The Cosmic Near-Infrared Background: Remnant light form early stars Journal Club talk 3.12.2010 A....
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The Cosmic Near-Infrared Background: Remnant light form early stars Journal Club talk 3.12.2010 A. B. Fry Ferdinand & Komatsu 2006 (F&K06) also Ferdinand
The Cosmic Near-Infrared Background: Remnant light form early
stars Journal Club talk 3.12.2010 A. B. Fry Ferdinand & Komatsu
2006 (F&K06) also Ferdinand & Komatsu et al. 2010
(F&K10)
Slide 2
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 examines intensity
fluctuations of the mean NIRB which could further constrain high-z
galaxy populations.
Slide 3
Slide 4
The cosmic infrared background radiation (CIBR) is the diffuse
light from faint galaxies that remains after Milky Way and zodiacal
light is subtracted.
Slide 5
http://www.astro.ucla.edu/~wright/CIB R/ 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 data.
Slide 6
Lets focus on the near infrared (1-3 m) background radiation
(NIRB) where redshifted ultraviolet light from early stars at z~10
contributes.
Slide 7
The observed NIRB seems too large to be accounted for by the
integrated light from galaxies, it could come from early stars
Slide 8
For example, suppose that most reionization occurred at z=9.
Then ultraviolet photons (~1000 ) produced at this redshift during
reionizaiton will then be redshifted to the near infrared regime
(~1m).
Slide 9
The NIRB offers invaluable information regarding the physics of
cosmic reionization that is difficult to probe by other means.
Slide 10
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 m (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.
Slide 11
The mean background intensity is computed in terms of the
volume emissivity, p( ,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 d 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 0 were emitted at a frequency 0 (1+z) si the flux
density is the luminosity at this frequency divided by the total
area divided by 1+z
Slide 12
p( ,z ) is the volume emissivity in units of energy per unit
time per unit frequency and unit commoving volume: The sum over
takes into account the various radiative process contributions to
the emissivity
Slide 13
p( ,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 p line is the emission
from recombination lines p cont is free-free and free-bound
continuum emissions p 2 is the two-photon emission
Slide 14
p( ,z ) is the volume emissivity in units of energy per unit
time per unit frequency and unit commoving volume: The
dimensionless quantity represents a ratio of the mass-weighted
average total radiative energy to the stellar rest-mass energy in a
unit frequency interval
Slide 15
p( ,z ) is the volume emissivity in units of energy per unit
time per unit frequency and unit commoving volume: d * /dt is the
mean star formation rate at the redshift of interest in units of M
yr -1 Mpc -3. It is very uncertain! L is a time averaged luminosity
for the radiative process (m) is the stellar main-sequence
lifetime
Slide 16
p( ,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
Slide 17
Salpeter Larson: Top-heavy:
Slide 18
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 stars 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 of the IGM. The Fate of
Massive Stars
Slide 19
Slide 20
The previous equations 1-3 allow us to predict the average
intensity (in units of nW m -1 sr -1 ) at 1-2 m:
Slide 21
Equations 1-3 allow us to predict the average intensity (in
units of nW m -1 sr -1 ) at 1-2 m:
Slide 22
3 to 1 m corresponds to.414 to 1.24 eV The spectrum of the
NIRB
Slide 23
The dependence on the initial mass spectrum f(m) is such that
heaver mass spectra tend to give higher background intensities. For
metal- rich stars Ly emission dominates. For metal-poor stars there
is a significant contribution form the stars themselves. The
predicted sensitivity is not sensitive to stellar metallicity The
spectrum of the NIRB
Slide 24
Metallicity changes the hardness of the stellar spectrum, it
affects the ratio of energy in the Ly and two-photon emission to
stellar emission energy: the harder the spectrum is the more
ionizing photons are emitted and thus the more the Ly and two
photon-emission energies. The spectrum of the NIRB
Slide 25
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 value for the star formation
rate.
Slide 26
The uncertainty in measurements of the NIRB are massive. They
vary from 2-50 nW m -2 sr -1 at 1- 2 m including the upper and
lower 1 bounds. The mean SFR d * /dt is constrained to.3-12 M yr -1
Mpc -3.
Slide 27
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!
Slide 28
F&K 2010 et al. present calculations of the power spectrum
and metallicity/initial-mass- spectrum dependence of the NIRB
fluctuations, as well as dependence on the star formation
efficiency and the escape fraction of ionizing photons.
Fluctuations
Slide 29
Slide 30
F&K 2010 et al. present calculations of the power spectrum
and metallicity/initial-mass- spectrum dependence of the NIRB
fluctuations, as well as dependence on the star formation
efficiency and the escape fraction of ionizing photons.
Fluctuations
Slide 31
Luminosity-density power spectrum of halos with Pop II stars
with an initial mass spectrum, f esc = 0.19, and f* = 0.5, assuming
a rectangular bandpass from 1 2 m.
Slide 32
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. Fluctuations
Slide 33
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 spectrum of the mean NIRB is determined by f * while the
angular power spectrum of the IGM can probe the ionization history.
Conclusions
Slide 34
Image credit: Robert Hurt, SSC, JPL, CalTech, NASA The first
stars may have lighted up the cosmos within 200 to 400 million
years after the Big Bang, and then clustered together into what
later became galaxiesSSCJPLCalTechNASA
Slide 35
*A note about the escape fraction for Ly which varies widely in
the literature: the fraction of ionizing photons escaping the
nebula does not alter the Ly luminosity very much because all of
the ionizing photons will eventually be converted to Ly photons
that in turn will escape freely via the cosmological redshift
therefore these predictions should be free from uncertainty in the
escape fraction.
Slide 36
The amplitude of Cl is, among other things, a sensitive probe
of the nature of high-z galaxies.
Slide 37
More
Slide 38
The authors find if the NIRB has a stellar origin metal-free
stars are not the only explanation of the excess NIRB; stars with
significant metals (e.g., Z = 1/50 Z ) can produce the same amount
of background intensity as metal- free stars. We predict * / ~48nWm
2 sr 1, where * is the mean star formation rate at z = 715 (solar
masses per year per cubic megaparsec) for stars more massive than 5
solar masses While the star formation rate at z = 715 inferred from
the current data is significantly higher than the local rate at
z