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ORBITAL PARAMETERS AND

SEYFERT GALAXY TYPES

by

Karl Erwin Hoisch Jr.

A THESIS

Submitted to
Michi on State University
in partial ent of the reqmrements
for the degree of

MASTER OF SCIENCE

Department of Physics and Astronomy

1991

ABSTRACT

ORBITAL PARAMETERS AND

SEYFERT GALAXY TYPES
by

Karl Erwin Haisch Jr.

The rate of pairing of Seyfert galaxies is explored by utilizing a sample of 79 Seyfert.
galaxies selected from the “Catalog of Seyfert Galaxies and Related Objects” by N.
Kaneko. Using computer simulations and data from the CfA Redshift Catalog, the
fraction of Seyfert galaxies found in pairs or groups is observed to be signiﬁcantly
higher than that found in many previous investigations. The corrected pairing rate
lies between 60 and 70 % for bright companions. This study supports the suggestion
by Kollatschny and Fricke that many Seyferts reside in groups. Seyferts appear to
have pairing rates similar to those for a sample of nearby normal spiral galaxies. An
excess of projected angular momentum values was observed for the Seyfert pairs, im-
plying the Seyfert companions are more bound than control companions. No evidence
for Seyferts having a signiﬁcant population of elliptical companions as compared to
normal spirals was observed. In addition, no evidence that the physical separation

between Seyfert 1 galaxies and their companions differs from that for Seyfert 2’s.

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Susan Simkin for suggesting this problem
and for her support and guidance during my graduate study. I am also grateful to

her for reading and correcting the manuscript.

I would also like to thank Debbie Benedict for taking the time to listen when

problems were encountered. It was greatly appreciated.

Finally, I would especially like to thank my best friend, Susan Shotkin for her
encouragement and support through the last few years. Her understanding and kind

words helped make the completion of this work possible.

iii

TABLE OF CONTENTS

Page
List of Tables ................................................................. v
List of Figures ................................................................ vi
Chapter 1: Introduction and overview of previous work ......................... 1
Chapter 2: Analysis of galaxy pairing ......................................... 12
I. Seyfert companions from the CfA catalog ...... ' ................. 12
II. Comparison with Non-Seyfert pairs ............................ 16
III. Analysis of results in section II. ............................... 27
IV. Angular Separation ......................... . .................. 36
Chapter 3: Morphology of the companions for Seyfert and control galaxies ..... 41
Chapter 4: Further analysis of galaxy pairing ................................. 44
Chapter 5: Conclusions ....................................................... 57

List of References ............................................................ 59

iv

LIST OF TABLES

 

Pase
Table 1: Table of Seyferts from list of Kaneko ................................. 13
Table 2: Statistics of companions for Kaneko Seyferts ......................... 16
Table 3: Mean Number of Companions (25 runs) .............................. 19
Table 4: Average velocity and pair average for 25 runs ........................ 26
Table 5: Comparison of morphologies of Seyfert and control companions ....... 42
Table 6: Companion number breakdown (20 runs) ............................ 54
Table 7: Companion number breakdown ...................................... 56

Figure 1:

Figure 2:

Figure 3:

Figure 4:

Figure 5:

Figure 6:
Figure 7:

Figure 8:

Figure 9:

LIST OF FIGURES

Page

Plot of multiple pairs to the Seyfert galaxies of Simkin (1990).

Note that the companions of the Seyfert 2’s lie closer to
their host than for the Seyfert 1’s .................................. 11

Velocit distributions of the CfA and Cases A, B and E. Also
plotte is the velocity distribution of the Seyferts ................... 21

Plot of the mean number distribution of companions found for

the ensembles in Cases A, B, D and E. Also plotted is
the mean number distribution of the Seyferts ....................... 23

Plot of the mean number distribution of companions found for
the ensembles in Cases A, Cl, E and F. Also plotted is
the mean number distribution of the Seyferts ....................... 25

Number distribution for all companions in Case E ................... 29
Number distribution for multiple companions in Case E ............. 31

Plot of “projected angular momentum” for the Seyferts and
Case E ............................................................ 33

Number distribution of companions of Seyferts and Case E with

total an ar momentum < ZOOOIcms'l s kpc. There is an

excess 0 low J values for the Seyferts as opposed to the

control sample ..................................................... 35

Plot of projected separation against radial velocit difference for

each Seyfert alaxy and its closest companions. o evidence

for a kinematic distinction between Seyfert 1 and Seyfert 2

galaxies is observed ................................................ 38

Figure 10: Plot of the companions with the smallest “projected angular

momentum” in Case E ............................................ 40

vi

Figure 11: Velocity distribution of the Seyferts. The Virgo cluster is
included .......................................................... 46

Figure 12: Velocity distribution of the Seyferts. The Virgo cluster has
been excluded ..................................................... 48

Figure 13: Histograms of the apparent magnitude of the companions for

the given cases. The apparent magnitudes of the companions
at greater velocities are fainter as is expected ...................... 51

Fi 14: Hist ams of the absolute m 'tude of the com anions for
8“" the gen cases. The absolute‘rsnﬂgnitudes of the gompanions

at larger velocities are brighter due to their greater
distances ......................................................... 53

CHAPTER 1: INTRODUCTION AND OVERVIEW

OF PREVIOUS WORK

I. Introduction

The majority of galaxies we observe are ordinary galaxies which show little ac-
tivity beyond what is expected for a collection of stars and gas. In a small percentage
of observed galaxies, however, there is violent activity well beyond the norm. Seyfert
galaxies, a particular class of active galaxy, emit strongly in the radio, infrared and
X-ray. Unlike ordinary galaxies, which have a spectrum consisting of a thermal con-
tinuum plus absorption lines, Seyferts exhibit a nonthermal continuum plus emission

lines.

