Some evolutionary characteristics of radio galaxies with double structures

Chinese Astronomy

4 (1980) 251-257

Pergamon Press. Printed in Great Britain 0146-6364/80/0901-0251-$07.50/0

Acta Astr. Sinica 20 (1979) 254-280

SOME

EVOLUTIONARY

NITH

DOUBLE

CHARACTERISTICS

OF R ~ D I O

GALAXIES

STRUCTURES

Qian S h a n - j i e

Liang B a o - l i u

Beijing Observatory, Academia Sinica Fang

Li-zhi

University of Science and Technology of China

ABSTRACT

In this paper a statistical investigation has been made on

some characteristics of the evolution of radio galaxies with double structure.

77 radio galaxies with known redshifts are selected.

results are as follows:

The main

I. In the angular size-redshift diagram, there

appears to be a lower bound (Smi n - z), which corresponds to a minimum linear size D . = 40 kpc. mln

It looks as though all double structures are

initially formed with this size.

2.

The radio luminosity

(L), volume (V)

and total energy (E) of individual components vary with the linear separation D.

There may be a critical separation D c : 600 kpc such that

when D < Dc, L, V and E increase steadily with the increasing D; while for

D > Dc, L, V and E remain essentially constant.

Somewhat unexpectedly,

there seems to be no correlation between E/V (or L/V) and D.

3.

Among

radio galaxies with the largest linear size, the absolute visual magnitudes appear to get fainter with increasing D at the rate of about +4.8m/Mpc.

i.

INTRODUCTION

Quasars and radio galaxies play an important role in the study of cosmic radio sources.

As

far as radio morphological structures are concerned, a majority of quasars and radio galaxies (~ 60%) have double structures, which is very remarkable.

There have been many

papers dealing with the formation, energy supply and evolution of double sources.

Wardle

and Miley [I] have investigated the relationship between radio size and redshift (z) of quasars and found that there appears to be a rather well-defined upper envelope (Sma x - z) in the (8, z)-distribution and that it passes over continuously to the envelope for radio galaxies

[2].

Lately, Hooley et al. [3] have obtained a more detailed (8, z) diagram for

3CR quasars and radio galaxies with known redshifts.

The data they used are taken from the

results of observation made with the 5 GHz synthesis-aperture telescope of ~ l l a r d Radio Astronomy Observatory.

In [4]

Zhou et at. concentrated on the evolution of quasars with

the largest angular sizes and, with the help of the redshift-distance [5]: d = C/H(z- 0.19z2),

formula derived in

they suggested that the radio linear size D of quasars may be an

252

Double Radio G a l a x i e s

important evolutionary parameter and found that, for the quasars, both the optical and the radio absolute magnitudes increase numerically with increasing D at a rate ~+lOm/Mpc.

In

this paper, we selected o~er 70 radio galaxies with double structures and known redshifts in an investigation of their evolution.

2.

DATA SELECTION

We c o l l e c t e d journals

high resolution

maps o f r a d i o g a l a x i e s p u b l i s h e d i n v a r i o u s a s t r o n o m i c a l

( a t two f r e q u e n c i e s

2"-10")and selected double structures the optical

the radio galaxies with typical

and d o u b l e - s t r u c t u r e s

Those s o u r c e s which a r e l i s t e d

maps were o m i t t e d a l t o g e t h e r .

o f g a l a x i e s w i t h common s t r u c t u r a l values.

Altogether,

redshifts,

o f 1 0 " - 5 0 " and

(including double-

For t h o s e s o u r c e s i n which

were made o n l y a f t e r

sample i s a w e l l - d e f i n e d

A l s o we r e q u i r e

the redshifts

77 r a d i o g a l a x i e s w i t h d o u b l e s t r u c t u r e s

spectrum index, for both components.

careful

a s d o u b l e i n some p a p e r s b u t h a v e no h i g h -

and 63 o f them h a v e s u c h p a r a m e t e r s a s f l u x d e n s i t y ,

we s h a l l n o t d e t a i l

3.

components).

