Preliminary results from a search for gravitational lensing within a sample of highly luminous quasars

PRELIMINARY RESIjLTS T|ROM

A

SEARCH FOR GRAVTTATIONAL LENSING WTTHIN

A

SAMPLE OF HIGHLY LI.JMINOUS _QUASARSI'

J. suRDEJl**, p. MAGA6I2, J.p. swnrtcsl, M. REMY3,

u.

BoRGEEST4, R. K.lysER4, s. Rersoet4, H. KIIHR5

I

Institut d'Astrophysiqrc - 4200 Cointe-Ougree (Belgium)

2 _{Europeon Souhern Obsen'atory}

-

_{8A46 Guching bei Miin;hen (FRG)} r _{European Southern Observatory - Santiago 19 (Chile)}

4 _{Hamburger Sternwste}

_-

_{2050 Hamburg (FRG)}

5 _{Max-Planck-lnstitutfiir Astronomie - 6gN Heid.elberg (FRG)}

*

_{Based on observations collected at the European Southern Obsewatory (La Silla, Chile)} ** Also, Chercheur Qualifré au Fonds National de la Recherche Scientifique (Belgium)

The purpose

of thrs

communrcation grven

at the firsb

DAEC

Workshop

in

Parrs

rs to

deseribe

out

present

optrcal

search for

gravitational

lensrng from

a drrect

CCD rmaging survey oF known

hrghly

lumrnous quasafs

(hereafter

HLQs; Mv

( -

29).

The motrvatron (why

_?),

_the

observaÈronal

strategy as

well

as

prelrmrnary

results of thrs

on-gorng

project are

brreFly

summarrzed hereafter.

l{hy ?

Gravrtatronal lensrng

may

affect our

vlew

of

the

distant

Unrverse

rn multrple

and

subtle

ways

(see

Canrzares,

1987, Blandford and Kochanec, 1987, and

Nottale,

19BB

for

diFferent revrews

on thrs subject).

The

most

obvrous

effects are

the

angular

deformatrons

(rF the

source

ls

berng resolved)

or

of

some

very

remote

objects.

The most spectacular one concerns

the possible

formatron

of multiple

images

(so

called

"gravrtatronal

mtragesrr) under nearJ-y

perfect

alrgnments between

the

source,

the

deflector

and

the

observer.

In

the

rematnder, we

shall

only

consider

this

kind

of

extreme

effects

because such

examples

of gravitational

lensrng

are the

easrest

ones

to

be proven observationally.

Because

the

answer

to

the

questron _'rHow frequent

are

gravl-tational

m:.rages

?" is

very much

related

to that to

"How does/do

the (visrble and/or dark) matter

drstr:-butron(s)

look

at

drfferent

scales

rn

the

Unlverse

?",

any

predrction

made

for

the expected number

of

mult:.pIy lensed

objects 1s

bound

to

be

strongly

model dependent. An observational approach

rs

therefore

requrred rn order to

evaLuate

the true

rmportance of

gravitational lensrng.

Since November 1986, we have

in:.tiated

a

systematic

search

for gravitatronal

lensrng

as follows.

We

consrder

that

the

apparently

(tvX

18.5)

and.intrrnsrcally

(MyS

-29

adoptrng

Hn

_{= 50}

km/secÂpc,

q^ =

0

)

Iumrnous quasàcs

constitute

very"promrsing candrdates t"o search

for

the

presence

oF gravitatronally

lensed

tmages

at

arcsec. and

sub-arcsee.

angular

scales.

Indeed :

(r)

the

HLQs form

a

partrcularly

hrgh

flux

lrmrted

sample of

QS0s

'

(rr)

the

HLQs

are the

most

lrkely

objects

for

whi-ch we may

assume

that therr

rntrtnsrc

brightness

is partrally

due to

lensrng,

(rrr)

the

HLQs

are

located

at

large

cosmologrcal drstances so

that

the

probabrlrty

of

findrng

an approprrate

lens

alonq

the Line-of-sight

rs

higher,

(rv)

we suspect

that

observational brases

are

responsrbl-e

for

the lack

of

detected gravrtatronal-

lens

systems

with

small angular separatrons.