Seyfert galaxies can be classiﬁed into two types depending on their emission
spectra. Type 1 Seyferts have very broad H I, Be I and He II emission lines with
full widths at half maximum (FWHM) on the order of 1 to 5 x 103kms“. The
forbidden lines, like [0 HIM/M959, 5007, [N II]AA6548, 6583 and [S H]AA6716, 6731
have FWHMs of order 5 x 10’kms‘1. The forbidden lines, therefore, are broader

than the emission lines in most starburst galaxies.

Type 2 Seyferts have permitted and forbidden lines with approximately the same

FWHMs, typically of order 500kms‘1. This is similar to the FWHMs of the forbidden

2

lines in Seyfert 1’s. Seyfert 2’s also possess relatively strong [0 III] emission lines,

with [0111p 5007/HB _>_ 3.

There are, however, lower-ionization Active Galactic Nuclei (AGN) called Low-
Ionization Narrow Emission-Line Regions (LINERs). These can be distinguished from
starburst or ﬁll galaxies in that LINERs have relatively strong [0 I] and [5 II], and
seem to be photoionized by the same type of hard spectrum as other AGNs. LINERs,
however, seem to have a smaller ionization parameter, I‘, which is the ratio of number
densities of ionizing photons [ f 01'3"] to free electrons. This sets the general level of

ionization (Osterbrock 1989).

In it’s most general sense, an ”active galaxy” refers to those few percent of all
galaxies which display an anomalous energy output from their nuclei compared to that
from. a ”normal” galaxy. It is generally accepted that this activity arises from the
interaction of matter with a supermassive black hole with a mass of ~ 103 — 10’°M@.
The problem which exists is in ”fuelling” the AGN. This is a two-fold problem; we
need to know what the fuel source is and how the fuel is transported to the black
hole. In this work, the question of fuel transportation is addressed, with a focus on
companion galaxies acting as possible mechanism in sustaining nuclear activity.

II.Overview of previous work

Almost a decade ago, the morphological similarities between patterns seen in
Seyfert galaxies and those produced by gravitational forcing led to the suggestion that
Seyfert activity might be fueled by material inﬂow induced by either a central bar or

a perturbing companion (Simkin, Su, and Schwarz, 1980). More recent theoretical

3

calculations suggest that such a feeding mechanism may involve a central bar-like
structure even if initially induced by the tidal effects of a companion galaxy (Noguchi,

1988a,b).

The recent literature on the prevalence of Seyfert galaxy companions, however,
is somewhat confusing and, at initial glance, contradictory (Byrd, et al., 1987, Dahari,
1984, 1985, Fuentes-Williams, and Stocke, 1988, Keel, et al., 1985, Kennicutt, and
Keel, 1984, Kollatschny and Fricke, 1989, Petrosian and Turatto, 1982, 1986). Most
studies ﬁnd either a weak correlation between excess companions or none at all. All of
these studies involve complex (and incommensurate) selection criteria. Most authors
have attributed their disparate conclusions to selection effects (op. cit.). It would be

instructive to look at the literature in greater detail.

Dahari (1984) has examined the region of the sky between -45 deg _<_ 6 S 90 deg
and z 5 0.03 for companions of 103 Seyfert galaxies, 18 of which were marginal or
uncertain Seyferts. The redshift limit was chosen so that cosmological evolutionary
effects would be umimportant. Dahari searched the Palomar Observatory Sky Survey
(hereafter POSS) plates for possible companions within three times the major axis to
the Seyferts (S=3D). This criterion was chosen speciﬁcally to avoid ﬁnding multiple
companions. 15% of the Seyferts had physical companions, compared to an upper
limit of 3.1% for the control sample. Calculating a factor denoted Q, which is the
gravitational interaction strength between two galaxies, Dahari found that 7.5% of
the Seyferts have very close companions, as opposed to 1% for the controls. Q will

be large for close and large companions.

4
One hundred sixty seven systems of interacting and asymmetric galaxies were
observed spectrophotometrically by Dahari (1985) in the range 4700-7100 A . Results
were compared with a sample of isolated galaxies. N o Seyfert nuclei were found in
elliptical or dwarf irregular galaxies. An excess of Seyfert nuclei among interacting
spirals was observed at the 90% conﬁdence level. This became statistically signiﬁcant

(98%) when only strongly interacting spirals were included.

Byrd et al. (1987) found (unlike Dahari) that Seyferts are more likely to have
close and/or more massive companions to perturb them, rather than simply being
more likely to have companions. Using the list of Dahari (1985) as their sample,
surroundings more distant than S=3D were studied using different catalogs. 12/14
Seyferts were found to have probable companions and 7/12 are conﬁrmed by their
radial velocity. They conclude that 19/26 (73%) or even 24/26 (92%) of Dahari’s
Seyfert sample have companions. This seems to indicate that tidal interaction may

be the predominant cause of Seyfert activity.

Fricke and Kollatschny (1988) analysed 113 galaxies: 15 groups around Seyfert
galaxies and 9 control groups around non-Seyfert galaxies of the same morphological
type. Membership in these groups was conﬁrmed spectroscopically. It was found that
on average near the Seyfert galaxies, companions are more active (strong emission-line
activity) than further out. They interpreted this in terms of interactions of closer

companions with their Seyfert galaxy.

Fuentes-Williams and Stocke (1988) have measured the density of galaxies within

1 Mpc of 53 Seyfert galaxies chosen from the list of Weedman (1977) and 30 control

galaxies chosen from the CfA redshift survey. The selection criteria used were:

1. 6 Z -10 deg
2. Ibnl Z 20 deg

3. 0.009 5 I. S 0.05

Criterion 1. was chosen so that the galaxies were accessible on the POSS plates
on which measurements were made; 2. allowed for the avoidance of areas of high ex-
tinction and confusion with foreground galactic objects and 3. excluded members of
the local supercluster and less luminous but signiﬁcant galaxies. The controls matched.
the morphology, absolute magnitude and redshift distribution of the Seyferts. They
found that the Seyferts didn’t possess a clear excess of luminous (M . S -18) com-
, panions relative to the control sample of normal spirals. No statistically signiﬁcant
difference was observed between the Seyfert and control samples in any of the quan-
tities measuring local galaxy density. When companion galaxies with diameters less
than 15 kpc. were included, the Seyferts showed a statistically signiﬁcant excess of
companions, however this signiﬁcance was less dramatic than found by Dahari or

MacKenty.

