Jonathan Biteau

​

2025.02.10, IFPU Focus Week: IGMF

What do we know about the propagation of astroparticles

in the intergalactic medium?

, nucleus

Credit: F. Bradascio

My main research interests

• Non-thermal and thermal extragalactic sources
• Propagation in the intergalactic medium
• Detection on Earth

Collaborations

• H.E.S.S. (‘10-’13)
• VERITAS (‘13-’15)
• Auger (‘15-’26)
• CTAO (‘10-X), incl. NectarCAM (‘15-X)

Some close collaborators

on topics related to this talk

Q. Luce ( ‘18), S. Marafico (PhD ‘21),

L. Gréaux (PhD ‘24), B. Biasuzzi (postdoc),

A. Condorelli (postdoc).

+ special thanks to: M. Meyer, E. Pueschel, I. Vovk,

O. Deligny, D. Harari, R. Adam, D. Williams, M. Nievas,

T. Hassan, J. Becker-Tjus, K.H. Kampert, C. Bérat

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2

Extragalactic astroparticles

Intro

astroparticles & cosmic backgrounds

The physics of propagation

radiative and catastrophic losses

deflections, delays and spreads

Inferences from observations

TeV gamma rays

EeV nuclei

Outro

summary & open questions

Broad-band spectra of the sources

4

Adapted from

C. Harrison’s thesis (2014)

Massive short-lived stars

Credits: NASA/ESA/Bacon

Light-weight long-lived stars

Credits: Gemini Obs./AURA/Cook

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Interstellar dust

Credits: Gemini Obs./AURA/Cook

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Broad-band spectra of the sources

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5

Non-jetted AGN

Credits: NASA/JPL-Caltech

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Jetted AGN

Credits: ESA/NASA/AVO/Padovani

Adapted from

C. Harrison’s thesis (2014)

Synthesis models of all galaxies

6

Solution to Olbers’ paradox

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Madau & Dickinson ‘14

7

Voids

Their accumulated contributions today

Where propagation matters

Intro

astroparticles & cosmic backgrounds

The physics of propagation

radiative and catastrophic losses

deflections, delays and spreads

Inferences from observations

TeV gamma rays

EeV nuclei

Outro

summary & open questions

The diffusion-loss equation (Fokker-Planck)

9

Starting from the Vlasov equation (e.g. review by Becker-Tjus & Merten ‘20)

• Test particle approach
• Stationary magnetic field
• Isotropy in momentum phase space

n ≡ differential number density in phase space

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Gamma-ray catastrophic losses: pair production on COB/CIB

10

Optical depth

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Light travel distance (ΛCDM)

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Mean free path (photon density, Breit-Wheeler cross section)

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where

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→

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1 TeV

1 eV

1 MeV²

JB & Williams ‘15

Cross-section integrated

over the line of sight

Relevant threshold for gamma-rays:

E ~ 100 GeV ↔ ϵ ~ 10 eV (UV bckgd)

Radiative losses of e⁺ e⁻: inverse Compton on CMB

11

1 meV

1 GeV

ɣ_e = 10⁶

Generation 1: TeV gamma-ray

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Generation 2: pair e⁺ e^-

• Diffuse in〈B²〉
• Excite electrostatic instability of beam (~ 10^-22 cm^-3) / intergalactic plasma (~ 10^-7 cm^-3)

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• Inefficient E-loss mechanism due to
• background MeV e^- (Yang+ ApJ ‘24)
• non-linear feedback (Alawashra & Pohl ApJ ‘24)
• B > 10^-17 G (λ_B/1 pc)^-½ (Alawashra & Pohl ApJ ‘22)
• Inverse Compton on CMB photons

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Generation 3: GeV gamma-ray → stop

4th generation if

E₀ ~ 10 TeV (plausible)

5th generation if

E₀ ~ 100 TeV

→ unobserved & Klein-Nishina suppressed

Continuous losses of protons: p-ɣ on the CMB

12

Credit: Aloisio ‘17

Threshold for π photoproduction

2m_p m_π / 4ϵ ~ 50 EeV x (λ / 1 mm)

