No WIMP mini-spikes in dwarf spheroidal galaxies

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

Wanders, Mark; Bertone, Gianfranco; Weniger, Christoph

The formation of black holes inevitably affects the distribution of dark and baryonic matter in their vicinity, leading to an enhancement of the dark matter density, called spike, and if dark matter is made of WIMPs, to a strong enhancement of the dark matter annihilation rate. Spikes at the center of galaxies like the Milky Way are efficiently disrupted by baryonic processes, but mini-spikes can form and survive undisturbed at the center of dwarf spheroidal galaxies. We show that Fermi LAT satellite data allow to set very stringent limits on the existence of mini-spikes in dwarf galaxies: for thermal WIMPsmore » with mass between 100 GeV and 1 TeV, we obtain a maximum black hole mass between 100 and 1000 M{sub ⊙}, ruling out black holes masses extrapolated from the M-σ relationship in a large region of the parameter space. We also performed Monte Carlo simulations of merger histories of black holes in dwarf spheroidals in a scenario where black holes form from the direct collapse of primordial gas in early halos, and found that this specific formation scenario is incompatible at the 84% CL with dark matter being in the form of thermal WIMPs.« less

Effects of the Sagittarius dwarf tidal stream on dark matter detectors.

PubMed

Freese, Katherine; Gondolo, Paolo; Newberg, Heidi Jo; Lewis, Matthew

2004-03-19

The Sagittarius dwarf tidal stream may be showering dark matter onto the solar neighborhood, which can change the results and interpretation of direct detection searches for weakly interacting massive particles (WIMPs). Stars in the stream may already have been detected in the solar neighborhood, and the dark matter in the stream is (0.3-25)% of the local density. Experiments should see an annually modulated steplike feature in the energy recoil spectrum that would be a smoking gun for WIMP detection. The total count rate in detectors is not a cosine curve in time and peaks at a different time of year than the standard case.

Dark Matter Limits from Dwarf Spheroidal Galaxies with the HAWC Gamma-Ray Observatory

NASA Astrophysics Data System (ADS)

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

2018-02-01

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field of view observatory sensitive to 500 GeV–100 TeV gamma-rays and cosmic rays. It can also perform diverse indirect searches for dark matter annihilation and decay. Among the most promising targets for the indirect detection of dark matter are dwarf spheroidal galaxies. These objects are expected to have few astrophysical sources of gamma-rays but high dark matter content, making them ideal candidates for an indirect dark matter detection with gamma-rays. Here we present individual limits on the annihilation cross section and decay lifetime for 15 dwarf spheroidal galaxies within the field of view, as well as their combined limit. These are the first limits on the annihilation cross section and decay lifetime using data collected with HAWC. We also present the HAWC flux upper limits of the 15 dwarf spheroidal galaxies in half-decade energy bins.

The Sagittarius tidal stream as a gravitationnal experiment in the Milky Way

NASA Astrophysics Data System (ADS)

Thomas, G. F.; Famaey, B.; Ibata, R.; Lüghausen, F.; Kroupa, P.

2015-12-01

Modified Newtonian Dynamics (MOND or Milgromian dynamics) gives a successful description of many galaxy properties that are hard to understand in the classical framework. The rotation curves of spiral galaxies are, for instance, perfectly reproduced and understood within this framework. Nevertheless, rotation curves only trace the potential in the galactic plane, and it is thus useful to test the shape of the potential outside the plane. Here we use the Sagittarius tidal stream as a gravitational experiment in the Milky Way, in order to check whether MOND can explain both its characteristics and those of the remnant dwarf spheroidal galaxy progenitor. We show that a MOND model of the Sagittarius stream can both perfectly reproduce the observed positions of stars in the stream, and even more strikingly, perfectly reproduce the observed properties of the remnant. Nevertheless, this first model does not reproduce well the observed radial velocities, which could be a signature of a rotating component in the progenitor or of the presence of a massive hot gaseous halo around the Milky Way.

The Sagittarius Dwarf Galaxy Survey (SDGS): Constraints on the Star Formation History of the Sgr dSph

NASA Astrophysics Data System (ADS)

Bellazzini, M.; Ferraro, F. R.; Buonanno, R.

1999-01-01

We present the first results of a large photometric survey devoted to the study of the star formation history in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three large (size: 9 x 35 arcmin2) and widely spaced fields located nearly along the Sgr dSph major axis [(l,b) = (6.5 -16);(6-14);(5-12)] have been observed in the V and I passbands with the ESO-NTT 3.5-m telescope (La Silla - Chile). Well-calibrated photometry has been obtained for ˜90000 stars toward Sgr dSph and for ˜9000 stars in a (9 x 24 arcmin2) control field down to a limiting magnitude of V 22. At present this is the largest photometric (CCD) sample of Sgr dSph stars and the wide spacing between field provides the first opportunity of studying the stellar content of different regions of the galaxy (over a range of ˜2 Kpc across). Age and metallicity estimates are obtained for the detected stellar populations and the very first evidences are presented for (a) spatial differences in the stellar content and (b) the detection of a very metal poor population in the field of the Sgr galaxy.

Solo dwarfs I: survey introduction and first results for the Sagittarius dwarf irregular galaxy

NASA Astrophysics Data System (ADS)

Higgs, C. R.; McConnachie, A. W.; Irwin, M.; Bate, N. F.; Lewis, G. F.; Walker, M. G.; Côté, P.; Venn, K.; Battaglia, G.

2016-05-01

We introduce the Solitary Local dwarfs survey (Solo), a wide-field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multiband imaging from Canada-France-Hawaii Telescope/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than MV ≃ -18 situated beyond the nominal virial radius of the Milky Way and M31 (≳300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius dwarf irregular galaxy (Sag DIG), one of the most isolated, low-mass galaxies, located at the edge of the Local Group. We analyse its resolved stellar populations and their spatial distributions. We provide updated estimates of its central surface brightness and integrated luminosity, and trace its surface brightness profile to a level fainter than 30 mag arcsec-2. Sag DIG is well described by a highly elliptical (disc-like) system following a single component Sérsic model. However, a low-level distortion is present at the outer edges of the galaxy that, were Sag DIG not so isolated, would likely be attributed to some kind of previous tidal interaction. Further, we find evidence of an extremely low level, extended distribution of stars beyond ˜5 arcmin (>1.5 kpc) that suggests Sag DIG may be embedded in a very low-density stellar halo. We compare the stellar and H I structures of Sag DIG, and discuss results for this galaxy in relation to other isolated, dwarf irregular galaxies in the Local Group.

ANDROMEDA XXIX: A NEW DWARF SPHEROIDAL GALAXY 200 kpc FROM ANDROMEDA

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

Bell, Eric F.; Slater, Colin T.; Martin, Nicolas F.

We report the discovery of a new dwarf galaxy, Andromeda XXIX (And XXIX), using data from the recently released Sloan Digital Sky Survey Data Release 8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15 Degree-Sign from M31, with a distance inferred from the tip of the red giant branch of 730 {+-} 75 kpc, corresponding to a three-dimensional separation from M31 of 207{sup +20}{sub -2} kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison tomore » the red giant branch luminosity function of the Draco dwarf spheroidal, is M{sub V} = -8.3 {+-} 0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of [Fe/H] {approx}-1.8. The half-light radius of And XXIX is 360 {+-} 60 pc and its ellipticity is 0.35 {+-} 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.« less

Andromeda's dwarf spheroidals and the universal mass profile

NASA Astrophysics Data System (ADS)

Collins, Michelle; Rich, R. M.; Martin, N.; Ibata, R.; Chapman, S. C.; McConnachie, A. W.; PAndAS

2014-01-01

As the faintest, least massive galaxies we are able to observe, dwarf spheroidal galaxies represent the fundamental galactic unit. Their study in the Milky Way has led to several interesting findings and are helping us to better understand the behaviour of dark matter on the smallest scales. In this talk, I will present work from the ongoing PAndAS spectroscopic follow up survey of Andromeda, focusing on our results for its dwarf galaxy population. I will show that by including the masses measured for these objects in our analysis of the mass profiles of all dwarf galaxies, we are able to demonstrate that the notion of a universal mass profile for these most minute of galaxies is false. I will also identify several interesting objects whose properties defy our expectations, and discuss what these mean for our understanding of the physics governing galactic evolution.

Model-independent constraints on dark matter annihilation in dwarf spheroidal galaxies

NASA Astrophysics Data System (ADS)

Boddy, Kimberly K.; Kumar, Jason; Marfatia, Danny; Sandick, Pearl

2018-05-01

We present a general, model-independent formalism for determining bounds on the production of photons in dwarf spheroidal galaxies via dark matter annihilation, applicable to any set of assumptions about dark matter particle physics or astrophysics. As an illustration, we analyze gamma-ray data from the Fermi Large Area Telescope to constrain a variety of nonstandard dark matter models, several of which have not previously been studied in the context of dwarf galaxy searches.

The globular cluster NGC 7492 and the Sagittarius tidal stream: together but unmixed

NASA Astrophysics Data System (ADS)

Carballo-Bello, J. A.; Corral-Santana, J. M.; Catelan, M.; Martínez-Delgado, D.; Muñoz, R. R.; Sollima, A.; Navarrete, C.; Duffau, S.; Côté, P.; Mora, M. D.

2018-03-01

We have derived from VIMOS spectroscopy the radial velocities for a sample of 71 stars selected from CFHT/Megacam photometry around the Galactic globular cluster NGC 7492. In the resulting velocity distribution, it is possible to distinguish two relevant non-Galactic kinematic components along the same line of sight: a group of stars at 〈vr〉 ˜ 125 km s-1 which is compatible with the velocity of the old leading arm of the Sagittarius tidal stream, and a larger number of objects at 〈vr〉 ˜ -110 km s-1 that might be identified as members of the trailing wrap of the same stream. The systemic velocity of NGC 7492 set at vr ˜ -177 km s-1 differs significantly from that of both components, thus our results confirm that this cluster is not one of the globular clusters deposited by the Sagittarius dwarf spheroidal in the Galactic halo, even if it is immersed in the stream. A group of stars with 〈vr〉 ˜ - 180 km s-1 might be comprised of cluster members along one of the tidal tails of NGC 7492.

Study of the boxlike dark matter signals from dwarf spheroidal galaxies with Fermi-LAT data

NASA Astrophysics Data System (ADS)

Li, Shang; Liang, Yun-Feng; Xia, Zi-Qing; Zu, Lei; Duan, Kai-Kai; Shen, Zhao-Qiang; Feng, Lei; Yuan, Qiang; Fan, Yi-Zhong

2018-04-01

The observation of a special spectral feature in the gamma-ray data would be one of the best ways to identify dark matter (DM). The box-shaped gamma-ray spectra could be generated by the decay of intermediate particles produced by DM annihilation or decay. It provides another kind of signal that can be relatively easily distinguished from astrophysical backgrounds besides the linelike signals. Dwarf spheroidal galaxies are expected to be dominated by DM and may be one of the most promising targets for indirect DM searches. In this paper, we study the box-shaped DM signals with Fermi-LAT observations of dwarf spheroidal galaxies. We analyze 106 months of Fermi-LAT data to derive the upper limits on the annihilation cross section or the decay timescale of DM. In addition, we compare the results for different sample selections and DM density distributions. We expect that more dwarf spheroidal galaxies will be found and the sensitivity of box-shaped gamma-ray signal searches will be significantly improved in the future.

WFPC2 Observations of the URSA Minor Dwarf Spheroidal Galaxy

NASA Technical Reports Server (NTRS)

Mighell, Kenneth J.; Burke, Christopher J.

1999-01-01

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F555W (approximately V) and F814W (approximately I) of the central region of the Ursa Minor dwarf spheroidal galaxy. The V versus V - I color-magnitude diagram features a sparsely populated blue horizontal branch, a steep thin red giant branch, and a narrow subgiant branch. The main sequence reaches approximately 2 magnitudes below the main-sequence turnoff (V(sup UMi, sub TO) approximately equals 23.27 +/- 0.11 mag) of the median stellar population. We compare the fiducial sequence of the Galactic globular cluster M92 (NGC 6341). The excellent match between Ursa Minor and M92 confirms that the median stellar population of the UMi dSph galaxy is metal poor ([Fe/H](sub UMi) approximately equals [Fe/H](sub M92) approximately equals -2.2 dex) and ancient (age(sub UMi)approximately equalsage(sub M92) approximately equals 14 Gyr). The B - V reddening and the absorption in V are estimated to be E(B - V) = 0.03 +/- 0.01 mag and A(sup UMi, sub V) = 0.09 +/- 0.03 mag. A new estimate of the distance modulus of Ursa Minor, (m - M)(sup UMi, sub 0) = 19.18 +/- 0.12 mag, has been derived based on fiducial-sequence fitting M92 [DELTA.V(sub UMi - M92) = 4.60 +/- 0.03 mag and DELTA(V - I)(sub UMi - M92) = 0.010 +/- 0.005 mag] and the adoption of the apparent V distance modulus for M92 of (m - M)(sup M92, sub V) = 14.67 +/- 0.08 mag (Pont et al. 1998, A&A, 329, 87). The Ursa Minor dwarf spheroidal galaxy is then at a distance of 69 +/- 4 kpc from the Sun. These HST observations indicate that Ursa Minor has had a very simple star formation history consisting mainly of a single major burst of star formation about 14 Gyr ago which lasted approximately < 2 Gyr. While we may have missed minor younger stellar populations due to the small field-of-view of the WFPC2 instrument, these observations clearly show that most of the stars in the central region Ursa Minor dwarf

Small-scale hero: Massive-star enrichment in the Hercules dwarf spheroidal

NASA Astrophysics Data System (ADS)

Koch, Andreas; Matteucci, Francesca; Feltzing, Sofia

2012-09-01

Dwarf spheroidal galaxies are often conjectured to be the sites of the first stars. The best current contenders for finding the chemical imprints from the enrichment by those massive objects are the ``ultrafaint dwarfs'' (UFDs). Here we present evidence for remarkably low heavy element abundances in the metal poor Hercules UFD. Combined with other peculiar abundance patterns this indicates that Hercules was likely only influenced by very few, massive explosive events - thus bearing the traces of an early, localized chemical enrichment with only very little other contributions from other sources at later times.

The dark matter content of Local Group dwarf spheroidals

NASA Astrophysics Data System (ADS)

Collins, Michelle; PAndAS Team

2016-01-01

Dwarf spheroidal galaxies are the most dark matter dominated objects we have observed in the Universe. By measuring the dynamics of their stellar populations, we can hope to map out the shapes of their central density profiles, and compare these to expectations from simulations. In this poster, we will present the central kinematics of a range of dwarf galaxies around the Milky Way and Andromeda, taken as part of the PAndAS Keck II DEIMOS survey. We will highlight a number of unusual objects, which have either very high mass to light ratios - indicating they may be promising candidates for indirect detection experiments - or those with exceptionally low central densities, whose kinematic profiles suggest that these systems are out of dynamical equilibrium.

Stellar streams as gravitational experiments. I. The case of Sagittarius

NASA Astrophysics Data System (ADS)

Thomas, Guillaume F.; Famaey, Benoit; Ibata, Rodrigo; Lüghausen, Fabian; Kroupa, Pavel

2017-07-01

Tidal streams of disrupting dwarf galaxies orbiting around their host galaxy offer a unique way to constrain the shape of galactic gravitational potentials. Such streams can be used as "leaning tower" gravitational experiments on galactic scales. The most well-motivated modification of gravity proposed as an alternative to dark matter on galactic scales is Milgromian dynamics (MOND), and we present here the first ever N-body simulations of the dynamical evolution of the disrupting Sagittarius dwarf galaxy in this framework. Using a realistic baryonic mass model for the Milky Way, we attempt to reproduce the present-day spatial and kinematic structure of the Sagittarius dwarf and its immense tidal stream that wraps around the Milky Way. With very little freedom on the original structure of the progenitor, constrained by the total luminosity of the Sagittarius structure and by the observed stellar mass-size relation for isolated dwarf galaxies, we find reasonable agreement between our simulations and observations of this system. The observed stellar velocities in the leading arm can be reproduced if we include a massive hot gas corona around the Milky Way that is flattened in the direction of the principal plane of its satellites. This is the first time that tidal dissolution in MOND has been tested rigorously at these mass and acceleration scales. The movie associated to Fig. 6 is available at http://www.aanda.org

Deep spectroscopy of the dwarf spheroidal NGC 185

NASA Astrophysics Data System (ADS)

Gonçalves, Denise R.; Magrini, Laura; Martins, Lucimara P.; Teodorescu, Ana M.; Quireza, Cintia; Lanfranchi, Gaia

2012-08-01

Dwarf galaxies are crucial to understand the formation and evolution of galaxies, since they constitute the most abundant galaxy population. Abundance ratios and their variations due to star formation and inflow/outflow of gas are key constraints to chemical evolution models. The determination of these abundances in the dwarf galaxies of the Local Universe is thus of extreme importance. NGC 185 is one of the four brightest dwarf companions of M31, but unlike the other three it has an important content of gas and dust. Interestingly enough, in an optical survey of bright nearby galaxies NGC 185 was classified as a Seyfert galaxy based on its integrated emission-line ratios in the nuclear regions. However, although its emission lines formally place it in the category of Seyfert it is probable that this galaxy does not contain a genuine active nucleus. In this contribution, we resume, firstly, our results of an empirical study of the galaxy, on which we characterise its emission-line population and obtain planetary nebulae abundance ratios (Gonçalves et al. 2012). And, secondly, we discuss our attempt to identify the possible ionization mechanisms for NGC 185 enlighting the controversial classification of this galaxy dwarf spheroidal (dSph) as well as Seyfert, via stellar population synthesis and chemical evolution modelling (Martins et al. 2011).

Effect of black holes in local dwarf spheroidal galaxies on gamma-ray constraints on dark matter annihilation

NASA Astrophysics Data System (ADS)

Gonzalez-Morales, Alma X.; Profumo, Stefano; Queiroz, Farinaldo S.

2014-11-01

Recent discoveries of optical signatures of black holes in dwarf galaxies indicates that low-mass galaxies can indeed host intermediate massive black holes. This motivates the assessment of the resulting effect on the host dark matter density profile, and the consequences for the constraints on the plane of the dark matter annihilation cross section versus mass, stemming from the nonobservation of gamma rays from local dwarf spheroidals with the Fermi Large Area Telescope. We compute the density profile using three different prescriptions for the black hole mass associated with a given spheroidal galaxy, and taking into account the cutoff to the density from dark matter pair-annihilation. We find that the limits on the dark matter annihilation rate from observations of individual dwarfs are enhanced by factors of a few up to 1 06 , depending on the specific galaxy, on the black hole mass prescription, and on the dark matter particle mass. We estimate limits from combined observations of a sample of 15 dwarfs, for a variety of assumptions on the dwarf black hole mass and on the dark matter density profile prior to adiabatic contraction. We find that if black holes are indeed present in local dwarf spheroidals, then, independent of assumptions, (i) the dark matter interpretation of the Galactic center gamma-ray excess would be conclusively ruled out, (ii) wino dark matter would be excluded up to masses of about 3 TeV, and (iii) vanilla thermal relic weakly interacting massive particles must be heavier than 100 GeV.

Ages and Heavy Element Abundances from Very Metal-poor Stars in the Sagittarius Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Hansen, Camilla Juul; El-Souri, Mariam; Monaco, Lorenzo; Villanova, Sandro; Bonifacio, Piercarlo; Caffau, Elisabetta; Sbordone, Luca

2018-03-01

Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events. Previous chemical studies were restricted mainly to a few, metal-rich ([Fe/H] \\gtrapprox -1) stars that suggested a top-light initial mass function (IMF). Here we present the first high-resolution, very metal-poor ([Fe/H] =‑1 to ‑3) sample of 13 giant stars in the main body of Sgr. We derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La, Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on previous studies. Our abundances from Sgr mimic those of the metal-poor halo, and our most metal-poor star ([Fe/H] ∼ -3) indicates a pure r-process pollution. Abundances of Sr, Pb, and Th are presented for the first time in Sgr, allowing for age determination using nuclear cosmochronology. We calculate ages of 9+/- 2.5 {Gyr}. Most of the sample stars have been enriched by a range of asymptotic giant branch (AGB) stars with masses between 1.3 and 5 M ⊙. Sgr J190651.47–320147.23 shows a large overabundance of Pb (2.05 dex) and a peculiar abundance pattern best fit by a 3 M ⊙ AGB star. Based on star-to-star scatter and observed abundance patterns, a mixture of low- and high-mass AGB stars and supernovae (15–25 M ⊙) is necessary to explain these patterns. The high level (0.29 ± 0.05 dex) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas. This result is in contrast with a top-light IMF with no massive stars polluting Sgr. Based on data obtained UVES/VLT ID: 083.B-0774, 075.B-0127.

Tracing the properties of the Sagittarius stream across the sky with LAMOST spectra

NASA Astrophysics Data System (ADS)

Walder, Madison Victoria; Carlin, Jeffrey

2018-01-01

The Sagittarius dwarf galaxy is a satellite that is currently being consumed by the Milky Way’s gravity. Its disruption has created the most prominent and widely studied tidal stream in our halo which wraps around our Galaxy with its leading arm in the northern Galactic hemisphere and its trailing arm in the southern hemisphere. Using optical spectra collected by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, we identify stars that belong to the Sagittarius tidal stream based on their positions, distances, velocities, stellar parameters, and metallicities. We trace the velocity, metallicity, and distance of the Sagittarius stream over 200 degrees of its extent on the sky using a homogenous spectroscopic data set. In doing this, we will be able to trace the stream in regions where the disk of the Galaxy makes it difficult to distinguish Sagittarius members from the far more numerous foreground stars, and therefore use the entirety of the stream to deepen our understanding of tidal disruption. We use the spectroscopic metallicities from LAMOST to derive the metallicity as a function of position along the stream, providing an important probe of the ongoing process of tidal disruption, and a window into the stellar populations that made up the Sagittarius dwarf before its cannibalization by the Milky Way.

APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Hasselquist, Sten; Shetrone, Matthew; Smith, Verne; Holtzman, Jon; McWilliam, Andrew; Fernández-Trincado, J. G.; Beers, Timothy C.; Majewski, Steven R.; Nidever, David L.; Tang, Baitian; Tissera, Patricia B.; Fernández Alvar, Emma; Allende Prieto, Carlos; Almeida, Andres; Anguiano, Borja; Battaglia, Giuseppina; Carigi, Leticia; Delgado Inglada, Gloria; Frinchaboy, Peter; García-Hernández, D. A.; Geisler, Doug; Minniti, Dante; Placco, Vinicius M.; Schultheis, Mathias; Sobeck, Jennifer; Villanova, Sandro

2017-08-01

The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] ≳ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function.

APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy

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

Hasselquist, Sten; Holtzman, Jon; Shetrone, Matthew

The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars withmore » [Fe/H] ≳ −0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function.« less

The Sagittarius Dwarf Galaxy Survey (SDGS) - I. Colour-magnitude diagrams, reddening and population gradients. First evidence of a very metal-poor population

NASA Astrophysics Data System (ADS)

Bellazzini, M.; Ferraro, F. R.; Buonanno, R.

1999-04-01

We present the first results of a large photometric survey devoted to the study of the star formation history of the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three wide strips (size ~ 9 x 35 arcmin ^2) located at ~ (l deg b deg) = (6.5;-16), (6;-14), (5;-12) have been observed. Each strip is roughly east-west oriented, nearly along the major axis of the galaxy. A control field (size ~ 9 x 24 arcmin ^2), located outside the body of Sgr dSph [~ (l deg b deg) = (354;-14)] has also been observed for statistical decontamination purposes. Accurate and well-calibrated V, I photometry down to V ~ 22 has been obtained for ~ 90 000 stars towards the Sgr dSph and ~ 8000 stars in the control field. This is the largest photometric sample (covering the widest spatial extension) ever observed in the Sgr dSph up to now. The main new results presented in this paper are: (1) the possible discovery of a strong asymmetry in the distribution of stars along the major axis, since the north-western arm of the Sgr galaxy (i.e. the region nearer to the Galactic bulge) apparently shows a significant deficiency of Sgr stars and (2) the first direct detection of a very metal-poor (and presumably old) population in the Sgr stellar content. Hints at a metallicity gradient towards the densest region of the galaxy are also reported.

Universal Dark Halo Scaling Relation for the Dwarf Spheroidal Satellites

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Ishiyama, Tomoaki; Ogiya, Go; Chiba, Masashi; Inoue, Shigeki; Mori, Masao

2017-07-01

Motivated by a recently found interesting property of the dark halo surface density within a radius, {r}\\max , giving the maximum circular velocity, {V}\\max , we investigate it for dark halos of the Milky Way’s and Andromeda’s dwarf satellites based on cosmological simulations. We select and analyze the simulated subhalos associated with Milky-Way-sized dark halos and find that the values of their surface densities, {{{Σ }}}{V\\max }, are in good agreement with those for the observed dwarf spheroidal satellites even without employing any fitting procedures. Moreover, all subhalos on the small scales of dwarf satellites are expected to obey the universal relation, irrespective of differences in their orbital evolutions, host halo properties, and observed redshifts. Therefore, we find that the universal scaling relation for dark halos on dwarf galaxy mass scales surely exists and provides us with important clues for understanding fundamental properties of dark halos. We also investigate orbital and dynamical evolutions of subhalos to understand the origin of this universal dark halo relation and find that most subhalos evolve generally along the {r}\\max \\propto {V}\\max sequence, even though these subhalos have undergone different histories of mass assembly and tidal stripping. This sequence, therefore, should be the key feature for understanding the nature of the universality of {{{Σ }}}{V\\max }.

The Distance to M54 using Infrared Photometry of RR Lyrae Variable Stars and the Implications of its Relation to the Sagittarius Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Gupta, Arvind F.; Beaton, Rachael L.; Majewski, Steven R.; SMHASH Team

2018-01-01

CDM cosmological models predict that dark matter halo density profiles will have central cusps. Yet for many dwarf spheroidal galaxies (dSphs), this expectation is in contrast with observations of cored, rather than cusped, halos. This 'cusp-core problem' is apparent in the Sagittarius Dwarf Galaxy (Sgr), one of the largest satellites of the Milky Way. The globular cluster M54, one of several clusters associated with Sgr, coincides in on-sky position with the center of the main body of Sgr. While several studies find that M54 lies within the center of Sgr, other findings show that M54 is offset from the center by several kiloparsecs along our line of sight. The latter requires Sgr to have a cored dark matter distribution. In the presence of a cuspy halo, the orbit of M54 would have decayed via dynamical friction and the cluster would have fallen to the center of Sgr. A clear determination of the relation of the two bodies may help us better understand the distribution of dark matter in Sgr and other dSphs. Here we present a measurement of the distance modulus to M54 using a set of RR Lyrae variable stars in near-infrared Magellan data mid-infrared Spitzer data. The magnitudes of individual stars are measured using multi-epoch PSF photometry and light curve fitting. From precise RR Lyrae period-luminosity relations at these wavelengths, we then find the mean M54 distance modulus to be 17.126 ± 0.023 (ran) ± 0.080 (sys). Our result is consistent with a distance measurement to Sgr derived via nearly identical methods and thus also consistent with the expectation of a central cusp in the dark matter density profile of Sgr.

The DART Imaging And CaT Survey of the Fornax Dwarf Spheroidal Galaxy

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

Battaglia, Giuseppina; Tolstoy, E.; Helmi, A.

2006-08-28

As part of the DART project we have used the ESO/2.2m Wide Field Imager in conjunction with the VLT/FLAMES* GIRAFFE spectrograph to study the detailed properties of the resolved stellar population of the Fornax dwarf spheroidal galaxy out to and beyond its tidal radius. Fornax dSph has had a complicated evolution and contains significant numbers of young, intermediate age and old stars. We investigate the relation between these different components by studying their photometric, kinematic and abundance distributions. We re-derived the structural parameters of the Fornax dwarf spheroidal using our wide field imaging covering the galaxy out to its tidalmore » radius, and analyzed the spatial distribution of the Fornax stars of different ages as selected from Colour-Magnitude Diagram analysis. We have obtained accurate velocities and metallicities from spectra in the Ca II triplet wavelength region for 562 Red Giant Branch stars which have velocities consistent with membership in Fornax dwarf spheroidal. We have found evidence for the presence of at least three distinct stellar components: a young population (few 100 Myr old) concentrated in the center of the galaxy, visible as a Main Sequence in the Colour-Magnitude Diagram; an intermediate age population (2-8 Gyr old); and an ancient population (> 10Gyr), which are distinguishable from each other kinematically, from the metallicity distribution and in the spatial distribution of stars found in the Colour-Magnitude Diagram. From our spectroscopic analysis we find that the ''metal rich'' stars ([Fe/H] > -1.3) show a less extended and more concentrated spatial distribution, and display a colder kinematics than the ''metal poor'' stars ([Fe/H] < -1.3). There is tentative evidence that the ancient stellar population in the center of Fornax does not exhibit equilibrium kinematics. This could be a sign of a relatively recent accretion of external material, such as the merger of another galaxy or other means of gas

Variable Stars in the Draco Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Harris, H. C.; Silberman, N. A.; Smith, H. A.

A new survey of the variable stars in the Draco dwarf spheroidal galaxy updates the pioneering study of this galaxy by Baade and Swope (1961). Our improved data, taken in BVI filters with CCD cameras on three telescopes at more than 80 epochs, allow us to investigate the known variables and to discover new, mostly low-amplitude variables. Approximately 300 variables are found and classified, more than double the number of variables analyzed previously. Most are RR Lyraes, with a small fraction of Anomalous Cepheids. This large sample of variables provides a unique opportunity to study the properties of these stars in a single system. This paper discusses the census of RR Lyraes, including RRc-type, double-mode, and Blazhko-effect RR Lyraes, as well as Anomalous Cepheids, and Type II Cepheids in Draco.

A spectroscopic binary in the Hercules dwarf spheroidal galaxy

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

Koch, Andreas; Hansen, Terese; Feltzing, Sofia

2014-01-01

We present the radial velocity curve of a single-lined spectroscopic binary in the faint Hercules dwarf spheroidal (dSph) galaxy, based on 34 individual spectra covering more than 2 yr of observations. This is the first time that orbital elements could be derived for a binary in a dSph. The system consists of a metal-poor red giant and a low-mass companion, possibly a white dwarf, with a 135 day period in a moderately eccentric (e = 0.18) orbit. Its period and eccentricity are fully consistent with metal-poor binaries in the Galactic halo, while the projected semimajor axis is small, at a{submore » p} sin i = 38 R {sub ☉}. In fact, a very close orbit could inhibit the production of heavier elements through s-process nucleosynthesis, leading to the very low abundances of neutron-capture elements that are found in this star. We discuss the further implications for the chemical enrichment history of the Hercules dSph, but find no compelling binary scenario that could reasonably explain the full, peculiar abundance pattern of the Hercules dSph galaxy.« less

Verlinde's emergent gravity versus MOND and the case of dwarf spheroidals

NASA Astrophysics Data System (ADS)

Diez-Tejedor, Alberto; Gonzalez-Morales, Alma X.; Niz, Gustavo

2018-06-01

In a recent paper, Erik Verlinde has developed the interesting possibility that space-time and gravity may emerge from the entangled structure of an underlying microscopic theory. In this picture, dark matter arises as a response to the standard model of particle physics from the delocalized degrees of freedom that build up the dark energy component of the Universe. Dark matter physics is then regulated by a characteristic acceleration scale a0, identified with the radius of the (quasi)-de Sitter universe we inhabit. For a point particle matter source, or outside an extended spherically symmetric object, MOND's empirical fitting formula is recovered. However, Verlinde's theory critically departs from MOND when considering the inner structure of galaxies, differing by a factor of 2 at the centre of a regular massive body. For illustration, we use the eight classical dwarf spheroidal satellites of the Milky Way. These objects are perfect testbeds for the model given their approximate spherical symmetry, measured kinematics, and identified missing mass. We show that, without the assumption of a maximal deformation, Verlinde's theory can fit the velocity dispersion profile in dwarf spheroidals with no further need of an extra dark particle component. If a maximal deformation is considered, the theory leads to mass-to-light ratios that are marginally larger than expected from stellar population and formation history studies. We also compare our results with the recent phenomenological interpolating MOND function of McGaugh et al., and find a departure that, for these galaxies, is consistent with the scatter in current observations.

Observations of MilkyWay Dwarf Spheroidal galaxies with the Fermi-LAT detector and

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

Abdo, A.A.; Ackermann, M.; Ajello, M.

We report on the observations of 14 dwarf spheroidal galaxies with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky {gamma}-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected {gamma}-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dwarf spheroidal galaxies, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearbymore » and among the most extreme dark matter dominated environments. No significant {gamma}-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the {gamma}-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10{sup -9} photons cm{sup -2}s{sup -1}. Using recent stellar kinematic data, the {gamma}-ray flux limits are combined with improved determinations of the dark matter density profile in 8 of the 14 candidate dwarfs to place limits on the pair annihilation cross-section ofWIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g. in models where supersymmetry breaking occurs via anomaly mediation. The {gamma}-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e{sup +}e{sup -} data, including low-mass wino-like neutralinos and models with TeV masses pair

APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy System

NASA Astrophysics Data System (ADS)

Hasselquist, Sten; Shetrone, Matthew D.; Smith, Verne V.; Holtzman, Jon A.; McWilliam, Andrew; APOGEE Team

2018-06-01

The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the chemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] > -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function. We then exploit the unique chemical abundance patters of the Sgr core to trace stars belonging to the Sgr tidal streams elsewhere in the Milky Way.

Chemical evolution of Local Group dwarf galaxies in a cosmological context - I. A new modelling approach and its application to the Sculptor dwarf spheroidal galaxy

NASA Astrophysics Data System (ADS)

Romano, Donatella; Starkenburg, Else

2013-09-01

We present a new approach for chemical evolution modelling, specifically designed to investigate the chemical properties of dwarf galaxies in a full cosmological framework. In particular, we focus on the Sculptor dwarf spheroidal galaxy, for which a wealth of observational data exists, as a test bed for our model. We select four candidate Sculptor-like galaxies from the satellite galaxy catalogue generated by implementation of a version of the Munich semi-analytic model for galaxy formation on the level 2 Aquarius dark matter simulations and use the mass assembly and star formation histories predicted for these four systems as an input for the chemical evolution code. We follow explicitly the evolution of several chemical elements, both in the cold gas out of which the stars form and in the hot medium residing in the halo. We take into account in detail the lifetimes of stars of different initial masses, the distribution of the delay times for Type Ia supernova explosions and the dependence of the stellar yields from the initial metallicity of the stars. We allow large fractions of metals to be deposited into the hot phase, either directly as stars die or through reheated gas flows powered by supernova explosions. We find that, in order to reproduce both the observed metallicity distribution function and the observed abundance ratios of long-lived stars of Sculptor, large fractions of the reheated metals must never re-enter regions of active star formation. With this prescription, all the four analogues to the Sculptor dwarf spheroidal galaxy extracted from the simulated satellites catalogue on the basis of luminosity and stellar population ages are found to reasonably match the detailed chemical properties of real Sculptor stars. However, all model galaxies do severely underestimate the fraction of very metal poor stars observed in Sculptor. Our analysis thus sets further constraints on the semi-analytical models and, at large, on possible metal enrichment

Improving the sensitivity of gamma-ray telescopes to dark matter annihilation in dwarf spheroidal galaxies

DOE PAGES

Carlson, Eric; Hooper, Dan; Linden, Tim

2015-03-01

The Fermi-LAT Collaboration has studied the gamma-ray emission from a stacked population of dwarf spheroidal galaxies and used this information to set constraints on the dark matter annihilation cross section. Interestingly, their analysis uncovered an excess with a test statistic (TS) of 8.7. If interpreted naively, this constitutes a 2.95σ local excess (p-value=0.003), relative to the expectations of their background model. In order to further test this interpretation, the Fermi-LAT team studied a large number of blank sky locations and found TS>8.7 excesses to be more common than predicted by their background model, decreasing the significance of their dwarf excessmore » to 2.2σ(p-value=0.027). We argue that these TS>8.7 blank sky locations are largely the result of unresolved blazars, radio galaxies, and star-forming galaxies, and show that multiwavelength information can be used to reduce the degree to which such sources contaminate the otherwise blank sky. In particular, we show that masking regions of the sky that lie within 1° of sources contained in the BZCAT or CRATES catalogs reduce the fraction of blank sky locations with TS>8.7 by more than a factor of 2. Taking such multiwavelength information into account can enable experiments such as Fermi to better characterize their backgrounds and increase their sensitivity to dark matter in dwarf galaxies, the most important of which remain largely uncontaminated by unresolved point sources. We also note that for the range of dark matter masses and annihilation cross sections currently being tested by studies of dwarf spheroidal galaxies, simulations predict that Fermi should be able to detect a significant number of dark matter subhalos. These subhalos constitute a population of subthreshold gamma-ray point sources and represent an irreducible background for searches for dark matter annihilation in dwarf galaxies.« less

The star formation history of the Sextans dwarf spheroidal galaxy: a true fossil of the pre-reionization era

NASA Astrophysics Data System (ADS)

Bettinelli, M.; Hidalgo, S. L.; Cassisi, S.; Aparicio, A.; Piotto, G.

