gamma-rays from dark matter mini-spikes in andromeda galaxy m31
DESCRIPTION
Gamma-rays from Dark Matter Mini-Spikes in Andromeda Galaxy M31. Mattia Fornasa and Marco Taoso. based on astro-ph/0703757 by M. Fornasa, M. Taoso and G.Bertone. 2nd IDAPP 2days Meeting - Giovedì 3 maggio 2007. Introduction. Evidences for Dark Matter (DM) WMAP measurement ( W m =0.25) - PowerPoint PPT PresentationTRANSCRIPT
Gamma-rays from Dark MatterMini-Spikes in Andromeda Galaxy M31
Mattia Fornasa and Marco Taoso
2nd IDAPP 2days Meeting - Giovedì 3 maggio 2007
based on astro-ph/0703757 by M. Fornasa, M. Taoso and G.Bertone
Introduction
M. Fornasa and M.Taoso 3 Maggio 2007
Evidences for Dark Matter (DM)• WMAP measurement (m=0.25)• rotation curves of galaxies• the “bullet” cluster
Open Problems• DM nature• DM interactions• DM formation mechanism
Detection techniques• signals from colliders • direct detection• indirect detection of annihilation products such as neutrinos, antiprotons or gamma-rays
Chandra photo album: X-ray image of 1E0657-558
Introduction
M. Fornasa and M.Taoso 3 Maggio 2007
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• HESS reported an excess of gamma-raysno possible interpretation as DM annihilation
HESS collaboration, astro-ph/0610509
Introduction
M. Fornasa and M.Taoso 3 Maggio 2007
• Intermediate Mass Black Holes (IMBHs)• located in mini-halos in the Galactic smooth DM profile• necessity to consider an extragalactic source (M31)
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
G. Bertone,astro-ph/0603148
G. Bertone,astro-ph/0603148
Intermediate Mass Black Holes (IMBHs)
M. Fornasa and M.Taoso 3 Maggio 2007
• mass from 20 M to 106 M
• no one actually ever “detected” an Intermediate Mass Black Hole
Miller, Colbert, astro-ph/0308402
Evidences for IMBHs:• Ultra Luminous X-ray sources (ULXs)• extrapolation of M- relation of SMBHs to globular clusters• IMBHs would provide massive seeds for the growth of SMBHs
G. Bertone,astro-ph/0603148
Intermediate Mass Black Holes (IMBHs)
M. Fornasa and M.Taoso 3 Maggio 2007
G. Bertone,astro-ph/0603148
Spike formation at the Galactic center
M. Fornasa and M.Taoso 3 Maggio 2007
Galactic halo density profile is supposed to be a Navarro-Frenk-White (NFW):
(3)
From a power-law density profile, a “spike” can form with a new slope:
(4)
(5)
G. Bertone,astro-ph/0603148
Spike formation at the Galactic center
M. Fornasa and M.Taoso 3 Maggio 2007
Ullio, Zhao, Kamionkowski, astro-ph/0101481
(6)
(7)
From a NFW (=-1) the final spike has sp=-7/3
G. Bertone,astro-ph/0603148
Spike formation at the Galactic center
M. Fornasa and M.Taoso 3 Maggio 2007
Arguments against spikes formation:• off-center black hole formation• gravitational interaction with stars• merger effects• “loss-cone”, DM that falls inside rSchw
Ullio, Zhao, Kamionkowski, astro-ph/0101481
Merritt, Milosavljevic, Verde, Jimenez astro-ph/0201376
G. Bertone,astro-ph/0603148
IMBHs catalogue (Bertone, Zentner, Silk)
M. Fornasa and M.Taoso 3 Maggio 2007
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
Bertone, Zentner, Silk,Astro-ph/0509565
G. Bertone,astro-ph/0603148
IMBHs catalogue for Andromeda
M. Fornasa and M.Taoso 3 Maggio 2007
Milky Way Andromeda
Distance to the center
8.5 kpc 784.0 kpc
Virial Mass 1.0·1012 M 6.8·1011 M
Virial Radius
205 kpc 180 kpc
How IMBHs are characterized:• realization ID• Black Hole Mass [M]• IMBH distance from the center of the Galaxy [kpc]• rsp [kpc]• (rsp) [M/kpc3]
Andromeda IMBHs are 65.2±14.5 per realization, with an average mass of 1.54·105 M and an average distance from M31 center of 32.3 kpc.
