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Title: The Search for Milky Way Halo Substructure WIMP Annihilations Using the GLAST LAT

Abstract

The GLAST LAT Collaboration is one among several experimental groups, covering a wide range of approaches, pursuing the search for the nature of dark matter. The GLAST LAT has the unique ability to find new sources of high energy gamma radiation emanating directly from WIMP annihilations in situ in the universe. Using it's wide band spectral and full sky spatial capabilities, the GLAST LAT can form ''images'' in high energy gamma-rays of dark matter substructures in the gamma-ray sky. We describe a preliminary feasibility study for indirect detection of milky way dark matter satellites using the GLAST LAT.

Authors:
;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
899209
Report Number(s):
SLAC-PUB-12339
TRN: US200708%%387
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Journal Name: Nucl.Phys.Proc.Suppl.173:60-63,2007; Conference: Prepared for 7th UCLA Symposium on Sources and Detection of Dark Matter and Dark Energy in the Universe, Marina de Rey, California, 22-24 Feb 2006
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DETECTION; GAMMA RADIATION; MILKY WAY; NONLUMINOUS MATTER; SATELLITES; SKY; UNIVERSE; Astrophysics,ASTRO

Citation Formats

Wai, Larry, and /SLAC. The Search for Milky Way Halo Substructure WIMP Annihilations Using the GLAST LAT. United States: N. p., 2007. Web. doi:10.2172/899209.
Wai, Larry, & /SLAC. The Search for Milky Way Halo Substructure WIMP Annihilations Using the GLAST LAT. United States. doi:10.2172/899209.
Wai, Larry, and /SLAC. Mon . "The Search for Milky Way Halo Substructure WIMP Annihilations Using the GLAST LAT". United States. doi:10.2172/899209. https://www.osti.gov/servlets/purl/899209.
@article{osti_899209,
title = {The Search for Milky Way Halo Substructure WIMP Annihilations Using the GLAST LAT},
author = {Wai, Larry and /SLAC},
abstractNote = {The GLAST LAT Collaboration is one among several experimental groups, covering a wide range of approaches, pursuing the search for the nature of dark matter. The GLAST LAT has the unique ability to find new sources of high energy gamma radiation emanating directly from WIMP annihilations in situ in the universe. Using it's wide band spectral and full sky spatial capabilities, the GLAST LAT can form ''images'' in high energy gamma-rays of dark matter substructures in the gamma-ray sky. We describe a preliminary feasibility study for indirect detection of milky way dark matter satellites using the GLAST LAT.},
doi = {10.2172/899209},
journal = {Nucl.Phys.Proc.Suppl.173:60-63,2007},
number = ,
volume = ,
place = {United States},
year = {Mon Feb 05 00:00:00 EST 2007},
month = {Mon Feb 05 00:00:00 EST 2007}
}