2018-05-01

We present the star formation history (SFH) of the Sextans dwarf spheroidal galaxy based on deep archive B, I photometry taken with Suprime-Cam at Subaru telescope focusing our analysis on the inner region of the galaxy, fully located within the core radius. Within the errors of our SFH, we have not detected any metallicity gradient along the considered radial distance interval. As a main result of this work, we can state that the Sextans dwarf spheroidal stopped forming stars less than ˜1.3 Gyr after big bang in correspondence to the end of the reionization epoch. We have been able to constrain the duration of the main burst of star formation to ˜0.6 Gyr. From the calculation of the mechanical luminosity released from supernovae (SNe) during the brief episode of star formation, there are strong indications that SNe could have played an important role in the fate of Sextans, by removing almost completely the gas component, so preventing a prolonged star formation.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

NASA Astrophysics Data System (ADS)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone; Dotti, Massimo; Moustakas, Leonidas A.

2017-02-01

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N-body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f gas, in the disk of the progenitor dwarf. Our numerical experiments incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs (f gas ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless (f gas = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f gas ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.

Dark matter in dwarf spheroidal galaxies and indirect detection: a review.

PubMed

Strigari, Louis E

2018-05-01

Indirect dark matter searches targeting dwarf spheroidal galaxies (dSphs) have matured rapidly during the past decade. This has been because of the substantial increase in kinematic data sets from the dSphs, the new dSphs that have been discovered, and the operation of the Fermi-LAT and many ground-based gamma-ray experiments. Here we review the analysis methods that have been used to determine the dSph dark matter distributions, in particular the 'J-factors', comparing and contrasting them, and detailing the underlying systematics that still affect the analysis. We discuss prospects for improving measurements of dark matter distributions, and how these interplay with future indirect dark matter searches.

Dark matter in dwarf spheroidal galaxies and indirect detection: a review

NASA Astrophysics Data System (ADS)

Strigari, Louis E.

2018-05-01

Indirect dark matter searches targeting dwarf spheroidal galaxies (dSphs) have matured rapidly during the past decade. This has been because of the substantial increase in kinematic data sets from the dSphs, the new dSphs that have been discovered, and the operation of the Fermi-LAT and many ground-based gamma-ray experiments. Here we review the analysis methods that have been used to determine the dSph dark matter distributions, in particular the ‘J-factors’, comparing and contrasting them, and detailing the underlying systematics that still affect the analysis. We discuss prospects for improving measurements of dark matter distributions, and how these interplay with future indirect dark matter searches.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

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

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N -body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f {sub gas}, in the disk of the progenitor dwarf. Our numerical experimentsmore » incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs ( f {sub gas} ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless ( f {sub gas} = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f {sub gas} ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.« less

The Dark Energy Survey view of the Sagittarius stream: discovery of two faint stellar system candidates

NASA Astrophysics Data System (ADS)

Luque, E.; Pieres, A.; Santiago, B.; Yanny, B.; Vivas, A. K.; Queiroz, A.; Drlica-Wagner, A.; Morganson, E.; Balbinot, E.; Marshall, J. L.; Li, T. S.; Neto, A. Fausti; da Costa, L. N.; Maia, M. A. G.; Bechtol, K.; Kim, A. G.; Bernstein, G. M.; Dodelson, S.; Whiteway, L.; Diehl, H. T.; Finley, D. A.; Abbott, T.; Abdalla, F. B.; Allam, S.; Annis, J.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Burke, D. L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Cunha, C. E.; D'Andrea, C. B.; Desai, S.; Doel, P.; Evrard, A. E.; Flaugher, B.; Fosalba, P.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Martini, P.; Miquel, R.; Nord, B.; Ogando, R.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Walker, A. R.

2017-06-01

We report the discovery of two new candidate stellar systems in the constellation of Cetus using the data from the first two years of the Dark Energy Survey (DES). The objects, DES J0111-1341 and DES J0225+0304, are located at a heliocentric distance of ˜25 kpc and appear to have old and metal-poor populations. Their distances to the Sagittarius orbital plane, ˜1.73 kpc (DES J0111-1341) and ˜0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (rh ≃ 4.55 pc) and luminosity (MV ≃ +0.3) of DES J0111-1341 are consistent with it being an ultrafaint stellar cluster, while the half-light radius (rh ≃ 18.55 pc) and luminosity (MV ≃ -1.1) of DES J0225+0304 place it in an ambiguous region of size-luminosity space between stellar clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, metallicity spread (-2.18 ≲ [Fe/H] ≲ -0.95) and distance gradient (23 kpc ≲ D⊙ ≲ 29 kpc), within the DES footprint in the Southern hemisphere, using the same DES data, also indicate a possible association between these systems. If these objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J0111-1341 and DES J0225+0304 would be the first ultrafaint stellar systems associated with the Sagittarius stream. Furthermore, DES J0225+0304 would also be the first confirmed case of an ultrafaint satellite of a satellite.

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

Hyde, E. A.; Keller, S.; Zucker, D. B.

Wrapping around the Milky Way, the Sagittarius stream is the dominant substructure in the halo. Our statistical selection method has allowed us to identify 106 highly likely members of the Sagittarius stream. Spectroscopic analysis of metallicity and kinematics of all members provides us with a new mapping of the Sagittarius stream. We find correspondence between the velocity distribution of stream stars and those computed for a triaxial model of the Milky Way dark matter halo. The Sagittarius trailing arm exhibits a metallicity gradient, ranging from −0.59 to −0.97 dex over 142°. This is consistent with the scenario of tidal disruptionmore » from a progenitor dwarf galaxy that possessed an internal metallicity gradient. We note high metallicity dispersion in the leading arm, causing a lack of detectable gradient and possibly indicating orbital phase mixing. We additionally report on a potential detection of the Sextans dwarf spheroidal in our data.« less

X-RAY SOURCES IN THE DWARF SPHEROIDAL GALAXY DRACO

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

Sonbas, E.; Rangelov, B.; Kargaltsev, O.

2016-04-10

We present the spectral analysis of an 87 ks XMM-Newton observation of Draco, a nearby dwarf spheroidal galaxy. Of the approximately 35 robust X-ray source detections, we focus our attention on the brightest of these sources, for which we report X-ray and multiwavelength parameters. While most of the sources exhibit properties consistent with active galactic nuclei, few of them possess the characteristics of low-mass X-ray binaries (LMXBs) and cataclysmic variable (CVs). Our analysis places constraints on the population of X-ray sources with L{sub X} > 3 × 10{sup 33} erg s{sup −1} in Draco, suggesting that there are no actively accreting black hole andmore » neutron star binaries. However, we find four sources that could be quiescent state LMXBs/CVs associated with Draco. We also place constraints on the central black hole luminosity and on a dark matter decay signal around 3.5 keV.« less

The Dark Energy Survey view of the Sagittarius stream: Discovery of two faint stellar system candidates

DOE PAGES

Luque, E.; Pieres, A.; Santiago, B.; ...

2017-02-17

We report the discovery of two new candidate stellar systems in the constellation of Cetus using the data from the first two years of the Dark Energy Survey (DES). The objects, DES J0111–1341 and DES J0225+0304, are located at a heliocentric distance of ~25 kpc and appear to have old and metal-poor populations. Their distances to the Sagittarius orbital plane, ~1.73 kpc (DES J0111–1341) and ~0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (rh ≃ 4.55 pc) and luminosity (MV ≃ +0.3) of DES J0111–1341 are consistent with it beingmore » an ultrafaint stellar cluster, while the half-light radius (rh ≃ 18.55 pc) and luminosity (MV ≃ –1.1) of DES J0225+0304 place it in an ambiguous region of size–luminosity space between stellar clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, metallicity spread (–2.18 ≲ [Fe/H] ≲ –0.95) and distance gradient (23 kpc ≲ D⊙ ≲ 29 kpc), within the DES footprint in the Southern hemisphere, using the same DES data, also indicate a possible association between these systems. If these objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J0111–1341 and DES J0225+0304 would be the first ultrafaint stellar systems associated with the Sagittarius stream. Moreover, DES J0225+0304 would also be the first confirmed case of an ultrafaint satellite of a satellite.« less

The Dark Energy Survey view of the Sagittarius stream: Discovery of two faint stellar system candidates

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

Luque, E.; Pieres, A.; Santiago, B.

We report the discovery of two new candidate stellar systems in the constellation of Cetus using the data from the first two years of the Dark Energy Survey (DES). The objects, DES J0111–1341 and DES J0225+0304, are located at a heliocentric distance of ~25 kpc and appear to have old and metal-poor populations. Their distances to the Sagittarius orbital plane, ~1.73 kpc (DES J0111–1341) and ~0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (rh ≃ 4.55 pc) and luminosity (MV ≃ +0.3) of DES J0111–1341 are consistent with it beingmore » an ultrafaint stellar cluster, while the half-light radius (rh ≃ 18.55 pc) and luminosity (MV ≃ –1.1) of DES J0225+0304 place it in an ambiguous region of size–luminosity space between stellar clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, metallicity spread (–2.18 ≲ [Fe/H] ≲ –0.95) and distance gradient (23 kpc ≲ D⊙ ≲ 29 kpc), within the DES footprint in the Southern hemisphere, using the same DES data, also indicate a possible association between these systems. If these objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J0111–1341 and DES J0225+0304 would be the first ultrafaint stellar systems associated with the Sagittarius stream. Moreover, DES J0225+0304 would also be the first confirmed case of an ultrafaint satellite of a satellite.« less

The formation of Dwarf Spheroidal galaxies by the dissolving star cluster model.

NASA Astrophysics Data System (ADS)

Alarcon, Alex; Theory and Star Formation Group

2018-01-01

Dwarf spheroidal (dSph) galaxies are regarded as key object in the formation of larger galaxies and are believed to be the most dark matter dominated systems known. There are several model that attempt to explain their formation, but they have problems to model the formation of isolated dSph. Here we will explain a possible formation scenario in which star clusters form in the dark matter halo of a dSph. these cluster suffer from low star formation efficiency and dissolve while orbiting inside the halo. Thereby they build the faint luminous components that we observe in dSph galaxies. Here we will show the main results of this simulations and how they would be corroborated using observational data.

THE DEARTH OF NEUTRAL HYDROGEN IN GALACTIC DWARF SPHEROIDAL GALAXIES

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

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

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

Internal kinematics and dynamical models of dwarf spheroidal galaxies around the Milky Way

NASA Astrophysics Data System (ADS)

Battaglia, Giuseppina; Helmi, Amina; Breddels, Maarten

2013-09-01

We review our current understanding of the internal dynamical properties of the dwarf spheroidal galaxies surrounding the Milky Way. These are the most dark matter dominated galaxies, and as such may be considered ideal laboratories to test the current concordance cosmological model, and in particular provide constraints on the nature of the dominant form of dark matter. We discuss the latest observations of the kinematics of stars in these systems, and how these may be used to derive their mass distribution. We tour through the various dynamical techniques used, with emphasis on the complementarity and limitations, and discuss what the results imply also in the context of cosmological models. Finally we provide an outlook on exciting developments in this field.

PAndAS' CUBS: DISCOVERY OF TWO NEW DWARF GALAXIES IN THE SURROUNDINGS OF THE ANDROMEDA AND TRIANGULUM GALAXIES

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

Martin, Nicolas F.; McConnachie, Alan W.; Irwin, Mike

We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from the first year data of the Pan-Andromeda Archaeological Survey, a photometric survey of the M31/M33 group conducted with the Megaprime/MegaCam Wide-Field Camera mounted on the Canada-France-Hawaii Telescope. Both satellites appear as spatial overdensities of stars which, when plotted in a color-magnitude diagram, follow metal-poor, [Fe/H] = -1.8, red giant branches at the distance of M31/M33. Andromeda XXI is a moderately bright dwarf galaxy (M{sub V} = -9.9 +- 0.6),more » albeit with low surface brightness, emphasizing again that many relatively luminous M31 satellites still remain to be discovered. It is also a large satellite, with a half-light radius close to 1 kpc, making it the fourth largest Local Group dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda II, and Sagittarius around the Milky Way, and supports the trend that M31 satellites are larger than their Milky Way counterparts. Andromeda XXII is much fainter (M{sub V} = -6.5 +- 0.8) and lies a lot closer in projection to M33 than it does to M31 (42 versus 224 kpc), suggesting that it could be the first Triangulum satellite to be discovered. Although this is a very exciting possibility in the context of a past interaction of M33 with M31 and the fate of its satellite system, a confirmation will have to await a good distance estimate to confirm its physical proximity to M33. Along with the dwarf galaxies found in previous surveys of the M31 surroundings, these two new satellites bring the number of dwarf spheroidal galaxies in this region to 20.« less

Tidal disruption of dwarf spheroidal galaxies: the strange case of Crater II

NASA Astrophysics Data System (ADS)

Sanders, Jason L.; Evans, N. W.; Dehnen, W.

2018-05-01

Dwarf spheroidal galaxies of the Local Group obey a relationship between the line-of-sight velocity dispersion and half-light radius, although there are a number of dwarfs that lie beneath this relation with suppressed velocity dispersion. The most discrepant of these (in the Milky Way) is the `feeble giant' Crater II. Using analytic arguments supported by controlled numerical simulations of tidally-stripped flattened two-component dwarf galaxies, we investigate interpretations of Crater II within standard galaxy formation theory. Heavy tidal disruption is necessary to explain the velocity-dispersion suppression which is plausible if the proper motion of Crater II is (μα*, μδ) = ( - 0.21 ± 0.09, -0.24 ± 0.09)mas yr-1. Furthermore, we demonstrate that the velocity dispersion of tidally-disrupted systems is solely a function of the total mass loss even for weakly-embedded and flattened systems. The half-light radius evolution depends more sensitively on orbital phase and the properties of the dark matter profile. The half-light radius of weakly-embedded cusped systems rapidly decreases producing some tension with the Crater II observations. This tension is alleviated by cored dark matter profiles, in which the half-light radius can grow after tidal disruption. The evolution of flattened galaxies is characterised by two competing effects: tidal shocking makes the central regions rounder whilst tidal distortion produces a prolate tidally-locked outer envelope. After ˜70% of the central mass is lost, tidal distortion becomes the dominant effect and the shape of the central regions of the galaxy tends to a universal prolate shape irrespective of the initial shape.

Correcting Velocity Dispersions of Dwarf Spheroidal Galaxies for Binary Orbital Motion

NASA Astrophysics Data System (ADS)

Minor, Quinn E.; Martinez, Greg; Bullock, James; Kaplinghat, Manoj; Trainor, Ryan

2010-10-01

We show that the measured velocity dispersions of dwarf spheroidal galaxies from about 4 to 10 km s-1 are unlikely to be inflated by more than 30% due to the orbital motion of binary stars and demonstrate that the intrinsic velocity dispersions can be determined to within a few percent accuracy using two-epoch observations with 1-2 yr as the optimal time interval. The crucial observable is the threshold fraction—the fraction of stars that show velocity changes larger than a given threshold between measurements. The threshold fraction is tightly correlated with the dispersion introduced by binaries, independent of the underlying binary fraction and distribution of orbital parameters. We outline a simple procedure to correct the velocity dispersion to within a few percent accuracy by using the threshold fraction and provide fitting functions for this method. We also develop a methodology for constraining properties of binary populations from both single- and two-epoch velocity measurements by including the binary velocity distribution in a Bayesian analysis.

On the Nature of Ultra-faint Dwarf Galaxy Candidates. II. The Case of Cetus II

NASA Astrophysics Data System (ADS)

Conn, Blair C.; Jerjen, Helmut; Kim, Dongwon; Schirmer, Mischa

2018-04-01

We obtained deep Gemini GMOS-S g, r photometry of the ultra-faint dwarf galaxy candidate Cetus II with the aim of providing stronger constraints on its size, luminosity, and stellar population. Cetus II is an important object in the size–luminosity plane, as it occupies the transition zone between dwarf galaxies and star clusters. All known objects smaller than Cetus II (r h ∼ 20 pc) are reported to be star clusters, while most larger objects are likely dwarf galaxies. We found a prominent excess of main-sequence stars in the color–magnitude diagram of Cetus II, best described by a single stellar population with an age of 11.2 Gyr, metallicity of [Fe/H] = ‑1.28 dex, an [α/Fe] = 0.0 dex at a heliocentric distance of 26.3 ± 1.2 kpc. As well as being spatially located within the Sagittarius dwarf tidal stream, these properties are well matched to the Sagittarius galaxy’s Population B stars. Interestingly, like our recent findings on the ultra-faint dwarf galaxy candidate Tucana V, the stellar field in the direction of Cetus II shows no evidence of a concentrated overdensity despite tracing the main sequence for over six magnitudes. These results strongly support the picture that Cetus II is not an ultra-faint stellar system in the Milky Way halo, but made up of stars from the Sagittarius tidal stream.

The dwarf spheroidal galaxy in Draco. I - New BV photometry. II - Galactic foreground reddening

NASA Technical Reports Server (NTRS)

Stetson, P. B.

1979-01-01

BV photoelectric photometry for 39 stars and BV photographic photometry for 514 stars in the field of the Draco dwarf spheroidal galaxy are presented. The color-magnitude diagram for 512 of these field stars is found to display a well-defined red horizontal branch as well as a red giant branch whose observed width is comparable to the accidental photometric error. The results also indicate that a more diffuse sequence of stars lies about 0.1 mag to the blue of the giant branch and that an upper horizontal branch of more massive core helium-burning stars may also be present. The foreground reddening toward Draco is then determined by narrow-band uvby-beta photometry of galactic B-A-F stars.

Mapping the Tidal Destruction of the Hercules Dwarf: A Wide-field DECam Imaging Search for RR Lyrae Stars

NASA Astrophysics Data System (ADS)

Garling, Christopher; Willman, Beth; Sand, David J.; Hargis, Jonathan; Crnojević, Denija; Bechtol, Keith; Carlin, Jeffrey L.; Strader, Jay; Zou, Hu; Zhou, Xu; Nie, Jundan; Zhang, Tianmeng; Zhou, Zhimin; Peng, Xiyan

2018-01-01

We investigate the hypothesized tidal disruption of the Hercules ultra-faint dwarf galaxy (UFD). Previous tidal disruption studies of the Hercules UFD have been hindered by the high degree of foreground contamination in the direction of the dwarf. We bypass this issue by using RR Lyrae stars, which are standard candles with a very low field-volume density at the distance of Hercules. We use wide-field imaging from the Dark Energy Camera on CTIO to identify candidate RR Lyrae stars, supplemented with observations taken in coordination with the Beijing–Arizona Sky Survey on the Bok Telescope. Combining color, magnitude, and light-curve information, we identify three new RR Lyrae stars associated with Hercules. All three of these new RR Lyrae stars lie outside its published tidal radius. When considered with the nine RR Lyrae stars already known within the tidal radius, these results suggest that a substantial fraction of Hercules’ stellar content has been stripped. With this degree of tidal disruption, Hercules is an interesting case between a visibly disrupted dwarf (such as the Sagittarius dwarf spheroidal galaxy) and one in dynamic equilibrium. The degree of disruption also shows that we must be more careful with the ways we determine object membership when estimating dwarf masses in the future. One of the three discovered RR Lyrae stars sits along the minor axis of Hercules, but over two tidal radii away. This type of debris is consistent with recent models that suggest Hercules’ orbit is aligned with its minor axis.

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

NASA Astrophysics Data System (ADS)

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

2014-02-01

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

Dark matter profiles and annihilation in dwarf spheroidal galaxies: prospectives for present and future γ-ray observatories - I. The classical dwarf spheroidal galaxies

NASA Astrophysics Data System (ADS)

Charbonnier, A.; Combet, C.; Daniel, M.; Funk, S.; Hinton, J. A.; Maurin, D.; Power, C.; Read, J. I.; Sarkar, S.; Walker, M. G.; Wilkinson, M. I.

2011-12-01

Due to their large dynamical mass-to-light ratios, dwarf spheroidal galaxies (dSphs) are promising targets for the indirect detection of dark matter (DM) in γ-rays. We examine their detectability by present and future γ-ray observatories. The key innovative features of our analysis are as follows: (i) we take into account the angular size of the dSphs; while nearby objects have higher γ-ray flux, their larger angular extent can make them less attractive targets for background-dominated instruments; (ii) we derive DM profiles and the astrophysical J-factor (which parametrizes the expected γ-ray flux, independently of the choice of DM particle model) for the classical dSphs directly from photometric and kinematic data. We assume very little about the DM profile, modelling this as a smooth split-power-law distribution, with and without subclumps; (iii) we use a Markov chain Monte Carlo technique to marginalize over unknown parameters and determine the sensitivity of our derived J-factors to both model and measurement uncertainties; and (iv) we use simulated DM profiles to demonstrate that our J-factor determinations recover the correct solution within our quoted uncertainties. Our key findings are as follows: (i) subclumps in the dSphs do not usefully boost the signal; (ii) the sensitivity of atmospheric Cherenkov telescopes to dSphs within ˜20 kpc with cored haloes can be up to ˜50 times worse than when estimated assuming them to be point-like. Even for the satellite-borne Fermi-Large Area Telescope (Fermi-LAT), the sensitivity is significantly degraded on the relevant angular scales for long exposures; hence, it is vital to consider the angular extent of the dSphs when selecting targets; (iii) no DM profile has been ruled out by current data, but using a prior on the inner DM cusp slope 0 ≤γprior≤ 1 provides J-factor estimates accurate to a factor of a few if an appropriate angular scale is chosen; (iv) the J-factor is best constrained at a critical

Dwarf spheroidal galaxies as degenerate gas of free fermions

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

Domcke, Valerie; Urbano, Alfredo, E-mail: valerie.domcke@sissa.it, E-mail: alfredo.urbano@sissa.it

2015-01-01

In this paper we analyze a simple scenario in which Dark Matter (DM) consists of free fermions with mass m{sub f}. We assume that on galactic scales these fermions are capable of forming a degenerate Fermi gas, in which stability against gravitational collapse is ensured by the Pauli exclusion principle. The mass density of the resulting con figuration is governed by a non-relativistic Lane-Emden equation, thus leading to a universal cored profile that depends only on one free parameter in addition to m{sub f}. After reviewing the basic formalism, we test this scenario against experimental data describing the velocity dispersionmore » of the eight classical dwarf spheroidal galaxies of the Milky Way. We find that, despite its extreme simplicity, the model exhibits a good fit to the data and realistic predictions for the size of DM halos providing that m{sub f}≅ 200 eV. Furthermore, we show that in this setup larger galaxies correspond to the non-degenerate limit of the gas. We propose a concrete realization of this model in which DM is produced non-thermally via inflaton decay. We show that imposing the correct relic abundance and the bound on the free-streaming length constrains the inflation model in terms of inflaton mass, its branching ratio into DM and the reheating temperature.« less

PAndAS' CUBS: Discovery of Two New Dwarf Galaxies in the Surroundings of the Andromeda and Triangulum Galaxies

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; McConnachie, Alan W.; Irwin, Mike; Widrow, Lawrence M.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Dubinski, John; Babul, Arif; Chapman, Scott; Fardal, Mark; Lewis, Geraint F.; Navarro, Julio; Rich, R. Michael

2009-11-01

We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from the first year data of the Pan-Andromeda Archaeological Survey, a photometric survey of the M31/M33 group conducted with the Megaprime/MegaCam Wide-Field Camera mounted on the Canada-France-Hawaii Telescope. Both satellites appear as spatial overdensities of stars which, when plotted in a color-magnitude diagram, follow metal-poor, [Fe/H] = -1.8, red giant branches at the distance of M31/M33. Andromeda XXI is a moderately bright dwarf galaxy (MV = -9.9 ± 0.6), albeit with low surface brightness, emphasizing again that many relatively luminous M31 satellites still remain to be discovered. It is also a large satellite, with a half-light radius close to 1 kpc, making it the fourth largest Local Group dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda II, and Sagittarius around the Milky Way, and supports the trend that M31 satellites are larger than their Milky Way counterparts. Andromeda XXII is much fainter (MV = -6.5 ± 0.8) and lies a lot closer in projection to M33 than it does to M31 (42 versus 224 kpc), suggesting that it could be the first Triangulum satellite to be discovered. Although this is a very exciting possibility in the context of a past interaction of M33 with M31 and the fate of its satellite system, a confirmation will have to await a good distance estimate to confirm its physical proximity to M33. Along with the dwarf galaxies found in previous surveys of the M31 surroundings, these two new satellites bring the number of dwarf spheroidal galaxies in this region to 20. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of

Spectroscopy of Six Red Giants in the Draco Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Smith, Graeme H.; Siegel, Michael H.; Shetrone, Matthew D.; Winnick, Rebeccah

2006-10-01

Keck Observatory LRIS-B (Low Resolution Imaging Spectrometer) spectra are reported for six red giant stars in the Draco dwarf spheroidal galaxy and several comparison giants in the globular cluster M13. Indexes that quantify the strengths of the Ca II H and K lines, the λ3883 and λ4215 CN bands, and the λ4300 G band have been measured. These data confirm evidence of metallicity inhomogeneity within Draco obtained by previous authors. The four brightest giants in the sample have absolute magnitudes in the range -2.6dwarf galaxy may have experienced relatively slow chemical evolution over a period of several billion years, allowing carbon-enhanced ejecta from intermediate-mass asymptotic giant branch stars to enrich the interstellar medium while star formation was still occurring. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

THE SPLASH SURVEY: SPECTROSCOPY OF 15 M31 DWARF SPHEROIDAL SATELLITE GALAXIES

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

Tollerud, Erik J.; Bullock, James S.; Yniguez, Basilio

2012-06-10

We present a resolved star spectroscopic survey of 15 dwarf spheroidal (dSph) satellites of the Andromeda galaxy (M31). We filter foreground contamination from Milky Way (MW) stars, noting that MW substructure is evident in this contaminant sample. We also filter M31 halo field giant stars and identify the remainder as probable dSph members. We then use these members to determine the kinematical properties of the dSphs. For the first time, we confirm that And XVIII, XXI, and XXII show kinematics consistent with bound, dark-matter-dominated galaxies. From the velocity dispersions for the full sample of dSphs we determine masses, which wemore » combine with the size and luminosity of the galaxies to produce mass-size-luminosity scaling relations. With these scalings we determine that the M31 dSphs are fully consistent with the MW dSphs, suggesting that the well-studied MW satellite population provides a fair sample for broader conclusions. We also estimate dark matter halo masses of the satellites and find that there is no sign that the luminosity of these galaxies depends on their dark halo mass, a result consistent with what is seen for MW dwarfs. Two of the M31 dSphs (And XV, XVI) have estimated maximum circular velocities smaller than 12 km s{sup -1} (to 1{sigma}), which likely places them within the lowest-mass dark matter halos known to host stars (along with Booetes I of the MW). Finally, we use the systemic velocities of the M31 satellites to estimate the mass of the M31 halo, obtaining a virial mass consistent with previous results.« less

Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies

PubMed Central

Qian, Yong-Zhong; Wasserburg, G. J.

2012-01-01

We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relationship between the total stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos. The model further predicts as a natural consequence that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease for stellar populations at the higher end of the [Fe/H] range in a dSph. We show that, for infall rates far below the net rate of gas loss to star formation and outflows, the MD in our model is very sharply peaked at one [Fe/H] value, similar to what is observed in most globular clusters. This result suggests that globular clusters may be end members of the same family as dSphs. PMID:22411827

Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies.

PubMed

Qian, Yong-Zhong; Wasserburg, G J

2012-03-27

We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relationship between the total stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos. The model further predicts as a natural consequence that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease for stellar populations at the higher end of the [Fe/H] range in a dSph. We show that, for infall rates far below the net rate of gas loss to star formation and outflows, the MD in our model is very sharply peaked at one [Fe/H] value, similar to what is observed in most globular clusters. This result suggests that globular clusters may be end members of the same family as dSphs.

A Kinematic Study of the Andromeda Dwarf Spheroidal System

NASA Astrophysics Data System (ADS)

Collins, Michelle L. M.; Chapman, Scott C.; Rich, R. Michael; Ibata, Rodrigo A.; Martin, Nicolas F.; Irwin, Michael J.; Bate, Nicholas F.; Lewis, Geraint F.; Peñarrubia, Jorge; Arimoto, Nobuo; Casey, Caitlin M.; Ferguson, Annette M. N.; Koch, Andreas; McConnachie, Alan W.; Tanvir, Nial

2013-05-01

We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the Keck I/LRIS and Keck II/DEIMOS spectrographs. Based on their g - i colors (taken with the CFHT/MegaCam imager), physical positions on the sky, and radial velocities, we assign probabilities of dSph membership to each observed star. Using this information, the velocity dispersions, central masses, and central densities of the dark matter halos are calculated for these objects, and compared with the properties of the Milky Way dSph population. We also measure the average metallicity ([Fe/H]) from the co-added spectra of member stars for each M31 dSph and find that they are consistent with the trend of decreasing [Fe/H] with luminosity observed in the Milky Way population. We find that three of our studied M31 dSphs appear as significant outliers in terms of their central velocity dispersion, And XIX, XXI, and XXV, all of which have large half-light radii (gsim 700 pc) and low velocity dispersions (σ v < 5 km s-1). In addition, And XXV has a mass-to-light ratio within its half-light radius of just [M/L]_half=10.3^{+7.0}_{-6.7}, making it consistent with a simple stellar system with no appreciable dark matter component within its 1σ uncertainties. We suggest that the structure of the dark matter halos of these outliers have been significantly altered by tides.

A KINEMATIC STUDY OF THE ANDROMEDA DWARF SPHEROIDAL SYSTEM

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

Collins, Michelle L. M.; Martin, Nicolas F.; Chapman, Scott C.

We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the Keck I/LRIS and Keck II/DEIMOS spectrographs. Based on their g - i colors (taken with the CFHT/MegaCam imager), physical positions on the sky, and radial velocities, we assign probabilities of dSph membership to each observed star. Using this information, the velocity dispersions, central masses, and central densities of the dark matter halos are calculated for these objects, and compared with the properties of the Milky Way dSph population. We also measure the average metallicity ([Fe/H]) frommore » the co-added spectra of member stars for each M31 dSph and find that they are consistent with the trend of decreasing [Fe/H] with luminosity observed in the Milky Way population. We find that three of our studied M31 dSphs appear as significant outliers in terms of their central velocity dispersion, And XIX, XXI, and XXV, all of which have large half-light radii ({approx}> 700 pc) and low velocity dispersions ({sigma}{sub v} < 5 km s{sup -1}). In addition, And XXV has a mass-to-light ratio within its half-light radius of just [M/L]{sub half}=10.3{sup +7.0}{sub -6.7}, making it consistent with a simple stellar system with no appreciable dark matter component within its 1{sigma} uncertainties. We suggest that the structure of the dark matter halos of these outliers have been significantly altered by tides.« less

MOND Calculations of Bulk Dispersions and Radial Dispersion Profiles of Milky Way and Andromeda Dwarf Spheroidal Galaxies

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

Alexander, S. G.; Walentosky, M. J.; Messinger, Justin

We present a new computational method for calculating the motion of stars in a dwarf spheroidal galaxy (dSph) that can use either Newtonian gravity or Modified Newtonian Dynamics (MOND). In our model, we explicitly calculate the motion of several thousand stars in a spherically symmetric gravitational potential, and we statistically obtain both the line-of-sight bulk velocity dispersion and dispersion profile. Our results for MOND calculated bulk dispersions for Local Group dSph’s agree well with previous calculations and observations. Our MOND calculated dispersion profiles are compared with the observations of Walker et al. for Milky Way dSph’s, and we present calculatedmore » dispersion profiles for a selection of Andromeda dSph’s.« less

MEASURING DARK MATTER PROFILES NON-PARAMETRICALLY IN DWARF SPHEROIDALS: AN APPLICATION TO DRACO

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

Jardel, John R.; Gebhardt, Karl; Fabricius, Maximilian H.

2013-02-15

We introduce a novel implementation of orbit-based (or Schwarzschild) modeling that allows dark matter density profiles to be calculated non-parametrically in nearby galaxies. Our models require no assumptions to be made about velocity anisotropy or the dark matter profile. The technique can be applied to any dispersion-supported stellar system, and we demonstrate its use by studying the Local Group dwarf spheroidal galaxy (dSph) Draco. We use existing kinematic data at larger radii and also present 12 new radial velocities within the central 13 pc obtained with the VIRUS-W integral field spectrograph on the 2.7 m telescope at McDonald Observatory. Ourmore » non-parametric Schwarzschild models find strong evidence that the dark matter profile in Draco is cuspy for 20 {<=} r {<=} 700 pc. The profile for r {>=} 20 pc is well fit by a power law with slope {alpha} = -1.0 {+-} 0.2, consistent with predictions from cold dark matter simulations. Our models confirm that, despite its low baryon content relative to other dSphs, Draco lives in a massive halo.« less

The PAndAS View of the Andromeda Satellite System. II. Detailed Properties of 23 M31 Dwarf Spheroidal Galaxies

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; Ibata, Rodrigo A.; Lewis, Geraint F.; McConnachie, Alan; Babul, Arif; Bate, Nicholas F.; Bernard, Edouard; Chapman, Scott C.; Collins, Michelle M. L.; Conn, Anthony R.; Crnojević, Denija; Fardal, Mark A.; Ferguson, Annette M. N.; Irwin, Michael; Mackey, A. Dougal; McMonigal, Brendan; Navarro, Julio F.; Rich, R. Michael

2016-12-01

We present a comprehensive analysis of the structural properties and luminosities of the 23 dwarf spheroidal galaxies that fall within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS). These dwarf galaxies represent the large majority of Andromeda’s known satellite dwarf galaxies and cover a wide range in luminosity (-11.6≲ {M}V≲ -5.8 or {10}4.2≲ L≲ {10}6.5 {L}⊙ ) and surface brightness (25.1≲ {μ }0≲ 29.3 mag arcsec-2). We confirm most previous measurements, but we find And XIX to be significantly larger than before ({r}h={3065}-935+1065 {pc}, {M}V=-{10.1}-0.4+0.8) and cannot derive parameters for And XXVII as it is likely not a bound stellar system. We also significantly revise downward the luminosities of And XV and And XVI, which are now {M}V˜ -7.5 or L˜ {10}5 {L}⊙ . Finally, we provide the first detailed analysis of Cas II/And XXX, a fairly faint system ({M}V=-{8.0}-0.3+0.4) of typical size ({r}h=270+/- 50 {pc}), located in close proximity to the two bright elliptical dwarf galaxies NGC 147 and NGC 185. Combined with the set of homogeneous distances published in an earlier contribution, our analysis dutifully tracks all relevant sources of uncertainty in the determination of the properties of the dwarf galaxies from the PAndAS photometric catalog. We further publish the posterior probability distribution functions of all the parameters we fit for in the form of MCMC chains available online; these inputs should be used in any analysis that aims to remain truthful to the data and properly account for covariance between parameters.

