Download The Cosmic Near-Infrared Background: Remnant light form

The Cosmic Near-Infrared
Background: Remnant light
form early stars
Ferdinand & Komatsu 2006 (F&K06)
also
Ferdinand & Komatsu et al. 2010 (F&K10)
Journal Club talk 3.12.2010 A. B. Fry
The Cosmic Near-Infrared
Background: Remnant light
form early stars
The cosmic infrared background radiation is the diffuse light from
faint galaxies that remains after Milky Way and zodiacal light is
subtracted. The near-infrared (1-3 um) background light (NIRB)
from redshifted stars at z~10 contributes to this backgorund. The
NIRB offers invaluable information regarding the physics of
cosmic reionization that is difficult to probe by other means.
Fernandez & Komatsu explore the uncertainty in the background
intensity from these stars due to metallicity, the mass spectrum,
and other parameters. The authors show that contrary to previous
results that the stellar component of the NIRB could come from
stars with some metals (Z=1/50 solar). A follow up paper
The cosmic
infrared
background
radiation (CIBR)
is the diffuse light
from faint
galaxies that
remains after
Milky Way and
zodiacal light is
subtracted.
The black data points between 1 and 300 microns on this graph come from the DIRBE
experiment on the COBE satellite. The red data points are from Wright, E.L. 2001 (ApJ,
553, 538) which use a different zodiacal light model than the one used by Hauser et
al. (1998, ApJ, 508, 25). The blue lower limit symbols are based on integrating galaxy
counts, while the purple upper limit symbols are based on limits on photon-photon
collisions from gamma-ray astronomy. The black data points at wavelengths shorter than
1 microns come from Dube, Wickes & Wilkinson (1979, ApJ, 232, 333), Toller (1983,
ApJL, 266, 79), and Hurwitz, Martin & Bowyer (1991, ApJ, 372, 167). The curve is the
Lambda CDM model with the Salpeter IMF from Primack et al., multiplied by a factor of
1.84, and with modifications for wavelengths longer than 300 microns to fit the FIRAS
distortion limits, and for wavelengths shorter than 0.8
microns to fit the optical and UV
http://www.astro.ucla.edu/~wright/CIB
Lets focus on the near infrared (1-3 µm)
background radiation (NIRB) where redshifted
ultraviolet light from early stars at z~10
contributes.
The observed NIRB seems too large to be
accounted for by the integrated light from
galaxies, it could come from early stars…
For example, suppose that most reionization
occurred at z=9. Then ultraviolet photons
(λ~1000Å) produced at this redshift during
reionizaiton will then be redshifted to the near
infrared regime (λ~1µm) .
The NIRB offers invaluable information
regarding the physics of cosmic reionization
that is difficult to probe by other means.
In F&K06 they discuss the simplified physics of
the NIRB, explore different metallicities and
initial mass spectra of the first stars, and
provide a relation to the NIBR and star
formation rate.
They predict the average intensity at 1-2 µm
(units of nW m-2 sr-1, just like previous plots)
which is a function of the mass spectrum of
early stars, the star formation rate, metallicity.
Etc.
The mean background intensity is computed
in terms of the volume emissivity, p( ʋ,z),
which is a function of the mass spectrum of
early stars, the star formation rate, metallicity.
Etc. The background intensity* (Peacock
1999, p. 91):
* Redshift affects the flux density in several ways
•Photon energies and arrival rates are redshfited reducing the flux density by a factor of
(1+z)2
•The bandwidth dʋ is reduced by a factor of 1+z so the energy flux per unit bandwidth
does down by one power of 1+z
•The observed photons at frequency ʋ0 were emitted at a frequency ʋ0(1+z) si the flux
density is the luminosity at this frequency divided by the total area divided by 1+z
p(ʋ,z) is the volume emissivity in units of
energy per unit time per unit frequency and
unit commoving volume:
The sum over α takes into account the various
radiative process contributions to the
emissivity…
p(ʋ,z) is the volume emissivity in units of
energy per unit time per unit frequency and
unit commoving volume:
p* is the continuum emission form the stars
themselves
pline is the emission from recombination lines
pcont is free-free and free-bound continuum
emissions
p(ʋ,z) is the volume emissivity in units of
energy per unit time per unit frequency and
unit commoving volume:
The dimensionless quantity <ε> represents a
ratio of the mass-weighted average total
radiative energy to the stellar rest-mass energy
in a unit frequency interval…
p( ʋ,z) is the volume emissivity in units of
energy per unit time per unit frequency and
unit commoving volume:
dρ*/dt is the mean star formation rate at the
redshift of interest in units of M⊙ yr-1 Mpc-3. It is
very uncertain!
