50 Years of the Cosmic Web

I’ve just given a lecture on cosmology during which I showed a version of this amazing image:

The picture was created in 1977 by Seldner et al. based on the galaxy counts prepared by Charles Donald Shane and Carl Alvar Wirtanen and published in 1967 (Publ. Lick. Observatory 22, Part 1). There are no stars in the picture: it shows the  distribution of galaxies in the Northern Galactic sky. The very dense knot of galaxies seen in the centre of the image is the Coma Cluster, which lies very close to the Galactic North pole.The overall impression  is of a frothy pattern, which we now know as the Cosmic Web. I don’t think it is an unreasonable claim that the Lick galaxy catalogue provided the first convincing evidence of the form of the morphology of the large-scale structure of the Universe.

The original Shane-Wirtanen Lick galaxy catalogue lists counts of galaxies in 1 by 1 deg of arc blocks, but the actual counts were made in 10 by 10 arcmin cells. The later visualization is based on a reduction of the raw counts to obtain a catalogue with the original 10 by 10 arcmin resolution. The map above based on the corrected counts  shows the angular distribution of over 800,000 galaxies brighter than a B magnitude of approximately 19.

The distribution of galaxies is shown only in projection on the sky, and we are now able to probe the distribution in the radial direction with large-scale galaxy redshift surveys in order to obtain three-dimensional maps, but counting so many galaxy images by eye on photographic plates was a Herculean task that took many years to complete. Without such heroic endeavours in the past, our field would not have progressed anything like as quickly as it has.

I’m sorry I missed the 50th anniversary of the publication of the Lick catalogue, and Messrs Shane and Wirtanen both passed away some years ago, but at last I can doff my cap in their direction and acknowledge their immense contribution to cosmological research!

UPDATE: In response to the comments below, I have updated this scan of the original rendition of the Lick counts:

534515-112918 (2)



5 Responses to “50 Years of the Cosmic Web”

  1. Bernard Jones Says:

    Shane and Wirtanen’s work was indeed amazing – no computers, photographic plates, eyeball counting and hand drawn graphics! They produced isopleth contour maps.

    The picture you show was, I am told, created by Jim Peebles’ daughters from those maps and so the points do not reflect the galaxy positions, just the density. A great poster nevertheless.

  2. The Frontispiece of Jim’s 1980 Large Scale Structure book is the Lick map as hand-colored by Jim and Alison (and perhaps other members of the family). The Seldner et al. plates were computer-produced using an “extensively modified” film scanner (converted into an inverse scanner). The two are included side by side (back to back) in the online Supplemental Material of Jim’s 2012 AARA autobiography _Seeing Cosmology Grow_.

    • telescoper Says:

      I’ve now included the version from Jim’s book in the above post. I’d forgotten it was there! It looks a bit strange to modern eyes, but it’s an important part of the story.

  3. By eye, most probably can’t tell such a map from the output of an N-body simulation. Such simulations are refined so that they agree better and better with better and better observations. However, the physics is not based on the primitive equations, but rather on various approximations, heuristics, etc. A devil’s advocate would ask whether such simulations could reproduce any observations. My question (as an outsider to the field) is whether there has ever been a robust prediction of such simulations which was later observationally confirmed.

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