Note: p @ 50 EeV → unobserved

Center of mass

(50 EeV x 1 meV)^½ ~ 0.2 GeV

Neutron = proton in the IGM

ɣcτ ~ 10 kpc x (E / 1 EeV)

c/H₀

Catastrophic losses of nuclei: photo-erosion/disintegration

13

Credit: Aloisio ‘17

Photo-erosion driven by

• ϵ_ɣ’ ~ 10 MeV: giant dipole resonance

→λ_ɣ ~ 0.5 mm (CMB) for E_X/A ~ 2 EeV

• ϵ_ɣ’ ~ 30 MeV: quasi-deuteron process
• ϵ_ɣ’ > 150 MeV: baryon resonance

→λ_ɣ ~ 30 µm (CIB) for E_X/A ~ 2 EeV

Lower energy nuclei and protons

→ with Lorentz boost nearly conserved

Cosmic-ray propagation on extragalactic scales

Addazi+, PrPNP ‘22, see also Allard, JCAP ‘06

14

D_T ~ 14 Gyr

D_L ~ 1 Gpc

or D_T ~ 2.5 Gyr

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Cosmic-ray propagation on extragalactic scales

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D_L ~ 1 Gpc

or z ~ 0.2

15

Addazi+, PrPNP ‘22, see also Allard, JCAP ‘06

Cosmic-ray propagation on extragalactic scales

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D_L ~ 150 Mpc

or z ~ 0.03

Tully+, Nature ‘14

16

Addazi+, PrPNP ‘22, see also Allard, JCAP ‘06

Cosmic-ray propagation on extragalactic scales

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D_L ~ 15 Mpc

McCall, MNRAS ‘14

17

Addazi+, PrPNP ‘22, see also Allard, JCAP ‘06

Intro

astroparticles & cosmic backgrounds

The physics of propagation

radiative and catastrophic losses

deflections, delays and spreads

Inferences from observations

TeV gamma rays

EeV nuclei

Outro

summary & open questions

19

200 Mpc

Credit: McCall MNRAS ‘14

(The Council of Giants)

l = 10 Mpc

Credit: Hackstein+ MNRAS ‘18 (Cosmic V-web constrained sim. / CLUES)

Cosmic web: relevant scales

20

200 Mpc

Credit: Oei+ A&A ‘22

Credit: Hackstein+ MNRAS ‘18 (Cosmic V-web constrained sim. / CLUES)

Cosmic web: volume filling fraction

21

Voids: B < 10 pG

Jedamzik & Saveliev ‘19

Sheets: B ~ 1-10 nG?

Clusters: B ~ 1-10 µG

e.g. Bonafede+ ‘10

200 Mpc

Credit: Hackstein+ MNRAS ‘18 (Cosmic V-web constrained sim. / CLUES)

Cosmic web: magnetic fields

Astrophysical B-seeds

Filaments: B ~ 10-100 nG

Vernstrom+ ‘21, Carretti+ ‘22

22

Voids: B < 10 pG

Jedamzik & Saveliev ‘19

Sheets: B ~ 1-10 nG?

Clusters: B ~ 1-10 µG

e.g. Bonafede+ ‘10

200 Mpc

Credit: Hackstein+ MNRAS ‘18 (Cosmic V-web constrained sim. / CLUES)

Cosmic web: magnetic fields

Filaments: B ~ 10-100 nG

Vernstrom+ ‘21, Carretti+ ‘22

Primordial B-seeds

Cosmic-ray propagation in a turbulent magnetic field

23

ultra-high energy cosmic rays

in the Local Sheet

• From first principles, assuming a quasi-static turbulent B-field:
• Treatment of propagation using stochastic differential equation

(see Achterberg+ ‘99, Marafico’s thesis - chap. 6, App. B)

• Signal delayed by τ_del, temporally spread by Δτ = τ_del √2 (superluminal!)
• Angularly spread by Δθ

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Voids: B < 10 pG

• Too low to have a sizeable impact within cosmic-ray horizon

(see Pierre Auger Collab. ‘24)

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The Local Sheet: B ~ B_filaments?