Lʋ is a time averaged luminosity for the radiative
process α
p( ʋ,z) is the volume emissivity in units of
energy per unit time per unit frequency and
unit commoving volume:
Finally, f(m) is the mass spectrum. They use
three different versions…
Salpeter
Larson:
Top-heavy:
The Fate of Massive Stars
From 6 to 8 M⊙, the O/Ne/Mg core of the star collapses, or the star ejects its outer
envelope, leaving a white dwarf or neutron star.
From 8 to 25 M⊙, the iron core collapses, the star explodes as a supernova, and a
neutron star is left as a remnant. A significant amount of metals are ejected.
From 25 to 40 M⊙, there is a weak supernova and a black hole is created by fallback.
The amount of metals that are ejected into the IGM decreases sharply, leaving most of
the metals locked in the black hole.
From 40 to 100 M⊙, the star directly collapses into a black hole. The only metals
produced are from mass loss during the star’s life.
From 100 to 140 M⊙, a pulsational pair instability supernova results. This ejects the
outer envelope of the star, and then the core collapses into a black hole. Metals in the
outer envelope pollute the IGM.
From 140 to 260 M⊙, a pair instability supernova results, which completely disrupts the
star and leaves no remnant. All the metals are ejected into the IGM.
Above 260 M⊙, the star collapses directly into a black hole, and there is no enrichment
The Fate of Massive Stars
The previous equations 1-3 allow us to predict
the average intensity (in units of nW m-1 sr-1) at
1-2 µm:
Equations 1-3 allow us to predict the average
intensity (in units of nW m-1 sr-1) at 1-2 µm:
The spectrum of the NIRB
3 to 1 µm corresponds to .414 to 1.24 eV
The spectrum of the NIRB
For metal-poor
stars there is a
significant
contribution
form the stars
themselves.
For metalrich stars Lyα
emission
dominates.
The predicted
sensitivity is not
sensitive to stellar
metallicity
The dependence on
the initial mass
spectrum f(m) is such
that heaver mass
spectra tend to give
higher background
intensities.
The spectrum of the NIRB
Metallicity changes the hardness of the stellar
spectrum, it affects the ratio of energy in the
Lyα and two-photon emission to stellar emission
energy: the harder the spectrum is the more
ionizing photons are emitted and thus the more
the Lyα and two photon-emission energies.
F&K06 find that a population of
metal-poor stars do not
overproduce metals that we
observe in the universe today,
except for the Larson mass
function upper 1 σ value for the
star formation rate.
F&K06 find that a population of
metal-poor stars do not
overproduce metals that we
observe in the universe today,
except for the Larson mass
function upper 1 σ value for the
star formation rate.
The uncertainty in measurements
of the NIRB are massive. They
vary from 2-50 nW m-2 sr-1 at 12µm including the upper and
lower 1σ bounds. The mean SFR
Measuring the absolute value of the NIRB is
very difficult due to systematic uncertainty in
zodiacal light subtraction, however, fluctuations
could be measured without this absolute
calibration!
Fluctuations
F&K 2010 et al. present calculations of the
power spectrum and metallicity/initial-massspectrum dependence of the NIRB
fluctuations, as well as dependence on the
star formation efficiency and the escape
fraction of ionizing photons.
Fluctuations
F&K 2010 et al. present calculations of the
power spectrum and metallicity/initial-massspectrum dependence of the NIRB
fluctuations, as well as dependence on the
star formation efficiency and the escape
fraction of ionizing photons.
Fluctuations
Luminosity-density power spectrum of halos with
Pop II stars with an initial mass spectrum, fesc =
0.19, and f* = 0.5, assuming a rectangular
Fluctuations
•The luminosity-density power spectra of halos
are approximately power-laws over the entire
range of wave numbers that the simulation
covers.
