The Extragalactic Background Light: Connecting Classical ...The Extragalactic Background Light:...

The Extragalactic Background Light:The Extragalactic Background Light:Connecting Classical andConnecting Classical andHigh Energy AstronomyHigh Energy Astronomy

Alberto Domínguez(Clemson University, South Carolina)

Collaborators:

Joel Primack, Marco Ajello, Francisco Prada, Justin Finke

Mainly based on the review article Domínguez & Primack (2015),

Reports on Progress in Physics, in prep. and also

partly on behalf of the Fermi collaboration

(Domínguez et al. 2013, ApJ, 770, 77 & Ackermann et al. 2015 in preparation)

NIRB2015 @ Garching bei München, Germany, June 1-3, 2015

Domínguez, Primack, Bell,Scientific American, 312, 6, June 2015

Diffuse extragalactic backgroundsDiffuse extragalactic backgrounds

From Genzel's lecture @ 2013 Jerusalem Winter School

● The EBL is the accumulated diffuse light produced by star formation processes and accreting black holes over the history of the Univere from the UV to the far-IR.

● It contains fundamental information about galaxy evolution, cosmology, and it is essential for the full energy balance of the Universe.

Scientific American, 312, 6, June 2015

The local spectral energy distribution of the EBLThe local spectral energy distribution of the EBL

optical

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

UV near-IR mid-IR far-IR

Domínguez & Primack, 15 in prep.

EBL modelsEBL models

ObservationalSemi-analytical(e.g. Gilmore+ 12,

Inoue+ 13)

Direct galaxy observations

(Luminosity functions)

Cosmic star-formation rate(e.g. Kneiske+ 10, Finke+ 10,

Khaire+ 14)

Over redshift(e.g. Domínguez+ 11,

Stecker+ 12, Helgason+ 12)

Mainly local(e.g. Stecker+ 06,Franceschini+ 08)

Type i: Forward evolutionType i: Forward evolution

Slide by Joel Primack

Examples of Λ Cold Dark Matter merger trees from

Wechsler+ 02

Our SAMs are based on Monte Carlo realizations of dark matter halo mergers histories calculated using the modified and extended Press-Schechter methods.

DEEP2 spectroscopic redshift: 4376 galaxiesPhotometric redshift with mean error less than 0.1: 1610 galaxies

Total: 5986 galaxies

EGS field

0.7 sq. deg.

Type iv: Direct galaxy observations over redshiftType iv: Direct galaxy observations over redshift

Data from the AEGIS collaboration, see Newman+ 13

Galaxy SED-type fractions, this work

Galaxy Spectral Energy Distributions (SEDs)SWIRE template library, Polletta+ 07

Galaxy luminosity functionrest-frame K-band, Cirasuolo+ 10

SED of the EBL

Type iv: Direct galaxy observations over redshiftType iv: Direct galaxy observations over redshift

Local EBL: Data and ModelsLocal EBL: Data and Models


Local EBL: Data and ModelsLocal EBL: Data and Models

Conclusion 1: The EBL contains a bolometric intensity between 50 and 70 nW/m2/sr (this is, about 5% of the CMB intensity).


Conclusion 2: Local galaxies typically have E_FIR/E_opt ≈ 0.3, while the EBL has E_FIR/E_opt = 1-2. Hence most high-redshift radiation was emitted in the far IR.

EBL evolution with redshiftEBL evolution with redshift


EBL evolution with redshiftEBL evolution with redshift


EBL models strongly diverge at high redshiftEBL models strongly diverge at high redshift

Improving the EBL modeling with galaxy surveysImproving the EBL modeling with galaxy surveys

COSMOS UDS

GOODS-SGOODS-N

EGS

Credit: ESA / AOES

Fields by Guillermo Barro

Gamma-Ray AttenuationGamma-Ray Attenuation

Scientific American, 312, 6, June 2015

Without EBL: intrinsic With EBL: observed

Distance (cosmology)

Cross section

EBL photon density evolution (cosmology)

Interaction angle


Local EBL: Local EBL: γ-ray dataγ-ray data

Different methodologies to estimate the intrinsic spectrum:

- No intrinsic curvature that leads to upper limits (e.g. Aharonian+ 06;Mazin & Raue, 07; Albert+ 08)

- Extrapolating the unattenuated Fermi spectra using different assumptions (e.g. Georganopoulos+ 2010; Orr+ 2011; Meyer+ 2012; Sánchez+ 2013)

- Stacking of Fermi spectra (e.g. Ackermann+ 2012)

- TeV statistical analysis (e.g. Abramowski+ 2013; Sinha+ 2014; Biteau+ 2015)

- Using broad-band photometry from radio/optical/X-rays to Fermi/Cherenkov energies (Domínguez+ 13)

Different methodologies to estimate the intrinsic spectrum:

