The Metagalactic Ultraviolet
Background
Jennifer E. Scott
Redshift
evolution of
Lya
absorbers
flattens with
redshift
Weymann et al. 1998
Kim et al. 2001
Dobrzycki et al. 2002
Evolution
primarily
driven by
evolution
in UVB
Dave et al. 1999
The Proximity Effect
classical method
The Lya forest
line density is
modified by the
presence of the
quasar:
Weyman, Carswell, & Smith 1981
Murdoch et al. 1986
Carswell et al. 1987
Bajtlik, Duncan, & Ostriker 1988
Lu et al. 1991
Redshift
evolutioncorrected
line
distribution
Proximity
effect
line deficit
Ratio of quasar flux to background flux
JS et al. 2002
Line counting methods
also
Lu et al. 1991
Cristiani et al. 1995
Giallongo et al. 1996
Srianand & Khare 1996
Lya Forest as FGPA
Assume
•photoionization equilibrium
2
6
2 2 

•negligible vpec
(1 z) (b h )






0
0.7
•thermal broadening
T H(z) (z)   
12
Use effective e.o.s.

 b h 

 0.0125 
  
2
2

 100 km/s/Mpc

H ( z)


 1
12

 Match mean flux decrement in
hydrodynamical simulations to
observations of Lya forest
 Use shape of flux decrement
distribution to test cosmological
models
Rauch et al. 1997
Bolton et al. 2005
Also
McDonald & Miralda-Escude (2001)
Meiksin & White (2004)
Songaila et al. (2004)
Tytler et al. (2004)
Bolton et al. (2005)
Kirkman et al. (2005)
D’Odorico et al. (2008)
Faucher-Giguere et al. (2008d)
Proximity effect revisited
Instead of counting lines use flux
transmission statistics
change in eff near quasars
eff = B(1+z)g+1(1+w)1-b
Lisk & Williger 2001
With high resolution & S/N
data detect PE in individual
quasar spectra and examine
the distribution of PE strengths
Bias (upwards) from using
global approach to PE
use modal value or “hybrid”
method using a subsample
with low overdensities and a
correction for sample
averaging using Monte-Carlo
simulations
Dall’Aglio et al. 2008a,b
Wisotzki
Quasar systemic redshifts
Many emission lines show shifts
of several x 100 km/s with
respect to systemic
VandenBerk et al. 2001
Also
Tytler & Fan 1992
McIntosh et al. 1999
Richards et al. 2002
Quasar Lyman limit fluxes
HST composite spectrum
Telfer et al. 2002
Quasars in overdense regions
(Loeb & Eisenstein 1995, Rollinde et al. 2005, Guimaraes et al. 2007, Hennawi &
Prochaska 2007, Prochaska & Hennawi 2009)
 Overdensities to ~4 Mpc
(D’Odorico et al. 2008, Faucher-Giguere et al. 2008a)
 Overdensities and infall each contribute ~equally to
overestimates of UVB from PE factor of ~(3.5,2.5,2) at z=(2,3,4)
(Faucher-Giguere et al. 2008a)
 Overdensities of factor of a few within 2.5 h-1 Mpc for chosen
metagalactic UVB but no systematic enhancement- therefore can
break degeneracy using overdensity distribution (high overdensity
leads to tail in PESD) (Dall’Aglio et al. 2008b)
UVB Sources
Quasar space density
Hopkins et al. 2007
UVB Sources