• Translucent, w/ angular spread θ_{obs, UHECR} ~ Δθ_{Local Sheet}
• Time spread → d_min = extent of B_{Local Sheet} ~ few Mpc

Galaxy filaments: B ~ 10-100 nG

• Translucent to UHE nuclei
• No need for specific treatment

Galaxy clusters: B ~ 1-10 µG

• Calorimeters for UHE nuclei

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EeV cosmic rays in the cosmic web

24

Condorelli, JB, Adam, ApJ ‘23

Cosmic-ray propagation in a turbulent magnetic field

25

• From first principles, assuming a quasi-static turbulent B-field:
• Treatment of propagation using stochastic differential equation

(see Achterberg+ ‘99, Marafico’s thesis - chap. 6, App. B)

• Signal delayed by τ_del, temporally spread by Δτ = τ_del √2
• Angularly spread by Δθ

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electrons from TeV gamma-rays in voids

Credit: Bray & Scaife ApJ ‘18

Cosmic-ray propagation in a turbulent magnetic field

26

• From first principles, assuming a quasi-static turbulent B-field:
• Treatment of propagation using stochastic differential equation

(see Achterberg+ ‘99, Marafico’s thesis - chap. 6, App. B)

• Signal delayed by τ_del, temporally spread by Δτ = τ_del √2
• Angularly spread by Δθ

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electrons from TeV gamma-rays in voids

secondary gamma-rays from these electrons

Voids

27

H.E.S.S. ApJL ‘23

Jonathan Biteau

​

2025.02.10, IFPU Focus Week: IGMF

What do we know about the propagation of astroparticles

in the intergalactic medium?

Part 2

Intro

astroparticles & cosmic backgrounds

The physics of propagation

radiative and catastrophic losses

deflections, delays and spreads

Inferences from observations

TeV gamma rays

EeV nuclei

Outro

summary & open questions

30

JB & Meyer, Galaxies ‘22

Fermi-LAT

(GeV range)

HESS, MAGIC, VERITAS

(TeV range)

Known extragalactic sources of gamma rays

Signature of the COB/CIB in gamma-ray spectra

31

TeV gamma-ray suppression

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with

Credit: L Gréaux

TeV gamma-ray suppression

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Gréaux & JB, ApJL ‘24

32

Fermi-LAT

(GeV range)

HESS, MAGIC, VERITAS

(TeV range)

Credit: L Gréaux

Signature of the COB/CIB in gamma-ray spectra

Dataset and analysis

Parameters: ɑ (EBL), Θ (intrinsic spectra)

with

Marginalization:

33

Dataset = 268 TeV spectra

= 3 x JB & Williams ‘15

Gréaux, JB, Nievas Rosillo, ApJL 2024

Credit: L Gréaux

for Michele

The cosmological optical convergence

34

Good match: probe of H₀ within ± 10%

as τ_ɣɣ ∝ I_EBL x c / H₀= (1+f_diff) x I_IGL x c / H₀

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New Horizons

Hubble

HESS, MAGIC, VERITAS

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Gréaux, JB, Nievas Rosillo, ApJL 2024

35

Credit: Neronov & Vovk 2010

Credit: JB+ 2020

Discovery of extreme TeV blazars in 2006

Hard TeV photon spectrum when corrected for absorption

Intrinsic emission expected to be faint in the GeV band

Reprocessed emission?

None in 2010 within point spread function

⇒ minimum B-field needed to spread out the signal

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Search for the e⁺ e⁻ reprocessed energy

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Expected for

B ~ 3 × 10^-16 G

36

Neronov & Vovk Science ‘10

H.E.S.S. ApJL ‘23

Search for the e⁺ e⁻ reprocessed energy

Observed

Constraints on magnetic fields in voids

37

Primordial origin

Status and expectations

Current-generation: B > 10-100 fG,

CTAO discovery at 5σ up to 300 fG (CTAO JCAP ‘21)

Patchy B-field generation models disfavored:

VFF < 0.67 excluded at 95% C.L. (Tjemsland+ ApJ ‘24)

Primordial ↗ - Astrophysical ↘

Credit: Hackstein+ MNRAS ‘18

Primordial B-seeds

Astrophysical B-seeds

H.E.S.S. ApJL ‘23

Intro

astroparticles & cosmic backgrounds

The physics of propagation

radiative and catastrophic losses

deflections, delays and spreads

Inferences from observations

TeV gamma rays

EeV nuclei

Outro

summary & open questions

The quest for UHECR origins

Auger, PRL (2020)

