High-energy gamma-ray and neutrino
diffuse backgrounds from star-forming galaxies
Irene Tamborra
GRAPPA Institute, University of Amsterdam
Neutrino Oscillation Workshop 2014
Conca Specchiulla, September 8, 2014
Outline
★
High-energy IceCube neutrino flux
★
Gamma-ray and neutrino backgrounds from star-forming galaxies
★
Implications for the starburst history
★
Conclusions
This talk is mainly based on work in collaboration with S. Ando and K. Murase,
arXiv: 1404.1189 [accepted by JCAP].
IceCube high-energy excess
★ IceCube observed 37 events over three years
(~ 10 events expected from conventional atmospheric contributions).
★ Mostly showers. 3 events with energy above 1 PeV, 12 above 100 TeV.
★ Zenith Distribution compatible with isotropic flux.
★ Energy spectrum harder than any expected atmospheric background.
E^(-2) spectrum with potential cutoff around 2-5 PeV.
★ Flavor distribution consistent with νe
: νµ : ντ = 1 : 1 : 1.
5.7 σ evidence for astrophysical flux
[see talk by J. Koskinen on Friday]
*
IceCube Collaboration, Science 342 (2013) 6161, PRL 113 (2014) 101101.
Where are these neutrinos coming from?
Where are these neutrinos coming from?
★ Galactic origin
★ Extragalactic origin:
• Gamma-ray bursts, blazars
• Active galactic nuclei
• Newborn pulsars
• Star-forming galaxies
★ New physics processes (i.e., superheavy dark matter, exotic neutrino models, Planck scale
phenomena).
[See talks on Friday]
Warning: More statistics needed! No strong preference so far.
* L. A. Anchordoqui et al., JHEAp 1-2 (2014) 1.
Diffuse backgrounds
from star-forming galaxies
p-p interactions in star-forming galaxies
Star-forming galaxies produce neutrinos by cosmic rays colliding with the dense interstellar
medium. These p-p collisions also produce high-energy gamma rays.
neutrinos
γ
γ
Gamma-ray and neutrino intensities are related by a simple relation.
�
α
Iνα (Eν ) � 6 Iγ (Eγ )
* L.A. Anchordoqui et al., PLB 600 (2004) 202.
with Eγ � 2Eν
gamma-rays
Diffuse background ingredients
time
z=0
neutrinos, gamma-rays
z=1
• Gamma-ray and neutrino energy fluxes
• Distribution of star-forming galaxies with redshift
• Comoving volume (cosmology)
neutrinos, gamma-rays
z=5
LIR
of are
the
relative
fraction
massiveassociated
star-forming
(with mass
M
interpreted
as
activities
withobjects
star formation
(hence
log L
(z)the of
,X (LIR , z)d
IR = ΦIR,X
L
(z)
IR,X
to those
contribute
significantly
toexcess
the massive
end of the to
mass
who exhibit
mid-IR
can be attributed
the functions
obscured at
or
> 1011 Mas),SB),
starting
classified
and
zlow-luminosity
> 1.
AGNs
The IR population
does
evolve
as a whole, but it is composed by different
(SF-AGN).
The SB selected
this
way all
will
1 not
Ltogether
IRfeature high star-formation rate as well as high
2
×
exp
−
d
logFollowing
LIR , of(2.2)
log
1
+
2 these features
gas density,
where both
make
the production
gamma
rays and neutrinos
galaxy
classes evolving
differently
and independently.
[42],
IR observations
report
L
(z)
2σ
IR,X
IR,X
efficient.
star-formation
rate obtained
the SB population
shown to be
on
38%
of NG,The
the specific
7% of SB
and the remaining
goes inforstar-forming
galaxiesiscontaining
AGN
1
average
order
magnitude
higher
than
that
forfor
the
NG
population
[31]. containing an
(SF-AGN).
Here
weLof
consider
galaxies,
and
star-forming
ves as a power
law for0.6
LIR
as a Gaussian
instarburst
log
LIR
LIR
LIR,X . galaxies
IR,X and spiral
gamma-ray
intensity
calculated
withisthe
gamma-ray
functionfunction
as
he redshift
evolution
of
LIR,X (z)
and
ΦIR,X
(z)
for each
population
as inthrough
Tableluminosity
8 the luminosity
AGN
asThe
gamma-ray
sources.
Theis
γ-ray
intensity
defined
as well as the values ofzαIR,X and
σIR,X . LWe then fix the normalization by fitting
zmax
Lγ,max
2 Vd2 V
γ,max
max
dL
dFdN
(L(L
, (1++z)E
z)E
) −τ (Eγ ,z)
γ[31]. dTable
γ,X
γ ,γ(1
γ ,γz)
X
1 shows
the
local
(z
=
0)
LIR,X (z) and
Φ
(z)
from
Fig.