Using the same selection criteria as Dahari, MacKenty (1989) constructed a
sample of 51 Seyfert and 51 control galaxies from the Markarian and N GC catalogues,
and compared their environments. He found that 71% of the Seyferts had apparent

companion galaxies within 10 galaxy diameters as opposed to only 26% for the

6

controls. Since no explicit correction for background noise was made, the true fraction
of companions will be lower in both samples by similar amounts. MacKenty also
found a higher fraction of Seyfert 2’s had close companions than Seyfert 1’s, however
the statistical signiﬁcance is marginal. In addition, he found that the non-Seyfert

Markarians had the same frequency of companions as the Seyfert Markarians.

Heckman (1989) expressed several possiblities for reconciling the differences in
the results found by Fuentes-Williams and Stocke with those of Dahari and MacK-

enty. These are:

1. ”Bad Luck” at the 2-30’ level.

2. A true excess of companions to Seyferts exists, but only for intrinsically faint
companions.

3. The' stronger excesses of companions found by Dahari and MacKenty are (in
part) artifacts of the way they deﬁned a control sample.

4. An excess of close companions may be stronger for Seyfert 2’s than for Seyfert 1’s.

Kollatschny and Fricke (1989) systematically studied the occurrence and qual-
itative properties of Seyfert 1 and Seyfert 2 galaxies as a function of the galaxy
environment. They selected 242 galaxies from the Catalogue of Quasars and Active

Nuclei (Veron and Veron 1989) with the criteria:

1. m, 515

7

2. Listed as Seyfert 1, 2 or 3

3. 11...; S 2000121'ns'1

The environments of the Seyferts were inspected on the POSS and ESO/SRC
plates. A search for companions was made out to 0.5 Mpc. A companion was deﬁned
as having a size between 20-200% the Seyfert size. The galaxy density within an
environment of 500 kpc radius was considered. No size dependence of morphology
on density class was observed. They concluded that a suitable group environment
provides only a necessary condition for the development of Seyfert activity which in

addition requires favorable conditions in the host galaxy itself.

MacKenty et a1. (1989) have investigated the morphologies of the Markarian
sample of 1500 UV excess galaxies and their environments using the 20 minute V
plates obtained for the construction of the Hubble Space Telescope Guide Star Cat-
alog. They ﬁnd that the type of nuclear activity present in the Markarian sample is

not dependent on either the morphology or the local environment of the galaxy.

An independent analysis of the material in many of these papers (Simkin, 1990)
seems to suggest an excess of nearby companions for Seyfert 2 galaxies, but not for
Seyfert 1 galaxies. On the other hand, two of the cited studies show no signiﬁcant
difference in excess companion density between the two Seyfert classes (Byrd, et al.,
1987, and Kollatschny and Fricke, 1989). Both of these latter studies, however, deal
with small numbers of objects. In addition, all of the studies use different criteria to

deﬁne the term “companion.”

8

An indiscriminant compilation of all of the data for objects with cz S 4000
Isms“, taken from all of the studies noted above, seems to suggest that Seyfert
1 galaxies are found preferentially in wide pairs while Seyfert 2’s have companions
which are closer (Simkin, 1990). This is shown in Figure 1, where most of the Seyfert
2 galaxies appear to lie within 100 Kpc of their companions while most of the Seyfert
1’s are found at distances beyond 100 Kpc (with Ho=100). If this effect is real, it
would explain the apparent deﬁciency of paired Seyfert 1 galaxies found in those
studies which selected only companion candidates within a few galactian diameters

of the target Seyfert.

Using a galaxy diameter approach to ﬁnd companions may bias the number of‘
companions found if the mean diameters of the galaxies in the samples differ. That is,
if one sample has a mean galaxy diameter that is larger than another, the sample with
the larger mean galaxy diameter will have a greater number of companions associated
with it. An approach using galaxy diameters would be better suited for potential tidal
effects. Chapter 2 outlines the use of velocity and physical separation as constraints
on determining companionship to the Seyfert galaxies. This gives a physical basis for

deﬁning companionship. A comparison with non-Seyfert pairs is discussed.

In Chapter 3, the morphologies of the companions to Seyfert and control spirals
is discussed. Fuentes-Williams and Stocke (1988) found a nonnegligible population of
ellipticals as companions to Seyfert galaxies as opposed to mostly spiral companions
for a control sample of normal spirals. It is demonstrated that no evidence was

observed for Seyferts having an overabundance of ellipticals as companions compared

to a sample of normal spirals.

In Chapter 4, the question of galaxy pairing is readdressed with a focus on the
frequency of pairing given different selection criteria. Also discussed are the results of
multiple simulations using randomly selected control samples. Chapter 5 summarizes

the results found in this study.

10

Figure 1: Plot of multiple pairs to the Seyfert
galaxies of Simkin (1990). Note that the
companions of the Seyfert 2’s lie closer to
their host than for the Seyfert 1’s

11

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CHAPTER 2: ANALYSIS OF GALAXY PAIRIN G

I. Seyfert Companions from the CfA catalog

To investigate more rigorously the apparent differences in results, possibly due
to selection effects, found in the studies listed in Chapter 1, a sample comprised of
79 Seyfert galaxies was selected from the “Catalog of Seyfert Galaxies and Related
Objects” by N. Kaneko (see Table 1). This was chosen to include all Seyferts with
cz _<_ 4000 Isms" and excluding the Virgo cluster. The ratio of Seyfert 1’s to Seyfert
2’s in this sample (approximately 1:2, Table 2) is similar to'that found for nearby,
volume limited samples of Seyfert galaxies irrespective of their status as companions

(Simkin, Su, and Schwarz, 1980).

