Microwave

Background

Image fromSpace TelescopeScience Institute

What What reionizedreionizedthe universe?the universe?

Observations of First Light Betsy Barton (UC Irvine)

Member, TMT SAC

Project Scientist, IRIS on TMT

The End of the cosmic dark ages

• What are the open questions at high (> 7) redshifts?

• What is happening with present-day (or near-future) instrumentation? How do we carry it far into the future?

• First light science with giant telescopes like TMT

• What can we learn about first light in the Universe in the end?

Observations constraining reionization• Wilkinson Microwave Anisotropy Probe (WMAP):

–– Reionization began at 7 < z < 20 Reionization began at 7 < z < 20 (Bennett et al. 2003; Spergel et al. 2007; depending on history)

• Becker et al. (2001); Fan et al. (2002):–– GunnGunn--Peterson troughs in distant quasar spectra show Peterson troughs in distant quasar spectra show

reionizationreionization ended near z ~ 6ended near z ~ 6• Fan et al. (2001):

–– Extrapolated quasar luminosity function not enough to Extrapolated quasar luminosity function not enough to reionizereionize the universethe universe

• Yan et al. (2005), Mobasher et al. (2005) and many others:–– Spitzer shows galaxies at z > 6 that are several hundred Spitzer shows galaxies at z > 6 that are several hundred MyrMyr

oldoldSTAR-FORMING GALAXIES probably

reionized the Universe(see Tinsley 1973!!)

How can we How can we find these find these galaxies?galaxies?

Early, ionizaing seed galaxies and reionization

(Iliev et al. http://www.cita.utoronto.ca/~iliev/dokuwiki/doku.php?id=reionization_sims)

How do we guess what is out there?• Theory tells us about

– dark matter halo sizes (small)– the IGM (neutral to “mixed” to ionized)– the very first stars (probably very big and hot)– the possible progress of ionization (probably

starts outside dense regions, then the bubbles coalesce)

Theory tells us less about the baryonic properties of first-light sources

How do we guess what is out there?• Extrapolate from “low” redshift (z < 6)

– Very (overly?) conservative– Problem is that we are searching for the epoch when things

change dramatically to metal-free star formation

• Try to parameterize high-z galaxies with a few parameters and see what you predict

– Very sensitive to what you choose

• Just do a thorough exploration of parameter space– Eventually, it should work– Expensive, and you don’t know when it will work

Detecting sources in the continuum: often too faint for follow-up

Bouwens et al. (2004)

Other technique: detecting emission-line sources

First generation experiment: Window at z=8.227 w/ Gemini/NIRI

Narrow-bandfilter (R=125)

Noise down byfactor of >10 from other Gemini/NIRInarrow-bandfilters

transmissiontransmission

skyskyemissionemission

(Barton et al. 2004)

Narrow-band filter

Hubble Deep Field

[OII] line emission at z=2.01, 15 hours with Gemini/NIRI

The Production and Escape of High-redshift Lyman-αPhotons

{{stellar initialstellar initialmass functionmass function

star formation ratestar formation rate

penetration through penetration through intergalactic mediumintergalactic medium

escape ofescape ofionizing andionizing andLyLyαα photonsphotons

partially neutral IGM(above z ~ 6.2)

Different Lyman α scenarios yield a huge range of possibilities

ScenarioIMF(MO)

Metallicity(ZO)

fIGM fesc fLyα

1.0

0.25

0.25

0.25

Optimistic 300-1000 0 0.35 2.1 x 1043

Plausible 50-500 0 0.1 6.4 x 1042

Heavy Salpeter 1-500 10-5 0.1 1.8 x 1042

Salpeter 1-100 0.2 0.1 7.3 x 1041

“optimistic”scenariosimulation

48 hour obs.8-meter tele.1.122μm20% throughputR=125 filter0.35-arcsec seeing

Springel &Hernquist (2003)model

(Barton et al. 2004)

z=8.2 galaxiesz=8.2 galaxies

10 10 hh--11 comovingcomoving MpcMpc=5.4 =5.4 arcminarcmin(e.g., Stark & Ellis

; Willis

& Courbin 2005;

Cuby et al. 2007; B

arton et al., i

n prep.)

What do we know now?

Definite sources and likely/possible candidates at z=5-10

Fluxes shifted to common luminosity distance at z=7.7

Stark et al. (2007)

The Next Steps for the US: FLAMINGOS 2 and MOSFIRE

Keck MOSFIRE:

6.2’ FOV

Gemini-SouthFLAMINGOS 2:

6.1’ FOV

DAZLE on VLT already in operation; results not publicized to date

F2T2F2T2An engineering prototype for the JWST Tunable Filter Imager…F2T2 will be fed by a multi-conjugate adaptive optics system

and be a facility-class instrument on Gemini next year.

An engineering prototype for the JWST Tunable Filter Imager…F2T2 will be fed by a multi-conjugate adaptive optics system

and be a facility-class instrument on Gemini next year.

A lensed cluster survey on Gemini with AO (F2T2)

Region of parameter space where expectation value of detected sources is >= 1

z=7.2-10Approx. 20 nights with

F2T2

A Single-field Deep (Unlensed) Survey

Region of parameter space where expectation value of detected sources is >= 1

z=7.7Approx. 13 hours with

Keck/MOSFIRE

Related science on VLT (DAZLE); planned for FLAMINGOS2

A Wide-field (Unlensed) Survey

Region of parameter space where expectation value of detected sources is >= 1

z=7.7Approx. 50 hours with

Keck/MOSFIRE

Related science on VLT (DAZLE); planned for FLAMINGOS2

What might we know by 2016?