Ultra-high energy cosmic rays (UHECRs)

Long thought to be of extragalactic origin > 5 EeV (0.8 J!), marking the ankle

Observed spectral features: instep at 10-15 EeV, toe at 40-50 EeV

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Credits: Jorge Cham

& Daniel Whiteson

39

Auger Coll; PRD ‘20, PRL ‘20, EPJC ‘21, PoS(ICRC2023) by Brichetto

Today’s picture on

Coleman+,

Astropart. Phys. ‘22

40

Combining observables to search for UHECR origins

Auger, PRL (2020)

Fit of synthetic model of source population

to spectrum and composition data

Spectral and composition observables integrated over the sphere

→ help constrain source distance distribution & source escape spectrum

Ankle at > 5 EeV (0.8 J!) marks the transition to a purely extragalactic origin,

with the onset of He nuclei

Observed spectral features: instep at 10-15 EeV, toe at 40-50 EeV

→ markers of ~Peters cycle (acceleration up to E_max(Z) ~ Z × 5 EeV)

→ hard nuclear emission at sources (dN/dE ∝ E^±1 vs E^-2, explained e.g. by escape

from magnetized region within the sources)

→ reservoir of heavy elements? Accelerated material from exceptional metal sources /

from sources low in H and He.

Anisotropy observables

→ break down the flux (and composition) vs arrival direction: pinpoint sources?

if cosmic magnetism does not prevent it!

Auger Coll., PRD/PRL ‘20

41

Some landmarks in Auger anisotropy studies

Auger, Science 2007

Auger (incl. JB), Science 2017

Auger, ApJL 2018, led by JB

~ 27 evts ≥ 57 EeV

~ 32,000 evts ≥ 8 EeV

~ 900 evts ≥ 39 EeV

First steps: hint

20 out of 27 evts within 3°

of nearby galaxies → ~3σ

10 evts in particular clustered

in the Centaurus region

Maturity: discovery

6σ dipolar-like flux

In line with nearby

galaxy stellar mass

distribution (2MRS)

Revival: a trail?

4σ evidence for ~10% excess from nearby

starbursts (23 brightest)

Now 4.5σ

Auger, JCAP ‘24

Alves Batista+ (incl. JB) ‘19

42

Why would UHECR sources be transient?

• Hillas-Lovelace-Waxman: high-luminosity sources
• Composition: H/He-poor material from (high-mass) stars
• Minimum distance: for an observer in a large-scale B-field

Starbursts host more frequent stellar explosions…

Credit: S. Marafico

B = 0

2d_min

UHECR burst

B > 0

Source

43

Marafico, JB+, ApJ ‘24

( 2MASS Photometric z catalog ⋂ WISE ) ✖ HyperLEDA (JB, ApJS ‘21)

Catalog of 400k galaxies out to d_max = 350 Mpc

Completeness in stellar mass: 50% at d_max (× 2 wrt 2MRS)

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Mapping out stellar matter in the GZK horizon

Marafico, JB+ ‘24

400k SFGs

XS~100%?

Cosmic V-web, Pomarède+ 2017

JB ‘21

~8k galaxies

~400k galaxies

44

JB, ApJ ‘21

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1D visualization vs d out to 350 Mpc (vs 135 Mpc in Karachentsev+ 2018)

→ Full-sky plateau beyond 100 Mpc matches deep-field observations (Driver+ 2018)

→ Northern matches Southern hemisphere beyond 100 Mpc: negligible N/S dipole ~ isotropic regime

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3D visualization out to 350 Mpc (see interactive figures of the Local Superclusters, Local Clusters and Local Sheet)

→ Good agreement with V-web from Cosmicflows (Hoffman+ 2017, Dupuy +2019) on supercluster scales

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Validation: do we grasp all M_★ and SFR?