After experimenting with the various criteria used to characterize “companions”
in the studies noted above, the following selection rules were adopted to identify pos-

sible physical pairs for these Seyferts from amongst all other galaxies with known

redshifts in the CfA catalog:

12

13'

Table 1: Table of Seyferts from list of Kaneko

 

 

Object

N 424
N1052
N1068
N1097
M1066
N1241
N 1358
N1365
N1386
N1566
N1808
N2110
MK3
N2273
0722-095
MK1210
N2639
N2691
0942+098
N2992
0945-307
N3031
N3081
N3079
N3185
N3227
N3281
1034+061
N3312
N3393
N3516
N3718
N3783

Sy type

NHNHNNNHHNNNNNNHNHNNNNNNN

rs
N

 

HHHNHNN

 

RA

1 9 9.8

23837.0
240 7.1

24412.0
25649.0
3 848.0

33112.0
33142.0
335 0.0

41854.0
5 6 0.0

54948.0
6 948.4

64538.4
72234.4
8 127.0

840 6.0

85130.0
94248.8
94317.0
94528.4
95130.0
95712.0
95836.0
101454.0
102048.0
102936.0
1034 0.0
103441.4
1046 0.0
11 322.8
112948.0
113630.0

 

 

 

 

De£_ V, (km/s) Dim (’)
-382056 3496 2.2 1.1
- 828 6 1475 1.8 1.0
— 01331 1153 9.0 8.0
-3029 0 1275 5.0 4.5
363718 3600 1.0 0.5
- 9 7 0 2168 3.3 2.2
- 51530 4013 2.0 1.5
-3618 0 1652 7.0 3.2
-3610 0 924 2.0 0.8
-55 4 0 1487 13.0 9.0
-3734 0 977 10.0 7.0
- 718 0 2311 0.7 0.5
71 311 3900 0.5 0.4
605416 1842 3.6 2.4
- 934 5 2400 1.8 1.6

51522 3900. 0.2 0.2
5023 0 3226 2.0 1.5
3944 0 4048 1.6 1.0
95048 3600 1.1 0.9
-14 549 2305 1.1 0.5
-304257 2500 1.6 0.6
6918 0 350 26.0 14.0
-2235 0 2413 1.1 0.9
5555 0 1114 8.7 1.6.
2156 0 1218 2.0 1.2
20 7 0 1138 6.5 4.5
-3436 0 3460 2.1 0.6

6 9 0 3600 0.6 0.4
-271814 2863 2.5 1.0
-245347 3730 4.0 4.0
725020 2602 2.1 1.8
5321 0 987 11.0 5.0
-3728 0 2550 0.9 0.8

 

 

 

 

14

Table 1 (cont’d).

 

 

Object
N 3786
MK745
N3982
N 3998
N 4051
N 4117
N4151
N4253
N4258

N 4278 '

N4507
N4594
F312
N4968
N5005
N5033
N5077
1331-234
1333-340
MK270
N5273
N 5347
N5427
N 5506
MK670
N5643
N5728

 

Sy Type

H

NNNHNNHNHNHHNNNHNHNHHNI—IHNN

 

RA

1137 4.9
113720.6
115353.0
115520.9
12 036.4
12 512.0
12 8 1.1
121555.6
121630.0
121736.2
123254.0
123724.0
1238 9.0
13 424.0
13 836.0
1311 9.2
131652.8
133151.2
1333 1.8
133941.2
133955.1
1351 5.4
14 049.0
141042.0
1412 0.2
142728.0
1439360

171355
5524 0
554355
444835
4324 0
3941 2
30 526
4735 0
293331
-3938 0
-1121 0
-362920
-232440
3719 0
365130
-122342
-232526
-34 228
675536
355421
3344 0
- 54726
- 258 0
265849
-435712
-17 2 0

 

 

Dec IV, (km/s)

321111

2723
3000
1188
1028
710
958
962
3876
449
643
3523
1128
3300
2957
1022
892
2823
2600
2300
2700
1089
2335
2730
1753
1700
1180
2834

 

Dim (’)

2.2 1.1
1.0 1.0
2.4 2.2
3.0 2.5
6.0 5.0
2.5 0.9
7.0 6.0
0.9 0.9
22.0 9.0
3.5 3.5
1.0 0.9
6.0 2.5
0.7 0.7
2.5 1.4
6.3 3.0
11.5 5.5
1.0 0.9
1.1 0.6
1.3 0.7
0.6 0.6
2.8 2.3
1.7 1.4
1.2 1.1
2.0 0.5
1.0 1.0
2.1 2.0
2.0 0.9

 

 

15

Table 1 (cont’d).

 

 

Object
N 5899
N5929
N5953
N6217
N 6221
N6300
14870
N6814
N6890

F348
15063
N7213
15201
N7314
N7 450
N7 496
N7 582
N 7 590
N7 672

 

Sy Type

M

NNNNHNNHNNNHNNNNNN

 

RA

151312.0
1524169
153212.0
1635 0.0
1648260
171217.0
1932460
193954.0
2014460
203324.0
204812.0
22 612.0
2217560
2233 0.0
2258160
23 7 0.0
2315360
231612.0
2324568

 

Dec

4214 0
415041
1522 0
7818 0
-59 8 0
-624554
-6556 0
-1027 0
-445748
-501550
-5716 0
-4725 0
-4617 0

-2618 0‘

-131114
-4342 0
-423836
-4231 0
12 635

 

V, (km/s)

2554
2550
1983
1370
1478
1107
852
1552
2419
2400
3402
1769
915
1430
3100
1657
1576
1509
4010

 

Dim (’)
2.8 1.2
1.0 0.9
1.7 1.3
3.6 3.6
6.2 5.0
7.1 5.3
2.2 1.2
1.3 1.1
1.4 1.2
0.7 0.6
4.4 3.0
2.5 2.5
14.4 7.9
3.0 1.0
1.6 1.6
2.1 1.2
8.0 3.0
1.9 0.6
0.5 0.4

 

 

l6

c2,“ - cramp] S 600 Isms"1
and

physical separation 5 720 kpc.

