Gamma-rays from Dark Matter Mini

Gamma-rays from Dark Matter
Mini-Spikes in Andromeda
Galaxy M31
Mattia Fornasa
Dipartimento di Fisica “G. Galilei”
I.N.F.N. Padova
based on astro-ph/0703757 by M. Fornasa, M. Taoso and G.Bertone
Journal Club Seminar – Giovedì 7 giugno 2007
Introduction
Evidences for Dark Matter (DM)
• WMAP measurement ( m=0.25)
• rotation curves of galaxies
• the “bullet” cluster
Open Problems
• DM nature
• DM interactions
Detection techniques
• signals from colliders
• direct detection
• indirect detection of annihilation
products such as neutrinos, antiprotons
or gamma-rays
M. Fornasa
Chandra photo album: X-ray
image of 1E0657-558
7 Giugno 2007
Introduction
Our work is focused on indirect detection: we are looking
for gamma-rays from DM annihilation in high-density
regions in the sky
(1)
• search for a signal from the Galactic Center
• H.E.S.S. reported an excess of gamma-rays
no possible interpretation as DM annihilation
H.E.S.S. collaboration,
astro-ph/0610509
M. Fornasa
7 Giugno 2007
Introduction
• Intermediate Mass Black Holes (IMBHs)
• located in mini-halos in the Galactic smooth DM profile
• necessity to consider an extragalactic source (M31)
G. Bertone,
astro-ph/
0603148
High-energy, point-like, unknown gamma-rays
sources in a 3° region around Andromeda would be
a clear and unquestionable signal for DM annihilations
around IMBHs
M. Fornasa
7 Giugno 2007
Intermediate Mass Black Holes (IMBHs)
• mass from 20 M to 106 M
• no one actually ever “detected” an
Intermediate Mass Black Hole
G. Bertone,
astro-ph/
0603148
Evidences for IMBHs:
• Ultra Luminous X-ray
sources (ULXs)
• extrapolation of Mrelation of SMBHs to
globular clusters
• IMBHs would provide
massive seeds for the
growth of SMBHs
Miller, Colbert, astro-ph/0308402
M. Fornasa
7 Giugno 2007
Intermediate Mass Black Holes (IMBHs)
1111111111111111111111
0000000000000000000000
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
0000000000000000000000
1111111111111111111111
G. Bertone,
astro-ph/
0603148
Koushiappas, Bullock, Dekel, astro-ph/0311487
M. Fornasa
7 Giugno 2007
Spike formation at the Galactic center
[M /kpc 3]
Galactic halo density profile is supposed to
be a Navarro-Frenk-White (NFW):
(3)
9
10
8
10
107
106
105
104
3
10
102
G. Bertone,
astro-ph/
0603148
From a power-law density
profile, a “spike” can form with
a new slope:
10
1
10-1 -2
10
10-1
1
10
102
3
10
r [kpc]
(4)
(5)
M. Fornasa
7 Giugno 2007
Spike formation at the Galactic center
Ullio, Zhao, Kamionkowski,
astro-ph/0101481
G. Bertone,
astro-ph/
0603148
From a NFW ( =-1) the final spike has
sp=-7/3
(6)
(7)
M. Fornasa
7 Giugno 2007
Spike formation at the Galactic center
Arguments against spikes formation:
• off-center black hole formation
• gravitational interaction with stars
• merger and BH binary effects
G. Bertone,
astro-ph/
0603148
Ullio, Zhao, Kamionkowski,
astro-ph/0101481
M. Fornasa
Merritt, Milosavljevic, Verde, Jimenez
astro-ph/0201376
7 Giugno 2007
IMBHs catalogue (Bertone, Zentner, Silk)
Focusing on astro-ph/0509565 by G. Bertone,
A. Zentner and J. Silk:
• initial catalogue of IMBHs
• merging tree
• selection of unmerged mini-halos
• no baryonic content and the BH lays in the center
G. Bertone,
astro-ph/
0603148
Bertone, Zentner, Silk,
Astro-ph/0509565
M. Fornasa
7 Giugno 2007
IMBHs catalogue for Andromeda
How IMBHs are characterized:
• realization ID
• Black Hole Mass [M ]
• IMBH distance from the center of the Galaxy [kpc]
• rsp [kpc]
• (rsp) [M /kpc3]
G. Bertone,
astro-ph/
0603148
Milky Way
Andromeda
Distance to
the center
8.5 kpc
784.0 kpc
Virial Mass
1.0B1012 M
6.8B1011 M
Virial Radius
205 kpc
180 kpc
Andromeda IMBHs are 65.2±14.5 per realization,
with an average mass of 1.5B105 M and
an average distance from M31 center of 32.3 kpc.
