Mark Dijkstra, PSU, June 2010 Seeing Through the Trough: Detecting Lyman Alpha from Early Generations of Galaxies ‘ Mark Dijkstra (ITC, Harvard) based on Dijkstra & Wyithe ‘10, arXiv: , MNRAS accepted

Mark Dijkstra, PSU, June 2010 Schematic History of the Universe Now Time Big Bang ‘Dark Ages’ CMB Reionization 400 kyr 1 Gyr 14 Gyr

Mark Dijkstra, PSU, June 2010 Ly  From ‘First’ Galaxies First generation of galaxies: lower metallicity=hotter stars. Tumlinson & Shull `00 Decreasing Z

Mark Dijkstra, PSU, June 2010 Ly  From First Galaxies Hotter stars produce more ionizing radiation-> Stronger nebular emission from HII regions around hotter stars, I.e more Ly . T=1e5 K T=3e4 K Lya Ly  line much stronger at higher z, EW higher by factor of ~ 15:

Mark Dijkstra, PSU, June 2010 Ly  line emission strongest spectral feature of first generation of galaxies (e.g. Partridge & Peebles ‘67, Bromm+01, Schaerer ‘02, Johnson+09). EW~1500 A (restframe). Ly  luminosity ~ 20% of bolometric luminosity. H  flux lower by factor of ~ 8 (deeper in IR). HeII H  ( = 1640 A) flux can be comparable to HI H , but this depends sensitively on stellar initial mass function (Johnson+09). Can we detect Ly  line? Ly  From First Galaxies

Mark Dijkstra, PSU, June 2010 First galaxies surrounded by neutral intergalactic medium. Optical depth to Lya is ~ Gunn-Peterson (GP) optical depth. The GP-optical depth is smaller for photons that first enter neutral intergalactic medium with some velocity off-set  v (redward of line center). (this is why Lya may be detected from galaxies that reside in large HII regions during later stages of the EoR, and why Lya emitting galaxies probe the EoR.) Can we Detect Ly  From First Galaxies?

Mark Dijkstra, PSU, June 2010 Redshifted Lya from Winds in Galaxies Winds appear present in all galaxies (Steidel+10) and affects Lya spectrum. Absorption by metals Lya scattered from backside

Mark Dijkstra, PSU, June 2010 Winds in Galaxies & Ly  Transfer Because winds can Doppler boost photons out of resonance, it promotes escape of Lya from galaxies (photons no longer resonantly `trapped’) Lya scattered from backside Handful of local starburst galaxies suggest that Lya f_esc does not depend on dust content when outflows are present; otherwise f_esc decreases with dust content (Kunth+94, Atek+08, also Giavalisco+96).

Mark Dijkstra, PSU, June 2010 Lya line shape in observed galaxies (z=0-5) can be reproduced using spherical shells of outflowing HI gas, with column density N HI and outflow speed v shell. (see Verhamme+06,08,Schaerer & Verhamme+08,Vanzella+10.). v shell Vanzella+10 N HI Winds in Galaxies & Ly  Transfer There can be flux at |v|> 1000 km/s.

Mark Dijkstra, PSU, June 2010 Observations at z<6 typically require log N HI = and v shell =0-500 km/s (Verhamme+08). Compute Lya spectrum emerging from Lya source surrounded by spherical shell with column density log N HI = and outflow speed v shell =0-200 km/s. Assume no dust. Compute what fraction is transmitted through neutral IGM. Winds & Ly  From the First Galaxies Red Blue Example: z=10, v shell =200 km/s, log N HI = 20 Line center

Mark Dijkstra, PSU, June 2010 Observations at z<6 typically require log N HI = and v shell =0-500 km/s (Verhamme+08). Compute Lya spectrum emerging from Lya source surrounded by spherical shell with column density log N HI = and outflow speed v shell =0-200 km/s. Assume no dust. Compute what fraction is transmitted through neutral IGM. Winds & Ly  From the First Galaxies Red Blue Example: z=10, v shell =200 km/s, log N HI = 20 Line center 4% directly transmitted to observer.

Mark Dijkstra, PSU, June 2010 Directly transmitted fraction f trans as a function of N HI and v shell.. Winds & Ly  From the First Galaxies f trans =3% MD & Wyithe transmitted fraction

Mark Dijkstra, PSU, June 2010 Consider a suite of models with different N HI and v shell. Winds & Ly  From the First Galaxies f trans =3% MD & Wyithe transmitted fraction

Mark Dijkstra, PSU, June 2010 It may be possible to directly transmit f trans > 3% of Ly  flux directly to observer through fully neutral IGM at z=10-15 (without HII `bubbles’!). Translates to observed restframe EW~45(f trans /0.03)(EW int /1500) A -> Strong Lyman Alpha emitters. Ly  provides opportunity for spectroscopic confirmation. –E.g. SFR~ 1M sun /yr –Line flux: NIRSPEC, R=1000, integration time 1e5 s, S/N ~3 –Continuum NIRCAM wide filter, same integration time, S/N~2. Ly  From the First Galaxies

Mark Dijkstra, PSU, June 2010 HIHII HI Ly  From First Galaxies

Mark Dijkstra, PSU, June 2010 The first galaxies were strong Ly  emitters (LAEs). Restframe EW~ 1500 A. Ly  luminosity can be 20% of bolometric luminosity. Observational evidence that outflows affect transport and facilitate escape of Lya from galaxies at z <6. Similar radiative transfer effects can cause >3% of emitted Lyman Alpha to be observed from galaxies at z>>6 even through a fully neutral IGM. This may facilitate the detection/spectroscopic confirmation of z >> 6 galaxies. Understanding outflows and their impact on Lya is crucial when assessing the impact of IGM (as well as of dust) on the Lya emission line, also at z<7 (outflows can strongly affect how one interprets existing data, e.g. through the `Zheng effect’). Conclusions

Mark Dijkstra, PSU, June 2010 But no one-to-one relation between dust content and Lya escape fraction. Dusty galaxies can be strong Lya emitters (Ono+10, arxiv ). Blue galaxies can emit no Lya at all (Kunth+98). `We …find that the velocity structure of the neutral gas in these galaxies is the driving factor that determines the detectability of Lyalpha in emission.’ Galaxies become bluer towards higher redshift, which implies dust attenuation is less important (Bouwens+10). Dust.