Technical Information on images

The galaxy morphological types should all be consistent with the "3rd Reference Catalog of Bright Galaxies" (de Vaucouleurs+ 1991).

The pictures on this site were taken using the MDM Observatory   McGraw-Hill 1.3-m telescope located on Kitt Peak 50 miles west of Tuscon, AZ. 
The 1.3-m is a Cassegrain telescope and it was operated with its secondary in f/7.5 mode.

A few images have been obtained from other sources on the Internet in order to completely sample the Hubble Types.  These will be labeled as such.

Two CCD (charge-coupled device) chips were used at the focal plane of the 1.3-m:

    1) Echelle - manufacturer = SITE,  type = thinned, backside ill.
        format = 2048x2048,  pixel size = 24 micron
        pixel scale = 0.50 "/pixel
        field of view = 17.0'

    2) Nellie - manufacturer = STIS, type = thick, frontside
        format = 2048x2048,  pixel size = 21 micron    
        pixel scale = 0.44 "/pixel
        field of view = 14.9'

The Johnson B (blue) and R (red) filters were used for the majority of galaxies.  A few were measured in V(yellow) and I (infrared). 

The CCD data were processed in the standard manner:   1) the bias was subtracted,  2) they were flat-fielded using a combination of dome, sky and median flats,  3) multiple, dithered exposures of the same galaxy were registered by shifting, and 4) images were combined.  We used the IRAF tasks CCDPROC, IMALIGN, and IMCOMBINE for these procedures.

The images were displayed in SAOimage/DS9.  We then use the GIMP image editor to capture the DS9 window, crop it, and convert it into a high-quality JPEG. 

The DS9 display can take on a vast range of appearances for a single CCD frame.  We generally used a logarithmic stretch rather than linear, but not always.  Our displaying strategy was different for the B and R band frames.  For the R-band, we sought to bring out the faint outer parts of the galaxy and show surrounding satellite galaxies.  (R is better than B for this purpose because it gathers more photons, and galaxies produce more red than blue photons.)  The B-band images were used to show detail in the central regions of the galaxy.  This was done by 1) zooming in on the central part of the image, and 2) adjusting the display so that the maximum greylevel (white) was greater than the peak count of the galaxy.  Sometimes, we reduced the number of greylevels allotted to the central count range so that the isophotal contours would become visible (a "stepped" appearance).  This was purposefully done to show the presence of dust, which shows up as a jag in an otherwise smooth elliptical contour.
In addition to the B and R images, we often present a third image.  Usually this is a ratio of the B and R image and in a few cases, it is a continuum subtracted narrow band image taken in the light of H-alpha emission (6563 Angstroms).   The H-alpha image reveals ionized gas clouds excited by hot stars and AGN (Active Galactic Nuclei).  The B/R ratio images indicate regions that are relatively blue as bright white, and regions that are relatively red as dark.  In so doing, we reveal regions of recent star formation where many blue stars remain, and the extent of the absorption by dust (which makes the color redder).  This is often more scientifically useful than a "color" image that has been processed just to look colorful.

We may add our HST WFPC2 images someday!
We will turn the tuning fork into an image map and do away with the table!  <-- DONE!!