Quasars account for all of
the observationally
estimated  at z<1, and
~50% at z~2-3
But the quasar luminosity
density drops off much
faster than  at higher z
z < 2: the faint quasar
contribution is important
z > 2: bright quasars
dominate the luminosity
density
Hopkins et al. 2007
Also Madau, Haardt, & Rees 1999
Bianchi, Cristiani, & Kim 2001
Bolton et al. (2005) (diamonds, z = 2-4)
Tytler et al. (2004) (star, z = 1.9)
Rollinde et al. (2005) (triangle, z = 2.75)
McDonald & Miralda-Escude (2001, 2003) (squares, z = 2.4-5.2)
Fan et al. (2006a) (circles, z = 5-6)
JS et al. (2000) (boxes, z ~ 0-1 and z ~ 2-4)
UVB Sources
Sokasian, Abel, & Hernquist 2003
Cosmological
simulations with
radiative transfer
require stellar
contribution to rise
at z>3 to
compensate for drop
in quasar space
density
Proximity effect measurements
UVB Sources
• UVB demands star
formation at z>3
• faint end slope?
(cf. Rauch et al. 2008 faint
LAEs 2.67<z<3.75)
Faucher-Giguere et al. 2008b
Sawicki & Thompson (2006)
(Keck Deep Fields)
Reddy et al. (2008) (Keck
LBG)
Yoshida et al. (2006) (Subaru
Deep Field)
Bouwens et al. (2007) (HUDF
& other deep HST fields).
Steidel et al. (1999) z~4 LBGs
w/LF values of Reddy et al.
(2008)
(Hernquist & Springel)
(Hopkins & Beacom)
Faucher-Giguere et al. 2008d
UVB Sources
UVB requires
fesc =0.01 at z<1
=0.1 at z>4
JS et al. 2000
Bolton et al. 2005
Fan et al. 2006b
--- QSOs
(Bianchi, Cristiani, & Kim 2001)
……galaxies
Inoue, Iwata, & Deharveng 2006
see also Sbrinovsky & Wyithe 2009
Composite spectrum- 29 LBGs
Direct detection of LyC photons
in only 2 of 14 LBGs
Residual Lyman continuum flux
Steidel, Pettini, & Adelberger 2001
Shapley et al. 2006
Siana et al. 2007
fesc*
~0.01
(+2009)
<0.02
~0.05-0.25**
*E(B-V)=0.15 and Calzetti et al. (2000) reddening law
**Iwata et al. (2009) find similar value for 7 LBGs in a
protocluster at z~3 with (f1500/f900)stel~1,
for (f1500/f900)stel=6, this becomes fesc~0.4
Yajima: 0.17 < fesc < 0.47 for high z LBGs/LAEs
Complicating factors include:
• intrinsic Ly break
• ISM/IGM reddening values, extinction laws
Low z and high z SFG spectra are similar (Schwartz et al. 2006)
Smaller fesc for low z galaxies explained if observed in pre-blowout
phase in which LyC photons are inhibited (Fujita et al. 2003)
Also larger outflow velocities in galaxies with higher SFR/M
(Grimes et al. 2009) and SFR/M increases with redshift (Damen et al.
2009)
Need fesc(t/z,L/M)
to account for outflows, galaxy masses (Gnedin et al. 2008)
and AGN duty cycles (McCandliss 2009)
UVB Spectrum probed by
IGM metals
(Ryan-Weber, Schaye, Becker, Fox, Bagla)
He II
Lya forest (Fechner, Worseck)
IGM photoheating from reionization
• HI (Bolton)
• b distribution (Bolton)
Spectrum of UVB: He II Lya forest
N (HeII )
<200 for AGN-dominated UVB