45

Local Group

Local Sheet

Virgo cluster

Laniakea supercluster

for Klaus

Increasing value of burst rate per star-formation unit k, for a given B-field in the Local Sheet

Transient model of UHECR sky

Spectral & composition model (see also Luce+ ApJ ‘22)

Marafico, JB, Condorelli, Deligny, Bregeon, ApJ ‘24

46

Candidate ultra-high-energy sources

Auger + TA data

Credits: L. Caccianiga for Auger & TA

Best-match transient scenario

Credits: Marafico, JB+ ‘24

UHECR Model ≈ UHECR Data

Δθ(hotspot_model, hotspot_data) < 40°

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47

Marafico, JB, Condorelli, Deligny, Bregeon, ApJ ‘24

Solution with at least 1 Northern & Southern hotspot found for

Local Sheet B_rms = 0.5 - 20 nG

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Auger + TA data

Credits: L. Caccianiga for Auger & TA

Best-match transient scenario

Credits: Marafico, JB+ ‘24

UHECR Model ≈ UHECR Data

Δθ(hotspot_model, hotspot_data) < 40°

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Candidate ultra-high-energy sources

48

Marafico, JB, Condorelli, Deligny, Bregeon, ApJ ‘24

X-ray transient rate vs kinetic energy

Tidal Disruption Events, Short GRB, Long GRB

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Coherent deflections in the Milky Way

Auger + TA data

Credits: L. Caccianiga for Auger & TA

Best-match transient scenario

Credits: Marafico, JB+ ‘24

Regular B_{Milky Way}

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49

​

Jansson & Farrar ‘12

Marafico, JB, Condorelli, Deligny, Bregeon, ApJ ‘24

Credits: Farrar ‘15

Intro

astroparticles & cosmic backgrounds

The physics of propagation

radiative and catastrophic losses

deflections, delays and spreads

Inferences from observations

TeV gamma rays

EeV nuclei

Outro

summary & open questions

• Measurement of the cosmic-ray spectrum above the ankle (5 EeV)

with 1% precision up to instep (15 EeV), 5% up to the suppression (40 EeV)

and 30% up to 100 EeV.

• Statistical measurement of nuclear composition up to 40 EeV: A↗ as E↗

(from shower-depth moments), ongoing improvements with surface detectors

⇾ further room for improvement with Auger Prime (radio signals, scintillators)

• High-precision (Z ~ 7σ) of 6% dipole above the ankle, exciting prospects

with Z ~ 5σ (soon?) for θ ~ 20° anisotropy above the suppression

⇾ observational confirmation of extragalactic origin, which sources?

• Propagation losses well constrained, cosmic magnetism too poorly known

⇾ although dipole and intermediate-scale anisotropies qualitatively reproduced,

even the best current models are unable to satisfactorily fit to both

• Emerging synthesis population models of UHECR sources, promising to solve a long-standing mystery (!),

but in-source processes (acceleration, losses, escape) still underconstrained.

⇾ use best-fit synthesis models to constrain B-fields (in particular Galactic)?

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Conclusions and outlook: cosmic-ray propagation

51

Local Sheet B_rms = 0.5 - 20 nG

Can it be measured

through radio observations?

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• Model-independent measurement of Extragalactic Background Light:

O-IR backgrounds at z = 0 with 10-25% precision depending on λ

• Precision on Hubble constant: 5% (model-dep.) to 10% (model-indep.)

assuming no unresolved diffuse component in galaxy counts

⇾ could become relevant if Hubble tension not solved by JWST observations

• Probe of UV emissivity at high z (e.g. z ~ 6 in Fermi-LAT Science ‘18)

room for improvement with archival and upcoming CTAO data?

⇾ timely in the context of JWST observations

• opportunity to probe B-field in voids (and study the intergalactic plasma)

little room left for plasma instabilities as main E-loss or p-diffusion mechanism

⇾ comparison with models goes in the direction of primordial origin of B-fields,

but without clearly preferred mechanism and without irrefutable observations (!)

