Constraining Cosmology with Peculiar Velocities of Type Ia Supernovae Cosmo 2007 Troels Haugbølle 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/ , astro-ph/ )

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 km/s The density field 90 Mpc h -1 away

How to measure v r ● Requisites: The redshift of the host galaxy: z The luminosity distance or the apparent and absolute magnitudes: d L 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=

How to measure v r ● Requisites: The redshift of the host galaxy: z The luminosity distance or the apparent and absolute magnitudes: d L 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= ● With upcoming surveys Type Ia Supernovae will have an intrinsic scatter of  m=

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 Hawaii Sky Mapper 256Mp 2008 Australia LSST 3.2Gp 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 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 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

Forecast ● The local supernova rate is approximately ● This gives 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 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 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 Mpc h -1 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

Consequences for cosmology ● The overall amplitude depends on   This combination break degeneracies,and   8 can be constrained: Using 6 redshift bins (3 yrs of data, 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/ )

● The overall amplitude depends on   This combination break degeneracies,and   8 can be constrained: Using 6 redshift bins (3 yrs of data, 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/ ) Consequences for cosmology Glass SupernovaeAll Supernovae Weak Lensing (a-ph/ )

● 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