•The clustering of halos is highly non-linearly
biased relative to the underlying matter
distribution.
•The growth of the power spectrum is partly
driven by the growth of linear matter fluctuations
as well as that of halo bias.
Conclusions
•The NIRB intensity contribution from early stars is
essentially determined by the mass-weighted mean
nuclear burning energy of the stars and the cosmic
star formation rate.
•The intensity is not sensitive to stellar metallicity.
•Variations in the NIRB can tell us details about the
first stars, reionization, and the high redshift host
galaxies/IGM.
•The amplitude of the (observable) angle power
Image credit: Robert Hurt, SSC, JPL, CalTech, NASA
‘T’he first stars may have lighted up the cosmos within 200 to 400
million years after the Big Bang, and then clustered together into
*A note about the escape fraction for Lyα which varies widely in
the literature: the fraction of ionizing photons escaping the
nebula does not alter the Lyα luminosity very much because all
of the ionizing photons will eventually be converted to Lyα
photons that in turn will escape freely via the cosmological
redshift therefore these predictions should be free from
uncertainty in the escape fraction.
The amplitude of Cl is,
among other things, a sensitive probe of the nature of high-z
galaxies.
More
The authors find
if the
has
stellar origin…
•metal-free
starsNIRB
are not the
onlyaexplanation
of the excess
NIRB; stars with significant metals (e.g., Z = 1/50 Zʘ) can
produce the same amount of background intensity as metalfree stars.
•We predict ʋ* /σ~4–8nWm−2 sr−1, where * is the mean star formation
rate at z = 7–15 (solar masses per year per cubic megaparsec)
for stars more massive than 5 solar masses
•While the star formation rate at z = 7–15 inferred from the
current data is significantly higher than the local rate at z<5, it
does not rule out the stellar origin of the cosmic near-infrared
background. In addition, we show that a reasonable initial
mass function, coupled with this star formation rate, does not
overproduce metals in the universe in most cases and may
produce as little as less than 1% of the metals observed in the
universe today.
The authors find
if the NIRB has a stellar origin…
• This is because the average intensity at 1–2 microns is
determined by the efficiency of nuclear burning in stars, which
is not very sensitive to metallicity.
•We have very little knowledge about the form of the mass
spectrum of early stars, the uncertainty in the average intensity
due to the mass spectrum could be large.
•An accurate determination of the near-infrared background
allows us to probe the formation history of early stars, which
is difficult to constrain by other means.
•A reasonable initial mass function, coupled with this star
formation rate, does not overproduce metals in the universe in
most cases and may produce as little as less than 1% of the
metals observed in the universe today.
Questions they asked
o When and how was the universe reionized?
o What does (the calculated bound on stellar
mass density) imply?
o Would metal-poor stars overproduce metals
that we observe in the universe today?
more
The Cosmic Infrared Background ExpeRiment (CIBER) is a rocket-borne
absolute photometry imaging and spectroscopy experiment optimized to detect
signatures of first-light galaxies present during reionization in the unresolved
IR background. CIBER-I consists of a wide-field two-color camera for fluctuation
measurements, a low-resolution absolute spectrometer for absolute EBL
measurements, and a narrow-band imaging spectrometer to measure and correct
scattered emission from the foreground zodiacal cloud. CIBER-I was successfully
flown on February 25th, 2009 and has one more planned flight in early 2010.
We propose, after several additional flights of CIBER-I, an improved CIBER-II
camera consisting of a wide-field 30 cm imager operating in 4 bands between 0.5
and 2.1 microns. It is designed for a high significance detection of unresolved IR
background fluctuations at the minimum level necessary for reionization. With a
FOV 50 to 2000 times largerthan existing IR instruments on satellites, CIBERII
will carry out the definitive study to establish the surface density of sources
responsible for reionization.
Cooray et al. 2009 http://arxiv.org/PS_cache/arxiv/pdf/0904/0904.2016
more
http://physics.ucsd.edu/~bkeating/CIBER
more
http://arxiv.org/PS_cache/astro-