Large-Scale Structure beyond the 2dF Galaxy Redshift Survey
Gavin Dalton Kyoto FMOS Workshop January 2004 (Oxford & RAL)
Overview Summary of 2dFGRS design Key results… defining contemporary cosmology Key results… galaxies as tracers of LSS Key results… relationship to CMB measurements
FMOS Possibilities – LSS beyond z=1 Input data: Wide-Field IR imaging surveys Survey Design Issues
Results from the 2dF Galaxy Redshift Survey
Target: 250,000 redshifts to B<19.45
(median z = 0.11)
250 nights AAT 4m time
1997-2002
SGP
Final 2dFGRS Sky Coverage
NGP
Final redshift total: 221,283
2dFGRS Redshift distribution
N(z) Still shows significant clustering at z < 0.1
The median redshift of the survey is <z> = 0.11
Almost all objects have z < 0.3.
Cone diagram: 4-degree wedge
Fine detail: 2-deg NGP slices (1-deg steps)
2dFGRS: bJ < 19.45
SDSS: r < 17.8
2dFGRS power-spectrum results
Dimensionless power:
d (fractional variance in density) / d ln k
Percival et al. MNRAS 327, 1279 (2001)
Confidence limits
‘Prior’:
h = 0.7 ± 10%
&
n = 1
mh = 0.20 ± 0.03
Baryon fraction = 0.15 ± 0.07
Power spectrum: Feb 2001 vs ‘final’
Model fits: Feb 2001 vs ‘final’
mh = 0.20 ± 0.03
Baryon fraction = 0.15 ± 0.07
mh = 0.18 ± 0.02
Baryon fraction = 0.17 ± 0.06
if n = 1: or mh = 0.18 e1.3(n-1)
Redshift-space clustering
z-space distortions due to peculiar velocities are quantified by correlation fn (,).
Two effects visible:– Small separations
on sky: ‘Finger-of-God’;
– Large separations on sky: flattening along line of sight
r
and Fit quadrupole/monopole ratio of
(,) as a function of r with model having 0.6/b and p (pairwise velocity dispersion) as parameters
Best fit for r > 8 h-1 Mpc (allowing
for correlated errors) gives:
= 0.6/b = 0.43 0.07 p = 385 50 km s-1
Applies at z = 0.17, L =1.9 L* (significant corrections)
Model fits to z-space distortions
= 0.3,0.4,0.5; p= 400
= 0.4, p= 300,500
99%
Mean spectrum
PC1
PC2
PC3 Early
Late
Galaxy Properties:Spectral classification by PCA
Apply Principal Component analysis to spectra.
PC1: emission lines correlate with blue continuum.
PC2: strength of emission lines without continuum.
PC3: strength of Balmer lines w.r.t. other emission.
Define spectral types as sequence of increasing strength of emission lines
Instrumentally robust Meaning: SFR sequence
Clustering as f(L)
Clustering increases at high luminosity:
b(L) / b(L*) = 0.85 + 0.15(L/L*)
suggests << L* galaxies are slightly antibiased
- and IRAS g’s even more so: b = 0.8
Redshift-space distortions and galaxy type
Passive:
= m0.6/b = 0.46 0.13
p = 618 50 km s-1
Active:
= m0.6/b = 0.54 0.15
p = 418 50 km s-1
Consistent with m = 0.26, bpassive = 1.2, bactive = 0.9
Power spectrum and galaxy type
shape independent of galaxy type within uncertainty on spectrum
Relation to CMB results
Combining LSS & CMB breaks degeneracies:
LSS measures mh only if power index n is known
CMB measures n and mh3 (only if curvature is known)
curvature
total density
baryons
2dFGRS + CMB: Flatness
CMB alone has a geometrical degeneracy: large curvature is not ruled out
Adding 2dFGRS power spectrum forces flatness:
| 1 - tot | < 0.04
Efstathiou et al. MNRAS 330, L29 (2002)
Impact of WMAP
likelihood contours pre-WMAP + 2dFGRS 147024 galsscalar only, flat models
likelihood contours post-WMAP + 2dFGRS 147024 galsscalar only, flat models- WMAP reduces errors by factor 1.5 to 2
likelihood contours post-WMAP + 2dFGRS 213947galsscalar only, flat models
Vacuum equation of state (P = w c2)
w shifts present horizon, so different m
needed to keep CMB peak
location for given h
w < - 0.54
similar limit from
Supernovae: w < - 0.8 overall
2dFGRS
Key Points Basic underlying cosmology now well determined CMB + 2dFGRS implies flatness
– CMB + Flatness measures m h3.4 = 0.078
– hence h = 0.71 ± 5%, m = 0.26 ± 0.04
w < - 0.54 by adding HST data on h (agrees with SN)
Clustering enhanced as F(L) Different bias for different galaxy types, but shape of P(k) is
identical.
Many diverse science goals realised in a single survey design
FMOS Possibilities for LSS at z>1 Wavelength Range (single exposure) 0.9m<<1.8m
– OII enters at z=1.4– 4000Å break enters at z=1.2– Hα enters at z=0.4– OII leaves at z=3.8– Hα leaves at z=1.74
Complex p(z) due to atmospheric bands and OH mask.New field setup time is FAST
Sensitivity: Clear IDs for H=20 magnitude limit: 20 minutes for late-types (50 minutes for early types)[But P(k) shape insensitive to type!!!]
Could obtain as many as 7000 galaxy spectra/night!
Input Data: Wide-Field IR Surveys Natural starting point is the UKIDSS DXS
• 35 square degrees to K=21.5, J=22.5 (5)
~ 60000 galaxies (zP1, HO20)
UKIDSS fields: 2-year plan
LAS
DXS
UDS
GPS
GCS
Upcoming wide-field IR imaging - VISTA1.67 degree focal plane,
16 2048x2048 HgCdTe arrays
Single instrument survey telescope
VISTA Capabilities FOV 1.67 degrees Pixel sampling 0.33 arcseconds YJHK filter set as baseline (3 empty slots)
70% of VISTA time must be dedicated to ‘public’ surveys with emphasis on meeting the science goals of the original VISTA consortium
Extension of UKIDSS DXS in 1 year would cover 500 square degrees.
Commissioning begins April 2006 Data processing and archiving in common with UKIDSS – fast
access to final catalogues. ESO effectively committed to supporting UKIDSS/VISTA
operations with complementary VST surveys.
FMOS Survey Design Issues Optimal survey speed influenced by reconfiguration and field
acquisition times…– Possibilities for large-scale surveys with relatively bright
limits. Optimal use of telescope time may dictate merged surveys (c.f.
2dF GRS & QSO surveys) with multiple science goals (i.e. evolution; clusters; EROs; SWIRE all may be included in LSS survey).
Input data for ambitious surveys will be available on appropriate timescales, but much preparation required.– No problem with spreading a large survey over several
years since effectively no competition! – e.g. think in terms of a survey of ~100 FMOS nights over 5 years.
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