• growing body of studies of cosmic-web impact on propagation (e.g. Bondarenko+ A&A ‘22, Abdalla+ MNRAS ‘24)

⇾ timely in the context of LSST and Euclid observations

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Conclusions and outlook: gamma-ray propagation

52

Web

CTAO-N

Game changer: The Cherenkov Telescope Array Observatory

53

By 2026

4 LSTs and 1 MSTs

installed on CTAO-N

2 MSTs and 2 MSTs

installed on CTAO-S

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CTAO-S

Jonathan Biteau

Backup

15 l_em

Detection of ɣ-rays near Earth

55

Telescope-based: 100 GeV - 100 TeV

O(10%) duty cycle, ~ 2 km above sea level

Cameras with O(1000) PMTs and ns sampling

Lead experiments: HESS, MAGIC, VERITAS

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Satellite-based: 100 MeV - 1 TeV

O(100%) duty cycle, ~ 550 km altitude

Tracker with SSDs, CsI(Tl) with photodiodes

Lead experiment: Fermi-LAT

Performance > 10 GeV

energy resolution ~10-20%

angular resolution ~0.1°

40 l_em

CTAO-N

CTAO-S

2 sites to access the entire sky

w/ breakthrough performance

Sensitivity: 5-10× better than current

E-range: 0.02-200 TeV (vs 0.1-10 TeV)

E-resolution: <10% (vs <17%) >0.2 TeV

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HEGRA (‘90s)

MAGIC (‘00s,’10s)

CTAO-N (‘20s-‘40s)

Game changer: The Cherenkov Telescope Array Observatory

CTAO-S (‘20s-‘40s)

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Magnetic fields in voids

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What is known about the extragalactic background

58

Back-of-envelope estimates

5.0 ± 0.6 eV / m³

15, 000 ± 600

eV / m³

Contaminants in the O/IR

59

Credits: L. Gréaux

Adapted from Leinert ‘97 & JB ‘23

Zodiacal light, integrated star light, diffuse galactic light (cirrus)¹

@ 0.55 µm

Credits: Lasue 2020

The light that remains once (all?) foregrounds are removed

60

Dark-patch estimates in 0.3-5µm

roughly consistent with 1% Zodi

Ca-II absorption lines by CIBER

→ unaccounted for (Kelsall+ ‘98)

faint spherical Zodi component

Status of COB-CIB models: a TeV appraisal @ z < 1

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Lowest tension with direct measurements and galaxy counts @ z = 0 Lowest tension with TeV ɣ rays

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Credit: L. Gréaux

(Biteau, Gréaux, Condorelli, in prep.)

62

The largest cosmic-ray observatory ever built

Credits: Alves Batista+ Front.Astron.Space ‘19

This talk

The Pierre Auger Observatory

West Argentina at 1,400m a.s.l., spread over 3,000 km² (~ Luxembourg or Rhode Island)

1600 water Cherenkov detectors (12t each) to measure secondary particles in air showers

+ 27 fluorescence telescopes (440 px / cam) to image the air showers during dark time

Phase 1 (2004-2021): ~150,000 events above the ankle over ~80,000 km² yr sr

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Exposure = A_eff × T

→ 40-70x larger than previous generation experiments (AGASA, HiRES)

→ 8x larger than complementary Northern hemisphere experiment (Telescope Array)

62

Event reconstruction: surface detector (SD)

Auger Coll., ApJS 2023

Example:

The hybrid event

with the highest energy

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Above the ankle:

ΔE/E < 15%

Δθ ~ 1°

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Event reconstruction: fluorescence detector (FD)

Auger Coll., ApJS 2023

Example:

The hybrid event

with the highest energy

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64

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# evolution along propagation:

Aloiso, Berezinsky, Grigorieva (2013)

Propagation of protons

No absorption term → sharp wall at ~ 100 EeV for D ~ 100 Mpc, pile-up feature

Propagation of nuclei

Dominated by single-nucleon photo-dissociation → ~ exp. attenuation at ~20/50 EeV for D ~ 100/10 Mpc

Single

source

nitrogen

Single

source

protons

Energy losses:

e^+/- or π production

Absorption:

photo-dissociation

Injection:

source or cascade

UHECR propagation on extragalactic scales

66

Credit: Hillas, Topical Review in J. Phys. G: Nucl. Part. Phys. 31 (2005)

Component A

fully ionized H, He, … , Fe with a slope ɣ ~ 2.7 up to R_A ~ 3 PV

Component B

Something still has to be added to the ‘KASCADE’ component ‘A’

M. Hillas (2005)

Component C EGT = EGp + EGHe

fully ionized H and He (heavier) with absorption features due to extragalactic propagation