T h u s , our s e l e c t e d

properties.

we h a v e s e l e c t e d

respectively

double structures

with central

c o i n c i d e s w i t h one o f t h e components s e l e c t i o n s

consideration. resolution

1 . 4 GHz and 5 GHz w i t h r e s o l u t i o n

T h e s e d a t a were c o l l e c t e d

diameter,

group

t o be m e a s u r e d and known

separation

and

from o v e r 30 s o u r c e s which

f o r want o f s p a c e .

(0 - 8) RELATION AND EVOLUTION OF RADIO GALAXIES WITH DOUBLE STRUCTURES

The (e - z) d i a g r a m f o r t h e r a d i o g a l a x i e s w i t h d o u b l e - s t r u c t u r e s (logarithm scale).

I t c a n be s e e n t h a t t h e r e

lower l i m i t

linear

for the

Dmin z 40 kpc ( i n t h i s

separation

a r e shown i n F i g .

1

i s a lower bound emin ~ 1/z, i . e . . t h e r e

between

t h e two c o m p o n e n t s .

is a

The v a l u e i s

p a p e r , we t a k e H u b b l e ' s c o n s t a n t H= 50 k m / s e c . M p c , and u s e t h e

f o r m u l a d= (C/H)Z f o r t h e d l s t a n c e .

The e x i s t e n c e o f t h i s

a selection

f o r r a d i o g a l a x i e s w i t h s m a l l e r z, t h e a v a i l a b l e

synthesis

effect,

because at least

aperture

telescopes

lower l i m i t

d o e s n o t seem t o be

could r e s o l v e even s m a l l e r double s t r u c t u r e s

if they existed.

z, D . = c o n s t . I t t h e r e f o r e s u g g e s t s t h a t d o u b l e s t r u c t u r e s a r e formed a t a mn s e p a r a t i o n ~D . a t t h e b e g i n n i n g b e f o r e t h e y s t a r t e v o l v i n g . mzn The u p p e r bound (emax - z) shown i n F i g . 1 a p p l i e s o n l y t o r a d i o g a l a x i e s w i t h d o u b l e For d i f f e r e n t

structures situated shall

(cf.[1],

[2] and [ 5 ] ) .

w e l l above t h i s b o u n d , i t

Such g i a n t r a d i o g a l a x i e s w i t h a s 3c256 and D240 a r e is likely

not i n c l u d e then i n our p r e s e n t

satisfactory

e x p l a n a t i o n on t h e o v e r a l l

example, the e - d i s t r i b u t i o n evolution etc.).

t h a t t h e y have v e r y s p e c i a l p r o p e r t i e s ,

consideration. distribution

At p r e s e n t ,

and we

i s no

o f p o i n t s i n t h e ( 0 - z) d i a g r a m .

f o r a f i x e d z v a l u e may be due t o a v a r i e t y

of effects

For

(projection

In t h e f o l l o w i n g d i s c u s s i o n we s h a l l n o t d e a l w i t h t h e s e e f f e c t s .

For t h e s e l e c t e d

77 r a d i o g a l a x i e s w i t h d o u b l e - s t r u c t u r e s ,

absolute visual magnitudes M applied the K-corrections galactic

there still

absorption correction

Av.

we h a v e c a l c u l a t e d

their

a s g i v e n by S c h i l d and Oke [4] and t h e

Double Radio G a l a x i e s

3000

The M-D d i a g r a m t h u s o b t a i n e d i s shown i n F i g . 2.

253

DA240

3C2..~ •

I t can be s e e n t h a t t h e r e a p p e a r s t o

be a c o r r e l a t i o n

|0Q0

b e t w e e n M and D f o r t h e

r a d i o g a l a x i e s which have D> D : 0.6Mpc ( i . e . C

t h o s e which have t h e l a r g e s t a n g u l a r s i z e s i n t h e (0 - z) diagram o f F i g . 1.

300

The e q u a t i o n

Z'.

of regression is

o~q

27.5. The correlation coefficient is ~0.67. M =

4.76D

-

I0(

-

standard deviation is ~0.77 m.

The

c.

