Particle dark
matter searches
via cross-correlation
betweengravitational lensing and gamma rays
Marco Regis(Torino)

The DM source
The DM-inducedemission is faintDM is the mostnumerous
population in theUniverse.
Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

General idea
Map

Even if DM halos are too
faint to be
individually detected,
they form the mostnumerous
population in theUniverse.

from

Lisa
nti+,
201
7The DM “cumulative” signal and its
spatial coherence (angular correlations)might be observable in the unresolved
extragalactic sky

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

Angular cross-correlation
Map where we believe a
DM-induced emission ispresent as unresolved component(or in the search for other types of sources:

BlazarMisaligned AGN

Star-forming GAL )Gravitational tracerof dark matter(e.g. lensing or galaxy catalog)< da(q1) db(q2) > → CCFab(|q1-q2|) → Clabcorrelation inphysical space

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

correlation inharmonic space

Marco RegisSearching for across-correlation signal between
the unresolved gamma-ray background andweak lensing cosmic shear
Chang+, 2017

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

A few attempts of measurement
Theoretical proposal in (Camera, Fornasa, Fornengo, MR, ApJL 2013)
Experimental
effort:2

CFHTLenS: 150 sq. deg. with 11 gal/arcmin , RCSLenS: 785 sq. deg. with 5.5 gal/arcmin2
Hyper Suprime-Cam 1yr: 137 sq. deg. with 25 gal/arcmin2, KIDS: 450 deg2 with 8 gal/arcmin2
Canada-France-Hawaii Lensing Survey(CFHTLenS) + 5yr Fermi LAT data
(Shirasaki+ PRD 2014)(CFHTLenS and RCSLenS) +7yr Pass8 Fermi LAT data
(Shirasaki+ PRD 2016)

1yr HSC +7yr Pass8 Fermi LAT data
(Shirasaki+ PRD 2018)(CFHTLenS, RCSLenS and KIDS) x 7yr Pass8Fermi LAT data between 0.5-500 GeV(Troester, MR+ MNRAS 2017)

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

DES x Fermi-LATDES 1yrXFermi-LAT 9yr

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

DES 1yr x Fermi-LAT 9yr
Dark Energy Survey (METACALIBRATION):
1500 sq. deg. with 5.5 gal/arcmin2

Fermi-LAT PASS8 9yr data
> 106 photons above 0.6 GeV(Zuntz+, MNRAS2018)

X
Prat+, PRD2018

432 data-points: 4 redshift bins (0.20 < z < 1.30) x 9 energy bins (0.6 GeV -1 TeV) x 12 angular bins (5 - 600 arcmin)
Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

First detection of the signal

Signaldetected withsignal-to-noise
ratio
S/N = 4.5

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

First detection of the signal
The signal is mostly localized atsmall angular scales.

Signaldetected withsignal-to-noise
ratio
S/N = 4.5

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

Energy and redshift dependence

The signal is mainly coming from γ-ray photons at energy above 5 GeV,
with a hard energy spectrum (spectral index > -2)
No strong indication about the redshift dependence.
Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

Where is the signal coming from?
Low-z: 0.20 < z < 0.63
High-z: 0.63 < z < 1.30

Low-E: E < 4.8 GeV
High-E: E > 4.8 GeV

Small-scales: < 3 x PSFFermi
Large-scales: > 3 x PSFFermi

The bulk of the signal comes from point-like sources
with a hard spectrum, most likely blazars hosted inmassive halos.
Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

Implications for particle dark matter
Hint (~2σ)) for a cross-correlation on “large” scales.
Possible interpretations:- statistical fluctuation or- population of blazars with different characteristics than those of resolved blazars or- additional component+ -ττCosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis

Summarizing
First ever detection of cross-correlation between
cosmic-shear and UGRB!
→  UGRB is correlated with mass distribution in the Universe
DM thermal cross section excluded for DM masses of tensof GeV and annihilations into hadronic channels, but
intriguing hints for higher masses/leptonic channels.
Stay tuned for the cross-correlation of Fermi -LAT datawith the forthcoming Year 3 and Year 5 DES data releases→  It will likely clarify the source of the signal

Cosmic Controversies Conference, 5 - 8 October 2019, Chicago

Marco Regis