Before the Pierre Auger Observatory

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Today’s picture

Auger Coll., PRD ‘20, PRL ‘20, Eur. Phys. J. C ‘21, PoS(ICRC2021) by Novotny, PoS(ICRC2023) by Brichetto

67

The UHECR Background

68

Credits: Tsunesada+ ‘21

Credits: Tinyakov+ ‘21

matched E-scales

Shower slant depth: a proxy for

Auger Coll., PoS(ICRC23) by Salamida

Independent measurements of X_max at the Pierre Auger Observatory

High Elevation Auger Telescopes (low E) Auger Engineering Radio Array

Fluorescence Detector Surface Detector (DNN)

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Auger Coll., sub. to PRL

69

Hillas: only the highest-energy

Confinement, i.e. large B-field, size, and shock velocity:

B ⨯ ( r ⨯ Γ ) ⨯ β_shock > ( E / Ze ).

Hillas-Lovelace-Waxman: only the brightest

In an expanding plasma, magnetic luminosity:

L_B > 3 ⨯ 10⁴⁴ erg/s ⨯ ( E/Z / 10 EeV )² ⨯ ( Γ²/β_shock / 10).

Arrival directions: only the numerous

UHECR flux above the ankle:

number density x luminosity > 10³⁰ UHECR / Mpc³ / s

No significant self-clustering above flux suppression:

number density > 10^-5 / Mpc³ (if deflections < 30°)

Work hypothesis: transient UHECR sources

Active Galactic Nuclei vs Gamma-ray bursts

Only the numerous, escape → low-luminosity preferred

Only the brightest → constrains the min luminosity

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Plausible ultra-high energy accelerators

Long GRBs

· mostly hosted by star-forming galaxies

· star-formation rate traced by thermal emission (UV, Hα, FIR)

Jetted AGNs

· mostly hosted by elliptical galaxies

· traced by non-thermal emission (radio, X rays, γ rays)

Alves Batista+, Front.Astron.Space Sci. 6 (2019) 23

70

Why would UHECR sources be transient?

• Hillas-Lovelace-Waxman: high-luminosity sources
• Composition: material from (high-mass) stars

Helium / Heavy nuclei proportion (Marafico, JB+ ‘24)

​

​

would be 18 ± 2 if ISM picked-up material

​

+ good agreement of heavy to intermediate-mass nuclei with

composition of massive stars stripped of their H-He envelopes

see also Zhang, Murase, Oikonomou ‘17

Starbursts host more frequent stellar explosions…

Marafico, JB+ ‘24

71

Exploiting the HyperLEDA database

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Limitations of GLADE / MANGROVE

Mix of overlapping catalogs: risk of duplicate entries, possibly direction-dependent flux limit

Fully exploiting distance databases

Local Volume (1k gal., d < 11 Mpc, Karachentsev+ 2018) and HyperLEDA (5M gal., Makarov+ 2014)

Distance revision: cosmic ladder > spectro-z > photo-z

Cosmic-ladder distances for ~1k nearby objects, spectro-z x 4 → 200k/400k within 350 Mpc

Stellar mass estimates

K-band for Local Volume, W1-band otherwise, with M_*/L = 0.6 (M_⊙/L_⊙), i.e. Chabrier IMF

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Association results

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• 671,593 / 743,480 HyperLEDA

pairings (others = 2MASS

objects not in HyperLEDA)

• 361 duplicates removed

• 1,387 excluded entries:

- dubious duplicates removed

- jetted AGN from HyperLEDA

Observations in the Local Volume

Aim for volume limited sample to d < 11 Mpc or v_LG < 600 km/s

Distances based on usual cosmic-ladder estimates (supernovae,

Cepheids, Tully-Fisher, Faber-Jackson) + tip of the red giant branch

→ avoid biases induced by peculiar motion, distance uncertainty: 5-25%

Information available from Karachentsev+ 2018

• M_★: stellar mass from K band (1022/1029)

• T: de Vaucouleurs’ morphology (1028/1029), special attention to dwarfs

• M(HI): atomic hydrogen mass, tracing gas (819/1029)

• SFR(FUV): mostly based on GALEX observations (647/1029)

• SFR(Hα): from literature & dedicated surveys (470/1029)

Main sequence of galaxies in the Local Volume?

