Thursday.
1312.0006
The dark matter contribution to galactic diffuse gamma ray emission
Yang, Silk, Szalay, Wyse, Bozek, Madau
Observation of diffuse galactic gamma ray emission (DGE) by Fermi LAT allow a detailed study of CRs and the ISM. However, diffuse emission models of the inner Galaxy under predict the Fermi-LAT data at energies above a few GeV and hint at possible non-astrophysical sources including DM annihilations or decays. Present a study of the possible emission components from DM using the high-res Via Lactea II N-body sims of a MW-sized DM halo. Generate full-sky maps of DM annihilation and decay signals that include modeling of the adiabatic contraction of the host density profile, Sommerfeld enhanced DM annihilations, p-wave annihilations, and decaying DM. Compare results with the DGE models produced by Fermi-LAT over different sky regions including the Galactic center, high galactic latitudes, and the Galactic anti-center. This work provides possible templates to fit the observational data that includes the contribution of the sub halo population to DM gamma-ray emission, with the significance depending n the annihilation/decay channels and the Galactic regions being considered.
1312.0016
Spatially resolved velocity maps of halo gas around two intermediate-redshift galaxies
Chen et al
Crude 3d map of halo gas around the (lens) galaxy, from absorption-line spectroscopy of multiply-lensed QSOs. Records the LoS velocity field at different locations in the gaseous halo. Two intermediate-z galaxies are targeted in the field around the quadruply-lensed QSO at z=1.689, and absorption spectroscopy along each of the lensed QSOs is carried out in the vicinities of these galaxies. One galaxy is a typical, star-forming L* galaxy at z=0.4188 and projected distance of rho-50kpc from the lensing galaxy. The other is a super-L* barred spiral at z=0.7818 and rho=33 kpc. Combining known orientations of the quadruply-lensed QSO to the two foreground galaxies with the observed MgII absorption profiles along individual QSO sight lines has for the first time led to spatially resolved kinematics of tenuous halo gas on scales of 5-10 kpc at z>0.2. A MgII absorber is detected in every sightline observed through the halos of the two galaxies, and the recorded absorber strength is typical of what is seen in previous close QSO-galaxy pair studies. While the multi-sightline study confirms the unity covering fraction of MgII absorbing gas at rho<50kpc from SF disks, the galaxies also present two contrasting examples of complex halo gas kinematics. Different models, including a rotating disk, collimated outflows, and gaseous streams from either accretion or tidal/ram-pressure stripping, are considered for comparisons with the absorption-line observations, and in falling streams/stripped gas of width >~10 kpc are found to best describe the observed gas kinematics across multiple sight lines.
1312.0025
Suppressing CMB low multipoles with ISW effect
Das, Souradeep
Investigate the possibility of ISW to explain the low l (<30) power deficit in the CMB angular power spectrum. ISW adds to the power at low multipoles; carry out an analytic study to show the there are some expansion histories in the ISW effect. Instead of adding power, provide negative contribution to the power at low multipoles. Present examples of features required in late time expansion history of the universe that could explain the power deficiency through ISW. Show that an ISW origin of power deficiency is consistent, at present, with other cosmological observations that probe the expansion history such as distance modulus, matter PS and the evolution of cluster number count. Show that the ISW effect may be distinguished from power deficit originating from features in the PPS [?] using the measurements of the CMB polarization spectrum at low multipoles expected from Planck. Conclude that the power at low multipoles of the CMB anisotropy could well be closely linked to DE puzzle in cosmology and this observation could be actually pointing to richer phenomenology of DE beyond the cosmological constant Lambda.
1312.0105
Dark matter n the local universe
Yepes, Gottloeber, Hoffman
Describe how DM halo and MW in the Local Group; proceed to describe DM distribution in the Local Universe. Depending on the nature of DM, numerical simulations predict different abundances of substructures in Local Group galaxies, in the number of void regions and in the abundance of low rotational velocity galaxies in the Local Universe. By comparing predictions with the most recent observations, strong constrains on DM particles can be derived. CLUES project: a special set of sims whose initial conditions are constrained by observational data from the Local Universe. The resulting simulations are designed to reproduce the observed strutters in the nearby universe. The CLUES provides a numerical laboratory for simulating the Local Group of galaxies and exploring the physics of galaxy formation in an environment designed to follow the observed Local Universe.
1312.0107
Galaxy formation
Silk, De Cintio, Dvorkin
[Lecture from cosmology school.] Galaxy formation is at the forefront of observation and theory in cosmology. An improved understanding is essential for improving the knowledge both of the cosmological parameters, of the contents of the universe, and of our origins. In these lectures intended for graduate students, galaxy formation theory is reviewed and confronted with recent observational issues. In Lecture 1, the following topics are presented: SF considerations, including IMF, SF efficiency and SFR, the origin of the galaxy LF, and feedback in dwarf galaxies. In lecture 2, describe formation of disks and massive spheroids, including the growth of SMBH, negative feedback in spheroids, the AGN-SF connection, SFR at high z and the baryon fraction in galaxies.
1312.0314
The real and apparent convergence of N-body simulations of the dark matter structures: is the Navarro-Frenk-White profile real?