Thus, it seems

3O

oO

that, for double-structure radio galaxies with

60g k pe

the largest angular sizes (or the largest linear sizes),

lO

the separation is a significant

parameter of evolution, and the optical 3

absolute visual magnitude M increases

,O=40kpc

algebraically with increasing separation D at a rate of ~+4.8m/Mpc.

0.01

0.03

()1.3

0'.|

'l

z

For a better comparison with the results

ei~ 1 The 0 - Z r e l a t i o n radio galaxies

from quasars, a new analysis with the same

f o r double

method was made t a k i n g t h e q u a s a r d a t a g i v e n i n [4] and [5] as a b a s i s and adding a n o t h e r f i v e w i t h d o u b l e - s t r u c t u r e s 3c154, 4c34.13 and 3c212). t h e method g i v e n i n

The diagram o b t a i n e d i s shown i n F i g . 3.

[4] t o c a l c u l a t e

the distances,

made c o r r e c t i o n s o f Au and Kv, and

d e r i v e d t h e a b s o l u t e v i s u a l m a g n i t u d e s and s e p a r a t i o n s . shown i n F i g . 4. i n [4].

The M-D diagram f o r t h e q u a s a r s i s

I t can be s e e n t h a t , when D > De : 600 kpc, t h e r e i s s t i l l

i n c r e a s i n g w i t h i n c r e a s i n g D.

( 3 c 6 8 . 1 , 4c28.40.

In a d d i t i o n , we used

a hint of M

The r a t e o f +gm/Mpc i s somewhat s m a l l e r t h a n t h e v a l u e g i v e n

But t h e a d d i t i o n o f a few q u a s a r s w i t h l a r g e l i n e a r s i z e s and t h e n e g l e c t o f

p r o j e c t i o n e f f e c t have g r e a t l y weakened t h e c o r r e l a t i o n . For r a d i o g a l a x i e s and q u a s a r s w i t h 0max, t h e above e v o l u t i o n a r y c h a r a c t e r i s t i c s i n c r e a s i n g s e p a r a t i o n s h o u l d be examined f u r t h e r by e x t e n d i n g t h e i n v e s t i g a t i o n

with

to f a i n t e r

objects.

4.

RELATIONS BETWEEN RADIO LUMINOSITY, VOLUME, TOTAL ENERGY OF COMPONENTS AND D

With t h e c o l l e c t e d d a t a on i n d i v i d u a l components o f r a d i o g a l a x i e s as a b a s i s , a statistical (V), t o t a l

investigation

on t h e r e l a t i o n s

b e t w e e n D and t h e r a d i o l u m i n o s i t y (L), volume

e n e r g y (E) and L/V, E/V o f t h e r a d i o components.

synchrotron radiation, L ~ 4~d 2 =

I

the formulas for c a l c u l a t i n g

Under t h e a s s u m p t i o n o f

t h e s e p a r a m e t e r s a r e as f o l l o w s [6]:

lO uO

l0T

we have made

( l + Z)l+%-~dv

0"431Z2(1 + Z)t+"s";'~ [10 s(t-~) - - 1] • 1042 e r g / s e c l--a

Double Radio G a l a x i e s

254

0(arcsec) 200

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Fig. 3 The O-Z r e l a t i o n f o r q u a s a r s w i t h d o u b l e s o u r c e s : x 8ma x s o u r c e s c h o s e n from [4]: • v a r i a b l e s o u r c e s : ~ newly added s o u r c e s : l a r g e a n g u l a r - s i z e s o u r c e s d e l e t e d i n [4].

--2(}

M Fig. 2 The r e l a t i o n between t h e a b s o l u t e m a g n i t u d e H and l i n e a r s e p a r a t i o n D f o r double radio galaxies

4 F = - - ~ w l t ~ d 3 = 0.303wtjm~Z 3 • 1070 cm 3 3 9

E ~

4

Ct3R ~ L ~ =

3

0.541C~sV ~ L {

erg

Here, v 0 i s t h e f r e q u e n c y i n 107 Hz, 80, t h e f l u x d e n s i t y i n dy a t t h i s spectral

index,

f r e q u e n c y , a, t h e

~,, ( ~ ! ) , t h e a n g u l a r d i a m e t e r o f components i n a r c s e c ,

energy (including the energy of relativistic

electrons

E t h e minimum t o t a l

and t h e m a g n e t i c e n e r g y i n

equipartition). The statistical relations obtained are shown in Fig. 5 and 6. that, radio luminosity, D when D < 600 kpc.

