Consequences of dark matter self-annihilation for galaxy formation     

Priyamvada Natarajan  Darren Croton  Gianfranco Bertone 《Monthly notices of the Royal Astronomical Society》2008,388(4):1652-1666

Galaxy formation requires a process that continually heats gas and quenches star formation in order to reproduce the observed shape of the luminosity function of bright galaxies. To accomplish this, current models invoke heating from supernovae, and energy injection from active galactic nuclei. However, observations of radio-loud active galactic nuclei suggest that their feedback are likely not to be as efficient as required, signaling the need for additional heating processes. We propose the self-annihilation of weakly interacting massive particles that constitute dark matter as a steady source of heating. In this paper, we explore the circumstances under which this process may provide the required energy input. To do so, dark matter annihilations are incorporated into a galaxy formation model within the Millennium cosmological simulation. Energy input from self-annihilation can compensate for all the required gas cooling and reproduce the observed galaxy luminosity function only for what appear to be extreme values of the relevant key parameters. The key parameters are: the slope of the inner density profile of dark matter haloes and the outer spike radius. The inner density profile needs to be steepened to slopes of −1.5 or more and the outer spike radius needs to extend to a few tens of parsecs on galaxy scales and a kpc or so on cluster scales. If neutralinos or any thermal relic Weakly Interacting Massive Particle with s-wave annihilation constitute dark matter, their self-annihilation is inevitable and could provide enough power to modulate galaxy formation. Energy from self-annihilating neutralinos could be yet another piece of the feedback puzzle along with supernovae and active galactic nuclei.  相似文献   

MHD Simulation of Comets: The Plasma Environment of Comet Hale-Bopp     

Gombosi  Tamas I.  Hansen  Kenneth C.  DeZeeuw  Darren L.  Combi  Michael R.  Powell  Kenneth G. 《Earth, Moon, and Planets》1997,79(1-3):179-207

MHD simulation results of the interaction of the expanding atmosphere of comet Hale-Bopp with the magnetized solar wind are presented. At the upstream boundary a supersonic and superalfvénic solar wind enters into the simulation box 25 million km upstream of the nucleus. The solar wind is continuously mass loaded with cometary ions originating from the nucleus. The effects of photoionization, recombination and ion-neutral frictional drag are taken into account in the model. The governing equations are solved on an adaptively refined unstructured Cartesian grid using our MUSCL-type upwind numerical technique, MAUS-MHD (Multiscale Adaptive Upwind Scheme for MHD). The combination of the adaptive refinement with the MUSCL-scheme allows the entire cometary atmosphere to be modeled, while still resolving both the shock and the diamagnetic cavity of the comet. Detailed simulation results for the plasma environment of comet Hale-Bopp for slow and fast solar wind conditions are presented. We also calculate synthetic H₂O⁺, CO⁺ and soft x-ray images for observing conditions on April 11, 1997. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The 2dF Galaxy Redshift Survey: spectra and redshifts     

Matthew Colless  Gavin Dalton  Steve Maddox  Will Sutherland  Peder Norberg  Shaun Cole  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Chris Collins  Warrick Couch  Nicholas Cross  Kathryn Deeley  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Darren Madgwick  John A. Peacock  Bruce A. Peterson  Ian Price  Mark Seaborne  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,328(4):1039-1063

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Macrozooplankton and micronekton of the lower San Francisco estuary: Seasonal, interannual, and regional variation in relation to environmental conditions     

