A Window on Cosmic Birth:
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A Window on Cosmic Birth:
Exploring our Origins with the SIRTF and NGST Space
Missions
Judith L. Pipher
University of Rochester
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Searching for Origins
How did galaxies form in the early universe?– How were galaxies different at early times?– When did galaxies first appear?– How do galaxies evolve?– Do galaxy collisions play a role?– What are galaxy luminosity sources? As evolve?
How and when do stars (and planets) form?
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Big Themes Big Space Experiments - IR
SIRTF - Space InfraRed Telescope Facility– cold, 0.85-m telescope; 7/02 launch– cameras 3 - 8 m; spectrometers
5 - 40 m; photometers 24, 70, 160 m; lo-res spectrometer 52-99 m
NGST - Next Generation Space Telescope– cold, 8-m telescope, planned for /08 launch– successor to the Hubble Space Telescope
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Why Infrared - IR?
Cool objects radiate in the infrared – max T-1 Wien’s blackbody law (e.g.
T=100K, max =30 m = 30,000 nm)
Dusty clouds (= stellar nurseries) redden & extinguish light from forming objects– extinction factor e-, where n where n =12
Distant galaxies recede from us – recession speed dependent on the distance– red-shift z = shifts galaxy emission to
red, IR (e.g. H 656.3 nm 4.6m at z=6)
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Why Space?
Earth and its atmosphere bright in the IR – T ~280K blackbody peaks at ~10 m = 10000 nm
Atmosphere blocks out much of the IR – from = 0.8 m - 1000 m = 1 mm
Atmosphere makes point-like objects fuzzy – “seeing” - atmospheric motion distorts image– space experiments can be diffraction limited
( ~ /D where D = telescope diameter)
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SIRTF and NGST Detector Array Development
SIRTF’s Infrared Array Camera using InSb arrays developed at UR – 256 x 256 pixels; 5’ field of view
NGST - detector array selection in 2002– 8Kx8K focal plane, diffraction limited at 2 m– UR working on NGST detector technologies
SIRTF and NGST Scientific Requirement– all instruments to be background limited - this
requirement means ultra-low dark current, ultra-low noise IR detector arrays
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SIRTF Background(# of detected photons/s-pix vs )
Fluctuations in background radiation are noise source
for = 1-5m, read noise < 10 e- and dark current < 1 e-/s
for NGST - noise < 3 e- and dark current < 0.005 e-/s1 10 100 1000
1
10
100
1000
1 104
1 105
N' ,,i .0.85 m ISIRTF i
sec1
beam ,i .0.85 m
arcsec
i
m
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SIRTF - A Window on Cosmic Birth
SIRTF will be considerably more sensitive at wavelengths between 3 and 200 m than previous IR missions, primary science goals Origins themes
The Early Universe Ultra-luminous IR galaxies - ULIRG Proto-planetary disks Brown Dwarf stars
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The Early Universe
All objects in HDF - Hubble Deep Field - are galaxies
Small, faint red objects the most distant (z 3.4)
SIRTF, NGST will study in IR to higher z (earlier times in the universe)
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The Early Universe (HST)Composite Visible and IR View
Blue = visible Green = 1.1 m (1100
nm) Red = 1600 nm Red objects could be
distant, or dusty, or contain old stars
need spectroscopy or other method to identify redshift z =
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NGST - Visiting a Time When Galaxies Were Young
NGST primary science goals (large, diffraction limited IR telescope - ~ 0.05”)
A Search for Galaxy Origins HST - Hubble Deep Field (galaxies that
formed a few by after Big Bang) NGST - will probe the era between that
probed by COBE (300,000 - 106 yr after Big Bang and the era probed by HST– to identify when galaxies form, state of universe
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Discovery Space for NGST
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Faint, Red Distant Galaxies
Investigators have produced UV-NIR images of a faint galaxy. NIR signature identifies it as distant, red-shifted galaxy: expands upon “Lyman drop-out galaxy” technique exploited on HST
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Nearby Dwarf Galaxies
Nature of objects contributing to the faint blue galaxy counts unknown
