Post on 17-Jan-2016
Simulations of Lyα emission:fluorescence, cooling,
galaxies
Jordi Miralda Escudé
ICREAUniversity of Barcelona, Catalonia
Berkeley, 9-2-2010
Collaborators:Juna Kollmeier, Zheng Zheng
David Weinberg, Neal Katz, Romeel Dave Renyue Cen, Hy Trac
Andy Gould
Östlin et al. 2009
HαUVLyα
ESO 338–IG04
White et al. 2003
Iye et al. 2006
Tanvir et al. 2009
• Quasars
• Lyα galaxies
fireball shots?
Exploring reionization with the highest redshift objects
• Gamma-ray burst afterglow:
Can we observe the IGM in 3D?
Santos et al. 2008
• 21 cm, epoch of reionization.
• Extended Lyα emission? This can be done at lower redshift.
Rauch et al. 2008
Possible origin of extended Lyα• Star-forming galaxies: the ionizing photons from stars
ionize the surrounding interstellar or intergalactic gas, which emits Lyα by recombinations.
• Radiative cooling: infalling gas is heated during dissipational galaxy formation, emitting Lyα after collisional ionization or line excitation.
• Fluorescence of the ionizing background: dense Lyman limit systems in the intergalactic medium are ionized by distant sources and recombine to emit Lyα.
• Scattering: Lyα forest systems scatter the continuum UV background radiation when it redshifts to the Lyα line.
Lyα blobs: large emission region outside of a star-
forming galaxy
Matsuda et al. 2010
Yang et al. 2009
Physical properties and abundance of Lyα blobs
• Abundance: ~ 3·10-6 Mpc-3, luminosity L > 1043 erg/s, size ~ 30 kpc.
• The luminosity implies 1054 recombinations/second.• The minimum gas density required is 0.1 cm-3 ~ 104 ρmean,
for the size of 30 kpc and no clumping, with a total mass of 1011 MSun.
• These atoms must be ionized every ~ 106 years to keep them emitting.
• The ionizing source should be a quasar with LUV > 1044 erg/s. When it is not seen, it is probably obscured and anisotropic.
• Cooling gaseous halos: better for blobs of L < 1042 erg/s (1011 MSun of gas emitting 10 Lyα photons over 3· 108 years).
Expected Lyα surface brightness from fluorescence of the ionizing background
• Measured intensity of the ionizing background: Jν ~ 3·10-22 erg/cm2/s/Hz/sr.
• Surface brightness of optically thick Lyman limit system: ~ 0.5 Jν νHI/β
• Observed surface brightness: ~ 10-17 erg/cm2/s/arcsec2 / (1+z)4
Hogan & Weymann 1987; Gould & Weinberg 1996
Lyα line
H
atom rest frame
H
laboratory frame
?surface brightnessfrequency change
Lyα Radiative Transfer: how to compute a Lyα image from any distribution of gas and
emission?
• a large number of scatterings• frequency change after each scattering
with Zheng Zheng
Monte Carlo Code for Lyα Radiative Transfer
1. Initialization of the photon
2. determine the spatial location of the scattering
3. choose the velocity of the atom that scatters the photon
4. scattering in the rest frame of the atom: new frequency and direction
5. repeat 2-5 until escape
Zheng & Miralda-Escudé 2002
Lyα
The code can be applied to systems with arbitrary
• gas geometry• gas emissivity distribution• gas density distribution• gas temperature distribution• gas velocity distributionwell suited for applying to
cosmological simulation outputs
The code outputs IFU-like data cube, which can be used to obtain Lyα image and 2D spectra.
Image Courtesy:Stephen Todd & Douglas Pierce-Price
x
y
λ
Application: z~3 fluorescent Lyα emission from cosmic structure: Kollmeier et al. 2009
Fluorescence of the background in an SPH simulation
Kollmeier et al. 2009
Spectra of the fluorescent emission
Fluorescence in the presence of a luminous quasar
• The damped wing of the Gunn-Peterson trough indicates that a source is being seen behind atomic intergalactic medium
• We may observe this on the spectrum of a fireball shot.
• Only a fraction of the intergalactic medium should be neutral, and this fraction will vary widely among different lines of sight.
• Main challenge: separating the host galaxy damped Lyα system from the intergalactic absorption.
Scattering of Lyα photons from star-forming galaxies and other luminous sources
Absorption profile of a neutral medium in Hubble expansion.
Observation of the spectrum of GRB050904
Totani et al. 2006
The absorption is due to local hydrogen with column density
NHI = 1021.6 cm-2
McQuinn et al. 2007
Lyα emitting galaxies: the damped IGM
absorption becomes a probe to the late
stages of reionization.
• The clustering of Lyα emittersincreases owing to a patchy reionization structure.
• An accurate radiative transfer calculation is required.
Lyman-alpha Radiative Transfer applied to galaxy sources placed in a simulation
at z=5.7 (with Cen, Trac): example of one halo
Shift in the Lyα Line Peak
Intrinsic and Apparent Lyα Luminosity
Comparison with Observation Lyα Equivalent Width Distribution
Ando et al. 2006
deficit of UV bright, high Lyα EW sources
• dust extinction?• age of stellar population?• gas density?• gas kinematics?
Ouchi et al. 2008
Comparison with Observation Lyα Equivalent Width Distribution
Observational effect of small survey volume decreasing UV LF towards high UV luminosity + decreasing EW distribution at fixed UV luminosity
LyLyααluminosity
LyLyααline profile
A Simple Model of LAEs
Intrinsic Intrinsic LyLyααemissemiss
ionion
Intrinsic Intrinsic LyLyααemissemiss
ionion
Apparent Apparent LyLyααemissemiss
ionion
Apparent Apparent LyLyααemissemiss
ionion
spectra
LyLyααEW
LyLyααLFLF
UV LF
morphology
clustering
...
Radiative Transfer
neutral gas distribution
✦ radiative transfer as the single factor in transforming the intrinsic properties of Lyα emission to observed ones
✦ natural interpretation of observations
✦ high predictive power
Effect on clustering of Lyα emitters.
Correlation functions
Angular correlation function
Large effects on the angular correlation function are induced by the special selection of Lyα emitters depending on the radiative transfer in their intergalactic environment.
Conclusions• We expect the sky background to contain a detailed map of
Lyα emission from the intergalactic medium.• Detecting fluorescence from the ionizing background
requires even greater depths than achieved so far. Fluorescence in the vicinity of quasars should more easily be detectable now. Lyα blobs likely are particular cases of high gas density near luminous quasars; we expect the lower luminosity ones to arise from cooling in galactic halos.
• The Lyα emission of star-forming galaxies is greatly affected by scattering in their surrounding medium. This can result in:– The wide distribution of equivalent widths in galaxies of different
UV luminosity.– A greatly enhanced correlation function along the line of sight, and
projected angular correlation function.• These Lyα emitting galaxies may provide a powerful probe
to the structure of the reionized intergalactic medium, but modelling the radiative transfer is fundamental.
Apparent Lyα Luminosity Function
Comparison with Observation
Lyα Luminosity Function
offset in Lyα luminosity✴ SFR✴ IMF ✴ intrinsic line width
Comparison with Observation
UV Luminosity Function
Broad distribution of apparent Lyα luminosity at fixed intrinsic (UV) luminosity