Galaxy gravitational redshifts and Lyman-alpha emission ...komatsu/meetings/lss2015/schedu… ·...
Transcript of Galaxy gravitational redshifts and Lyman-alpha emission ...komatsu/meetings/lss2015/schedu… ·...
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Galaxy gravitational redshifts and Lyman-alpha emission intensity: Results from SDSS/BOSS
Rupert Croft Shadab Alam Shirley Ho Jordi Miralda-Escude Zheng Zheng + SDSS/BOSS collaboration
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precision cosmology:
BAO lensing redshift distortions …
?
observational cosmology
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precision cosmology:
BAO lensing redshift distortions …
observational cosmology
(1) Gravitational redshifts from large-scale structure
(2) Lya intensity mapping
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light received
light emi-ed
gravita/onal redshi3 gravita/onal poten/al difference
Test of GR: lab measurement of gravita/onal redshi3s.
1960 Pound-‐Rebka experiment
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czg= czg~ 1 km/s
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best place to look: galaxy cluster
predic/on: cz=10-‐50 km/s (No-ale 1976)
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redshi3 of a galaxy:
cz = Hd + v + c
Hubble expansion
Peculiar velocity
Gravita/onal redshi3
d
v
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Redshi3 map of SDSS galaxies
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Redshi3 map of SDSS galaxies
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Peculiar mo/ons of galaxies in clusters give velocity dispersion >1000 km/s
have ~100 galaxies so Poisson error on mean is ~100 km/s
zg signal is ~10 km/s
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center of cluster
edge of cluster
relative blueshift
simulations
Solu/on: average over many clusters
(Kim & RC 2004)
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First applica/on to observa/onal data (SDSS) by Wojtak et al. (2011): (Nature 477, 576)
rela/ve redshi3
distance to central galaxy
2.8 sigma
(other measurements: Dominguez 2012, Sadeh 2015, Jimeno 2015)
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SDSS galaxies
What about gravitational redshifts from large-scale structure?
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Use all data: average over all pairs of galaxies:
most massive one in a pair will have higher zg
c
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predic/on from halo model (RC, 2013)
2d (parallel and perp to line of sight) cross-‐correla/on func/on of top mass half and bo-om mass half of galaxies.
grav. redshift x 500 !
real space
pec. vels only
grav. redshi3 only
combined
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Es/mator: compare mean redshi3 of pairs of galaxies in shells
Analy/c theory vs simula/on
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Other relativistic effects: Zhao & Peacock (2012), Kaiser(2013), Bonvin et al. (2014), McDonald (2009) e.g., special relativistic beaming:
Galaxy behind big galaxy is falling towards observer: is brighter
see more of them in survey
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Halo model of relativistic effects:
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First measurement from SDSS data (CMASS+LOWZ):
Shadab Alam et al., in prep.
S/ll more possible : op/mal weigh/ng+ more data available now
What will be possible with new surveys in ~10 years?
(using jackknife covariances: ~3.8 sigma)
(preliminary)
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Simula/on mock catalogs and analy/c predic/ons for Euclid galaxy redshi3 survey:
(including mass-‐dependent weigh/ng)
Rela/ve redshi3
Distance to central galaxy
Will measure gravita/onal redshi3 amplitude to 2%.
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Lya intensity mapping of the cosmic web
RC et al. 2015, arxiv:1504.0488
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Star forming galaxies at z=3 in a simula/on
They are sources of Lya emission
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A smoothed “intensity map”
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RA, Dec
z
Observing the Lya map (spectra of every sky pixel observed)
How to deal with interloper emission?
We want to measure:
Mean Lya intensity Lya clustering
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rCross-‐correlate Lya intensity with objects with known redshi3s (in our case, quasars)
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Why do intensity mapping?
It avoids biases from:
source detection, luminosity measurement in an aperture determination of backgrounds extrapolation to faint objects
It is sensitive to all clustered emission.
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1,000,000 SDSS/BOSS fiber spectra (galaxy spectra with galaxy subtracted)
100,000 SDSS/BOSS quasars
our observational setup: cross-correlation of quasar positions with residual flux in pixels
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the predicted quasar-Lya emission cross-correlation:
quasar bias lya emission bias Kaiser redshift distortion factor mean Lya surface brightness CDM correlation function
units are (SB):
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model has two parameters:
amplitude
shape of CDM correlation function parametrized by ΩΜ (hold others fixed)
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SDSS/BOSS
result
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CDM model fit
Planck value=0.3
3.3x10-20
P(k) shape
(using 100 jacknives to compute covariance matrix)
8 sigma detection
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We measure
What is ?
(mean Lya surface brightness at <z>=2.55)
Use other observations to constrain these
(note: scales with poorly known bias factor of Lya emission, should be ~3)
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Interpretation
(1) Lya emission from star formation in galaxies.
Convert:
Lya SB -> luminosity density -> SFRD
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Interpretation: other possible sources
(2) Scattering of quasar Lya (3) Fluorescence of quasar radiation (4) Fluorescence of UVBG (5) Scattering of Lya from UVBG (6) Cooling radiation (7) Observed Low SB Lya halos
All expected to be negligible
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Consequences
This is 30x larger than previous results individually detected Lya emitters! It is ~the same as the dust-corrected SFRD at this redshift. Lya “escape fraction” is 100%
to explain this, we need all star forming galaxies to be surrounded by low surface brightness halos which have so far escaped detection.
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Summary
2 results from SDSS/BOSS not in survey design
(1) First measurement of gravitational redshifts from LSS
(2) First intensity mapping measurement in the optical
future: Euclid 50x more data
future: we only used 1/200,000 of sky area!