ANDROMEDA DWARFS IN LIGHT OF MODIFIED NEWTONIAN DYNAMICS

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

McGaugh, Stacy; Milgrom, Mordehai

We compare the recently published velocity dispersions for 17 Andromeda dwarf spheroidals with estimates of the modified Newtonian dynamics predictions, based on the luminosities of these dwarfs, with reasonable stellar mass-to-light values and no dark matter. We find that the two are consistent within the uncertainties. We further predict the velocity dispersions of another 10 dwarfs for which only photometric data are currently available.

The Outer Profile of the Draco Dwarf Spheroidal Galaxy: Measuring the Mass-Loss Rate

NASA Astrophysics Data System (ADS)

Armandroff, Taft; Pryor, Carlton; Olszewski, Edward

1999-02-01

The existence and properties of dark matter in dwarf galaxies have fundamental implications for cosmology and galaxy formation. We are engaged in a long-term effort to observe and model the structure, kinematics, and mass-to-light ratios of the Draco and UMi dwarf spheroidal (dSph) galaxies. Here we propose to extend our work with a search for outlying members and tidal tails of the Draco dSph galaxy, motivated by observational, theoretical, and technical advances. Recent sophisticated modeling of tidal interactions with the Galactic potential clarifies the interpretation of tidal tails and shows how to calculate the rate at which stars have been lost from a dSph or globular from the density profile of the tidal debris. Also, the radius of the transition between bound and unbound stars yields the outer boundary and total mass of the dark matter halos in the dSphs. While central mass densities and central mass-to-light ratios are generally available for dSphs, determination of their total masses (like those of any galaxy) has remained elusive. We will map a 24 square degree area along the major axis of Draco, plus six square degrees of background. Use of a 3-filter technique will result in an unprecedentedly clean census of distant Draco stars and, thus, a major-axis density profile to a radius of ~6°. Our long-term goal is to investigate the kinematics of the outer members and tidal-tail stars in order to compare in detail with the models.

A COMPREHENSIVE, WIDE-FIELD STUDY OF PULSATING STARS IN THE CARINA DWARF SPHEROIDAL GALAXY

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

Vivas, A. Katherina; Mateo, Mario, E-mail: akvivas@cida.ve, E-mail: mmateo@umich.edu

2013-12-01

We report the detection of 388 pulsating variable stars (and some additional miscellaneous variables) in the Carina dwarf spheroidal galaxy over an area covering the full visible extent of the galaxy and extending a few times beyond its photometric (King) tidal radius along the direction of its major axis. Included in this total are 340 newly discovered dwarf Cepheids (DCs), which are mostly located ∼2.5 mag below the horizontal branch and have very short periods (<0.1 days), typical of their class and consistent with their location on the upper part of the extended main sequence of the younger populations ofmore » the galaxy. Several extra-tidal DCs were found in our survey up to a distance of ∼1° from the center of Carina. Our sample also includes RR Lyrae stars and anomalous Cepheids, some of which were found outside the galaxy's tidal radius as well. This supports past works that suggest that Carina is undergoing tidal disruption. We use the period-luminosity relationship for DCs to estimate a distance modulus of μ{sub 0} = 20.17 ± 0.10 mag, in very good agreement with the estimate from RR Lyrae stars. We find some important differences in the properties of the DCs of Carina and those in Fornax and the LMC, the only extragalactic samples of DCs currently known. These differences may reflect a metallicity spread, depth along the line of sight, and/or different evolutionary paths of the DC stars.« less

Phase-space mass bound for fermionic dark matter from dwarf spheroidal galaxies

NASA Astrophysics Data System (ADS)

Di Paolo, Chiara; Nesti, Fabrizio; Villante, Francesco L.

2018-04-01

We reconsider the lower bound on the mass of a fermionic dark matter (DM) candidate resulting from the existence of known small dwarf spheroidal galaxies, in the hypothesis that their DM halo is constituted by degenerate fermions, with phase-space density limited by the Pauli exclusion principle. By relaxing the common assumption that the DM halo scale radius is tied to that of the luminous stellar component and by marginalizing on the unknown stellar velocity dispersion anisotropy, we prove that observations lead to rather weak constraints on the DM mass, which could be as low as tens of eV. In this scenario, however, the DM haloes would be quite large and massive, so that a bound stems from the requirement that the time of orbital decay due to dynamical friction in the hosting Milky Way DM halo is longer than their lifetime. The smallest and nearest satellites Segue I and Willman I lead to a final lower bound of m ≳ 100 eV, still weaker than previous estimates but robust and independent on the model of DM formation and decoupling. We thus show that phase-space constraints do not rule out the possibility of sub-keV fermionic DM.

Scaling Laws for Dark Matter Halos in Late-type and Dwarf Spheroidal Galaxies

NASA Astrophysics Data System (ADS)

Kormendy, John; Freeman, K. C.

2016-02-01

Dark matter (DM) halos of Sc-Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes MV > -18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention versus supernova-driven losses or decreasing baryon capture after cosmological reionization. (2) The structural differences between S+Im and Sph galaxies are small. Both are affected mostly by the physics that controls baryon depletion. (3) There is a linear correlation between the maximum rotation velocities of baryonic disks and the outer circular velocities Vcirc of test particles in their DM halos. Baryons become unimportant at Vcirc = 42 ± 4 km s-1. Smaller galaxies are dim or dark. (4) We find that, absent baryon “depletion” and with all baryons converted into stars, dSph galaxies would be brighter by ˜4.6 mag and dIm galaxies would be brighter by ˜3.5 mag. Both have DM halos that are massive enough to help to solve the “too big to fail” problem with DM galaxy formation. (5) We suggest that there exist many galaxies that are too dark to be discovered by current techniques, as required by cold DM theory. (6) Central surface densities of DM halos are constant from MB ˜ -5 to -22. This implies a Faber-Jackson law with halo mass M ∝ (halo dispersion)4.

SCALING LAWS FOR DARK MATTER HALOS IN LATE-TYPE AND DWARF SPHEROIDAL GALAXIES

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

Kormendy, John; Freeman, K. C., E-mail: kormendy@astro.as.utexas.edu, E-mail: kenneth.freeman@anu.edu.au

2016-02-01

Dark matter (DM) halos of Sc–Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes M{sub V} > −18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention versus supernova-driven losses or decreasing baryon capture after cosmological reionization. (2) The structural differences betweenmore » S+Im and Sph galaxies are small. Both are affected mostly by the physics that controls baryon depletion. (3) There is a linear correlation between the maximum rotation velocities of baryonic disks and the outer circular velocities V{sub circ} of test particles in their DM halos. Baryons become unimportant at V{sub circ} = 42 ± 4 km s{sup −1}. Smaller galaxies are dim or dark. (4) We find that, absent baryon “depletion” and with all baryons converted into stars, dSph galaxies would be brighter by ∼4.6 mag and dIm galaxies would be brighter by ∼3.5 mag. Both have DM halos that are massive enough to help to solve the “too big to fail” problem with DM galaxy formation. (5) We suggest that there exist many galaxies that are too dark to be discovered by current techniques, as required by cold DM theory. (6) Central surface densities of DM halos are constant from M{sub B} ∼ −5 to −22. This implies a Faber–Jackson law with halo mass M ∝ (halo dispersion){sup 4}.« less

Unbiased constraints on ultralight axion mass from dwarf spheroidal galaxies

NASA Astrophysics Data System (ADS)

González-Morales, Alma X.; Marsh, David J. E.; Peñarrubia, Jorge; Ureña-López, Luis A.

2017-12-01

It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with ma ∼ 10-22 eV are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here, we use realistic kinematic mock data catalogues of Milky Way (MW) dSph's to show that the 'mass-anisotropy degeneracy' in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components, this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with reported stellar subcomponents, Fornax and Sculptor, and assuming that the halo profile has not been acted on by baryons, yields core radii rc > 1.5 and 1.2 kpc, respectively, and ma < 0.4 × 10-22 eV at 97.5 per cent confidence. These bounds are in tension with the number of observed satellites derived from simple (but conservative) estimates of the subhalo mass function in MW-like galaxies. We discuss how baryonic feedback might affect our results, and the impact of such a small axion mass on the growth of structures in the Universe.

A New View of the Dwarf Spheroidal Satellites of the Milky Way From VLT/FLAMES: Where are the Very Metal Poor Stars?

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

Helmi, Amina; Irwin, M.J.; Tolstoy, E.

As part of the Dwarf galaxies Abundances and Radial-velocities Team (DART) Programme, we have measured the metallicities of a large sample of stars in four nearby dwarf spheroidal galaxies (dSph): Sculptor, Sextans, Fornax and Carina. The low mean metal abundances and the presence of very old stellar populations in these galaxies have supported the view that they are fossils from the early Universe. However, contrary to naive expectations, we find a significant lack of stars with metallicities below [Fe/H] {approx} -3 dex in all four systems. This suggests that the gas that made up the stars in these systems hadmore » been uniformly enriched prior to their formation. Furthermore, the metal-poor tail of the dSph metallicity distribution is significantly different from that of the Galactic halo. These findings show that the progenitors of nearby dSph appear to have been fundamentally different from the building blocks of the Milky Way, even at the earliest epochs.« less

Static structure of chameleon dark matter as an explanation of dwarf spheroidal galaxy cores

NASA Astrophysics Data System (ADS)

Chanda, Prolay Krishna; Das, Subinoy

2017-04-01

We propose a novel mechanism that explains the cored dark matter density profile in recently observed dark matter rich dwarf spheroidal galaxies. In our scenario, dark matter particle mass decreases gradually as a function of distance towards the center of a dwarf galaxy due to its interaction with a chameleon scalar. At closer distance towards the Galactic center the strength of attractive scalar fifth force becomes much stronger than gravity and is balanced by the Fermi pressure of the dark matter cloud; thus, an equilibrium static configuration of the dark matter halo is obtained. Like the case of soliton star or fermion Q-star, the stability of the dark matter halo is obtained as the scalar achieves a static profile and reaches an asymptotic value away from the Galactic center. For simple scalar-dark matter interaction and quadratic scalar self-interaction potential, we show that dark matter behaves exactly like cold dark matter (CDM) beyond a few kpc away from the Galactic center but at closer distance it becomes lighter and Fermi pressure cannot be ignored anymore. Using Thomas-Fermi approximation, we numerically solve the radial static profile of the scalar field, fermion mass and dark matter energy density as a function of distance. We find that for fifth force mediated by an ultralight scalar, it is possible to obtain a flattened dark matter density profile towards the Galactic center. In our scenario, the fifth force can be neglected at distance r ≥1 kpc from the Galactic center and dark matter can be simply treated as heavy nonrelativistic particles beyond this distance, thus reproducing the success of CDM at large scales.

The SPLASH Survey: Spectroscopy of 15 M31 Dwarf Spheroidal Satellite Galaxies

NASA Astrophysics Data System (ADS)

Tollerud, Erik J.; Beaton, Rachael L.; Geha, Marla C.; Bullock, James S.; Guhathakurta, Puragra; Kalirai, Jason S.; Majewski, Steve R.; Kirby, Evan N.; Gilbert, Karoline M.; Yniguez, Basilio; Patterson, Richard J.; Ostheimer, James C.; Cooke, Jeff; Dorman, Claire E.; Choudhury, Abrar; Cooper, Michael C.

2012-06-01

We present a resolved star spectroscopic survey of 15 dwarf spheroidal (dSph) satellites of the Andromeda galaxy (M31). We filter foreground contamination from Milky Way (MW) stars, noting that MW substructure is evident in this contaminant sample. We also filter M31 halo field giant stars and identify the remainder as probable dSph members. We then use these members to determine the kinematical properties of the dSphs. For the first time, we confirm that And XVIII, XXI, and XXII show kinematics consistent with bound, dark-matter-dominated galaxies. From the velocity dispersions for the full sample of dSphs we determine masses, which we combine with the size and luminosity of the galaxies to produce mass-size-luminosity scaling relations. With these scalings we determine that the M31 dSphs are fully consistent with the MW dSphs, suggesting that the well-studied MW satellite population provides a fair sample for broader conclusions. We also estimate dark matter halo masses of the satellites and find that there is no sign that the luminosity of these galaxies depends on their dark halo mass, a result consistent with what is seen for MW dwarfs. Two of the M31 dSphs (And XV, XVI) have estimated maximum circular velocities smaller than 12 km s-1 (to 1σ), which likely places them within the lowest-mass dark matter halos known to host stars (along with Boötes I of the MW). Finally, we use the systemic velocities of the M31 satellites to estimate the mass of the M31 halo, obtaining a virial mass consistent with previous results. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Search for gamma-ray emission from the nearby dwarf spheroidal galaxies with 9 years of Fermi-LAT data

NASA Astrophysics Data System (ADS)

Li, Shang; Duan, Kai-Kai; Liang, Yun-Feng; Xia, Zi-Qing; Shen, Zhao-Qiang; Li, Xiang; Liao, Neng-Hui; Feng, Lei; Yuan, Qiang; Fan, Yi-Zhong; Chang, Jin

2018-06-01

In this work, we search for γ -ray emission from nearby Milky Way dwarf spheroidal galaxies (dSphs) and candidates with the publicly available Pass 8 data of Fermi-LAT. Our sample includes 12 sources with the distances <50 kpc . Very weak γ -ray excesses (˜2 σ ) are found in some dSphs/candidates, consistent with those reported in the previous literature. Intriguingly, the peak test statistic (TS) value of the weak emission from Reticulum II rises continually. If interpreted as dark matter (DM) annihilation, the peak TS value is 13.5 for the annihilation channel of χ χ →τ+τ- and the DM mass of mχ˜16 GeV . The combination of all these nearby sources yields a more significant (with local significance >4 σ ) γ -ray signal.

Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data

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

Drlica-Wagner, A.; et al.

Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with massesmore » $$\\lesssim 20\\,\\mathrm{GeV}$$ annihilating via the $$b\\bar{b}$$ or τ(+)τ(-) channels.« less

Search for gamma-ray emission from des dwarf spheroidal galaxy candidates with Fermi LAT data

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

Drlica-Wagner, A.; Albert, A.; Bechtol, K.

Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. Here, we found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with massesmore » $$\\lesssim 20\\;\\mathrm{GeV}$$ annihilating via the $$b\\bar{b}$$ or τ +τ - channels.« less

Search for gamma-ray emission from des dwarf spheroidal galaxy candidates with Fermi LAT data

DOE PAGES

Drlica-Wagner, A.; Albert, A.; Bechtol, K.; ...

2015-08-04

Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. Here, we found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with massesmore » $$\\lesssim 20\\;\\mathrm{GeV}$$ annihilating via the $$b\\bar{b}$$ or τ +τ - channels.« less

The influence of Sagittarius and the Large Magellanic Cloud on the stellar disc of the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Laporte, Chervin F. P.; Johnston, Kathryn V.; Gómez, Facundo A.; Garavito-Camargo, Nicolas; Besla, Gurtina

2018-06-01

We present N-body simulations of a Sagittarius-like dwarf spheroidal galaxy (Sgr) that follow its orbit about the Milky Way (MW) since its first crossing of the Galaxy's virial radius to the present day. As Sgr orbits around the MW, it excites vertical oscillations, corrugating and flaring the Galactic stellar disc. These responses can be understood by a two-phase picture in which the interaction is first dominated by torques from the wake excited by Sgr in the MW dark halo before transitioning to tides from Sgr's direct impact on the disc at late times. We show for the first time that a massive Sgr model simultaneously reproduces the locations and motions of arc-like over densities, such as the Monoceros Ring and the Triangulum Andromeda stellar clouds, that have been observed at the extremities of the disc, while also satisfying the solar neighbourhood constraints on the vertical structure and streaming motions of the disc. In additional simulations, we include the Large Magellanic Cloud (LMC) self consistently with Sgr. The LMC introduces coupling through constructive and destructive interference, but no new corrugations. In our models, the excitation of the current structure of the outer disk can be traced to interactions as far back as 6-7 Gyr ago (corresponding to z ≤ 1). Given the apparently quiescent accretion history of the MW over this timescale, this places Sgr as the main culprit behind the vertical oscillations of the disc and the last major accretion event for the Galaxy with the capacity to modulate its chemodynamical structure.

Searching for Dark Matter Annihilation from Milky Way Dwarf Spheroidal Galaxies with Six Years of Fermi Large Area Telescope Data.

PubMed

Ackermann, M; Albert, A; Anderson, B; Atwood, W B; Baldini, L; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Bissaldi, E; Blandford, R D; Bloom, E D; Bonino, R; Bottacini, E; Brandt, T J; Bregeon, J; Bruel, P; Buehler, R; Caliandro, G A; Cameron, R A; Caputo, R; Caragiulo, M; Caraveo, P A; Cecchi, C; Charles, E; Chekhtman, A; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cuoco, A; Cutini, S; D'Ammando, F; de Angelis, A; de Palma, F; Desiante, R; Digel, S W; Di Venere, L; Drell, P S; Drlica-Wagner, A; Essig, R; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Gomez-Vargas, G A; Grenier, I A; Guiriec, S; Gustafsson, M; Hays, E; Hewitt, J W; Horan, D; Jogler, T; Jóhannesson, G; Kuss, M; Larsson, S; Latronico, L; Li, J; Li, L; Llena Garde, M; Longo, F; Loparco, F; Lubrano, P; Malyshev, D; Mayer, M; Mazziotta, M N; McEnery, J E; Meyer, M; Michelson, P F; Mizuno, T; Moiseev, A A; Monzani, M E; Morselli, A; Murgia, S; Nuss, E; Ohsugi, T; Orienti, M; Orlando, E; Ormes, J F; Paneque, D; Perkins, J S; Pesce-Rollins, M; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Ritz, S; Sánchez-Conde, M; Schulz, A; Sehgal, N; Sgrò, C; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Strigari, L; Tajima, H; Takahashi, H; Thayer, J B; Tibaldo, L; Torres, D F; Troja, E; Vianello, G; Werner, M; Winer, B L; Wood, K S; Wood, M; Zaharijas, G; Zimmer, S

2015-12-04

The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are some of the most dark matter (DM) dominated objects known. We report on γ-ray observations of Milky Way dSphs based on six years of Fermi Large Area Telescope data processed with the new Pass8 event-level analysis. None of the dSphs are significantly detected in γ rays, and we present upper limits on the DM annihilation cross section from a combined analysis of 15 dSphs. These constraints are among the strongest and most robust to date and lie below the canonical thermal relic cross section for DM of mass ≲100  GeV annihilating via quark and τ-lepton channels.

Searching for dark matter annihilation from Milky Way dwarf spheroidal galaxies with six years of Fermi Large Area Telescope data

DOE PAGES

Ackermann, M.

2015-11-30

The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are some of the most dark matter (DM) dominated objects known. We report on γ-ray observations of Milky Way dSphs based on six years of Fermi Large Area Telescope data processed with the new Pass8 event-level analysis. None of the dSphs are significantly detected in γ rays, and we present upper limits on the DM annihilation cross section from a combined analysis of 15 dSphs. As a result, these constraints are among the strongest and most robust to date and lie below the canonical thermal relic cross section for DMmore » of mass ≲100 GeV annihilating via quark and τ-lepton channels.« less

Stellar kinematics and dark matter in dwarf galaxies

NASA Astrophysics Data System (ADS)

Battaglia, Giuseppina

2015-08-01

In this review I will tour through the most recent findings on the internal kinematic properties of Local Group dwarf galaxies, as determined from extensive spectroscopic surveys of their stellar component.I will also discuss the current status on determinations of the dark matter content and distribution in these objects, with particular focus on the Milky Way dwarf spheroidals, for which the available data-sets allow the application of sophisticated mass modeling techniques.

Foreground effect on the J-factor estimation of classical dwarf spheroidal galaxies

NASA Astrophysics Data System (ADS)

Ichikawa, Koji; Ishigaki, Miho N.; Matsumoto, Shigeki; Ibe, Masahiro; Sugai, Hajime; Hayashi, Kohei; Horigome, Shun-ichi

2017-07-01

The gamma-ray observation of the dwarf spheroidal galaxies (dSphs) is a promising approach to search for the dark matter annihilation (or decay) signal. The dSphs are the nearby satellite galaxies with a clean environment and dense dark matter halo so that they give stringent constraints on the O(1) TeV dark matter. However, recent studies have revealed that current estimation of astrophysical factors relevant for the dark matter searches are not conservative, where the various non-negligible systematic uncertainties are not taken into account. Among them, the effect of foreground stars on the astrophysical factors has not been paid much attention, which becomes more important for deeper and wider stellar surveys in the future. In this article, we assess the effects of the foreground contamination by generating the mock samples of stars and using a model of future spectrographs. We investigate various data cuts to optimize the quality of the data and find that the cuts on the velocity and surface gravity can efficiently eliminate the contamination. We also propose a new likelihood function that includes the foreground distribution function. We apply this likelihood function to the fit of the three types of the mock data (Ursa Minor, Draco with large dark matter halo and Draco with small halo) and three cases of the observation. The likelihood successfully reproduces the input J-factor value while the fit without considering the foreground distribution gives a large deviation from the input value by a factor of 3.

The Structure and Dark Halo Core Properties of Dwarf Spheroidal Galaxies

NASA Astrophysics Data System (ADS)

Burkert, A.

2015-08-01

The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal (DIS) model of an isothermal, non-self-gravitating stellar system embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions. The stellar core scale length a* is sensitive to the central dark matter density ρ0,d. The maximum stellar radius traces the dark halo core radius {r}c,d. The concentration c* of the stellar system, determined by a King profile fit, depends on the ratio of the stellar-to-dark-matter velocity dispersion {σ }*/{σ }d. Simple empirical relationships are derived that allow us to calculate the dark halo core parameters ρ0,d, {r}c,d, and σd given the observable stellar quantities σ*, a*, and c*. The DIS model is applied to the Milky Way’s dSphs. All dSphs closely follow the same universal dark halo scaling relations {ρ }0,d× {r}c,d={75}-45+85 M⊙ pc-2 that characterize the cores of more massive galaxies over a large range in masses. The dark halo core mass is a strong function of core radius, {M}c,d˜ {r}c,d2. Inside a fixed radius of ˜400 pc the total dark matter mass is, however, roughly constant with {M}d=2.6+/- 1.4× {10}7 M⊙, although outliers are expected. The dark halo core densities of the Galaxy’s dSphs are very high, with {ρ }0,d ≈ 0.2 M⊙ pc-3. dSphs should therefore be tidally undisturbed. Evidence for tidal effects might then provide a serious challenge for the CDM scenario.

Identifying Type Ia Supernova Mechanisms in Dwarf Spheroidal Galaxies through Analysis of Iron-peak Elemental Abundances

NASA Astrophysics Data System (ADS)

Guo, Rachel; Xie, Justin Long; Kirby, Evan N.

2017-01-01

Through the fusion of nucleons to produce elements heavier than hydrogen and helium, stellar nucleosynthesis produces most of the elements in the universe. Such is the case in a supernova explosion, which creates most of the elements on the periodic table—including iron-peak elements, atomic numbers 21 through 30—through nucleosynthesis and ejects them into the interstellar medium. In this study, we determine the best theoretical supernova model appropriate for the stars in the dwarf spheroidal galaxies Sculptor, Fornax, Ursa Minor, and Leo II by calculating the abundances of iron-peak elements in these stars. To determine iron-peak elemental abundances, we compare synthesized spectra with observed spectra from medium-resolution spectroscopy and determine the best-fitting spectrum by way of a chi-squared minimization. Through inspecting the relationship between the iron-peak element abundances and the abundance of iron itself and by comparing them to previously hypothesized supernova model theories, we discover that the near-Chandrasekhar mass “n1” model, as predicted by Seitenzahl et al., most accurately represents the trends and patterns within our data, presenting new insight into Type Ia supernovae mechanisms within the Milky Way and beyond.

The metal-poor knee in the Fornax dwarf spheroidal galaxy

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

Hendricks, Benjamin; Koch, Andreas; Lanfranchi, Gustavo A.

2014-04-20

We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ∼ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ –2.5 continuously to [Fe/H] ≈ –0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus tomore » trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined 'knee' caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ –1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ∼10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general.« less

n-capture elements in the Sculptor dwarf spheroidal galaxy

NASA Astrophysics Data System (ADS)

Skúladóttir, Ása

2018-06-01

Sculptor is a well studied dwarf galaxy in the Local Group, which is dominated by an old stellar population (>10 Gyr) and is therefore an ideal system to study early chemical evolution. With high-resolution VLT/FLAMES spectra, R~20,000, we are able to get accurate abundances of several n-capture elements in ~100 stars, from both the lighter n-capture elements (Y) as well as the heavier ones, both tracers of the s-process (e.g. Ba) and the r-process (e.g. Eu). I will discuss the similarities and differences in the n-capture elements in Sculptor and the Milky Way, as well as other dwarf galaxies.

Evidence for dwarf stars at D of about 100 kiloparsecs near the Sextans dwarf spheroidal galaxy

NASA Technical Reports Server (NTRS)

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

1992-01-01

A method is presented for detecting individual, metal-poor, dwarf stars at distances less than about 150 kpc - a method specifically designed to filter out stars from among the much more numerous faint background field galaxies on the basis of broad-band colors. This technique is applied to two fields at high Galactic latitude, for which there are deep CCD data in four bands ranging from 3600 to 9000 A. The field in Sextans probably contains more than about five dwarf stars with BJ not greater than 25.5. These are consistent with being at a common distance about 100 kpc and lie about 1.7 deg from the newly discovered dwarf galaxy in Sextans whose distance is about 85 +/- 10 kpc. The stars lie near the major axis of the galaxy and are near or beyond the tidal radius. The second field, toward the south Galactic pole, may contain up to about five extra-Galactic stars, but these show no evidence for being at a common distance. Possible applications of this type technique are discussed, and it is shown that even very low surface brightness star clusters or dwarf galaxies may be detected at distances less than about 1 Mpc.

THE PRIMEVAL POPULATIONS OF THE ULTRA-FAINT DWARF GALAXIES

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

Brown, Thomas M.; Tumlinson, Jason; Kalirai, Jason S.

We present new constraints on the star formation histories of the ultra-faint dwarf (UFD) galaxies, using deep photometry obtained with the Hubble Space Telescope (HST). A galaxy class recently discovered in the Sloan Digital Sky Survey, the UFDs appear to be an extension of the classical dwarf spheroidals to low luminosities, offering a new front in efforts to understand the missing satellite problem. They are the least luminous, most dark-matter-dominated, and least chemically evolved galaxies known. Our HST survey of six UFDs seeks to determine if these galaxies are true fossils from the early universe. We present here the preliminarymore » analysis of three UFD galaxies: Hercules, Leo IV, and Ursa Major I. Classical dwarf spheroidals of the Local Group exhibit extended star formation histories, but these three Milky Way satellites are at least as old as the ancient globular cluster M92, with no evidence for intermediate-age populations. Their ages also appear to be synchronized to within {approx}1 Gyr of each other, as might be expected if their star formation was truncated by a global event, such as reionization.« less

Foreground effect on the J-factor estimation of ultra-faint dwarf spheroidal galaxies

NASA Astrophysics Data System (ADS)

Ichikawa, Koji; Horigome, Shun-ichi; Ishigaki, Miho N.; Matsumoto, Shigeki; Ibe, Masahiro; Sugai, Hajime; Hayashi, Kohei

2018-05-01

Dwarf spheroidal galaxies (dSphs) are promising targets for the gamma-ray dark matter (DM) search. In particular, DM annihilation signal is expected to be strong in some of the recently discovered nearby ultra-faint dSphs, which potentially give stringent constraints on the O(1) TeV WIMP DM. However, various non-negligible systematic uncertainties complicate the estimation of the astrophysical factors relevant for the DM search in these objects. Among them, the effects of foreground stars particularly attract attention because the contamination is unavoidable even for the future kinematical survey. In this article, we assess the effects of the foreground contamination on the astrophysical J-factor estimation by generating mock samples of stars in the four ultra-faint dSphs and using a model of future spectrographs. We investigate various data cuts to optimize the quality of the data and apply a likelihood analysis which takes member and foreground stellar distributions into account. We show that the foreground star contaminations in the signal region (the region of interest) and their statistical uncertainty can be estimated by interpolating the foreground star distribution in the control region where the foreground stars dominate the member stars. Such regions can be secured at future spectroscopic observations utilizing a multiple object spectrograph with a large field of view; e.g. the Prime Focus Spectrograph mounted on Subaru Telescope. The above estimation has several advantages: The data-driven estimation of the contamination makes the analysis of the astrophysical factor stable against the complicated foreground distribution. Besides, foreground contamination effect is considered in the likelihood analysis.

Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. 3; Measurement for URSA Minor

NASA Technical Reports Server (NTRS)

Piatek, Slawomir; Pryor, Carlton; Bristow, Paul; Olszewski, Edward W.; Harris, Hugh C.; Mateo, Mario; Minniti, Dante; Tinney, Christopher G.

2005-01-01

This article presents a measurement of the proper motion of the Ursa Minor dwarf spheroidal galaxy determined from images taken with the Hubble Space Telescope in two distinct fields. Each field contains a quasi-stellar object that serves as the "reference point". Integrating the motion of Ursa Minor in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 40 (10, 76) and 89 (78, 160) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.39 (0.09, 0.79), and the orbital period is 1.5 (1.1, 2.7) Gyr. The orbit is retrograde and inclined by 124 degrees (94 deg, 36 deg ) to the Galactic plane. Ursa Minor is not a likely member of a proposed stream of galaxies on similar orbits around the Milky Way, nor is the plane of its orbit coincident with a recently proposed planar alignment of galaxies around the Milky Way. Comparing the orbits of Ursa Minor and Carina shows no reason for the different star formation histories of these two galaxies. Ursa Minor must contain dark matter to have a high probability of having survived disruption by the Galactic tidal force until the present.

An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10.

PubMed

Reines, Amy E; Sivakoff, Gregory R; Johnson, Kelsey E; Brogan, Crystal L

2011-02-03

Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

A Dwarf Dissolving? - A Kinematic Analysis of Andromeda XXVII and the Northern Arc

NASA Astrophysics Data System (ADS)

Collins, Michelle; Rich, R. M.; Chapman, S. C.; Ibata, R.; Irwin, M.; McConnachie, A. W.

2013-01-01

We report internal kinematics for an unusual M31 dwarf spheroidal galaxy, And XXVII, which is superposed against the Northern Arc Stream feature, isolated in the PandAS (Pan-Andromeda Archaeological Survey). In contrast to the coherent, cold velocity fields of most Andromeda dwarf spheroidals, And XXVII has a trimodal velocity distribution spanning 100 km/sec, with a relatively cold central peak at -530 km/sec , and a velocity dispersion of sigma= 8 km/sec. While all of the candidate members are < 2' (or approximately one half light radii, ~600 pc) from the core, the full velocity range is not consistent with a system of luminosity Mv=-7.9. We propose that And XXVII may be in the process of dissolving into the Northern Arc.

Probing Cold Dark Matter Substructure with Wide Binaries in Dwarf Spheroidal Galaxies

NASA Astrophysics Data System (ADS)

Chaname, Julio

2013-10-01

The mass function of dark matter {DM} halos is a central piece in the current framework of hierarchical structure formation. Although a wealth of information is available on the properties of DM halos with M>1e8 solar masses {Msun}, lower-mass halos remain virtually inaccessible. In particular, we do not know whether there is substructure on scales below dwarf spheroidal {dSph} galaxies, nor whether the DM power spectrum cuts off at some low-mass value. Here we propose an experiment that, using resolved binary systems as gravitational test particles, will probe these unexplored regimes for the first time. We will measure the stellar 2-point correlation function in 370 square arcmin of the Ursa Minor dSph down to separations of 40 mas, corresponding to 3000 AU. If there is no DM substructure on small scales, we will detect a 6-sigma excess due to "wide" binaries at the smallest separations. On the other hand, if DM substructure exists on scales of 1e4 Msun at even 10% of the level predicted by standard theory, then these binaries will have been destroyed and there will be no excess at small separations. Because the wide-binary separation function is identical in the Milky Way disk and halo {despite being radically different dynamical environments}, it is almost certain that dSphs were originally endowed with the same wide-binary distribution. Moreover, the interpretation of the resulting data is free from ambiguities, as there are no known mechanisms for destroying these binaries within dSph environments, other than DM subhalos. Thus this is, to the best of our knowledge, the only current experiment that could detect or rule out DM clustering on M=1e4 Msun scales.

The ISLAnds Project. III. Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies

NASA Astrophysics Data System (ADS)

Martínez-Vázquez, Clara E.; Monelli, Matteo; Bernard, Edouard J.; Gallart, Carme; Stetson, Peter B.; Skillman, Evan D.; Bono, Giuseppe; Cassisi, Santi; Fiorentino, Giuliana; McQuinn, Kristen B. W.; Cole, Andrew A.; McConnachie, Alan W.; Martin, Nicolas F.; Dolphin, Andrew E.; Boylan-Kolchin, Michael; Aparicio, Antonio; Hidalgo, Sebastian L.; Weisz, Daniel R.

2017-12-01

We present a census of variable stars in six M31 dwarf spheroidal satellites observed with the Hubble Space Telescope. We detect 870 RR Lyrae (RRL) stars in the fields of And I (296), II (251), III (111), XV (117), XVI (8), and XXVIII (87). We also detect a total of 15 Anomalous Cepheids, three eclipsing binaries, and seven field RRL stars compatible with being members of the M31 halo or the Giant Stellar Stream. We derive robust and homogeneous distances to the six galaxies using different methods based on the properties of the RRL stars. Working with the up-to-date set of Period-Wesenheit (I, B-I) relations published by Marconi et al., we obtain distance moduli of μ 0 = [24.49, 24.16, 24.36, 24.42, 23.70, 24.43] mag (respectively), with systematic uncertainties of 0.08 mag and statistical uncertainties <0.11 mag. We have considered an enlarged sample of 16 M31 satellites with published variability studies, and compared their pulsational observables (e.g., periods and amplitudes) with those of 15 Milky Way satellites for which similar data are available. The properties of the (strictly old) RRL in both satellite systems do not show any significant difference. In particular, we found a strikingly similar correlation between the mean period distribution of the fundamental RRL pulsators (RRab) and the mean metallicities of the galaxies. This indicates that the old RRL progenitors were similar at the early stage in the two environments, suggesting very similar characteristics for the earliest stages of evolution of both satellite systems. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 13028 and 13739.

CARBON ABUNDANCES FOR RED GIANTS IN THE DRACO DWARF SPHEROIDAL GALAXY

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

Shetrone, Matthew D.; Stanford, Laura M.; Smith, Graeme H.

2013-05-15

Measurements of [C/Fe], [Ca/H], and [Fe/H] have been derived from Keck I LRISb spectra of 35 giants in the Draco dwarf spheroidal galaxy. The iron abundances are derived by a spectrum synthesis modeling of the wavelength region from 4850 to 5375 A, while calcium and carbon abundances are obtained by fitting the Ca II H and K lines and the CH G band, respectively. A range in metallicity of -2.9 {<=} [Fe/H] {<=} -1.6 is found within the giants sampled, with a good correlation between [Fe/H] and [Ca/H]. The great majority of stars in the sample would be classified asmore » having weak absorption in the {lambda}3883 CN band, with only a small scatter in band strengths at a given luminosity on the red giant branch. In this sense the behavior of CN among the Draco giants is consistent with the predominantly weak CN bands found among red giants in globular clusters of metallicity [Fe/H] < -1.8. Over half of the giants in the Draco sample have [Fe/H] > -2.25, and among these there is a trend for the [C/Fe] abundance to decrease with increasing luminosity on the red giant branch. This is a phenomenon that is also seen among both field and globular cluster giants of the Galactic halo, where it has been interpreted as a consequence of deep mixing of material between the base of the convective envelope and the outer limits of the hydrogen-burning shell. However, among the six Draco giants observed that turn out to have metallicities -2.65 < [Fe/H] < -2.25 there is no such trend seen in the carbon abundance. This may be due to small sample statistics or primordial inhomogeneities in carbon abundance among the most metal-poor Draco stars. We identify a potential carbon-rich extremely metal-poor star in our sample. This candidate will require follow-up observations for confirmation.« less

Searching for Flickering Giants in the Ursa Minor Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Montiel, Edward J.; Mighell, K. J.