SFR-M_* branch occupied by Irregular (Irr.) and Spiral (S.) galaxies

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Antennae: NGC4038/4039

(ESA/Hubble)

Small Magellanic Cloud

(ESO/VISTA VMC)

Messier 83

(ESO)

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Karachentsev+ 2013

Equatorial coordinates

Main sequence in the Local Volume

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SFR tracers in the Local Volume

• Hα: 5-10 Myrs timescale, fraction of ionizing photons from young massive stars absorbed before being reprocessed into Hα

• FUV: 100-300 Myrs timescale, fraction of FUV photons from OB stars absorbed, often combined with total IR to estimate SFR

→ both corrected for extinction, i.e. escape from the galaxy

3 SFR-M_★ branches

→ E-S0: linear (ꞵ = 1.0-1.1 ± 0.10), i.e. no active star formation

→ S: sub-linear (ꞵ = 0.81-0.69 ± 0.07), active star formation >10 Myrs ago

→ Irr: super-linear (ꞵ = 1.22 ± 0.04), active star formation <10 Myrs ago

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Fit results with best morphological divide

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• KS-test p-value for Gaussian residuals ~ 5%,

4σ outliers → hidden variables (metallicity, environment)

• SFR dispersion of S: 0.24 dex (FUV-Hα), 0.34 dex (M_*-Hα)

J. Biteau – CTA-SFR – 2022.04.06

Incompleteness with increasing distance

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Mass function

Full-sky, including clones in the ZoA and weights as a function of galactic latitude

Best-fit double Schechter from GAMA-field observations (Wright+ 2017) scaled to observed integral, accounting for local overdensity

Low-mass end: (luminosity function) ✕ (fraction of observable objects above 2MPZ sensitivity limit, provided distances)

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Completeness

From integral of (GAMA mass function) ✕ M_* above 2MPZ sensitivity limit: weights = completeness(d) ✕ completeness(b) ∈ [0.26,1]

→ probed volume from 140 Mpc (2MRS) to 350 Mpc (2MPZ) at similar completeness: ✕ 2.6 (distance), ✕ 18 (volume)

→ further increase by ✕ 4 (distance) to be expected if full WISE x SuperCOSMOS potential exploited

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SFR estimation in and out the Local Volume

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~700 galaxies with tabulated Local Volume morphology

• SFR(Hα) measured > SFR(Hα) from M_*, T_LV

→ UL / LL on SFR(Hα) if larger / lower SFR(Hα) from M_★, T_LV

~150k galaxies with tabulated HyperLEDA morphology

• Exploit mapping of T_LV vs T_HL established in Local Volume

→ Irr / E-S0 confusion at 10-15% level

→ Mass-dependent Irr / S confusion

• SFR(Hα) from M_*, T_LV(T_HL)

~ 260k galaxies without morphological information

• Estimate average T_LV(T_HL) fraction assuming no selection bias

• Weighted average SFR(Hα) from M_*, T_LV(T_HL) for 3 morphologies

Correction for ionising fraction

• Account for ionising fraction f = 0.57 ± 0.21 (Hirashita+ 2003)

→ SFR(total) = SFR(Hα) / f - Note: large systematic from uncertainty on f

Incompleteness as a function of distance

• Weighted average of ∫ (GAMA mass function) ✕ M_★^ꞵ: weights(d,b) ∈ [0.16,1]

→ under the assumption of constant weights vs d (partly wrong < 50 Mpc)

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Bilicki+ 2013

galaxy

cloning

Incompleteness in the Zone of Avoidance

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Estimated based on galaxy counts in 100-300 Mpc (nearly isotropic distribution)

Equal area galactic latitude bins in inner and outer plane regions (|l|=30°)

Cosmic variance estimated from bin-to-bin fluctuations at l > 45°

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Corrections

Empirical Gaussian(sin b) fit used to infer galaxy weights:

• re-weighting sufficient in outer plane, insufficient in inner plane
• ZoA cut placed at ~50% incompleteness: l = 3° / 20° for outer / inner plane
• galaxy cloning (as in Lavaux & Hudson’s 2M++ 2011) in ZoA region