Physics 162
Galaxies & Cosmology

H. E. Smith                                                                                                            Spring 2001

Physics 162 - Galaxy Classification Lab
Due: Thursday, April 26

In this exercise you will apply the Hubble Classification scheme for galaxies to selected galaxies on prints from the National Geographic -- Palomar Observatory Sky Survey (POSS). Begin by reading The Hubble Atlas of Galaxies by Allan Sandage, comparing carefully the galaxy images and the classification criteria as described by Sandage. Attached are two lists of galaxies with millimeter coordinates on the POSS prints. The first is a list of well known comparison galaxies whose classifications are given to allow you to ``calibrate" your eye and the POSS prints. I suggest that you look up these galaxies on the POSS prints and classify them yourself before you look at the catalogued classification. The second list contains coordinates locating bright (V < 10.5) galaxies on the POSS prints for you to classify. Use the eyepieces provided to study each of the program objects, write down a description of the galaxy and a class under the Hubble classification scheme as described by Sandage. Also, attempt assigning a luminosity class for the spiral galaxies only. Pay closest attention to the Hubble type as this counts for most of the credit.
You are encouraged to discuss the classification schemes with one another. I request, however, that you inspect the POSS prints individually and also that the detailed classification submitted for credit be solely your own work. Submit your classifications and brief galaxy descriptions (neatly transcribed, concentrating on classification criteria) on the sheets provided, by 4:00 pm April 26.

The National Geographic - Palomar Observatory Sky Survey (POSS)

During the 1950s a major survey of the northern sky was undertaken at Palomar Observatory with the support of the National Geographic Society. This survey, made with the 48" Schmidt telescope, covers the sky from the north celestial pole to --33 declination on blue sensitive (Kodak 103a-O) and red sensitive (103a-E) photographic plates. The original 14"x 14" glass plates were printed through transfer positives as negative contact prints. Each print represents a 6° x 6° area of the sky with a scale of 67 arcseconds per mm. The blue passband is comparable to the classical photographic band, m_pg, and the red is centered around H (6563Å). The blue (``O'') plates go more that one half magnitude fainter than the red (``E'') plates with limiting magnitudes of approximately m_b = 21.1 and m_r = 20.5 respectively.
The plates are catalogued as pairs in 6° declination strips around the sky in order of right ascension. A data block in the upper left (northeast) corner contains the exposure date, the 1950.0 celestial coordinates (Right Ascension = ; Declination = ) of the plate center, and a print number preceeded with an ``O`` or ``E'' for the emulsion type. For example, the prints catalogued as +06° 19^h 36^m are prints O/E 171 with plate center = 19^h 40^m 39^s and = +06° 13' 22". Further information about the survey and prints is given by Minkowski and Abell (1963) and some applications described by Lund and Dixon (1973). King and Raff (1977) give an empirical calibration of the aparent magnitude as a function of image diameter for the prints.
More recently Palomar has undertaken a second generation sky survey using higher resolution, more sensitive photographic emulsions - the POSS-II. This survey is similar to the original POSS, but uses three colors: blue (IIIaJ), red (IIIaF), similar in passband to the old POSS, and near-infrared (IV-N) at about 8000Å. These plates are being digitally processed at the Space Telescope Science Institute and are partially available online
The POSS prints are housed in the CASS Marlar Library. The prints are in atlas cases in the Library Atlas Room along with copies of the Hubble Atlas, the van den Bergh Luminosity Classification, and eyepieces for use in inspecting the prints. Please handle the prints with great care: make certain that your hands are clean, be certain that the prints are laid flat while you are working with them, do not place other articles on them or write on them or on top of them, and return them carefully to the box from which they came. You will need a mm ruler to find the galaxy positions, which are to be measured from the lower left corner of the plate. Susan Rappoport, CASS Librarian, will be available when the atlas room is open, M-F 9:30--6:30.
There is an alternative way to access the POSS via the Web at the Space Telescope Science Institute Digitized Sky Survey (DSS) where you can pull up digitized images. The J2000 coordinates of the appropriate galaxies may be found on one of the pages below.
I strongly recommend that you begin your exercise with the actual POSS prints; in the case of galaxies the highly nonlinear response of photographic emulsions provide a substantial advantage in the ability to see the high-surface brightness nuclear regions simultaneously with the faint outer regions. You will find that you need to download the image (GIF or FITS format; if you don't know about FITS or are using a PC or Mac, download GIF) from the DSS and use your favorite image display tool to play around with the gamma of the image extensively in order to get a classifiable image. Use the POSS-II fields where available - the galaxies show up much more readily. For most of the classification galaxies a field of a few arcminutes will be sufficient, but the comparison galaxies below were selected to give you a tour of nearby bright objects and may be pretty big images (e.g. the major axis of M31 is about a degree).

