Lower Redshift Analogues of the

Sources of Reionization M. Rauch (OCIW)

CollaboratorsESO data :

Haehnelt (IoA), Bunker (Oxford), Becker (KICC), Marleau (IPAC), Graham (UCB), Cristiani (Trieste), Jarvis (Hertfordshire), Lacey (Durham), Morris (Durham),

Peroux (Marseille), Rottgering (Leiden), Theuns (Durham)Keck data:

Becker (KICC), Sargent (CIT), Simcoe (MIT)

LCO data: Becker, Haehnelt, Gauthier (UChic), Ravindranath (IUCAA), Sargent

Cambridge, July 2011

New Horizons, Old Horizons

higher redshifts

first galaxies, IGM at high z

fainter objects main body of galaxy population, gaseous reservoir, sources of reionization

detailed astrophysical processes

physics of ionizing sources, gasdynamics of galaxy formation

How did reionization happen ?

(1) detect faint sources likely to be responsible for reionization (e.g. Trenti et al 2010).

(2) identify the process by which ionizing radiation escapes

Not possible for the actual sources of HI reionization

However, coherent picture has started to emerge at z~3

How to find the faint galaxies ?

CDM structure formation sucessfully predicts properties of the intergalactic medium / Lya forest. The same picture suggests

phenomenon of Damped Lyman Alpha absorption systems (DLAS) is caused by (groups of) low mass, faint, dwarf galaxy halos (e.g., Haehnelt, Steinmetz & Rauch 2000)

Few (very faint) counterparts of DLAS in emission found

Fynbo et al 1999; Moller et al 2004DLA absorption trough

Lyman alpha emission from DLA host

QSO

27 single line emitters, mostly without detectable continuum, over 4457 - 5776 A.Fluxes a few ; mean redshift 3.2 !10!18

erg cm!2

s!1

VLT FORS2longslit92 hours z=2.67 z=3.75

y

!

collaborationincludingM. HaehneltG. BeckerA. Bunker

Rauch et al 2008

Accidental discoveries from a long-slit, blind spectroscopic survey for Lyman alpha fluorescence:

2-d spectra, 2” x 15 “ x 1510 km/s wide;

turquoise contour corresponds to xt1.5 ! 10!20ergs!1cm!2A!1

luminosity function steeper than expected for modelling with constant Lya escape fraction :

escape fraction (extinction) simply may not be constant:

dust diminishing towards fainter objects?

Lyman alpha luminosity function probes uncharted territory:

detections within

retrievedinput

for 2”x2” aperture

! ! "2.2, L! = 9.1# 1042erg s"1

5! 10!3 L" < Lobs < 0.2 L"

Preliminary luminosity function:

Lyalpha induced by star-formation:

< SF rate < 7 ! 10!2M" yr!1 1.5 M! yr"1

Other mechanisms of Lyalpha emission generally unimportant:

-fluorescence of the IGM too faint, not as spatially concentrated

-cooling radiation too weak for these low mass galaxies to be seen

-occasional AGN contribution cannot be ruled out, but unlikely

(2.67 < z < 3.75) =98

- comoving density

- total masses

- virial velocities (Mo & White 2002, Wang et al 2007)

!2N

!z!!

3 ! 10!2Mpc!3

arcmin!2

> 3 ! 1010 M!

vc > 50 km s!1

many similarities suggest an identification of the faint Lyalpha emitters with Damped Lyman alpha systems:

both must be extended, optically thick gas

dN/dz similar to DLAS (large HI extent, large comoving density of objects)

low star formation rate (0.07 - 1.5 ) low metallicity of DLAS

steep luminosity function - low dust contents of DLAS (?)

low mass and small size of SF region in Lya emitters consistent with upper limits on extended SF in DLAS Wolfe & Chen (2006).

DLA hosts and Lyman alpha emitters can be reconciled with the same low massDM halos (Barnes & Haehnelt 2009,2010)

M! yr"1

Independent evidence for identification of faint Lya emitters with DLA hosts comes from stacked spectra of DLAS from the SDSS.

Idea: Search bottom of DLA trough for Lyman alpha emission within the3” wide fiber centered on each QSO. Obtain average luminosity of DLA host. (Rahmani et al 2010).

-600 -400 -200 0 200 400 600rest frame velocity [kms-1]

-1.0

-0.5

0.0

0.5

flux

dens

ity [1

0-17 e

rg c

m-2 s

-1 A

-1]

Reanalysis of Rahmani et al data actually shows mean Lya emission in DLA trough, , very similar to the average flux of our Lya sample, . .

DLA hosts and Lyman alpha emitter show the same mean luminosity

(5± 2)! 10!18erg s!1cm!2

3.7! 10!18erg s!1cm!2

(Rauch & Haehnelt 2011)

asymmetric profile is expected for Lya emission from High z gals.

LLy! ! LDLA

At z~3, Damped Lyman alpha systems are a manifestation of faint emitters w. L<< L*.

If this relation between DLAS and low mass halos holds to the redshift of reionization, DLAS will be the only way to learn anything about the main sources of reionization.

Finding new z>7 QSOs important.

(1) ESO large program with VLT and FORS2 low resolution spectrograph (single 2” wide slit, VPH grism).