2010-01-01

We present a preliminary analysis of three epochs of archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) observations of a single field in the Ursa Minor (UMi) dwarf spheroidal (dSph) galaxy. These observations were obtained in 2000, 2002, and 2004 (GO-7341, GO-8776, GO-2004; PI: Olszewski). We expand upon the work of Mighell and Roederer 2004 who reported the existence of low-amplitude variability in red giant stars in the UMi dSph. We report the 16 brightest point sources (F606W <= 21.5 mag) that we are able to match between all 3 epochs. The 112 observations were analyzed with HSTphot. We tested for variability with a chi-squared statistic that had a softened photometric error where 0.01 mag was added in quadrature to the reported HSTphot photometric error. We find that all 13 stars and 3 probable galaxies exhibit the same phenomenon as described in Mighell and Roederer with peak to peak amplitudes ranging from 54 to 125 mmags on 10 minute timescales. If these objects were not varying, the deviates should be normally distributed. However, we find that the deviates have a standard deviation of 1.4. This leads to three possible conclusions: (1) the observed phenomenon is real, (2) an additional systematic error of 7 mmag needs to be added to account for additional photometric errors (possibly due to dithering), or (3) there was a small instrumental instability with the WFPC2 instrument from 2000 to 2004. E.J.M. was supported by the NOAO/KPNO Research Experience for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program and the Department of Defense ASSURE program through Scientific Program Order No. 13 (AST-0754223) of the Cooperative Agreement No.AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF.

The size and structure of the spheroid of IC 1613

NASA Astrophysics Data System (ADS)

Battinelli, P.; Demers, S.; Artigau, É.

2007-05-01

Context: Nearby galaxies, spirals as well as irregulars, have been found to be much larger than previously believed. The structure of the huge spheroid surrounding dwarf galaxies could give clues to their past gravitational history. Thanks to wide field imagers, nearby galaxies with diameter of dozens of arcmin can be effectively surveyed. Aims: We obtain, from the CFHT archives, a series of i' and g' MegaCam images of IC 1613 in order to determine the stellar surface density of the field and determine the shape of its spheroid. Methods: From the colour magnitude diagram we select some 36 000 stars, in the first three magnitudes of the red giant branch. The spatial distribution of these stars is used to establish the structure of the spheroid. Results: The position angle of the major axis of the stellar spheroid is found to be ≈90°, some 30° from the major axis of the HI cloud surrounding IC 1613. The surface density profile of the spheroid is not exponential over all the length of the major axis. A King profile, with a core radius of 4.5' and a tidal radius of 24' fits the data. The tidal truncation of the spheroid suggests that IC 1613 is indeed a satellite of M 31. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Do Perturbations from Dwarf Galaxies Produce Moving Groups in the Milky Way Disk?

NASA Astrophysics Data System (ADS)

Craig, Peter; Newberg, Heidi Jo; Chakrabarti, Sukanya

2018-01-01

We compare Solar neighborhood disk moving groups with velocity perturbations produced in hydrodynamic simulations of dwarf galaxy interactions with the disk. The hydrodynamic simulations were generated using Gadget 2, and mimic the interaction of the Sagittarius dwarf galaxy and several others with the Milky Way. The properties of the identified moving groups change as the simulations evolve. We identified moving groups in regions of the simulation that are within 1 kpc of the nominal location of the Sun (8 kpc from the Galactic center) that are similar to moving groups observed within the Milky Way. Such groups are found at locations all the way around the disk. This suggests that some of the groups that are observed near our sun are a result of an interaction between the Milky Way and a colliding dwarf galaxy. It also suggests that the existence of such groups here implies the existence of similar groups in other parts of the Milky Way.

Dynamical Constraints on the Dark Matter Distribution of the Sculptor Dwarf Spheroidal from Stellar Proper Motions

NASA Astrophysics Data System (ADS)

Strigari, Louis E.; Frenk, Carlos S.; White, Simon D. M.

2018-06-01

We compare the transverse velocity dispersions recently measured within the Sculptor dwarf spheroidal galaxy to the predictions of our previously published dynamical model. This was designed to fit the observed number count and velocity dispersion profiles of both metal-rich and metal-poor stars, both in cored and in cusped potentials. At the projected radius where the proper motions (PMs) were measured, this model (with no change in parameters) predicts transverse dispersions in the range of 6–9.5 km s‑1, with the tangential dispersion about 1 km s‑1 larger than the (projected) radial dispersion. Both dispersions are predicted to be about 1 km s‑1 larger for metal-poor than for metal-rich stars. At this projected radius, cored and cusped potentials predict almost identical transverse dispersions. The measured tangential dispersion (8.5 ± 3.2 km s‑1) agrees remarkably well with these predictions, while the measured radial dispersion (11.5 ± 4.3 km s‑1) differs only at about the 1σ level. Thus, the PM data are in excellent agreement with previous data, but do not help to distinguish between cored and cusped potentials. This will require velocity dispersion data (either from PMs or from radial velocities) with uncertainties well below 1 km s‑1 over a range of projected radii.

`Skinny Milky Way please', says Sagittarius

NASA Astrophysics Data System (ADS)

Gibbons, S. L. J.; Belokurov, V.; Evans, N. W.

2014-12-01

Motivated by recent observations of the Sagittarius stream, we devise a rapid algorithm to generate faithful representations of the centroids of stellar tidal streams formed in a disruption of a progenitor of an arbitrary mass in an arbitrary potential. Our method works by releasing swarms of test particles at the Lagrange points around the satellite and subsequently evolving them in a combined potential of the host and the progenitor. We stress that the action of the progenitor's gravity is crucial to making streams that look almost indistinguishable from the N-body realizations, as indeed ours do. The method is tested on mock stream data in three different Milky Way potentials with increasing complexity, and is shown to deliver unbiased inference on the Galactic mass distribution out to large radii. When applied to the observations of the Sagittarius stream, our model gives a natural explanation of the stream's apocentric distances and the differential orbital precession. We, therefore, provide a new independent measurement of the Galactic mass distribution beyond 50 kpc. The Sagittarius stream model favours a light Milky Way with the mass 4.1 ± 0.4 × 1011 M⊙ at 100 kpc, which can be extrapolated to 5.6 ± 1.2 × 1011 M⊙ at 200 kpc. Such a low mass for the Milky Way Galaxy is in good agreement with estimates from the kinematics of halo stars and from the satellite galaxies (once Leo I is removed from the sample). It entirely removes the `Too Big To Fail Problem'.

Milky Way red dwarfs in the BoRG survey; galactic scale-height and the distribution of dwarf stars in WFC3 imaging

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

Holwerda, B. W.; Bouwens, R.; Trenti, M.

2014-06-10

We present a tally of Milky Way late-type dwarf stars in 68 Wide Field Camera 3 (WFC3) pure-parallel fields (227 arcmin{sup 2}) from the Brightest of Reionizing Galaxies survey for high-redshift galaxies. Using spectroscopically identified M-dwarfs in two public surveys, the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey and the Early Release Science mosaics, we identify a morphological selection criterion using the half-light radius (r {sub 50}), a near-infrared J – H, G – J color region where M-dwarfs are found, and a V – J relation with M-dwarf subtype. We apply this morphological selection of stellar objects, color-color selectionmore » of M-dwarfs, and optical-near-infrared color subtyping to compile a catalog of 274 M-dwarfs belonging to the disk of the Milky Way with a limiting magnitude of m {sub F125W} < 24(AB). Based on the M-dwarf statistics, we conclude that (1) the previously identified north-south discrepancy in M-dwarf numbers persists in our sample; there are more M-dwarfs in the northern fields on average than in southern ones, (2) the Milky Way's single disk scale-height for M-dwarfs is 0.3-4 kpc, depending on subtype, (3) the scale-height depends on M-dwarf subtype with early types (M0-4) high scale-height (z {sub 0} = 3-4 kpc) and later types M5 and above in the thin disk (z {sub 0} = 0.3-0.5 kpc), (4) a second component is visible in the vertical distribution, with a different, much higher scale-height in the southern fields compared to the northern ones. We report the M-dwarf component of the Sagittarius stream in one of our fields with 11 confirmed M-dwarfs, seven of which are at the stream's distance. In addition to the M-dwarf catalog, we report the discovery of 1 T-dwarfs and 30 L-dwarfs from their near-infrared colors. The dwarf scale-height and the relative low incidence in our fields of L- and T-dwarfs in these fields makes it unlikely that these stars will be interlopers in great numbers in color-selected samples of

On The gamma-ray emission from Reticulum II and other dwarf galaxies

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

Hooper, Dan; Linden, Tim

2015-09-01

The recent discovery of ten new dwarf galaxy candidates by the Dark Energy Survey (DES) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) could increase the Fermi Gamma-Ray Space Telescope's sensitivity to annihilating dark matter particles, potentially enabling a definitive test of the dark matter interpretation of the long-standing Galactic Center gamma-ray excess. In this paper, we compare the previous analyses of Fermi data from the directions of the new dwarf candidates (including the relatively nearby Reticulum II) and perform our own analysis, with the goal of establishing the statistical significance of any gamma-ray signal from these sources.more » We confirm the presence of an excess from Reticulum II, with a spectral shape that is compatible with the Galactic Center signal. The significance of this emission is greater than that observed from 99.84% of randomly chosen high-latitude blank-sky locations, corresponding to a local detection significance of 3.2σ. We caution that any dark matter interpretation of this excess must be validated through observations of additional dwarf spheroidal galaxies, and improved calculations of the relative J-factor of dwarf spheroidal galaxies. We improve upon the standard blank-sky calibration approach through the use of multi-wavelength catalogs, which allow us to avoid regions that are likely to contain unresolved gamma-ray sources.« less

Ring Structure and Warp of NGC 5907: Interaction with Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Shang, Zhaohui; Zheng, Zhongyuan; Brinks, Elias; Chen, Jiansheng; Burstein, David; Su, Hongjun; Byun, Yong-ik; Deng, Licai; Deng, Zugan; Fan, Xiaohui; Jiang, Zhaoji; Li, Yong; Lin, Weipeng; Ma, Feng; Sun, Wei-hsin; Wills, Beverley; Windhorst, Rogier A.; Wu, Hong; Xia, Xiaoyang; Xu, Wen; Xue, Suijian; Yan, Haojing; Zhou, Xu; Zhu, Jin; Zou, Zhenlong

1998-09-01

The edge-on, nearby spiral galaxy NGC 5907 has long been used as the prototype of a ``noninteracting'' warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC 5907 close to one of the ring's foci. This suggests that the ring material is in orbit around NGC 5907. No gaseous component to the ring has been detected either with deep Hα images or in Very Large Array H I 21 cm line maps. The visible material in the ring has an integrated luminosity <=108 Lsolar, and its brightest part has a color R-I~0.9. All of these properties are consistent with the ring being a tidally disrupted dwarf spheroidal galaxy. Second, we find that NGC 5907 has a dwarf companion galaxy, PGC 54419, which is projected to be only 36.9 kpc from the center of NGC 5907, close in radial velocity (ΔV=45 km s-1) to the giant spiral galaxy. This dwarf is seen at the tip of the H I warp and in the direction of the warp. Hence, NGC 5907 can no longer be considered noninteracting but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies. Partially based on observations taken with the Very Large Array of the National Radio Astronomy Observatory is a facility of the National Science Foundation operated by a cooperative agreement with Associated Universities, Inc.

Star Formation Histories of Local Group Dwarf Galaxies. (Ludwig Biermann Award Lecture 1996)

NASA Astrophysics Data System (ADS)

Grebel, E. K.

The star formation histories of dwarf galaxies in the Local Group are reviewed. First the question of Local Group membership is considered based on various criteria. The properties of 31 (36) galaxies are consistent with likely (potential) Local Group membership. To study the star formation histories of these galaxies, a multi-parameter problem needs to be solved: Ages, metallicities, population fractions, and spatial variations must be determined, which depend crucially on the knowledge of reddening and distance. The basic methods for studying resolvable stellar populations are summarized. One method is demonstrated using the Fornax dwarf spheroidal galaxy. A comprehensive compilation of the star formation histories of dwarf irregulars, dwarf ellipticals, and dwarf spheroidals in the Local Group is presented and visualized through Hodge's population boxes. All galaxies appear to have differing fractions of old and intermediate-age populations, and those sufficiently massive and undisturbed to retain and recycle their gas are still forming stars today. Star formation has occurred either in distinct episodes or continuously over long periods of time. Metallicities and enrichment vary widely. Constraints on merger and remnant scenarios are discussed, and a unified picture based on the current knowledge is presented. Primary goals for future observations are: accurate age determinations based on turnoff photometry, detection of subpopulations distinct in age, metallicity, and/or spatial distribution; improved distances; and astrometric studies to derive orbits and constrain past and future interactions.

Modeling the Structure and Dynamics of Dwarf Spheroidal Galaxies with Dark Matter and Tides

NASA Astrophysics Data System (ADS)

Muñoz, Ricardo R.; Majewski, Steven R.; Johnston, Kathryn V.

2008-05-01

We report the results of N-body simulations of disrupting satellites aimed at exploring whether the observed features of dSphs can be accounted for with simple, mass-follows-light (MFL) models including tidal disruption. As a test case, we focus on the Carina dwarf spheroidal (dSph), which presently is the dSph system with the most extensive data at large radius. We find that previous N-body, MFL simulations of dSphs did not sufficiently explore the parameter space of satellite mass, density, and orbital shape to find adequate matches to Galactic dSph systems, whereas with a systematic survey of parameter space we are able to find tidally disrupting, MFL satellite models that rather faithfully reproduce Carina's velocity profile, velocity dispersion profile, and projected density distribution over its entire sampled radius. The successful MFL model satellites have very eccentric orbits, currently favored by CDM models, and central velocity dispersions that still yield an accurate representation of the bound mass and observed central M/L ~ 40 of Carina, despite inflation of the velocity dispersion outside the dSph core by unbound debris. Our survey of parameter space also allows us to address a number of commonly held misperceptions of tidal disruption and its observable effects on dSph structure and dynamics. The simulations suggest that even modest tidal disruption can have a profound effect on the observed dynamics of dSph stars at large radii. Satellites that are well described by tidally disrupting MFL models could still be fully compatible with ΛCDM if, for example, they represent a later stage in the evolution of luminous subhalos.

Two Cepheid variables in the Fornax dwarf galaxy

NASA Technical Reports Server (NTRS)

Light, R. M.; Armandroff, T. E.; Zinn, R.

1986-01-01

Two fields surrounding globular clusters 2 and 3 in the Fornax dwarf spheroidal galaxy have been searched for short-period variable stars that are brighter than the horizontal branch. This survey confirmed as variable the two suspected suprahorizontal-branch variables discovered by Buonanno et al. (1985) in their photometry of the clusters. The observations show that the star in cluster 2 is a W Virginis variable of 14.4 day period. It is the first W Vir variable to be found in a dwarf spheroidal galaxy, and its proximity to the center of cluster 2 suggests that it is a cluster member. The other star appears to be an anomalous Cephpeid of 0.78 day period. It lies outside or very near the boundary of cluster 3, and is therefore probably a member of the field population of Fornax. Although no other suprahorizontal-branch variables were discovered in the survey, it did confirm as variable two of the RR Lyrae candidates of Buonanno et al., which appeared at the survey limit. The implications of these observations for the understanding of the stellar content at Fornax are discussed.

Searching for Decaying Dark Matter in Deep XMM-Newton Observation of the Draco Dwarf Spheroidal

NASA Technical Reports Server (NTRS)

Ruchayskiy, Oleg; Boyardsky, Alex; Iakbovskyi, Dmytro; Bulbul, Esra; Eckert, Domique; Franse, Jeron; Malyshev, Denys; Markevitch, Maxim; Neronov, Andrii

2016-01-01

We present results of a search for the 3.5 keV emission line in our recent very long (approx. 1.4 Ms) XMM-Newton observation of the Draco dwarf spheroidal galaxy. The astrophysical X-ray emission from such dark matter-dominated galaxies is faint, thus they provide a test for the dark matter origin of the 3.5 keV line previously detected in other massive, but X-ray bright objects, such as galaxies and galaxy clusters. We do not detect a statistically significant emission line from Draco; this constrains the lifetime of a decaying dark matter particle to tau >(7-9) × 10(exp 27) s at 95% CL (combining all three XMM-Newton cameras; the interval corresponds to the uncertainty of the dark matter column density in the direction of Draco). The PN camera, which has the highest sensitivity of the three, does show a positive spectral residual (above the carefully modeled continuum) at E = 3.54 +/- 0.06 keV with a 2.3(sigma) significance. The two MOS cameras show less-significant or no positive deviations, consistently within 1(sigma) with PN. Our Draco limit on tau is consistent with previous detections in the stacked galaxy clusters, M31 and the Galactic Centre within their 1 - 2(sigma) uncertainties, but is inconsistent with the high signal from the core of the Perseus cluster (which has itself been inconsistent with the rest of the detections). We conclude that this Draco observation does not exclude the dark matter interpretation of the 3.5 keV line in those objects.

STRUCTURAL PROPERTIES OF NON-SPHERICAL DARK HALOS IN MILKY WAY AND ANDROMEDA DWARF SPHEROIDAL GALAXIES

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

Hayashi, Kohei; Chiba, Masashi, E-mail: kohei.hayashi@ipmu.jp, E-mail: chiba@astr.tohoku.ac.jp

We investigate the non-spherical density structure of dark halos of the dwarf spheroidal (dSph) galaxies in the Milky Way and Andromeda galaxies based on revised axisymmetric mass models from our previous work. The models we adopt here fully take into account velocity anisotropy of tracer stars confined within a flattened dark halo. Applying our models to the available kinematic data of the 12 bright dSphs, we find that these galaxies associate with, in general, elongated dark halos, even considering the effect of this velocity anisotropy of stars. We also find that the best-fit parameters, especially for the shapes of darkmore » halos and velocity anisotropy, are susceptible to both the availability of velocity data in the outer regions and the effect of the lack of sample stars in each spatial bin. Thus, to obtain more realistic limits on dark halo structures, we require photometric and kinematic data over much larger areas in the dSphs than previously explored. The results obtained from the currently available data suggest that the shapes of dark halos in the dSphs are more elongated than those of ΛCDM subhalos. This mismatch needs to be solved by theory including baryon components and the associated feedback to dark halos as well as by further observational limits in larger areas of dSphs. It is also found that more diffuse dark halos may have undergone consecutive star formation history, thereby implying that dark-halo structure plays an important role in star formation activity.« less

Life and death of a hero - lessons learned from modelling the dwarf spheroidal Hercules: an incorrect orbit?

NASA Astrophysics Data System (ADS)

Blaña, M.; Fellhauer, M.; Smith, R.; Candlish, G. N.; Cohen, R.; Farias, J. P.

2015-01-01

Hercules is a dwarf spheroidal satellite of the Milky Way, found at a distance of ≈138 kpc, and showing evidence of tidal disruption. It is very elongated and exhibits a velocity gradient of 16 ± 3 km s-1 kpc-1. Using these data a possible orbit of Hercules has previously been deduced in the literature. In this study, we make use of a novel approach to find a best-fitting model that follows the published orbit. Instead of using trial and error, we use a systematic approach in order to find a model that fits multiple observables simultaneously. As such, we investigate a much wider parameter range of initial conditions and ensure we have found the best match possible. Using a dark matter free progenitor that undergoes tidal disruption, our best-fitting model can simultaneously match the observed luminosity, central surface brightness, effective radius, velocity dispersion, and velocity gradient of Hercules. However, we find it is impossible to reproduce the observed elongation and the position angle of Hercules at the same time in our models. This failure persists even when we vary the duration of the simulation significantly, and consider a more cuspy density distribution for the progenitor. We discuss how this suggests that the published orbit of Hercules is very likely to be incorrect.

Nuclei of dwarf spheroidal galaxies KKs 3 and ESO 269-66 and their counterparts in our Galaxy

NASA Astrophysics Data System (ADS)

Sharina, M. E.; Shimansky, V. V.; Kniazev, A. Y.

2017-10-01

We present the analysis of medium-resolution spectra obtained at the Southern African Large Telescope for nuclear globular clusters (GCs) in two dwarf spheroidal galaxies (dSphs). The galaxies have similar star formation histories, but they are situated in completely different environments. ESO 269-66 is a close neighbour of the giant S0 NGC 5128. KKs 3 is one of the few truly isolated dSphs within 10 Mpc. We estimate the helium abundance Y = 0.3, age = 12.6 ± 1 Gyr, [Fe/H] = -1.5, -1.55 ± 0.2 dex, and abundances of C, N, Mg, Ca, Ti, and Cr for the nuclei of ESO 269-66 and KKs 3. Our surface photometry results using Hubble Space Telescope images yield the half-light radius of the cluster in KKs 3, rh = 4.8 ± 0.2 pc. We demonstrate the similarities of medium-resolution spectra, ages, chemical compositions, and structure for GCs in ESO 269-66 and KKs 3 and for several massive Galactic GCs with [Fe/H] ∼ -1.6 dex. All Galactic GCs posses Extended Blue Horizontal Branches and multiple stellar populations. Five of the selected Galactic objects are iron-complex GCs. Our results indicate that the sample GCs observed now in different environments had similar conditions of their formation ∼1 Gyr after the Big Bang.

PAndAS' PROGENY: EXTENDING THE M31 DWARF GALAXY CABAL

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

Richardson, Jenny C.; Irwin, Mike J.; Chapman, Scott C.

2011-05-10

We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were discovered during the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 subgroup conducted with the MegaPrime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope. The current PAndAS survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of {approx}150 kpc. Here we present for the first time the metal-poor stellar density map for this whole region, not only as an illustration of the discovery spacemore » for satellite galaxies, but also as a birds-eye view of the ongoing assembly process of an L{sub *} disk galaxy. Four of the newly discovered satellites appear as well-defined spatial overdensities of stars lying on the expected locus of metal-poor (-2.5 < [Fe/H] < -1.3) red giant branch stars at the distance of M31. The fifth overdensity, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. Based on distance estimates from horizontal branch magnitudes, all five have metallicities typical of dwarf spheroidal galaxies ranging from [Fe/H] =-1.7 {+-} 0.2 to [Fe/H] =-1.9 {+-} 0.2 and absolute magnitudes ranging from M{sub V} = -7.1 {+-} 0.5 to M{sub V} = -10.2 {+-} 0.5. These five additional satellites bring the number of dwarf spheroidal galaxies in this region to 25 and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies, we also revisit the spatial distribution of this population and in particular we find that, within the current projected limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of

Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. IV. Measurement for Sculptor

NASA Astrophysics Data System (ADS)

Piatek, Slawomir; Pryor, Carlton; Bristow, Paul; Olszewski, Edward W.; Harris, Hugh C.; Mateo, Mario; Minniti, Dante; Tinney, Christopher G.

2006-03-01

This article presents a measurement of the proper motion of the Sculptor dwarf spheroidal galaxy determined from images taken with the Hubble Space Telescope using the Space Telescope Imaging Spectrograph in the imaging mode. Each of two distinct fields contains a quasi-stellar object that serves as the ``reference point.'' The measured proper motion of Sculptor, expressed in the equatorial coordinate system, is (μα, μδ)=(9+/-13, 2+/-13) mas century-1. Removing the contributions from the motion of the Sun and the motion of the local standard of rest produces the proper motion in the Galactic rest frame: (μGrfα, μGrfδ)=(-23+/-13, 45+/-13) mas century-1. The implied space velocity with respect to the Galactic center has a radial component of Vr=79+/-6 km s-1 and a tangential component of Vt=198+/-50 km s-1. Integrating the motion of Sculptor in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 68 (31, 83) and 122 (97, 313) kpc, respectively, where the values in the parentheses represent the 95% confidence interval derived from Monte Carlo experiments. The eccentricity of the orbit is 0.29 (0.26, 0.60), and the orbital period is 2.2 (1.5, 4.9) Gyr. Sculptor is on a polar orbit around the Milky Way: the angle of inclination is 86° (83°, 90°). 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 NAS5-26555.

Dwarf spheroidal satellites of M31. I. Variable stars and stellar populations in Andromeda XIX

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

Cusano, Felice; Clementini, Gisella; Garofalo, Alessia

We present B, V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.'2) of Andromeda's dwarf spheroidal companions, which we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23' × 23' area centered on And XIX and present the deepest color-magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V ∼ 26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which extends to the blue to significantly populate the classicalmore » instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and three of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ((P {sub ab}) = 0.62 days, σ = 0.03 days) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average luminosity of the RR Lyrae stars ((V(RR)) = 25.34 mag, σ = 0.10 mag), we determine a distance modulus of (m – M){sub 0} = 24.52 ± 0.23 mag in a scale where the distance to the Large Magellanic Cloud (LMC) is 18.5 ± 0.1 mag. The ACs follow a well-defined Period-Wesenheit (PW) relation that appears to be in very good agreement with the PW relationship defined by the ACs in the LMC.« less

A search for HI in some peculiar faint dwarf galaxies

NASA Astrophysics Data System (ADS)

Begum, Ayesha; Chengalur, Jayaram N.

2005-09-01

We present a deep Giant Metrewave Radio Telescope (GMRT) search for HI 21-cm emission from three dwarf galaxies, viz. POX 186, SC 24 and KKR 25. Based, in part, on previous single-dish HI observations, these galaxies have been classified as a blue compact dwarf (BCD), a dwarf irregular and a transition galaxy, respectively. However, in conflict with previous single-dish detections, we do not detect HI in SC 24 or KKR 25. We suggest that the previous single-dish measurements were probably confused with the local Galactic emission. In the case of POX 186, we confirm the previous non-detection of HI but with substantially improved limits on its HI mass. Our derived upper limits on the HI mass of SC 24 and KKR 25 are similar to the typical HI mass limit for dwarf spheroidal (dSph) galaxies, whereas in the case of POX 186, we find that its gas content is somewhat smaller than is typical of BCD galaxies.

ANDROMEDA XXVIII: A DWARF GALAXY MORE THAN 350 kpc FROM ANDROMEDA

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

Slater, Colin T.; Bell, Eric F.; Martin, Nicolas F.

We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently released Sloan Digital Sky Survey Data Release 8. The galaxy is a likely satellite of Andromeda, and, at a separation of 365{sup +17}{sub -1} kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is 650{sup +150}{sub -80} kpc, and analysis of its structure and luminosity shows that it has an absolute magnitude of M{sub V} = -8.5{sup +0.4}{sub -1.0} and half-light radius of r{sub h} = 210{sup +60}{sub -50} pc, similar to many other faint Local Group dwarfs. Withmore » presently available imaging we are unable to determine whether there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or a dwarf irregular.« less

CEMP Stars in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Thidemann Hansen, Terese

2018-06-01

Exploration of the metal-poor stellar halo population of the Milky Way over the past decades has revealed a large number of stars strongly enhanced in carbon (CEMP stars). However, these stars are not as commonly detected in the dwarf galaxy satellites of the Milky Way (MW). The present-day satellites are thought to be similar to systems from which the MW and in particular its halo was formed via hierarchical mergers. I will present the results of abundance analysis for new samples of extremely metal-poor stars in Sculptor and Carina exploring the fraction of CEMP stars at low metallicity in these systems. I will also present the detailed abundance analyses of six CEMP stars detected in the Carina dwarf spheroidal galaxy. Five of these stars also show enhancement in slow neutron-capture elements and can thus be classified as CEMP-s stars, while the most metal-poor star with [Fe/H]=-2.5 shows no such enhancement and belongs to the CEMP-no class. The detection of CEMP stars in dwarf galaxies supports the hierarchical assembly of the MW halo and by providing a birth environment, can help to further constrain the formation of these stars.

First detection of the white dwarf cooling sequence of the galactic bulge

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

Calamida, A.; Sahu, K. C.; Anderson, J.

2014-08-01

We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3'× 3'), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr{sup –1} (≈4 km s{sup –1}) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr{supmore » –1} (≈20 km s{sup –1}) at F606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P ≲ 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.« less

Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

NASA Astrophysics Data System (ADS)

Wheeler, Coral Rose

2016-06-01

The high dark matter content and the shallow potential wells of low mass galaxies (10^3 Msun < Mstar < 10^9.5 Msun) make them excellent testbeds for differing theories of galaxy formation. Additionally, the recent up-tick in the number and detail of Local Group dwarf galaxy observations provides a rich dataset for comparison to simulations that attempt to answer important questions in near field cosmology: why are there so few observed dwarfs compared to the number predicted by simulations? What shuts down star formation in ultra-faint galaxies? Why do dwarfs have inverted age gradients and what does it take to convert a dwarf irregular (dIrrs) into a dwarf spheroidal (dSph) galaxy?We to attempt to answer these questions by running ultra-high resolution cosmological FIRE simulations of isolated dwarf galaxies. We predict that many ultra-faint dwarfs should exist as satellites of more massive isolated Local Group dwarfs. The ultra-faints (Mstar < 10^4 Msun) formed in these simulations have uniformly ancient stellar populations (> 10 Gyr), having had their star formation shut down by reionization. Additionally, we show that the kinematics and ellipticities of isolated simulated dwarf centrals are consistent with observed dSphs satellites without the need for harassment from a massive host. We further show that most (but not all) observed *isolated* dIrrs in the Local Volume also have dispersion-supported stellar populations, contradicting the previous view that these objects are rotating. Finally, we investigate the stellar age gradients in dwarfs — showing that early mergers and strong feedback can create an inverted gradient, with the older stars occupying larger galactocentric radii.These results offer an interesting direction in testing models that attempt to solve dark matter problems via explosive feedback episodes. Can the same models that create large cores in simulated dwarfs preserve the mild stellar rotation that is seen in a minority of isolated d

V3885 Sagittarius: A Comparison With a Range of Standard Model Accretion Disks

DTIC Science & Technology

2009-10-01

is greater than that in previous models. Blaes et al. (2006) show that magnetic support has a significant effect on synthetic spectra of black hole ...reserved. Printed in the U.S.A. V3885 SAGITTARIUS : A COMPARISON WITH A RANGE OF STANDARD MODEL ACCRETION DISKS∗ Albert P. Linnell1, Patrick Godon2, Ivan...Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius , on an absolute flux basis, selects a model that

Predicting the Velocity Dispersions of the Dwarf Satellite Galaxies of Andromeda

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.

2016-05-01

Dwarf Spheroidal galaxies in the Local Group are the faintest and most diffuse stellar systems known. They exhibit large mass discrepancies, making them popular laboratories for studying the missing mass problem. The PANDAS survey of M31 revealed dozens of new examples of such dwarfs. As these systems were discovered, it was possible to use the observed photometric properties to predict their stellar velocity dispersions with the modified gravity theory MOND. These predictions, made in advance of the observations, have since been largely confirmed. A unique feature of MOND is that a structurally identical dwarf will behave differently when it is or is not subject to the external field of a massive host like Andromeda. The role of this "external field effect" is critical in correctly predicting the velocity dispersions of dwarfs that deviate from empirical scaling relations. With continued improvement in the observational data, these systems could provide a test of the strong equivalence principle.

Star formation in proto dwarf galaxies

NASA Technical Reports Server (NTRS)

Noriega-Crespo, A.; Bodenheimer, P.; Lin, D. N. C.; Tenorio-Tagle, G.

1990-01-01

The effects of the onset of star formation on the residual gas in primordial low-mass Local-Group dwarf spheroidal galaxies is studied by a series of hydrodynamical simulations. The models have concentrated on the effect of photoionization. The results indicate that photoionization in the presence of a moderate gas density gradient can eject most of the residual gas on a time scale of a few 10 to the 7th power years. High central gas density combined with inefficient star formation, however, may prevent mass ejection. The effect of supernova explosions is discussed briefly.

SPECTROSCOPIC CONFIRMATION OF THE DWARF SPHEROIDAL GALAXY d0994+71 AS A MEMBER OF THE M81 GROUP OF GALAXIES

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

Toloba, Elisa; Sand, David; Crnojević, Denija

2016-10-10

We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual stars and measure a heliocentric radial velocity of −38 ± 10 km s{sup −1}. This velocity is consistent with d0944+71 being gravitationally bound to M81. We coadd the spectra of the 23 stars that are consistent with being red giant branch stars and measure an overall metallicity ofmore » [Fe/H] = −1.3 ± 0.3 based on the calcium triplet lines. This metallicity is consistent with d0944+71 following the metallicity−luminosity relation for Local Group dSphs. We investigate several potential sources of observational bias but find that our sample of targeted stars is representative of the metallicity distribution function of d0944+71 and any stellar contamination due to seeing effects is negligible. The low ellipticity of the galaxy and its position in the metallicity−luminosity relation suggest that d0944+71 has not been affected by strong tidal stripping.« less

The interstellar medium in Andromeda's dwarf spheroidal galaxies - II. Multiphase gas content and ISM conditions

NASA Astrophysics Data System (ADS)

De Looze, Ilse; Baes, Maarten; Cormier, Diane; Kaneko, Hiroyuki; Kuno, Nario; Young, Lisa; Bendo, George J.; Boquien, Médéric; Fritz, Jacopo; Gentile, Gianfranco; Kennicutt, Robert C.; Madden, Suzanne C.; Smith, Matthew W. L.; Wilson, Christine D.

2017-03-01

We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC 147, NGC 185 and NGC 205). Ancillary H I, CO, Spitzer Infrared Spectrograph spectra, Hα and X-ray observations are combined to trace the atomic, cold and warm molecular, ionized and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [C I] observations of NGC 205 to revise its molecular gas content. We derive total gas masses of Mg = 1.9-5.5 × 105 M⊙ for NGC 185 and Mg = 8.6-25.0 × 105 M⊙ for NGC 205. Non-detections combine to an upper limit on the gas mass of Mg ≤ 0.3-2.2 × 105 M⊙ for NGC 147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR ∼ 37-107 and 48-139 are also considerably lower compared to the expected GDR ∼ 370 and 520 for the low metal abundances in NGC 185 (0.36 Z⊙) and NGC 205 (0.25 Z⊙), respectively. To simultaneously account for the gas deficiency and low gas-to-dust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (∼1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC 147, NGC 185 and NGC 205.

Prospects of the "WSO-UV" Project for Star Formation Study in Nearby Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Makarova, L. N.; Makarov, D. I.

2017-12-01

In the present work we consider the questions of star formation and evolution of nearby dwarf galaxies. We describe the method of star formation history determination based on multicolor photometry of resolved stars and models of color-magnitude diagrams of the galaxies. We present the results of star formation rate determination and its dependence on age and metallicity for dwarf irregular and dwarf spheroidal galaxies in the two nearby galaxy groups M81 and Cen A. Similar age of the last episode of star formation in the central part of the M81 group and also unusually high level of metal enrichment in the several galaxies of the Cen A group are mentioned. We pay special attention to the consideration of perspectives of star formation study in nearby dwarf galaxies with he new WSO-UV observatory.

Gas-rich dwarfs and accretion phenomena in early-type galaxies

NASA Technical Reports Server (NTRS)

Silk, J.; Norman, C.

1979-01-01

An analysis is presented of the combined effects of cloud accretion and galactic winds and coronae. An accretion model is developed wherein gas-rich dwarf galaxies are accreted into galactic halos, which provides an adequate source of H I to account for observations of neutral gas in early-type galaxies. Accretion is found to fuel the wind, thereby regulating the accretion flow and yielding a time-dependent model for star formation, enrichment, and nuclear activity. The permissible parameter range for intergalactic gas clouds and galaxy groups is discussed, along with the frequency of gas-rich dwarfs and their large ratios of gas mass to luminosity. Also considered is the occurrence of gas stripping and the consequent formation of dwarf spheroidal systems that remain in the halo, and gas clouds that dissipate and suffer further infall. A cosmological implication of the model is that, because the characteristic time scale of a gas-rich dwarf galaxy to be accreted and lose its gas is comparable to a Hubble time, there may have been a far more extensive primordial distribution of such systems at earlier epochs.

