of central galaxies can also be obtained by modelling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-to-halo mass relation. Finally, we show that the combination of weak lensing with the stellar mass function can be used to test the purity of group catalogues.

  14. The gaseous galactic halo as inferred from the line spectra of the galaxies Markarian 509 and Fairall 9

    NASA Technical Reports Server (NTRS)

    York, D. G.; Songaila, A.; Blades, J. C.; Cowie, L. L.; Morton, D. C.; Wu, C.-C.

    1982-01-01

    Narrow interstellar absorption lines of S II 1259.52, Si II 1260.42, and Fe II 1608.46 due to gas in the disk and the halo of the Galaxy have been detected in the spectrum of the Seyfert galaxy Mrk 509 with the International Ultraviolet Explorer. This gas is also seen at higher resolution in the Ca II and Na I absorption lines in two components at LSR velocities of +6 and +62 km/s. In addition, narrow Ly-alpha and C IV absorption near the Seyfert redshift seem to be present in the spectrum. Si II 1260.42 absorption from the galactic disk and from the Magellanic Stream or the halo of the SMC have been detected with the IUE in the spectrum of Fairall 9. The observations of these two objects when combined with existing results are shown to be consistent with a corotating galactic halo having a height of less than 10 kpc at the sun.

  15. PROBING THE OUTER GALACTIC HALO WITH RR LYRAE FROM THE CATALINA SURVEYS

    SciTech Connect

    Drake, A. J.; Djorgovski, S. G.; Graham, M. J.; Mahabal, A.; Donalek, C.; Williams, R.; Catelan, M.; Torrealba, G.; Belokurov, V.; Koposov, S. E.; Prieto, J. L.; Larson, S.; Christensen, E.; Beshore, E.

    2013-01-20

    We present analysis of 12,227 type-ab RR Lyraes (RRLs) found among the 200 million public light curves in Catalina Surveys Data Release 1. These stars span the largest volume of the Milky Way ever surveyed with RRLs, covering {approx}20,000 deg{sup 2} of the sky (0 Degree-Sign < {alpha} < 360 Degree-Sign , -22 Degree-Sign < {delta} < 65 Degree-Sign ) to heliocentric distances of up to 60 kpc. Each of the RRLs is observed between 60 and 419 times over a six-year period. Using period finding and Fourier fitting techniques we determine periods and apparent magnitudes for each source. We find that the periods are generally accurate to {sigma} = 0.002% in comparison to 2842 previously known RRLs and 100 RRLs observed in overlapping survey fields. We photometrically calibrate the light curves using 445 Landolt standard stars and show that the resulting magnitudes are accurate to {approx}0.05 mag using Sloan Digital Sky Survey (SDSS) data for {approx}1000 blue horizontal branch stars and 7788 RRLs. By combining Catalina photometry with SDSS spectroscopy, we analyze the radial velocity and metallicity distributions for >1500 of the RRLs. Using the accurate distances derived for the RRLs, we show the paths of the Sagittarius tidal streams crossing the sky at heliocentric distances from 20 to 60 kpc. By selecting samples of Galactic halo RRLs, we compare their velocity, metallicity, and distance with predictions from a recent detailed N-body model of the Sagittarius system. We find that there are some significant differences between the distances and structures predicted and our observations.

  16. May 2005 Halo CMEs and Galactic Cosmic Ray Flux Changes at Earth's Orbit

    NASA Astrophysics Data System (ADS)

    Ahluwalia, H. S.; Alania, M. V.; Wawrzynczak, A.; Ygbuhay, R. C.; Fikani, M. M.

    2014-05-01

    The pressure corrected hourly data from the global network of cosmic ray detectors, measurements of the interplanetary magnetic field (IMF) intensity ( B) at Earth's orbit and its components B x , B y , B z (in the geocentric solar ecliptic coordinates) are used to conduct a comprehensive study of the galactic cosmic ray (GCR) intensity fluctuations caused by the halo coronal mass ejection of 13 May 2005. Distinct differences exist in GCR timelines recorded by neutron monitors (NMs) and multidirectional muon telescopes (MTs), the latter respond to the high rigidity portion of the GCR differential rigidity spectrum. The Forbush decrease (FD) onset in MTs is delayed (˜5 h) with respect to the onset of a geomagnetic storm sudden commencement (SSC) and a large pre-increase is present in MT data before, during, and after the SSC onset, of unknown origin. The rigidity spectrum, for a range of GCR rigidities (≤200 GV), is a power law in rigidity (R) with a negative exponent ( γ=-1.05) at GCR minimum intensity, leading us to infer that the quasi-linear theory of modulation is inconsistent with observations at high rigidities (>1 GV); the results support the force field theory of modulation. At present, we do not have a comprehensive model for the FD explaining quantitatively all the observational features but we present a preliminary model listing physical processes that may contribute to a FD timeline. We explored the connections between different phases of the FD and the power spectra of IMF components but did not find a sustained relationship.

