16,015 research outputs found

    The Role of Stellar Feedback and Dark Matter in the Evolution of Dwarf Galaxies

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    Supernova and multiple supernova events regulate several structural properties of dwarf galaxies. In particular, they govern the metal enrichment and the energy budget of the ISM; they might induce partial (blowout) or total (blowaway) gas removal from the galaxy; the morphology of the galactic gaseous body. Significant amounts of dark matter may play an equally important role: the dark matter gravitational potential tends to concentrate baryons towards the center, thus enhancing both the star formation rate and metal production. Also, the dynamical properties of the ISM, and the occurrence of a blowout or blowaway are shown to be determined by the dark matter content. We present detailed analytical/numerical models describing the evolution of dwarf Irregular galaxies including the above and other effects. The main results are: (i) dwarfs with total masses M\simlt 5\times 10^6 M_\odot are blown away; those with gas masses up to 109M\simeq 10^9 M_\odot lose mass in an outflow; (ii) metallicities are found to correlate tightly with dark matter content and are consistent with a range of dark-to-visible mass ratios ϕ030\phi\approx 0-30 with about 65% of the dwarfs in the sample having ϕ010\phi\approx 0-10; (iii) we predict a lower limit to the oxygen abundance in dIs of 12+log(O/H)7.212+log(O/H)\approx 7.2; (iv) outflows are not particularly important for the metallicity evolution of dwarf galaxies and certainly less than star formation for gas consumption; however, dwarfs with gas masses few ×108M\times 10^8 M_\odot are shown to be the major pollutants of the IGM; (v) the ISM HI velocity dispersion correlates with metallicity and, indepentently of dark matter, scales as Z3.5Z^{3.5}. (Abridged)Comment: 56 pages, aasms4.sty, LaTeX, 12 figures. MNRAS, submitte

    Superconformal Field Theories, Multiplet Shortening, and the AdS5_5/SCFT4_4 Correspondence

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    We review the unitarity bounds and the multiplet shortening of UIR's of 4 dimensional superconformal algebras SU(2,2N)SU(2,2|N), (N=1,2,4N=1,2,4) in view of their dual role in the AdS/SCFT correspondence. Some applications to KK spectra, non-perturbative states and stringy states are given.Comment: minor changes, references adde

    Probing high-redshift galaxies with Lyα\alpha intensity mapping

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    We present a study of the cosmological Lyα\alpha emission signal at z>4z > 4. Our goal is to predict the power spectrum of the spatial fluctuations that could be observed by an intensity mapping survey. The model uses the latest data from the HST legacy fields and the abundance matching technique to associate UV emission and dust properties with the halos, computing the emission from the interstellar medium (ISM) of galaxies and the intergalactic medium (IGM), including the effects of reionization, self-consistently. The Lyα\alpha intensity from the diffuse IGM emission is 1.3 (2.0) times more intense than the ISM emission at z=4(7)z = 4(7); both components are fair tracers of the star-forming galaxy distribution. However the power spectrum is dominated by ISM emission on small scales (k>0.01hMpc1k > 0.01 h{\rm Mpc}^{-1}) with shot noise being significant only above k=1hMpc1k = 1 h{\rm Mpc}^{-1}. At very lange scales (k<0.01hMpc1k < 0.01h{\rm Mpc}^{-1}) diffuse IGM emission becomes important. The comoving Lyα\alpha luminosity density from IGM and galaxies, ρ˙LyαIGM=8.73(6.51)×1040ergs1Mpc3\dot \rho_{{\rm Ly}\alpha}^{\rm IGM} = 8.73(6.51) \times 10^{40} {\rm erg}{\rm s}^{-1}{\rm Mpc}^{-3} and ρ˙LyαISM=6.62(3.21)×1040ergs1Mpc3\dot \rho_{{\rm Ly}\alpha}^{\rm ISM} = 6.62(3.21) \times 10^{40} {\rm erg}{\rm s}^{-1}{\rm Mpc}^{-3} at z=4(7)z = 4(7), is consistent with recent SDSS determinations. We predict a power k3PLyα(k,z)/2π2=9.76×104(2.09×105)nW2m4sr2k^3 P^{{\rm Ly}\alpha}(k, z)/2\pi^2 = 9.76\times 10^{-4}(2.09\times 10^{-5}){\rm nW}^2{\rm m}^{-4}{\rm sr}^{-2} at z=4(7)z = 4(7) for k=0.1hMpc1k = 0.1 h {\rm Mpc}^{-1}.Comment: 14 Pages, 13 figure

    The Hubble Deep Field Reveals a Supernova at z~0.95

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    We report the discovery of a variable object in the Hubble Deep Field North (HDF-N) which has brightened, during the 8.5 days sampled by the data, by more than 0.9 mag in I and about 0.7 mag in V, remaining stable in B. Subsequent observations of the HDF-N show that two years later this object has dimmed back to about its original brightness in I. The colors of this object, its brightness, its time behavior in the various filters and the evolution of its morphology are consistent with being a Type Ib supernova in a faint galaxy at z~0.95.Comment: 5 pages including 2 figures. Accepted for publication in MNRA