Darren S. Gewant  Stephen M. Bollens 《Estuaries and Coasts》2005,28(3):473-485

Macrozooplankton and micronekton are intermediaries linking lower trophic levels (e.g., phytoplankton and mesozooplankton) to higher ones (e.g., fishes and birds). These organisms have not been extensively studied in the San Francisco Estuary (SFE), California. The objective of this study was to determine the distribution and abundance of macrozooplankton and micronekton in the SFE and to describe how these vary seasonally, interannually, and regionally in relation to environmental variables. Water column macrozooplankton and micronekton were sampled monthly from September 1997 to December 2000 at 6 stations spanning North, Central, and South Bays using a Methot Trawl. The macrozo oplankton and micronekton in the lower SFE were dominated by 4 fishes and 7 invertebrates that comprised 98% of the total catch. Correspondence analyses revealed 4 groups of species that exhibited similar patterns of distribution and abundance. The assemblages changed between the wet and dry seasons and with distance from the coastal ocean. Based on abundance patterns, the dominant taxa in the lower SFE can be classified as: organisms spawned from common members of neritic assemblages that use mostly North Bay and that are abundant during the dry season (Clupea pallasi, Spirinchus thaleichthys, Porichthys notates); estuarine-dependent organisms with broad distributions in the estuary year-round (Crangon franciscorum, Crangon nigricauda, Engraulis mordax); resident species remaining within the estuary but occurring mostly in South Bay during the wet season (Palaemon macrodactlyus, Synidotea laticauda, Neomysis kadiakensis); and gelatinous species (Pleurobrachia bachei, Polyorchis spp.) occuring in all three bays with a single peak in abundance in December and January in North and South Bays. The variation in distribution, abundance, and composition of macrozooplankton and micronekton was related to life history strategies, distance from the coastal ocean, and season.  相似文献   

SPIRE point source photometry: within the Herschel interactive processing environment (HIPE)     

Chris Pearson  Tanya Lim  Chris North  George Bendo  Luca Conversi  Darren Dowell  Matt Griffin  Terry Jin  Nicolas Laporte  Andreas Papageorgiou  Bernhard Schulz  Dave Shupe  Anthony J. Smith  Kevin Xu 《Experimental Astronomy》2014,37(2):175-194

The different algorithms appropriate for point source photometry on data from the SPIRE instrument on-board the Herschel Space Observatory, within the Herschel Interactive Processing Environment (HIPE) are compared. Point source photometry of a large ensemble of standard calibration stars and dark sky observations is carried out using the 4 major methods within HIPE: SUSSEXtractor, DAOphot, the SPIRE Timeline Fitter and simple Aperture Photometry. Colour corrections and effective beam areas as a function of the assumed source spectral index are also included to produce a large number of photometric measurements per individual target, in each of the 3 SPIRE bands (250, 350, 500μm), to examine both the accuracy and repeatability of each of the 4 algorithms. It is concluded that for flux densities down to the level of 30mJy that the SPIRE Timeline Fitter is the method of choice. However, at least in the 250 and 350μm bands, all 4 methods provide photometric repeatability better than a few percent down to at approximately 100mJy. The DAOphot method appears in many cases to have a systematic offset of ～8 % in all SPIRE bands which may be indicative of a sub-optimal aperture correction. In general, aperture photometry is the least reliable method, i.e. largest scatter between observations, especially in the longest wavelength band. At the faintest fluxes, <30mJy, SUSSEXtractor or DAOphot provide a better alternative to the Timeline Fitter.  相似文献   

The impacts of climate change on tribal traditional foods     

Kathy Lynn  John Daigle  Jennie Hoffman  Frank Lake  Natalie Michelle  Darren Ranco  Carson Viles  Garrit Voggesser  Paul Williams 《Climatic change》2013,120(3):545-556

American Indian and Alaska Native tribes are uniquely affected by climate change. Indigenous peoples have depended on a wide variety of native fungi, plant and animal species for food, medicine, ceremonies, community and economic health for countless generations. Climate change stands to impact the species and ecosystems that constitute tribal traditional foods that are vital to tribal culture, economy and traditional ways of life. This paper examines the impacts of climate change on tribal traditional foods by providing cultural context for the importance of traditional foods to tribal culture, recognizing that tribal access to traditional food resources is strongly influenced by the legal and regulatory relationship with the federal government, and examining the multi-faceted relationship that tribes have with places, ecological processes and species. Tribal participation in local, regional and national climate change adaption strategies, with a focus on food-based resources, can inform and strengthen the ability of both tribes and other governmental resource managers to address and adapt to climate change impacts.  相似文献   

Middle Pleistocene environments,landscapes and tephrostratigraphy of the Armenian Highlands: evidence from Bird Farm 1, Hrazdan Valley     

Jenni E. Sherriff  Keith N. Wilkinson  Poppy Harding  Hayley Hawkins  Rhys G. O. Timms  Daniel S. Adler  Emily J. Beverly  Simon P. E. Blockley  Boris Gasparyan  Christina J. Manning  Darren Mark  Samvel Nahapetyan  Katie J. Preece 《第四纪科学杂志》2022,37(1):6-27

The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale.  相似文献