Download Tests and Constraints on Theories of Galaxy Formation and

The Near Infrared Background Excess and
Star Formation in the HUDF
Rodger Thompson
Steward Observatory
University of Arizona
Blameless Collaborators
Mark Dickinson
Daniel Eisenstein
Xiaohui Fan
Garth Illingworth
Rob Kennicutt
Marcia Rieke
Topics
The near infrared background excess
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The lack thereof
Star formation history of the HUDF
Near Infrared Background Excess
Claims of a Near InfraRed Background
(NIRBE) of ~70 nW m-2 sr-1, not due to
known galaxies, stars or zodiacal light, that
peaks at 1.4-1.6 mm.
Resolved objects in the NUDF and NHDF
contribute 6-7 nW m-2 sr-1, a factor of 10
below the claimed background.
Fluctuations in deep 2MASS images claimed
as evidence for a population of very high
redshift (10-15) Pop. III stars. (Kashlinsky et
al. 2006)
Implications of the NIRB
Most popular model for the NIRB is the light from the
high redshift Pop. III stars that reionized the
universe.
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Requires that the total number of baryons turned into stars
in the first 3% of the age of the universe be greater than or
equal to the total number of baryons converted to stars in
the remaining 97%.
The metals produced by this conversion must be hidden in
black holes.
There must be no x-ray producing accretion onto the black
holes.
The NIRB must not interact with TeV emission from distant
blazars.
Fluctuation Analysis of the
NICMOS UDF F160W Image
Results of the Fluctuation
Analysis
The fluctuations observed in the 2MASS field
can be completely accounted for by the
redshift 0-7 galaxies such as those observed
in the NUDF
There is no need for an excess population of
high redshift Pop.III stars to account for the
fluctuations
Fluctuations have been removed as evidence
for a NIRBE at 1.6 mm
The IRTS NIRBE
Wide field of view spectrometer
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Aperture almost 17 times the size of the
NUDF
Zodiacal light and contributions from
sources determined from models
After subtraction of modeled
components, 70 out of 330 nW m-2 sr-1
remain and is attributed to a NIRBE
The NIRBE According to IRTS
IRTS vs NICMOS FLUX ALLOCATIONS
All fluxes in nW m-2 Sr-1
350
300
Observed
250
Modeled
200
IRTS
NHDF
150
100
50
0
Total
Zodiacal
Sources
Background
Differences
The zodiacal component determined by
medianed images in the NUDF exceeds the
IRTS modeled component by 100 nW m-2 sr-1.
Dwek et al. 2006 point out that the IRTS
spectrum is better fit by a zodiacal spectrum
than a high z Pop.III spectrum.
The IRTS NIRBE is most likely due to an
under estimate of the zodiacal light
component by the model.
Caveats
A NIRBE component that is flat on scales of greater
than 100” would be mistaken for zodiacal light in our
reduction.
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At odds with CMB predictions
A NIRBE component that is clumped on the order of
several arc minutes could be missed by our two small
fields.
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Archival proposal to check other fields
However the light in a NIRB can not be distributed in
the same manner as the light from baryonic matter at
redshifts of 6 and less.
Scattering of UV Light at High Z
Emission from massive Pop. III stars
will be primarily shortward of 912 Å and
will be degraded into Ly a photons.
In a metal and dust free gas they can
scatter to large distances and become
smooth on scales of 10-100 arc
seconds.
Smoothing on 10 arc second
Scales
Portion of the NUDF at 1.6 mm
Same portion with background
in 10” gaussians
Star Formation History in the
NICMOS UDF
The F775W Mag. vs Redshift
AGN
Star Formation Rates
Star formation rate determined from the
rest frame 1500 Å flux via the Madau
relation.
The flux is measured from the selected
SED without extinction to produce an
extinction corrected SFR.
Star Formation Intensity
Distribution
The star formation intensity x is the SFR in M
per year per proper square kpc.
The distribution function h(x) is the sum of all
proper areas in an x interval, divided by that
interval and divided by the comoving volume
defined by the field and redshift interval.*
Under this definition SFR is the first moment
of h(x);
SFR = ∫x h(x) dx
* Lanzetta et al. 1999, ASP Conf. Ser. 191, 223
Star Formation Density
Redshift = 1
95%
complete
Log(h(x))
60%
complete
Starburst
Log Star Formation Intensity x in M per year per kpc2
About 80% of the stars are formed in a “starburst region”
Application of the Distribution
The SFR is calculated for every pixel
that is part of a galaxy.
Assumes a uniform SED and extinction
within a galaxy
Assumes that the rest frame 1500 Å
light is distributed in the same way as
the observed flux in the ACS F775W
band.
The Observed h(x)
Star Formation History of the
NUDF
Comparison with the NHDF
Conclusions
Fluctuations have been removed as evidence
for a NIRBE at 1.6 mm.
The IRTS NIRBE is probably zodiacal flux.
Any NIRBE must be either maximally flat or
maximally clumped.
The star formation history of the universe is
roughly constant from z=1-6.
The vast majority of star formation occurs in
a minority of galaxies at any one time.