It is clear from Fig. 5

volume and total energy of radio components increase with increasing

When D > 600 kpc, Lj V and E remain essentially constant.

It should be

emphasized that the critical separation here is also about 600 kpc the same as that arisen in our M-D analysis.

I t can be s e e n

from F i g . 6 t h a t a t l e a s t o v e r a c o n s i d e r a b l e r a n g e (up t o ~1 } ~ c ) , e n e r g y

d e n s i t y and r a d i o l u m i n o s i t y p e r u n i t volume o f r a d i o components do n o t seem t o v a r y w i t h i n c r e a s i n g D and t h i s These two r e s u l t s

is contrary to the usual expectation. provide a statistical

components move away from t h e i r volume and t o t a l unchanged.

energy both increase,

But a f t e r

picture

while their

reaching the separation

approximately constant,

o f e v o l u t i o n o f r a d i o components: when t h e

parent galaxy, within a certain D,

distance

energy density remains essentially t h e volume and t o t a l

energy both remain

and t h e e n e r g y - l o s s due t o s y n c h r o t r o n - r a d i a t i o n

compensated by t h e e n e r g y s u p p l i e d .

Certainly,

(D
we can e x p e c t

that,

is precisely

a t even l a r g e r

Double Radio Galaxies

255

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72

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71

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F i g . 5 . 1 R e l a t i o n b e t w e e n volume and l i n e a r f o r d o u b l e r a d i o ~ a l a x i e s a t 1.~ CPz

separation

45

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F i g . 5 . 2 R e l a t i o n b e t w e e n r a d i o l u m i n o s i t y ~nd l ~ n e a r s e p a r a t i o n f o r d o u b l e r a d i o g a l a x i e s a t 1 . 4 GHz.

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F i g . 5 . 3 R e l a t i o n b e t w e e n s o u r c e e n e r g y and l i n e a r s e p a r a t i o n f o r d o u b l e r a d i o g a l a x i e s a t 1 . 4 GHz

256

Double Radio Galaxies

-23 -24

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--28

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Fig. 6.1 Relation between luminosity per unit volume and linear separation for double radio galaxies at 1.4 @Iz

9I ~-lo L t x

11

f

. •

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i

1

~ " ~::

:. , ,

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D(Mpc) Relation between energy density and linear for double radio galaxies a t 1 . 4 GHz

Fig. 6,2 separation

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D(Mpc) - l t , r per u n i t volume ~i~. 6 . 3 Relation between 11~Ino~i_ linear separation for double radio galaxies at 5 CHz •

and

Double Radio Galaxies

257

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--26 --~$ --24 --23 --22 " 2 1 M Fig. 4 Relation between the absolute optical "magnitude M and linear separation D for quasars with double sources (symbols as in Fig. 3) separations

(for example D ~ 1.5 Mpc), E/V and E would decrease with increasing D, but at

present the lack of data makes it impossible for us to deduce such a picture. Finally, we would like to thank Jiang Shu-hui and Liu Bu-lin for their help with calculations.

REFERENCES [ 1] [2]

[ 3"] [4 ] [5 ] [6 ]

Wardle, J. F. C & Miley, G. K . : Astr(m. ~ Astrophy~. 30(1974), 305. Mfley, G. K. (1975) : i~l " T h e phymcs of non-~ermal radio ~ u r c e s " (ed. G. Settl), p. 9. Hooley, A. et al.: Moa. Not. Roy.. Astron. 8oe., 182(1978), No. 1. Zhou You-yuan et al., Acta Astronomica Sinica ]8 (1977) 115-128. English translation in Chinese Astron. 2 (1978) 147-164. Fang Li-zhi et al., Acta Astronomica Sinica ]7 (1976) 154-146. English translation in Chinese Astron., ] (1977) 278-291. Pacholczyk, A. G., "Radio Astrophysics".

(Translated

b y Mr. O i a n S h a n - j i e )