The CfA Redshift Survey was started in 1977 by Marc Davis, John Huchra, Dave Latham and John Tonry. The First CfA Survey, completed in 1982, (Huchra, Davis, Latham and Tonry, 1983, ApJS 52, 89) had as its goal the measurement of radial velocities for all galaxies brighter than 14.5 and at high galactic latitude in the merged catalogs of Zwicky and Nilson (the UGC). This survey produce the first large area and moderately deep maps of large scale structure in the nearby universe, as well as the first crude but truly quantitative measurements of the 3-D clustering properties of galaxies. Redshifts are the simplest link to determine galaxy distances. A description of the redshift is given here THE REDSHIFT 马耳他瓦莱塔幸运飞艇季军. Basically, since in most places outside the cores of galaxy clusters or in the very, very local Universe (the Local Group of Galaxies), the expansion of the universe, commonly called the Hubble Flow, is smooth, redshift is a surrogate for distance:
马耳他瓦莱塔幸运飞艇季军 Distance = velocity/(Hubble's Constant) = V/H0
So the measurment of a galaxy's redshift givers you an estimate of that galaxy's distance --- thus allowing astronomers to map the nearby Universe.
The second CfA survey (CfA2) was started by John Huchra and Margaret Geller in the winter of 1984/5. Between 1985 and 1995, we and our students and co-workers measured relative distances via redshifts for about 18,000 bright galaxies in the northern sky.
Red V < 3000 km/s
马耳他瓦莱塔幸运飞艇季军 Blue 3000 < V < 6000 km/s
马耳他瓦莱塔幸运飞艇季军 Magenta 6000 < V < 9000 km/s
Cyan 9000 < V < 12000 km/s
Green 12000 < V km/s
The large read area at the center of the map (12 hours, +10 degrees) is the dense central region of the Virgo Cluster of galaxies which is the core of the Local Supercluster (see below). The dark blue points which dominate the RHS of the map (0-4 hours +30 to +40 degrees) show the location of the Pisces-Perseus Supercluster, which has been well studied by Giovanelli & Haynes. The cyan points at 15 hours running almost from the equator to +40 degrees declination are the Hercules Supercluster studied by Pauline Barmby and myself. The blank areas running mor eor less north-south and looping over the north celestial pole are the regions of the sky inaccessible to optical surveys due to dust extinction when looking through the Milky Way, aka the "Zone of Avoidance." (see 2MASS for how to fix this!)
This initial map was quite surprising, showing that the distribution of galaxies in space was anything but random, with galaxies actually appearing to be distributed on surfaces, almost bubble like, surrounding large empty regions, or ``voids.'' You can get a clean postscript version of this figure here . If you use this or any other image from this site, please credit the Smithsonian Astrophysical Observatory and the appropriate authors.
马耳他瓦莱塔幸运飞艇季军 Here's the map with six contiguous 6 degree slices in the northern galactic cap. The structure running all the way across between 8 hours and 17 hours RA and 5,000 and 10,000 km/s is called the ``Great Wall,'' perhaps the largest single structure yet detected in any redshift survey. Its dimensions are about 600x250x30 million light years, sort of like a giant quilt of galaxies across the sky. (see Geller and Huchra 1989, Science 246, 897.)
The Great Wall itself can be viewed in this simple planar projection of all galaxies in the CfA Survey with velocities between 6,500 and 11,500 km/s in the north galactic cap. Galaxies with velocities between 6,500 and 8,500 km/s are plotted as red points and those between 8,500 and 11,500 are blue. Because the Great Wall is slightly tilted in velocity space (see the previous figure), the higher velocity end dominates the eastern portion of the figure. The Great Wall is a surface that has, as expected, considerable two-dimensional structure --- embedded clusters and groups of galaxies as well as some filaments and other, more amorphous structures - basically both low and high density regions (see, for example, Ramella, Geller and Huchra ApJ 384, 404, 1992). The Coma Cluster is the dense region right near the center of the plot (13h and +29d).
马耳他瓦莱塔幸运飞艇季军 The redshift distribution of the CfA2 survey can also be seen in this polar projection of the redshifts for all the galaxies in the CfA2 survey out to 12,000 km/s. This is a section of a cylinder in equatorial coordinates looking down from the north pole to the equator with a height of 12,000 km/s and a radius of 12,000 km/s. Tha major structures seen are again the Local Superluster just above the middle of the plot, the Great Wall cutting from 9 hours and 5,500 km/s to 15 hours and 9,000 km/s and the Pisces-Perseus supercluster centered around 1 hor and 4,000 km/s. The geometry of this projection is similar to that of a hockey puck.