  17. Formation of warped disks by galactic flyby encounters. I. Stellar disks

    SciTech Connect

    Kim, Jeonghwan H.; An, Sung-Ho; Yoon, Suk-Jin; Peirani, Sebastien; Kim, Sungsoo; Ann, Hong Bae

    2014-07-01

    Warped disks are almost ubiquitous among spiral galaxies. Here we revisit and test the 'flyby scenario' of warp formation, in which impulsive encounters between galaxies are responsible for warped disks. Based on N-body simulations, we investigate the morphological and kinematical evolution of the stellar component of disks when galaxies undergo flyby interactions with adjacent dark matter halos. We find that the so-called 'S'-shaped warps can be excited by flybys and sustained for even up to a few billion years, and that this scenario provides a cohesive explanation for several key observations. We show that disk warp properties are governed primarily by the following three parameters: (1) the impact parameter, i.e., the minimum distance between two halos; (2) the mass ratio between two halos; and (3) the incident angle of the flyby perturber. The warp angle is tied up with all three parameters, yet the warp lifetime is particularly sensitive to the incident angle of the perturber. Interestingly, the modeled S-shaped warps are often non-symmetric depending on the incident angle. We speculate that the puzzling U- and L-shaped warps are geometrically superimposed S-types produced by successive flybys with different incident angles, including multiple interactions with a satellite on a highly elongated orbit.

  18. REPRODUCING THE STELLAR MASS/HALO MASS RELATION IN SIMULATED {Lambda}CDM GALAXIES: THEORY VERSUS OBSERVATIONAL ESTIMATES

    SciTech Connect

    Munshi, Ferah; Governato, F.; Loebman, S.; Quinn, T.; Brooks, A. M.; Christensen, C.; Shen, S.; Moster, B.; Wadsley, J.

    2013-03-20

    We examine the present-day total stellar-to-halo mass (SHM) ratio as a function of halo mass for a new sample of simulated field galaxies using fully cosmological, {Lambda}CDM, high-resolution SPH + N-body simulations. These simulations include an explicit treatment of metal line cooling, dust and self-shielding, H{sub 2}-based star formation (SF), and supernova-driven gas outflows. The 18 simulated halos have masses ranging from a few times 10{sup 8} to nearly 10{sup 12} M{sub Sun }. At z = 0, our simulated galaxies have a baryon content and morphology typical of field galaxies. Over a stellar mass range of 2.2 Multiplication-Sign 10{sup 3}-4.5 Multiplication-Sign 10{sup 10} M{sub Sun} we find extremely good agreement between the SHM ratio in simulations and the present-day predictions from the statistical abundance matching technique presented in Moster et al. This improvement over past simulations is due to a number systematic factors, each decreasing the SHM ratios: (1) gas outflows that reduce the overall SF efficiency but allow for the formation of a cold gas component; (2) estimating the stellar masses of simulated galaxies using artificial observations and photometric techniques similar to those used in observations; and (3) accounting for a systematic, up to 30% overestimate in total halo masses in DM-only simulations, due to the neglect of baryon loss over cosmic times. Our analysis suggests that stellar mass estimates based on photometric magnitudes can underestimate the contribution of old stellar populations to the total stellar mass, leading to stellar mass errors of up to 50% for individual galaxies. These results highlight that implementing a realistic high density threshold for SF considerably reduces the overall SF efficiency due to more effective feedback. However, we show that in order to reduce the perceived tension between the SF efficiency in galaxy formation models and in real galaxies, it is very important to use proper techniques to

  19. Age determination of the nuclear stellar population of Active Galactic Nuclei using Locally Weighted Regression

    NASA Astrophysics Data System (ADS)

    Estrada-Piedra, T.; Torres-Papaqui, J. P.; Terlevich, R.; Fuentes, O.; Terlevich, E.

    2004-07-01

    We present a new technique to segregate old and young stellar populations in galactic spectra using machine learning methods. We used an ensemble of classifiers, each classifier in the ensemble specializes in young or old populations and was trained with locally weighted regression and tested using ten-fold cross-validation. Since the relevant information concentrates in certain regions of the spectra we used the method of sequential floating backward selection offline for feature selection. The application to Seyfert galaxies proved that this technique is very insensitive to the dilution by the Active Galactic Nucleus (AGN) continuum. Comparing with exhaustive search we concluded that both methods are similar in terms of accuracy but the machine learning method is faster by about two orders of magnitude.