An upper limit of the physical separation of 720 kpc was selected based on measure-
ments of Schneider and Salpeter (1989). They constructed a detailed model in which
they traced orbital parameters for a' full population of galaxy pairs from the time
of their formation, at which time they would have been expanding with the Hubble
flow. It was observed that an upper limit of the physical separation of 720 kpc is a
naturally occurring quantity. The characteristics of candidate pairs chosen with the

criteria listed above are shown in Table 2.

Table 2: Statistics of companions for Kaneko Seyferts

 

Galaxy Type Sy1T2‘ (90) Syl (%) Sy2 We)
Total Sample (oz 5 4000 Isms") 79 (100) 26 33 53 67
Number with Companions 61 77 22 85 39 74
Number with 2.1 Companions 46 58 20 77 26 49

 

II. Comparison with Non-Seyfert pairs

To assess the signiﬁcance of the results in Table 2, various tests were devised
to estimate the probability that a suitably chosen “random” sample of galaxies from

the CfA would exhibit a similar companion density. These are described below:

17

CASE A:

An ensemble of 25 sets of 79 galaxies was constructed from objects chosen at
random from the CfA (with the only restriction that their radial velocity be less than
4000 Isms"). The Virgo cluster dominates the velocity distribution at lower redshifts
and strongly biases towards ﬁnding companions. It has, therefore, been excluded in
this analysis. The CfA was then searched with the same technique as was used to
identify Seyfert companions, using each simulated set in place of the original Seyfert
list. The mean number of companions found for these sets is shown in Table 3 and the
distribution in this number is shown in Figures 2, 3 and 4 respectively. The velocity
distribution of this sample is (as expected) similar to that of the CfA (Figures 2A
and B).

CASE B:

To assess the possibility that galaxies with velocities chosen “at random” from
the CfA catalog exhibit more than average clustering, an ensemble of 25 sets of
79 galaxies was constructed from objects chosen at random ﬁ'om the CfA with the
further restriction that the radial velocity of each galaxy chosen match that for its
corresponding Seyfert to within 50 Isms". The velocity distribution for this case
and the Kaneko Seyferts with Virgo excluded is shown in Figure 2C. Using the same
search technique as above, yields the mean number of companions for the galaxies in
this ensemble shown in Table 3 and the corresponding distribution plotted in Figure
3. The companion density is slightly higher for this case than for the unconstrained

random sample.

18

CASE C:
To test the possibility that the areas surounding nearby Seyfert galaxies have
been surveyed more extensively and thus have a higher percentage of measured red-

shifts than areas not graced by Seyferts, the following tests were set up:

a. C1: Catalog limit = 4000 Isms"

The CfA catalog was searched for all galaxies with measured redshifts less than
4000 Isms" in a conical solid angle of 6 deg, centered on each Kaneko Seyfert. Of
the 163 objects which ﬁt these restrictions, 24 ﬁt the criteria for ‘pairing’ with the
Kaneko Seyferts. The remaining 139 (distributed over 40 ﬁelds) were then used to
construct an ensemble of 25 sets of 40 “random” galaxies which were analyzed for
pairing as before. This simulation yielded a signiﬁcantly lower. percentage of “pairs”

than did either Case A or Case B (Table 3, and Figure 4).

b. C2: Catalog limit = 6000 Isms"

The CfA catalog was then searched for all of the galaxies with measured redshifts
less than 6000 Isms" in a conical solid angle of 6 deg, centered on each Kaneko
Seyfert. Of the 229 objects which ﬁt these restrictions, 24 ﬁt the criteria for ‘pairing’
with the Kaneko Seyferts. The remaining 205 (distributed over 52 ﬁelds) were then
used to construct an ensemble of 25 sets of 52 “random” galaxies which were analyzed
for pairing as before. This simulation again yielded a signiﬁcantly lower percentage

of “pairs” than did either Case A or Case B (Table 4). This, along with C1 above,

19

suggests that galaxies in the Seyfert ﬁelds are not over-represented in the catalog.

Table 3: Mean Number of Companions (25 runs)

 

 

 

 

Galaxy Type Sy1+2
Kaneko Seyferts 61
Case A (Random) 49.2 .
Case B (restricted V,) 52.8 66.8 18.3 70.4 34.5 65.1

Case Cl restricted sky positions 53.3 67.5 22.9 72.5 30.4 64.2
Case 02 restricted sky positions 35.3 44.7 15.7 57.3 19.6 (38.)

Case D

An ensemble of 25 sets of 79 galaxies was chosen at random from the CfA with
the restriction that the morphology and inclination of each galaxy match that for its
respective Seyfert. The velocity was constrained to v, S 4000Isms" for the controls.
The CIA was searched for companions as before. The results for the average velocity

and pair average is shown in Table 4. The average velocity is higher than that for

the Seyferts.

Case E

Again an ensemble of 25 sets of 79 galaxies was selected at random from the
CfA, in this case matching morphology and recessional velocity to within 600Isms".
The average velocity and average number of pairs is shown in Table 4. The velocity
and number distributions are plotted in Figures 2, 3 and 4. It is apparent from Figure
2 that the velocity distribution for this case is not as good a match as that for Case

B. This is due to the fact that the velocities of the controls in Case B were matched

20

Figure 2: Velocity distributions of the CfA and
Cases A, B and E. Also plotted is the velocity
distribution of the Seyferts.

