247

Astron. Nachr., Ud. 302, H. 5 (1981)

Selection, Statistics and Photometry of Compact Galaxies with Different Instrumental Equipment, Part II. The Cluster Abell 1775

N. RICHTERt, Weimar, and A. SCHNELL, Wien

With 5 Figures (Received 1980 May 30; revised 1981 March 10)

In Fortsetzung von Teil I unserer Untersuchung wird mit zwei groBen photographischen Teleskopen stark verschiedener optischer Konstanten ein Feld von 0.8 0" in der NBhe des galaktischen Nordpoles auf kompakte Galaxien untersucht. Das Feld enthat den Haufen Abell 1775. Statistik und Photometrie besatigen die Resultate von Teil I. Der Prozent- satz von optisch kompakten Galaxien bis zur Identifikationshelligkeit 18mg an der Cesamtheit der Haufengalaxien ergibt sich 211 mehr als 30%. Die Daten einer bcsonderen Standard-Sternsequenz, die far die Photometric der Galaxien bestimmt werden muate. werclen mitgeteilt.

In continuation of part I of our investigation a field of 0.8 no near the galactic north pole is investigated with two large photographic telescopes of very different optical constants. The field contains the cluster Abell 1775. Statistics and photo- metry confirm the results of part I. The fraction of optical compact galaxies up to the identification magnitude 18% (R) is found to IH: more than 30% of the total number of cluster galaxies. The data for a secondary photometric scqurncr. which had to 1% clcterminetl for the photometry of tlic galaxies, are presented.

In a preceeding publication (1979) the authors published the results of a selection, statistics and photometry of compact galaxies in an area of 1.5 0" including two fields near the globular cluster M3 and one field near M92 using plates of two very different instruments. These were the Tautenburg Schmidt and the Ritchey-Chretien teles- cope of the Fig1 Observatory for Astrophysics (FOA). This publication is a continuation of this work in another field of 0.8 0" near M3. This test field is of special character, i t includes the cluster of galaxies Abell 1775. For this reason this second part comprises mainly a statistics of compact cluster galaxies while the first part of our study contained field galaxies.

Tlic optical properties of the two telescopes are dcscribed in part I (Table I) as arc tlir methods of selection.

- - 31'

- 300

- 290

- 280

- 270

- 260

I 1 1 I V I I

52 48 44 40 ?I6 32 28

13h Fig. I. Positions of 745 compact galaxies of Richtcrs cataloque containing Zwickys clusters of galaxics. Area z contains the cluster

Abell 1775. Its central part is marked by a small square.

248 N. RICHTER, A. SCHNBLL: Compact Galaxies. The Cluster Abcll 1775

Fig. 2. The central part of the cluster Abell 1775. The compact galaxies both selected on Tautenburg and FOA plates are marked with arrows.

For this investigation FOA plate No 267, system B, photometric limiting magnitude 2om0, exposed under seeing conditions of 3“ was used.

The cluster Abell 1775 has recently been studied by BAIER and ZIENER (1977). Its position is within the cluster area 1341.6 + 2614 marked by ZWICKY and HERZOG (1963). In the “Catalogue and Finding Charts of 745 Compact Galaxies” by RICHTER and RICHTER (1977) the member galaxies in field z and field 4 are marked with C6. Figure I shows all selected galaxies of Richters catalogue and the borders of Zwickys clusters, especially the areas No 2 (p. 328) and No 5 (p. 296). The small square is the cluster Abell 1775. Figure z shows the central part of the cluster. All compact galaxies selected on Tautenburg and FOA plates are marked with an arrow.

a) Selection

Table I gives the result of the selection statistics.

Table I

NT = all on Tautenburg plates selected compact galaxies Nw = all on FOA plates selected compact galaxies N I = identical objects selected on plates of both telescopes

= 31 = 38 = 18

= rg - N w = Tautenburg objects not recognised on FOA plates +Nw = objects rccogniscd additionally on 1;Oh plates

Of special interest are the --Nw and +Nw objects. A re-inspection of the plates had the following result : Regarding the - N , objects on the FOA plate, 6 of them should have been recognised but were overlooked; 2 objects appear starlike with a very strong nucleus, the weak halo is not visible; z objects are doubtful t o classify; 2 objects are too faint for classification.

The re-inspection of the + N , objects on the Tautenburg platcs had tlic following result: 14 sccni starlike and cannot be detected as compacts; 2 appear elliptical and therefore are not classified; z were overlooked; I ob- ject is not classified as compact.

Conclusion: By combination of both instruments about 50% of the selected objects are identical and approxi- mately 40% more objects are found than with one single instrument. This agrees with the results of part I .

= I 2

b) Photometric Comparison

Table z shows the photometric comparison of Tautenburg catalogue magnitudes with FOA magnitudes both determined by iris photometry. The magnitudes determined on the FOA plate arc on the average om4 fainter than

N. RICHTER, A. SCHNELL: Compact Galaxies. The Cluster Abell 1775 249

on Tautenburg plates. The reason may be that the photometric limiting magnitude of the FOA plate is om4 brighter than that of the Tautenburg plates.

Table 2. Test f i e ld Abe l l 1775 w i t h i n t h e larger Tautenburg c a t a l o g u e f i e ld I 1 FOA plate No. 267, limiting photometric magnitude 20?o Tautenburg plates limiting magnitude 20?4 mT Tautenburg catalogue manitude miy = FOA magnitude

S y s t e m B

Object No.