- No intrinsic curvature that leads to upper limits (e.g. Aharonian+ 06;Mazin & Raue, 07; Albert+ 08)

- Extrapolating the unattenuated Fermi spectra using different assumptions (e.g. Georganopoulos+ 2010; Orr+ 2011; Meyer+ 2012; Sánchez+ 2013)

- Stacking of Fermi spectra (e.g. Ackermann+ 2012)

- TeV statistical analysis (e.g. Abramowski+ 2013; Sinha+ 2014; Biteau+ 2015)

- Using broad-band photometry from radio/optical/X-rays to Fermi/Cherenkov energies (Domínguez+ 13)

Local EBL: Local EBL: γ-ray dataγ-ray data


VHE region30 GeV<E<30 TeV

Blazars: AGNs emitting at all wavelengthwith energetic jets pointing towards us.

Emission described by homogeneoussynchrotron/synchrotron-self Compton model.

Sample and Synchrotron Self-Compton ModelsSample and Synchrotron Self-Compton Models

Quasi-simultaneous multiwavelength catalog of 15 BL Lacs (based on the compilation by Zhang et al. 2012).

SED Multiwavelength FitsSED Multiwavelength Fits

A one-zone synchrotron/SSC model is fit to the multiwavelength data excluding the Cherenkov data, which are EBL attenuated. Then, this fit is extrapolated to the VHE regime

representing the intrinsic VHE spectrum. Technique similar to Mankuzhiyil et al. 2010.

PKS 2155-304 z = 0.116

Variability time scale 104 s (fast)

Domínguez+ 13 on behalf of the Fermi collaboration

Maximum likelihood technique with three EBL-model independent conditions:Maximum likelihood technique with three EBL-model independent conditions:

1.- The optical depth is lower than 1 at E = 0.03 TeV.1.- The optical depth is lower than 1 at E = 0.03 TeV.

2.- The optical depth is lower than the optical depth calculated from2.- The optical depth is lower than the optical depth calculated from

the EBL upper limits from Mazin & Raue, 07; especially 1 < the EBL upper limits from Mazin & Raue, 07; especially 1 < τ < UL(z) τ < UL(z) at E = 30 TeV.at E = 30 TeV.

3.- The polynomial is monotonically increasing with the energy.3.- The polynomial is monotonically increasing with the energy.

The cosmic gamma-ray horizon (CGRH) is by definition

the energy E0 as a function of redshift at which the optical depth due to EBL is unity.


The measurement of the CGRH is a primary scientific goal of the Fermi Gamma-Ray Telescope

(Hartmann 07; Stecker 07; Kashlinsky & Band 07)

The measurement of the CGRH is a primary scientific goal of the Fermi Gamma-Ray Telescope

(Hartmann 07; Stecker 07; Kashlinsky & Band 07)

Albert+ 08Albert+ 08

Abdo+ 10Abdo+ 10Gilmore+ 12Gilmore+ 12

Cosmic Cosmic γ-ray Horizon: Resultsγ-ray Horizon: Results

There are 4 out of 15 cases where our maximum likelihood methodology could not be applied since the prediction from the There are 4 out of 15 cases where our maximum likelihood methodology could not be applied since the prediction from the

synchrotron/SSC model was lower than the detected flux by the Cherenkov telescopes.synchrotron/SSC model was lower than the detected flux by the Cherenkov telescopes.

Two other cases where the statistical uncertainties were too large to set any constraint on E0.Two other cases where the statistical uncertainties were too large to set any constraint on E0.



There are 4 out of 15 cases where our maximum likelihood methodology could not be applied since the prediction from the There are 4 out of 15 cases where our maximum likelihood methodology could not be applied since the prediction from the

synchrotron/SSC model was lower than the detected flux by the Cherenkov telescopes.synchrotron/SSC model was lower than the detected flux by the Cherenkov telescopes.

Two other cases where the statistical uncertainties were too large to set any constraint on E0.Two other cases where the statistical uncertainties were too large to set any constraint on E0.


Conclusion 3: Constrains contribution from light that escapes

to galaxy surveys or any other potential contribution

Conclusion 3: Constrains contribution from light that escapes

to galaxy surveys or any other potential contribution



More attenuatingMore attenuating Less attenuatingLess attenuating

Preliminary

EBL model Rejection

Kneiske+ 04 Best Fit 1.62σ

Stecker+ 06 Baseline 6.37σ

Franceschini+ 08 0.29σ

Kneiske & Dole 10 1.54σ

Finke+ 10 0.06σ

Domínguez+ 11 0.29σ

Gilmore+ 12 Fiducial 0.25σ

Helgason+ 12 0.09σ

Inoue+ 13 Baseline 2.12σ

Khaire+ 15 LMC2 1.27σ

Preliminary data courtesy of Marco Ajello

H0 = 71.8 +4.6

-5.6 +7.2

-13.8 km/s/Mpc

Cosmological Dependence: Assumed flat Cosmological Dependence: Assumed flat ΛΛCDMCDM

