BelGrav weekly meeting "Talk" format
https://cern.zoom.us/j/8354516554?pwd=N3lSOWdhczdLcnNUSkZLRVNMeDFkQT09
virtual - zoom
News and announcements: link to slides
Archisman:
VSC meeting
- No decision was taken on whether or when Virgo will join. However, now we’re drafting a statement saying that Virgo will need at least 3 months to reach the required sensitivity.
- Elections for the current upgrade coordinator are coming up. Advanced Virgo upgrade coordinator, i.e.: replacement of Raffaelle Flaminio.
- Document that describes the tasks of the upgrade coordinator: link
Archisman: MOA review has been circulated: needed for 6th of October. Fill in activities to be done for the next two years.
Giacomo: Viviana Fafone will be in charge of post O5.
Maxime: announcement of new PostDoc Dixeena
Giacomo: announcement: new positions in UC Louvain! Highly recommend for applications.
----------------------------------------------
Talk by Cezary Turski and Freija Beirnaert: link to slides
Freija: LVK paper presentation. Result from O3, cosmology group, where they inferred the H constant:
The previous method (gwcosmo) was very slow and impractical to continue using it. Hence why we have written a new code.
Cesary: Dark Siren method:
Direct detection gives the dL distribution. Galaxy gives an idea on z. By combining this we can compute a not very informative H0. If we combine multiple events, i.e.: multiplying the individual posteriors for H0, we get an informative H0 distribution:
The old method had to compute many integrals. In the new one, we use the line of sight redshift prior, which can be pre-computed:
That gives us a 1000 times faster code.
Freia: LOS redshift prior: for each dir in sky, we create a distribution of z as a function of z. Each galaxy corresponds to a Gaussian peak.
There is an implicit dependency inherent to this method. Angular resolution dependence. We need to go to a fine grid to properly locate galaxies. But that leads to convergence issues (empty pixels will start to dominate).
Before we compute the LOS, we compute sky maps with effective number of galaxies, e.g.:
E.g.: We chose GW190814 to show the method. The obtained z prior is:
The horizontal line at 1 corresponds to no catalog information. Below 1: underdensity.
Cezary: the resolution in sky was discussed by Freia, but we also need resolution in z. E.g.: Glade catalog:
Something else has been improved, apart from the LOS, such as spectral sirens. GW Selection effects are now also calculated (in the past it was only for H0, given the computational burden of the previous code).
Freija: results are in good agreement with icarogw:
Most informative event:
- Blue solid (O3 results), used to compare with
- All the dashed lines correspond to results obtained using our method:
The final analysis: combined cosmological and population inference:
J.R.Cudell: why does the distribution go up for large H0?
Cezary: tehre are a few overdensities that could affect or explain this feature.
----------------------------------------------