  20. A hadronic-leptonic model for the Fermi bubbles: Cosmic-rays in the galactic halo and radio emission

    SciTech Connect

    Fujita, Yutaka; Ohira, Yutaka; Yamazaki, Ryo

    2014-07-01

    We investigate non-thermal emission from the Fermi bubbles in a hadronic model. Cosmic-ray (CR) protons are accelerated at the forward shock of the bubbles. They interact with the background gas in the Galactic halo and create π{sup 0}-decay gamma-rays and secondary electrons through proton-proton interaction. We follow the evolution of the CR protons and electrons by calculating their distribution functions. We find that the spectrum and the intensity profiles of π{sup 0}-decay gamma-rays are consistent with observations. We predict that the shock front is located far ahead of the gamma-ray boundary of the Fermi bubbles. This naturally explains the fact that a clear temperature jump of thermal gas was not discovered at the gamma-ray boundary in recent Suzaku observations. We also consider re-acceleration of the background CRs in the Galactic halo at the shock front. We find that it can significantly affect the gamma-rays from the Fermi bubbles, unless the density of the background CRs is ≲ 10% of that in the Galactic disk. We indicate that secondary electrons alone cannot produce the observed radio emission from the Fermi bubbles. However, the radio emission from the outermost region of the bubbles can be explained if electrons are directly accelerated at the shock front with an efficiency of ∼0.1% of that of protons.

  1. Where stellar halos coexist with intracluster light: a case study of the giant Virgo-central galaxy M87

    NASA Astrophysics Data System (ADS)

    Longobardi, Alessia

    2016-01-01

    What is the role that accretion events play in the evolution of galaxies in dense environments, such as galaxy clusters? Cosmological simulations allow us to study in detail the evolution of galaxies' halos in cluster environments and have shown that the formation of extended halos around central cluster galaxies and intracluster light (ICL) is closely correlated to the morphological transformation of galaxies in clusters. However, the extremely low surface brightness of these components makes it difficult to gather observational constraints. Planetary nebulas (PNs) offer a unique tool to investigate these environments owing to their strong [OIII] emission line. I will present a study of the light and stellar motion in the halo of the giant elliptical galaxy M87 and its surrounding IC component at the centre of the Virgo cluster, prime targets to shed light on the hierarchical assembly of structure in the Universe. We make use of a deep and extended PN sample (~ 300 objects) to study out to ~150 kpc in radius M87. We show that at all distance the galaxy halo overlap with theVirgo ICL. However, they are dynamically distinct components with different density profiles, and parent stellarpopulations, consistent with the halo of M87 being redder and more metal rich than the ICL. Moreover, the synergy between PN kinematical information and deep V/B-band photometry made it possible to unveal an ongoing accretion process in the outskirt of M87, that has caused a non-negligible modification of the halo properties. The ongoing assembly of this galaxy at distances R>60 kpc is also shown by the overall PN halo kinematics, reflecting the dynamical complexity of a still growing system.

  2. Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, B.

    2002-01-01

    The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory (LLNL) to study X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in existing experimental and theoretical understanding of this atomic physics process, and are needed to explain all or part of the observed X-ray emission from the soft X-ray background, stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae. Progress made during the first year of the grant is described, as is work planned for the second year.

  3. Open and Globular Cluster Distances for Extragalactic, Galactic, and Stellar Astrophysics

    NASA Technical Reports Server (NTRS)

    Worthey, Guy S.

    2004-01-01

    One of the hallmarks of SIM's few-milliarcsecond astrometric precision is its ability to obtain accurate parallax measurements across more than half of the Galaxy. The "open and globular" project obtains parallax distances to a set of star clusters. One important, goal is to pinpoint the zeropoint of the distance scale for main-sequence fitting. Another goal is to improve stellar evolutionary isochrones and integrated light models. Another goal is to use the clusters themselves to address unsolved problems of late-stage stellar evolution and Galactic and extragalactic chemical evolution. The clusters to be observed are chosen to span the widest possible range of abundance and age, to be as rich as possible, and to be as well-studied as possible.

  4. The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters

    SciTech Connect

    Lee, Y.S.; Beers, T.C.; Sivarani, T.; Johnson, J.A.; An, D.; Wilhelm, R.; Prieto, C.Allende; Koesterke, L.; Re Fiorentin, P.; Bailer-Jones, C.A.L.; Norris, J.E.

    2007-10-01

    The authors validate the performance and accuracy of the current SEGUE (Sloan Extension for Galactic Understanding and Exploration) Stellar Parameter Pipeline (SSPP), which determines stellar atmospheric parameters (effective temperature, surface gravity, and metallicity) by comparing derived overall metallicities and radial velocities from selected likely members of three globular clusters (M 13, M 15, and M 2) and two open clusters (NGC 2420 and M 67) to the literature values. Spectroscopic and photometric data obtained during the course of the original Sloan Digital Sky Survey (SDSS-1) and its first extension (SDSS-II/SEGUE) are used to determine stellar radial velocities and atmospheric parameter estimates for stars in these clusters. Based on the scatter in the metallicities derived for the members of each cluster, they quantify the typical uncertainty of the SSPP values, {sigma}([Fe/H]) = 0.13 dex for stars in the range of 4500 K {le} T{sub eff} {le} 7500 K and 2.0 {le} log g {le} 5.0, at least over the metallicity interval spanned by the clusters studied (-2.3 {le} [Fe/H] < 0). The surface gravities and effective temperatures derived by the SSPP are also compared with those estimated from the comparison of the color-magnitude diagrams with stellar evolution models; they find satisfactory agreement. At present, the SSPP underestimates [Fe/H] for near-solar-metallicity stars, represented by members of M 67 in this study, by {approx} 0.3 dex.

