constraining cosmology with peculiar velocities of type ia supernovae cosmo 2007 troels haugbølle...
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Constraining Cosmology with Peculiar Velocities of Type Ia SupernovaeCosmo 2007
Troels Haugbø[email protected]
Institute for Physics & Astronomy, Århus University
Collaborators: Steen Hannestad, Bjarne Thomsen, (Århus) Jesper Sollerman , Johan Fynbo (DARK, NBI) Ariel Goobar, Edvard Mörtsell, (Stockholm)
(see also astro-ph/0612137, astro-ph/0705.0979)
Peculiar Velocity Fields
● Velocity trace mass:
(k is the density contrast)
Peculiar Velocity Fields
● Velocity trace mass:
(k is the density contrast)
● The peculiar velocity field is sourced by the gravitational potential: It is directly dependent on the dark matter distribution
Peculiar Velocity Fields
● Further away than ~100 Mpc h-1 cosmic variance is small, and we can constrain cosmological models
● Because of the extra k-factor the velocity field is smoother than the density field
The velocity field 90 Mpc h-1 away
-1100 1100 km/s
The density field 90 Mpc h-1 away
How to measure vr● Requisites:
The redshift of the host galaxy: zThe luminosity distance or the apparent and absolute
magnitudes: dL or m-M● Traditionally used methods to obtain the distance include
● The Tully-Fisher relation● Surface brightness fluctuations● Fundamental plane
● They all have an intrinsic scatter of at least m=0.3-0.4QuickTime™ and aTIFF (Uncompressed) decompressor
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How to measure vr● Requisites:
The redshift of the host galaxy: zThe luminosity distance or the apparent and absolute
magnitudes: dL or m-M● Traditionally used methods to obtain the distance include
● The Tully-Fisher relation● Surface brightness fluctuations● Fundamental plane
● They all have an intrinsic scatter of at least m=0.3-0.4
● With upcoming surveys Type Ia Supernovae will have an intrinsic scatter of m=0.08-0.1
Upcoming surveys● Lensing/asteroid surveys are better for local supernovae,
than the high-z SNe surveys. They scan the sky continuously, and observe in many bands (typically 6)
Pan-Starrs
4x1.4Gp
2007+
Hawaii
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Sky Mapper
256Mp
2008
Australia
LSST3.2Gp
2013
Chile
Goals● Predict how well we can probe the local velocity
field, with upcoming supernovae surveys
● Design the optimal observational strategy to maximize science output
● Understand how the angular power spectrum of the peculiar velocity field can be used as a tool for
● constraining cosmology● finding the (scale dependent) bias● removing scatter in the redshift magnitude diagram
Goals● Predict how well we can probe the local velocity
field, with upcoming supernovae surveys
● Design the optimal observational strategy to maximize science output
● Understand how the angular power spectrum of the peculiar velocity field can be used as a tool for
● constraining cosmology● finding the (scale dependent) bias● removing scatter in the redshift magnitude diagram
Goals● Predict how well we can probe the local velocity
field, with upcoming supernovae surveys
● Design the optimal observational strategy to maximize science output
● Understand how the angular power spectrum of the peculiar velocity field can be used as a tool for
● constraining cosmology● finding the (scale dependent) bias● removing scatter in the redshift magnitude diagram at low redshift
Forecast● The local supernova rate is approximately
● This gives 60000 potential Type Ia SN per year with distances less than 500 h-1 Mpc (z < 0.17)
Forecast● The local supernova rate is approximately
● This gives 60000 potential Type Ia SN per year with distances less than 500 h-1 Mpc (z < 0.17)
● There are light curves from survey telescopes, but precise redshifts are needed
● Follow up on Low redshift Type Ia Supernovae is not a priority right now QuickTime™ and a
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Forecast● The local supernova rate is approximately
● This gives 60000 potential Type Ia SN per year with distances less than 500 h-1 Mpc (z < 0.17)
● There are light curves from survey telescopes, but precise redshifts are needed
● Follow up on Low redshift Type Ia Supernovae is not a priority right now
● A dedicated 1m telescope would be able to take ~7000 spectra per year, or roughly 25% of the Type Ia SNe
Goals● Predict how well we can probe the local velocity
field, with upcoming supernovae surveys
● Design the optimal observational strategy to maximize science output
● Understand how the angular power spectrum of the peculiar velocity field can be used as a tool for
● constraining cosmology● finding the (scale dependent) bias● removing scatter in the redshift magnitude diagram
Observational Strategy
●The precision we can measure the angular powerspectrum with depends crucially on the geometric distribution on the sphere
●Essentially power can “leak out” if there are big holes on the sky.
●We know where the SNe are before finding the redshift from the surveys
How to make a supernova survey
Make Nbody sim
Find density and velocity on a spherical shell
Populate with Supernovae
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Calculate Angular Power spectrum
Size of voids/Max of matter PS
Size of clusters
Goals● Predict how well we can probe the local velocity
field, with upcoming supernovae surveys
● Design the optimal observational strategy to maximize science output
● Understand how the angular power spectrum of the peculiar velocity field can be used as a tool for
● constraining cosmology● finding the (scale dependent) bias● removing scatter in the redshift magnitude diagram
Connecting the matter and velocity powerspectrum
● Velocity trace mass:
● The angular velocity powerspectrum is related to the matter powerspectrum:
Connecting the matter and velocity powerspectrum
● Many cosmological parameters are already probed efficiently by other means
●CMB, LSS, High redshift SnIa, BAO, Cluster density, BBN all give strong bounds on:
●But! Peculiar velocities probe DM potential directly. It is very sensitive to the amplitude:
●Weak lensing give similar limits, but different systematics
Connecting the matter and velocity powerspectrum
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Small scale amplitude 8
Small scale amplitude or 8
● Amplitude on large scales is fixed by the CMB●8 can be affected by
●Massive neutrinoes less power
256
Mp
c h
-1
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Standard CDM 2.3 eV neutrinoes
Small scale amplitude or 8
● Amplitude on large scales is fixed by the CMB●8 can be affected by
●Massive neutrinoes less power●Features in the primordial power spectrum
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Consequences for cosmology● The overall amplitude depends on
This combination break
degeneracies,and8 can be constrained: Using 6 redshift bins (3 yrs of data, 23.000 glass Sne), and a simple 2 analysis, we find
a determination of 8 with 95% confidence
● Current 95% limits are ~20% (Pike & Hudson astro-ph/0511012)
● The overall amplitude depends on
This combination break
degeneracies,and8 can be constrained: Using 6 redshift bins (3 yrs of data, 23.000 glass Sne), and a simple 2 analysis, we find
a determination of 8 with 95% confidence
● Current 95% limits are ~20% (Pike & Hudson astro-ph/0511012)
Consequences for cosmologyGlass SupernovaeAll Supernovae
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Weak Lensing(a-ph/0502243)
● Peculiar velocities or bulk flows can be measured using low redshift supernovae
● The peculiar velocity field is important to understand● It tells out about the structure of the local Universe● It has to be corrected for in the Hubble diagram● We can directly probe the gravitational potential, do
Cosmology, and learn about the bias
● Upcoming survey telescopes will observe thousands of low redshift supuernovae - but this potential can only be realised if time at support telescopes is allocated
● We forecast that with 3 years of LSST data we can constrain 8 to roughly 5%
Summary