constraining cosmology with peculiar velocities of type ia supernovae cosmo 2007 troels haugbølle...

Constraining Cosmology with Peculiar Velocities of Type Ia SupernovaeCosmo 2007

Troels Haugbøllehaugboel@phys.au.dk

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