  5. AN XMM-NEWTON SURVEY OF THE SOFT X-RAY BACKGROUND. III. THE GALACTIC HALO X-RAY EMISSION

    SciTech Connect

    Henley, David B.; Shelton, Robin L.

    2013-08-20

    We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on {approx}4/5 of our sight lines. The temperature is fairly uniform (median = 2.22 Multiplication-Sign 10{sup 6} K, interquartile range = 0.63 Multiplication-Sign 10{sup 6} K), while the emission measure and intrinsic 0.5-2.0 keV surface brightness vary by over an order of magnitude ({approx}(0.4-7) Multiplication-Sign 10{sup -3} cm{sup -6} pc and {approx}(0.5-7) Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively, with median detections of 1.9 Multiplication-Sign 10{sup -3} cm{sup -6} pc and 1.5 Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper.

  6. The outer regions of the giant Virgo galaxy M 87 Kinematic separation of stellar halo and intracluster light

    NASA Astrophysics Data System (ADS)

    Longobardi, Alessia; Arnaboldi, Magda; Gerhard, Ortwin; Hanuschik, Reinhard

    2015-07-01

    Aims: We present a spectroscopic study of a sample of 287 planetary nebulas (PNs) around the brightest cluster galaxy (BCG) M 87 in Virgo A, of which 211 are located between 40 kpc and 150 kpc from the galaxy centre. With these data we can distinguish the stellar halo from the co-spatial intracluster light (ICL) and study both components separately. Methods: We obtained PN velocities with a high resolution FLAMES/VLT survey targeting eight fields in a total area of ~0.4 deg2. We identified PNs from their narrow and symmetric redshifted λ5007 Å [OIII] emission line, the presence of the second λ4959 Å [OIII] emission line, and the absence of significant continuum. We implement a robust technique to measure the halo velocity dispersion from the projected phase-space to identify PNs associated with the M 87 halo and ICL. Using photometric magnitudes, we construct PN luminosity functions (PNLFs), which are complete down to m5007 = 28.8. Results: The velocity distribution of the spectroscopically confirmed PNs is bimodal, containing a narrow component centred on the systemic velocity of the BCG and an off-centred broader component, which we identify as halo and ICL, respectively. We find that 243 PNs are part of the velocity distribution of the M 87 halo, while the remaining subsample of 44 PNs are intracluster PNs (ICPNs). Halo and ICPNs have different spatial distributions: the number density of halo PNs follow the galaxy's surface brightness profile, whereas the ICPNs are characterised by a shallower power-law profile, IICL ∝ Rγ with γ in the range [-0.34, -0.04 ]. No evidence is found for an asymmetry in the halo and ICPN density distributions when the NW and SE fields are studied separately. A study of the composite PN number density profile confirms the superposition of different PN populations associated with the M 87 halo and the ICL, characterised by different PN specific numbers α. We derive αhalo = 1.06 × 10-8NPN L⊙,bol-1 and αICL = 2.72 × 10

  7. Dynamical population synthesis: constructing the stellar single and binary contents of galactic field populations

    NASA Astrophysics Data System (ADS)

    Marks, Michael; Kroupa, Pavel

    2011-11-01

    The galactic field's late-type stellar single and binary populations are calculated on the observationally well-constrained supposition that all stars form as binaries with invariant properties in discrete star formation events. A recently developed tool (Marks, Kroupa & Oh) is used to evolve the binary star distributions in star clusters for a few million years until an equilibrium situation is achieved which has a particular mixture of single and binary stars. On cluster dissolution the population enters the galactic field with these characteristics. The different contributions of single stars and binaries from individual star clusters, which are selected from a power-law-embedded star cluster mass function, are then added up. This gives rise to integrated galactic field binary distribution functions (IGBDFs), resembling a galactic field's stellar content (dynamical population synthesis). It is found that the binary proportion in the galactic field of a galaxy is larger the lower the minimum cluster mass, Mecl, min, the lower the star formation rate, SFR, the steeper the embedded star cluster mass function (described by index β) and the larger the typical size of forming star clusters in the considered galaxy. In particular, period, mass ratio and eccentricity IGBDFs for the Milky Way (MW) are modelled using Mecl, min= 5 M⊙, SFR = 3 M⊙ yr-1 and β= 2 which are justified by observations. For rh≈ 0.1-0.3 pc, the half-mass radius of an embedded cluster, the aforementioned theoretical IGBDFs agree with independently observed distributions, suggesting that the individual discrete star formation events in the MW generally formed compact star clusters. Of all late-type binaries, 50 per cent stem from Mecl≲ 300 M⊙ clusters, while 50 per cent of all single stars were born in Mecl≳ 104 M⊙ clusters. Comparison of the G-dwarf and M-dwarf binary populations indicates that the stars are formed in mass-segregated clusters. In particular, it is pointed out that

  8. The Stellar Mass-Halo Mass Relation for Low-mass X-Ray Groups At 0.5< z< 1 in the CDFS With CSI

    NASA Astrophysics Data System (ADS)

    Patel, Shannon G.; Kelson, Daniel D.; Williams, Rik J.; Mulchaey, John S.; Dressler, Alan; McCarthy, Patrick J.; Shectman, Stephen A.

