Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stsci.edu/jwst/doc-archive/presentations/JWST-STScI-000442.pdf Äàòà èçìåíåíèÿ: Unknown Äàòà èíäåêñèðîâàíèÿ: Tue Feb 5 12:06:24 2013 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 106

Frascati Workshop 2003 27 May 2003

Primordial Stellar Populations and the James Webb Space Telescope
Nino Panagia (ESA/STScI)
(Based on work done in collaboration with Massimo Stiavelli, Harry Ferguson, and Peter Stockman)
To be submitted to ApJ, Summer 2003


Who is JW?
James E. Webb, NASA administrator 1961-1969.
Webb believed that NASA had to strike a balance between human space flight and science because such a combination would serve as a catalyst for strengthening the nation's universities and aerospace industry. Webb's vision of a balanced program resulted in today. During his tenure, NASA invested in the environment so that astronauts could do so later, 1965, Webb also had written that a major space become a major NASA effort. a decade of space science research that remains unparalleled development of robotic spacecraft, which explored the lunar and it sent scientific probes to Mars and Venus. As early as telescope, then known as the Large Space Telescope, should

By the time Webb retired just a few months before the first moon landing in July 1969, NASA had launched more than 75 space science missions to study the stars and galaxies, our own Sun and the as-yet unknown environment of space above the Earth's atmosphere. These missions built the foundation for the most Primordial Stellar Populations 2 successful period of astronomical discovery in history.


The James Webb Space Telescope: JWST at a Glance
· NASA+ESA+CSA joint project · 25 m2 primary mirror · 0.6-10+ µm wavelength range · 5 year mission life (10 year goal) · Passively cooled to <50K · L2 orbit · Launcher Ariane V · To be launched in 2011
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Why JWST is better than HST& Ground !
· 6m telescope is required to probe the origins of stars and galaxies at large redshifts (early days). · A cooled telescope provides 103 to 108 lower background · JWST imaging diffraction-limited over >10 arcmin2 FOV
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Early Galaxies &. 8m telescope


JWST will work at the Second Lagrange Point
· Metastable orbit, 1.5 million km from Earth. · Solar radiation pressure is dominant torque. · Thermally stable. · 10 Mbs downlink is straightforward. · Orbit corrections every month
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JWST Science Instruments
NIRCam (NASA) Near-IR and visible camera
sensitive over the 0.6-5 micron wavelength range 4'x4' field of view 0.04" pixels (lambda/2 D) at 2.4 micron possibly a R=100 spectral capability (slit+grism) possibly a coronographic capability

NIRSpec (ESA)

Multi-object dispersive spectrograph (MOS)
sensitive over the 1-5 micron wavelength range > 3'x3' field of view ~0.1" pixels R~1000 spectral capability, maybe an R~100 capability capable of observing >100 objects simultaneously probably with MEMs (micro-electro-mechanical) technology

MIRI (ESA/NASA)

Mid-IR camera and slit spectrograph
sensitive over the 5-28 micron wavelength range 2'x2' field of view imaging or R=1500 slit spectrograph a preference for a single focal plane array

FGS (CSA)

Fine Guide Sensor: Enable stable pointing
Primordial Stellar Populations at the milli-arcsec level sensitivity and field of view to allow guiding with 95% probability at any point on the sky 6


JWST Science Goals
· Cosmology and the Structure of the Universe · The Origin and Evolution of Galaxies · The History of the Milky Way and Its Neighbors · The Birth and Formation of Stars · The Origins and Evolution of Planetary Systems
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Seeking the origins of the Universe
· Observations of very distant galaxies can tell us how the Universe formed and evolved · In particular: - How matter "coagulated" into galaxies - What type of stars were formed first - How did they evolve and enrich their environments of heavy elements
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A brief history of the Universe

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The Hubble Deep Field
z: 1.01 z: 5.34

z: 2.01 z: 5.60 z: 2.93

z: 2.97

z: 3.43

Williams et al. (1996)


Distant Galaxies in the HDFs
· Galaxy sizes were smaller at higher redshifts (or number of small bright objects larger). · Fraction of irregular and multiple component systems increases with redshift.
HDF North HST · NICMOS HDF South