Conference:
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  • The LAT Dark Matter and New Physics Working group has been developing approaches for the indirect astrophysical detection of annihilation of dark matter. Our work has assumed that a significant component of dark matter is a new type of Weakly Interacting Massive Particle (WIMP). The annihilation of two WIMPs usually results in the production of many high energy gamma rays (>1 GeV) that can be well measured in the GLAST LAT if present. There is also the possibility to observe {gamma} lines from annihilation into {gamma}{gamma} and or {gamma}Z final states. In popular SUSY theories these line decays occur atmore » the 10{sup -4} to 10{sup -2} branching fraction level. Estimates of LAT sensitivity (at 5{sigma} above background) and upper limits (upper limit at the 95% confidence level) to these WIMP lines will be presented. These sensitivities are given in photons/cm2/sec/sr and so do not depend on the WIMP models. However, they do depend on the diffuse background model. The latter is derived from GALPROP[1] based on EGRET and other data in the EGRET energy range. We use extrapolations, provided by the GALPROP team to the higher energy range of 150 GeV explored in the preliminary line sensitivity study presented here. Comparison with theory depends upon the WIMP model (e.g., line energy and 1 or 2 lines), the DM halo model, and other astrophysics backgrounds. Thus estimates of the ability of the LAT to actually observe WIMP lines can vary over orders of magnitude depending upon which models are chosen.« less
  • The LAT Dark Matter and New Physics Working group has been developing approaches for the indirect astrophysical detection of annihilation of dark matter. Our work has assumed that a significant component of dark matter is a new type of Weakly Interacting Massive Particle (WIMP). The annihilation of two WIMPs usually results in the production of many high energy gamma rays (>1 GeV) that can be well measured in the GLAST LAT if present. There is also the possibility to observe {gamma} lines from annihilation into {gamma}{gamma} and or {gamma}Z final states. In popular SUSY theories these line decays occur atmore » the 10-4 to 10-2 branching fraction level. Estimates of LAT sensitivity (at 5{sigma} above background) and upper limits (upper limit at the 95% confidence level) to these WIMP lines will be presented. These sensitivities are given in photons/cm2/sec/sr and so do not depend on the WIMP models. However, they do depend on the diffuse background model. The latter is derived from GALPROP based on EGRET and other data in the EGRET energy range. We use extrapolations, provided by the GALPROP team to the higher energy range of 150 GeV explored in the preliminary line sensitivity study presented here. Comparison with theory depends upon the WIMP model (e.g., line energy and 1 or 2 hues), the DM halo model, and other astrophysics backgrounds. Thus estimates of the ability of the LAT to actually observe WIMP lines can vary over orders of magnitude depending upon which models are chosen.« less
  • We discuss the possibility of GLAST detecting gamma-rays from the annihilation of neutralino dark matter in the Galactic halo. We have used 'Via Lactea', currently the highest resolution simulation of cold dark matter substructure, to quantify the contribution of subhalos to the annihilation signal. We present a simulated allsky map of the expected gamma-ray counts from dark matter annihilation, assuming standard values of particle mass and cross section. In this case GLAST should be able to detect the Galactic center and several individual subhalos. One of the most exciting discoveries that the Gamma-ray Large Area Space Telescope (GLAST) could make,more » is the detection of gamma-rays from the annihilation of dark matter (DM). Such a measurement would directly address one of the major physics problems of our time: the nature of the DM particle. Whether or not GLAST will actually detect a DM annihilation signal depends on both unknown particle physics and unknown astrophysics theory. Particle physics uncertainties include the type of particle (axion, neutralino, Kaluza-Klein particle, etc.), its mass, and its interaction cross section. From the astrophysical side it appears that DM is not smoothly distributed throughout the Galaxy halo, but instead exhibits abundant clumpy substructure, in the form of thousands of so-called subhalos. The observability of DM annihilation radiation originating in Galactic DM subhalos depends on their abundance, distribution, and internal properties. Numerical simulations have been used in the past to estimate the annihilation flux from DM substructure, but since the subhalo properties, especially their central density profile, which determines their annihilation luminosity, are very sensitive to numerical resolution, it makes sense to re-examine their contribution with higher resolution simulations.« less
  • We identify 10-seven for the first time-elements of cold halo substructure (ECHOS) in the volume within 17.5 kpc of the Sun in the inner halo of the Milky Way. Our result is based on the observed spatial and radial velocity distribution of metal-poor main-sequence turnoff (MPMSTO) stars in 137 Sloan Extension for Galactic Understanding and Exploration lines of sight. We point out that the observed radial velocity distribution is consistent with a smooth stellar component of the Milky Way's inner halo overall, but disagrees significantly at the radial velocities that correspond to our detections. We show that all of ourmore » detections are statistically significant and that we expect no false positives. These ECHOS represent the observable stellar debris of ancient merger events in the stellar accretion history of the Milky Way, and we use our detections and completeness estimates to infer a formal upper limit of 0.34{sup +0.02} {sub -0.02} on the fraction of the MPMSTO population in the inner halo that belong to ECHOS. Our detections and completeness calculations also suggest that there is a significant population of low fractional overdensity ECHOS in the inner halo, and we predict that 1/3 of the inner halo (by volume) harbors ECHOS with MPMSTO star number densities n approx 15 kpc{sup -3}. In addition, we estimate that there are of order 10{sup 3} ECHOS in the entire inner halo. ECHOS are likely older than known surface brightness substructure, so our detections provide us with a direct measure of the accretion history of the Milky Way in a region and time interval that has yet to be fully explored. In concert with previous studies, our result suggests that the level of merger activity has been roughly constant over the past few Gyr and that there has been no accretion of single stellar systems more massive than a few percent of a Milky Way mass in that interval.« less
  • We find that the relative contribution of satellite galaxies accreted at high redshift to the stellar population of the Milky Way's smooth halo increases with distance, becoming observable relative to the classical smooth halo about 15 kpc from the Galactic center. In particular, we determine line-of-sight-averaged [Fe/H] and [{alpha}/Fe] in the metal-poor main-sequence turnoff (MPMSTO) population along every Sloan Extension for Galactic Understanding and Exploration (SEGUE) spectroscopic line of sight. Restricting our sample to those lines of sight along which we do not detect elements of cold halo substructure (ECHOS), we compile the largest spectroscopic sample of stars in themore » smooth component of the halo ever observed in situ beyond 10 kpc. We find significant spatial autocorrelation in [Fe/H] in the MPMSTO population in the distant half of our sample beyond about 15 kpc from the Galactic center. Inside of 15 kpc however, we find no significant spatial autocorrelation in [Fe/H]. At the same time, we perform SEGUE-like observations of N-body simulations of Milky Way analog formation. While we find that halos formed entirely by accreted satellite galaxies provide a poor match to our observations of the halo within 15 kpc of the Galactic center, we do observe spatial autocorrelation in [Fe/H] in the simulations at larger distances. This observation is an example of statistical chemical tagging and indicates that spatial autocorrelation in metallicity is a generic feature of stellar halos formed from accreted satellite galaxies.« less