A VLT/FORS2 spectroscopic survey of individual stars in a transforming dwarf galaxy

NASA Astrophysics Data System (ADS)

Battaglia, G.; Kacharov, N.; Rejkuba, M.

2017-03-01

Understanding the properties of dwarf galaxies is important not only to put them in their proper cosmological context, but also to understand the formation and evolution of the most common type of galaxies. Dwarf galaxies are divided into two main classes, dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs), which differ from each other mainly because the former are gas-rich objects currently forming stars, while the latter are gas-deficient with no on-going star formation. Transition types (dT) are thought to represent dIs in the process of losing their gas, and can therefore shed light into the possible process of dwarf irregulars (dIrrs) becoming gas-deficient, passively evolving galaxies. Here we present preliminary results from our wide-area VLT/FORS2 MXU spectroscopic survey of the Phoenix dT, from which we obtained line-of-sight velocities and metallicities from the nIR Ca II triplet lines for a large sample of individual Red Giant Branch stars.

The Star Formation History and Morphological Evolution of the Draco Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Aparicio, Antonio; Carrera, Ricardo; Martínez-Delgado, David

2001-11-01

The photometric and morphological properties, as well as the star formation history, of the Draco dwarf spheroidal galaxy are analyzed on the basis of wide-field CCD photometry of the resolved stars covering about 1 deg2. Draco is at a distance of d=80+/-7 kpc and has a metallicity, [Fe/H], of -1.8+/-0.2. No metallicity gradient is detected. The star surface density distribution can be fitted by a single exponential law of scale length α=5.0‧+/-0.1‧. The central surface magnitude is μ''V''=24.4+/-0.5, and the core radius is rc=7.5‧+/-0.3‧ (equivalent to rc=175+/-7 pc). Within errors, the same scale lengths are found for the density profiles along the semimajor and semiminor axes (rescaled to semimajor-axis units, using the ellipticity of the galaxy) of Draco. There are hence no evidences of a tidal tail associated with Draco. The tidal radius of the galaxy is found to be rt~=42' (~=1 kpc). The possibility that the large mass-to-light relation in Draco could be accounted for by a convenient spatial orientation is tested. An upper limit to Draco's size along the line of sight is ~14 kpc. This is too small to account for the velocity dispersion of Draco if it were due to projection effects only, and it implies that other mechanisms (e.g., dark matter) are required. The stellar population of Draco is mainly old. Although some intermediate-age population is present in Draco, most of the star formation (up to 90%) took place before ~10 Gyr ago. No significant star formation activity is detected in the last ~2 Gyr. Two methods (partial model and subgiant) have been used to investigate the star formation history of Draco, both producing results in good qualitative agreement. No difference is found between the scale lengths of the distributions of old (>~9 Gyr) and young (~2-3 Gyr) stars, indicating either that both populations were formed under the same kinematic conditions, or that any initial difference was afterward erased.

Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy

NASA Astrophysics Data System (ADS)

Susmitha, A.; Koch, A.; Sivarani, T.

2017-10-01

Carbon-enhanced metal-poor (CEMP) stars bear important imprints of the early chemical enrichment of any stellar system. While these stars are known to exist in copious amounts in the Milky Way halo, detailed chemical abundance data from the faint dwarf spheroidal (dSph) satellites are still sparse, although the relative fraction of these stars increases with decreasing metallicity. Here, we report the abundance analysis of a metal-poor ([ Fe / H ] = - 2.5 dex), carbon-rich ([C/Fe] = 1.4 dex) star, ALW-8, in the Carina dSph using high-resolution spectroscopy obtained with the ESO/UVES instrument. Its spectrum does not indicate any over-enhancements of neutron capture elements. Thus classified as a CEMP-no star, this is the first detection of this kind of star in Carina. Another of our sample stars, ALW-1, is shown to be a CEMP-s star, but its immediate binarity prompted us to discard it from a detailed analysis. The majority of the 18 chemical elements we measured are typical of Carina's field star population and also agree with CEMP stars in other dSph galaxies. Similar to the only known CEMP-no star in the Sculptor dSph and the weak-r-process star HD 122563, the lack of any strong barium-enhancement is accompanied by a moderate overabundance in yttrium, indicating a weak r-process activity. The overall abundance pattern confirms that, also in Carina, the formation site for CEMP-no stars has been affected by both faint supernovae and by standard core collapse supernovae. Whichever process was responsible for the heavy element production in ALW-8 must be a ubiquitous source to pollute the CEMP-no stars, acting independently of the environment such as in the Galactic halo or in dSphs. Based on observations collected at the European Southern Observatory at Paranal, Chile; Large Programme proposal 171.B- 0520.Table A.1 is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http

A Rogues’ Gallery of Andromeda's Dwarf Galaxies. I. A Predominance of Red Horizontal Branches

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; Weisz, Daniel R.; Albers, Saundra M.; Bernard, Edouard; Collins, Michelle L. M.; Dolphin, Andrew E.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Laevens, Benjamin; Lewis, Geraint F.; Mackey, A. Dougal; McConnachie, Alan; Rich, R. Michael; Skillman, Evan D.

2017-11-01

We present homogeneous, sub-horizontal branch photometry of 20 dwarf spheroidal satellite galaxies of M31 observed with the Hubble Space Telescope. Combining our new data for 16 systems with archival data in the same filters for another four, we show that Andromeda dwarf spheroidal galaxies favor strikingly red horizontal branches or red clumps down to ˜104.2 L ⊙ (M V ˜ -5.8). The age-sensitivity of horizontal branch stars implies that a large fraction of the M31 dwarf galaxies have extended star formation histories (SFHs), and appear inconsistent with early star formation episodes that were rapidly shutdown. Systems fainter than ˜105.5 L ⊙ show the widest range in the ratios and morphologies of red and blue horizontal branches, indicative of both complex SFHs and a diversity in quenching timescales and/or mechanisms, which is qualitatively different from what is currently known for faint Milky Way (MW) satellites of comparable luminosities. Our findings bolster similar conclusions from recent deeper data for a handful of M31 dwarf galaxies. We discuss several sources for diversity of our data such as varying halo masses, patchy reionization, mergers/accretion, and the environmental influence of M31 and the Milky Way on the early evolution of their satellite populations. A detailed comparison between the histories of M31 and MW satellites would shed signifiant insight into the processes that drive the evolution of low-mass galaxies. Such a study will require imaging that reaches the oldest main-sequence turnoffs for a significant number of M31 companions.

Detection of the Intrinsic Size of Sagittarius A* Through Closure Amplitude Imaging

NASA Astrophysics Data System (ADS)

Bower, Geoffrey C.; Falcke, Heino; Herrnstein, Robeson M.; Zhao, Jun-Hui; Goss, W. M.; Backer, Donald C.

2004-04-01

We have detected the intrinsic size of Sagittarius A*, the Galactic center radio source associated with a supermassive black hole, showing that the short-wavelength radio emission arises from very near the event horizon of the black hole. Radio observations with the Very Long Baseline Array show that the source has a size of 24 +/- 2 Schwarzschild radii at 7-millimeter wavelength. In one of eight 7-millimeter epochs, we also detected an increase in the intrinsic size of 60+25-17%. These observations place a lower limit to the mass density of Sagittarius A* of 1.4 × 104 solar masses per cubic astronomical unit.

Faint dwarf galaxies in Hickson Compact Group 90*

NASA Astrophysics Data System (ADS)

Ordenes-Briceño, Yasna; Taylor, Matthew A.; Puzia, Thomas H.; Muñoz, Roberto P.; Eigenthaler, Paul; Georgiev, Iskren Y.; Goudfrooij, Paul; Hilker, Michael; Lançon, Ariane; Mamon, Gary; Mieske, Steffen; Miller, Bryan W.; Peng, Eric W.; Sánchez-Janssen, Rubén

2016-12-01

We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with Very Large Telescope/Visible Multi-Object Spectrograph. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range 0.7 ≲ reff/kpc ≲ 1.5 with luminosities of -11.65 ≲ MU ≲ -9.42 and -12.79 ≲ MI ≲ -10.58 mag, corresponding to a colour range of (U - I)0 ≃ 1.1-2.2 mag and surface brightness levels of μU ≃ 28.1 mag arcsec-2 and μI ≃ 27.4 mag arcsec-2. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z⊙ metallicities we obtain stellar masses in the range M*|Z⊙ ≃ 105.7 - 6.3 M⊙ and M_{*}|_{0.02 Z_{⊙} ≃ 10^{6.3-8} M_{⊙}. Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ˜2 Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with ˜2 kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of reff ≃ 46-63 pc and magnitude MU, 0 = -7.42 mag and (U - I)0 = 1.51 mag, which is consistent with a nuclear stellar disc with a stellar mass in the range 104.9 - 6.5 M⊙.

R-process enrichment from a single event in an ancient dwarf galaxy.

PubMed

Ji, Alexander P; Frebel, Anna; Chiti, Anirudh; Simon, Joshua D

2016-03-31

Elements heavier than zinc are synthesized through the rapid (r) and slow (s) neutron-capture processes. The main site of production of the r-process elements (such as europium) has been debated for nearly 60 years. Initial studies of trends in chemical abundances in old Milky Way halo stars suggested that these elements are produced continually, in sites such as core-collapse supernovae. But evidence from the local Universe favours the idea that r-process production occurs mainly during rare events, such as neutron star mergers. The appearance of a plateau of europium abundance in some dwarf spheroidal galaxies has been suggested as evidence for rare r-process enrichment in the early Universe, but only under the assumption that no gas accretes into those dwarf galaxies; gas accretion favours continual r-process enrichment in these systems. Furthermore, the universal r-process pattern has not been cleanly identified in dwarf spheroidals. The smaller, chemically simpler, and more ancient ultrafaint dwarf galaxies assembled shortly after the first stars formed, and are ideal systems with which to study nucleosynthesis events such as the r-process. Reticulum II is one such galaxy. The abundances of non-neutron-capture elements in this galaxy (and others like it) are similar to those in other old stars. Here, we report that seven of the nine brightest stars in Reticulum II, observed with high-resolution spectroscopy, show strong enhancements in heavy neutron-capture elements, with abundances that follow the universal r-process pattern beyond barium. The enhancement seen in this 'r-process galaxy' is two to three orders of magnitude higher than that detected in any other ultrafaint dwarf galaxy. This implies that a single, rare event produced the r-process material in Reticulum II. The r-process yield and event rate are incompatible with the source being ordinary core-collapse supernovae, but consistent with other possible sources, such as neutron star mergers.

V3885 Sagittarius: A Comparison With a Range of Standard Model Accretion Disks

NASA Technical Reports Server (NTRS)

Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion, Edward M; Szkody, Paula; Barrett, Paul E.

2009-01-01

A chi-squared analysis of standard model accretion disk synthetic spectrum fits to combined Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius, on an absolute flux basis, selects a model that accurately represents the observed spectral energy distribution. Calculation of the synthetic spectrum requires the following system parameters. The cataclysmic variable secondary star period-mass relation calibrated by Knigge in 2006 and 2007 sets the secondary component mass. A mean white dwarf (WD) mass from the same study, which is consistent with an observationally determined mass ratio, sets the adopted WD mass of 0.7M(solar mass), and the WD radius follows from standard theoretical models. The adopted inclination, i = 65 deg, is a literature consensus, and is subsequently supported by chi-squared analysis. The mass transfer rate is the remaining parameter to set the accretion disk T(sub eff) profile, and the Hipparcos parallax constrains that parameter to mas transfer = (5.0 +/- 2.0) x 10(exp -9) M(solar mass)/yr by a comparison with observed spectra. The fit to the observed spectra adopts the contribution of a 57,000 +/- 5000 K WD. The model thus provides realistic constraints on mass transfer and T(sub eff) for a large mass transfer system above the period gap.

PAndAS' Progeny: Extending the M31 Dwarf Galaxy Cabal

NASA Astrophysics Data System (ADS)

Richardson, Jenny C.; Irwin, Mike J.; McConnachie, Alan W.; Martin, Nicolas F.; Dotter, Aaron L.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Chapman, Scott C.; Lewis, Geraint F.; Tanvir, Nial R.; Rich, R. Michael

2011-05-01

We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were discovered during the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 subgroup conducted with the MegaPrime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope. The current PAndAS survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ~150 kpc. Here we present for the first time the metal-poor stellar density map for this whole region, not only as an illustration of the discovery space for satellite galaxies, but also as a birds-eye view of the ongoing assembly process of an L * disk galaxy. Four of the newly discovered satellites appear as well-defined spatial overdensities of stars lying on the expected locus of metal-poor (-2.5 < [Fe/H] < -1.3) red giant branch stars at the distance of M31. The fifth overdensity, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. Based on distance estimates from horizontal branch magnitudes, all five have metallicities typical of dwarf spheroidal galaxies ranging from [Fe/H] =-1.7 ± 0.2 to [Fe/H] =-1.9 ± 0.2 and absolute magnitudes ranging from MV = -7.1 ± 0.5 to MV = -10.2 ± 0.5. These five additional satellites bring the number of dwarf spheroidal galaxies in this region to 25 and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies, we also revisit the spatial distribution of this population and in particular we find that, within the current projected limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of satellites varying as r -1, a result

The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run?

NASA Astrophysics Data System (ADS)

Mateo, Mario; Olszewski, Edward W.; Walker, Matthew G.

2008-03-01

We present new kinematic results for 387 stars near the Milky Way satellite dwarf spheroidal galaxy Leo I. Spectra were obtained with the Hectochelle multiobject echelle spectrograph on the MMT, centered in the optical near 5200 Å. From 297 repeat measurements of 108 stars, we estimate the mean velocity error (1 σ) of our sample to be 2.4 km s-1, with a systematic precision of <=1 km s-1. The final sample of 328 Leo I members gives a mean heliocentric velocity of 282.9 +/- 0.5 km s-1 and a dispersion of 9.2 +/- 0.4 km s-1. The dispersion profile of Leo I is flat to beyond its classical "tidal" radius. We fit the profile to various equilibrium dynamical models. We strongly rule out all models where mass follows light. Anisotropic Sérsic+NFW models fit the dispersion profile well, but isotropic models are ruled out at a 95% confidence level. Inside a projected radius of ~1040 pc, the mass and V-band mass-to-light ratio of Leo I from equilibrium models are in the ranges (5-7) × 107 M⊙ and 9-14 (solar units), respectively. Leo I members outside a "break radius" of Rb ~ 400'' (500 pc) exhibit significant velocity anisotropy, whereas stars interior to this radius are consistent with an isotropic velocity distribution. We interpret the break radius as the tidal radius of Leo I at perigalacticon some 1-2 Gyr ago. This interpretation accounts for the complex star formation history of Leo I, population segregation within the galaxy, and Leo I's large outward galactocentric velocity. The lack of evident tidal arms in Leo I suggests that the galaxy may have been injected into its present highly elliptical orbit by a third body a few Gyr before its last perigalacticon. This scenario is plausible within current hierarchical structure formation models.

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

Koch, Andreas; Burkert, Andreas; Rich, R. Michael

We report on the discovery of strong tidal features around a dwarf spheroidal galaxy in the Hydra I galaxy cluster, indicating its ongoing tidal disruption. This very low surface brightness object, HCC-087, was originally classified as an early-type dwarf in the Hydra Cluster Catalogue (HCC), but our re-analysis of the ESO-VLT/FORS images of the HCC unearthed a clear indication of an S-shaped morphology and a large spatial extent. Its shape, luminosity (M{sub V} = -11.6 mag), and physical size (at a half-light radius of 3.1 kpc and a full length of {approx}5.9 kpc) are comparable to the recently discovered NGCmore » 4449B and the Sagittarius dwarf spheroidal, all of which are undergoing clear tidal disruption. Aided by N-body simulations we argue that HCC-087 is currently at its first apocenter, at 150 kpc, around the cluster center and that it is being tidally disrupted by the galaxy cluster's potential itself. An interaction with the nearby (50 kpc) S0 cluster galaxy HCC-005, at M{sub *} {approx} 3 Multiplication-Sign 10{sup 10} M{sub Sun} is rather unlikely, as this constellation requires a significant amount of dynamical friction and thus low relative velocities. The S-shaped morphology and large spatial extent of the satellite would, however, also appear if HCC-087 would orbit the cluster center. These features appear to be characteristic properties of satellites that are seen in the process of being tidally disrupted, independent of the environment of the destruction. An important finding of our simulations is an orientation of the tidal tails perpendicular to the orbit.« less

COMPARING THE OBSERVABLE PROPERTIES OF DWARF GALAXIES ON AND OFF THE ANDROMEDA PLANE

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

Collins, Michelle L. M.; Martin, Nicolas F.; Rich, R. M.

The thin, extended planes of satellite galaxies detected around both the Milky Way and Andromeda are not a natural prediction of the Λ-cold dark matter paradigm. Galaxies in these distinct planes may have formed and evolved in a different way (e.g., tidally) from their off-plane neighbors. If this were the case, one would expect the on- and off-plane dwarf galaxies in Andromeda to have experienced different evolutionary histories, which should be reflected by the chemistries, dynamics, and star formation histories of the two populations. In this work, we present new, robust kinematic observations for two on-plane M31 dwarf spheroidal galaxiesmore » (And XVI and XVII) and compile and compare all available observational metrics for the on- and off-plane dwarfs to search for a signal that would corroborate such a hypothesis. We find that, barring their spatial alignment, the on- and off-plane Andromeda dwarf galaxies are indistinguishable from one another, arguing against vastly different formative and evolutionary histories for these two populations.« less

Outskirts of Local Group Dwarf Galaxies Revealed by Subaru Hyper Suprime-Cam

NASA Astrophysics Data System (ADS)

Komiyama, Yutaka

2017-03-01

Local Group galaxies are important targets since their stellar populations can be resolved, and their properties can be investigated in detail with the help of stellar evolutionary models. The newly-built instrument for the 8.2m Subaru Telescope, Hyper Suprime-Cam (HSC), which has a 1 Giga pixel CCD camera with 1.5 degrees field of view, is the best instrument for observing Local Group galaxies. We have carried out a survey for Local Group dwarf galaxies using HSC aiming to shed light on the outskirts of these galaxies. The survey covers target galaxies out beyond the tidal radii down to a depth unexplored by previous surveys. Thanks to the high spatial resolution and high sensitivity provided by the Subaru Telescope, we are able to investigate properties such as spatial distribution and stellar population from the very center of galaxies to the outskirts. In this article, I will show results for the dwarf irregular galaxy NGC 6822 and the dwarf spheroidal galaxy Ursa Minor.

The Metal-poor non-Sagittarius (?) Globular Cluster NGC 5053: Orbit and Mg, Al, and Si Abundances

NASA Astrophysics Data System (ADS)

Tang, Baitian; Fernández-Trincado, J. G.; Geisler, Doug; Zamora, Olga; Mészáros, Szabolcs; Masseron, Thomas; Cohen, Roger E.; García-Hernández, D. A.; Dell’Agli, Flavia; Beers, Timothy C.; Schiavon, Ricardo P.; Sohn, Sangmo Tony; Hasselquist, Sten; Robin, Annie C.; Shetrone, Matthew; Majewski, Steven R.; Villanova, Sandro; Schiappacasse Ulloa, Jose; Lane, Richard R.; Minnti, Dante; Roman-Lopes, Alexandre; Almeida, Andres; Moreno, E.

2018-03-01

Metal-poor globular clusters (GCs) exhibit intriguing Al–Mg anti-correlations and possible Si–Al correlations, which are important clues to decipher the multiple-population phenomenon. NGC 5053 is one of the most metal-poor GCs in the nearby universe and has been suggested to be associated with the Sagittarius (Sgr) dwarf galaxy, due to its similarity in location and radial velocity with one of the Sgr arms. In this work, we simulate the orbit of NGC 5053, and argue against a physical connection between Sgr and NGC 5053. On the other hand, the Mg, Al, and Si spectral lines, which are difficult to detect in the optical spectra of NGC 5053 stars, have been detected in the near-infrared APOGEE spectra. We use three different sets of stellar parameters and codes to derive the Mg, Al, and Si abundances. Regardless of which method is adopted, we see a large Al variation, and a substantial Si spread. Along with NGC 5053, metal-poor GCs exhibit different Mg, Al, and Si variations. Moreover, NGC 5053 has the lowest cluster mass among the GCs that have been identified to exhibit an observable Si spread until now.

Symbolics of the constellations of sagittarius and centaurus in russian traditional culture

NASA Astrophysics Data System (ADS)

Bagdasarov, R.

2001-12-01

Centaurus falls into the category of 'imaginary animals'. The Russian tradition used not only the symbol Sgr (a result of its acquaintance with the circle of Zodiac), but also the symbol Cen, which fact, as we shall demonstrate, is an evidence of certain mythological-astronomical conceptions. Both the constellations Sagittarius (Sgr) and Centaurus (Cen) are usually represented as versions of the picture of a fantastic being, a Centaur, shaped as man from head to waist, and as an animal, mostly, a horse, from waist down. 'Centaurus' (from the Greek word kev (or kevw)) for 'kill' and o, for 'bull') means 'bull killer', and is probably related to the opposition of the zodiacal constellations Taurus and Sagittarius. When the latter begins to rise on to the night sky, the former disappears completely from view. Sagittarius is represented at ancient monuments related to astronomy as a centaur holding a bow and pointing at certain stars. The constellation of Centaurus is also symbolised by a centaur, but holding not a bow, but a staff or a spear in one hand and an 'animal of sacrifice' in the other (Higinus, Astronomica, III, 37, 1; Chernetsov, 1975, Figure 1). The attributes stand for the Peliases Spear (The Mithological Dictionary, 1991), depicted in astrological maps as The Spear of Centaurus1, The Wolf (Lupus), the Panther or the Beast (Flammarion, 1994).

Antlia B: A Faint Dwarf Galaxy Member of the NGC 3109 Association

NASA Astrophysics Data System (ADS)

Sand, D. J.; Spekkens, K.; Crnojević, D.; Hargis, J. R.; Willman, B.; Strader, J.; Grillmair, C. J.

2015-10-01

We report the discovery of Antlia B, a faint dwarf galaxy at a projected distance of ˜72 kpc from NGC 3109 ({M}V ˜ -15 {mag}), the primary galaxy of the NGC 3109 dwarf association at the edge of the Local Group. The tip of the red giant branch distance to Antlia B is D = 1.29 ± 0.10 Mpc, which is consistent with the distance to NGC 3109. A qualitative analysis indicates the new dwarf's stellar population has both an old, metal-poor red giant branch (≳ 10 {{Gyr}}, [Fe/H] ˜ -2), and a younger blue population with an age of ˜200-400 Myr, analogous to the original Antlia dwarf, another likely satellite of NGC 3109. Antlia B has H i gas at a velocity of {v}{helio,{{H}} {{I}}} = 376 km s-1, confirming the association with NGC 3109 (vhelio = 403 km s-1). The H i gas mass (MH i = 2.8 ± 0.2 × 105 {M}⊙ ), stellar luminosity (MV = -9.7 ± 0.6 mag) and half light radius (rh = 273 ± 29 pc) are all consistent with the properties of dwarf irregular and dwarf spheroidal galaxies in the Local Volume, and is most similar to the Leo P dwarf galaxy. The discovery of Antlia B is the initial result from a Dark Energy Camera survey for halo substructure and faint dwarf companions to NGC 3109 with the goal of comparing observed substructure with expectations from the Λ+Cold Dark Matter model in the sub-Milky Way regime.

The Hunt for Missing Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-11-01

galaxies that resemble the UDGs found in Virgo and Coma clusters, verifying that such objects exist in environments beyond only massive clusters.And at the faint end of the sample, the authors find additional extremely low-surface-brightness dwarfs that are several orders of magnitude fainter even than classical UDGs.The authors describe the properties of these galaxies and compare them to systems like classical UDGs and dwarf spheroidal galaxies in our own Local Cluster. The next step is to determine which of the differences between the sample of NGFS dwarfs and previously known systems are explained by the environmental factors of their host cluster, and which are simply due to sample biases.With much more data from the NGFS still to come, it seems likely that we will soon be able to examine an even larger sample of no-longer-missing dwarfs!CitationRoberto P. Muoz et al 2015 ApJ 813 L15. doi:10.1088/2041-8205/813/1/L15

Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows.

PubMed

Governato, F; Brook, C; Mayer, L; Brooks, A; Rhee, G; Wadsley, J; Jonsson, P; Willman, B; Stinson, G; Quinn, T; Madau, P

2010-01-14

For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.

A Multi-epoch Kinematic Study of the Remote Dwarf Spheroidal Galaxy Leo II

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

Spencer, Meghin E.; Mateo, Mario; Walker, Matthew G.

2017-02-20

We conducted a large spectroscopic survey of 336 red giants in the direction of the Leo II dwarf galaxy using Hectochelle on the Multiple Mirror Telescope, and we conclude that 175 of them are members based on their radial velocities and surface gravities. Of this set, 40 stars have never before been observed spectroscopically. The systemic velocity of the dwarf is 78.3 ± 0.6 km s{sup −1} with a velocity dispersion of 7.4 ± 0.4 km s{sup −1}. We identify one star beyond the tidal radius of Leo II but find no signatures of uniform rotation, kinematic asymmetries, or streams.more » The stars show a strong metallicity gradient of −1.53 ± 0.10 dex kpc{sup −1} and have a mean metallicity of −1.70 ± 0.02 dex. There is also evidence of two different chemodynamic populations, but the signal is weak. A larger sample of stars would be necessary to verify this feature.« less

Equilibrium figures of dwarf planets

NASA Astrophysics Data System (ADS)

Rambaux, Nicolas; Chambat, Frederic; Castillo-Rogez, Julie; Baguet, Daniel

2016-10-01

Dwarf planets including transneptunian objects (TNO) and Ceres are >500 km large and display a spheroidal shape. These protoplanets are left over from the formation of the solar System about 4.6 billion years ago and their study could improve our knowledge of the early solar system. They could be formed in-situ or migrated to their current positions as a consequence of large-scale solar system dynamical evolution. Quantifying their internal composition would bring constraints on their accretion environment and migration history. That information may be inferred from studying their global shapes from stellar occultations or thermal infrared imaging. Here we model the equilibrium shapes of isolated dwarf planets under the assumption of hydrostatic equilibrium that forms the basis for interpreting shape data in terms of interior structure. Deviations from hydrostaticity can shed light on the thermal and geophysical history of the bodies. The dwarf planets are generally fast rotators spinning in few hours, so their shape modeling requires numerically integration with Clairaut's equations of rotational equilibrium expanded up to third order in a small parameter m, the geodetic parameter, to reach an accuracy better than a few kilometers depending on the spin velocity and mean density. We also show that the difference between a 500-km radius homogeneous model described by a MacLaurin ellipsoid and a stratified model assuming silicate and ice layers can reach several kilometers in the long and short axes, which could be measurable. This type of modeling will be instrumental in assessing hydrostaticity and thus detecting large non-hydrostatic contributions in the observed shapes.

Chemically-Deduced Star Formation Histories Of Dwarf Galaxies Using Barium

NASA Astrophysics Data System (ADS)

Duggan, Gina; Kirby, Evan

2017-06-01

Dwarf galaxies offer a unique opportunity to study the competing forces of galaxy evolution. Their simpler history (i.e., small size, fewer major mergers, and lack of active galactic nuclei) enables us to isolate different physical mechanisms more easily. The effects of these mechanisms are imprinted on the galaxy's star formation history. Traditionally, star formation histories are determined from color-magnitude diagrams. However, chemical abundances can increase the precision of this measurement. Here we present a simplistic galactic chemical evolution model to infer the star formation history. Chemical abundances are measured from spectra obtained with Keck/DEIMOS medium-resolution spectroscopy for over a hundred red giant stars from several satellite dwarf spheroidal galaxies and globular clusters. We focus our work on iron and barium abundances because they predominantly trace Type Ia supernovae and asymptotic giant branch stars, respectively. The different timescales of these two nucleosynthetic sources can be used to measure a finely resolved star formation history, especially when combined with existing [α/Fe] measurements. These models will inform the details of early star formation in dwarf galaxies and how it is affected by various physical processes, such as reionization and tidal stripping.

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

THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?

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

Gallart, Carme; Monelli, Matteo; Aparicio, Antonio

We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that startedmore » their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.« less

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

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

Correnti, M.; Ferraro, F. R.; Bellazzini, M.

2010-09-20

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

Effects of magnetic fields and slow rotation in white dwarfs

NASA Astrophysics Data System (ADS)

Terrero, D. Alvear; Paret, D. Manreza; Martínez, A. Pérez

In this work we use Hartle’s formalism to study the effects of rotation in the structure of magnetized white dwarfs within the framework of general relativity. We describe the inner matter by means of an equation of state for electrons under the action of a constant magnetic field, which introduces an anisotropy in the pressures. Solutions correspond to typical densities of white dwarfs and values of magnetic field below 1013G considering perpendicular and parallel pressures independently, as if associated to two different equations of state. Rotation effects obtained account for an increase of the maximum mass for both magnetized and nonmagnetized stable configurations, up to about 1.5M⊙. Further effects studied include the deformation of the stars, which become oblate spheroids and the solutions for other quantities of interest, such as the moment of inertia, quadrupolar momentum and eccentricity. In all cases, rotation effects are dominant with respect to those of the magnetic field.

Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. III. Measurement for Ursa Minor

NASA Astrophysics Data System (ADS)

Piatek, Slawomir; Pryor, Carlton; Bristow, Paul; Olszewski, Edward W.; Harris, Hugh C.; Mateo, Mario; Minniti, Dante; Tinney, Christopher G.

2005-07-01

This article presents a measurement of the proper motion of the Ursa Minor dwarf spheroidal galaxy determined from images taken with the Hubble Space Telescope in two distinct fields. Each field contains a quasi-stellar object that serves as the ``reference point.'' The measured proper motion for Ursa Minor, expressed in the equatorial coordinate system, is (μα,μδ)=(-50+/-17,22+/-16) mas century-1. Removing the contributions of the solar motion and the motion of the local standard of rest yields the proper motion in the Galactic rest frame: (μGrfα,μGrfδ)=(-8+/-17,38+/-16) mas century-1. The implied space velocity with respect to the Galactic center has a radial component of Vr=-75+/-44 km s-1 and a tangential component of Vt=144+/-50 km s-1. Integrating the motion of Ursa Minor in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 40 (10, 76) and 89 (78, 160) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.39 (0.09, 0.79), and the orbital period is 1.5 (1.1, 2.7) Gyr. The orbit is retrograde and inclined by 124° (94°, 136°) to the Galactic plane. Ursa Minor is not a likely member of a proposed stream of galaxies on similar orbits around the Milky Way, nor is the plane of its orbit coincident with a recently proposed planar alignment of galaxies around the Milky Way. Comparing the orbits of Ursa Minor and Carina shows no reason for the different star formation histories of these two galaxies. Ursa Minor must contain dark matter to have a high probability of having survived disruption by the Galactic tidal force until the present. 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 NAS5-26555.

METALLICITY EVOLUTION OF THE SIX MOST LUMINOUS M31 DWARF SATELLITES

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

Ho, Nhung; Geha, Marla; Tollerud, Erik J.

We present global metallicity properties, metallicity distribution functions (MDFs), and radial metallicity profiles for the six most luminous M31 dwarf galaxy satellites: M32, NGC 205, NGC 185, NGC 147, Andromeda VII, and Andromeda II. The results presented are the first spectroscopic MDFs for dwarf systems surrounding a host galaxy other than the Milky Way (MW). Our sample consists of individual metallicity measurements for 1243 red giant branch member stars spread across these six systems. We determine metallicities based on the strength of the Ca II triplet lines using the empirical calibration of Carrera et al., which is calibrated over the metallicity range –4 < [Fe/H] <+0.5. We findmore » that these M31 satellites lie on the same luminosity-metallicity relationship as the MW dwarf satellites. We do not find a trend between the internal metallicity spread and galaxy luminosity, contrary to previous studies. The MDF widths of And II and And VII are similar to the MW dwarf spheroidal (dSph) satellites of comparable luminosity; however, our four brightest M31 dwarf satellites are more luminous than any of the MW dSphs and have broader MDFs. The MDFs of our six M31 dwarf satellites are consistent with the leaky box model of chemical evolution, although our metallicity errors allow a wide range of evolution models. We find a significant radial gradient in metallicity in only two of our six systems, NGC 185 and Andromeda II, and flat radial metallicity gradients in the rest of our sample with no observed correlation between rotational support and radial metallicity gradients. Although the average properties and radial trends of the M31 dwarf galaxies agree with their MW counterparts at similar luminosity, the detailed MDFs are different, particularly at the metal-rich end.« less

Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

NASA Astrophysics Data System (ADS)

Wheeler, Coral Rose

that can continue to form stars in isolation after reionization. Finally, we perform a systematic Bayesian analysis of rotation vs. dispersion support (vrot/sigma) in 40 dwarf galaxies throughout the Local Volume (LV) over a stellar mass range 103.5 M sun < M* < 108 Msun. We find that the stars in 80% of the LV dwarf galaxies studied -- both satellites and isolated systems -- are dispersion-supported. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally-supported stellar disks, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion supported stars. We apply the same Bayesian analysis to four of the FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dwarf galaxies (109 Msun < M vir < 1010 Msun) and show that the simulated isolated dIrr galaxies have stellar ellipticities and stellar vrot/sigma ratios that are consistent with the observed population of dIrrs and dSphs without the need to subject these dwarfs to any external perturbations or tidal forces. We posit that most dwarf galaxies form as puffy, dispersion-dominated systems, rather than cold, angular momentum-supported disks. If this is the case, then transforming a dIrr into a dSph may require little more than removing its gas.

Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. II. Measurement for Carina

NASA Astrophysics Data System (ADS)

Piatek, Slawomir; Pryor, Carlton; Olszewski, Edward W.; Harris, Hugh C.; Mateo, Mario; Minniti, Dante; Tinney, Christopher G.

2003-11-01

This article presents and discusses a measurement of the proper motion for the Carina dwarf spheroidal galaxy (dSph) from images in two distinct fields in the direction of Carina taken with the Hubble Space Telescope, at three epochs. Each field contains a confirmed quasi-stellar object that is the reference point for measuring the proper motion of the dSph. The consecutive epochs are 1-2 yr apart. The components of the measured proper motion for Carina, expressed in the equatorial coordinate system, are μα=22+/-9 mas century-1 and μδ=15+/-9 mas century-1. The quoted proper motion is a weighted mean of two independent measurements and has not been corrected for the motions of the Sun and of the local standard of rest. Given the proper motion and its uncertainty, integrating the family of possible orbits of Carina in a realistic gravitational potential for the Milky Way indicates that Carina is bound gravitationally to the Milky Way and is close to apogalacticon. The best estimate of, and the 95% confidence interval for, the apogalacticon of the orbit is 102 kpc and (102,113) kpc, for the perigalacticon is 20 kpc and (3.0,63) kpc, and for the orbital period is 1.4 Gyr and (1.3,2.0) Gyr. Carina does not seem to be on a polar orbit. The best estimate of the inclination of the orbit with respect to the Galactic plane is 39°, but the 95% confidence interval is so wide, (23°,102°), that it includes a polar orbit. We are unable to confirm or to rule out the membership of Carina in a ``stream'' of galaxies in the Galactic halo because the difference between the observed and predicted directions of the proper motion is 1.6 times the uncertainty of the difference. Carina must contain dark matter to have survived the tidal interaction with the Milky Way until the present. The triggering of star formation by perigalacticon passages and crossings of the Galactic disk do not explain the history of star formation in Carina. Based on observations with NASA/ESA Hubble Space

The no-spin zone: rotation versus dispersion support in observed and simulated dwarf galaxies

NASA Astrophysics Data System (ADS)

Wheeler, Coral; Pace, Andrew B.; Bullock, James S.; Boylan-Kolchin, Michael; Oñorbe, Jose; Elbert, Oliver D.; Fitts, Alex; Hopkins, Philip F.; Kereš, Dušan

2017-02-01

We perform a systematic Bayesian analysis of rotation versus dispersion support (vrot/σ) in 40 dwarf galaxies throughout the local volume (LV) over a stellar mass range of 10^{3.5} M_{⊙}< M_{star }< 108 M_{⊙}. We find that the stars in ˜80 per cent of the LV dwarf galaxies studied - both satellites and isolated systems - are dispersion-supported. In particular, we show that 6/10 isolated dwarfs in our sample have vrot/σ ≲ 1.0, while all have vrot/σ ≲ 2.0. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally supported stellar discs, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion-supported stars. We see no clear trend between vrot/σ and distance to the closest L⋆ galaxy, nor between vrot/σ and M⋆ within our mass range. We apply the same Bayesian analysis to four FIRE hydrodynamic zoom-in simulations of isolated dwarf galaxies (10^9 M_{⊙}< M_{vir}< 10^{10} M_{⊙}) and show that the simulated isolated dIrr galaxies have stellar ellipticities and stellar vrot/σ ratios that are consistent with the observed population of dIrrs and dSphs without the need to subject these dwarfs to any external perturbations or tidal forces. We posit that most dwarf galaxies form as puffy, dispersion-dominated systems, rather than cold, angular-momentum-supported discs. If this is the case, then transforming a dIrr into a dSph may require little more than removing its gas.