N (HI )
n(HeII ) a HeII HI
for photoionization equilibrium

n(HI ) a HI HeII
J HI (3  a HeII ) 0.055
 1.7
T4.3
J HeII (3  a HI )
Measure He II Lya at z> 2
(FUSE) or z >2.8 (HST) to
constrain ratio of UVB intensity
or shape at 1 and 4 Ryd
He II quasars
Q0302-003
z=3.3
Jakobsen et al. 1994, Heap et al. 2000
Q1157+3143
z=3.0
Reimers et al. 2005
HS1700+6416
z=2.7
Davidsen et al. 1996, Fechner et al. 2006a,b
PKS1935-692
z=3.1
Tytler et al. 1995
SDSSJ2346-0016
z=3.5
Zheng et al. 2004
HE2347-4342
z=2.8
Reimers et al. 1997, Kriss et al. 2001
More to come… Syphers et al. 2008
Zheng et al. 2008
Worseck
HE 2374-4342
Large
observed
1000
fluctuations
in  imply
fluctuations 100
in HeII since
HI ~uniform 10
at these
redshifts
1
Zheng et al. 2004
Fluctuations expected at He II reionization epoch from:
 discrete sources and small He II ionizing photon mpf
(esp. relative to HI) (Fardal et al. 1998, Bolton et al. 2006, McQuinn et al.
2008, Furlanetto & Oh 2008a, Furlanetto 2009a,b)
 large dispersion of as (Telfer et al. 2002, JS et al. 2004)
 radiative transfer effects (Abel & Haehnelt 1999, Sokasian et al. 2002,
Masseli & Ferrara 2005, Tittley & Meiksin 2007, McQuinn et al. 2008)
 local sources (Jakobsen et al. 2003, Worseck & Wisotzki 2006, Worseck et
al. 2007)
He II reionization
Consistent with
increase in IGM
temperature from
photoionization
Opacity increase at z~3
Ricotti et al. 2000
Schaye et al. 2000
Theuns et al. 2002
But see
Bolton, Oh, & Furlanetto
2009a
Agafonova et al. 2005, 2007
Reimers et al. 2006
Also Zheng et al. 2004
Spectrum of UVB:
Metals
 3-4 Ryd UVB
needed for
ionization
corrections to
measure IGM
metallicity
Change at z~3
Epoch of He II reionization
 Si IV & C IV IP
straddle He II
 Hardening at
z≤3
Vladilo et al. 2003
Agafonova et al.
2005, 2007
Songaila 1998, 2005
Spectrum of UVB:
Metals
But others find no
break
Also
Aguirre et al. 2004
find observed IGM Si, C
absorption cannot be
reproduced using a
spectrum with a transition
due to He II ionization at
z=3.2
Kim, Cristiani, & D’Odorico 2002
also Boksenberg et al. 2003
Spectrum of UVB:
Metals
HS1700+6416
HE2347-4342
Sawtooth
modulation
from
He II Ly
series can
depress
UVB at 3-4
Ryd
Madau &
Haardt 2009
No contribution from SFG needed to reproduce metal absorption
-> fesc<0.05
Agafonova et al. 2007
HI optical depth
Dip at z~3.2:
• change in TIGM?
• change in ne?
• enhancement in HI ?
(Bolton, Oh, & Furlanetto 2009b,
Faucher-Giguere et al. 2008d)
small filled circles 796 SDSS QSOs S/N >4
stars Sargent et al. (1989),
diamonds Schneider et al. (1991)
squares Zuo & Lu (1993)
triangles McDonald et al. (2000)
large filled circles Schaye et al. (2000)
Bernardi et al. 2003
Also
Faucher-Giguere et al. 2008c
Dall’Aglio et al. 2008
But not seen by McDonald et al. 2005
Doppler parameter distribution
Schaye et al. 2000
Also Ricotti et al. 2000, Theuns et al. 2002
Not seen by McDonald et al. 2001, Zaldarriaga et al. 2001
Complications
He II reionization process can lead to complex, multi-valued,
even inverted EOS
(Gleser et al. 2005, Becker et al. 2007, Furlanetto & Oh 2008b, Bolton et al.
2008) But see McQuinn et al. 2008
If hard photons deposit energy into high NHI systems, this will
not be reflected in b boost to low NHI absorbers observed thus far
uncertainty in interpreting temperature boost in IGM
(Bolton, Oh, Furlanetto 2009a)
UVB models
 Haardt & Madau 1996 QSOs + recombination emission
 Haardt & Madau 2001 HM96 + galaxies
 Bolton et al. 2005 scaling relations with cosmological
parameters (e.g. b, s8) and IGM properties (e.g. eff, T)
 Madau & Haardt 2009 He II forest
 Faucher-Giguere et al. 2009
Updated galaxy, AGN LF
Explicit consideration of He II reionization
Lesser contribution from recombination emission,
as informed by photoionization calculations
Ionizing spectra
similar in shape
after He II
reionization
Quasar
contribution
drops more
rapidly than HM
at z >2 but HI
boosted by
enhanced galaxy
contribution
Faucher-Giguere et al. 2009
Future Work
Luminosity functions at high z: faint source contributions
Galaxy fesc
 AGN duty cycles
 Quasar environments
 Quasar systemic redshifts
 Direct fluorescence measurements
 COS: He II Lya forest- fluctuations in / local sources
IGM Legacy- low z UVB
 Models:
Radiative transport
Luminosity-dependent parameters, e.g. AGN spectral slope, fesc