Ruling out thermal dark matter with a black hole induced spiky profile in the M87 galaxy Based on arxiv:1505.00785 (IAP, Paris) in collaboration with Joseph Silk (IAP) & Céline Bœhm (IPPP, Durham) PACIFIC 2015 September 12-19, 2015
Introduction Indirect detection promising avenue to look for DM particles using astrophysical observations Here focus on DM annihilations Annihilation signals ρ 2 especially interesting at the centers of galaxies due to overdensities Challenging to disentangle DM signatures from more conventional sources look for characteristic features
DM spike Slow growth of supermassive black hole (BH) at the center of a galaxy dense DM spike ρ(r) r 7/3 (Gondolo & Silk 1999) Strong annihilation signals Caveats Spike can be destroyed by mergers; weaker cusp if BH growth not 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: 10 5 Gyr vs several Gyr for the Milky Way M87 dynamically young spike much more likely to have survived in M87 huge potential for indirect detection signals
Spectral energy distribution from DM Upper limits Prompt emission dominant contribution to γ-rays Large magnetic fields expected in the inner region significant contribution from synchrotron emission 10-10 10-11 10-12 10-10 10-8 10-6 E γ (GeV) 10-4 10-2 10 0 10 2 10 4 m DM =100 GeV, σv =3.94 10 29 cm 3 s 1 νf ν (erg cm 2 s 1 ) 10-12 10-13 10-14 10-15 10-16 10-17 bb DM HESS 2004 MOJAVE 2009 Fermi LAT 10 months Historical Chandra VERITAS 2007 MAGIC 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 10 26 10 28 ν (Hz)
Spectral energy distribution from DM Upper limits Upper limits from requirement that DM-induced signal do not overshoot the data 10-25 spike 10-26 σv (cm 3 s 1 ) 10-27 10-28 10-29 10-30 10-31 e + e µ + µ τ + τ bb Thermal s-wave qq tt Z Z h h 10 1 10 2 10 3 10 4 10 5 m DM (GeV)
Spectral energy distribution from DM Upper limits These limits exclude thermal s-wave DM up to 100 TeV! Caveat: assumption that spike with ρ r 7/3 was effectively produced 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
Spectral energy distribution from DM Upper limits Much weaker constraints in the absence of a spike (NFW only) s 1 ) 10-18 10-19 10-20 10-21 e + e µ + µ τ + τ bb Thermal s-wave NFW qq tt Z Z h h σv (cm 3 10-22 10-23 10-24 10-25 10-26 10 1 10 2 10 3 10 4 10 5 m DM (GeV)
Dark matter spikes around black holes The jet Synchrotron self-compton model Upper limits with DM+jet DM and TeV gamma-ray emission Powerful jet in M87 Look for emission brighter than the jet But jet model not yet perfectly constrained
The jet Synchrotron self-compton model Upper limits with DM+jet DM and TeV gamma-ray emission SSC model from Finke et al. 2008, parameters from Abdo et al. 2009 10-10 10-11 10-12 10-10 10-8 10-6 E γ (GeV) 10-4 10-2 10 0 10 2 10 4 B =55 mg, δ D =3.9, R b =4.5 mpc νf ν (erg cm 2 s 1 ) 10-12 10-13 10-14 10-15 10-16 SSC model HESS 2004 MOJAVE 2009 Fermi LAT 10 months Historical Chandra VERITAS 2007 MAGIC 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 10 26 10 28 ν (Hz)
The jet Synchrotron self-compton model Upper limits with DM+jet DM and TeV gamma-ray emission Exclusion if departure from the best fit at 2σ 10-25 spike +jet σv (cm 3 s 1 ) 10-26 10-27 10-28 10-29 10-30 10-31 10-32 10-33 e + e µ + µ τ + τ bb Thermal s-wave qq tt Z Z h h 10 1 10 2 10 3 10 4 10 5 m DM (GeV)
The jet Synchrotron self-compton model Upper limits with DM+jet DM and TeV gamma-ray emission SSC model underestimates the TeV emission... 10-10 10-11 10-12 10-10 10-8 10-6 E γ (GeV) 10-4 10-2 10 0 10 2 10 4 B =55 mg, δ D =3.9, R b =4.5 mpc νf ν (erg cm 2 s 1 ) 10-12 10-13 10-14 10-15 10-16 SSC model HESS 2004 MOJAVE 2009 Fermi LAT 10 months Historical Chandra VERITAS 2007 MAGIC 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 10 26 10 28 ν (Hz)
The jet Synchrotron self-compton model Upper limits with DM+jet DM and TeV gamma-ray emission Unless we include TeV DM! Suggested by Saxena et al. 2011 for NFW 10-10 10-11 10-12 10-10 10-8 10-6 E γ (GeV) 10-4 10-2 10 0 10 2 10 4 m DM =23.0 TeV, σv =3.9 10 27 cm 3 s 1 νf ν (erg cm 2 s 1 ) 10-12 10-13 10-14 10-15 10-16 bb DM SSC model DM +SSC HESS 2004 MOJAVE 2009 Fermi LAT 10 months Historical Chandra VERITAS 2007 MAGIC 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 10 26 10 28 ν (Hz) But with spike much smaller cross section needed
The jet Synchrotron self-compton model Upper limits with DM+jet DM and TeV gamma-ray emission Good fit for channels with spectra softer than electrons and muons 10-10 10-11 10-12 10-10 10-8 10-6 E γ (GeV) 10-4 10-2 10 0 10 2 10 4 m DM =2.1 TeV, σv =4.4 10 28 cm 3 s 1 νf ν (erg cm 2 s 1 ) 10-12 10-13 10-14 10-15 10-16 τ + τ DM SSC model DM +SSC HESS 2004 MOJAVE 2009 Fermi LAT 10 months Historical Chandra VERITAS 2007 MAGIC 10 10 10 12 10 14 10 16 10 18 10 20 10 22 10 24 10 26 10 28 ν (Hz)
Conclusion Strong case for a DM spike with ρ r 7/3 in M87 (heating by stars negligible) Extremely stringent constraints on σv vs m DM that exclude thermal 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 annihilation cross sections 10 27 cm 3 s 1 in the presence of a spike Similar results expected for galaxies with similar SMBH Strong motivations to look for DM spikes!
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