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A galaxy building block at z6?
Combined HST-WFPC2 and Keck observations have revealed the most distant dwarf galaxy ever found
Gravitationally lensed (â33) by the Abell 2218 galaxy cluster, the small red galaxy is estimated to be at a redshift z=5.6, to have a mass of about 106 M , and a young stellar population as young as 2-3 Myrs.
R. Ellis et al. 2001 R. Ellis et al. 2001
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Searches for high-z galaxies
· Lyman-break galaxies (i.e. blue continuum with sharp short wavelength cutoff), e.g. Steidel & Hamilton (1992) + ... Giavalisco et al. (1994) + ... · Strong Lyman- emitters, e.g., Blank field surveys ( Hu et al. 1991... Cowie & Hu 1998, ...) LALA survey (Malhotra & Rhoads 2002) z2.4 Ly- search (Stiavelli et al. 2001) · High photometric redshifts, e.g. Lanzetta et al. (...) revealed galaxies up to z 13 (!?) in the HDFs
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Primordial Stars?
Question: How do I recognize primordial stellar populations? Answer: I check that is no sign of metal pollution in their spectra : the Next Generation is expected to have ZZsun/1000, so that I([OIII]5007)I(H)/10
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Primordial Stars are expected to be:
· · · · Metal free (Z=0) Hot (Teff~100,000 K) Formed in ~106 M clouds Massive (>>10 M , possibly >100M )
e.g., Ezer & Cameron (1971), Ezer (1972), Cary(1974), Castellani & Paolicchi (1975), Woosley & Weaver (1981), Bond et al. (1982, 1983), Forieri (1982), Salpeter et al. (1983), El-Heid et al. (1983), Castellani et al. (1983), Chieffi & Tornambe` (1984), Cassisi & Castellani (1993), Haiman et al. (1996), Tegmark et al. (1997), Miralda-EscudÈ & Rees (1997), Tumlinson & Shull (2000), Baraffe et al. (2001), Bromm et al. (2001), Madau et al. (2001), Ciardi & Ferrara (2001), Omukai & Palla (2001), Marigo et al. (2001)... and many, MANY more!
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Low metallicity stars are hotter

Tumlinson & Shull (2000)
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Zero- metallicity stars: Ionizing Photon Fluxes for HI, HeI and HeII
HI HeI

HeII

Tumlinson & Shull (2000)
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Population III stars can be very massive and are all very hot

Baraffe et al. (2001)
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The spectra of massive Population III stars are very similar to black-bodies

Bromm et al. (2001)
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How to detect primordial stellar populations?
· High Teff values imply low optical-NUV fluxes, about 3-8 times lower than in the local Universe · On the other hand, the ionizing fluxes are high

· Therefore, detection of primordial stars will be possible through the study of associated HII regions
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The properties of the surrounding HII regions are:
· Highly ionized gas with presence of He++ · High electron temperature Teff > 20,000 K · No metal ions · No dust absorption
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Model calculations for local Universe and primordial HII regions

The calculations were made using CLOUDY90 (Ferland et al. 1998), adopting ne=102 cm-3 and scaled solar abundances.
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An optical image of a primordial HII region will display:

· Fainter blue stars · Red-orange nebula · No dust absorption

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The UV/optical spectrum of a primordial HII region is characterized by:
· · · · Strong HI and HeI emission lines Moderately strong HeII lines No metal lines Flatter UV continuum

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In particular we expect:
· Strong Ly emission L(Ly)~0.46Ltot Weq(Ly)~3000å I(1640)~ I(H) (2q emission)

· "Intense" HeII lines · Flatter UV continuum

· Steep Balmer decrement H/H~ 3.2
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HII Region Electron Temperature

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Local Universe and Primordial HII Regions

Model calculations made using CLOUDY90 (Ferland et al. 1998), adopting ne=102 cm-3 and scaled solar abundances.
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The Ly- line is considerably brighter at low metallicities because of collisional excitation 1s-2p