11
of
Ref.
Φγ,XΦ(L
,
z)
I(Eγ IR,X
) =I(Eγ ) =dz
(L
,
z)
,e
(2.1),
dLγ
dz
Xγ γ
2
ln(10)L
dΩdz
dE
dΩdz
dE
γ
γγ
Lγ,min procedure.
ese parameters as the 0result of0 Lsuch
γ,min a fitting
X X
(2.1)
egrating the luminosity function, one obtains the IR luminosity density ρIR (z):
2
2
where
ΦX
, z) = d N N/dV
dL is the luminosity function for each galaxy family
X =
where
Φ(L
each galaxy
γ,Xγ(Lγ , z) = d X
X /dV dγlog Lγ is the gamma-ray luminosity function for
EBL
correction
2 V /dΩdz the comoving
SG,
SF
− AGN
,SB,
dN
(Lγ ,Φ(1 + (L
z)E
)/dE
flux,
X
γ, z),
family
X =
{NG,
SF-AGN},
dFIRγ,X
(Lγ ,γ(1is+the
z)Eγ-ray
differential gammaγ , z)/dE
γ isdthe
ρSB,
d
log
L
L
(2.3)
IR (z) =
IR
IR
IR,X
comoving
volume
2
volume
[43],
we assume
5. X at the redshift z, d V /dΩdz
ray flux
atand
energy
Eγ fromXzmax
a source
the comoving
volume
gamma-ray
flux
luminosity
function
For each population, we adopt a parametric estimate
of the luminosity function in the
2
1
Φ
(L
,
z)
=
d
N
/dV
dLorder
Some
adopts
the values
in
to define NG and SB popuX rate
γstar-formation
X rate
γ
eved to be
correlated
to the
cosmic
star-formation
density. The
adopted
IRwell
range
atliterature
different
redshifts
[42]:of the specific
But wefunction
note thatof
both
conventions
consistent with
each other
as shown in Fig. 15 of Ref. [31].
ions for thelations.
luminosity
each
family Xarereproduce
the total
IR lumi1−αX
ty data summarized
in PEP/HerMES
Fig. 17 of Ref.∗survey
[31].LIRprovides
Lfor
1
Herschel
IR luminosity
function
IR each population X of
2
log
1
+
Φ
(L
)d
log
L
=
Φ
exp
−
d log LIR ,
(2.2)
X
IR
IR
X
∗
∗
2
ermi data show
a correlation
between
gamma-ray
(0.1–100
GeV) and
star-forming
galaxies
(up
to L
zX
> 4). luminosity 2σ
L
X
X
ty (8–1000 µm). Although such correlation is not conclusive at present due to the
∗– 4
– asscaling
that behaves
power rays,
law for
LIR theLfollowing
a Gaussian
in log LIR for log LIR for
stics of starbursts
foundasinagamma
we adopt
relation:
X and
LIR
L∗X . The four parameters (αX , σX , L∗X and Φ∗X ) are different for each population X
Lγ as in Table 8 ofLIR
and are
[42]. + β ,
= α log
(2.4)relation from Fermi data.
logdefined−1
Gamma-ray-IR linear
10
erg
s
10
L
The data show a linear correlation between gamma-ray luminosity and IR luminosity
(8 − 1000αµm).
We
theβfit
given
[39],
e solar luminosity,
= 1.17
± adopt
0.07 and
= scaling
39.28 ± relationship
0.08 [6]. While
thisinparame-
Gamma-ray background
from star-forming galaxies
calibrated in a local volume, we assume
that it GeV
is also valid at higher
L0.1−100
LIR redshifts
log
= α log
+β ,
* C.these
Gruppioni
et al., MNRAS
432 (2013)
Ackermann
Astrophys.
J. 755 in
(2012) 164.
erg 23.
s−1M.
1010[31]
L results
that adopting for
parameters
the values
directly
from
Table 8etofal.,Ref.
of the gamma-ray intensity, since the table summarizes the values of LIR,X and ΦIR,X for
with Lfromthe
Sun at
luminosity,
= 1.17
hich are different
the values
z = 0 shown α
in Table
1. and β = 39.28 [39]. Note that
(2.3)
this equation
Gamma-ray diffuse background
from star-forming galaxies
Herschel provides IR luminosity function for each population X of star-forming galaxies.
Normal galaxies
(i.e., Milky Way, Andromeda)
Injection spectral index in our
canonical model (E> 600 MeV):
ΓNG = 2.7
Starburst galaxies
(i.e., M82, NGC 253)
SF-AGN
(galaxies with dim/low
luminosity AGN)
Injection spectral index in our
canonical model (E > 600 MeV):
Injection spectral index in our
canonical model (E > 600 MeV):
ΓSB = 2.2
SB-like or NG-like according to z.