    2015-02-01

    Since z˜ 1, the stellar mass density locked in low-mass groups and clusters has grown by a factor of ˜8. Here, we make the first statistical measurements of the stellar mass content of low-mass X-ray groups at 0.5\\lt z\\lt 1, enabling the calibration of stellar-to-halo mass scales for wide-field optical and infrared surveys. Groups are selected from combined Chandra and XMM-Newton X-ray observations in the Chandra Deep Field South. These ultra-deep observations allow us to identify bona fide low-mass groups at high redshift and enable measurements of their total halo masses. We compute aggregate stellar masses for these halos using galaxies from the Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Stars comprise ˜3%-4% of the total mass of group halos with masses {{10}12.8}\\lt {{M}200}/{{M}⊙ }\\lt {{10}13.5} (about the mass of Fornax and one-fiftieth the mass of Virgo). Complementing our sample with higher mass halos at these redshifts, we find that the stellar-to-halo mass ratio decreases toward higher halo masses, consistent with other work in the local and high redshift universe. The observed scatter about the stellar-halo mass relation is σ ˜ 0.25 dex, which is relatively small and suggests that total group stellar mass can serve as a rough proxy for halo mass. We find no evidence for any significant evolution in the stellar-halo mass relation since z≲ 1. Quantifying the stellar content in groups since this epoch is critical given that hierarchical assembly leads to such halos growing in number density and hosting increasing shares of quiescent galaxies. This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

  9. Nuclear planetology: understanding habitable planets as Galactic bulge stellar remnants (black dwarfs) in a Hertzsprung-Russell (HR) diagram

    NASA Astrophysics Data System (ADS)

    Roller, Goetz

    2016-04-01

    model constraining the evolution of a rocky planet like Earth or Mercury from a stellar precursor of the oldest population to a Fe-C BLD, shifting through different spectral classes in a HR diagram after massive decompression and tremendous energy losses. In the light of WD/BLD cosmochronology [1], solar system bodies like Earth, Mercury and Moon are regarded as captured interlopers from the Galactic bulge, Earth and Moon possibly representing remnants of an old binary system. Such a preliminary scenario is supported by similar ages obtained from WD's for the Galactic halo [1] and, independently, by means of 187Re-232Th-238U nuclear geochronometry [2, 4, 5], together with recent observations extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way [6]. This might be further elucidated in the near future by Th/U cosmochronometry based upon a nuclear production ratio Th/U = 0.96 [5] and additionally by means of a newly developed nucleogeochronometric age dating method for stellar spectroscopy, which will be presented in a forthcoming paper. The model shall stimulate geochemical data interpretation from a different perspective to constrain the (thermal) evolution of a habitable planet as to its geo-, bio-, hydro- and atmosphere. [1] Fontaine et al. (2001), Public. Astron. Soc. of the Pacific 113, 409-435. [2] Roller (2015), Abstract T34B-0407, AGU Spring Meeting 2015. [3] Arevalo et al. (2010), Chem. Geol. 271, 70-85. [4] Roller (2015), Geophys. Res. Abstr. 17, EGU2015-2399. [5] Roller (2015), 78th Annu. Meeting Met. Soc., Abstract #5041. [6] Howes et al. (2015), Nature 527, 484-487.

  10. Infalling young clusters in the Galactic Centre: implications for IMBHs and young stellar populations

    NASA Astrophysics Data System (ADS)

    Petts, J. A.; Gualandris, A.

    2017-06-01

    The central parsec of the Milky Way hosts two puzzlingly young stellar populations, a tight isotropic distribution of B stars around SgrA* (the S-stars) and a disc of OB stars extending to ˜0.5 pc. Using a modified version of Sverre Aarseth's direct summation code nbody6, we explore the scenario in which a young star cluster migrates to the Galactic Centre within the lifetime of the OB disc population via dynamical friction. We find that star clusters massive and dense enough to reach the central parsec form a very massive star via physical collisions on a mass segregation time-scale. We follow the evolution of the merger product using the most up to date, yet conservative, mass-loss recipes for very massive stars. Over a large range of initial conditions, we find that the very massive star expels most of its mass via a strong stellar wind, eventually collapsing to form a black hole of mass ˜ 20-400 M⊙, incapable of bringing massive stars to the Galactic Centre. No massive intermediate mass black hole can form in this scenario. The presence of a star cluster in the central ˜10 pc within the last 15 Myr would also leave an ˜2 pc ring of massive stars, which is not currently observed. Thus, we conclude that the star cluster migration model is highly unlikely to be the origin of either young population, and in situ formation models or binary disruptions are favoured.

