1a.introduction 1b.popiii stars and galaxies --> « top down » theoretical approach 2.,3a.ly ...

1a. Introduction1b. PopIII stars and galaxies

--> « top down » theoretical approach

2.,3a. Ly physics and astrophysics

3.b,4. Distant/primeval galaxies: - observational searches- current knowledge about high-z galaxies--> « bottom up » observational approach and confrontation with theory

Outline of the Outline of the lectureslectures

Outline of Part 2+3aOutline of Part 2+3a

Ly physics and astrophysics

ISM emissionLy: the observational « problem »Lessons from local starburstsLy radiation transfer (+dust)Lessons from Lyman Break Galaxies

Ly trough the InterGalactic MediumLy from sources prior to reionisationLy Luminosity Function and reionisation

Ly Emission

Galaxies with intense star formation (starbursts):

Intense UV radiation, ionising flux (>13.6 eV), and emission lines from HII regions and diffuse ionised ISM H, He recombination lines, [semi-]forbidden metal lines … case B: L(Ly, H, …) = cl * QH and I(Ly)/I(Hn) = c(T,ne)

2/3 of recombinations lead to emission of 1 Lya photon(cf. lectures G. Stasinska)

Ly Emission

At (very) low metallicity: strong/dominant Ly ! since• increased ionising flux from stellar pops.• dominant cooling line (few metals)• emissivity increased by collisional excitation(higher nebular temperature, Te)--> up to ~10% of Lbol emitted in Ly!==> potentially detectable out to highest redshifts!!

…searches unsuccessful until 1990ies --> Part 3

Partridge & Peebles (1967)

GENERAL: fate of Ly photonsscattering until escape --> Ly halo

Ly destruction by dust destruction through 2 photon emission (only in HII region)

Ly - the «problem »• Observable UV (>912 Ang): galaxies optically

thin • However, very rapidly optically thick in Ly

line (NHI >~ 1013 cm-2 )

--> Radiation transfer within the galaxy determines the emergent line profile and Ly « transmission » !

• Furthermore: dust may destroy Ly photons

Ly TRANSFER

0 E_B-V 0.1

Ly escapefraction

{

The Ly puzzle(s) in nearby starbursts• 1980-90ies: several searches for Ly emission from

z~2-3 primordial galaxies unsuccesful --> 1 or 2 puzzles: small number of galaxies and/or lower Ly emission?

• IUE satellite: UV spectra of nearby starbursts (Ly) + optical spectra (H,H)

==> 1) extinction corrected I(Ly)/I(H) << case B

Ly: THE « OBSERVATIONAL » PROBLEM

Valls-Gabaud (1993)Terlevich et al. (1993)

(Meier & Terlevich 1981, Hartmann et al. 1984, Deharveng et al. 1986,… Giavalisco et al. 1996)

The Ly puzzle(s) in nearby starbursts• 1980-90ies: several searches for Ly emission from z~2-3

primordial galaxies unsuccesful --> 1 or 2 puzzles: small number of galaxies and/or lower Ly emission?

• IUE satellite: UV spectra of nearby starbursts (Ly) + optical spectra (H,H)

==> 1) extinction corrected I(Ly)/I(H) << case B and W(Ly) smaller than expected (synthesis models)

==> 2) no trend with metallicity (O/H)


Possible explanations:-dust (Charlot & Fall 1993) (but 2!)-With « appropriate » (metallicity-dependent) extinction law no problem. Also underlying stellar Ly absorption

(Valls-Gabaud 1993)

-Inhomogeneous ISM geometry primarily determining factor, not dust (Giavalisco et al. 1996)

-Short « duty cycle » of SF may explain small number of Ly emitters

The Ly puzzle(s) in nearby starbursts

Possible explanations for individual objects:

- dust ? - With « appropriate » (metallicity-

dependent) extinction law no problem. Also underlying stellar Ly absorption

RULED out as SOLE explanations by IZw18, SBS 0335-052 (most metal poor stabursts known) which show no Ly emission !!

- Inhomogeneous ISM geometry primarily determining factor, not dust

OK, but quantitatively ?


Kunth et al. (1994)

The Ly puzzle(s) in nearby starbursts

Detection of (neutral gas) outflows in 4 starbursts with Ly in emission

- metallicities 12+log(O/H)~8.0…8.4..solar

- EB-V ~ 0.1 - 0.55

==> outflows, superwinds main crucial/determining factor for Ly escape!?

Ly:LESSONS FROM LOCAL STARBURST

Kunth et al. (1998)


Hayes et al. (2005)Ly line image (cont.subtracted)

2-3 D studies of Ly in nearby starbursts

ACS/HST imaging in Ly + narrow continuum filter

WFPC2/HST images in 5 other filters --> stellar population, UV slope …

==> Diffuse Ly emission seen ! Contains 2/3 of total flux in large aperture (IUE…) --> confirmation of Ly resonant scattering halo

* different regions: different H kinematics

--> but no constraint on HI kinematics at this spatial scale (requires SKA)!


Imaging (ACS)+ kinematics (H Integral Field, Ly long-slit STIS)

ESO 350-IG038: knots B + C: similar, high

extinction one shows emission other not.Kinematics, NOT DUST, dominant

SBS 0335-052:only absorption seen. If dust

affects Ly, it must do so at even small scale (1 pixel ~ 6-9 pc!)


Kunth et al. (1998)Kunth et al. (2003)


Diversity of line profiles explained by evolutionary sequence of staburst driven supershells / superwind?


Tenorio-Tagle et al. (1999)Mas-Hesse et al. (2003)

1

2

4

1 2

3, 4 5,6 M82

Lessons from nearby starbursts

• W(Ly) and Ly/Hb < case B prediction ! • No clear correlation of Ly with metallicity, dust,

other parameters found.• Strong variation of Ly observed within a galaxy• Ly scattering « halo » observed• Starbursts show complex structure (super star

clusters + diffuse ISM); outflows ubiquitousLy affected by:• ISM kinematics• ISM (HI) geometry• DustPrecise order of importance unclear!

Quantitative modeling including known constraints (stars, emitting gas, HI, dust + kinematics) with 3D radiation transfer model remains to be done


Ly transfer: basics

Ly TRANSFER: THE ESSENTIALS

Verhamme, Schaerer, Masseli (2006)

Cross section in atoms frame

Optical depth taking Maxwellian velocity distr. into account

Ly optical depth (in convenient units)<==> ~1 at line center for NH=3.1013 cm-2 (and T=104K)

Line absorption profile (Voigt)

Ly transfer: basics

Ly TRANSFER: THE ESSENTIALS

From Hubeny

• >> 1 at line center for NH >3.1013 cm-2 (and T=104K)• Very large number of scatterings required to escape. E.g. NH=1020 --> Nscatt ~ 107 for static slabBUT: velocity fields or inhomogeneous medium can ease escape

(Ly) line scattering NOT a random walk:- walk in coupled spatial and frequency space- transport dominated by excursions to line wing! --> lower opacity --> longer mean free path

1a.introduction 1b.popiii stars and galaxies --> « top down » theoretical approach 2.,3a.ly ...

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