M. Fornasa
7 Giugno 2007
Annihilation Flux
(8)
G. Bertone,
astro-ph/
0603148
To compute the differential energy spectrum a particular
model of physics beyond the SM is needed:
(9)
(10)
M. Fornasa
7 Giugno 2007
Differential energy spectrum
FPS (Fornengo-Pieri-Scopel)
• MSSM is assumed and the DM candidate is the lightest
neutralino
• focused on hadronization of b quarks
• fit from simulated data, using standard package as PYTHIA
(x=E/m )
(10)
G. Bertone,
astro-ph/
0603148
a=-1.5
b=0.37
c=-16.05
d=18.01
e=-19.50
for m =1 TeV
M. Fornasa
7 Giugno 2007
Thresold effect
(11)
(12)
(Ethr=4 GeV)
G. Bertone,
astro-ph/
0603148
M. Fornasa
m = 50 GeV
5.26B10-11 cm-2s-1
m = 150 GeV
7.65B10-11 cm-2s-1
m = 300 GeV
6.92B10-11 cm-2s-1
m = 500 GeV
5.81B10-11 cm-2s-1
Ethr
m
ACTs
100 GeV
1 TeV
GLAST
4 GeV (see later)
150 GeV
7 Giugno 2007
Detection of IMBHs with ACTs
• m =1 TeV and v=3B10-26 cm3s-1
• Eth=100 GeV
• typical ACT angular resolution is 0.1°
• typical ACT effective area is 3B104 m2
• exposure time is 100 hours
M. Fornasa
7 Giugno 2007
Detection of IMBHs with ACTs
(13)
Origin of background:
• EGRET:
(14)
• Hadronic and electronic:
(15)
(16)
M. Fornasa
7 Giugno 2007
Detection of IMBHs with ACTs
ACT sensitivity for a 5 detection
results 1.6B10-12 cm-2s-1,
higher than the brightest bins of the previous sky map.
M. Fornasa
7 Giugno 2007
Detection of IMBHs with ACTs
Number of IMBHs over ACT sensitivity is
5.2 ± 3.1 for m =1 TeV
M. Fornasa
7 Giugno 2007
Detection of IMBHs with GLAST
• m =150 GeV and the energy threshold is 10 MeV
• GLAST angular resolution is expected to be 3° (from 10
MeV to 500 MeV), 0.5° (from 500 MeV to 4 GeV) and 0.15°
(above 4 GeV)
• a selection is made and only high-energy photons (above
4 GeV) are considered
• extragalactic background
• hadronic and electronic backgrounds are absent
• the effective area times the exposition time is roughly
8B109 cm2s
• the resulting sensitivity for a 2 months period is
1.1B10-10cm-2s-1
M. Fornasa
7 Giugno 2007
Detection of IMBHs with GLAST
Number of IMBHs over GLAST sensitivity is
17.1 ± 5.8 for m =150 GeV
M. Fornasa
7 Giugno 2007
Detection of IMBHs with GLAST
M. Fornasa
7 Giugno 2007
Conclusions
• fluxes from DM annihilations in mini-halos around IMBHs
that populate the Andromeda Galaxy have been computed
• detection with an ACT is very challenging, due to the
hadron background
• the scenario with GLAST is more promising, even if the
best angular resolution is achieved only after a strict selection
(very high-energy photons)
• the picture is that of isolated, point-like, bright sources
in a region 3° wide around the Andromeda center
M. Fornasa
7 Giugno 2007
Differential energy spectrum
FPS (Fornengo-Pieri-Scopel)
• MSSM is assumed and the DM candidate is a neutralino
• focused only on the main channel (hadronization of b quarks)
• fit from simulated data, using standard package as PYTHIA
(x=E/m )
• differential spectrum for leptons hadronization is
presented too (see later)
(17)
(a, b, c, d, e)=(-1.5, 0.37, -16.05, 18.01, -19.50)
(a, b, c, d, e)=(-1.31, 6.94, -4.93, -0.51, -4.53)
Kretzer Fragmentation Functions
• DM candidate is again a neutralino
• FF is the probability to have an hadron h with xQ2 from a parton
p with Q2
M. Fornasa
7 Giugno 2007
Differential energy spectrum
• focused on the photon production from a
quarks b (i.e. p=b, h= 0)
0
resulting from
(18)
• a flat spectrum for photons from pions is assumed
(19)
BBEG (Bergstrom-Bringmann-Eriksson-Gustafsson)
• differential spectrum is calculated for a DM candidate from
Universal Extra-Dimension, what is called B(1)
• contribution of primary photons from charged leptons is
no longer neglected (B(1)B(1) l+l-)
(20)
M. Fornasa
7 Giugno 2007
Differential energy spectrum
Flux from Andromeda
FPS
1.33B10-14 cm-2s-1
Kretzer FFs
9.79B10-13 cm-2s-1
BBEG
1.60B10-14 cm-2s-1
From now on, only the FPS parametrization
will be used
M. Fornasa
7 Giugno 2007
Exclusion Plot
• Solid line: all realizations with at least one
detectable IMBH
• Dashed line: 20 realizations over 200 with at
least one detectable IMBH
3
v [cm s-1]
10-24
10-25
10-26
10-27
10%
-28
10
10-29 0
M. Fornasa
200
400
600
800
1000
m [GeV]
7 Giugno 2007