Ruling out thermal dark matter with a black hole induced ...

Dark matter spikes around black holesWhy M87?

Upper limits on the annihilation cross section with DM onlyDM and AGN jet in M87

Ruling out thermal dark matter with a blackhole induced spiky profile in the M87 galaxy

Based on arXiv:1505.00785

Thomas Lacroix (IAP, Paris)in collaboration with Joseph Silk (IAP) & Céline Bœhm (IPPP, Durham)

PACIFIC 2015

September 12-19, 2015

Thomas Lacroix Ruling out thermal DM with a BH induced spiky profile in M87



IntroductionIndirect detection promising avenue to look for DM particlesusing astrophysical observations

Here focus on DM annihilations

Annihilation signals ∝ ρ2

⇒ especially interesting at the centers of galaxies due tooverdensities

Challenging to disentangle DM signatures from moreconventional sources⇒ look for characteristic features




DM spike

Slow growth of supermassive black hole (BH) at the center of agalaxy⇒ dense DM spike ρ(r) ∝ r−7/3 (Gondolo & Silk 1999)⇒ Strong annihilation signals

CaveatsSpike can be destroyed by mergers; weaker cusp if BH growthnot exactly at the center (Gnedin & Primack 2004): ρ(r) ∝ r−1/2

−→ Lots of uncertainty on these processes

Most importantly: scattering of DM particles off stars (Gnedin& Primack 2004, Vasiliev & Zelnikov 2008)⇒ smoother profile ρ(r) ∝ r−3/2

−→ Unavoidable in principle




Why is M87 interesting?

Dynamical relaxation time in M87: 105 Gyr vs several Gyr for theMilky Way⇒ M87 dynamically young⇒ spike much more likely to have survived in M87⇒ huge potential for indirect detection signals




Spectral energy distribution from DMUpper limits

Prompt emission dominant contribution to γ-raysLarge magnetic fields expected in the inner region⇒ significantcontribution from synchrotron emission

1010 1012 1014 1016 1018 1020 1022 1024 1026 1028

ν (Hz)

10-17

10-16

10-15

10-14

10-13

10-12

10-11

10-10

νFν(e

rgcm

−2

s−1)

mDM =100 GeV,⟨σv⟩=3.94×10−29 cm3 s−1

b̄b

DM

HESS 2004

MOJAVE 2009

Fermi−LAT 10 months

Historical

Chandra

VERITAS 2007

MAGIC

10-12 10-10 10-8 10-6 10-4 10-2 100 102 104Eγ (GeV)





Upper limits from requirement that DM-induced signal do notovershoot the data

101 102 103 104 105

mDM (GeV)

10-31

10-30

10-29

10-28

10-27

10-26

10-25

⟨ σv⟩(c

m3

s−1)

spike

e+ e−

µ+ µ−

τ+ τ−

b̄b

Thermal s-wave

q̄q

t̄t

Z Z

h h





These limits exclude thermal s-wave DM up to 100 TeV!

Caveat: assumption that spike with ρ ∝ r−7/3 was effectivelyproduced and survived

Constraints essentially given by prompt γ-ray emission⇒ independent of the magnetic field model

Robust to absorption processes

Conversely if thermal s-wave DM confirmed, spike ruled out⇒ information on history of the galaxy





Much weaker constraints in the absence of a spike (NFW only)

101 102 103 104 105

mDM (GeV)

10-26

10-25

10-24

10-23

10-22

10-21

10-20

10-19

10-18⟨ σv⟩

(cm

3s−

1)

NFW

e+ e−

µ+ µ−

τ+ τ−

b̄b

Thermal s-wave

q̄q

t̄t

Z Z

h h




The jetSynchrotron self-Compton modelUpper limits with DM+jetDM and TeV gamma-ray emission

Powerful jet in M87

Look for emission brighterthan the jet

But jet model not yetperfectly constrained





SSC model from Finke et al. 2008, parameters from Abdo et al. 2009

1010 1012 1014 1016 1018 1020 1022 1024 1026 1028

ν (Hz)

10-16

10-15

10-14

10-13

10-12

10-11

10-10νF

ν(e

rgcm

−2

s−1)

B=55 mG, δD =3.9, R ′b =4.5 mpc

SSC model

HESS 2004

MOJAVE 2009


Historical

Chandra

VERITAS 2007

MAGIC

10-12 10-10 10-8 10-6 10-4 10-2 100 102 104Eγ (GeV)





Exclusion if departure from the best fit at 2σ

101 102 103 104 105

mDM (GeV)

10-33

10-32

10-31

10-30

10-29

10-28

10-27

10-26

10-25⟨ σv⟩

(cm

3s−

1)

spike+jet

e+ e−

µ+ µ−

τ+ τ−

b̄b

Thermal s-wave

q̄q

t̄t

Z Z

h h





SSC model underestimates the TeV emission...

1010 1012 1014 1016 1018 1020 1022 1024 1026 1028

ν (Hz)

10-16

10-15

10-14

10-13

10-12

10-11

10-10νF

ν(e

rgcm

−2

s−1)

B=55 mG, δD =3.9, R ′b =4.5 mpc

SSC model

HESS 2004

MOJAVE 2009


Historical

Chandra

VERITAS 2007

MAGIC

10-12 10-10 10-8 10-6 10-4 10-2 100 102 104Eγ (GeV)





Unless we include TeV DM! Suggested by Saxena et al. 2011 for NFW

1010 1012 1014 1016 1018 1020 1022 1024 1026 1028

ν (Hz)

10-16

10-15

10-14

10-13

10-12

10-11

10-10νF

ν(e

rgcm

−2

s−1)

mDM =23.0 TeV,⟨σv⟩=3.9×10−27 cm3 s−1

b̄b

DM

SSC model

DM +SSC

HESS 2004

MOJAVE 2009


Historical

Chandra

VERITAS 2007

MAGIC

10-12 10-10 10-8 10-6 10-4 10-2 100 102 104Eγ (GeV)

But with spike much smaller cross section neededThomas Lacroix Ruling out thermal DM with a BH induced spiky profile in M87




Good fit for channels with spectra softer than electrons and muons

1010 1012 1014 1016 1018 1020 1022 1024 1026 1028

ν (Hz)

10-16

10-15

10-14

10-13

10-12

10-11

10-10νF

ν(e

rgcm

−2

s−1)

mDM =2.1 TeV,⟨σv⟩=4.4×10−28 cm3 s−1

τ+ τ−

DM

SSC model

DM +SSC

HESS 2004

MOJAVE 2009


Historical

Chandra

VERITAS 2007

MAGIC

10-12 10-10 10-8 10-6 10-4 10-2 100 102 104Eγ (GeV)




ConclusionStrong case for a DM spike with ρ ∝ r−7/3 in M87 (heating bystars negligible)

Extremely stringent constraints on 〈σv〉 vs mDM that excludethermal s-wave DM up to ∼ 100 TeV

Requirement: spike effectively formed and not destroyed

TeV DM can account for the TeV γ-ray emission for annihilationcross sections . 10−27 cm3 s−1 in the presence of a spike

Similar results expected for galaxies with similar SMBH

Strong motivations to look for DM spikes!




Thank you for your attention!


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