马耳他瓦莱塔幸运飞艇季军 The combination of several new surveys also provides a new view of the Local Supercluster. The above plot shows the all-sky distribution of all the galaxies in ZCAT with heliocentric velocities less than 3000 km/s. This set is essentially made up of objects fromt he CfA Survey in the north, the SSRS2 survey in the south, the ORS survey in regions not covered by the others plus the IRAS 1.2-Jy survey all over, especially at low galactic latitudes (the small points sprinkled throughout the map). Despite the poor coverage at low galactic latitudes, the LSC and the central regions around its core, the Virgo Cluster, stand out quite dramatically.
To give you some idea of the statistical characteristics of the CfA2 catalog, these two plots show the count statistics (log N - log S) and the V/Vm statitics for the CfA2 catalog above |b| = 30 degrees log(n)-log(s) , V/Vm . For a uniform distribution in Euclidean space, V/Vm shoul ve 0.50. These plots show first, an excess of brighter galaxies relative to a normalization at m_pg=13.5, which has long been associated with the presence of the local supercluster, and second, an apparent slight excess below 15th magnitude that may be associated with the Great Wall. Note that the plots are both integral statistics (its difficult to define V/Vm for differential counts!) Part of the excess at faint magnitudes may also be due to nonlinearities in the Zwicky-Nilson magnitude scale (e.g. Huchra 1976, AJ 81, 952 and many following references). The luminosity function for the catalog (a measure of the selection function), calculated using the simple V/Vm method (Schmidt 1968; Huchra & Sargent 1973), is given in log phi , where phi is the number density of galaxies per luminosity interval, i.e. the number of galaxies per magnitude interval per cubic Megaparsec. This is computed for a an area of the sky given by the boundaries (0-90d, 8h-17h, -2.5-90d, 20h-4h), which covers 36.15% of the sky, and assumes a Virgo infall of 250 km/s, H_0=75 km/s/Mpc, and an extinction correction of 0.15csc(b). There are 13,977 galaxies in this subset catalog.
Here is a link to the CfA Redshift Catalog description: ZCAT DESCRIPTION. 马耳他瓦莱塔幸运飞艇季军 You can access the CfA Redshift Survey data data at this website. The main ZCAT2000 catalog can ve downloaded here:
ZCAT2000 Version June 2008
It is necessary to download the file via ftp because of its size. There is a README file describing the data stored there available for public use, sources for redshifts etc. and information about how to reference these if you do use them. The compressed public version of the CfA Redshift Catalogue is in "velocity.dat.gz". There are also files for the CfA1 survey data (cfa1.dat), the published CfA2 slices, and subdirectories for the IRAS 1.2 Jy sample, the UZC, the ORS and many other available redshift surveys.
Some of the small catalogs can be downloaded directly from the web. These are:
In addition, here are a few of the parent catalogs like the Uppsala General Catalogue (UGC) of Nilson, and a machine readeble version of the merged Zwicky-Nilson Catalogue:
马耳他瓦莱塔幸运飞艇季军 JPH's AGN lists can also be obtained from his home page
The sources for the CfA surveys and for ZCAT and the ancillary catalog redshifts can be found in a downloadable TeX file:
or as a postscript file:
马耳他瓦莱塔幸运飞艇季军 The last update of this file is from April 20 of 2005. Questions about sources should be addressed to J. Huchra. If you have published a paper or database that is *not* in our list, please let me know wo we can include it!
马耳他瓦莱塔幸运飞艇季军 Finally, here is a partial list of the template stars and galaxies we use for velocity checks and studies:
and a useful, short list of standard stars for spectrophotometry:
Nowadays, most of the actual templates used are synthetic and can be obtained from Doug Mink or Mike Kurtz of the SAO Telescope Data Center.
马耳他瓦莱塔幸运飞艇季军 If you have questions about the use of the Catalogue or anything else here please contact me at the e-mail address below. I won't promise a prompt response but I will promise a curteous one! Nathalie Martimbeu (email@example.com) is also responsible for corrections and information, and, if you don't get me try her.
马耳他瓦莱塔幸运飞艇季军 John Huchra