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