* C. Gruppioni et al., MNRAS 432 (2013) 23. Credits for images: ESA, Hubble, NASA web-sites.
Gamma-ray diffuse background
from star-forming galaxies
Fermi data
Diffuse gamma-ray intensity
gamma-IR uncertainty band
* I. Tamborra, S. Ando, K. Murase, arXiv: 1404.1189.
See also: Strong et al. (1976), Thompson et al. (2006), Fields et al. (2010), Makiya et al. (2011), Stecker&Venters(2011).
Gamma-ray diffuse background
from star-forming galaxies
Differential
contributions to the EGRB intensity
ï
a ïïïï
ï
Normal galaxies leading contribution up to z=0.5. SF-AGN and SB dominate at higher z.
* I. Tamborra, S. Ando, K. Murase, arXiv: 1404.1189.
Gamma-ray diffuse background
from star-forming galaxies
Diffuse gamma-ray intensity for all EGRB components
ï
ï ï
ï
a aa ï
ï
ï
ï
ï
a
SF-AGN give the larger contribution to the total EGRB intensity.
* I. Tamborra, S. Ando, K. Murase, arXiv: 1404.1189.
Neutrino diffuse background
from star-forming galaxies
ï
Diffuse neutrino intensity
iiiïïï
ï
ï
i
Neutrino intensity with its astrophysical uncertainty band within IceCube band for E<0.5 PeV.
* I. Tamborra, S. Ando, K. Murase, arXiv: 1404.1189.
See also: Loeb&Waxman (2006), Lacki et al. (2011), Murase et al. (2013).
The injection spectral index of the gamma-ray spectrum of starbursts is poorly constrained
as well as the fraction of SF-AGN that behaves similarly to SB. Here we consider as free
parameters ΓSB as well as the fraction of galaxies containing AGN that behaves similarly to
starbursts (0 ≤ fSB−AGN ≤ 1), and compute their allowed variation region compatible with
2.1 becomes
both the
anddata
Icecube
data. Therefore
Eq.abundance
Fermi
and Fermi
IceCube
can constrain
starburst
and their injection spectral index.
Constraints from Fermi and IceCube data
Iγ (Eγ ) = Iγ,NG (Eγ )+Iγ,SB (Eγ , ΓSB )+[fSB−AGN Iγ,SB (Eγ , ΓSB ) + (1 − fSB−AGN ) Iγ,NG (Eγ )] .
(4.1)
2.1SB-AGN
and our previous
for fSB−AGN
= 0.and IceCube data
Note
it recovers
Eq.and
SB as
spectral
index
fraction results
compatible
with Fermi
Figure 3 shows the exclusion regions by Fermi and IceCube data in the plane defined by
the injection spectral index (ΓSB ) and the fraction of starburst (fSB−AGN ), compatible with
the Fermi data [39] and IceCube ones as in Eq. 1.1. Note as the Fermi data at the moment
exclude a larger region of the parameter space than the IceCube ones. We can conclude
that very hard spectra for SB (i.e., ΓSB < 2.2) are excluded from present data and there is
a tendency to allow more abundant starbursts as much as the spectral index is softer since
they give a lower contribution to the high energy tail of the spectrum.
5
Extragalactic gamma-ray diffuse background adopting the star formation rate
In this Section, for comparison to previous results, the γ-ray and neutrino diffuse background
adopting the cosmological star formation rate is derived adopting, as template galaxies, the
MW as normal galaxy and M82 and NGC 253 as examples of starbursts.
* I. Tamborra, S. Ando, K. Murase, arXiv: 1404.1189.
–6–
Constraints from Fermi and IceCube data
ï
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ï
ï!
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ï
ï
i# !
ï
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ï
"
K
ï
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ï
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The SB spectral index matching simultaneously
Fermi and IceCube data is ΓSB � 2.15 .
ï
ï
* I. Tamborra, S. Ando, K. Murase, arXiv: 1404.1189.
See also A. Loeb, E. Waxman, JCAP 0605 (2006) 003, K. Murase, M. Ahlers, B. Lacki, PRD 88 (2013) 12, 121301.
Conclusions
★ Origin of IceCube high-energy neutrinos unknown.
★ Diffuse neutrino flux from star-forming galaxies is one natural possibility.
★ Multi-messenger approach: Starburst spectral index matching simultaneously Fermi
and IceCube data close to ΓSB � 2.15.
Thank you
for your attention!
Back-up slides
Gamma-ray diffuse background
from star-forming galaxies
* M. Ackermann et al. [Fermi LAT Collaboration], ApJ 755 (2012) 164.