G. Bertone,astro-ph/0603148
Annihilation Flux
M. Fornasa and M.Taoso 3 Maggio 2007
(8)
To compute the differential energy spectrum a particular model of physics beyond the SM is needed:
(9)
(10)
G. Bertone,astro-ph/0603148
M. Fornasa and M.Taoso 3 Maggio 2007
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)
(a, b, c, d, e)=(-1.5, 0.37, -16.05, 18.01, -19.50)
(10)
Differential energy spectrum
Kretzer Fragmentation Functions (www.pv.infn.it/%7Eradici/FFdatabase)• DM candidate is again a neutralino• photon production from a 0 resulting from quarks b
(11)
G. Bertone,astro-ph/0603148
M. Fornasa and M.Taoso 3 Maggio 2007
(12)
Differential energy spectrum
BBEG (Bergstrom-Bringmann-Eriksson-Gustafsson)• 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-)
M. Fornasa and M.Taoso 3 Maggio 2007
Detection of IMBHs with ACTs
• m=1 TeV and v=3·10-26 cm3s-1
• Eth=100 GeV• typical ACT angular resolution is 0.1°• typical ACT effective area is 3·104 m2
• exposure time is 100 hours
M. Fornasa and M.Taoso 3 Maggio 2007
Detection of IMBHs with ACTs
(13)
(14)
Origin of background:• EGRET:
• Hadronic and electronic:
(16)
(15)
M. Fornasa and M.Taoso 3 Maggio 2007
Detection of IMBHs with ACTs
ACT sensitivity for a 5 detectionresults 1.6·10-12 cm-2s-1, higher than the brightest bins of the previous sky map.
M. Fornasa and M.Taoso 3 Maggio 2007
Detection of IMBHs with ACTs
Number of IMBHs over ACT sensitivity is 5.2 ± 3.1 for m=1 TeV
M. Fornasa and M.Taoso 3 Maggio 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 8·109 cm2s
• the resulting sensitivity for a 2 months period is 1.1·10-10cm-2s-1
M. Fornasa and M.Taoso 3 Maggio 2007
Detection of IMBHs with GLAST
Number of IMBHs over GLAST sensitivity is 17.1 ± 5.8 for m=150 GeV
M. Fornasa and M.Taoso 3 Maggio 2007
Detection of IMBHs with GLAST
M. Fornasa and M.Taoso 3 Maggio 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 and M.Taoso 3 Maggio 2007
Differential energy spectrum
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
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)
(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)
(17)
• focused on the photon production from a 0 resulting from quarks b (i.e. p=b, h=0)
• a flat spectrum for photons from pions is assumed
(18)
(19)
M. Fornasa and M.Taoso 3 Maggio 2007
Differential energy spectrum
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 and M.Taoso 3 Maggio 2007
Differential energy spectrum
Flux from Andromeda
FPS 1.33·10-14 cm-2s-1
Kretzer FFs
9.79·10-13 cm-2s-1
BBEG 1.60·10-14 cm-2s-1
From now on, only the FPS parametrization will be used
M. Fornasa and M.Taoso 3 Maggio 2007
Differential energy spectrum
(Ethr=4 GeV)
m = 50 GeV
5.26·10-11 cm-
2s-1
m = 150 GeV
7.65·10-11 cm-
2s-1
m = 300 GeV
6.92·10-11 cm-
2s-1
m = 500 GeV
5.81·10-11 cm-
2s-1
Ethr m
ACTs 100 GeV 1 TeV
GLAST
4 GeV (see later)
150 GeV
(20)
(21)
M. Fornasa and M.Taoso 3 Maggio 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