References

Minkowski, R. and Abell, G. 1963 in Basic Astronomical Data, K. Strand, ed. (Chicago: University of Chicago Press).
Lund, J. and Dixon, R. 1973, PASP, 85, 230.
King, I. and Raff, M. 1977, PASP, 89, 120.
For galaxy positions:
Click here if your data set is Lab #1 (first plate on your exercise is -24° 00^h 52^m (300,067)).
Click here if your data set is Lab #2 (first plate on your exercise is -24° 03^h 28^m (106,026)).
Click here if your data set is Lab #3 (first plate on your exercise is +36° 02^h 20^m (054,306)).

Comparison Galaxies
Galaxy Position POSS Coordinates Classification

Plate (X,Y)

NGC 205 00^h 40^m 22^s +41° 41' 26" +42° 00^h 30^m 148,115 E7

M31 00^h 42^m 44^s +41° 16' 09" +42° 00^h 30^m 123,092 Sb I-II

M32 00^h 42^m 42^s +40° 51' 52" +42° 00^h 30^m 123,071 E0

M33 01^h 33^m 51^s +30° 39' 37" +30° 01^h 18^m 085,171 Sc(s) II-III

M81 09^h 55^m 33^s +69° 03' 55" +72° 10^h 12^m 305,062 Sb(r) I-II

M82 09^h 55^m 52^s +69° 40' 47" +72° 10^h 12^m 300,096 Irr

NGC 3351 10^h 43^m 58^s +11° 42' 14" +12° 12^h 48^m 326,199 SBb(r) II

M87 13^h 30^m 49^s +12° 23' 28" +12° 12^h 24^m 179,238 E0

NGC 4594 12^h 39^m 59^s -11° 37' 23" -12° 12^h 24^m 062,236 Sab

M101 14^h 03^m 12^s +54° 20' 55" +54° 13^h 56^m 158,230 Sc(s) I

NGC 6946 20^h 34^m 52^s +60° 09' 14" +60° 20^h 32^m 173,155 Sc II

Comparison Galaxies
Galaxy	Position		POSS Coordinates		Classification
			Plate	(X,Y)
NGC 205	00^h 40^m 22^s	+41° 41' 26"	+42° 00^h 30^m	148,115	E7
M31	00^h 42^m 44^s	+41° 16' 09"	+42° 00^h 30^m	123,092	Sb I-II
M32	00^h 42^m 42^s	+40° 51' 52"	+42° 00^h 30^m	123,071	E0
M33	01^h 33^m 51^s	+30° 39' 37"	+30° 01^h 18^m	085,171	Sc(s) II-III
M81	09^h 55^m 33^s	+69° 03' 55"	+72° 10^h 12^m	305,062	Sb(r) I-II
M82	09^h 55^m 52^s	+69° 40' 47"	+72° 10^h 12^m	300,096	Irr
NGC 3351	10^h 43^m 58^s	+11° 42' 14"	+12° 12^h 48^m	326,199	SBb(r) II
M87	13^h 30^m 49^s	+12° 23' 28"	+12° 12^h 24^m	179,238	E0
NGC 4594	12^h 39^m 59^s	-11° 37' 23"	-12° 12^h 24^m	062,236	Sab
M101	14^h 03^m 12^s	+54° 20' 55"	+54° 13^h 56^m	158,230	Sc(s) I
NGC 6946	20^h 34^m 52^s	+60° 09' 14"	+60° 20^h 32^m	173,155	Sc II

Physics 162 Galaxies & Cosmology

H. E. Smith Spring 2001

The National Geographic - Palomar Observatory Sky Survey (POSS)

References

Physics 162
Galaxies & Cosmology