Star-forming galaxies with AGN (SF-AGN)
Table 2. Fractions of SF-AGN (non-SB) and SF-AGN (SB) as functions of the redshift adopted in
our canonical model, on the basis of Tab. 9 of Ref. [27]. We assume ΓSF−AGN(non−SB) = ΓNG for
SF-AGN (non-SB) and ΓSF−AGN(SB) = ΓSB for SF-AGN (SB).
redshift range
0.0<z<0.3
0.3<z<0.45
0.45<z<0.6
0.6<z<0.8
0.8<z<1.0
1.0<z<1.2
1.2<z<1.7
1.7<z<2.0
2.0<z<2.5
2.5<z<3.0
3.0<z<4.2
SF-AGN (non-SB)
85
91
99
87
73
32
75
75
19
24
28
%
%
%
%
%
%
%
%
%
%
%
SF-AGN (SB)
15 %
9%
1%
13 %
27 %
68 %
25 %
25 %
81 %
76 %
72 %
diffusion, the spectral index difference δCR ≡ ΓNG − ΓSB ∼ 0.5 is interpreted as the energy
dependence of the diffusion coefficient.
Other emission components such as the inverse-Compton scattering due to primary
electrons can be also relevant especially at lower energies [62]. Although we do not take them
into account in this work, including them will not change our main results and conclusions.
AGN as gamma-ray sources. The γ-ray intensity is defined through the luminosity function
zmax
I(Eγ ) =
Lγ,max
dLγ
dz
d2 V
dΩdz
ΦX (Lγ , z)
dNX (Lγ , (1 + z)Eγ )
,
dEγ
(2.1)
Gamma-ray diffuse background
where Φ (L , z) = d N /dV dL is the luminosity function for each galaxy family X =
SG, SB, SF
− AGN , star-forming
dN (L , (1 + z)E )/dE is thegalaxies
γ-ray flux, d V /dΩdz the comoving
from
Lγ,min
0
X
2
γ
X
X
γ
X
γ
γ
2
γ
volume [43], and we assume zmax 5.
For eachapopulation,
adopt a of
parametric
estimate offunction
the luminosity
function
in the
For each population,
parametricweestimate
the IR luminosity
provided
by Herschel
IR range
at different redshifts [42]:
PEP/HerMES
survey.
ΦX (LIR )d log LIR =
24
1−αX
LIR
L∗X
Φ∗X
exp −
LIR
1
2
log
1
+
2
L∗X
2σX
d log LIR ,
(2.2)
The Fermi LAT Collaboration
that behaves as a power law -1for LIR
L∗X and as a Gaussian in log LIR for log LIR for
SFR
(M
yr
)
LIR
L∗X . The-2 four -1parameters (αX , 2σX , L3 ∗X and Φ∗X ) are different for each population X
10
10
10
10
1
10
and are defined as in Table 8 of [42].
Non-detected (Upper Limit)
1043 dataLATshow
The
a with
linear
correlation
between gamma-ray luminosity and IR luminosity
LAT Non-detected
AGN (Upper
Limit)
LAT Detected
(8 − 100042 µm).
We adopt the fit scaling relationship given in [39],
LAT Detected with AGN
Arp 220
L0.1-100 GeV (erg s-1)
10
41
10
Best-fit
Fit Uncertainty
Dispersion
L0.1−100 GeV
erg s−1
NGC 2146
Calorimetric Limit
50
(E ! = 10 erg)
log
NGC 1068
M82
SN
1040
NGC 4945
M83
NGC 253
NGC 6946
IC 342
= α log
LIR
1010 L
+β ,
(2.3)
The IR luminosity is linearly related
with L the Sun luminosity, α = 1.17 and β = 39.28 [39]. Note that this equation
to
thetotal
gamma-ray
luminosity.
parametrizes
the
relationship
between
gamma-ray
and
IR
luminosity
up to z
2,
39
10
8
we assume that it is also valid at higher redshifts (up to zmax
5) and assume 10 L ≤
38
14
LIR ≤ 10
10 L .
M31
Milky Way
M33
LMC
2.2
37
SMC
10
Gamma-ray
luminosity flux
108
109 of 10
1012
As for the distribution
γ10as 10
a 11function
of the energy, we here adopt a broken power-law
L8-1000 µm (L )
fit to the GALPROP conventional model of energy diffuse γ-ray emission and parametrize it
-1
* C. Gruppioniaset[6]
al., arXiv: 1302.5209. SFR (M yr )
-2
10-1
102
103
1
10
M. Ackermann et al., arXiv: 10
1206.1346.
−1.5
Eγ
LAT Non-detected (Upper Limit)
s−1 MeV−1 for Eγ < 600 MeV
-1
, Eγ ) with AGN (Upper Limit) 600 MeV
10dNX (L
LAT γ
Non-detected
(2.4)
= aX (Lγ )
LAT Detected
−ΓX
E
γ
dE
−1
−1
γ
LAT Detected with AGN
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