1. HII regions at high redshift
Anticipating JWST NIRSpec spectroscopy
Bob Fosbury, Space Telescope - European Coordinating Facility, Garching, Germany
European Space Agency

2. March 2004, RAEF
High z HII regions

3. March 2004, RAEF
High z HII regions

4. Example: The Lynx arc z = 3.357
Richness of UV spectrum
High colour temperature of ionizing source(s)
High ionization parameter (cf. PNe)
Nebular metal abundance ~ 10-2 Solar
Stellar abundances ???
Huge Lyman continuum luminosity
Top-heavy IMF ?
March 2004, RAEF
High z HII regions

5. Time - redshift <- µwave background comes from z~1000 LBG
3C radio galaxies
Lynx arc
A1835 IR1916, z = 10
Highest redshift quasar
Lynx cluster
z ~ 2.5 radio galaxies
Earth forms
Now
March 2004, RAEF
High z HII regions

6. Outline
A primary scientific driver for NIRSpec is a survey of ~2500 galaxies to measure the redshifted nebular emission lines
Known as: “Kennicutt Science”
Use familiar techniques to measure SFR, reddening, element (nebular) abundances, kinematics and presence of AGN
Predicated on the use of the restframe optical spectrum ([OII] > [SII] 6725)
Gives Ha to z ~ 6.6 and [OII] to z ~ 12.4
March 2004, RAEF
High z HII regions

7. This programme is severely limited from the ground
Expectation is that many galaxies at high z will have emission line spectra representing the higher SFR at earlier epochs
This programme is severely limited from the ground
Giving Ha only to z ~ 2.8
However, progress can be made from the ground using the restframe UV spectrum
What might we expect to measure and what can be deduced about the gas in the early universe in the presence of star formation or AGN?
March 2004, RAEF
High z HII regions

8. Systematics of AGN spectra
AGN in the UV are characterised by resonance and intercombination emission lines from regions of different density
The lines result from recombination and collisional excitation processes
They tell us about
the nature of the ionization processes
the physical condition of the gas: Te and ne
the kinematics
and, to some extent, the chemical composition
March 2004, RAEF
High z HII regions

9. Complexities include:
Resonance line transfer
The various effects of dust
Accounting for regions of different density and continuum opacity (radiation and matter-bounded clouds)
Photoionization codes can be used to understand the general behaviour of the nebulosities in the UV — but it is more difficult than in the optical
March 2004, RAEF
High z HII regions

10. TXS z = 2.340
March 2004, RAEF
High z HII regions

11. Quasar BLR
Comparison of the kpc-scale ISM data from radio galaxies with the Quasar BLR data discussed by Hamann & Ferland
March 2004, RAEF
High z HII regions

12. Spectral sequence
From low-polarization, metal-poor (?) radio galaxies to High-polarization, metal-rich (?) ULIRG
March 2004, RAEF
High z HII regions

13. Lya/CIV & NV/CIV vs P(%) correlations
March 2004, RAEF
High z HII regions

14. UV spectra of AGN and Ly-break
Lya
NIV]
HeII
NIII]
CIII]
SiIV
OIV NV
CIV
OIII]
SiIII]
March 2004, RAEF
High z HII regions

15. Systematics of Ly-break galaxies
See: Shapley et al. 2003, ApJ, 588, 65
Hot stars, HII regions, dust, outflows
Relationships seen between Lya EW, continuum slope and interstellar kinematics
Likely to be determined by the nature of the outflows (covering factor and velocity) and the metallicities of the HII regions
March 2004, RAEF
High z HII regions

16. Composite Ly-break spectra
March 2004, RAEF
High z HII regions

17. HII regions in the UV
Local HII regions have a UV spectrum dominated by the continuum from the stellar population
Emission lines are weak since the nebular excitation is quite low — ionizing O stars are typically Teff ~ 40,000K
The presence of dust can render observations difficult
e.g., FOS spectroscopy of M101 HII regions by Rosa & Benvenuti (1994)
March 2004, RAEF
High z HII regions

