motivation

1. Theoretical Properties of Ly Cooling Radiation’Mark Dijkstra (CfA) Collaborators: Z. Haiman, M.Spaans & A. Lidz Texas Symposium, Melbourne

2. ‘Theoretical Properties of Ly Cooling Radiation’Mark Dijkstra (CfA) Collaborators: Z. Haiman & M.Spaans . motivation Texas Symposium, Melbourne

3. ‘Theoretical Properties of Ly Cooling Radiation’Mark Dijkstra (CfA) Collaborators: Z. Haiman, M.Spaans & Lidz Outline of talk • Gas cooling & Ly emission • Observable properties of Ly cooling emission (DHS 06a,b) • Observable properties of continuum cooling radiation (D, submitted to MNRAS) Texas Symposium, Melbourne

4. Gas cooling Primordial Cooling curve T < 6.e4 K: H cooling dominates Thoul & Weinberg ‘95 Texas Symposium, Melbourne

5. The Impact of Cooling on Gas Collapse • Adiabatic collapse: Gas shell virializes at r=rmax/2 And heated to virial T of halo • Turn on cooling mechanism tcool<<tdyn Gas cools to 1e4 K rapidly Thoul & Weinberg ‘95 Texas Symposium, Melbourne

6. The Impact of Cooling on Gas Collapse. • Gas collapses at T=1e4 K (no virial shock, for M<Mcrit) • Cooling @ T=1.e4 K is dominated by collisional excitation of H • Collisions to 2p and 2s states of H • 2p 1s: Ly cooling • 2s 1s: 2- emission Thoul & Weinberg ‘95 Texas Symposium, Melbourne

7. Gas cooling. • Gas cooling is dominated by Ly emission • Spatially extends up to ~100 kpc. • Luminosities in the range L=1e42-1e44 erg/s (Haiman et al ‘00, Fardal et al ‘01, Yang et al ‘06) Yang et al ‘06 Texas Symposium, Melbourne

8. Lyman Alpha ‘Blobs’ • Observed Spatially extended Ly emission up to ~ 100 kpc. • Several tens have been discovered at z=3-5. (e.g. Matsuda et al, 2004; Saito et al, 2006/2007) • Luminosities ~ 1e42-1e44 erg/s • Powered by cooling radiation? • Alternatives: • Obscured starburst/AGN • Shock heating by superwinds. • Fluoresence (next talk) Steidel et al. (2000) Texas Symposium, Melbourne

9. Ly Cooling Radiation: Properties • Observational signatures of cooling radiation? • Cooling clouds are optically thick to Ly-> radiative transfer (RT). Well studied problem (> 60 years) HARD Texas Symposium, Melbourne

10. Ly Transfer • A simple problem: a Ly source inside a uniform static neutral H cloud. • Calculate emerging spectrum Harrington ‘73, Neufeld ‘90, DHS06a • Generally no analytic solution can be found: • Monte-Carlo. Texas Symposium, Melbourne

11. Ly Transfer • Calculate Ly transfer through series of models representing cooling clouds • Goal: To extract basic properties of Ly cooling radiation • Use Monte-Carlo: follow individual photons through the collapsing cloud. • The code is reliable. Texas Symposium, Melbourne

12. Ly Transfer • Cute: deuterium • N_H=2e19 (static) Texas Symposium, Melbourne

13. Ly Cooling Radiation: Properties • Use Monte-Carlo method to calculate emerging Ly spectrum+surface brightness profiles. • Result 1: Radiative Transfer of Ly through collapsing (optically thick) gas results in a blueshift of the line. The opposite is true for outflows. • Frequency off-set of Ly-line constrains gas motion. Frequency-> Surface brightness Radius Texas Symposium, Melbourne Data: Smith & Jarvis, 2007

14. Ly Cooling Radiation: Properties • What if one can’t tell whether there is an off-set? • Ly cooling radiation has frequency dependent surface brightness profile: Red: reddest 15% of Ly Blue: bluest 15% of Lya Texas Symposium, Melbourne

15. Ly Cooling Radiation: Properties • Why a frequency dependent surface brightness profile? Texas Symposium, Melbourne

16. Ly Cooling Radiation: Properties • Caution: Spectra shown are affected by IGM. The impact of the IGM is non-trivial (e.g. Santos ‘04; D, Wyithe & Lidz ‘07) Texas Symposium, Melbourne

17. Ly Cooling Radiation: Properties • Has cooling radiation from cold accretion been seen? • Perhaps (e.g. talk by M.Rauch) • Saito et al’07 find asymmetric Ly profiles with enhanced blue emission. Texas Symposium, Melbourne

18. Ly Cooling Radiation: Properties • Cooling radiation seen? Wilman et al ‘05 Texas Symposium, Melbourne

19. Cooling Radiation: Properties Part II (=short) Texas Symposium, Melbourne

20. 2- Cooling Radiation: Properties • 1 collisional excitation 1s2p is accompanied by 0.6 excitations 1s2s • 2s1s++, 2 photons have combined energy of 10.2 eV. • Results in continuum emission redward of Ly-a. The spectrum of this emission has been calculated by Spitzer & Greenstein (‘51) Texas Symposium, Melbourne

21. 2- Cooling Radiation: Properties • How weak is continuum? Prominence of Ly line relative to continuum is quantified by the equivalent width (EW) EW=1000-1500 Å Emitted restframe EW However IGM opaque to Ly; Observed restframe EW EW< 200 Å Texas Symposium, Melbourne

22. 2- Cooling Radiation: Properties • Shape of continuum can also ‘betray’ cooling Cooling powered or resonant scattering or recombination emission? Texas Symposium, Melbourne

23. ‘Theoretical Properties of Ly-a Cooling Radiation’Mark Dijkstra (CfA) Collaborators: Z. Haiman & M.Spaans Summary • Gas cooling is accompanied by copious Ly emission (especially the ‘cold’ mode). • Observational signposts of this emission are: • Intrinsic blueshift of line • Steepening of surface brightness towards bluer Ly wavelength • Faint continuum redward of Ly with weird spectrum. • Caution: Absence does not immediately rule out cooling radiation. • Currently, no convincing observational evidence exists, but d/dt(almost convincing) > 0. Texas Symposium, Melbourne