The Extragalactic
Background Light in theFermi-LAT era
Alberto Domínguez
Universidad Complutense de Madrid

M. Ajello, K. Helgason, J. Finke, A. Desai, V. Paliyaand also R. Wojtak, F. Prada, L. Marcotulli, D. Hartmann

Fermi-LAT Collaboration, 2018, Science, 362, 1031
Desai et al., 2019, ApJL, 874, 7
Domínguez et al., 2019, arXiv:1903.12097
Domínguez, Primack, Bell
Scientific American, June 2015

Seminar @ Institute for Cosmic-Ray Research - September 4, 2019

The Extragalactic
Background Light in theFermi-LAT era
Alberto Domínguez
Universidad Complutense de Madrid

M. Ajello, K. Helgason, J. Finke, A. Desai, V. Paliya
and also R. Wojtak, F. Prada, L. Marcotulli, D. Hartmann

Fermi-LAT Collaboration, 2018, Science, 362, 1031
Desai et al., 2019, ApJL, 874, 7Olber's Paradox

Domínguez et al., 2019, arXiv:1903.12097

Domínguez, Primack, Bell
Scientific American, June 2015

Seminar @ Institute for Cosmic-Ray Research - September 4, 2019

Galaxy Evolution and Cosmology
Ωb baryons

Scientific American, June 2015

Ωm = Ωb + ΩDΩm + ΩΛ= 1ΩΛ dark energyΩD dark matterCosmic Diffuse Extragalactic Backgrounds

Artistic representationof a binary system
Crab Nebula

From Reinhard Genzel's lecture@ Jerusalem Winter School 2013

Artistic representationof a blazar

Orion Nebula(birth place of stars)

Measuring the Extragalactic Background Light

DIRBE imaged the sky in 10 photometricbands from 1.25 to 240 microns with abeam size of 0.7x0.7 sq. degrees

Measuring the Extragalactic Background LightEBL

EBL is an order of magnitude
lower than foregrounds and subject
to large systematic uncertainties,e.g. Gorjian+ 00
Zodiacal light, visible under the right conditions: typicallyafter the sunset in Spring and right before sunrise in Autumn

Measuring the Extragalactic Background Light

Stars + AGNs

UV

opticalnear-IR

Dust + AGNs

mid-IR

far-IR

M31 view from the UV to the far-IR, Credit: NASA & ESA

Measuring the Extragalactic Background Light

Number counts in the
Hubble Deep Field,e.g. Madau & Pozzetti, 2000

Measuring the Extragalactic Background Light

UV

opticalnear-IR

mid-IR

far-IR

M31 view from the UV to the far-IR, Credit: NASA & ESA

Measuring the Extragalactic Background LightTheoretical(e.g. Gilmore+ 12; Inoue+ 13)

Direct galaxyobservations

Over redshift(e.g. Domínguez+ 11;
Helgason+ 12; Stecker+ 16)

Observational
TheoreticalIndirect observations(e.g. Kneiske+ 10; Finke+ 10;
Khaire+ 14)

Local(e.g. Stecker+ 06;
Franceschini+ 08)

Extragalactic Background Light (Local)

z=0Extragalactic Background Light (Evolution)

Strong divergenceGamma-ray Attenuation
Extragalactic source:
e.g. Blazar
Blazars: AGNs emitting at all wavelengthwith energetic jets pointing towards us.

Pair-production interaction
Reverse of most known electron-positronannhilation process

Telescopes: Fermi-LAT andImaging Atmospheric
Cherenkov Telescopes(IACTs)Ilustration: Nina McCurdy & Joel Primack

Gamma-ray Attenuation

distancecross section
EBL photon density evolution

Ilustration: Nina McCurdy & Joel Primack

Gamma-ray Telescopes
Fermi-LAT

All-sky, Energy range
100 MeV – 100 GeV

CTA North, La Palma (Spain)
VERITAS, Arizona (USA)

IACTs
Small field of view, Highsensitivity, Energy range
100 GeV – 10s TeV
H.E.S.S., Namibia

MAGIC, La Palma (Spain)

Gamma-ray Cherenkov Telescopes (IACTs)

Gamma-ray Cherenkov Telescopes (IACTs)

Gamma-ray Cherenkov Telescopes (IACTs)

NASA’s Fermi Gamma-Ray Space Telescope
Launch June 11, 2008
Celebrating
10th year Anniversary

1. Tracking system:- convert an incident gamma-ray to an electron-positron pair
- reconstruct the gamma-ray direction from the tracks of the pair
2. Calorimeter:- measure the photon energy
3. Anti-coincidence detector:- limit the cosmic-ray background● Wide field of view (2.4 sr, 20% ofthe sky)
● Large effective area (~0.9 m2
above 1 GeV)
● Low dead time (~27 μs)s)

The Gamma-Ray Sky

2000

Fermi-LAT All-Sky Map Above 1 GeV

2000

2018

Gamma-ray Fermi-LAT Catalogs
4FGL
8 years (P8), 5065 sources
3FHL
7 years (P8), 1556 sources
2FHL
1FHL

6.7 years (P8), 360 sources

3 years (P7), 514 sources

3FGL

4 years (P7Rep), 3033 sources

0.1

110GeV

1001000

Blazars

Boston University - Cosmovision

Emission described by homogeneoussynchrotron/synchrotron-self Compton model.

Optical Depths from Gamma-ray Data

Optical Depths from Gamma-ray Data

Optical Depths from Gamma-ray Data
From detection (2012) to characterization (Now)

4 billion yearsCosmic Gamma-Ray Horizon

Cosmic Gamma-Ray Horizon

See also Fazio & Stecker 1970,
Domínguez et al. 2013

Cosmic Gamma-Ray Horizon

See also Fazio & Stecker 1970,
Domínguez et al. 2013

Galaxy Luminosity Densities and EBL
Luminosity density evolution as sumof log-normal distributions that canevolve independently

Galaxy Luminosity Densities and EBLFirst EBL determination at z>0Cosmic Star Formation RateUV (0.16 microns) to SFR:(1) Initial Mass Function(2) Average Galaxy Extinction

Re-ionization of the Universe

Re-ionization of the Universe

Constraints fromgamma-ray attenuation

Optical Depths from Gamma-ray Data

Extragalactic Background Light from Gamma Rays

Local Extragalactic Background Light(also see works by the MAGIC, VERITAS, andH.E.S.S. Collaborations)Tension on H0 Measurements

Gamma-ray Attenuation

distancecross section
EBL photon density evolution
See Domínguez & Prada 13,
Biteau & Williams 15

Ilustration: Nina McCurdy & Joel Primack

Measuring H0 with Gamma-ray AttenuationTension on H0 Measurements

Measuring H0 and Ωmwith Gamma-ray Attenuation

Take Home Messages
1.- Very significant detection and characterization of the EBL attenuation up to z~3.
2.- Complete derivation so far of the local EBL and its evolution over redshift
from Fermi-LAT and Cherenkov data.
3.- Derived Cosmic Star formation Rate Density up to z~5 unbiased fromdifferent galaxy survey incompleteness.
4.- Cosmological measurement of H 0 and Ωm from our independent technique.

Gamma-ray astronomy has matured enoughand is providing useful measurements ingalaxy evolution and cosmology

BackupCosmology Dependence on the Optical Depth

Comparison with other Methodologies

Combination oftechniques is important
to control systematics

EBL models: Finke+ 10

EBL models: Domínguez+ 11

0.7 sq. deg.
EGS field

SED fitting

Total: 5986 galaxies

Galaxy luminosity function
rest-frame K-band, Cirasuolo+ 10