11 96 I1 103 1 1 111 11 I12 11 113 I1 116 I1 125 I 1 126 I1 127 1 1 '34 I V I I V 6 IV 7 I V I 0 I V I 1 I V I2

I V 20 I \ ' I )

.

mT

I 6m94 18.31 17.93 17.98 16.90 18.11 17.96 18.40 18.30 17.88 17.89 18.24 18.74 17.03 18.49 17.88 17.93 18.31

I 7?58 18.58 18.00 18.50 17.77 18.80 18.28 19.10 18.84 18.16 18.30 18.48 19.00 17.73 18.48 18.27 18.45 18.74

+ 0?64 +0.27 +0.07 +0.52 +0.87 +0.69 1-0.32 +0.70 +0.54 t0 .28 -1-0.41 -1-0.24 +0.26 +0.70 -0.01 -1 0.39 -1 0.52 +0*43

3:74 I .78 2.14 2.31 2.31 1.78 2.67 I .g6 2.14 2.67 3.03 1.78 I .96 3.03 I .g6 I 46 I .gG I .60

mw/o"

20?18 19.57 19.39 20.06

19.33 19.79 20.15 20.30 20.23 20.03

20.44 19.47

19.87 19.68 19.47 19.65 19.50

2 0 . 2 0

c) Equidensitometric diameters, diameter magnitude diagram and surface brightness

W. HOGNER (Karl-Schwarzschild-Observatory) made an equidensitometric copy from FOA plate No 267. This allows t o determine maximum angular diameters of the compact galaxies in system B and the corresponding surface brightnesses of the objects. These parameters are compiled in Table 2. Figure 3 shows a diameter magni- tude diagram, Figure 4 gives the corresponding relation between surface brightness mw/O" and integral brightness

X

U Ic x u

I 1 I

11 18 19 mV4

Fig. 3. Diameter versus magnitude diagram for maximum cquiden- sitometric diameters dw of I'OA plate No 267 (B). nqy = integral brithness (0' represent stars of the standard sequence, x compact

galaxies)

17

. * . . .* . .

10 n m,

Fig. 4. Relation between surface brigthness m w / n " and integral hrigthness mw of compact galaxies on

I'OA plate No 267 (R)

d ) The fraction of comfiact galaxies in the centre of the cluster Abell177.5

As centre of the cluster we choose an area of 12' radius which lies within ring No 7 defined by BAIER and ZIENER (1977). According to them there are 228 galaxies up t o the limiting identification magnitude 19?6 (B) within this area.

By combination of FOA and Tautenburg plates we selected in this areas 33 optical compact galaxies up to 18'!'7 for Tautenburg and 19m1 for FOA magnitudes. We assume a mean limiting identification magnitude of 18m9 in system B. Assuming that the relation between the cumulative number N ( m ) of galaxies and the brightness m follows the general formula

d log N ( m ) dnr = 0.6

260 N. RICHTER, A. SCHNELL: Compact Galaxies, The Cluster Abell 1775

and a total number of 228 galaxies up to 1gm6 we find a total number of 87 galaxies up to our selection limiting magnitude 18?9. In the centre of Abell1775 the 33 selected optical compact galaxies correspond to a fraction of 38% if we assume that those objects are identical with objects found by BAIER and ZIENER. Considering the case that not one of our objects is identical with those of their selection we find an upper limit for the total numlwr o f compact galaxies in the centre of Abell 1775 of 120 objects. In this case the optical compact galaxies correspond to a fraction of 27.5%. We may conclude that in the cluster Abell 1775 the fraction of compacts is at Icn\t more than 30%.

Appendix

A secondary pho tomet r i c sequence i n B a n d V n e a r t h e c lus t e r Abel l 1775

In order to determine the magnitudes of the selected compacts on the FOA plate No 267 it was necessary to determine a secondary photometric sequence near the cluster Abell 1775 because the standard sequence for the Tautenburg statistics used of the cluster M 3 was not within the area of the FOA plate. Using Tautenburg plates containing M3 it was possible to determine a secondary photometric sequence located on the FOA plate. Table 3 gives the magnitudes in B and I.' on the basis of 3 Tautenburg plates for each system. In Figure 5 a map of these standard stars is given.

Tablc 3

Star No

I5

I7 18 9

I3

4

I4 8

19 3 6

5

2

21

I 0

20

141118 14.78 15-40 15.78 16.00 16.06 16.14 16.24 16.45 17.26 17.57 I 7.61 17.67 18.51 18.53 19.01

Star No.

2

17 18 9

21

13 3

19 I 2 I 1

I 0

5 23 20 22

24

mv

13?93 14.46 15.05 15.10 15.37 15.58 15.80 15.87 15.93 15.96 15.97 17-17 17.44 17.59 17.96 18.40

Fig. 5. Map of the secondary photometric sequence near the cluster Ah11 1775.

a-9 -.

t/--O-?.-Q -.-# a 1 f 26'55'

*-f4 0- f5

f7-a . W--. .

Acknowledgements

One of us (A.S.) greatfully acknowledges the generous hospitality of the Karl-Schwarzschild-Observatory during data reduction.

References

DAIER, F. W. and ZIESER, R . : 1977, Astron. Nachr. 298, 87. RICHTER, N. and RICHTER, L. : 1977, Mitt. I<arl-Schaarzschild-Obs. lautcnburg No 80. RICHTER, N. and SCHNELL, A.: 1979, Astron. Nachr. 300, 269. ZWICKY, F. and HBRZOG, E.: 1963, Catalouge of Galaxies and of Clusters of Galaxics, Vol. 11, Calif. Inst. of Tcchn.

Addresscs of thc authors:

NIKOLAUS RICHTER Am Bahnhof Nohra 16 DDR-5301 Weimar, German Democratic Republic

ANNELIESE SCHNELL Institut for Astronomie der Univrrsitlt Wicn TOrkenschanzstraOe I 7 A-I 180 Vienna, Austria