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