News and Updates
We plan to release a DR10 void catalog soon, and this summer we will release VIDE (Void IDentificaiton and Examination), which is our extension of ZOBOV as well as a void analysis tool suite. Stay tuned!
Recently, Nadathur & Hotchkiss (2013) submitted a paper discussing a new cosmic void catalog. This paper includes claims about the void catalog described in Sutter et al. (2012). We have posted a note in which we respond to those claims, clarify some discrepancies between the text of Sutter et al. (2012) and the most recent version of the catalog, and provide some comments on the differences between our catalog and that of Nadathur & Hotchkiss (2013).
We would like to thank Mark Neyrinck, Seshadri Nadathur, and Shaun Hotchkiss for pointing out an inconsistency regarding density thresholds between the text of our Sutter et al. (2012) paper and the actual implementation. In the text, we state that we impose an overall density threshold to limit voids to less than 0.2 the mean density (rho_mean).
What is actually implemented is a 0.2*rho_mean criterion for merging zones (here, a "zone" is a group of Voronoi cells sharing a common basin) together in the process of creating larger parent voids, as described in Neryrinck (2008). Zones are only added to a void if the minimum density in that zone is < 0.2*rho_mean. This corresponds to a value of 0.2 (suitably adjusted to account for the presence of boundary particles) as the last argument to the jovoz code. Please see the ZOBOV manual page for more details.
Thus, voids presented in our catalog will be overdense on average, since the watershed algorithm naturally includes high-density edge galaxies in the void definition. Also, even the minimum density of a void can be greater than 0.2*rho_mean, since voids can (and do) consist of only a single zone, and this criterion is not applied until the zone-merging step. This, again, is discussed in Neyrinck (2008). However, as we discuss in Sutter et al. (2012), the centers of our identified voids are still underdense.
This becomes much more severe as the void size approaches the mean particle separation, since small voids tend to be surrounded by very large overcompensated regions. The philosophy of this catalog is to produce as many voids as possible and allow users to make their own cuts as they see fit. As we have before, we strongly urge caution in the use of the smallest reported voids!
We apologize for this misunderstanding, and look forward to further improvements of our catalog.
After numerous requests, we have posted the volume-limited galaxy samples used to construct the public void catalog. See the "Public Catalogs" tab for the link.
This summer, we will make publicly available our void catalogs from SDSS DR9 as well as many simulations. Stay tuned!
We have updated the private catalog to include all the latest bug fixes, improvements, and additions available in the public catalog.
We have released a new catalog with a bug fix and several new additions:
There have been a few questions raised recently about apparent inconsistencies among the three (July, August, and November) releases. We would like to take this opportunity to explain the differences in more detail.
If you are not already doing so, please use the November release!
The catalog inconsistencies can be explained by:
1) A lower radius threshold for including voids in the November release. Previously, it was two times the mean galaxy separation. We now include voids all the way down to the mean galaxy separation. Also note that we miscalculated the mean galaxy separation for the dim1 sample; this has been corrected. Use the smallest voids at your own risk; you may wish to impose an arbitrary cutoff (e.g., 2*r_min or 4*r_min) for your analysis.
2) Different handling of the high-redshift cap of each subsample. In July and August, we were placing mock particles along the cap and treating voids there just like voids at the mask boundaries (i.e., these would appear as "edge" voids). However, this procedure was giving us difficulty at higher redshift, so we switched to a simpler approach: we no longer place mock particles at the redshift cap and remove all voids that might intersect the upper redshift boundary of the subsample.
3) A bug fix in the central density calculation. Previously, all voids were using a fixed radius to determine the central density. This is not what we intended. We fixed this to calculate central densities using 1/4 of the effective radius, as we state in the paper. So some voids that were excluded are now included and vice-versa.
4) The August release (but not the July release) contained a bug in the barycenter calculation. Centers were still inside the voids but slightly offset from the true barycenter. This has been fixed for November.
5) There was a bug in the catalog release pipeline script which switched the "central" voids with the "edge" voids. This has been corrected for November: "central" voids are now actually central voids!
Changes 1) and 2) generally explain the different void populations in the "all" sample. The redshift cap handling especially affected the lrgbright sample. If you were using the "all" sample, then change 5) didn't affect you. However, if you are using the "central" sample, then you will see a completely different catalog in November.
Thank you for your understanding!
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