Download contributed talk - Dark Cosmology Centre

On the enhancement of the Lya equivalent width by a
multiphase interstellar medium
– or: debunking the Neufeld scenario
Peter Laursen
With Florent Duval &
Göran Östlin (OKC)
www.dark-cosmology.dk/~pela
Dark Cosmology Centre
| Niels Bohr Institutet | Københavns Universitet
Motivation
Lyman α emitting galaxies (LAEs) are important probes of
the high-redshift Universe:
• Epoch of Reionization
• Baryonic Acoustic Oscillations
• Luminosity function (faint end)
These are statistical properties. Individual observations are
hampered by insufficient knowledge about radiative transfer
effects. One way, however, to probe individual galaxies is by
looking at the equivalent width of Lyα.
2
Motivation
Equivalent width:
Boost:
“Max 240 Å!”,
say Charlot & Fall (1993),
and Schaerer (2003).
“But… but…”,
say Kudritzki et al. (2000), Malhotra & Rhoads
(2002), Rhoads et al. (2003), Dawson et al.
(2004), Hu et al. (2004), Shimasaku et al.
(2006), Ouchi et al. (2008), Nilsson et al. (2009),
Kashikawa et al. (2011), etc.
“Clumpiness!”,
say Chapman et al. (2005), Finkelstein et al.
(2007, 2008, 2009a,b,c, 2011a,b), Dayal et al.
(2008, 2009, 2010, 2011), Niino et al. (2009),
Yuma et al. (2010), Kobayashi et al. (2010),
Blanc et al. (2011), Nakajima et al. (2012), etc.
3
Multiphase medium
Neufeld (1991); Hansen & Oh
(2006)
4
Neufeld 1991
Enter Hansen & Oh (2006)
5
Systematic approach
MOCALATA
(Laursen et al. 2009)
6
Varying the input parameters
“Fiducial” model:
3
1 cm-3
Z
0 km s-1
0 km s-1
0 cm-3
0
Central
0
0
104 K; 106 K
100 pc
• Covering factor, fc
• Cloud HI density, nHI,cl
• Cloud dust density ( metallicity, Zcl)
• Cloud velocity dispersion, σV,cl
• Galactic outflow velocity, Vout
• Intercloud HI density, nHI,ICM
• Intercloud dust density ( ZICM)
• Emission scale length, H
• Emission/cloud correlation factor, Pcl
• Intrinsic line width, σline
• Gas temperature, Tcl; TICM
• Cloud size distribution, rcl,min; rcl,max; β
7
Varying the input parameters
(on at a time)
• Covering factor, fc
8
Varying the input parameters
• Cloud HI density, nHI,cl
9
Varying the input parameters
• Cloud dust density ( metallicity, Zcl)
10
Varying the input parameters
• Cloud velocity dispersion, σV,cl
11
Varying the input parameters
• Galactic outflow velocity, Vout
12
Varying the input parameters
• Intercloud HI density, nHI,ICM
13
Varying the input parameters
• Intercloud dust density ( ZICM)
14
Varying the input parameters
• Emission scale length, H
15
Varying the input parameters
• Emission/cloud correlation factor, Pcl
16
Varying the input parameters
• Intrinsic line width, σline
17
Varying the input parameters
• Gas temperature, Tcl; TICM
18
Varying the input parameters
• Cloud size distribution, rcl,min; rcl,max; β
19
From ideal to semi-realistic
(varying in
unison)
20
From ideal to semi-realistic
(each
dot is the
result of
a model)
21
From ideal to semi-realistic
22
From ideal to semi-realistic
23
From ideal to semi-realistic
24
Line profiles
Average spectrum of
boost-yielding (extreme)
models
— not realistic (too narrow)
25
Alternative scenarios
• Top-heavy IMF (Malhotra & Rhoads 02)
• Population III stars (Schaerer 03, Tumlinson 03)
• Delayed escape of Lyα (Roy+ 10, Xu+ 11)
• AGN activity (<5%, Wang+ 04, Gawiser+ 06)
• Viewing angle (Laursen 07/09, Verhamme 12)
• Cooling radiation (Dijkstra+ 09, Laursen+ 09, Dayal+ 10)
• Measuring errors (Henry+ 10)
• Star formation stochasticity (Forero-Romero & Dijkstra 12)
• Inhomogeneous escape (Hayes+ 07)
26
Alternative scenarios
• Viewing angle (Laursen 07/09, Verhamme 12)
27
Viewing angle
(even in a
homogeneou
s medium,
without dust,
a “boost” can
be measured)
28
Alternative scenarios
• Cooling radiation (Dijkstra+ 09, Laursen+ 09, Dayal+ 10)
29
Conclusion:
• No astrophysically realistic scenario can boost
the Lyα equivalent width by clumpiness alone.
Rather, a combination of clumpiness, orientation
orientation,
radiation etc. adds to
cool ingradiation,
top-heavy IMF, cooling
create a boost.
• Whereas in the scenario originally proposed by
Neufeld the boost increases with cloud covering
factor, even a small cloud velocity dispersion
inverts this relation.
30