2016A&A...595A..25S

Query : 2016A&A...595A..25S

2016A&A...595A..25S - Astronomy and Astrophysics, volume 595A25-25 (2016/11-1)

Search for 511 keV emission in satellite galaxies of the Milky Way with INTEGRAL/SPI.

SIEGERT T., DIEHL R., VINCENT A.C., GUGLIELMETTI F., KRAUSE M.G.H. and BOEHM C.

Abstract (from CDS):

Context. The positron (e+) annihilation γ-ray signal in the Milky Way (MW) shows a puzzling morphology: a very bright bulge and a very low surface-brightness disk. A coherent explanation of the e+ origin, propagation through the Galaxy and subsequent annihilation in the interstellar medium has not yet been found. Tentative explanations involve e+s from radioactivity, X-ray binaries, and dark matter (DM).
Aims. Dwarf satellite galaxies (DSGs) are believed to be dominated by DM and hence are promising candidates in the search for 511keV emission as a result of DM annihilation into e+e–-pairs. The goal of this study is to constrain possible 511keV γ-ray signals from 39 DSGs of the MW and to test the annihilating DM scenario.
Methods. We used the spectrometer SPI on INTEGRAL to extract individual spectra for the studied objects in the range 490-530keV. As the diffuse galactic 511keV emission dominates the overall signal, we modelled the large-scale morphology of the MW accordingly and included this in a maximum likelihood analysis. Alternatively, a distance-weighted stacked spectrum was determined, representing an average DSG seen in 511keV.
Results. Only Reticulum II (Ret II) shows a 3.1σ signal. Five other sources show tentative 2σ signals. The ratio of mass to 511keV luminosity, Υ511, shows a marginal trend towards higher values for intrinsically brighter objects in contrast to the mass-to-light ratio, ΥV in the V band, which is generally used to uncover DM in DSGs.
Conclusions. All derived 511keV flux values or upper limits are above the flux level implied by a DM interpretation of the MW bulge signal. The signal detected from Ret II is unlikely to be related to a DM origin alone, otherwise, the MW bulge would be ∼100 times brighter in 511keV than what is seen with SPI. Ret II is exceptional considering the DSG sample and rather points to enhanced recent star formation activity if its origins are similar to processes in the MW. Understanding this emission may provide further clues regarding the origin of the annihilation emission in the MW bulge.

Abstract Copyright: © ESO 2016

Journal keyword(s): gamma rays: general - ISM: general - galaxies: dwarf - techniques: spectroscopic - dark matter

Simbad objects: 43

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Number of rows : 43
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 HD 225001 * 00 02 32.3999067312 +16 15 23.627167164   7.29 7.23     A0 22 0
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 12317 1
3 NAME Sculptor Dwarf Galaxy G 01 00 09.4 -33 42 32   9.79 8.6 8.81   ~ 1498 4
4 NAME Phoenix Dwarf Galaxy Sy1 01 51 06.3 -44 26 41   13.48 13.2 12.69   ~ 575 2
5 NAME Segue 2 G 02 19 16.0 +20 10 31     15.2     ~ 299 0
6 NAME Eri III G 02 22 45.480 -52 17 04.92           ~ 79 0
7 MCG-06-07-001 G 02 39 59.3 -34 26 57   9.02 7.4     ~ 1894 1
8 NAME Hor I G 02 55 31.7 -54 07 08           ~ 169 0
9 NAME Reticulum II G 03 35 42.1 -54 02 57           ~ 375 0
10 NAME Eridanus II G 03 44 21.1 -43 32 00           ~ 216 0
11 NAME Pic I G 04 43 47.4 -50 16 59           ~ 58 0
12 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
13 M 1 SNR 05 34 31.8 +22 01 03           ~ 6516 1
14 ESO 206-20A G 06 41 36.7 -50 57 58   22.14 11.0 19.47   ~ 1190 0
15 NAME CMa Dwarf Galaxy G 07 12.6 -27 40     -0.1     ~ 203 1
16 NAME UMa II Galaxy G 08 51 30.0 +63 07 48     13.3     ~ 410 0
17 NAME Leo T G 09 34 53.4 +17 03 05     15.1     ~ 434 0
18 NAME Segue 1 G 10 07 03.2 +16 04 25     15.3     ~ 517 1
19 Z 64-73 G 10 08 28.12 +12 18 23.4   11.3 10.0     ~ 1284 1
20 NAME Sextans dSph LSB 10 13 02.9 -01 36 53   12 10.4     ~ 921 0
21 NAME UMa I Galaxy G 10 34 52.80 +51 55 12.0     14.4     ~ 355 1
22 NAME Willman 1 G 10 49 21.0 +51 03 00     15.2     ~ 345 0
23 NAME UMa Region reg 11 00 +50.0           ~ 333 0
24 Z 126-111 G 11 13 28.13 +22 09 10.1   12.9 12.0     ~ 899 0
25 NAME Leo V LSB 11 31 09.60 +02 13 12.0     16.0     ~ 234 0
26 NAME Leo IV LSB 11 32 57.0 -00 32 00     15.1     ~ 419 1
27 NAME Coma Dwarf Galaxy G 12 26 59.0 +23 54 15     14.1     ~ 482 1
28 NAME CVn II dSph G 12 57 09.6 +34 19 12     16.1     ~ 287 2
29 NAME Bootes III G 13 57 07.4 +26 46 30     12.6     ~ 115 1
30 NAME Bootes II G 13 58 00.0 +12 51 00     15.4     ~ 269 0
31 NAME Bootes Dwarf Spheroidal Galaxy G 14 00 00.0 +14 30 00     12.8     ~ 491 0
32 Z 318-18 G 15 09 08.0 +67 13 21   13.60 10.6     ~ 1459 0
33 NAME Hercules Dwarf Galaxy G 16 31 02.0 +12 47 30     14.0     ~ 379 1
34 NAME Galactic Center Spur Rad 16 41 -39.1           ~ 13 1
35 Z 300-12 G 17 20 14.335 +57 55 16.39   12.40 10.6     ~ 1428 1
36 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 16269 0
37 NAME SDG G 18 55 19.0 -30 32 43   4.5 3.6     ~ 2438 2
38 NGC 6822 G 19 44 56.199 -14 47 51.29   18 8.1     ~ 1661 0
39 HD 226868 HXB 19 58 21.6757355952 +35 12 05.784512688 9.38 9.72 8.91 8.42   O9.7Iabpvar 4590 0
40 NAME Tuc II G 22 51 55.1 -58 34 08           ~ 192 0
41 NAME Grus I G 22 56 42.4 -50 09 48           ~ 126 0
42 NAME Pisces II G 22 58 31.0 +05 57 09     16.3     ~ 283 0
43 NAME Phe II G 23 39 59.4 -54 24 22           ~ 107 0

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