21

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Figure 3: Plot of the mean number distribution of
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D and E. Also plotted is the mean number distribution
of the Seyferts.

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E and F. Also plotted is the mean number distribution
of the Seyferts.

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to within 50kms" of their respective Seyferts, whereas in this case a velocity range
of 600Isms" was allowed. This produced a smearing of the three peaks found in
the Seyfert velocity distribution. The velocity and pair average match that for the
Seyferts very well. This was concluded to be the correct control sample in modelling

Seyfert companionship.

Case F

In order to examine the effect of morphology on ﬁnding companions, an ensemble
of 25 sets of 79 galaxies was chosen at random from the CfA which match their
respective Seyfert in recessional velocity but have a large difference in morphology.

In this case, elliptical galaxies were selected. See Table 4 and Figure 4 for results.

Case G
The same analysis has been done here as in the previous case, but now the

morphologies were selected to be late type spirals. The results are shown in Table 4.

Table 4: Average velocity and pair average for 25 runs

 

Case Avera e 1:, pair average

 

A 25 5 49.7
B 2131 52.8
CI 2690 53.3
C2 3508 35.3
D 2321 60.04
E 2176 60.16
F 2180 66.4
G 2096 55.56

Kaneko 2131 61.

 

27

111. Analysis of results in section II.

Number distributions for Cases A, B, D and E and Cases A, C, E and F are
plotted in Figures 3 and 4 respectively. Again, it is concluded that Case E was the
best match for the Seyferts and is the correct control sample to use when modelling
the Seyfert pairing rates. The lower average pair values found in Cases A, B and C

is postulated to be due to a combination of:

1. The higher mean velocity in Case C2 implies that there are fewer high velocity

galaxies in the CfA catalog.

2. Random picks with random morphologies include late type spirals which yield

fewer pairs.

The Seyfert type distribution for Case E is plotted in Figures 5 and 6 respectively.
Figure 5 shows all companions while Figure 6 plots only multiple companions. Also
shown is the distribution for the Kaneko Seyferts. It is concluded that the distribution
of single pairs is the same for the Seyferts and controls, BUT there may be a deﬁciency

of multiple pairs for the Seyfert 2’s and an excess for the Seyfert 1’s.

The “projected angular momentum”, J, for the pairs in Case E was then ex-
amined. Plotted in Figure 7 is the distribution of “projected angular momentum”
for pairs with the minimum J. There appears to be an excess of low J values for the
Seyfert pairs as opposed to the control pairs. The total number of companions for the
controls and Seyferts is plotted in Figure 8. The average number of Seyfert pairs with

J 5 2000 km/s*kpc is 24 as compared to 13.8 for pairs in Case E. The probability

28

Figure 5: Number distribution for all companions in Case E.

 

 

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Seyferts 11:3 CueE

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Figure 8: Number distribution of com anions of Seyferts
and Case E with total angular momentum
< 2000kms"1 :- kpc. There is an excess of low J values
far the Seyferts as opposed to the control sample.

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36

that this occurs by chance is less than 4%. This implies that the companions to the
Seyferts are different in some respect to those for the controls. One possibility is that
the companions of the Seyferts are more bound than the control companions.

IV. Angular Separation

Converting to projected physical separation using a distance based on H. =
100, the Seyfert galaxy pairs were examined for any evidence of a difference in radial
separation as a function of Seyfert class (such as appears in in Figure 1). No such
distinction was found. Plotting projected separation against radial velocity difference
for each Seyfert galaxy and its closest companion gives the results shown in Figure 9.
Again, this plot shows no evidence for any difference in projected separation between
Seyfert 1 and Seyfert 2 galaxies. Figure 10 plots the pairs with the smallest J values.
Note the resemblance to Figure 9. Since the data in Figure 1 represent a compilation
of multiple pairs subject to incommensurate selection effects, while those in Figure
9 represent only closest pairs from a much larger sample with uniform selection, it
was concluded that there is no evidence for a kinematic distinction between Seyfert

1 and Seyfert 2 galaxies.

37

Figure 9: Plot of pro ected se aration against radial
velocity diiference or each Seyfert galaxy and its
closest companion. No evidence for a kinematic distinction
between Seyfert 1 and Seyfert 2 galaxies is observed.

38

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CHAPTER 3: MORPHOLOGY OF THE COMPANIONS

FOR. SEYFERT AND CONTROL GALAXIES

Fuentes-Williams and Stocke (1988) have measured and compared the galax-
ian environment around their sample of Seyferts and control spirals. Measurements
were made using the two-dimensional Grant measuring engine at the Kitt Peak Na-
tional Observatory on the blue copies of the Palomar Observatory Sky Survey. They .
considered a circle of 1 Mpc projected radius centered on each Seyfert or control and
measured only those galaxies whose sizes were greater than about 1/4 the size of
the central galaxy. Morphologies of these galaxies were classiﬁed as either spiral or
elliptical and a rough determination of Hubble types for galaxies with small angular
diameters ($10 arcsec) was made simply by looking at apparent ellipticity. It was
observed that there was a nonnegligible population of ellipticals as companions to the

Seyferts as opposed to mostly spiral companions for normal spiral galaxies.

To investigate this effect in greater detail, a sample of 51 normal spiral galaxies
was constructed using the CfA redshift survey with as 5 4000kms'1. The control

sample was matched with the Seyfert sample so that the only differentiating

41

42

characteristic was nuclear activity. To be precise, a good match was sought between
redshift, morphology and inclination to the line of sight. A search for companions was
performed in the same manner as for the Seyferts. The Virgo cluster is excluded in
this analysis as it will bias the results in preferentially ﬁnding elliptical companions.
The morphologies of all companions for the Seyferts and controls were found using
the NASA Extragalactic Database through the IRAS Processing and Analysis Center
(IPAC). Morphologies were able to be determined for 277 of the Seyfert companions

and 192 of the control companions. The results are shown in Table 5.