92 hours on source, median seeing 1.07”, surface brightness limit in aperture. Median z ~ 3.28 ! 10!20erg s!1cm!2arcsec!2

1!

1 arcsec

So far, three campaigns of longslit observations,including fields with excellent optical imaging:

(2) Keck LRIS low resolution spectrograph (single 2” wide slit, blue and red channels) spectrum in the HDFN.

40 hours on source, similar SFB limits. Largest wavelength coverage

(3) Magellan LDSS3 low resolution spectrograph (single 2” wide slit), spectrum in the HUDF.

61 hours on source, SFB limits 1! 10!19erg s!1cm!2arcsec!2

Keck LRIS longslit in HDFN

Spectroscopy deep enough to addressgas dynamics of high redshift galaxies

Fundamental questions we may be able to address:

- How do metals and ionizing radiation escape from galaxies ?- How does the gas get into galaxies ?

Four of the brightest of our objects: Note small blue peak and dominant, anvil shaped red peak

120 kpc

Most Lyalpha emitters have compact core, wide, low SFB apron, are symmetric in the spatial direction, relative to the continuum.

But this may not be the whole story...

DLA hosts: DLAS are groups of Protogalactic Clumps (PGCs),building blocks of present day galaxies (Haehnelt, Steinmetz & Rauch 2000,2001)

LoS clustering key to understanding DLA cross section, velocity width of DLAS

Lyman alpha emitters: tensions between predicted and observed clustering (Hamana et al 2004)

close pairs of Lybreak galaxies tend to be Ly alpha emitters (Cooke et al 2010)

Clustering, environment seem to play a role for both DLAS and emitters

Sub-population of unusual emitters apparently associated with tidal interaction: z~3.444 lyman alpha emitting V~27 galaxy

longslit spectrum(61h) w. LDSS3in the HUDF

ACS F606 image

Lyman alpha emission line

Lyman alpha forestDLA!trough

6"

1000 km/s

z

6"

slit

NE

Rauch et al 2011b

DLA sits in front of blueshifted, extragalactic gas --> Infall

infalling filament fluoresces in Lyalpha (double-humped profile!) Urbaniak & Wolfe 81

N

emission ridges

5"continuum

1000 km/semission ridgesemission ridges

"red core"

"blue fan"

blue, E red, W

profile FWHM narrower than slit - filament ?tilted towards continuum - accelerated infall ?

~50 % of ionizing photons escape galaxyto hit blue infalling gas

fluorescing screen

fluorescing filament

red coreslit

N

S

DLADLA

view through slit view rotated by 90 degs

Rauch et al 2011b

shocks likely in an interactionmay be boosting emission of Lya, LyC. But unlikely to explain all of the flux

Escape of Lyalpha, ionizing radiation, triggered by interaction.

Is this how the universe gets reionized?

6"

1000 km/s

z

6"

slit

NE

W

2570 km/s

6.7"

N

Another extended Lyman alpha halo at z~2.63:

disturbed continuum (stellar) feature

Again there is an extended (tidal ?) smudge associated with a multi-galaxy Lyalpha emitting halo

enhanced cross-sections for Lya emission, and presumably for DLA

Interaction may trigger Lya emission, escape of ionizing photons

- Lyalpha pattern could mimic “outflow”

- enhanced Lya emission, LyC escape could be temporary (duty cycle)

(b) interaction with passing galaxy

(a) undisturbed HI halo

Yet another extended, asymmetric Lyman alpha halo at z~3.049:

Obscured QSO (detected in X rays)

Loss of ionizing radiation generally associated with asymmetric Lya emitters ?

! " #! #" $!

fluorescent HI in sideways opening

faint foreground galaxy

emission asymmetricwrt. continuum

“Protogalactic groups” “Lyman break” galaxies

complex and asymmetric in space and velocity.Tidal features.Escape of Lya (and LyC ? metals ?) triggered by interaction.

compact, symmetric wrt. continuum in the spatialdirection.

why don’t we see outflows?

“Protogalactic groups”

Space density:

Fluxes: a few

Sizes: tens of kpc

O(10!3)Mpc!3

!10!17erg s!1cm!2

The future: -no alternative yet to long-slit spectroscopy (dea(r)th of blue spectrographs) -higher resolution and or IFUs/image slicers can tackle brightest objects

3-D spectroscopy ofSXDS bright z~3.1 emitter with Keck ESI-IFU

2-D higher resolution spectroscopy ofbright z~2.2 SXDS emitter (Ouchi et al 2008) with Magellan/MagE

ConclusionsBlind spectroscopic surveys have uncovered a population of faint Ly alpha emitters with high space density, z~3 analogues of the faint galaxies possibly responsible for reionization

Unification of DLAS and faint Lya emitters suggested by many common features. Can study these objects in DLA absorption to much higher z than possible in emission. DLAS currently our main hope to see the actual sources of ionization.

At z~3, studying the gasdynamics of galaxy formation becoming possible with low surface brightness Lyman alpha emission: kinematics,accretion (cold and otherwise), photon budget, mergers, outflows Interacting groups of protogalaxies key to a number of cosmic phenomena, including DLA cross-section and kinematics, the escape of Lya and ionizing radiation and probably, to reionization itself.