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The Ly- equivalent width increases strongly at low metallicities because : (a) the line intensity increases and (b) the continuum flux decreases

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The intensity of the [OIII] 5007å line increases linearly with O abundance at low metallicities

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Indeed, the [OIII] 5007å line intensity is approximately proportional to the Oxygen abundance in Blue Dwarf Galaxies

>5 I([OIII]5007)/I([OII]3727) 2.5-5 < 2.5

[Data from Izotov & Thuan 1999]
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The first generation supernovae pollute their primordial clouds
· The first supernova will eject at least 10 M of metals

· The ejecta will be stopped in about 1 Myr inside the parent cloud whose mass is about 106 M · Correspondingly the cloud will be polluted to a level of about Z 0.00001 Z /2000 · Subsequent SNe will pollute further, up to as much as Z Z /200
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Metal Yield from Primordial Supernovae

Oh et al. (2001), adapted from Heger & Woosley (2002) Primordial Stellar Populations 33


The first generation supernovae enrich a primordial cloud to Z Z /1000, which sets the stage for The Next Generation
characterized by revealing properties · Metal lines are present and detectable, e.g. [OIII] 5007å with I(5007)/I(H) 0.1 · Dust may form and absorb as much as 30% of the Ly- line intensity, so that L(MIR-FIR)~0.15Ltot
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THE BIG QUESTION: "When is low metallicity low enough?" Or "If we do not detect metal lines in the HII region spectrum, how will we be sure that the gas is metal free?" THE ANSWER: "There are no metals if I(5007å)/I(H)<0.1"
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Local Universe and "second" generation HII regions

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"second" generation and "primordial" HII regions

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Pristine stars + pristine gas

Pristine stars + polluted gas Enriched stars + enriched gas

Local universe stars + gas

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Can we see Ly- before re-ionization? Lyman- transmission through neutral IGM
(Gunn & Peterson 1965)

100% neutral

Miralda-EscudÈ 1998, Madau & Rees 2000, Panagia et al. 2002, 2003
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Observed Ly- Luminosity: a considerable fraction of the emitted one!

Model calculations assuming a Ly- line width of 250 km s
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-1

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Do we have the means to study such distant stars?
· "Yes" and "No"... · YES, we can detect distant galaxies Ly- · NO, we cannot characterize them fully, YET NGST will be able to do so
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Expected JWST Sensitivity

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Observing a 106 M starburst with JWST

Limiting fluxes for exposure time 4â105s and S/N=10
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Limiting total luminosities and star formation rates to detect emission lines with an exposure time of 10 hours at S/N=5 ([OIII] and HeII) and S/N=10 (H, H and Ly)

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Spectroscopy with JWST
will be able to detect an [OIII]5007A line I(5007)/I(H) ~ 0.1 with an exposure time of 10 hours at a S/N=5 level up to z=10 for SFR 0.1 M yr-1 up to z=15 for SFR 1 M yr-1 allowing us to discern bona fide primordial stellar populations from those polluted by early supernovae
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Studying Primordial Stellar Populations
· Search for - Ly-c and/or Ly- dropouts in I,J,H,K bands - strong Ly- emitters candidates at redshifts >6 ground-based 8-10m HST (Rhoads et al., Cy. 11/12) NGST (NIR: grism, imaging)

· Study the UV and optical rest-frame spectrum of suitable candidates with JWST in the NIR/MIR "strong" HeII 1640 line top-heavy IMF "detectable" [OIII] line next-gen stars
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What about Supernovae?
Type Ia (MB=-19.5) Type II (MB=-17.5)

5 10 20

5 10 20

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Primordial Supernovae [SNIII]
Massive (M140-260M ) population III stars can produce much brighter (â100-200) SNe (Heger et al 2001) These SNIII can be detected up to z=20 and beyond!

5µm

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Conclusions
It is possible to discern truly primordial stellar populations from next generation stars ([OIII] 5007å) It is possible to identify the properties of the dominant stars (HeII 1640å) It is possible to measure metallicities of galaxies up to redshifts 10-15 Primordial supernovae (SNIII) can be detected individually up to z=20 and beyond.
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