Irregular, peculiar galaxies in composite colors (HST) formed at similar rates at higher z - but faint– Bright blue = episode of
star formation
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Galaxies asCosmological Tools
Studies of galaxies probe cosmology in several ways– galaxies at z 1 have significant ‘look-back time’ -
or early age (0.4 current age) quasars & luminous galaxies observed to redshifts z ~ 6
– space density as function of z – star formation rates as function of z, morphological
galaxy type important to study distribution of average and dwarf
galaxies to higher z
– need contributions to extragalactic background
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Mapping Dark Matter at High z with Gravitational Lensing
HST image of massive galaxy cluster A2218: can deduce Mgal+halo
NGST simulations of lensed features for broad distribution of galaxies to z ~ 10, with evolution applied, and size-dependence with z deduce core size of cluster mass dist’n
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Starburst Galaxies
luminous nearby galaxies have bursts of massive star formation taking place - NGC 4214
during starburst epoch(s) galaxy luminosity can be 100-1000 x Milky Way luminosity
starburst triggers?
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Starburst Activity Quantified
Star formation rate a function of z (age) normalized to the present epoch
HST observations suggest steep rise in starburst soon after the Big Bang; ground-based observations show decline
HST, SIRTF, NGST probe the peak and early times
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Ultraluminous Galaxies
Some galaxies are ULIRG - ultraluminous infrared galaxies - 1000 x luminosity of Milky Way galaxy
Many of these are examples of multiple colliding systems
Relation to starbursts? AGNs?
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The Early UniverseVisible and Deep X-Ray View
6 galaxies in the HDF N are X-ray emitters – one, an extremely red edge-on
spiral, hosts AGN (Active Galactic Nucleus with accretion disk, 109 M black hole)
– AGN– 3 ellipticals– 1 spiral
X-ray sources: AGN; hot gas emission; X-ray binary
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Formation of Stars
Well established that stars form in GMCs (giant molecular clouds), and that formation of a disk and high velocity outflows a signature– yields important information on cloud support; how
angular momentum conserved as protostars shrink
– Stars blow away disk as evolve to main sequence
If star forms planetary system, onset of debris disk
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Disks and Jets
HH111 shows pair of 12 ly jets blasted from system of 3 stars located near a tilted edge-on dusty torus, episodic ejections
NGST will image in close to the central YSO - both SIRTF and NGST can extend sample to nearby galaxies
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Debris and Proto-planetary Disks IRAS discovered that ordinary stars had
disks emitting in the far IR– Many examples studied with a coronograph from the
ground - most famous example, Pictoris
– Early solar system had disk (proto-planetary disks)
– New studies (HST, ground) show resonant gaps
SIRTF will FIR images and spectroscopy of debris disks (structure, mass, composition); NGST can exploit superior sensitivity and spatial resolution
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Debris andProtoplanetary Disks
Debris Disk Pictoris Note resonant cleared gap - major planet
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Brown Dwarfs Importance of low mass “failed
stars” as halo constituents in our own Milky Way Galaxy, and in clusters within our Galaxy unknown– Gliese 229B best known methane dwarf example -
few dozen now known– L dwarfs - objects T <2000K; few hundred known
Spectra dominated by molecular bands SIRTF surveys & spectroscopy; NGST surveys -
contribution to mass budget
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Brown Dwarfs in Orion Swarm of Newborn Brown Dwarfs
found in Orion stellar nursery
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Conclusion
SIRTF and then NGST will take us back to the early times when galaxies formed, and will address– range in z that formation took place; AGN, starburst
phases in galaxy evolution; pin down cosmological parameters
– bottom-up or top-down scenario for star formation in galaxies; mass function of galaxies
SIRTF and NGST will define the history of planetary systems around other stars