Spheroid imaging of phase-diversity homodyne OCT

NASA Astrophysics Data System (ADS)

Senda, Naoko; Osawa, Kentaro

2017-02-01

Non-invasive 3D imaging technique is essential for regenerative tissues evaluation. Optical coherence tomography (OCT) is one of 3D imaging tools with no staining and is used extensively for fundus examination. We have developed Phase-Diversity Homodyne OCT which enables cell imaging because of high resolution, whereas conventional OCT was not used for cell imaging because of low resolution. We demonstrated non-invasive imaging inside living spheroids with Phase-Diversity Homodyne OCT. Spheroids are spheroidal cell aggregates and used as regenerative tissues. Cartilage cells were cultured in low-adhesion 96-well plates and spheroids were manufactured. Cell membrane and cytoplasm of spheroid were imaged with OCT.

Acoustic scattering on spheroidal shapes near boundaries

NASA Astrophysics Data System (ADS)

Miloh, Touvia

2016-11-01

A new expression for the Lamé product of prolate spheroidal wave functions is presented in terms of a distribution of multipoles along the axis of the spheroid between its foci (generalizing a corresponding theorem for spheroidal harmonics). Such an "ultimate" singularity system can be effectively used for solving various linear boundary-value problems governed by the Helmholtz equation involving prolate spheroidal bodies near planar or other boundaries. The general methodology is formally demonstrated for the axisymmetric acoustic scattering problem of a rigid (hard) spheroid placed near a hard/soft wall or inside a cylindrical duct under an axial incidence of a plane acoustic wave.

Scattering of elastic waves by a spheroidal inclusion

NASA Astrophysics Data System (ADS)

Johnson, Lane R.

2018-03-01

An analytical solution is presented for scattering of elastic waves by prolate and oblate spheroidal inclusions. The problem is solved in the frequency domain where separation of variables leads to a solution involving spheroidal wave functions of the angular and radial kind. Unlike the spherical problem, the boundary equations remain coupled with respect to one of the separation indices. Expanding the angular spheroidal wave functions in terms of associated Legendre functions and using their orthogonality properties leads to a set of linear equations that can be solved to simultaneously obtain solutions for all coupled modes of both scattered and interior fields. To illustrate some of the properties of the spheroidal solution, total scattering cross-sections for P, SV and SH plane waves incident at an oblique angle on a prolate spheroid, an oblate spheroid and a sphere are compared. The waveforms of the scattered field exterior to the inclusion are calculated for these same incident waves. The waveforms scattered by a spheroid are strongly dependent upon the angle of incidence, are different for incident SV and SH waves and are asymmetrical about the centre of the spheroid with the asymmetry different for prolate and oblate spheroids.

Bar-spheroid interaction in galaxies

NASA Technical Reports Server (NTRS)

Hernquist, Lars; Weinberg, Martin D.

1992-01-01

N-body simulation and linear analysis is employed to investigate the secular evolution of barred galaxies, with emphasis on the interaction between bars and spheroidal components of galaxies. This interaction is argued to drive secular transfer of angular momentum from bars to spheroids, primarily through resonant coupling. A moderately strong bar, having mass within corotation about 0.3 times the enclosed spheroid mass, is predicted to shed all its angular momentum typically in less than about 10 exp 9 yr. Even shorter depletion time scales are found for relatively more massive bars. It is suggested either that spheroids around barred galaxies are structured so as to inhibit strong coupling with bars, or that bars can form by unknown processes long after disks are established. The present models reinforce the notion that bars can drive secular evolution in galaxies.

The distribution of alpha elements in Andromeda dwarf galaxies

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

Vargas, Luis C.; Geha, Marla C.; Tollerud, Erik J., E-mail: luis.vargas@yale.edu

We present alpha to iron abundance ratios for 226 individual red giant branch stars in nine dwarf galaxies of the Andromeda (M31) satellite system. The abundances are measured from the combined signal of Mg, Si, Ca, and Ti lines in Keck/DEIMOS medium-resolution spectra. This constitutes the first large sample of alpha abundance ratios measured in the M31 satellite system. The dwarf galaxies in our sample exhibit a variety of alpha abundance ratios, with the average values in each galaxy ranging from approximately solar ([α/Fe] ∼ + 0.0) to alpha-enhanced ([α/Fe] ∼ + 0.5). These variations do not show a correlationmore » with internal kinematics, environment, or stellar density. We confirm radial gradients in the iron abundance of two galaxies out of the five with sufficient data (NGC 185 and And II). There is only tentative evidence for an alpha abundance radial gradient in NGC 185. We homogeneously compare our results to the Milky Way classical dwarf spheroidals, finding evidence for wider variation in average alpha abundance. In the absence of chemical abundances for the M31 stellar halo, we compare to the Milky Way stellar halo. A stellar halo comprised of disrupted M31 satellites is too metal-rich and inconsistent with the Milky Way halo alpha abundance distribution even if considering only satellites with predominantly old stellar populations. The M31 satellite population provides a second system in which to study chemical abundances of dwarf galaxies and reveals a wider variety of abundance patterns than the Milky Way.« less

Light scattering properties of spheroidal particles

NASA Technical Reports Server (NTRS)

Asano, S.

1979-01-01

In the present paper, the light scattering characteristics of spheroidal particles are evaluated within the framework of a scattering theory developed for a homogeneous isotropic spheroid. This approach is shown to be well suited for computing the scattering quantities of spheroidal particles of fairly large sizes (up to a size parameter of 30). The effects of particle size, shape, index of refraction, and orientation on the scattering efficiency factors and the scattering intensity functions are studied and interpreted physically. It is shown that, in the case of oblique incidence, the scattering properties of a long slender prolate spheroid resemble those of an infinitely long circular cylinder.

Dark matter constraints from a joint analysis of dwarf Spheroidal galaxy observations with VERITAS

DOE PAGES

Archambault, S.; Archer, A.; Benbow, W.; ...

2017-04-05

We present constraints on the annihilation cross section of weakly interacting massive particles dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events.

On the Formation of Extended Galactic Disks by Tidally Disrupted Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Peñarrubia, Jorge; McConnachie, Alan; Babul, Arif

2006-10-01

We explore the possibility that extended disks, such as that recently discovered in M31, are the result of a single dwarf (109-1010 Msolar) satellite merger. We conduct N-body simulations of dwarf NFW halos with embedded spheroidal stellar components on coplanar, prograde orbits in an M31-like host galaxy. As the orbit decays due to dynamical friction and the system is disrupted, the stellar particles relax to form an extended, exponential-disk-like structure that spans the radial range 30-200 kpc. The disk scale length Rd correlates with the initial extent of the stellar component within the satellite halo: the more embedded the stars, the smaller the resulting disk scale length. If the progenitors start on circular orbits, the kinematics of the stars that make up the extended disk have an average rotational motion that is 30-50 km s-1 lower than the host's circular velocity. For dwarf galaxies moving on highly eccentric orbits (e~=0.7), the stellar debris exhibits a much lower rotational velocity. Our results imply that extended galactic disks might be a generic feature of the hierarchical formation of spiral galaxies such as M31 and the Milky Way.

The central spheroids of Milky Way mass-sized galaxies

NASA Astrophysics Data System (ADS)

Tissera, Patricia B.; Machado, Rubens E. G.; Carollo, Daniela; Minniti, Dante; Beers, Timothy C.; Zoccali, Manuela; Meza, Andres

2018-01-01

We study the properties of the central spheroids located within 10 kpc of the centre of mass of Milky Way mass-sized galaxies simulated in a cosmological context. The simulated central regions are dominated by stars older than 10 Gyr, mostly formed in situ, with a contribution of ∼30 per cent from accreted stars. These stars formed in well-defined starbursts, although accreted stars exhibit sharper and earlier ones. The fraction of accreted stars increases with galactocentric distance, so that at a radius of ∼8-10 kpc, a fraction of ∼40 per cent, on average, is detected. Accreted stars are slightly younger, lower metallicity, and more α-enhanced than in situ stars. A significant fraction of old stars in the central regions come from a few (2-3) massive satellites (∼1010 M⊙). The bulge components receive larger contributions of accreted stars formed in dwarfs smaller than ∼109.5 M⊙. The difference between the distributions of ages and metallicities of old stars is thus linked to the accretion histories - those central regions with a larger fraction of accreted stars are those with contributions from more massive satellites. The kinematical properties of in situ and accreted stars are consistent with the latter being supported by their velocity dispersions, while the former exhibit clear signatures of rotational support. Our simulations demonstrate a range of characteristics, with some systems exhibiting a co-existing bar and spheroid in their central regions, resembling in some respect the central region of the Milky Way.

Measurement of oxygen tension within mesenchymal stem cell spheroids.

PubMed

Murphy, Kaitlin C; Hung, Ben P; Browne-Bourne, Stephen; Zhou, Dejie; Yeung, Jessica; Genetos, Damian C; Leach, J Kent

2017-02-01

Spheroids formed of mesenchymal stem cells (MSCs) exhibit increased cell survival and trophic factor secretion compared with dissociated MSCs, making them therapeutically advantageous for cell therapy. Presently, there is no consensus for the mechanism of action. Many hypothesize that spheroid formation potentiates cell function by generating a hypoxic core within spheroids of sufficiently large diameters. The purpose of this study was to experimentally determine whether a hypoxic core is generated in MSC spheroids by measuring oxygen tension in aggregates of increasing diameter and correlating oxygen tension values with cell function. MSC spheroids were formed with 15 000, 30 000 or 60 000 cells per spheroid, resulting in radii of 176 ± 8 µm, 251 ± 12 µm and 353 ± 18 µm, respectively. Oxygen tension values coupled with mathematical modelling revealed a gradient that varied less than 10% from the outer diameter within the largest spheroids. Despite the modest radial variance in oxygen tension, cellular metabolism from spheroids significantly decreased as the number of cells and resultant spheroid size increased. This may be due to adaptive reductions in matrix deposition and packing density with increases in spheroid diameter, enabling spheroids to avoid the formation of a hypoxic core. Overall, these data provide evidence that the enhanced function of MSC spheroids is not oxygen mediated. © 2017 The Author(s).

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

NASA Astrophysics Data System (ADS)

Tudorica, A.; Georgiev, I. Y.; Chies-Santos, A. L.

2015-09-01

Context. Age, metallicity, and spatial distribution of globular clusters (GCs) provide a powerful tool for reconstructing major star-formation episodes in galaxies. IKN is a faint dwarf spheroidal (dSph) in the M 81 group of galaxies. It contains five old GCs, which makes it the galaxy with the highest known specific frequency (SN = 126). Aims: We estimate the photometric age, metallicity, and spatial distribution of the poorly studied IKN GCs. We search SDSS for GC candidates beyond the HST/ACS field of view, which covers half of IKN. Methods: To break the age-metallicity degeneracy in the colour, we used WHT/LIRIS KS-band photometry and derived photometric ages and metallicities by comparison with SSP models in the V,I,Ks colour space. Results: IKN GCs' VIKs colours are consistent with old ages (≥8 Gyr) and a metallicity distribution with a higher mean than is typical for such a dSph ([Fe/H] ≃ -1.4-0.2+0.6 dex). Their photometric mass range (0.5 < ℳGC< 4 × 105 M⊙) implies an unusually high mass ratio between GCs and field stars, of 10.6%. Mixture model analysis of the RGB field stars' metallicity suggests that 72% of the stars may have formed together with the GCs. Using the most massive GC-SFR relation, we calculated a star formation rate (SFR) of ~10 M⊙/yr during its formation epoch. We note that the more massive GCs are closer to the galaxy photometric centre. IKN GCs also appear spatially aligned along a line close to the major axis of the IKN and nearly orthogonal to the plane of spatial distribution of galaxies in the M 81 group. We identify one new IKN GC candidate based on colour and the PSF analysis of the SDSS data. Conclusions: The evidence of i) broad and high metallicity distribution of the field IKN RGB stars and its GCs, ii) high fraction, and iii) spatial alignment of IKN GCs supports a scenario for tidally triggered, complex IKN's star formation history in the context of interactions with galaxies in the M 81 group.

The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Kirby, Evan N.; Cohen, Judith G.; Guhathakurta, Puragra; Cheng, Lucy; Bullock, James S.; Gallazzi, Anna

2013-12-01

We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* \\propto M_*^{0.30+/- 0.02}. The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M * = 1012 M ⊙. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of star formation due to ram pressure stripping. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Analytical study of spheroidal dust grains in plasma

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

Zahed, H.; Mahmoodi, J.; Sobhanian, S.

2006-05-15

Using the modified spheroidal equations, the potential of a spheroidal conducting grain, floated in a plasma, is calculated. The electric field and capacitance for both prolate and oblate spheroidal grains are investigated. The solutions, obtained up to the second-order approximation, show that the plasma screening causes the equipotential surfaces around the grain to be more elongated or flattened than the potential spheroids of the Laplace equation. This leads to the variation of the plasma concentration around the grain.

Chandra X-Ray Observatory Image of Sagittarius A

NASA Technical Reports Server (NTRS)

2003-01-01

A 2 week observation through the optic eye of the Chandra X-Ray Observatory revealed this sturning explosion occurring in the super massive black hole at the Milky Way's center, known as Sagittarius A or Sgr A*. Huge lobes of 20-million degree Centigrade gas ( red loops in image) flank both sides of the black hole and extend over dozens of light years indicating that enormous explosions occurred several times over the last 10 thousand years. Weighing in at 3-million times the mass of the sun, the Sgr A* is a starved black hole, possibly because explosive events in the past have cleared much of the gas around it.

Unsuccessful mitosis in multicellular tumour spheroids.

PubMed

Molla, Annie; Couvet, Morgane; Coll, Jean-Luc

2017-04-25

Multicellular spheroids are very attractive models in oncology because they mimic the 3D organization of the tumour cells with their microenvironment. We show here using 3 different cell types (mammary TSA/pc, embryonic kidney Hek293 and cervical cancer HeLa), that when the cells are growing as spheroids the frequency of binucleated cells is augmented as occurs in some human tumours.We therefore describe mitosis in multicellular spheroids by following mitotic markers and by time-lapse experiments. Chromosomes alignment appears to be correct on the metaphasic plate and the passenger complex is well localized on centromere. Moreover aurora kinases are fully active and histone H3 is phosphorylated on Ser 10. Consequently, the mitotic spindle checkpoint is satisfied and, anaphase proceeds as illustrated by the transfer of survivin on the spindle and by the segregation of the two lots of chromosomes. However, the segregation plane is not well defined and oscillations of the dividing cells are observed. Finally, cytokinesis fails and the absence of separation of the two daughter cells gives rise to binucleated cells.Division orientation is specified during interphase and persists throughout mitosis. Our data indicate that the cancer cells, in multicellular spheroids, lose their ability to regulate their orientation, a feature commonly encountered in tumours.Moreover, multicellular spheroid expansion is still sensitive to mitotic drugs as pactlitaxel and aurora kinase inhibitors. The spheroids thus represent a highly relevant model for studying drug efficiency in tumours.

Hypothermic maintenance of hepatocyte spheroids.

PubMed

Lai, Pamela H; Meng, Qin; Sielaff, Timothy D; Hu, Wei-Shou

2005-01-01

Primary hepatocytes form spheroids under some culture conditions. These spheroids exhibit many tissue-like ultrastructures and retain many liver-specific functions over a long period of time. They are attractive for many applications employing liver cells. The ability to maintain their viability and functions at a reduced temperature to allow for transportation to the site of their application will facilitate their use. Furthermore, with their structural and functional similarity, they could possibly be used as a model system for studying various liver ischemias. The effect of hypothermic treatment was assessed by oxygen consumption rate, ATP, H2O2, and caspase 8 content, as well as albumin and urea synthesis, during and posttreatment. No single outcome variable gives a superlative quantification of hypothermic damage. Taken together, the hypothermic treatment can be seen as increasingly damaging as the temperature decreases from 21 degrees C to 15 degrees C and 4 degrees C. The addition of the chemical protectants glutathione, N-acetyl-L-cystein (NAC), and tauroursodeoxycholic acid (TUDCA) decreased the damaging effect of hypothermic treatment. This protection effect was even more profound when spheroids were preincubated with the protectant for 24 h, and was most prominent at 4 degrees C. The viability of the hypothermically treated hepatocyte spheroids was confirmed by laser scanning confocal microscopy. The method reported provides a means of maintaining spheroids' viability and may allow for their distribution to application sites at a distance.

STAR FORMATION IN DWARF GALAXIES OF THE NEARBY CENTAURUS A GROUP

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

Cote, Stephanie; Draginda, Adam; Skillman, Evan D.

2009-10-15

We present H{alpha} narrow-band imaging of 17 dwarf irregular (dI) galaxies in the nearby Centaurus A Group. Although all large galaxies of the group are or recently have been through a period of enhanced star formation, the dIs have normal star formation rates (SFRs) and do not contain a larger fraction of dwarf starbursts than other nearby groups such as the Sculptor Group or the Local Group. Most of the galaxies in the group now have fairly accurately known distances, which enables us to obtain relative distances between dIs and larger galaxies of the group. We find that the dImore » SFRs do not depend on local environment, and in particular they do not show any correlation with the distance of the dI to the nearest large galaxy of the group. There is a clear morphology-density relation in the Centaurus A Group, similar to the Sculptor Group and Local Group, in the sense that dwarf ellipticals (dEs)/dwarf spheroidals (dSphs) tend to be at small distances from the more massive galaxies of the group, while dIs are on average at larger distances. We find four transition dwarfs in the Group, dwarfs that show characteristics of both dE/dSphs and dIs, and which contain cold gas but no current star formation. Interestingly, the transition dwarfs have an average distance to the more massive galaxies, which is intermediate between those of the dEs/dSphs and dIs and which is quite large: 0.54 {+-} 0.31 Mpc. This large distance poses some difficulty for the most popular scenarios proposed for transforming a dI into a dE/dSph (ram-pressure with tidal stripping or galaxy harassment). If the observed transition dwarfs are indeed missing links between dIs and dE/dSphs, their relative isolation makes it less likely to have been produced by these mechanisms. An inhomogeneous intergalactic medium containing higher density clumps would be able to ram-pressure strip the dIs at larger distances from the more massive galaxies of the group.« less

Integrated Light Chemical Abundance Analyses of 7 M31 Outer Halo Globular Clusters from the Pan-Andromeda Archaeological Survey

NASA Astrophysics Data System (ADS)

Sakari, Charli; Venn, Kim; Mackey, Dougal; Shetrone, Matthew D.; Dotter, Aaron L.; Wallerstein, George

2015-01-01

Detailed chemical abundances of globular clusters provide insight into the formation and evolution of galaxies and their globular cluster systems. This talk presents detailed chemical abundances for seven M31 outer halo globular clusters (with projected radii greater than 30 kpc), as derived from high resolution integrated light spectra. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS). The integrated abundances show that 4 of these clusters are metal-poor ([Fe/H] < -1.5) while the other 3 are more metal-rich. The most metal-poor globular clusters are α-enhanced, though 3 of the 4 are possibly less α-enhanced than MW stars (at the 1σ level). Other chemical abundance ratios ([Ba/Eu], [Eu/Ca], and [Ni/Fe]) are consistent with origins in low mass dwarf galaxies (similar to Fornax). The most metal-rich cluster ([Fe/H] ~ -1) stands out as being chemically distinct from Milky Way field stars of the same metallicity---its chemical abundance ratios agree best with the stars and clusters in the Large Magellanic Cloud (LMC) and the Sagittarius dwarf spheroidal (Sgr) than with the Milky Way field stars. The other metal-rich clusters, H10 and H23, look similar to the LMC and Milky Way field stars in all abundance ratios. These results indicate that M31's outer halo is being at least partially built up by the accretion of dwarf satellites, in agreement with previous observations.

Dark Matter Annihilation Cross-Section Limits of Dwarf Spheroidal Galaxies with the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory and on the design of a Water Cherenkov Detector Prototype

NASA Astrophysics Data System (ADS)

Proper, Megan Longo

I present an indirect search for Dark Matter using the High Altitude Water Cherenkov (HAWC) gamma-ray observatory. There is significant evidence for dark matter within the known Universe, and we can set constraints on the dark matter annihilation cross-section using dark matter rich sources. Dwarf spheroidal galaxies (dSphs) are low luminosity galaxies with little to no gas or dust, or recent star formation. In addition, the total mass of a dwarf spheroidal galaxy, as inferred from gravitational effects observed within the galaxy, is many times more than the luminous mass, making them extremely dark matter rich. For these reasons dSphs are prime targets for indirect dark matter searches with gamma rays. Dark matter annihilation cross-section limits are presented for 14 dSphs within the HAWC field of view, as well as a combined limit with all sources. The limits presented here are for dark matter masses ranging from 0.5 TeV to 1000 TeV. At lower dark matter masses, the HAWC-111 limits are not competitive with other gamma-ray experiments, however it will be shown that HAWC is currently dominating in the higher dark matter mass range. The HAWC observatory is a water Cherenkov detector and consists of 300 Water Cherenkov Detectors (WCDs). The detector is located at 4100 m above sea level in the Sierra Negra region of Mexico at latitude 18°59'41" N and longitude 97°18'28" W. Each WCD is instrumented with three 8 inch photomultiplier tubes (PMTs) and one 10 inch high efficiency PMT, anchored to the bottom of a 5 m deep by 7.3 m diameter steel tank. The tank contains a multilayer hermetic plastic bag, called a bladder, which holds 200,000 L of ultra-purified water. I will also present the design, deployment, and operation of a WCD prototype for HAWC built at Colorado State University (CSU). The CSU WCD was the only full-size prototype outside of the HAWC site. It was instrumented with 7 HAWC PMTs and scintillator paddles both under and above the volume of water. In

Directly spheroidizing during hot deformation in GCr15 steels

NASA Astrophysics Data System (ADS)

Zhu, Guo-hui; Zheng, Gang

2008-03-01

The spheroidizing heat treatment is normally required prior to the cold forming in GCr15 steel in order to improve its machinability. In the conventional spheroidizing process, very long annealing time, generally more than 10 h, is needed to assure proper spheroidizing. It results in low productivity, high cost, and especially high energy consumption. Therefore, the possibility of directly spheroidizing during hot deformation in GCr15 steel is preliminarily explored. The effect of hot deformation parameters on the final microstructure and hardness is investigated systematically in order to develop a directly spheroidizing technology. Experimental results illustrate that low deformation temperature and slow cooling rate is the favorite in directly softening and/or spheroidizing during hot deformation, which allows the properties of asrolled GCr15 to be applicable for post-machining without requirement of prior annealing.

THE SPLASH SURVEY: KINEMATICS OF ANDROMEDA's INNER SPHEROID

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

Dorman, Claire E.; Guhathakurta, Puragra; Fardal, Mark A., E-mail: cdorman@ucolick.org, E-mail: raja@ucolick.org, E-mail: fardal@astro.umass.edu

2012-06-20

The combination of large size, high stellar density, high metallicity, and Sersic surface brightness profile of the spheroidal component of the Andromeda galaxy (M31) within R{sub proj} {approx} 20 kpc suggests that it is unlike any subcomponent of the Milky Way. In this work we capitalize on our proximity to and external view of M31 to probe the kinematical properties of this 'inner spheroid'. We employ a Markov chain Monte Carlo (MCMC) analysis of resolved stellar kinematics from Keck/DEIMOS spectra of 5651 red giant branch stars to disentangle M31's inner spheroid from its stellar disk. We measure the mean velocitymore » and dispersion of the spheroid in each of five spatial bins after accounting for a locally cold stellar disk as well as the Giant Southern Stream and associated tidal debris. For the first time, we detect significant spheroid rotation (v{sub rot} {approx} 50 km s{sup -1}) beyond R{sub proj} {approx} 5 kpc. The velocity dispersion decreases from about 140 km s{sup -1} at R{sub proj} = 7 kpc to 120 km s{sup -1} at R{sub proj} = 14 kpc, consistent to 2{sigma} with existing measurements and models. We calculate the probability that a given star is a member of the spheroid and find that the spheroid has a significant presence throughout the spatial extent of our sample. Lastly, we show that the flattening of the spheroid is due to velocity anisotropy in addition to rotation. Though this suggests that the inner spheroid of M31 more closely resembles an elliptical galaxy than a typical spiral galaxy bulge, it should be cautioned that our measurements are much farther out (2-14r{sub eff}) than for the comparison samples.« less

Ground-based Opportunities for Astrometry

DTIC Science & Technology

2013-01-01

those stars (Dinescu eta/. 2005) leads to a measurement of the tangential velocity of the Sagittarius dwarf and a definitive orbit. Several other...Currently accepted Lambda cold-dark-matter (CDM) cosmological models (see also Chapter 28) predict several hundred merging dwarf galaxies within 1...nination of tations with I) diagrams. o parallaxes lial velocity tarius dwarf of possible eta/. 2005) a definitive ttion of their uti on. :Is

New White Dwarf-Brown Dwarf Binaries

NASA Astrophysics Data System (ADS)

Casewell, S. L.; Geier, S.; Lodieu, N.

2017-03-01

We present follow-up spectroscopy to 12 candidate white dwarf-brown dwarf binaries. We have confirmed that 8 objects do indeed have a white dwarf primary (7 DA, 1 DB) and two are hot subdwarfs. We have determined the Teff and log g for the white dwarfs and subdwarfs, and when combining these values with a model spectrum and the photometry, we have 3 probable white dwarf-substellar binaries with spectral types between M6 and L6.

Digital microfluidics for automated hanging drop cell spheroid culture.

PubMed

Aijian, Andrew P; Garrell, Robin L

2015-06-01

Cell spheroids are multicellular aggregates, grown in vitro, that mimic the three-dimensional morphology of physiological tissues. Although there are numerous benefits to using spheroids in cell-based assays, the adoption of spheroids in routine biomedical research has been limited, in part, by the tedious workflow associated with spheroid formation and analysis. Here we describe a digital microfluidic platform that has been developed to automate liquid-handling protocols for the formation, maintenance, and analysis of multicellular spheroids in hanging drop culture. We show that droplets of liquid can be added to and extracted from through-holes, or "wells," and fabricated in the bottom plate of a digital microfluidic device, enabling the formation and assaying of hanging drops. Using this digital microfluidic platform, spheroids of mouse mesenchymal stem cells were formed and maintained in situ for 72 h, exhibiting good viability (>90%) and size uniformity (% coefficient of variation <10% intraexperiment, <20% interexperiment). A proof-of-principle drug screen was performed on human colorectal adenocarcinoma spheroids to demonstrate the ability to recapitulate physiologically relevant phenomena such as insulin-induced drug resistance. With automatable and flexible liquid handling, and a wide range of in situ sample preparation and analysis capabilities, the digital microfluidic platform provides a viable tool for automating cell spheroid culture and analysis. © 2014 Society for Laboratory Automation and Screening.

The dynamics of Andromeda's dwarf galaxies and stellar streams

NASA Astrophysics Data System (ADS)

Collins, Michelle L. M.; Rich, R. Michael; Ibata, Rodrigo; Martin, Nicolas; Preston, Janet; PAndAS Collaboration

2017-03-01

As part of the Z-PAndAS Keck II DEIMOS survey of resolved stars in our neighboring galaxy, Andromeda (M31), we have built up a unique data set of measured velocities and chemistries for thousands of stars in the Andromeda stellar halo, particularly probing its rich and complex substructure. In this contribution, we will discuss the structural, dynamical and chemical properties of Andromeda's dwarf spheroidal galaxies, and how there is no observational evidence for a difference in the evolutionary histories of those found on and off M31's vast plane of satellites. We will also discuss a possible extension to the most significant merger event in M31 - the Giant Southern Stream - and how we can use this feature to refine our understanding of M31's mass profile, and its complex evolution.

Morphological and Immunohistochemical Characterization of Canine Osteosarcoma Spheroid Cell Cultures.

PubMed

Gebhard, C; Gabriel, C; Walter, I

2016-06-01

Spheroid cell culture emerges as powerful in vitro tool for experimental tumour research. In this study, we established a scaffold-free three-dimensional spheroid system built from canine osteosarcoma (OS) cells (D17). Spheroids (7, 14 and 19 days of cultivation) and monolayer cultures (2 and 7 days of cultivation) were evaluated and compared on light and electron microscopy. Monolayer and spheroid cultures were tested for vimentin, cytokeratin, alkaline phosphatase, osteocalcin and collagen I by means of immunohistochemistry. The spheroid cell culture exhibited a distinct network of collagen I in particular after 19-day cultivation, whereas in monolayer cultures, collagen I was arranged as a lamellar basal structure. Necrotic centres of large spheroids, as observed in 14- and 19-day cultures, were characterized by significant amounts of osteocalcin. Proliferative activity as determined by Ki-67 immunoreactivity showed an even distribution in two-dimensional cultures. In spheroids, proliferation was predominating in the peripheral areas. Metastasis-associated markers ezrin and S100A4 were shown to be continuously expressed in monolayer and spheroid cultures. We conclude that the scaffold-free spheroid system from canine OS cells has the ability to mimic the architecture of the in vivo tumour, in particular cell-cell and cell-matrix interactions. © 2015 The Authors. Anatomia, Histologia, Embryologia Published by Blackwell Verlag GmbH.

Citral induced apoptosis in MDA-MB-231 spheroid cells.

PubMed

Nigjeh, Siyamak Ebrahimi; Yeap, Swee Keong; Nordin, Norshariza; Kamalideghan, Behnam; Ky, Huynh; Rosli, Rozita

2018-02-13

Breast cancer remains a leading cause of death in women worldwide. Although breast cancer therapies have greatly advanced in recent years, many patients still develop tumour recurrence and metastasis, and eventually succumb to the disease due to chemoresistance. Citral has been reported to show cytotoxic effect on various cancer cell lines. However, the potential of citral to specifically target the drug resistant breast cancer cells has not yet been tested, which was the focus of our current study. The cytotoxic activity of citral was first tested on MDA-MB-231 cells in vitro by MTT assay. Subsequently, spheroids of MDA-MB-231 breast cancer cells were developed and treated with citral at different concentrations. Doxorubicin, cisplatin and tamoxifen were used as positive controls to evaluate the drug resistance phenotype of MDA-MB-231 spheroids. In addition, apoptosis study was performed using AnnexinV/7AAD flowcytometry. Aldefluor assay was also carried out to examine whether citral could inhibit the ALDH-positive population, while the potential mechanism of the effect of citral was carried out by using quantitative real time- PCR followed by western blotting analysis. Citral was able to inhibit the growth of the MDA-MB-231 spheroids when compared to a monolayer culture of MDA-MB-231 cells at a lower IC 50 value. To confirm the inhibition of spheroid self-renewal capacity, the primary spheroids were then cultured to additional passages in the absence of citral. A significant reduction in the number of secondary spheroids were formed, suggesting the reduction of self-renewal capacity of these aldehyde dehydrogenase positive (ALDH + ) drug resistant spheroids. Moreover, the AnnexinV/7AAD results demonstrated that citral induced both early and late apoptotic changes in a dose-dependent manner compared to the vehicle control. Furthermore, citral treated spheroids showed lower cell renewal capacity compared to the vehicle control spheroids in the mammosphere formation

Life is 3D: Boosting Spheroid Function for Tissue Engineering.

PubMed

Laschke, Matthias W; Menger, Michael D

2017-02-01

Spheroids provide a 3D environment with intensive cell-cell contacts. As a result of their excellent regenerative properties and rapid progress in their high-throughput production, spheroids are increasingly suggested as building blocks for tissue engineering. In this review, we focus on innovative biotechnological approaches that increase the quality of spheroids for this specific type of application. These include in particular the fabrication of coculture spheroids, mimicking the complex morphology and physiological tasks of natural tissues. In vitro preconditioning under different culture conditions and incorporation of biomaterials improve the function of spheroids and their directed fusion into macrotissues of desired shapes. The continuous development of these sophisticated approaches may markedly contribute to a broad implementation of spheroid-based tissue engineering in future regenerative medicine. Copyright © 2016 Elsevier Ltd. All rights reserved.

Self-assembly of tissue spheroids on polymeric membranes.

PubMed

Messina, Antonietta; Morelli, Sabrina; Forgacs, Gabor; Barbieri, Giuseppe; Drioli, Enrico; De Bartolo, Loredana

2017-07-01

In this study, multicellular tissue spheroids were fabricated on polymeric membranes in order to accelerate the fusion process and tissue formation. To this purpose, tissue spheroids composed of three different cell types, myoblasts, fibroblasts and neural cells, were formed and cultured on agarose and membranes of polycaprolactone (PCL) and chitosan (CHT). Membranes prepared by a phase-inversion technique display different physicochemical, mechanical and transport properties, which can affect the fusion process. The membranes accelerated the fusion process of a pair of spheroids with respect to the inert substrate. In this process, a critical role is played by the membrane properties, especially by their mechanical characteristics and oxygen and carbon dioxide mass transfer. The rate of fusion was quantified and found to be similar for fibroblast, myoblast and neural tissue spheroids on membranes, which completed the fusion within 3 days. These spheroids underwent faster fusion and maturation on PCL membrane than on agarose, the rate of fusion being proportional to the value of oxygen and carbon dioxide permeances and elastic characteristics. Consequently, tissue spheroids on the membranes expressed high biological activity in terms of oxygen uptake, making them more suitable as building blocks in the fabrication of tissues and organs. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Media additives to promote spheroid circularity and compactness in hanging drop platform.

PubMed

Leung, Brendan M; Lesher-Perez, Sasha Cai; Matsuoka, Toshiki; Moraes, Christopher; Takayama, Shuichi

2015-02-01

Three-dimensional spheroid cultures have become increasingly popular as drug screening platforms, especially with the advent of different high throughput spheroid forming technologies. However, comparing drug efficacy across different cell types in spheroid culture can be difficult due to variations in spheroid morphologies and transport characteristics. Improving the reproducibility of compact, circular spheroids contributes to standardizing and increasing the fidelity of the desired gradient profiles in these drug screening three-dimensional tissue cultures. In this study we discuss the role that circularity and compaction has on spheroids, and demonstrate the impact methylcellulose (MethoCel) and collagen additives in the culture media can contribute to more compact and circular spheroid morphology. We demonstrate that improved spheroid formation is not a simple function of increased viscosity of the different macromolecule additives, suggesting that other macromolecular characteristics contribute to improved spheroid formation. Of the various macromolecular additives tested for hanging drop culture, MethoCel provided the most desirable spheroid formation. Additionally, the higher viscosity of MethoCel-containing media improved the ease of imaging of cellular spheroids within hanging drop cultures by reducing motion-induced image blur.

Dark Matter Constraints from Observations of 25 Milky Way Satellite Galaxies with the Fermi Large Area Telescope

NASA Technical Reports Server (NTRS)

Ackermann, M.; Albert, A.; Anderson, B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.;

Biomaterial Substrate-Mediated Multicellular Spheroid Formation and Their Applications in Tissue Engineering.

