University of Durham Astronomical Instrumentation Group
Report on work done for NIO
GSMT book
Simon Morris
With Cedric Lacey,
Robert Content, Marc Dubbledam
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Simulated
NGST Image
(Im 2001)
2’x2’
10 hr exposure
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
High z Lyman α Emitters
Ellis et al. z=5.6 lensed Lyman Alpha emitters
Brighter object observed I=26, lensed by factor ~33
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
ELT MEIFU
Emission Line Sensitivity Calculation
‘Natural Seeing’
•Exposure 4x8 hours (~105 seconds), sky I=19.9
• 27% sky-to-hard-disk throughput
• 50% of object flux in 0.6x0.6 arcsec box
• All of line flux in 2 spectral pixels (1.7 nm)
• 5σ Detection for 3x10-19 ergs cm-2 s-1
• Z=6 (Observed λ=851.2 nm) gives 1x1041 ergs s-1 luminosity
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Emission Line Sensitivity Calculation
AO corrected and ‘diffraction limited’
• Assumption as in previous slide, except:
• 50% of object flux in 0.2x0.2 arcsec box
• 5σ Detection for 1x10-19 ergs cm-2 s-1
• Z=6 (Observed λ=851.2 nm) gives 3x1040 ergs s-1 luminosity
• 50% of object flux in 0.006x0.006 arcsec box (50% EE
diameter for 30m Airy Pattern at 790 nm)
• N.B. this also implies a different plate scale to sample this
properly.
• 5σ Detection for 3x10-21 ergs cm-2 s-1
• Z=6 (Observed λ=851.2 nm) gives 1x1039 ergs s-1 luminosity
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Semi-analytic surface density prediction
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Semi-analytic continuum mag prediction
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Spatial Correlation
Function in co-moving
coordinates for Lyman
α emitters.
Assumed constant fixed
escape fraction.
Single flux range
Points = Lyman α
emitters
Lines = Dark Matter
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Fluorescent Lyman Alpha Emitters
• Can we detect neutral hydrogen clouds excited by
the general UV background?
• Gould and Weinberg 1996, ApJ, 468
• Bunker, Marleau and Graham 1998, AJ, 116, 2086
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Re-Calculate above using most recent estimates for the UV
background
• Calculations done in mathCAD, electronic version of this (and also the sensitivity
calculation) will be included in the final delivery.
• Algorithm:
• Assume ‘consensus’ cosmology
• Use Haardt and Madau (1996) functional form for UV background strength and
shape as function of z, but with latest version for parameters (Haardt, Private
Comunication, CUBA code)
• Use Power law approx. to hydrogen photoionisation cross section (simplifies code,
but not necessary)
• Consider clouds both optically thin and optically thick to UV background as separate
cases using Gould and Weinberg formalism
• Calculate cloud luminosities given a characteristic size
• Convert these to fluxes and surface brightnesses given the redshift
• Given known number of absorbers as a function of column density and redshift, and
assuming the same characteristic size, calculate volume density of clouds expected
satisfying given flux and surface brightness limits.
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
14
Ly α Flux
⎛ Fthick( Rchar, z p) ⎞
log⎜
⎟
−2 −1
⎝ erg⋅ cm ⋅ s ⎠
16
⎛ Fthin( Nchar, Rchar, z p) ⎞
log⎜
⎟
−2 −1
erg⋅ cm ⋅ s
⎝
⎠
18
20
22
0
1
2
3
4
5
6
zp
17
(
)
⎞
⎟
−2 −1
−2
⎝ erg⋅ cm ⋅ s ⋅ arcsec ⎠
⎛
log⎜
SBthick Rchar, z p
⎛ SBthin( Nchar, Rchar, z p) ⎞
log⎜
⎟
−2 −1
−2
⎝ erg⋅ cm ⋅ s ⋅ arcsec ⎠
SBBunker( z p)
⎞
⎛
log⎜
⎟
−2 −1
−2
⎝ erg⋅ cm ⋅ s ⋅ arcsec ⎠
18
Ly α Surface
Brightness
19
20
21
22
0
1
2
3
4
5
6
7
zp
ELT Science Case, Oxford, 28.04.03
7
University of Durham Astronomical Instrumentation Group
30
20
Angular Size
(Rchar=50 kpc)
Rchar
( )
dA z p ⋅ arcsec
10
0
0
1
2
3
4
5
6
zp
2
2.2
⎛ ρ( Nthick , z p , Rchar) ⎞ 2.4
⎟
−3
Mpc
⎝
⎠ 2.6
log⎜
Volume Density of optically
thick absorber/emitters
2.8
3
0
2
4
6
8
zp
ELT Science Case, Oxford, 28.04.03
7
University of Durham Astronomical Instrumentation Group
Lyα emitters,
25% complete?
What are we selecting?
Log (Number Mpc-3)
LBG,
80% complete?
Log(SFR M~/yr)
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
GSMT
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
MEIFU Mechanical design
for fixed Cassegrain
GSMT focus
ELT Science Case, Oxford, 28.04.03
University of Durham Astronomical Instrumentation Group
Ballpark Mass Budget
(no lightweighing)
Fused Silica glass ~ 2.2 g/cm3
⇒ Single Spectrograph glass mass ~ 400 kg
⇒ 1000 kg per spectrograph
⇒ 24,000 kg for all spectrographs
⇒ 16,000 kg for remaining structure
⇒ 40,000 kg for whole instrument
ELT Science Case, Oxford, 28.04.03