FIRST LIGHT IN THE UNIVERSE Richard Ellis, Caltech 1.Role of Observations in Cosmology & Galaxy Formation 2.Galaxies & the Hubble Sequence 3.Cosmic Star Formation Histories 4.Stellar Mass Assembly 5.Witnessing the End of Cosmic Reionization 6.Into the Dark Ages: Lyman Dropouts 7.Gravitational Lensing & Lyman Alpha Emitters 8.Cosmic Infrared Background 9.Future Observational Prospects Saas-Fee, April 2006

Strong lensing & the hi-z Universe Zwicky (1937) predicted its utility

Arcs & Multiple Images Origin of arcs: pattern depends on alignment of background source & lens SourceAlignment Image Courtesy: J-P Kneib

Source Plane and Image Plane The Real SkyWhat Observer Sees In the general case (here elliptical lens) as background source moves closer in alignment, multiple images, some highly magnified appear. Lines where magnification is maximized are known as `caustics’ in the source plane, `critical lines’ in the image plane. Position of source relative to lens is crucial! No rings: giant arcs with counter images

Charting Regions of Maximum Magnification In well- constrained clusters we can define precisely the “critical lines” of high magnification for sources at any redshift of interest. How do we locate where these critical lines lie?

The exquisite resolution of Hubble locates same source seen in 3 different locations! This is particularly informative if the distances to the lensed sources can be determined as the geometrical arrangement provides a tight constraint on the distribution of DM in the lens Multiple Images

Generating a Mass Model By identifying multiple images, measuring their redshifts etc, a comprehensive mass model is constructed Using `ray- tracing’ in GR, we can then `predict’ how background sources of any z will be lensed

Multiple images in Abell 2218 z=5.6 z=6.8

Spitzer Detection of Lensed z~6.8 Pair IRAC flux densities: f (3.6  m) = 1.2  0.3  Jy f (4.5  m) = 1.0  0.2  Jy

SED Implies Established Stellar z~7 Key parameters: SFR = 2.6 M  yr -1 M star ~ M  z ~ 6.8  0.1 age 40 – 450 Myr (7 < z F < 12) Age > e-folding SF time  more luminous during active phase? (Egami et al 2005, Ap J 618, L5) Given small search area, such sources may be very common

Searching for Lensed Dropouts with HST & Spitzer 8 well-constrained clusters with IRAC imaging (Egami & Rieke) 11 NICMOS pointings in 6 lensing clusters (4 orbits J/F110W, 5 orbits H/F160W) ACS/F850LP imaging of 3 clusters (11 orbits) Completed with available ACS/NICMOS archive data K-band ground based imaging with Keck/NIRC Ultra-deep IRAC imaging (10 hr) for A1689 & A2218 (Egami) MS H Critical line Magnification > 2 mags Richard, Egami, Stark, Kneib & RSE

Candidates are Being Found Abell 2218: ACS/z & 1 NICMOS pointing MS : ACS/z & 2 NICMOS pointings NICMOS 5  depth: J AB ~26.7 H AB ~26.8 Already a few faint (H~ ) candidates! ACS/Z (F850LP)NICMOS/J (F110W)NICMOS/H (F160W) Richard, Egami, Stark, Kneib & RSE

IRAC detections will be of great utility As well as foreground removal

z > 6 Lyman  Surveys Complementary techniques: - nb (f  < cgs, L  < cgs, SFR~3 M  yr -1, V~ Mpc 3 ) - lensed spectra (f  < , L  < 10 41, SFR~0.1 M  yr -1, V <50 Mpc 3 ) Origin: ionizing flux absorbed by H gas  Ly  photons Efficient: < 6-7% of young galaxy light may emerge in L  depending on IMF, metallicity etc. 1 M  yr -1 = ergs sec -1 (Kennicutt 1998)

Panoramic Imaging Camera on Subaru Megacam Suprime-Cam Can survey distant Universe for Lyman alpha emitters by constructing narrow-band filters and comparing with signal in suitably-chosen broad-band filters

Large Scale z=5.7 via 515 Ly  emitters Ouchi et al 2005 Ap J 620 L1

Narrow bands in `quiet’ windows in night sky spectrum z(L  ) = Requires panoramic imaging as  z range is small Airglow spectrum

Selection & spectroscopic verification of interlopers Hu et al (2003) z=5.7 survey Compare signal in nb filter with broad- band signal using Subaru bb-nb Spectroscopic follow- up of candidates with Keck 5007Å 3727Å 1216Å

Example: Ly  Emitters at z=6.5 Very distant Subaru Ly  emitters: = (a)z=6.541, W = 130, SFR=9 (b)z=6.578, W = 330, SFR=5 Kodaira et al (2003) PASJ 55, 17 spectra

Critical Line Mapping with Keck From arclet spectroscopy the location of the “critical lines” is known precisely for z=1 and for z=5 Blind Ly  search with LRIS: hi-res follow-up with ESI Utilizing strong magnification (  10-30) of clusters, probe much fainter than other methods in small areas (<0.1 arcmin 2 cluster -1 )

Mag x30  unlensed f(L  )= cgs; 20  fainter than unlensed searches Unlensed L  luminosity (10 42 cgs)  SFR  0.5 M  yr -1 Faint continuum (< cgs Å -1 ) implies age < 1-2 Myr Galaxy with 10 7 M  at z=5.7