    Molecular hydrogen in damped Ly-alpha systems: clues to interstellar physics at high-redshift

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    In order to interpret H2 (molecular hydrogen) quasar absorption line observations of damped Ly-alpha systems (DLAs) and sub-DLAs, we model their H2 abundance as a function of dust-to-gas ratio, including H2 self-shielding and dust extinction against dissociating photons. Then, we constrain the physical state of gas by using H2 data. Using H2 excitation data for DLA with H2 detections, we derive a gas density 1.5 < log n [cm^-3] < 2.5, temperature 1.5 < log T [K] < 3, and internal UV radiation field (in units of the Galactic value) 0.5 < log \chi < 1.5. We then find that the observed relation between molecular fraction and dust-to-gas ratio of the sample is naturally explained by the above conditions. However, it is still possible that H2 deficient DLAs and sub-DLAs with H2 fractions less than ~ 10^-6 are in a more diffuse and warmer state. The efficient photodissociation by the internal UV radiation field explains the extremely small H2 fraction (< 10^-6) observed for \kappa < 1/30 (\kappa is the dust-to-gas ratio in units of the Galactic value); H2 self-shielding causes a rapid increase and the large variations of H2 abundance for \kappa > 1/30. We finally propose an independent method to estimate the star formation rates of DLAs from H2 abundances; such rates are then critically compared with those derived from other proposed methods. The implications for the contribution of DLAs to the cosmic star formation history are briefly discussed.Comment: 15 pages, 5 figures, accepted for publication in MNRA

    Some Pathways in non-Linear Supersymmetry: Special Geometry Born-Infeld's, Cosmology and dualities

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    This review is devoted to some aspects of non-linear Supersymmetry in four dimensions that can be efficiently described via nilpotent superfields, in both rigid and curved Superspace. Our focus is mainly on the partial breaking of rigid N=2N=2 Supersymmetry and on a class of generalized Born-Infeld systems that originate from Special Geometry and on some prototype cosmological models, starting from the Supergravity embedding of Starobinsky inflation. However, as an aside we also review briefly some interesting two-field extensions of the Born-Infeld Lagrangian whose field equations enjoy extended duality symmetries.Comment: Contribution to the Proceedings of "Group Theory, Probability, and the Structure of Spacetime", A Conference on the Occasion of Professor V.S. Varadarajan's Retirement, UCLA Mathematics Department, November 7-9, 2014. To appear in a special issue of "p-Adic Numbers, Ultrametric Analysis and Applications". 35 pages LaTeX, 1 eps figure. Typos corrected, reference adde

    Massive Born--Infeld and Other Dual Pairs

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    We consider massive dual pairs of p-forms and (D-p-1)-forms described by non-linear Lagrangians, where non-linear curvature terms in one theory translate into non-linear mass-like terms in the dual theory. In particular, for D=2p and p even the two non-linear structures coincide when the non-linear massless theory is self-dual. This state of affairs finds a natural realization in the four-dimensional massive N=1 supersymmetric Born-Infeld action, which describes either a massive vector multiplet or a massive linear (tensor) multiplet with a Born-Infeld mass-like term. These systems should play a role for the massive gravitino multiplet obtained from a partial super-Higgs in N=2 Supergravity.Comment: 17 pages, LaTeX. Misprints corrected. Final version to appear in JHE

    N=8 non-BPS Attractors, Fixed Scalars and Magic Supergravities

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    We analyze the Hessian matrix of the black hole potential of N=8, d=4 supergravity, and determine its rank at non-BPS critical points, relating the resulting spectrum to non-BPS solutions (with non-vanishing central charge) of N=2, d=4 magic supergravities and their ``mirror'' duals. We find agreement with the known degeneracy splitting of N=2 non-BPS spectrum of generic special Kahler geometries with cubic holomorphic prepotential. We also relate non-BPS critical points with vanishing central charge in N=2 magic supergravities to a particular reduction of the N=8, 1/8-BPS critical points.Comment: 1+25 pages, 4 Tables, no figures; v2: minor changes and corrections, Ref. adde

    Bulk Gauge Fields in AdS Supergravity and Supersingletons

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    We describe conformal operators living at the boundary of AdSd+1AdS_{d+1} in a general setting. Primary conformal operators at the threshold of the unitarity bounds of UIR's of O(d,2) correspond to singletons and massless fields in AdSd+1AdS_{d+1}, respectively. For maximal supersymmetric theories in AdSd+1AdS_{d+1} we describe ``chiral'' primary short supermultiplets and non-chiral primary long supermultiplets. Examples are exhibited which correspond to KK and string states. We give the general contribution of a primary conformal operator to the OPE and Green's functions of primary fields, which may be relevant to compute string corrections to the four-point supergraviton amplitude in Anti-de-Sitter space. The material in this paper was presented by one of the authors (S.F) at String 98, Santa Barbara.Comment: 16 pages, harvmac, String 98 on-line proceeding
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