Gamma-rays from Dark Matter Mini-Spikes in Andromeda Galaxy M31

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Gamma-rays from Dark Matter Mini-Spikes in Andromeda Galaxy M31 Mattia Fornasa and Marco Taoso 2nd IDAPP 2days Meeting - Giovedì 3 maggio 200 based on astro-ph/0703757 by M. Fornasa, M. Taoso and G.Bert

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 Presentation

Transcript of Gamma-rays from Dark Matter Mini-Spikes in Andromeda Galaxy M31

Page 1: Gamma-rays from Dark Matter Mini-Spikes in Andromeda  Galaxy M31

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

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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

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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

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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

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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

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G. Bertone,astro-ph/0603148

Intermediate Mass Black Holes (IMBHs)

M. Fornasa and M.Taoso 3 Maggio 2007

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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)

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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

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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

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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

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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.

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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)

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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)

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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-)

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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

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Detection of IMBHs with ACTs

(13)

(14)

Origin of background:• EGRET:

• Hadronic and electronic:

(16)

(15)

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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.

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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

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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

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Detection of IMBHs with GLAST

Number of IMBHs over GLAST sensitivity is 17.1 ± 5.8 for m=150 GeV

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M. Fornasa and M.Taoso 3 Maggio 2007

Detection of IMBHs with GLAST

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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

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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)

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• 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)

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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

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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)

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Exclusion Plot

• Solid line: all realizations with at least one detectable IMBH• Dashed line: 20 realizations over 200 with at least one detectable IMBH