  11. No Evidence for Multiple Stellar Populations in the Low-mass Galactic Globular Cluster E 3

    NASA Astrophysics Data System (ADS)

    Salinas, Ricardo; Strader, Jay

    2015-08-01

    Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M˜ 1.4× {10}4 {M}⊙ ) globular cluster E3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue cyanogen (CN) absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multistellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found. Based on observations obtained at the Southern Astrophysical Research (SOAR) Telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  12. Constraining Stellar Population Models. I. Age, Metallicity and Abundance Pattern Compilation for Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Roediger, Joel C.; Courteau, Stéphane; Graves, Genevieve; Schiavon, Ricardo P.

    2014-01-01

    We present an extensive literature compilation of age, metallicity, and chemical abundance pattern information for the 41 Galactic globular clusters (GGCs) studied by Schiavon et al. Our compilation constitutes a notable improvement over previous similar work, particularly in terms of chemical abundances. Its primary purpose is to enable detailed evaluations of and refinements to stellar population synthesis models designed to recover the above information for unresolved stellar systems based on their integrated spectra. However, since the Schiavon sample spans a wide range of the known GGC parameter space, our compilation may also benefit investigations related to a variety of astrophysical endeavors, such as the early formation of the Milky Way, the chemical evolution of GGCs, and stellar evolution and nucleosynthesis. For instance, we confirm with our compiled data that the GGC system has a bimodal metallicity distribution and is uniformly enhanced in the α elements. When paired with the ages of our clusters, we find evidence that supports a scenario whereby the Milky Way obtained its globular clusters through two channels: in situ formation and accretion of satellite galaxies. The distributions of C, N, O, and Na abundances and the dispersions thereof per cluster corroborate the known fact that all GGCs studied so far with respect to multiple stellar populations have been found to harbor them. Finally, using data on individual stars, we verify that stellar atmospheres become progressively polluted by CN(O)-processed material after they leave the main sequence. We also uncover evidence which suggests that the α elements Mg and Ca may originate from more than one nucleosynthetic production site. We estimate that our compilation incorporates all relevant analyses from the literature up to mid-2012. As an aid to investigators in the fields named above, we provide detailed electronic tables of the data upon which our work is based at http

  13. Calibrated and completeness-corrected optical stellar density maps of the northern Galactic plane

    NASA Astrophysics Data System (ADS)

    Farnhill, H. J.; Drew, J. E.; Barentsen, G.; González-Solares, E. A.

    2016-03-01

    Following on from the second release of calibrated photometry from IPHAS, the INT/WFC Photometric Hα Survey of the Northern Galactic Plane, we present incompleteness-corrected stellar density maps in the r and i photometric bands. These have been computed to a range of limiting magnitudes reaching to 20th magnitude in r and 19th in i (Vega system), and with different angular resolutions - the highest resolution available being 1 arcmin2. The maps obtained cover 94 per cent of the 1800 square degree IPHAS footprint, spanning the Galactic latitude range, -5° < b < +5°, north of the celestial equator. The corrections for incompleteness, due to confusion and sensitivity loss at the faint limit, have been deduced by the method of artificial source injection. The presentation of this method is preceded by a discussion of other more approximate methods of determining completeness. Our method takes full account of position-dependent seeing and source ellipticity in the survey data base. The application of the star counts to testing reddened Galactic disc models is previewed by a comparison with predicted counts along three constant-longitude cuts at ℓ ≃ 30°, 90° and 175°: some overprediction of the most heavily reddened ℓ ≃ 30° counts is found, alongside good agreement at ℓ ≃ 90° and 175°.

  14. Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge

    SciTech Connect

    Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok; Sohn, Young-Jong

    2015-01-01

    We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color–magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  15. Tidal Stripping Stellar Substructures Around Four Metal-Poor Globular Clusters in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok; Sohn, Young-Jong

    2015-01-01

    We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color-magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  16. ON THE ORIGIN OF THE ANGULAR MOMENTUM PROPERTIES OF GAS AND DARK MATTER IN GALACTIC HALOS AND ITS IMPLICATIONS

    SciTech Connect

    Sharma, Sanjib; Bland-Hawthorn, Joss; Steinmetz, Matthias

    2012-05-10

    We perform a set of non-radiative hydrodynamical simulations of merging spherical halos in order to understand the angular momentum (AM) properties of the galactic halos seen in cosmological simulations. The universal shape of AM distributions seen in simulations is found to be generically produced as a result of mergers. The universal shape is such that it has an excess of low AM material and hence cannot explain the exponential structure of disk galaxies. A resolution to this is suggested by the spatial distribution of low AM material which is found to be in the center and a conical region close to the axis of rotation. A mechanism that preferentially discards the material in the center and prevents the material along the poles from falling onto the disk is proposed as a solution. We implement a simple geometric criterion for the selective removal of low AM material and show that in order for 90% of halos to host exponential disks one has to reject at least 40% of material. Next, we explore the physical mechanisms responsible for distributing the AM within the halo during a merger. For dark matter there is an inside-out transfer of AM, whereas for gas there is an outside-in transfer, which is due to differences between collisionless and gas dynamics. This is responsible for the spin parameter {lambda} and the shape parameter {alpha} of AM distributions being higher for gas compared to dark matter. We also explain the apparent high spin of dark matter halos undergoing mergers and show that a criterion stricter than what is currently used would be required to detect such unrelaxed halos. Finally, we demonstrate that the misalignment of AM between gas and dark matter only occurs when the intrinsic spins of the merging halos are not aligned with the orbital AM of the system. The self-misalignment (orientation of AM when measured in radial shells not being constant), which could be the cause of warps and anomalous rotation in disks galaxies, also occurs under similar

  17. 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.