Lyman Alpha Emission and the IGM Lyman alpha emission: n=2  1, E=10.199eV, 1216Å Resonant transition: foreground H gas cloud scatters away Ly  photons in direction and frequency in partly ionized IGM, scattering is maximum at 1216Å in rest- frame of gas cloud - affects blue side of observed line in fully neutral IGM, scattering far from resonance can occur - damping wings As a result many workers have stressed the importance of monitoring evolution in the Ly  LF and the line profile Miralda-Escude 1998 Ap J 501, 15 Haiman 2002 Ap J 576, L1 Barkana & Loeb 2004 Ap J 601, 64 Santos 2004 MNRAS 349, 1137

Ly  damping wing is absorbed by HI and thus valuable tracer of x HI (Miralda-Escude 1998) In weaker systems, such as those found via strong lensing, Ly  may be a sensitive probe of reionisation Unfortunately, evolution of Ly  LF depends on many messy details (Furlanetto et al 2005) Weak Ly  : Effective Indicator of Reionization? NB-limit Lensed limit

Survey for Lensed Emitters 9 well-constrained lensing clusters 11 L  emitters 2.2 < z < 5.7 Probe luminosities > cgs Santos et al Ap J 606, 683 (2004)

Cumulative Ly  LF: 4.7<z<5.7 Cumulative Ly  LF: 4.7<z<5.7 Santos, Ellis, Kneib & Kuijken Ap J 606, 683 (2004) Other L  surveys LBGs “converted ” to L  CDM halos log M(halo) Lens survey

No Evolution in Ly  LF 5.7 < z < 6.5? No evolution in Ly  LF used to claim x HI < 0.3 (Malhotra & Rhoads 2004), but: small dynamic range of present LF data limits utility of test realistic models of ionized spheres suggest weaker constraint (Furlanetto et al 2005) indicating strong emitters will persist until x HI ~ 0.5 lensed emitters no data

z=5.7 Ly  Luminosity Function Shimasaku et al astro-ph/ Comprehensive Subaru nb survey of 725 arcmin 2 89 candidates 28/39 spec. confirmed ~230 Å - normal stellar popn. Malhotra & Rhoads 2004

Ly  Emitters at z~6.6 (Taniguchi et al 2005) Two color criteria: (z - NB921) > 1.0 and(i - z) > 1.3 Yields 58 candidates Spectra confirm 9-14 out of 20 (45-70%) Two key results: -L  emitters less significant than dropouts as contributors to SFR at z~6.6 -Yet an increasing fraction with increasing redshift (less evolution from z~3-6 than dropouts)

Unusually Strong L  Emitters? Nagao et al (2005) utilize NB921 depression to restrict i-z dropouts to those likely to have strong L  emission elsewhere in z-band. Spectra confirm most are likely strong 6<z<6.5 emitters suggesting redshift evolution in EW distribution nb921 z’

No Evolution of Ly  Line Profiles Hu et al astro-ph/

D. Stark Keck Science Meeting, 2005 Lyman Alpha Emitters z > 7: Critical Line Mapping With Keck Abell 370 NIRSPEC Slit Positions Critical line mapping of 10 clusters in J-band, corresponding to Ly  at 8.5 < z < Clusters limited to those where the location of the critical line is precisely known (<20 all-sky). Sensitive to sources 0.1 M  yr -1 over 31 Mpc 3 (comoving)

Example: Abell 2390 Cluster critical line for z S > 7 NIRSPEC slit positions Wavelength sensitivity (1.5hr) cgs 10 clusters completed October 2005 (Stark et al, in prep): 1 convincing (6  ) Ly  emission candidate 6 moderately-convincing candidates (3-4.5  ) In process of attempting to confirm these

D. Stark Keck Science Meeting, 2005 Significance 3.7  z = 8.99 f = (2.2±0.6)x cgs SFR(unlensed)=0.1 M  yr x0.76 arcsec NIRSPEC slit Abell 2219 NIRSPEC 2D Spectrum Abell 2219 HST R-band image No coincident optical detection; await future deep NIR broadband image from HST NICMOS to search for coincident NIR continuum emission. Candidate Ly  Emitters: I

f =1.2±0.2 x cgs mag ~  50; L= 2.5x10 41 cgs Candidate Ly  Emitters: II Abell 68:  m, z=9.3? No broad-band detection but close companion at z=1.58 Extensive LRIS/NIRSPEC followup fails to reveal associated lines (e.g. if source is at low z or a companion of z=1.58 object):  a promising possibility with 0.25 M  yr -1.

Did feeble sources with 7<z<10 cause reionization? Absence suggests faint sources alone may not cause reionization NIRSPEC survey (Stark et al) Bouwens et al 2004 z~7 Kneib et al 2004 z=6.8 Oct 05 Bouwens et al 2005 z~10 arcmin -2 Adopt worst case scenario: none of the candidate lensed Ly  emitters is real: is this a surprise?

Summary of Lecture #7 Although the Ly  emission has become a standard redshift diagnostic for high z galaxies, the distribution of line profiles, equivalent widths and luminosity function can act as a sensitive gauge of the neutral fraction, x HI, because of scattering by H clouds As with early i-band dropouts, measures of the 5<z<7 Ly  LF remain in dispute; early claims (Malhotra & Rhoads) for no evolution (and hence x HI <0.3) are not necessarily correct There is no convincing evidence that line profiles are evolving or that the equivalent width distribution requires anomalous populations Searches for z>8 lensed Ly  emitters are underway: candidates are being found but their follow up will be tough. New instruments are coming online to make these searches more efficient (Lecture #9)