Domínguez & Prada, 13

Statistical uncertainties Systematic uncertainties

Methodology theoretically explored by Blanch & Martínez 05

Multiple paths to independent determinations of

the Hubble constant are needed in order to access and

control systematic uncertainties

2FHL Catalog: Preliminary Numbers2FHL Catalog: Preliminary Numbers

• Analysis focused in the energy range 50 GeV – 2 TeV:– More than 6 years of data– Pass 8– Position accuracy of 2 arcmin (68% uncertainty)– Median source flux of approximately 1e-11 erg/cm^2/s

● Detections:

– Around 350 sources– 84 detected by ACTs (TeVCat)– 238 detected in 1FHL (3 years, up to 500 GeV)– 300 detected in 3FGL (4 years, up to 300 GeV)– Around 35 brand new sources– About 10% of the sources are of Galactic type

These numbers are not definitive since they depend on IRFs and diffuse emission model, which are subject to change

Bottom line: 270 sources not in TeVCat, 130 not in 1FHL, and 60 not in the 3FGL

2FHL Catalog2FHL Catalog

Preliminary

Preliminary

Preliminary

SummarySummary

1.- Independent methodologies converge within a factor 2 or better1.- Independent methodologies converge within a factor 2 or better

in the local EBL intensity from the UV to the mid-IR.in the local EBL intensity from the UV to the mid-IR.

However, the far-IR and the EBL evolution is still largely unknown.However, the far-IR and the EBL evolution is still largely unknown.

2.- The CGRH detection is compatible with the recent EBL direct detection in the optical,2.- The CGRH detection is compatible with the recent EBL direct detection in the optical,

galaxy counts, and upper limits from gamma-ray attenuation.galaxy counts, and upper limits from gamma-ray attenuation.

This constrains the contribution to the low redshift EBLThis constrains the contribution to the low redshift EBL

from faint or high redshift galaxies that escape to current galaxy surveysfrom faint or high redshift galaxies that escape to current galaxy surveys

and any other potential contribution.and any other potential contribution.

3.- The detection of the CGRH allows us to derive the expansion rate of the Universe3.- The detection of the CGRH allows us to derive the expansion rate of the Universe

(the Hubble constant) from a novel technique using (the Hubble constant) from a novel technique using γ-ray attenuation,γ-ray attenuation,

whose value is compatible with other rather mature techniques.whose value is compatible with other rather mature techniques.

HH0 0 = 71.8 = 71.8 +4.6+4.6-5.6 -5.6

+7.2+7.2-13.8-13.8 km/s/Mpc km/s/Mpc

4.- The cosmological parameters Ω4.- The cosmological parameters Ωmm and and ww cannot be constrained with current data. cannot be constrained with current data.

5.- The publication of the Second Fermi catalog of hard sources is imminent.5.- The publication of the Second Fermi catalog of hard sources is imminent.

SummarySummary

1.- Independent methodologies converge within a factor 2 or better1.- Independent methodologies converge within a factor 2 or better

in the local EBL intensity from the UV to the mid-IR.in the local EBL intensity from the UV to the mid-IR.

However, the far-IR and the EBL evolution is still largely unknown.However, the far-IR and the EBL evolution is still largely unknown.

2.- The CGRH detection is compatible with the recent EBL direct detection in the optical,2.- The CGRH detection is compatible with the recent EBL direct detection in the optical,

galaxy counts, and upper limits from gamma-ray attenuation.galaxy counts, and upper limits from gamma-ray attenuation.

This constrains the contribution to the low redshift EBLThis constrains the contribution to the low redshift EBL

from faint or high redshift galaxies that escape to current galaxy surveysfrom faint or high redshift galaxies that escape to current galaxy surveys

and any other potential contribution.and any other potential contribution.

3.- The detection of the CGRH allows us to derive the expansion rate of the Universe3.- The detection of the CGRH allows us to derive the expansion rate of the Universe

(the Hubble constant) from a novel technique using (the Hubble constant) from a novel technique using γ-ray attenuation,γ-ray attenuation,

whose value is compatible with other rather mature techniques.whose value is compatible with other rather mature techniques.

HH0 0 = 71.8 = 71.8 +4.6+4.6-5.6 -5.6

+7.2+7.2-13.8-13.8 km/s/Mpc km/s/Mpc

4.- The cosmological parameters Ω4.- The cosmological parameters Ωmm and and ww cannot be constrained with current data. cannot be constrained with current data.

5.- The publication of the Second Fermi catalog of hard sources is imminent.5.- The publication of the Second Fermi catalog of hard sources is imminent.

Synergy between

different communities

is essential! Lots of

exciting results

coming soon.. Stay

tuned!

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