  18. The role of cosmic rays and Alfven waves in the structure of the galactic halo

    NASA Technical Reports Server (NTRS)

    Dougherty, M. K.; Mckenzie, J. F.; Westergaard, N. J.

    1985-01-01

    The effect that cosmic rays and the Alfven waves they generate have on the structure of the plasma distribution perpendicular to the galactic disk is examined. It is shown that the plasma distribution exhibits two length scales and the predicted values of gas density far from the galactic plane indicate that models involving hydrostatic equilibrium should be replaced by those allowing for a galactic wind.

  19. On the physical origin of galactic conformity

    NASA Astrophysics Data System (ADS)

    Hearin, Andrew P.; Behroozi, Peter S.; van den Bosch, Frank C.

    2016-09-01

    Correlations between the star formation rates (SFRs) of nearby galaxies (so-called galactic conformity) have been observed for projected separations up to 4 Mpc, an effect not predicted by current semi-analytic models. We investigate correlations between the mass accretion rates (dMvir/dt) of nearby haloes as a potential physical origin for this effect. We find that pairs of host haloes `know about' each others' assembly histories even when their present-day separation is greater than thirty times the virial radius of either halo. These distances are far too large for direct interaction between the haloes to explain the correlation in their dMvir/dt. Instead, halo pairs at these distances reside in the same large-scale tidal environment, which regulates dMvir/dt for both haloes. Larger haloes are less affected by external forces, which naturally gives rise to a mass dependence of the halo conformity signal. SDSS measurements of galactic conformity exhibit a qualitatively similar dependence on stellar mass, including how the signal varies with distance. Based on the expectation that halo accretion and galaxy SFR are correlated, we predict the scale-, mass- and redshift-dependence of large-scale galactic conformity, finding that the signal should drop to undetectable levels by z ≳ 1. These predictions are testable with current surveys to z ˜ 1; confirmation would establish a strong correlation between dark matter halo accretion rate and central galaxy SFR.

  20. Evidence for Gamma-ray Halos Around Active Galactic Nuclei and the First Measurement of Intergalactic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Ando, Shin'ichiro; Kusenko, Alexander

    2010-10-01

    Intergalactic magnetic fields (IGMFs) can cause the appearance of halos around the gamma-ray images of distant objects because an electromagnetic cascade initiated by a high-energy gamma-ray interaction with the photon background is broadened by magnetic deflections. We report evidence of such gamma-ray halos in the stacked images of the 170 brightest active galactic nuclei (AGNs) in the 11 month source catalog of the Fermi Gamma-Ray Space Telescope. Excess over the point-spread function in the surface brightness profile is statistically significant at 3.5σ (99.95% confidence level), for the nearby, hard population of AGNs. The halo size and brightness are consistent with IGMF, B IGMF ≈ 10-15 G. The knowledge of IGMF will facilitate the future gamma-ray and charged-particle astronomy. Furthermore, since IGMFs are likely to originate from the primordial seed fields created shortly after the big bang, this potentially opens a new window on the origin of cosmological magnetic fields, inflation, and the phase transitions in the early universe.

  1. Stellar wind paleontology. II - Faint halos and historical mass ejection in planetary nebulae

    NASA Astrophysics Data System (ADS)

    Balick, Bruce; Gonzalez, Guillermo; Frank, Adam; Jacoby, George

    1992-06-01

    The large, faint, generally circular, and limb-brightened nebular structures (called "halos") surrounding some planetary nebulae (PN) are explored using deep CCD images of NGC 40, 650-1, 1535, 2392, 6210, 6543, 6720, 6803, 6804, 6826, 6853, 6891, 6894, 7009, 7662, IC 1454, 3568, 4593, Abell 1, 2, 3, and BD +30 deg 3639. New halos have been discovered in a few objects (IC 1454, 4593, and possibly NGC 40, 6210, and 6803), and known halos have been mapped in detail in several PN (e.g., NGC 6543, 6720, 6826, 6853 and 7662). The present deep search does not reveal similar large and faint halos in NGC 1535, 2392, 6894, 7009, and IC 3568-PN whose inner regions are morphologically similar to others with easily observable halos.

  2. The Relationship Between Active Galactic Nuclei and the Growth of Stellar Spheroids

    NASA Astrophysics Data System (ADS)

    Pierce, Christina M.