PubMed

Tseng, Ting-Chen; Wong, Chui-Wei; Hsieh, Fu-Yu; Hsu, Shan-Hui

2017-12-01

Three-dimentional (3D) multicellular aggregates (spheroids), compared to the traditional 2D monolayer cultured cells, are physiologically more similar to the cells in vivo. So far there are various techniques to generate 3D spheroids. Spheroids obtained from different methods have already been applied to regenerative medicine or cancer research. Among the cell spheroids created by different methods, the substrate-derived spheroids and their forming mechanism are unique. This review focuses on the formation of biomaterial substrate-mediated multicellular spheroids and their applications in tissue engineering and tumor models. First, the authors will describe the special chitosan substrate-derived mesenchymal stem cell (MSC) spheroids and their greater regenerative capacities in various tissues. Second, the authors will describe tumor spheroids derived on chitosan and hyaluronan substrates, which serve as a simple in vitro platform to study 3D tumor models or to perform cancer drug screening. Finally, the authors will mention the self-assembly process for substrate-derived multiple cell spheroids (co-spheroids), which may recapitulate the heterotypic cell-cell interaction for co-cultured cells or crosstalk between different types of cells. These unique multicellular mono-spheroids or co-spheroids represent a category of 3D cell culture with advantages of biomimetic cell-cell interaction, better functionalities, and imaging possibilities. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Delivery of Human Adipose Stem Cells Spheroids into Lockyballs.

PubMed

Silva, Karina R; Rezende, Rodrigo A; Pereira, Frederico D A S; Gruber, Peter; Stuart, Mellannie P; Ovsianikov, Aleksandr; Brakke, Ken; Kasyanov, Vladimir; da Silva, Jorge V L; Granjeiro, José M; Baptista, Leandra S; Mironov, Vladimir

2016-01-01

Adipose stem cells (ASCs) spheroids show enhanced regenerative effects compared to single cells. Also, spheroids have been recently introduced as building blocks in directed self-assembly strategy. Recent efforts aim to improve long-term cell retention and integration by the use of microencapsulation delivery systems that can rapidly integrate in the implantation site. Interlockable solid synthetic microscaffolds, so called lockyballs, were recently designed with hooks and loops to enhance cell retention and integration at the implantation site as well as to support spheroids aggregation after transplantation. Here we present an efficient methodology for human ASCs spheroids biofabrication and lockyballs cellularization using micro-molded non-adhesive agarose hydrogel. Lockyballs were produced using two-photon polymerization with an estimated mechanical strength. The Young's modulus was calculated at level 0.1362 +/-0.009 MPa. Interlocking in vitro test demonstrates high level of loading induced interlockability of fabricated lockyballs. Diameter measurements and elongation coefficient calculation revealed that human ASCs spheroids biofabricated in resections of micro-molded non-adhesive hydrogel had a more regular size distribution and shape than spheroids biofabricated in hanging drops. Cellularization of lockyballs using human ASCs spheroids did not alter the level of cells viability (p › 0,999) and gene fold expression for SOX-9 and RUNX2 (p › 0,195). The biofabrication of ASCs spheroids into lockyballs represents an innovative strategy in regenerative medicine, which combines solid scaffold-based and directed self-assembly approaches, fostering opportunities for rapid in situ biofabrication of 3D building-blocks.

A MegaCam Survey of Outer Halo Satellites. VI. The Spatially Resolved Star-formation History of the Carina Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Santana, Felipe A.; Muñoz, Ricardo R.; de Boer, T. J. L.; Simon, Joshua D.; Geha, Marla; Côté, Patrick; Guzmán, Andrés E.; Stetson, Peter; Djorgovski, S. G.

2016-10-01

We present the spatially resolved star-formation history (SFH) of the Carina dwarf spheroidal galaxy, obtained from deep, wide-field g and r imaging and a metallicity distribution from the literature. Our photometry covers ˜2 deg2, reaching up to ˜10 times the half-light radius of Carina with a completeness higher than 50% at g ˜ 24.5, more than one magnitude fainter than the oldest turnoff. This is the first time a combination of depth and coverage of this quality has been used to derive the SFH of Carina, enabling us to trace its different populations with unprecedented accuracy. We find that Carina’s SFH consists of two episodes well separated by a star-formation temporal gap. These episodes occurred at old (\\gt 10 Gyr) and intermediate (2-8 Gyr) ages. Our measurements show that the old episode comprises the majority of the population, accounting for 54 ± 5% of the stellar mass within 1.3 times the King tidal radius, while the total stellar mass derived for Carina is 1.60+/- 0.09× {10}6 {M}⊙ , and the stellar mass-to-light ratio is 1.8 ± 0.2. The SFH derived is consistent with no recent star formation, which hints that the observed blue plume is due to blue stragglers. We conclude that the SFH of Carina evolved independently of the tidal field of the Milky Way, since the frequency and duration of its star-formation events do not correlate with its orbital parameters. This result is supported by the age-metallicity relation observed in Carina and the gradients calculated indicating that outer regions are older and more metal-poor. Based on observations obtained with the MegaCam imager on the Magellan II-Clay telescope at Las Campanas Observatory in the Atacama Region, Chile. This telescope is operated by a consortium consisting of the Carnegie Institution of Washington, Harvard University, MIT, the University of Michigan, and the University of Arizona.

Coulomb energy of uniformly charged spheroidal shell systems.

PubMed

Jadhao, Vikram; Yao, Zhenwei; Thomas, Creighton K; de la Cruz, Monica Olvera

2015-03-01

We provide exact expressions for the electrostatic energy of uniformly charged prolate and oblate spheroidal shells. We find that uniformly charged prolate spheroids of eccentricity greater than 0.9 have lower Coulomb energy than a sphere of the same area. For the volume-constrained case, we find that a sphere has the highest Coulomb energy among all spheroidal shells. Further, we derive the change in the Coulomb energy of a uniformly charged shell due to small, area-conserving perturbations on the spherical shape. Our perturbation calculations show that buckling-type deformations on a sphere can lower the Coulomb energy. Finally, we consider the possibility of counterion condensation on the spheroidal shell surface. We employ a Manning-Oosawa two-state model approximation to evaluate the renormalized charge and analyze the behavior of the equilibrium free energy as a function of the shell's aspect ratio for both area-constrained and volume-constrained cases. Counterion condensation is seen to favor the formation of spheroidal structures over a sphere of equal area for high values of shell volume fractions.

Star Formation in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly

NASA Astrophysics Data System (ADS)

Stierwalt, Sabrina; Johnson, K. E.; Kallivayalil, N.; Patton, D. R.; Putman, M. E.; Besla, G.; Geha, M. C.

2014-01-01

We present early results from the first systematic study a sample of isolated interacting dwarf pairs and the mechanisms governing their star formation. Low mass dwarf galaxies are ubiquitous in the local universe, yet the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) are currently unconstrained. Studies of Local Group dwarfs credit stochastic internal processes for their complicated star formation histories, but a few intriguing examples suggest interactions among dwarfs may produce enhanced star formation. We combine archival UV imaging from GALEX with deep optical broad- and narrow-band (Halpha) imaging taken with the pre- One Degree Imager (pODI) on the WIYN 3.5-m telescope and with the 2.3-m Bok telescope at Steward Observatory to confirm the presence of stellar bridges and tidal tails and to determine whether dwarf-dwarf interactions alone can trigger significant levels of star formation. We investigate star formation rates and global galaxy colors as a function of dwarf pair separation (i.e. the dwarf merger sequence) and dwarf-dwarf mass ratio. This project is a precursor to an ongoing effort to obtain high spatial resolution HI imaging to assess the importance of sequential triggering caused by dwarf-dwarf interactions and the subsequent affect on the more massive hosts that later accrete the low mass systems.

Robotic printing and drug testing of 384-well tumor spheroids.

PubMed

Ham, Stephanie L; Thakuri, Pradip S; Tavana, Hossein

2015-08-01

A major impediment to anti-cancer drug development is the lack of a reliable and inexpensive tumor model to test the efficacy of candidate compounds. This need has emerged due to the insufficiency of widely-used monolayer cultures to predict drug efficacy in vivo. Spheroids, 3D compact clusters of cancer cells, mimic important characteristics of tumors and provide a tissue analog for drug testing. Here we present a novel spheroid formation microtechnology that is simple to use and allows high throughput drug screening in 384-microwell plates. This approach is based on a polymeric aqueous two-phase system. The denser aqueous phase is mixed with cancer cells at a desired density. Using a robotic liquid handler, a drop of this cell suspension is dispensed into each well of a 384-microwell plate containing the second, immersion aqueous phase. Cancer cells remain contained in the drop, which rests on the well bottom, and form a spheroid during incubation. The use of liquid handling robotics ensures precise dispensing of a single drop, resulting in a single spheroid per well and homogenously sized spheroids within each plate. We confirmed the consistency of production of spheroids and demonstrated their biological relevance to tumors. A proof of concept study with spheroids of triple negative breast cancer cells treated with a standard chemotherapeutic compound, doxorubicin, showed the potential of this method for drug testing. This spheroid culture microtechnology presents key advantages over existing methods such as the ease of drug and viability reagent addition, ability to analyze spheroids without transferring them to a new plate, and the elimination of the need for specialized plates or devices to form spheroids. Incorporating this technology in anti-cancer drug development pipeline will help examine the efficacy of drug candidates more effectively and expedite discovery of novel drugs.

Complexity on Small Scales. III. Iron and α Element Abundances in the Carina Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Koch, Andreas; Grebel, Eva K.; Gilmore, Gerard F.; Wyse, Rosemary F. G.; Kleyna, Jan T.; Harbeck, Daniel R.; Wilkinson, Mark I.; Wyn Evans, N.

2008-04-01

We have obtained high-resolution spectroscopy of ten red giants in the Carina dwarf spheroidal (dSph) galaxy with the ultraviolet and visual echelle spectrograph at the European Southern Observatory Very Large Telescope in order to study the detailed chemical evolution of this Galactic satellite. Here we present the abundances of O, Na, Mg, Si, Ca, Ti, and Fe. By comparison of the derived iron abundances [Fe/H] with metallicities based on the well-established calcium triplet (CaT) calibration, [Fe/H]CaT, we show that the empirical CaT technique yields good agreement with the high-resolution data for [Fe/H] gsim 2 dex, but tends to deviate from these data at lower metallicities. With [Fe/H] ~ 1.7 dex the mean iron abundance of our targets is fully consistent with the peak metallicity of Carina as derived from medium-resolution spectroscopy and previous photometric studies, all calibrated onto iron via Galactic globular cluster scales. We identify two metal-poor stars with iron abundances of 2.72 and 2.50 dex. These stars are found to have enhanced [α/Fe] ratios similar to the elemental ratios of stars in the Milky Way halo. In this context, it is conceivable that the moderately metal-poor halo stars may originate from an early dSph accretion event. The bulk of the Carina red giants exhibit a depletion in the [α/Fe] abundance ratios with respect to the Galactic halo at a given metallicity. One of our targets with a moderately low [Fe/H] of 1.5 dex is considerably depleted in almost all of the α-elements by ~0.5 dex compared to the solar values. Such low values of the ratio of α-elements to iron can be produced by stochastical fluctuations in terms of an incomplete mixing of single type Ia and type II supernova (SN) events into the interstellar medium. Moreover, the system's slow star-formation (SF) rate grants sufficient time for SNe I to occur. Our derived chemical element ratios are consistent with the episodic and extended SF in Carina previously derived from

A DEEP STUDY OF THE DWARF SATELLITES ANDROMEDA XXVIII AND ANDROMEDA XXIX

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

Slater, Colin T.; Bell, Eric F.; Martin, Nicolas F.

We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomposing the horizontal branch into blue (metal-poor, assumed to be older) and red (relatively more metal-rich, assumed to be younger) populations shows that the metal-rich are alsomore » more spatially concentrated in the center of the galaxy. We use spectroscopic measurements of the calcium triplet, combined with the improved precision of the Gemini photometry, to measure the metallicity of the galaxies, confirming the metallicity spread and showing that they both lie on the luminosity–metallicity relation for dwarf satellites. Taken together, the galaxies exhibit largely typical properties for dSphs despite their significant distances from M31. These dwarfs thus place particularly significant constraints on models of dSph formation involving environmental processes such as tidal or ram pressure stripping. Such models must be able to completely transform the two galaxies into dSphs in no more than two pericentric passages around M31, while maintaining a significant stellar population gradient. Reproducing these features is a prime requirement for models of dSph formation to demonstrate not just the plausibility of environmental transformation but the capability of accurately recreating real dSphs.« less

Comparative analysis of tumor spheroid generation techniques for differential in vitro drug toxicity

PubMed Central

Raghavan, Shreya; Rowley, Katelyn R.; Mehta, Geeta

2016-01-01

Multicellular tumor spheroids are powerful in vitro models to perform preclinical chemosensitivity assays. We compare different methodologies to generate tumor spheroids in terms of resultant spheroid morphology, cellular arrangement and chemosensitivity. We used two cancer cell lines (MCF7 and OVCAR8) to generate spheroids using i) hanging drop array plates; ii) liquid overlay on ultra-low attachment plates; iii) liquid overlay on ultra-low attachment plates with rotating mixing (nutator plates). Analysis of spheroid morphometry indicated that cellular compaction was increased in spheroids generated on nutator and hanging drop array plates. Collagen staining also indicated higher compaction and remodeling in tumor spheroids on nutator and hanging drop arrays compared to conventional liquid overlay. Consequently, spheroids generated on nutator or hanging drop plates had increased chemoresistance to cisplatin treatment (20-60% viability) compared to spheroids on ultra low attachment plates (10-20% viability). Lastly, we used a mathematical model to demonstrate minimal changes in oxygen and cisplatin diffusion within experimentally generated spheroids. Our results demonstrate that in vitro methods of tumor spheroid generation result in varied cellular arrangement and chemosensitivity. PMID:26918944

High-throughput image analysis of tumor spheroids: a user-friendly software application to measure the size of spheroids automatically and accurately.

PubMed

Chen, Wenjin; Wong, Chung; Vosburgh, Evan; Levine, Arnold J; Foran, David J; Xu, Eugenia Y

2014-07-08

The increasing number of applications of three-dimensional (3D) tumor spheroids as an in vitro model for drug discovery requires their adaptation to large-scale screening formats in every step of a drug screen, including large-scale image analysis. Currently there is no ready-to-use and free image analysis software to meet this large-scale format. Most existing methods involve manually drawing the length and width of the imaged 3D spheroids, which is a tedious and time-consuming process. This study presents a high-throughput image analysis software application - SpheroidSizer, which measures the major and minor axial length of the imaged 3D tumor spheroids automatically and accurately; calculates the volume of each individual 3D tumor spheroid; then outputs the results in two different forms in spreadsheets for easy manipulations in the subsequent data analysis. The main advantage of this software is its powerful image analysis application that is adapted for large numbers of images. It provides high-throughput computation and quality-control workflow. The estimated time to process 1,000 images is about 15 min on a minimally configured laptop, or around 1 min on a multi-core performance workstation. The graphical user interface (GUI) is also designed for easy quality control, and users can manually override the computer results. The key method used in this software is adapted from the active contour algorithm, also known as Snakes, which is especially suitable for images with uneven illumination and noisy background that often plagues automated imaging processing in high-throughput screens. The complimentary "Manual Initialize" and "Hand Draw" tools provide the flexibility to SpheroidSizer in dealing with various types of spheroids and diverse quality images. This high-throughput image analysis software remarkably reduces labor and speeds up the analysis process. Implementing this software is beneficial for 3D tumor spheroids to become a routine in vitro model

Coulomb explosion of uniformly charged spheroids

NASA Astrophysics Data System (ADS)

Grech, M.; Nuter, R.; Mikaberidze, A.; di Cintio, P.; Gremillet, L.; Lefebvre, E.; Saalmann, U.; Rost, J. M.; Skupin, S.

2011-11-01

A simple, semianalytical model is proposed for nonrelativistic Coulomb explosion of a uniformly charged spheroid. This model allows us to derive the time-dependent particle energy distributions. Simple expressions are also given for the characteristic explosion time and maximum particle energies in the limits of extreme prolate and oblate spheroids as well as for the sphere. Results of particle simulations are found to be in remarkably good agreement with the model.

Fusion of uniluminal vascular spheroids: a model for assembly of blood vessels

PubMed Central

Fleming, Paul A.; Argraves, W. Scott; Gentile, Carmine; Neagu, Adrian; Forgacs, Gabor; Drake, Christopher J.

2010-01-01

Here, we evaluated the self-assembly properties of uniluminal vascular spheroids having outer layers of vascular smooth muscle cells and a contiguous inner layer of endothelial cells lining a central lumen. We showed that while pairs of uniluminal vascular spheroids suspended in culture medium fused to form a larger diameter spheroidal structure, spheroids in collagen hydrogels formed elongated structures. These findings highlight the potential use of uniluminal vascular spheroids as modules to engineer blood vessels. We also demonstrate that uniluminal vascular spheroid fusion conforms to models describing the coalescence of liquid drops. Furthermore, the fusion of uniluminal vascular spheroids in vitro closely resembled the in vivo process by which the descending aorta forms from the fusion of the paired dorsal aortae during embryonic development. Together, the findings indicate that tissue liquidity underlies uniluminal vascular spheroid fusion and that in vivo anastomosis of blood vessels may involve a similar mechanism. PMID:19918756

TASI: A software tool for spatial-temporal quantification of tumor spheroid dynamics.

PubMed

Hou, Yue; Konen, Jessica; Brat, Daniel J; Marcus, Adam I; Cooper, Lee A D

2018-05-08

Spheroid cultures derived from explanted cancer specimens are an increasingly utilized resource for studying complex biological processes like tumor cell invasion and metastasis, representing an important bridge between the simplicity and practicality of 2-dimensional monolayer cultures and the complexity and realism of in vivo animal models. Temporal imaging of spheroids can capture the dynamics of cell behaviors and microenvironments, and when combined with quantitative image analysis methods, enables deep interrogation of biological mechanisms. This paper presents a comprehensive open-source software framework for Temporal Analysis of Spheroid Imaging (TASI) that allows investigators to objectively characterize spheroid growth and invasion dynamics. TASI performs spatiotemporal segmentation of spheroid cultures, extraction of features describing spheroid morpho-phenotypes, mathematical modeling of spheroid dynamics, and statistical comparisons of experimental conditions. We demonstrate the utility of this tool in an analysis of non-small cell lung cancer spheroids that exhibit variability in metastatic and proliferative behaviors.

A remarkable oxygen-rich asymptotic giant branch variable in the Sagittarius Dwarf Irregular Galaxy

NASA Astrophysics Data System (ADS)

Whitelock, Patricia A.; Menzies, John W.; Feast, Michael W.; Marigo, Paola

2018-01-01

We report and discuss JHKS photometry for Sgr dIG, a very metal-deficient galaxy in the Local Group, obtained over 3.5 years with the Infrared Survey Facility in South Africa. Three large amplitude asymptotic giant branch variables are identified. One is an oxygen-rich star that has a pulsation period of 950 d, which was until recently undergoing hot bottom burning, with Mbol ∼ -6.7. It is surprising to find a variable of this sort in Sgr dIG, given their rarity in other dwarf irregulars. Despite its long period the star is relatively blue and is fainter, at all wavelengths shorter than 4.5 μm, than anticipated from period-luminosity relations that describe hot bottom burning stars. A comparison with models suggests it had a main-sequence mass Mi ∼ 5 M⊙ and that it is now near the end of its asymptotic giant branch evolution. The other two periodic variables are carbon stars with periods of 670 and 503 d (Mbol ∼ -5.7 and -5.3). They are very similar to other such stars found on the asymptotic giant branch of metal-deficient Local Group galaxies and a comparison with models suggests Mi ∼ 3 M⊙. We compare the number of asymptotic giant branch variables in Sgr dIG to those in NGC 6822 and IC 1613, and suggest that the differences may be due to the high specific star formation rate and low metallicity of Sgr dIG.

Viscoelastic modeling of the fusion of multicellular tumor spheroids in growth phase.

PubMed

Dechristé, Guillaume; Fehrenbach, Jérôme; Griseti, Elena; Lobjois, Valérie; Poignard, Clair

2018-06-08

Since several decades, the experiments have highlighted the analogy of fusing cell aggregates with liquid droplets. The physical macroscopic models have been derived under incompressible assumptions. The aim of this paper is to provide a 3D model of growing spheroids, which is more relevant regarding embryo cell aggregates or tumor cell spheroids. We extend the past approach to a compressible 3D framework in order to account for the tumor spheroid growth. We exhibit the crucial importance of the effective surface tension, and of the inner pressure of the spheroid to describe precisely the fusion. The experimental data were obtained on spheroids of colon carcinoma human cells (HCT116 cell line). After 3 or 6 days of culture, two identical spheroids were transferred in one well and their fusion was monitored by live videomicroscopy acquisition each 2 h during 72 h. From these images the neck radius and the diameter of the assembly of the fusing spheroids are extracted. The numerical model is fitted with the experiments. It is worth noting that the time evolution of both neck radius and spheroid diameter are quantitatively obtained. The interesting feature lies in the fact that such measurements characterise the macroscopic rheological properties of the tumor spheroids. The experimental determination of the kinetics of neck radius and overall diameter during spheroids fusion characterises the rheological properties of the spheroids. The consistency of the model is shown by fitting the model with two different experiments, enhancing the importance of both surface tension and cell proliferation. The paper sheds new light on the macroscopic rheological properties of tumor spheroids. It emphasizes the role of the surface tension and the inner pressure in the fusion of growing spheroid. Under geometrical assumptions, the model reduces to a 2-parameter differential equation fit with experimental measurements. The 3-D partial differential system makes it possible to study

The remnant of a merger between two dwarf galaxies in Andromeda II.

PubMed

Amorisco, N C; Evans, N W; van de Ven, G

2014-03-20

Driven by gravity, massive structures like galaxies and clusters of galaxies are believed to grow continuously through hierarchical merging and accretion of smaller systems. Observational evidence of accretion events is provided by the coherent stellar streams crossing the outer haloes of massive galaxies, such as the Milky Way or Andromeda. At similar mass scales, around 10(11) solar masses in stars, further evidence of merging activity is also ample. Mergers of lower-mass galaxies are expected within the hierarchical process of galaxy formation, but have hitherto not been seen for galaxies with less than about 10(9) solar masses in stars. Here we report the kinematic detection of a stellar stream in one of the satellite galaxies of Andromeda, the dwarf spheroidal Andromeda II, which has a mass of only 10(7) solar masses in stars. The properties of the stream show that we are observing the remnant of a merger between two dwarf galaxies. This had a drastic influence on the dynamics of the remnant, which is now rotating around its projected major axis. The stellar stream in Andromeda II illustrates the scale-free character of the formation of galaxies, down to the lowest galactic mass scales.

High Throughput, Polymeric Aqueous Two-Phase Printing of Tumor Spheroids

PubMed Central

Atefi, Ehsan; Lemmo, Stephanie; Fyffe, Darcy; Luker, Gary D.; Tavana, Hossein

2014-01-01

This paper presents a new 3D culture microtechnology for high throughput production of tumor spheroids and validates its utility for screening anti-cancer drugs. We use two immiscible polymeric aqueous solutions and microprint a submicroliter drop of the “patterning” phase containing cells into a bath of the “immersion” phase. Selecting proper formulations of biphasic systems using a panel of biocompatible polymers results in the formation of a round drop that confines cells to facilitate spontaneous formation of a spheroid without any external stimuli. Adapting this approach to robotic tools enables straightforward generation and maintenance of spheroids of well-defined size in standard microwell plates and biochemical analysis of spheroids in situ, which is not possible with existing techniques for spheroid culture. To enable high throughput screening, we establish a phase diagram to identify minimum cell densities within specific volumes of the patterning drop to result in a single spheroid. Spheroids show normal growth over long-term incubation and dose-dependent decrease in cellular viability when treated with drug compounds, but present significant resistance compared to monolayer cultures. The unprecedented ease of implementing this microtechnology and its robust performance will benefit high throughput studies of drug screening against cancer cells with physiologically-relevant 3D tumor models. PMID:25411577

EXPLAINING THE OBSERVED VELOCITY DISPERSION OF DWARF GALAXIES BY BARYONIC MASS LOSS DURING THE FIRST COLLAPSE

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

Gritschneder, Matthias; Lin, Douglas N. C., E-mail: gritschneder@ucolick.org

2013-03-01

In the widely adopted {Lambda} cold dark matter ({Lambda}CDM) scenario for galaxy formation, dwarf galaxies are the building blocks of larger galaxies. Since they formed at relatively early epochs when the background density was relatively high, they are expected to retain their integrity as satellite galaxies when they merge to form larger entities. Although many dwarf spheroidal galaxies are found in the galactic halo around the Milky Way, their phase-space density (or velocity dispersion) appears to be significantly smaller than that expected for satellite dwarf galaxies in the {Lambda}CDM scenario. In order to account for this discrepancy, we consider themore » possibility that they may have lost a significant fraction of their baryonic matter content during the first infall at the Hubble expansion turnaround. Such mass loss arises naturally due to the feedback by relatively massive stars that formed in their centers briefly before the maximum contraction. Through a series of N-body simulations, we show that the timely loss of a significant fraction of the dSphs initial baryonic matter content can have profound effects on their asymptotic half-mass radius, velocity dispersion, phase-space density, and the mass fraction between residual baryonic and dark matter.« less

Dark matter constraints from observations of 25 Milky Way satellite galaxies with the Fermi Large Area Telescope

DOE PAGES

Ackermann, M.; Albert, A.; Anderson, B.; ...

2014-02-11

The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via γ rays. We report on γ -ray observations of 25 Milky Way dwarf spheroidal satellite galaxies based on 4 years of Fermi Large Area Telescope (LAT) data. None of the dwarf galaxies are significantly detected in γ rays, and we present γ -ray flux upper limits between 500 MeVmore » and 500 GeV. We determine the dark matter content of 18 dwarf spheroidal galaxies from stellar kinematic data and combine LAT observations of 15 dwarf galaxies to constrain the dark matter annihilation cross section. Furthermore, we set some of the tightest constraints to date on the annihilation of dark matter particles with masses between 2 GeV and 10 TeV into prototypical standard model channels. We also find these results to be robust against systematic uncertainties in the LAT instrument performance, diffuse γ -ray background modeling, and assumed dark matter density profile.« less

Development of lacrimal gland spheroids for lacrimal gland tissue regeneration.

PubMed

Massie, Isobel; Spaniol, Kristina; Barbian, Andreas; Geerling, Gerd; Metzger, Marco; Schrader, Stefan

2018-04-01

Severe dry eye syndrome resulting from lacrimal gland (LG) dysfunction can cause blindness, yet treatments remain palliative. In vitro reconstruction of LG tissue could provide a curative treatment. We aimed to combine epithelial cells with endothelial cells and mesenchymal stem cells (MSCs) to form a 3D functional unit. Epithelial cells and MSCs were isolated from porcine LG; endothelial cells were isolated from human foreskin. MSCs were characterised (flow cytometry and differentiation potential assays). All 3 cell types were combined on Matrigel and spheroid formation observed. Spheroids were characterised [immunohistochemistry (IHC) and transmission electron microscopy] and function assessed (β-hexosaminidase assay). Spheroids were transferred to decellularised jejunum (SIS-Muc) in dynamic cultures for 1 week before further characterisation. MSCs did not express CD31 but expressed CD44 and CD105 and differentiated towards osteogenic and adipogenic lineages. Spheroids formed on Matrigel within 18 hr, contracting to ~10% of the well area (p < .005). IHC revealed presence of all 3 cells within spheroids. Transmission electron microscopy revealed cell-cell contacts and polarisation at the apical surface. In static cultures, function was increased in spheroids cf. monolayer controls (p < .05) but over 72 hr, spheroid function (p < .05), viability (p < .05), and proliferation decreased, whilst apoptosis increased. On SIS-Muc under dynamic culture, however, spheroids continued to proliferate to repopulate SIS-Muc. IHC revealed LG epithelial cells coexpressing pan-cytokeratin and lysozyme, as well as endothelial cells and MSCs and cells remained capable of responding to carbachol (p < .05). These spheroids could form the basis of a regenerative medicine treatment approach for dry eye syndrome. In vivo studies are required to evaluate this further. Copyright © 2017 John Wiley & Sons, Ltd.

Early gas stripping as the origin of the darkest galaxies in the Universe.

PubMed

Mayer, L; Kazantzidis, S; Mastropietro, C; Wadsley, J

2007-02-15

The known galaxies most dominated by dark matter (Draco, Ursa Minor and Andromeda IX) are satellites of the Milky Way and the Andromeda galaxies. They are members of a class of faint galaxies, devoid of gas, known as dwarf spheroidals, and have by far the highest ratio of dark to luminous matter. None of the models proposed to unravel their origin can simultaneously explain their exceptional dark matter content and their proximity to a much larger galaxy. Here we report simulations showing that the progenitors of these galaxies were probably gas-dominated dwarf galaxies that became satellites of a larger galaxy earlier than the other dwarf spheroidals. We find that a combination of tidal shocks and ram pressure swept away the entire gas content of such progenitors about ten billion years ago because heating by the cosmic ultraviolet background kept the gas loosely bound: a tiny stellar component embedded in a relatively massive dark halo survived until today. All luminous galaxies should be surrounded by a few extremely dark-matter-dominated dwarf spheroidal satellites, and these should have the shortest orbital periods among dwarf spheroidals because they were accreted early.

Magnetic Flattening of Stem-Cell Spheroids Indicates a Size-Dependent Elastocapillary Transition

NASA Astrophysics Data System (ADS)

Mazuel, Francois; Reffay, Myriam; Du, Vicard; Bacri, Jean-Claude; Rieu, Jean-Paul; Wilhelm, Claire

2015-03-01

Cellular aggregates (spheroids) are widely used in biophysics and tissue engineering as model systems for biological tissues. In this Letter we propose novel methods for molding stem-cell spheroids, deforming them, and measuring their interfacial and elastic properties with a single method based on cell tagging with magnetic nanoparticles and application of a magnetic field gradient. Magnetic molding yields spheroids of unprecedented sizes (up to a few mm in diameter) and preserves tissue integrity. On subjecting these spheroids to magnetic flattening (over 150 g ), we observed a size-dependent elastocapillary transition with two modes of deformation: liquid-drop-like behavior for small spheroids, and elastic-sphere-like behavior for larger spheroids, followed by relaxation to a liquidlike drop.

Infrared Colors of Dwarf-Dwarf Galaxy Interactions

NASA Astrophysics Data System (ADS)

Liss, Sandra; Stierwalt, Sabrina; Johnson, Kelsey; Patton, Dave; Kallivayalil, Nitya

2015-10-01

We request Spitzer Warm Mission IRAC Channel 1 & 2 imaging for a sample of 60 isolated dwarf galaxy pairs as a key component of a larger, multi-wavelength effort to understand the role low-mass mergers play in galaxy evolution. A systematic study of dwarf-dwarf mergers has never been done, and we wish to characterize the impact such interactions have on fueling star formation in the nearby universe. The Spitzer imaging proposed here will allow us to determine the extent to which the 3.6 and 4.5 mum bands are dominated by stellar light and investigate a) the extent to which interacting pairs show IR excess and b) whether the excess is related to the pair separation. Second, we will use this IR photometry to constrain the processes contributing to the observed color excess and scatter in each system. We will take advantage of the wealth of observations available in the Spitzer Heritage Archive for 'normal' non-interacting dwarfs by comparing the stellar populations of those dwarfs with the likely interacting dwarfs in our sample. Ultimately, we can combine the Spitzer imaging proposed here with our current, ongoing efforts to obtain groundbased optical photometry to model the star formation histories of these dwarfs and to help constrain the timescales and impact dwarf-dwarf mergers have on fueling star formation. The sensitivity and resolution offered by Spitzer are necessary to determine the dust properties of these interacting systems, and how these properties vary as a function of pair separation, mass ratio, and gas fraction.

Convection in Slab and Spheroidal Geometries

NASA Technical Reports Server (NTRS)

Porter, David H.; Woodward, Paul R.; Jacobs, Michael L.

2000-01-01

Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.

NuSTAR Detection of High-Energy X-Ray Emission and Rapid Variability from Sagittarius A(star) Flares

NASA Technical Reports Server (NTRS)

Barriere, Nicolas M.; Tomsick, John A.; Baganoff, Frederick K.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Dexter, Jason; Grefenstette, Brian; Hailey, Charles J.; Zhang, William W.

2014-01-01

Sagittarius A(star) harbors the supermassive black hole that lies at the dynamical center of our Galaxy. Sagittarius A(star) spends most of its time in a low luminosity emission state but flares frequently in the infrared and X-ray, increasing up to a few hundred fold in brightness for up to a few hours at a time. The physical processes giving rise to the X-ray flares are uncertain. Here we report the detection with the NuSTAR observatory in Summer and Fall 2012 of four low to medium amplitude X-ray flares to energies up to 79 keV. For the first time, we clearly see that the power-law spectrum of Sagittarius A(star) X-ray flares extends to high energy, with no evidence for a cut off. Although the photon index of the absorbed power-law fits are in agreement with past observations, we find a difference between the photon index of two of the flares (significant at the 95% confidence level). The spectra of the two brightest flares (approx. 55 times quiescence in the 2- 10 keV band) are compared to simple physical models in an attempt to identify the main X-ray emission mechanism, but the data do not allow us to significantly discriminate between them. However, we confirm the previous finding that the parameters obtained with synchrotron models are, for the X-ray emission, physically more reasonable than those obtained with inverse-Compton models. One flare exhibits large and rapid (less than 100 s) variability, which, considering the total energy radiated, constrains the location of the flaring region to be within approx. 10 Schwarzschild radii of the black hole.

DISCOVERY OF SUPER-Li-RICH RED GIANTS IN DWARF SPHEROIDAL GALAXIES

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

Kirby, Evan N.; Fu, Xiaoting; Deng, Licai

2012-06-10

Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of kelvin, hot enough for the {sup 7}Li(p, {alpha}){sup 4}He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants-14 of which are new discoveries-among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] {approx}< -0.7) Li-richmore » red giants, and it includes the most-metal-poor Li-enhanced star known ([Fe/H] = -2.82, A(Li){sub NLTE} = 3.15). Because most of the stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and it seems rare only because it is brief.« less

Correlation between grade of pearlite spheroidization and laser induced spectra

NASA Astrophysics Data System (ADS)

Yao, Shunchun; Dong, Meirong; Lu, Jidong; Li, Jun; Dong, Xuan

2013-12-01

Laser induced breakdown spectroscopy (LIBS) which is used traditionally as a spectrochemical analytical technique was employed to analyze the grade of pearlite spheroidization. Three 12Cr1MoV steel specimens with different grades of pearlite spheroidization were ablated to produce plasma by pulse laser at 266 nm. In order to determine the optimal temporal condition and plasma parameters for correlating the grade of pearlite spheroidization and laser induced spectra, a set of spectra at different delays were analyzed by the principal component analysis method. Then, the relationship between plasma temperature, intensity ratios of ionic to atomic lines and grade of pearlite spheroidization was studied. The analysis results show that the laser induced spectra of different grades of pearlite spheroidization can be readily identifiable by principal component analysis in the range of 271.941-289.672 nm with 1000 ns delay time. It is also found that a good agreement exists between the Fe ionic to atomic line ratios and the tensile strength, whereas there is no obvious difference in the plasma temperature. Therefore, LIBS may be applied not only as a spectrochemical analytical technique but also as a new way to estimate the grade of pearlite spheroidization.

Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

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

Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea, E-mail: alis@ucolick.org

Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with amore » lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.« less

Spheroidal models of the exterior gravitational field of Asteroids Bennu and Castalia

NASA Astrophysics Data System (ADS)

Sebera, Josef; Bezděk, Aleš; Pešek, Ivan; Henych, Tomáš

2016-07-01

Gravitational field of small bodies can be modeled e.g. with mascons, a polyhedral model or in terms of harmonic functions. If the shape of a body is close to the spheroid, it is advantageous to employ the spheroidal basis functions for expressing the gravitational field. Spheroidal harmonic models, similarly to the spherical ones, may be used in navigation and geophysical tasks. We focus on modeling the exterior gravitational field of oblate-like Asteroid (101955) Bennu and prolate-like Asteroid (4769) Castalia with spheroidal harmonics. Using the Gauss-Legendre quadrature and the spheroidal basis functions, we converted the gravitational potential of a particular polyhedral model of a constant density into the spheroidal harmonics. The results consist of (i) spheroidal harmonic coefficients of the exterior gravitational field for the Asteroids Bennu and Castalia, (ii) spherical harmonic coefficients for Bennu, and (iii) the first and second-order Cartesian derivatives in the local spheroidal South-East-Up frame for both bodies. The spheroidal harmonics offer biaxial flexibility (compared with spherical harmonics) and low computational costs that allow high-degree expansions (compared with ellipsoidal harmonics). The obtained spheroidal models for Bennu and Castalia represent the exterior gravitational field valid on and outside the Brillouin spheroid but they can be used even under this surface. For Bennu, 5 m above the surface the agreement with point-wise integration was 1% or less, while it was about 10% for Castalia due to its more irregular shape. As the shape models may produce very high frequencies, it was crucial to use higher maximum degree to reduce the aliasing. We have used the maximum degree 360 to achieve 9-10 common digits (in RMS) when reconstructing the input (the gravitational potential) from the spheroidal coefficients. The physically meaningful maximum degree may be lower (≪ 360) but its particular value depends on the distance and/or on the

The microenvironment induces collective migration in SDHB-silenced mouse pheochromocytoma spheroids.

PubMed

D'Antongiovanni, Vanessa; Martinelli, Serena; Richter, Susan; Canu, Letizia; Guasti, Daniele; Mello, Tommaso; Romagnoli, Paolo; Pacak, Karel; Eisenhofer, Graeme; Mannelli, Massimo; Rapizzi, Elena

2017-10-01

Pheochromocytomas (Pheos) and paragangliomas (PGLs) are neuroendocrine tumors. Approximately 30-40% of Pheos/PGLs are due to germline mutations in one of the susceptibility genes, including those encoding the succinate dehydrogenase subunits A-D ( SDHA-D ). Up to 2/3 of patients affected by SDHB mutated Pheo/PGL develop metastatic disease with no successful cure at present. Here, for the first time, we evaluated the effects of SDHB silencing in a three dimension (3D) culture using spheroids of a mouse Pheo cell line silenced or not (wild type/wt/control) for the SDHB subunit. We investigated the role of the microenvironment on spheroid growth and migration/invasion by co-culturing SDHB -silenced or wt spheroids with primary cancer-activated fibroblasts (CAFs). When spheroids were co-cultured with fibroblasts, SDHB -silenced cells showed a significant increase in matrigel invasion as demonstrated by the computation of the migratory areas ( P  < 0.001). Moreover, cells detaching from the SDHB -silenced spheroids moved collectively, unlike the cells of wt spheroids that moved individually. Additionally, SDHB- silenced spheroids developed long filamentous formations along which clusters of cells migrated far away from the spheroid, whereas these structures were not present in wt spheroids. We found that lactate, largely secreted by CAFs, plays a specific role in promoting migration only of SDHB -silenced cells. In this study, we demonstrated that SDHB silencing per se increases tumor cell migration/invasion and that microenvironment, as represented by CAFs, plays a pivotal role in enhancing collective migration/invasion in Pheo SDHB -silenced tumor cells, suggesting their role in increasing the tumor metastasizing potential. © 2017 Society for Endocrinology.

An injectable spheroid system with genetic modification for cell transplantation therapy.

PubMed

Uchida, Satoshi; Itaka, Keiji; Nomoto, Takahiro; Endo, Taisuke; Matsumoto, Yu; Ishii, Takehiko; Kataoka, Kazunori

2014-03-01

The new methodology to increase a therapeutic potential of cell transplantation was developed here by the use of three-dimensional spheroids of transplanting cells subsequent to the genetic modification with non-viral DNA vectors, polyplex nanomicelles. Particularly, spheroids in regulated size of 100-μm of primary hepatocytes transfected with luciferase gene were formed on the micropatterned culture plates coated with thermosensitive polymer, and were recovered in the form of injectable liquid suspension simply by cooling the plates. After subcutaneously transplanting these hepatocyte spheroids, efficient transgene expression was observed in host tissue for more than a month, whereas transplantation of a single-cell suspension from a monolayer culture resulted in an only transient expression. The spheroid system contributed to the preservation of innate functions of transplanted hepatocytes in the host tissue, such as albumin expression, thereby possessing high potential for expressing transgene. Intravital observation of transplanted cells showed that those from spheroid cultures had a tendency to localize in the vicinity of blood vessels, making a favorable microenvironment for preserving cell functionality. Furthermore, spheroids transfected with erythropoietin-expressing DNA showed a significantly higher hematopoietic effect than that of cell suspensions from monolayer cultures, demonstrating high potential of this genetically-modified spheroid transplantation system for therapeutic applications. Copyright © 2013 Elsevier Ltd. All rights reserved.

Generating Chondromimetic Mesenchymal Stem Cell Spheroids by Regulating Media Composition and Surface Coating.

PubMed

Sridharan, BanuPriya; Laflin, Amy D; Detamore, Michael S

2018-04-01

Spheroids of mesenchymal stem cells (MSCs) in cartilage tissue engineering have been shown to enhance regenerative potential owing to their 3D structure. In this study, we explored the possibility of priming spheroids under different media to replace the use of inductive surface coatings for chondrogenic differentiation. Rat bone marrow-derived MSCs were organized into cell spheroids by the hanging drop technique and subsequently cultured on hyaluronic acid (HA) coated or non-coated well plates under different cell media conditions. Endpoint analysis included cell viability, DNA and Glycosaminoglycan (GAG) and collagen content, gene expression and immunohistochemistry. For chondrogenic applications, MSC spheroids derived on non-coated surfaces outperformed the spheroids derived from HA-coated surfaces in matrix synthesis and collagen II gene expression. Spheroids on non-coated surfaces gave rise to the highest collagen and GAG when primed with medium containing insulin-like growth factor (IGF) for 1 week during spheroid formation. Spheroids that were grown in chondroinductive raw material-inclusive media such as aggrecan or chondroitin sulfate exhibited the highest Collagen II gene expression in the non-coated surface at 1 week. Media priming by growth factors and raw materials might be a more predictive influencer of chondrogenesis compared to inductive-surfaces. Such tailored bioactivity of the stem cell spheroids in the stage of the spheroid formation may give rise to a platform technology that may eventually produce spheroids capable of chondrogenesis achieved by mere media manipulation, skipping the need for additional culture on a modified surface, that paves the way for cost-effective technologies.

Indirect dark matter searches in the dwarf satellite galaxy Ursa Major II with the MAGIC telescopes

NASA Astrophysics Data System (ADS)

Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Arcaro, C.; Baack, D.; Babić, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Berse, R. Ch.; Berti, A.; Bhattacharyya, W.; Biland, A.; Blanch, O.; Bonnoli, G.; Carosi, R.; Carosi, A.; Ceribella, G.; Chatterjee, A.; Colak, S. M.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Cumani, P.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Delfino, M.; Delgado, J.; Di Pierro, F.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Elsaesser, D.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinović, N.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Ishio, K.; Konno, Y.; Kubo, H.; Kushida, J.; Kuveždić, D.; Lelas, D.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; Maggio, C.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Masuda, S.; Mazin, D.; Mielke, K.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Moreno, V.; Moretti, E.; Nagayoshi, T.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nigro, C.; Nilsson, K.; Ninci, D.; Nishijima, K.; Noda, K.; Nogués, L.; Paiano, S.; Palacio, J.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Pedaletti, G.; Peresano, M.; Persic, M.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Garcia, J. R.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saito, T.; Satalecka, K.; Schweizer, T.; Sitarek, J.; Šnidarić, I.; Sobczynska, D.; Stamerra, A.; Strzys, M.; Surić, T.; Takahashi, M.; Takalo, L.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Teshima, M.; Torres-Albà, N.; Treves, A.; Tsujimoto, S.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.; Ward, J. E.; Will, M.; Zarić, D.

2018-03-01

The dwarf spheroidal galaxy Ursa Major II (UMaII) is believed to be one of the most dark-matter dominated systems among the Milky Way satellites and represents a suitable target for indirect dark matter (DM) searches. The MAGIC telescopes carried out a deep observation campaign on UMaII between 2014 and 2016, collecting almost one hundred hours of good-quality data. This campaign enlarges the pool of DM targets observed at very high energy (E gtrsim 50 GeV) in search for signatures of DM annihilation in the wide mass range between ~100 GeV and ~100 TeV. To this end, the data are analyzed with the full likelihood analysis, a method based on the exploitation of the spectral information of the recorded events for an optimal sensitivity to the explored DM models. We obtain constraints on the annihilation cross-section for different channels that are among the most robust and stringent achieved so far at the TeV mass scale from observations of dwarf satellite galaxies.

Improvement of Mechanical Properties of Spheroidized 1045 Steel by Induction Heat Treatment

NASA Astrophysics Data System (ADS)

Kim, Minwook; Shin, Jung-Ho; Choi, Young; Lee, Seok-Jae

2016-04-01

The effects of induction heat treatment on the formation of carbide particles and mechanical properties of spheroidized 1045 steel were investigated by means of microstructural analysis and tensile testing. The induction spheroidization accelerated the formation of spherical cementite particles and effectively softened the steel. The volume fraction of cementite was found to be a key factor that affected the mechanical properties of spheroidized steels. Further tests showed that sequential spheroidization by induction and furnace heat treatments enhanced elongation within a short spheroidization time, resulting in better mechanical properties. This was due to the higher volume fraction of spherical cementite particles that had less diffusion time for particle coarsening.

Kinematic properties and dark matter fraction of Virgo dwarf early-type galaxies

NASA Astrophysics Data System (ADS)

Toloba, E.; Boselli, A.; Peletier, R.; Gorgas, J.

2015-03-01

What happens to dwarf galaxies as they enter the cluster potential well is one of the main unknowns in studies of galaxy evolution. Several evidence suggests that late-type galaxies enter the cluster and are transformed to dwarf early-type galaxies (dEs). We study the Virgo cluster to understand which mechanisms are involved in this transformation. We find that the dEs in the outer parts of Virgo have rotation curves with shapes and amplitudes similar to late-type galaxies of the same luminosity (Fig. 1). These dEs are rotationally supported, have disky isophotes, and younger ages than those dEs in the center of Virgo, which are pressure supported, often have boxy isophotes and are older (Fig. 1). Ram pressure stripping, thus, explains the properties of the dEs located in the outskirts of Virgo. However, the dEs in the central cluster regions, which have lost their angular momentum, must have suffered a more violent transformation. A combination of ram pressure stripping and harassment is not enough to remove the rotation and the spiral/disky structures of these galaxies. We find that on the the Faber-Jackson and the Fundamental Plane relations dEs deviate from the trends of massive elliptical galaxies towards the position of dark matter dominated systems such as the dwarf spheroidal satellites of the Milky Way and M31. Both, rotationally and pressure supported dEs, however, populate the same region in these diagrams. This indicates that dEs have a non-negligible dark matter fraction within their half light radius.

Equilibrium electrodeformation of a spheroidal vesicle in an ac electric field

NASA Astrophysics Data System (ADS)

Nganguia, H.; Young, Y.-N.

2013-11-01

In this work, we develop a theoretical model to explain the equilibrium spheroidal deformation of a giant unilamellar vesicle (GUV) under an alternating (ac) electric field. Suspended in a leaky dielectric fluid, the vesicle membrane is modeled as a thin capacitive spheroidal shell. The equilibrium vesicle shape results from the balance between mechanical forces from the viscous fluid, the restoring elastic membrane forces, and the externally imposed electric forces. Our spheroidal model predicts a deformation-dependent transmembrane potential, and is able to capture large deformation of a vesicle under an electric field. A detailed comparison against both experiments and small-deformation (quasispherical) theory showed that the spheroidal model gives better agreement with experiments in terms of the dependence on fluid conductivity ratio, permittivity ratio, vesicle size, electric field strength, and frequency. The spheroidal model also allows for an asymptotic analysis on the crossover frequency where the equilibrium vesicle shape crosses over between prolate and oblate shapes. Comparisons show that the spheroidal model gives better agreement with experimental observations.

Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Chiti, Anirudh; Simon, Joshua D.; Frebel, Anna; Thompson, Ian B.; Shectman, Stephen A.; Mateo, Mario; Bailey, John I., III; Crane, Jeffrey D.; Walker, Matthew

2018-04-01

The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ∼ 2000) spectra taken with the Magellan/Michigan Fiber System mounted on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] < ‑3.0) and 21 carbon-enhanced metal-poor (CEMP) star candidates. Eight carbon-enhanced stars are classified with at least 2σ confidence, and five are confirmed as such with follow-up R ∼ 6000 observations using the Magellan Echellette Spectrograph on the Magellan-Baade 6.5 m telescope. We measure a CEMP fraction of 36% for stars below [Fe/H] = ‑3.0, indicating that the prevalence of carbon-enhanced stars in Sculptor is similar to that of the halo (∼43%) after excluding likely CEMP-s and CEMP-r/s stars from our sample. However, we do not detect that any CEMP stars are strongly enhanced in carbon ([C/Fe] > 1.0). The existence of a large number of CEMP stars both in the halo and in Sculptor suggests that some halo CEMP stars may have originated from accreted early analogs of dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

7 Millimeter VLBA Observations of Sagittarius A*

NASA Astrophysics Data System (ADS)

Bower, Geoffrey C.; Backer, Donald C.

1998-04-01

We present 7 mm Very Long Baseline Array observations of the compact nonthermal radio source in the Galactic center, Sagittarius A*. These observations confirm the hypothesis that the image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of an intervening thermal plasma. The measured major axis of Sgr A* is 0.76+/-0.04 mas, consistent with the predicted scattering size of 0.67+/-0.03. We find an axial ratio of 0.73+/-0.10 and a position angle of 77.0d +/- 7.4d. These results are fully consistent with VLBI observations at longer wavelengths and at 3 mm. We find no evidence for any additional compact structure to a limit of 35 mJy. The underlying radio source must be smaller than 4.1 AU for a Galactocentric distance of 8.5 kpc. This result is consistent with the conclusion that the radio emission from Sgr A* results from synchrotron or cyclo-synchrotron radiation of gas in the vicinity of a black hole with a mass near 106 Msolar.

Physiologically Low Oxygen Enhances Biomolecule Production and Stemness of Mesenchymal Stem Cell Spheroids

PubMed Central

Shearier, Emily; Xing, Qi; Qian, Zichen

2016-01-01

Multicellular human mesenchymal stem cell (hMSC) spheroids have been demonstrated to be valuable in a variety of applications, including cartilage regeneration, wound healing, and neoangiogenesis. Physiological relevant low oxygen culture can significantly improve in vitro hMSC expansion by preventing cell differentiation. We hypothesize that hypoxia-cultured hMSC spheroids can better maintain the regenerative properties of hMSCs. In this study, hMSC spheroids were fabricated using hanging drop method and cultured under 2% O2 and 20% O2 for up to 96 h. Spheroid diameter and viability were examined, as well as extracellular matrix (ECM) components and growth factor levels between the two oxygen tensions at different time points. Stemness was measured among the spheroid culture conditions and compared to two-dimensional cell cultures. Spheroid viability and structural integrity were studied using different needle gauges to ensure no damage would occur when implemented in vivo. Spheroid attachment and integration within a tissue substitute were also demonstrated. The results showed that a three-dimensional hMSC spheroid cultured at low oxygen conditions can enhance the production of ECM proteins and growth factors, while maintaining the spheroids' stemness and ability to be injected, attached, and potentially be integrated within a tissue. PMID:26830500

Stellar Abundances for Galactic Archaeology Database. IV. Compilation of stars in dwarf galaxies

NASA Astrophysics Data System (ADS)

Suda, Takuma; Hidaka, Jun; Aoki, Wako; Katsuta, Yutaka; Yamada, Shimako; Fujimoto, Masayuki Y.; Ohtani, Yukari; Masuyama, Miyu; Noda, Kazuhiro; Wada, Kentaro

2017-10-01

We have constructed a database of stars in Local Group galaxies using the extended version of the SAGA (Stellar Abundances for Galactic Archaeology) database that contains stars in 24 dwarf spheroidal galaxies and ultra-faint dwarfs. The new version of the database includes more than 4500 stars in the Milky Way, by removing the previous metallicity criterion of [Fe/H] ≤ -2.5, and more than 6000 stars in the Local Group galaxies. We examined the validity of using a combined data set for elemental abundances. We also checked the consistency between the derived distances to individual stars and those to galaxies as given in the literature. Using the updated database, the characteristics of stars in dwarf galaxies are discussed. Our statistical analyses of α-element abundances show that the change of the slope of the [α/Fe] relative to [Fe/H] (so-called "knee") occurs at [Fe/H] = -1.0 ± 0.1 for the Milky Way. The knee positions for selected galaxies are derived by applying the same method. The star formation history of individual galaxies is explored using the slope of the cumulative metallicity distribution function. Radial gradients along the four directions are inspected in six galaxies where we find no direction-dependence of metallicity gradients along the major and minor axes. The compilation of all the available data shows a lack of CEMP-s population in dwarf galaxies, while there may be some CEMP-no stars at [Fe/H] ≲ -3 even in the very small sample. The inspection of the relationship between Eu and Ba abundances confirms an anomalously Ba-rich population in Fornax, which indicates a pre-enrichment of interstellar gas with r-process elements. We do not find any evidence of anti-correlations in O-Na and Mg-Al abundances, which characterizes the abundance trends in the Galactic globular clusters.

Three dimensional spheroid cell culture for nanoparticle safety testing.

PubMed

Sambale, Franziska; Lavrentieva, Antonina; Stahl, Frank; Blume, Cornelia; Stiesch, Meike; Kasper, Cornelia; Bahnemann, Detlef; Scheper, Thomas

2015-07-10

Nanoparticles are widely employed for many applications and the number of consumer products, incorporating nanotechnology, is constantly increasing. A novel area of nanotechnology is the application in medical implants. The widespread use of nanoparticles leads to their higher prevalence in our environment. This, in turn, raises concerns regarding potential risks to humans. Previous studies have shown possible hazardous effects of some nanoparticles on mammalian cells grown in two-dimensional (2D) cultures. However, 2D in vitro cell cultures display several disadvantages such as changes in cell shape, cell function, cell responses and lack of cell-cell contacts. For this reason, the development of better models for mimicking in vivo conditions is essential. In the present work, we cultivated A549 cells and NIH-3T3 cells in three-dimensional (3D) spheroids and investigated the effects of zinc oxide (ZnO-NP) and titanium dioxide nanoparticles (TiO2-NP). The results were compared to cultivation in 2D monolayer culture. A549 cells in 3D cell culture formed loose aggregates which were more sensitive to the toxicity of ZnO-NP in comparison to cells grown in 2D monolayers. In contrast, NIH-3T3 cells showed a compact 3D spheroid structure and no differences in the sensitivity of the NIH-3T3 cells to ZnO-NP were observed between 2D and 3D cultures. TiO2-NP were non-toxic in 2D cultures but affected cell-cell interaction during 3D spheroid formation of A549 and NIH-3T3 cells. When TiO2-NP were directly added during spheroid formation in the cultures of the two cell lines tested, several smaller spheroids were formed instead of a single spheroid. This effect was not observed if the nanoparticles were added after spheroid formation. In this case, a slight decrease in cell viability was determined only for A549 3D spheroids. The obtained results demonstrate the importance of 3D cell culture studies for nanoparticle safety testing, since some effects cannot be revealed in 2D

THREE NEW ECLIPSING WHITE-DWARF-M-DWARF BINARIES DISCOVERED IN A SEARCH FOR TRANSITING PLANETS AROUND M-DWARFS

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

Law, Nicholas M.; Kraus, Adam L.; Street, Rachel

2012-10-01

We present three new eclipsing white-dwarf/M-dwarf binary systems discovered during a search for transiting planets around M-dwarfs. Unlike most known eclipsing systems of this type, the optical and infrared emission is dominated by the M-dwarf components, and the systems have optical colors and discovery light curves consistent with being Jupiter-radius transiting planets around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part of the Palomar Transient Factory (PTF). We present a graphics processing unit (GPU)-based box-least-squares search for transits that runs approximately 8 Multiplication-Sign faster than similar algorithms implemented on general purpose systems. For the discovered systems, we decomposemore » low-resolution spectra of the systems into white-dwarf and M-dwarf components, and use radial velocity measurements and cooling models to estimate masses and radii for the white dwarfs. The systems are compact, with periods between 0.35 and 0.45 days and semimajor axes of approximately 2 R{sub Sun} (0.01 AU). The M-dwarfs have masses of approximately 0.35 M{sub Sun }, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000 K and have masses of approximately 0.5 M{sub Sun }. We use the Robo-AO laser guide star adaptive optics system to tentatively identify one of the objects as a triple system. We also use high-cadence photometry to put an upper limit on the white-dwarf radius of 0.025 R{sub Sun} (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that 0.08%{sub -0.05%}{sup +0.10%} (90% confidence) of M-dwarfs are in these short-period, post-common-envelope white-dwarf/M-dwarf binaries where the optical light is dominated by the M-dwarf. The lack of detections at shorter periods, despite near-100% detection efficiency for such systems, suggests that binaries including these relatively low-temperature white dwarfs are preferentially found at

Melanoma Spheroid Formation Involves Laminin-Associated Vasculogenic Mimicry

PubMed Central

Larson, Allison R.; Lee, Chung-Wei; Lezcano, Cecilia; Zhan, Qian; Huang, John; Fischer, Andrew H.; Murphy, George F.

2015-01-01

Melanoma is a tumor where virulence is conferred on transition from flat (radial) to three-dimensional (tumorigenic) growth. Virulence of tumorigenic growth is governed by numerous attributes, including presence of self-renewing stem-like cells and related formation of patterned networks associated with the melanoma mitogen, laminin, a phenomenon known as vasculogenic mimicry. Vasculogenic mimicry is posited to contribute to melanoma perfusion and nutrition in vivo; we hypothesized that it may also play a role in stem cell–driven spheroid formation in vitro. Using a model of melanoma in vitro tumorigenesis, laminin-associated networks developed in association with three-dimensional melanoma spheroids. Real-time PCR analysis of laminin subunits showed that spheroids formed from anchorage-independent melanoma cells expressed increased α4 and β1 laminin chains and α4 laminin expression was confirmed by in situ hybridization. Association of laminin networks with melanoma stem cell–associated nestin and vascular endothelial growth factor receptor-1 also was documented. Moreover, knockdown of nestin gene expression impaired laminin expression and network formation within spheroids. Laminin networks were remarkably similar to those observed in melanoma xenografts in mice and to those seen in patient melanomas. These data indicate that vasculogenic mimicry–like laminin networks, in addition to their genesis in vivo, are integral to the extracellular architecture of melanoma spheroids in vitro, where they may serve as stimulatory scaffolds to support three-dimensional growth. PMID:24332013

Proper motion of the Draco dwarf galaxy from Subaru Suprime-Cam data

NASA Astrophysics Data System (ADS)

Casetti-Dinescu, Dana I.; Girard, Terrence M.

2016-09-01

We have measured the absolute proper motion of the Draco dwarf spheroidal galaxy using Subaru Suprime-Cam images taken at three epochs, with time baselines of 4.4 and 7 yr. The magnitude limit of the proper-motion study is I = 25, thus allowing for thousands of background galaxies and Draco stars to be used to perform extensive astrometric tests and to derive the correction to an inertial reference frame. The derived proper motion is (μα, μδ) = (-0.284 ± 0.047, -0.289 ± 0.041) mas yr-1. This motion implies an orbit that takes Draco to a pericentre of ˜20 kpc; a somewhat disruptive orbit suggesting that tides might account for the rising velocity-dispersion profile of Draco seen in line-of-sight velocity studies. The orbit is only marginally consistent with Draco's membership to the vast polar structure of Galactic satellites, in contrast to a recent Hubble Space Telescope proper-motion measurement that finds alignment very likely. Our study is a test case to demonstrate that deep imaging with mosaic cameras of appropriate resolution can be used for high-accuracy, ground-based proper-motion measurement. As a useful by-product of the study, we also identify two faint brown-dwarf candidates in the foreground field.

Constraining the Nature of Dark Matter with the Star-formation History of the Faintest Local Group Dwarf Galaxy Satellites

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

Chau, Alice; Mayer, Lucio; Governato, Fabio

Λ warm dark matter (ΛWDM), realized by collisionless particles of 1–3 keV, has been proposed as an alternative scenario to Λ-Cold-Dark Matter (ΛCDM) for the dwarf galaxy scale discrepancies. We present an approach to test the viability of such WDM models using star-formation histories (SFHs) of the dwarf spheroidal galaxies (dSphs) in the Local Group. We compare their high-time-resolution SFHs with the collapse redshift of their dark halos in CDM and WDM. Collapse redshift is inferred after determining the subhalo infall mass. This is based on the dwarf current mass inferred from stellar kinematics, combined with cosmological simulation results onmore » subhalo evolution. WDM subhalos close to the filtering mass scale, forming significantly later than CDM, are the most difficult to reconcile with early truncation of star formation ( z ≥ 3). The ultra-faint dwarfs (UFDs) provide the most stringent constraints. Using six UFDs and eight classical dSphs, we show that a 1 keV particle is strongly disfavored, consistently with other reported methods. Excluding other models is only hinted for a few UFDs. Other UFDs for which the lack of robust constraints on halo mass prevents us from carrying out our analysis rigorously, show a very early onset of star formation that will strengthen the constraints delivered by our method in the future. We discuss the various caveats, notably the low number of dwarfs with accurately determined SFHs and the uncertainties when determining the subhalo infall mass, most notably the baryonic physics. Our preliminary analysis may serve as a pathfinder for future investigations that will combine accurate SFHs for local dwarfs with direct analysis of WDM simulations with baryons.« less

Magnetically levitated mesenchymal stem cell spheroids cultured with a collagen gel maintain phenotype and quiescence

PubMed Central

Lewis, Natasha S; Lewis, Emily EL; Mullin, Margaret; Wheadon, Helen; Dalby, Matthew J; Berry, Catherine C

2017-01-01

Multicellular spheroids are an established system for three-dimensional cell culture. Spheroids are typically generated using hanging drop or non-adherent culture; however, an emerging technique is to use magnetic levitation. Herein, mesenchymal stem cell spheroids were generated using magnetic nanoparticles and subsequently cultured within a type I collagen gel, with a view towards developing a bone marrow niche environment. Cells were loaded with magnetic nanoparticles, and suspended beneath an external magnet, inducing self-assembly of multicellular spheroids. Cells in spheroids were viable and compared to corresponding monolayer controls, maintained stem cell phenotype and were quiescent. Interestingly, core spheroid necrosis was not observed, even with increasing spheroid size, in contrast to other commonly used spheroid systems. This mesenchymal stem cell spheroid culture presents a potential platform for modelling in vitro bone marrow stem cell niches, elucidating interactions between cells, as well as a useful model for drug delivery studies. PMID:28616152

Ovarian carcinoma ascites spheroids adhere to extracellular matrix components and mesothelial cell monolayers.

PubMed

Burleson, Kathryn M; Casey, Rachael C; Skubitz, Keith M; Pambuccian, Stephan E; Oegema, Theodore R; Skubitz, Amy P N

2004-04-01

Ovarian carcinoma cells form multicellular aggregates, or spheroids, in the peritoneal cavity of patients with advanced disease. The current paradigm that ascites spheroids are non-adhesive leaves their contribution to ovarian carcinoma dissemination undefined. Here, spheroids obtained from ovarian carcinoma patients' ascites were characterized for their ability to adhere to molecules encountered in the peritoneal cavity, with the goal of establishing their potential to contribute to ovarian cancer spread. Spheroids were recovered from the ascites fluid of 11 patients with stage III or stage IV ovarian carcinoma. Adhesion assays to extracellular matrix (ECM) proteins and human mesothelial cell monolayers were performed for each of the ascites spheroid samples. Subsequently, inhibition assays were performed to identify the cell receptors involved. Most ascites samples adhered moderately to fibronectin and type I collagen, with reduced adhesion to type IV collagen and laminin. Monoclonal antibodies against the beta1 integrin subunit partially inhibited this adhesion. Ascites spheroids also adhered to hyaluronan. Additionally, spheroids adhered to live, but not fixed, human mesothelial cell monolayers, and this adhesion was partially mediated by beta1 integrins. The cellular content of the ascites fluid has often been considered non-adhesive, but our findings are the first to suggest that patient-derived ascites spheroids can adhere to mesothelial extracellular matrix via beta1 integrins, indicating that spheroids should not be ignored in the dissemination of ovarian cancer.

THE SPLASH SURVEY: INTERNAL KINEMATICS, CHEMICAL ABUNDANCES, AND MASSES OF THE ANDROMEDA I, II, III, VII, X, AND XIV DWARF SPHEROIDAL GALAXIES {sup ,}

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

Kalirai, Jason S.; Beaton, Rachael L.; Majewski, Steven R.

2010-03-10

We present new Keck/DEIMOS spectroscopic observations of hundreds of individual stars along the sightline to the first three of the Andromeda (M31) dwarf spheroidal (dSph) galaxies to be discovered, And I, II, and III, and combine them with recent spectroscopic studies by our team of three additional M31 dSphs, And VII, X, and XIV, as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo). Member stars of each dSph are isolated from foreground Milky Way dwarf stars and M31 field contamination using a variety of photometric and spectroscopic diagnostics. Our final spectroscopic sample of membermore » stars in each dSph, for which we measure accurate radial velocities with a median uncertainty (random plus systematic errors) of 4-5 km s{sup -1}, includes 80 red giants in And I, 95 in And II, 43 in And III, 18 in And VII, 22 in And X, and 38 in And XIV. The sample of confirmed members in the six dSphs is used to derive each system's mean radial velocity, intrinsic central velocity dispersion, mean abundance, abundance spread, and dynamical mass. This combined data set presents us with a unique opportunity to perform the first systematic comparison of the global properties (e.g., metallicities, sizes, and dark matter masses) of one-third of Andromeda's total known dSph population with Milky Way counterparts of the same luminosity. Our overall comparisons indicate that the family of dSphs in these two hosts have both similarities and differences. For example, we find that the luminosity-metallicity relation is very similar between L {approx} 10{sup 5} and 10{sup 7} L{sub sun}, suggesting that the chemical evolution histories of each group of dSphs are similar. The lowest luminosity M31 dSphs appear to deviate from the relation, possibly suggesting tidal stripping. Previous observations have noted that the sizes of M31's brightest dSphs are systematically larger than Milky Way satellites of similar luminosity. At lower

Gravity-oriented microfluidic device for uniform and massive cell spheroid formation

PubMed Central

Lee, Kangsun; Kim, Choong; Young Yang, Jae; Lee, Hun; Ahn, Byungwook; Xu, Linfeng; Yoon Kang, Ji; Oh, Kwang W.

2012-01-01

We propose a simple method for forming massive and uniform three-dimensional (3-D) cell spheroids in a multi-level structured microfluidic device by gravitational force. The concept of orienting the device vertically has allowed spheroid formation, long-term perfusion, and retrieval of the cultured spheroids by user-friendly standard pipetting. We have successfully formed, perfused, and retrieved uniform, size-controllable, well-conditioned spheroids of human embryonic kidney 293 cells (HEK 293) in the gravity-oriented microfluidic device. We expect the proposed method will be a useful tool to study in-vitro 3-D cell models for the proliferation, differentiation, and metabolism of embryoid bodies or tumours. PMID:22662098

Naming Disney's Dwarfs.

ERIC Educational Resources Information Center

Sidwell, Robert T.

1980-01-01

Discusses Disney's version of the folkloric dwarfs in his production of "Snow White" and weighs the Disney rendition of the dwarf figure against the corpus of traits and behaviors pertaining to dwarfs in traditional folklore. Concludes that Disney's dwarfs are "anthropologically true." (HOD)

Contragenic functions on spheroidal domains

NASA Astrophysics Data System (ADS)

García-Ancona, Raybel; Morais, Joao; Porter, R. Michael

2018-05-01

We construct bases of polynomials for the spaces of square-integrable harmonic functions which are orthogonal to the monogenic and antimonogenic $\\mathbb{R}^3$-valued functions defined in a prolate or oblate spheroid.

The kinetic equations for rotating and gravitating spheroidal body

NASA Astrophysics Data System (ADS)

Krot, A.

2003-04-01

In papers [1],[2] it has been proposed a statistical model of the gravitational interaction of particles.In the framework of this model bodies have fuzzy outlines and are represented by means of spheroidal forms. A con- sistency of the proposed statistical model the Einstein general relativity [3], [4], [5] has been shown. In work [6], which is a continuation of the paper[2], it has been investigated a slowly evolving in time process of a gravitational compression of a spheroidal body close to an unstable equilibrium state. In the paper [7] the equation of motion of particles inside the weakly gravitating spheroidal body modeled by means of an ideal liquid has been obtained. It has been derived the equations of hyperbolic type for the gravitational field of a weakly gravitating spheroidal body under observable values of velocities of particles composing it [7],[8]. This paper considers the case of gravitational compres- sion of spheroidal body with observable values of parti- cles.This means that distribution function of particles inside weakly rotating spheroidal body is a sum of an isotropic space-homogeneous stationary distribution function and its change (disturbance) under influence of dymanical gravitational field. The change of initial space-homogeneous stationary distribution function satisfyes the Boltzmann kinetic equation. This paper shows that if gravitating spheroidal body is rotating uniformly or is being at rest then distribution function of its particles satisfyes the Liouville theorem. Thus, being in unstable statistical quasiequilibrium the gravi- tating spheroidal body is rotating with constant angular velocity (or, in particular case, is being at rest). The joint distribution function of spheroidal body's particles in to coordinate space and angular velocity space is introduced. References [1] A.M.Krot, Achievements in Modern Radioelectronics, special issue "Cosmic Radiophysics",no. 8, pp.66-81, 1996 (Moscow, Russia). [2] A.M.Krot, Proc. SPIE 13

Hubble Space Telescope survey of the Perseus cluster - III. The effect of local environment on dwarf galaxies

NASA Astrophysics Data System (ADS)

Penny, Samantha J.; Conselice, Christopher J.; de Rijcke, Sven; Held, Enrico V.; Gallagher, John S.; O'Connell, Robert W.

2011-01-01

We present the results of a Hubble Space Telescope (HST) study of dwarf galaxies in the outer regions of the nearby rich Perseus cluster, down to MV=-12, and compare these with the dwarf population in the cluster core from our previous HST imaging. In this paper, we examine how properties such as the colour-magnitude relation, structure and morphology are affected by environment for the lowest mass galaxies. Dwarf galaxies are excellent tracers of the effects of environment due to their low masses, allowing us to derive their environmentally based evolution, which is more subtle in more massive galaxies. We identify 11 dwarf elliptical (dE) and dwarf spheroidal (dSph) galaxies in the outer regions of Perseus, all of which are previously unstudied. We measure the (V-I)0 colours of our newly discovered dEs, and find that these dwarfs lie on the same red sequence as those in the cluster core. The morphologies of these dwarfs are examined by quantifying their light distributions using concentration, asymmetry and clumpiness (CAS) parameters, and we find that dEs in the cluster outskirts are on average more disturbed than those in the core, with = 0.13 ± 0.09 and = 0.18 ± 0.08, compared to = 0.02 ± 0.04, = 0.01 ± 0.07 for those in the core. Based on these results, we infer that these objects are `transition dwarfs', likely in the process of transforming from late-type to early-type galaxies as they infall into the cluster, with their colours transforming before their structures. When we compare the number counts for both the core and outer regions of the cluster, we find that below MV=-12, the counts in the outer regions of the cluster exceed those in the core. This is evidence that in the very dense region of the cluster, dwarfs are unable to survive unless they are sufficiently massive to prevent their disruption by the cluster potential and interactions with other galaxies. Based on observations made with the NASA/ESA HST, obtained (from the Data