Difficult/impossible to explore with 8-10-m class telescopes at z > 7

z beyond ~8-10 essentially impossible

First-light science in the era of large telescopes

Thirty Meter Telescope

TMT first-light IR instruments that will tackle first light:

•IRMS: 2 arcminutefield-of-view; can use for narrow-band imaging•IRIS: 15-arcsecond fov DL imager/0.26-3.2 arcsecond IFU

IRMS: InfraRed Multi-object Spectrograph

• Based on Keck/MOSFIRE• 0.95-2.45 μm• All of Y, J, H, or K at once• 2 arcminute field of view• 46 reconfigurable cryogenic slits• <= 60-80 mas arcsecond sampling• 80% energy in 2x2 pixels• R ~ 4660

IRIS

IFU:• 64 x 64 “pixel” IFU; up to 128 x 128 in some modes (?)• 0.8-2.5 μm requirement• 4 plate scales: 4, 10, 25, 50 mas• 4 fields of view for IFU, at least: 0.26, 0.64, 1.60, 3.20 arcsec• Full Y, J, H, or K coverage at once• R ~ 4000• Design currently lenslet AND image slicer

IMAGER:– 15 arcsecond fov– 4 mas sampling

(Taylor & Prieto)

TMT Instruments + AO

• ~100 mas IQ, 2 arcmin. field• Ideal to follow-up JWST

surveys with spectroscopy• With narrow-band filter, can

pursue blind Lyman α searches

• Measure luminosity function, topology of reionization, maybe presence of fainter features

• IFU and imager• Can sample best image

quality produced by facility AO

• Mode is follow-up to IRMS or JWST

• In principle, best sensitivity for tiny sources (like clusters)

• Spatially resolved spectroscopy of larger/brighter early galaxies

IRMS IRIS

Can we benefit from adaptive optics for first-light Lyman αscience?

• Early galaxies are predicted to be smaller than the seeing limit

– (argument that IGM will scatter sources to appear big doesn’t really hold water; if the IGM around them is neutral, forget about it)

– Stark et al. (2007) empirical best-guess scaling: mean size ~ 0.1”/(1+z/7) (right size for IRMS/coarse IRIS modes)

• Tiny, luminous star clusters in formation are not beyond the reach of ELTs

– Nominal star formation rate of unresolved 1 solar mass per year yields detectability well beyond z=10 (right size for IRIS)

What can we hope to understand with ELTs and AO?• When did galaxies assemble and “turn on”?

– Luminosity functions to z=20 and even beyond (JWST + Lyman α searches with ELTs?)

– Keys are sensitivity and wide field

• How did reionization proceed? (Topology, rate, effects.)– Maps for Mpc-scale clustering (e.g., Mesinger & Furlanetto

2007; ELTs?)– Keys are sensitivity and wide field

• When did Population III (metal-free) stars form?– Other spectral features like HeII with ELTs– Key is extreme sensitivity

When did galaxies assemble and “turn on”?

• Baseline projects:– Narrow-band filters in IRMS at range of

wavelengths in J and maybe H– 1-night “deep” exposures (single z)– ~4-night wide surveys (single z)– ~4-8-night cluster surveys (40 redshifts)

– 9-13 nights for extremely comprehensive measure of z > 7-8 Lyman alpha luminosity function

Changes in the ELT Era

Blind surveys in the 10-19 regime; lensed surveys in the 10-20 regime

Fluxes shifted to common luminosity distance at z=7.7

How did reionization proceed?

Approach 1:

• “Brute force” IRMS wide-field survey for clustering of fainter sources (same survey 4-night baseline above)

• Clustering tells about ionized bubble sizes/fraction (e.g., Mesinger & Furlanetto 2007)

(Iliev et al.)

How did reionization proceed?

Approach 2:

• Find target sources in continuum (e.g., JWST legacy surveys)

• Search around for “ionized bubbles” by finding surrounding fainter Ly α sources

– Specific bubble mapping: 1 IRMS field ~ 5 Mpccomoving

– Simple surveys in

Topology of Reionization: Penetrating the IGM with ionized bubbles

Furlanetto & Oh (2005)Furlanetto, Zaldarriaga, & Hernquist (2004)

And many others…

Step 1: Identify bright sources with JWST (or maybe IRMS?)

Penetrating the IGM with ionized bubbles

Best places to find PopIII Lyα may be small galaxies inside these ionized bubbles

Step 2: Use narrow-band imaging with IRMS or IRIS to find smaller, fainter sources in surrounding ionized bubbles

When did Population III (metal-free) stars form?

Best places to find PopIII Lyα may be small galaxies inside these ionized bubbles

Luminous sources already enriched(e.g., Davé, Finlator, & Oppenheimer 2005)

Step 3: Deep spectroscopy to find potential PopIII sources in surrounding ionized bubbles

HeII (1640): signature of Pop III

Pop III

Pop II

• Only PopIII has detectable HeII (1640) emission

• Schaerer (2003) predicts high (>~ 20 Angstrom) equivalent widths for young, zero-metal bursts

TMT (1/2

night)

First-light Summary

By 2016, z > 7 sources may become routine with 8-10-meter class telescopes and wide-field OR AO imagers

• GSMT+AO/JWST future will include – luminosity functions even to z=20; from ground, will

be largely narrow-band imaging (unless OH suppression makes broad-band approaches more competitive with space)

– topology of reionization– searches for PopIII (metal-free) star formation, or “the

first stars”• All are “finite” projects, range of 0.5-8 nights with TMT

first-light instrumentation• Almost all have ancillary science associated with them