Texas Symposium, MelbourneDecember 14th 2006 Theoretical Properties of Ly  Cooling Radiation’ Mark Dijkstra (CfA) Collaborators: Z. Haiman, M.Spaans & A. Lidz

Texas Symposium, MelbourneDecember 14th 2006 ‘Theoretical Properties of Ly  Cooling Radiation’ Mark Dijkstra (CfA) Collaborators: Z. Haiman & M.Spaans. motivation

Texas Symposium, MelbourneDecember 14th 2006 ‘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, MelbourneDecember 14th 2006 Gas cooling Primordial Cooling curve T < 6.e4 K: H cooling dominates Thoul & Weinberg ‘95

Texas Symposium, MelbourneDecember 14th 2006 The Impact of Cooling on Gas Collapse Adiabatic collapse: Gas shell virializes at r=r max /2 And heated to virial T of halo Turn on cooling mechanism t cool <<t dyn Gas cools to 1e4 K rapidly Thoul & Weinberg ‘95

Texas Symposium, MelbourneDecember 14th 2006 The Impact of Cooling on Gas Collapse. Gas collapses at T=1e4 K (no virial shock, for M<M crit ) 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, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 Lyman Alpha ‘Blobs’ Steidel et al. (2000) 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)

Texas Symposium, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 Ly  Transfer Cute: deuterium N_H=2e19 (static)

Texas Symposium, MelbourneDecember 14th 2006 Ly  Cooling Radiation: Properties Frequency-> Data: Smith & Jarvis, 2007 Radius Surface brightness 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.

Texas Symposium, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 Ly  Cooling Radiation: Properties Why a frequency dependent surface brightness profile?

Texas Symposium, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 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, MelbourneDecember 14th 2006 Ly  Cooling Radiation: Properties Cooling radiation seen? Wilman et al ‘05

Texas Symposium, MelbourneDecember 14th 2006 Cooling Radiation: Properties Part II (=short)

Texas Symposium, MelbourneDecember 14th  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, MelbourneDecember 14th  Cooling Radiation: Properties How weak is continuum? Prominence of Ly  line relative to continuum is quantified by the equivalent width (EW) EW= Å Emitted restframe EW However IGM opaque to Ly  ; Observed restframe EW EW< 200 Å

Texas Symposium, MelbourneDecember 14th  Cooling Radiation: Properties Shape of continuum can also ‘betray’ cooling Cooling powered or resonant scattering or recombination emission?

Texas Symposium, MelbourneDecember 14th 2006 ‘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.