Table 51 Comparison of morphologies of Seyfert and control companions

 

Morphology Seyfert Number We) Control Number 0

 

Spiral - 156— 56 ~—‘112 58

so 71 26 65 - 34
Elliptical 29 11 18 (9)
Spiral + Ellip. 185 67 130 68
Spiral + $0 227 82 177 E92

 

No evidence for a signiﬁcant population of ellipticals as Seyfert companions as op-
posed to control companions is observed. One possibility is that many of the ellipticals
observed by FW-Stocke were really 80’s mistaken for ellipticals due to their rough
determination of morphologies. The Seyferts do exhibit 2.5 times more SO’s than
ellipticals as companions. 50’s (or lenticulars) are smooth and featureless, like ellip-

tical galaxies, but obey the exponential surface-brightness law characteristic of spiral

43

galaxies. This is given by:

I(R) = Ioezp(-R/R4),

where R4 is the disk scale length. The surface-brightness proﬁles for most ellipticals,

on the other hand, are ﬁt by the Rm or deVaucoulers law,

I (R) = I (0)ezp(-IcR°°") E I.ezp{-7.67[(R/R.)°"‘ - 1]},

where the effective radius R. is the radius of the isophote containing half of the
total luminosity and I. is the surface brightness at R. (Binney and Tremaine, 1987).
This approach to determining morphology may eliminate the effect observed by FW-

Stocke.

The lack of a signiﬁcant population of elliptical companions around Seyferts seems to
suggest that the similarity in Seyfert and control environment, which is demonstrated
in the following chapter, is real. The percentages of galaxies in a given location that
are elliptical seem to decrease monotonically from the central regions of rich clusters
to the ”ﬁeld” (Dressler 1984). Had an overabundance of elliptical companions been
observed around Seyferts, the environment of the Seyferts would have been expected
to be of a higher density than that for normal spiral galaxies. A higher density
environment around Seyferts was observed by FW-Stocke in their analysis because

they found a signiﬁcant population of ellipticals as companions to the Seyferts.

CHAPTER 4: FURTHER ANALYSIS OF GALAXY PAIRING

In order to examine the frequency of pairing of Seyfert galaxies as opposed to

non-Seyferts, the following tests were set up:

CASE 1: MATCH T, s, i

As an initial selection criterion, a program was constructed to search the CfA
Redshift Catalog and retrieve those galaxies which matched their respective Seyfert
in morphology (denoted in the CfA by deVaucoulers T notation), recessional velocity
and inclination to the line of sight. Histograms both including and excluding the
Virgo cluster were made. These are shown as Figures 11 and 12 respectively. This
was done for reference in the later cases. Each Seyfert had a list of potential controls
after this was done. From this list, the best match for the Seyfert was obtained and
the CfA was searched for companions of these galaxies. The “best’? match refers to
the galaxy which most closely matches the selection criteria (in this case, T, z and i).
This deﬁnition applies for the following cases as well. The results are shown in Table
7. The number of control companions is observed to occur with relatively the same

frequency as the Seyfert companions.

CASE 2: MATCH z, i

The CfA was again searched for possible controls matching recessional velocity

44

45

Figure 11: Velocity distribution of the Seyferts. The
Virgo cluster is included.

46

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47

Figure 12: Velocity distribution of the Seyferts. The
Virgo cluster has been excluded.

48

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49

and inclination. The best match for each Seyfert was chosen and the CfA searched
for companions. The results are listed in Table 7. Again the frequency of companions

occurring is the same as in Case 1 above.

CASE 3: MATCH T, i

Again the CfA was searched for controls, this time matching morphology and
inclination to the line of sight. The velocity was constrained to within 6000lm'ns‘l
and the average velocity of the sample was over IOOOIems‘l greater than that of the
Seyferts. The best match for each Seyfert was selected and the controls searched for
companions as above (See Table 7). The number of controls with no companions as

opposed to the Seyferts has increased.

CASE 4: MATCH i

.The CfA was searched for controls as above, in this case matching only inclina-
tion to the line of sight. The velocity restrictions were the same as in Case 3 above.
Companions were found for the best match and the results outlined in Table 7. There

are more galaxies-that were found to have no companions.

It should be noted that the Virgo cluster has been excluded in the above anal-
ysis, as it introduces a bias toward ﬁnding multiple companions. Histograms of the
apparent and absolute magnitudes of the companions in each of the above cases were
made and are shown in Figures 13 and 14 respectively. Each histogram has been
normalized to 100 galaxies. As can be seen, the average apparent magnitude in the
velocity constrained cases is brighter than for the unconstrained cases. The average

absolute magnitude is brighter for the case matching T and i. This was due to the

50

Figure 13: Histograms of the apparent magnitude of the

companions for the given cases. The apparent magnitudes
of the co

mdpanions at greater velocities are fainter as
is expecte .

51

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54

average velocity of the companions being greater in this case. The greater frequency
of zero companions for the unconstrained velocity sample is postulated to be due to a
selection effect in that dimmer companions are not observed around the more distant

galaxies.

To obtain more signiﬁcant results, the following test has been constructed. A
program was written to select 20 ensembles of control galaxies for each Seyfert. The
controls were selected at random from the lists constructed in each of the above cases.
These ensembles were then searched for companions as before. A match for T, a and
i was expected to yield the same results as in Case 1 above since there were very few
controls possible for each Seyfert. For this reason, the above test was not done for

this case.

The above test was run for Cases 2 and 3 above. The results are listed in Table

6 below.