    2007-12-01

    Recently acquired data from the All-wavelength Extended Groth Strip International Survey (AEGIS) allow us to explore the origin of the observed relationship between the masses of stellar spheroids and the black holes inhabiting them. We describe the results of two projects which probe the relationships between active galactic nuclei (AGNs) and their host galaxies. For the first project, we select AGNs using three independent methods: X-ray luminosity, radio luminosity, and optical spectrum signatures. Morphologies (merger, E/S0/Sa, or Sb-Irr) of the host galaxies are determined by using the second moment of the light, M20, and the Gini coefficient, and close galaxy pairs containing at least one AGN are identified based on kinematics. For AGN hosts identified as kinematically and/or morphologically interacting, we estimate the stage of the interaction and compare it to the AGN energy output. This allows us to test quantitative predictions regarding the timing of galaxy interactions and AGN detectability and energy output based on simulations of merging galaxies. For the second project, we stack the X-ray emissions from a sample of morphologically interacting galaxies that are not detected as X-ray sources, in search of obscured AGNs. We compare the intrinsic X-ray luminosity of early-stage mergers to that of late-stage mergers in order to constrain the relative time-scales of AGNs and the growth of stellar spheroids. Galaxy merger simulations offer constraints on the time-scales of stellar spheroid formation, while results from this project constrain the time-scales of the early stages of AGNs. Taken together, we are beginning to answer the question - does the AGN control the growth of the stellar spheroid, or vice versa?

  3. Galactic and stellar dynamics in the era of high resolution surveys

    NASA Astrophysics Data System (ADS)

    Boily, C. M.; Combes, F.; Hensler, G.; Spurzem, R.

    2008-12-01

    The conference Galactic and Stellar Dynamics in the Era of High Resolution Surveys took place at the European Doctoral College (EDC) in Strasbourg from 2008 March 16 to 20. The event was co-sponsored by the Astronomische Gesellschaft (AG) and the Société Fran\\c{c}aise d'Astronomie et d'Astrophysique (SF2A), a joint venture aiming to set a new trend of regular thematic meetings in specific areas of research. This special issue of the Astronomische Nachrichten is a compilation of the papers presented at the meeting. We give an outline of the meeting together with a short history of the relations of the two societies.

  4. Optical evidence for the unification of active galactic nuclei and quasi-stellar objects.

    PubMed

    Miller, J S

    1995-12-05

    There is a variety of optical evidence for some unification of different types of active galactic nuclei and quasi-stellar objects (QSOs). The case is very strong for the unification of at least some Seyfert galaxies, where polarization data show that the type assigned to the Seyfert galaxy must depend on viewing direction. It has been proposed that Fanaroff-Riley type 2 (FR2) radio galaxies are quasars seen in a direction from which the quasar is obscured, and there is some limited direct evidence for this picture. The broad absorption line QSOs may be normal QSOs seen from a special direction. Some of the sources observed to have high luminosities in the far infrared could be obscured QSOs and active nuclei. Mergers and interactions are likely to play an important role in nuclear activity, and active galaxies and QSOs could change their apparent types through these encounters followed by subsequent evolution.

  5. First Spectroscopic Identification of Massive Young Stellar Objects in the Galactic Center

    NASA Technical Reports Server (NTRS)

    An, Deokkeun; Ramirez, V.; Sellgren, Kris; Arendt, Richard G.; Boogert, A. C.; Schultheis, Mathias; Stolovy, Susan R.; Cotera, Angela S.; Robitaille, Thomas P.; Smith, Howard A.

    2009-01-01

    We report the detection of several molecular gas-phase and ice absorption features in three photometrically-selected young stellar object (YSO) candidates in the central 280 pc of the Milky Way. Our spectra, obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, reveal gas-phase absorption from CO2 (15.0 microns), C2H2 (13.7 microns) and HCN (14.0 microns). We attribute this absorption to warm, dense gas in massive YSOs. We also detect strong and broad 15 microns CO2 ice absorption features, with a remarkable double-peaked structure. The prominent long-wavelength peak is due to CH3OH-rich ice grains, and is similar to those found in other known massive YSOs. Our IRS observa.tions demonstra.te the youth of these objects, and provide the first spectroscopic identification of massive YSOs in the Galactic Center.

  6. Optical evidence for the unification of active galactic nuclei and quasi-stellar objects.

    PubMed Central

    Miller, J S

    1995-01-01

    There is a variety of optical evidence for some unification of different types of active galactic nuclei and quasi-stellar objects (QSOs). The case is very strong for the unification of at least some Seyfert galaxies, where polarization data show that the type assigned to the Seyfert galaxy must depend on viewing direction. It has been proposed that Fanaroff-Riley type 2 (FR2) radio galaxies are quasars seen in a direction from which the quasar is obscured, and there is some limited direct evidence for this picture. The broad absorption line QSOs may be normal QSOs seen from a special direction. Some of the sources observed to have high luminosities in the far infrared could be obscured QSOs and active nuclei. Mergers and interactions are likely to play an important role in nuclear activity, and active galaxies and QSOs could change their apparent