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Abdo A.A.,U.S. Navy | Abdo A.A.,National Academy of science | Ackermann M.,Kavli Institute for Particle Astrophysics and Cosmology | Ajello M.,Kavli Institute for Particle Astrophysics and Cosmology | And 205 more authors.
Astrophysical Journal | Year: 2010

We report on the observations of 14 dwarf spheroidal galaxies (dSphs) 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 γ-ray survey in the 20 MeV to >300GeV energy range, provides a new opportunity to test particle dark matter models through the expected γ-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dSphs, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant γ-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the γ-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 10-9 photons cm-2 s-1. Using recent stellar kinematic data, the γ-ray flux limits are combined with improved determinations of the dark matter density profile in eight of the 14 candidate dwarfs to place limits on the pair-annihilation cross section of WIMPs 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 γ-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e + e - data, including low-mass wino-like neutralinos and models with TeV masses pair annihilating into muon-antimuon pairs. © 2010. The American Astronomical Society.


Rasmussen J.,Copenhagen University | Bai X.-N.,Princeton University | Mulchaey J.S.,Carnegie Observatories | Van Gorkom J.H.,Columbia University | And 6 more authors.
Astrophysical Journal | Year: 2012

The role of environmentally induced gas stripping in driving galaxy evolution in groups remains poorly understood. Here we present extensive Chandra and Very Large Array mosaic observations of the hot and cold interstellar medium within the members of the nearby, X-ray bright NGC2563 group, a prime target for studies of the role of gas stripping and interactions in relatively small host halos. Our observations cover nearly all group members within a projected radius of 1.15Mpc (∼1.4 R vir) of the group center, down to a limiting X-ray luminosity and H I mass of 3 × 10 39ergs-1 and 2 × 108 M ⊙, respectively. The X-ray data are consistent with efficient ram pressure stripping of the hot gas halos of early-type galaxies near the group core, but no X-ray tails are seen and the limited statistics preclude strong conclusions. The H I results suggest moderate H I mass loss from the group members when compared to similar field galaxies. Six of the 20 H I-detected group members show H I evidence of ongoing interactions with other galaxies or with the intragroup medium. Suggestive evidence is further seen for galaxies with close neighbors in position-velocity space to show relatively low H I content, consistent with tidal removal of H I. The results thus indicate removal of both hot and cold gas from the group members via a combination of ram pressure stripping and tidal interactions. We also find that 16 of the 20 H I detections occur on one side of the group, reflecting an unusual morphological segregation whose origin remains unclear. © 2012. The American Astronomical Society. All rights reserved.


Cuesta A.J.,Institute Astrofisica Of Andalucia Csic | Jeltema T.E.,UCO Lick Observatories | Zandanel F.,Institute Astrofisica Of Andalucia Csic | Profumo S.,University of California at Santa Cruz | And 10 more authors.
Astrophysical Journal Letters | Year: 2011

We present all-sky simulated Fermi maps of γ-rays from dark matter (DM) decay and annihilation in the local universe. The DM distribution is obtained from a constrained cosmological simulation of the neighboring large-scale structure provided by the CLUES project. The DM fields of density and density squared are then taken as an input for the Fermi observation simulation tool to predict the γ-ray photon counts that Fermi would detect in 5 years of an all-sky survey for given DM models. Signal-to-noise ratio (S/N) sky maps have also been obtained by adopting the current Galactic and isotropic diffuse background models released by the Fermi Collaboration. We point out the possibility for Fermi to detect a DM γ-ray signal in local extragalactic structures. In particular, we conclude here that Fermi observations of nearby clusters (e.g., Virgo and Coma) and filaments are expected to give stronger constraints on decaying DM compared to previous studies. As an example, we find a significant S/N in DM models with a decay rate fitting the positron excess as measured by PAMELA. This is the first time that DM filaments are shown to be promising targets for indirect detection of DM. On the other hand, the prospects for detectability of annihilating DM in local extragalactic structures are less optimistic even with extreme cross-sections. We make the DM density and density squared maps publicly available online. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.


Hallman E.J.,University of Colorado at Boulder | Hallman E.J.,Harvard - Smithsonian Center for Astrophysics | Hallman E.J.,National Science Foundation | Skillman S.W.,University of Colorado at Boulder | And 5 more authors.
Astrophysical Journal | Year: 2010

We examine the incidence of cold fronts in a large sample of galaxy clusters extracted from a (512 h-1 Mpc) hydrodynamic/N-body cosmological simulation with adiabatic gas physics computed with the Enzo adaptive mesh refinement code. This simulation contains a sample of roughly 4000 galaxy clusters with M ≥ 1014M⊙ at z = 0. For each simulated galaxy cluster, we have created mock 0.3-8.0 keV X-ray observations and spectroscopic-like temperature maps. We have searched these maps with a new automated algorithm to identify the presence of cold fronts in projection. Using a threshold of a minimum of 10 cold front pixels in our images, corresponding to a total comoving length Lcf 156 h-1 kpc, we find that roughly 10%-12% of all projections in a mass-limited sample would be classified as cold front clusters. Interestingly, the fraction of clusters with extended cold front features in our synthetic maps of a mass-limited sample trends only weakly with redshift out to z = 1.0. However, when using different selection functions, including a simulated flux limit, the trending with redshift changes significantly. The likelihood of finding cold fronts in the simulated clusters in our sample is a strong function of cluster mass. In clusters with M ≥ 7.5 × 1014M⊙ the cold front fraction is 40%-50%. We also show that the presence of cold fronts is strongly correlated with disturbed morphology as measured by quantitative structure measures. Finally, we find that the incidence of cold fronts in the simulated cluster images is strongly dependent on baryonic physics. © 2010 The American Astronomical Society.


Simcoe R.A.,Massachusetts Institute of Technology | Burgasser A.J.,University of California at San Diego | Bochanski J.J.,Massachusetts Institute of Technology | Schechter P.L.,Massachusetts Institute of Technology | And 7 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We describe the construction and commissioning of FIRE, a new 0.8-2.5μm echelle spectrometer for the Magellan/ Baade 6.5 meter telescope. FIRE delivers continuous spectra over its full bandpass with nominal spectral resolution R = 6000. Additionally it offers a longslit mode dispersed by the prisms alone, covering the full z to K bands at R ∼ 350. FIRE was installed at Magellan in March 2010 and is now performing shared-risk science observations. It is delivering sharp image quality and its throughput is sufficient to allow early observations of high redshift quasars and faint brown dwarfs. This paper outlines several of the new or unique design choices we employed in FIRE's construction, as well as early returns from its on-sky performance. © 2010 Copyright SPIE - The International Society for Optical Engineering.

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