Table 6: Companion Number Breakdown (20 runs)

Match z,i

Number with 1 Companion 11.5 (14)
Number with Z 1 Companion 50 (60)
Number with 0 Companions 21.5 (26)

Match T,i

Number with 1 Companion 14.2 18
Number with 2 1 Companion 38.2 48
Number with 0 Companions 26.7 34

Comparing the above results with those in Table 7, it is observed that there is

55

good agreement between the results. The discrepancy between the numbers for the
case of multiple companions is due to the presence of the Virgo cluster in Table 6. If
Virgo is removed as was the case in Table 7, the data would agree very closely. This
suggests that no bias exists in selecting the best control match for each Seyfert and

examining them for companions. Similar results are hypothesized for Case 4.

The similarity in the pairing rates between the Seyferts and controls matched
to the Seyferts in every respect except nuclear activity seems to suggest that tidal
interaction with companion galaxies is not suﬁcient on its own to sustain the fuelling
of AGNs. In fact, a large-scale nonaxisymmetric disturbance of a galaxy, such as
a stellar bar, appears capable of inducing global shocks, which drives the inﬂow of '
gas towards the center. Shlosman et al. (1989) have proposed that the gas which
accumulates in the central kpc or. so as a result of the inﬂow in the stellar bar forms
a disk which under certain conditions goes dynamically unstable and forms a gaseous
bar. A condition for this instability was derived using a simple model, and argue that
the resulting inﬂow can extend all the way in to the center (the inner ~ 10 pc.). It
may be that companions could induce a stellar bar, at which time the above process

occurs, but it is not necessary.

56

Table 7: Companion Number Breakdown

Match T,z,i

 

 

Galaxy Type Seyferts ‘70) Controls (75)
Number with 1 Companion 12 19 11 18
Number with Z 1 Companions 34 55 39 63
Number with 0 Companions 16 26 12 19
Match z,i
Galaxy Type Seyferts %) Controls (70)
Number with 1 Companion 14 20 11 16
Number with Z 1 Companions ~ 40 57 39 56
Number with 0 Companions 16 23 20 28
Match T,i
Galaxy Type Seyferts (%) Controls (70)
Number with 1 Companion 14 20 1.1 16
Number with _>_ 1 Companions 40 56 32 45
Number with 0' Companions 17 24 28. 39
Match i
Galaxy Type Seyferts %) Controls (95)
Number with 1 Companion 13 19 9 (13)
Number with Z 1 Companions 40 59 28 41
Number with 0 Companions 15 22 31 46

 

CHAPTER 5: CONCLUSIONS

A sample of 79 Seyfert galaxies with as S 40001¢ms"1 and excluding the Virgo
cluster was constructed from the ”Catalog of Seyfert Galaxies and Related Objects”

by N. Kaneko. A search for companions to these Seyferts was then performed using

the CfA Redshift Catalog.

The statistical tests which have been run suggest that approximately 60% of
the nearby Seyfert galaxies have bright physical companions. This is similar to the
number of bright IRAS galaxies with companions (Lawrence, 1987). This study
shows none of the kinematic orbital differences found in the published studies of
Seyfert companions. It does, however, ﬁnd a substantial excess of companions for
both Seyfert 1 and Seyfert 2 galaxies and supports the conclusion of Kollatschny and

Fricke that these objects frequently reside in physical groups.

Number distributions were plotted for the various cases studied in Chapter 2,
and it was concluded that a match for T and z is the correct control sample to use
when modelling Seyfert pairing rates. There is also evidence that the distribution of
single pairs is the same for the Seyferts and controls, BUT there may be a deﬁciency

of multiple pairs for the Seyfert 2’s and an excess for the Seyfert 1’s.

The “projected angular momentum”, J, for the Seyfert and control companions

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was plotted and an excess of low J values was observed for the Seyfert pairs as
opposed to the control pairs. This would imply that the companions to the Seyferts
are different in some respect to those for the controls. One possiblity is that there

are more bound companions for the Seyferts than the controls.

Seyfert galaxies appear to have pairing rates similar to that for a sample of
nearby normal spiral galaxies. This seems to suggest that companion galaxies alone
are not sufﬁcient to serve as a mechanism for prolonged refuelling of an AGN. Indeed,
large-scale nonaxisymmetric disturbances of galaxies, such as a stellar bar, appear
capable of inducing global shocks which drive the inﬂow of gas towards the central
regions. The passage of close companions may induce such stellar bars, but as noted

by Shlosman et al. (1989), this is not necessary.

Finally, the morphologies of the companions for the Seyfert and control samples
were compared in an attempt to reproduce the results of Fuentes-Williams and Stocke.
They observed a signiﬁcant population of elliptical companions around Seyfert galax-
ies as compared to their control sample. An examination of the companions of Seyfert
and normal spirals yielded no evidence for Seyferts having a nonnegligible population
of ellipticals compared to the normal spiral galaxies, which implies that the similarity

of pairing rates for the control sample matching T, z and i and the Seyferts is real.

LIST OF REFERENCES

LIST OF REFERENCES

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Dahari, 0., 1985, A.J., so, 1772.

Dahari, O., 1985, Ap. J. Suppl., 57, 643.

Dressler, A., 1984, Annu. Rev. Astron. Astrophys., 22, 185.
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Heckman, T. M., 1989, IAU Colloquium No. 124.

Huchra, J. P., Wyatt, W. F. and Davis, M., 1982, Astron. J ., 87 , 1628.
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Noguchi, M., 1988b, IAU Collquium No. 96.

Osterbrock, D. E., ”Astrophysics of Gaseous Nebulae and Active Galactic Nuclei”,
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Petrosian, A. R., 1982, Astroﬁzika, 18, 548.

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Shlosman, 1., Frank, J ., and Begelman, M. C., prepﬂ'iu. Simkin, S. M., Su, H-J., and
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