18. M101 HII regions
March 2004, RAEF
High z HII regions

19. LHb - s relation Terlevich2 & Melnick 2002
March 2004, RAEF
High z HII regions

20. Expectations for HII galaxies at high z
Low stellar metallicities
Massive (hot) stars => high ionization nebulæ
Top-heavy IMF for 1st generation (Pop III)
Low gas metallicities
but get rapid pollution by Type II supernovæ
The high stellar Teff means that, for a given bolometric luminosity (which is mostly below the Lyman limit) the UV/optical continuum is relatively weaker (~ T-3eff in the Rayleigh-Jeans tail)
can mean that the SED longward of Lya is dominated by the 2-photon continuum
March 2004, RAEF
High z HII regions

21. Models: Panagia et al. Dependence of [OIII] on Z and Teff
March 2004, RAEF
High z HII regions

22. Can we observe sources like this?
Look at the Lya emitters and distinguish between AGN and stellar-ionized nebulæ
Search for sources dominated by emission lines => characteristic loci in colour-colour diagrams
Get lucky -> the Lynx arc
Magnified sources: the ‘critical line’ searches
March 2004, RAEF
High z HII regions

23. The Lynx arc, z = 3.357
Discovered as part of the ROSAT Deep Cluster Survey (Holden et al. 2001)
Studied in detail by Fosbury et al. (2003)
Magnified by ~ x10 by two clusters at z ~ 0.5
March 2004, RAEF
High z HII regions

24. March 2004, RAEF
High z HII regions

25. UV spectrum
March 2004, RAEF
High z HII regions

26. Optical spectrum
March 2004, RAEF
High z HII regions

27. SED
March 2004, RAEF
High z HII regions

28. Lensing model Marco Lombardi
Lensed by two clusters at z = 0.57 and z = 0.54
Close to a caustic in the source plane
Total magnification between 8 and 16
(but could be some differential effects)
March 2004, RAEF
High z HII regions

29. ‘Vital statistics’ Ionizing source Nebula TBB = 80,000 ± 10,000K
Qion = 1.6 x 1055 ph s-1 (assuming µ(A,B) = 10)
=> 105–6 massive (Pop III - like) stars
Nebula
ne ≤ 1000 cm-3 (from CIII]), Te ~ 20,000K, U = 0.1
Z/Zsun = 0.05, sgas ≈ 30 km s-1 (from CIII] and OIII])
March 2004, RAEF
High z HII regions

30. They produce ~ 20 x too few ionizing photons
The nebular continuum (light blue line) is simply scaled from the observed Hb flux with no reddening
S99 population models are for 107 Msun with a Salpeter IMF (a = 2.35; 1–100Msun) and Z/Zsun = 0.05
They produce ~ 20 x too few ionizing photons
March 2004, RAEF
High z HII regions

31. Can we find these sources in the field?
Colour-redshift loci determined predominantly by the emission lines (Lynx is VERY bright at K due to [OIII])
Will appear as Lyman forest dropouts at high z
March 2004, RAEF
High z HII regions

32. GOODS CDF-S BViz
March 2004, RAEF
High z HII regions

33. GOODS ACS (V1.7) #6746 zAB = 24.43 z = 5.6 r ~ 1kpc Lya cf. Lynx
F814WAB = 23.1
z = 3.36
Dm(Dz)=1.32
Lya
NIV] CIV
March 2004, RAEF
High z HII regions

34. Conclusions
The very early phase of these massive starbursts is very bright
We don’t see ANY starlight directly – just the HII region glow
These are efficient H-ionization engines
The restrame UV spectra are a lot more interesting than those of local, metal-rich HII regions – the intercombination lines are good for abundance determinations
March 2004, RAEF
High z HII regions

35. They are considerably more massive than globular clusters
We estimated ~ 109 Msun for Lynx
The ionizing stars are close to our expectation for Pop III
Are these the very early phase of collapse of the galaxies that produce the metals seen in the oldest globular cluster stars (~ -2 dex)?
March 2004, RAEF
High z HII regions