HII regions at high redshift

HII regions at high redshift

Anticipating JWST NIRSpec spectroscopy

Bob Fosbury, Space Telescope - European Coordinating Facility, Garching, Germany

[email protected] www.stecf.org/~rfosbury

European Space Agency

mailto:[email protected]

mailto:[email protected]

http://www.stecf.org/~rfosbury

March 2004, RAEF High z HII regions 2



Example: The Lynx arcz = 3.357

Richness of UV spectrumHigh colour temperature of ionizing source(s)High ionization parameter (cf. PNe)Nebular metal abundance ~ 10-2 SolarStellar abundances ???Huge Lyman continuum luminosityTop-heavy IMF ?


Time - redshift

Hig

hest

red

shift

qua

sar

Lynx

arc

Ear

th f

orm

s

Now

Lynx

clu

ster

<- µwave background comes from z~1000

A18

35 I

R19

16,

z =

10

z ~

2.5

rad

io g

alax

ies

3C radio galaxiesLBG


OutlineA 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] 3727 -> [SII] 6725)Gives H to z ~ 6.6 and [OII] to z ~ 12.4


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 groundGiving H 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?


Systematics of AGN spectraAGN 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 kinematicsand, to some extent, the chemical composition


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


TXS0211-122 z = 2.340


Comparison of the kpc-scale ISM data from radio galaxies with the Quasar BLR data discussed by Hamann & Ferland

Quasar BLR


Spectral sequence

From low-polarization, metal-poor (?) radio galaxies

to

High-polarization, metal-rich (?) ULIRG


Ly/CIV & NV/CIV vs P(%) correlations


UV spectra of AGN and Ly-break

Ly

NVSiIVOIV

NIV] HeII

OIII]

CIII]

CIV

NIII]

SiIII]


Systematics of Ly-break galaxiesSee: Shapley et al. 2003, ApJ, 588, 65

Hot stars, HII regions, dust, outflows

Relationships seen between Ly 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


Composite Ly-break spectra


HII regions in the UVLocal 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)


M101 HII regions


LH - relationTerlevich2 & Melnick 2002


Expectations for HII galaxies at high z

Low stellar metallicitiesMassive (hot) stars => high ionization nebulæTop-heavy IMF for 1st generation (Pop III)

Low gas metallicitiesbut 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-3

eff in the Rayleigh-Jeans tail)can mean that the SED longward of Ly is dominated by

the 2-photon continuum


Models: Panagia et al.

Dependence of [OIII] on Z and Teff


Can we observe sources like this?

Look at the Ly 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 arcMagnified sources: the ‘critical line’ searches


QuickTime™ and aSorenson Video decompressorare needed to see this picture.

The Lynx arc, z = 3.357Discovered 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


QuickTime™ and aSorenson Video decompressorare needed to see this picture.


UV spectrum


Optical spectrum


SED


Lensing modelMarco Lombardi

Lensed by two clusters at z = 0.57 and z = 0.54

Close to a caustic in the source planeTotal magnification between 8 and 16

(but could be some differential effects)


‘Vital statistics’

Ionizing sourceTBB = 80,000 ± 10,000K

Qion = 1.6 x 1055 ph s-1 (assuming µ(A,B) = 10)

=> 105–6 massive (Pop III - like) stars

Nebulane ≤ 1000 cm-3 (from CIII]), Te ~ 20,000K, U = 0.1

Z/Zsun = 0.05, gas ≈ 30 km s-1 (from CIII] and OIII])


The nebular continuum (light blue line) is simply scaled from the observed H flux with no reddening

S99 population models are for 107 Msun with a Salpeter IMF ( = 2.35; 1–100Msun) and Z/Zsun = 0.05

They produce ~ 20 x too few ionizing photons


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


GOODS CDF-S BViz


GOODS ACS (V1.7) #6746

zAB = 24.43

z = 5.6

r ~ 1kpc

cf. Lynx

F814WAB = 23.1

z = 3.36

m(z)=1.32

Ly

NIV] CIV


ConclusionsThe very early phase of these massive

starbursts is very brightWe don’t see ANY starlight directly – just

the HII region glowThese are efficient H-ionization enginesThe restrame UV spectra are a lot more

interesting than those of local, metal-rich HII regions – the intercombination lines are good for abundance determinations


They are considerably more massive than globular clustersWe 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)?

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HII regions at high redshift