Baushev
Consider the reasons why a cuspy NFW-like profile presets in N-body simulations, in contradiction to some astronomical observations. Routine N-body sims neglects 2-body scattering effect; check how sensitive the formed structures are to this parameter setting(s). Results suggest a minor role of particle collisions: the central density profile remains untouched and close to NFW, even if the simulation time significantly exceeds the collisional relaxation time tau_r. Analyze a test body distribution in the halo center with Fokker-Planck equation; turns out that the Fokker-Planck diffusion transforms any reasonable initial distribution into NFW-like profile rho~r^-1 in a time shorter than tau_r. On the contrary, profile rho~r^-1 should survive much longer, being a sort of attractor: the Fokker-Planck diffusion is self-compensated in this case. Thus the test body scattering may create a stable NFW-like pseudo-solution that can be mixed up with the real convergence. This fact might help to eliminate the well-known 'cusp vs. core' problem.
1312.0358
Dark matter halo assembly bias: environmental dependence in the non-Markovian excursion set theory
Zhang, Ma, Riotto
In the standard excursion set model for the growth of structure, the statistical properties of haloes are governed by the halo mass and are independent of the large scale environment in which the haloes reside. Numerical simulations, however, have found the spatial distributions of haloes to depend not only on their mass but also on the details of their assembly history and environment. Present a theoretical framework for incorporating this "assembly bias" into the excursion set model. Derivations are based on modifications of the path integral approach of Maggiore & Riotto (2010) that models halo formation as a non-Markovian random walk process. The perturbed density field is assumed to evolve stochastically with the smoothing scale and exhibits correlated walks in the presence of a density barrier. Write down conditional probabilities for multiple barrier crossings, and derive from them analytic expressions for descendant and progenitor halo mass functions and halo merger rates as a function of both halo mass and the linear over density of the larger-scale environment of the halo. Results predict a higher halo merger rate and higher progenitor halo mass function in regions of higher over density, consistent with the behavior seen in N-body simulations.
1312.0364
Genuine Irregular Galaxies as a relic of building blocks of galaxies
Terao et al
GIGs == isolated galaxies without regular structures (spheroid, bulge, disk, bar, spiral arm, and nucleus). Find GIGs have smaller sizes, lower optical luminosities, bluer rest-frame optical colors, lower surface stellar mass densities, and lower gas metallicity than normal galaxies. All these properties suggest that they are in chemically and dynamically younger phases even in the nearby universe.
1312.0430
Cosmic shear full nulling: sorting out dynamics, geometry and systematics
Bernardeau, Nishimichi, Taruya
An explicit full nulling scheme for cosmic shear observations is presented. It makes possible the construction of shear maps from extended source distributions for which the lens distance distribution is restricted to a definite interval. Such a construction allows to build totally independent shear maps, at all scales, that can be taken advantage of to constrain background cosmological parameters and systematics using the full statistical power of cosmic shear observations. Another advantage of such construction is that, as the lens redshift distribution can be made arbitrarily narrow, scale mixing due to projection effects can bel limited allowing controlled predictions on the large scale shear power spectrum from perturbation theory calculations.
1312.0460
A survey of infrared supernova remnants in the Large Magellanic Cloud
Seok, Koo, Onaka
Comprehensive IR study of SNRs in LMC using near- to mid-IR images by IRAC and MIPS on Spitzer. Among the 47 true LMC SNRs, 29 were detected in IR, giving a high detection rate of 62%. All 29 SNRs show emission at 24 um, and 20/29 show emission in one or several IRAC bands. Present 4.5, 8, 24 and 70 um images and a table summarizing their Spitzer fluxes. Find that the LMC SNRs are considerably fainter than the Galactic SNRs, and among there LNC SNRs, Type Ia SNRs are significantly fainter than core-collapse SNRs. Conclude that the MIPS emission of essentially all SNRs originates from dust emission, where as their IRAC emissions originate from ionic/molecular lines, PAH emission, or synchrotron emission. The IR fluxes show correlation with radio and X-ray fluxes. For SNRs that have similar morphology in IR and X-rays, the ratios of 24 to 70 um fluxes have good correlation with the electron density of hot plasma. The overall correlation is explained well by the emission from collisionally-heated silicate grains of 0.1 um size, but for mature SNRs with relatively low gas temperatures, the smaller-sized grain population is favored more. FOr those that appear different between IR and X-rays, the emission in the MIPS band is probably from dust heated by shock radiation.
1312.0558
IceCube's Neutrinos: the beginning of extra-Galactic neutrino astrophysics?
Waxman
The flux, spectrum and angular distribution of the excess neutrino signal detected by IceCube between 50 TeV and 2 PeV are inconsistent with those expected for Galactic sources. The coincidence of the excess with the Waxman-Bahcall (WB) bound is probably a clue to the origin of IceCube's neutrinos. The most natural explanation of this coincidence is that both the neutrino excess and the UHECR (>1e19 eV) flux are produced by the same population of cosmologically distributed sources, producing CRs, likely protons, at a similar rate across a wide range of energies from 1e15 eV to 1e20 eV, and residing in environments (such as SB galaxies) in which CRs of rigidity E/Z<1e17 eV lose much of their energy to pion production. Identification of the neutrino sources will allow one to identify the UHECR accelerators, to resolve open questions related to the accelerator models, and to study neutrino properties (related e.g. to flavor oscillations and coupling to gravity) with an accuracy many orders of magnitude better than is currently possible. The most promising method for identifying the sources is by association of a neutrino with and EM signal accompanying a transient event responsible for its generation. The neutrino flux that is produced within thesaurus, and that may thus be directly associated with transient events, may be significantly lower than the total observed neutrino flux, which may be dominated by neutrino production at the environment in which the sources reside.
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