Archive for Lick Map

50 Years of the Cosmic Web

Posted in The Universe and Stuff with tags , , , , , , on November 21, 2018 by telescoper

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:

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