Wlth

the

above arguments

rn

mrnd, we

belreve

that

hrgh anguJ.ar

resolution

imaging

with

ground based

optical

telescopes under

optimal seeing conditions

will bring

important clues

on

the

occurrence

of

lensing

effects

by galaxies

or

any

other class

of

unknown masslve objects.

OBSERVATIONAL STRATEGY AND PRELIMINARY RESULTS

As

ofl 1

January 19BB' we have used

the

ES0/MPI

2.?

n

teles-cope

during

18 aLloeated

nrghts

wrth

a

CCD camera

+

broad- and

narrow- band

filters.

Under

an

avefage

seerng

(FWHM)

of

1.?

arcsec.,

we have imaged

a total. of

111 HLQs.

Twenty-five of

these

turn

out

to

be

interesting objects

on

the

basrs

of

their

*-morphologtcal

appearance

(multrple or

elonqated

rmage(s), presence-of

a

nearby

galaxy,

etc.).

More

details

are

glven

ln

burdej

et al.

( 1 gBBa)

.

Frve

of

these

25

HLQs constrtute

excelient

candrdates

for

gravrtational lensing.

Two oF these 5

candidates,

ESo GL1=UM67l

and

ESo GLz = H1413+117r

are

now

confirmed

to

be

two

deFinrte

new

cases

of

multrply

lensed quasars.

1.

ESO GL1 ₌ UM671

-TEe-t{LroM-

Q0142-100=PHL]70J was found

to

consist

of

two

lensed

rmages,

A

(m,,=

17.0)

_and

B

(mV=

19.1),

separated

by

2.?2

arcsec.

at a

redshrlt

z^ =

2.719 '(see

Frg.

1).

The lensing

oalaxv

(m^

₌

_19,

z,

₌

OJ193) has

also

been

rdentiFred.

It

lies

i"ro

'n""J thu

itn"t

connecting

the

two

Q50 rmages,

at =

0'B

"r"â"".

from

the fainter

one.

Applrcatron

of

grayltatronal

optometry

to

thrs

system leads bo

a

valu". Mn

=

2'4.

1O."

_Yg

fol

b'he mass-of

the

lensrng galaxy

projected

beUween

the

two lénsed

Q50 tmages and

to

At

=

7

weeks

for

the

most

likely

travel-trme drffereÀce between

the

two

li.ght

paths

to

the

QSO. More detarLs

about

th:.s

new

gravitatronal

lens

system may

be

found

in

surdej

et

al

,

(987

and 19BB b).

2.

E50 GL2 ₌ H141J+117

Q and broad absorption

line

(BAL) quasar

H1413+117

has recently

been

resolved

rnto

four

lensed

lmages

havrng comparable Urightnesses (mv

=

18.4_-18.8) and separations

of

thé order

of

on"

âr""u".

at

a'redshrft

_{zn = 2.55}

(see Frg.

2).

Two narrow absorptron

line

systems have been

identrfied

at

redshrfts

z =

1.44

and

1.66 1n

the

spectrum

of

one

of

the

rmages.

tr

tnese are

due

to

rntervening

gas

clouds

associated w:.tË

the

lens(es),

thp

mass

of

the

deflector

must

be

of

the

order

of

M^

₌

4-7'

1Ot

I

M,.,

whrle

the

delay between

the

travel

fir""

of

t#o

opposrte rrage%

rs

estimated

to

be = 2-t

months. A

more

detailed

account

of

our

observations

on

this

quadruply

lensed quasar

is

given by Magain

et

al.

(1988)'

CONCLUSIONS

Our optrcal

search

for gravrtational lensrng can

be consrdered

to

be very

successful

since

more

than

?o oÂ

of

the

rnvestigated

HLQs show

signs

which

are

poss:.bly

related

to

the HLQ phànomenon. Furthermôre,

at least 5 (out of

111)

HLQ'

conslrtute

excell.ent candidates

for being

gravrtatronally

Iensed,

two

of

which (UM67l and H1413+117)

are

now

definitely

*q

We

have

comprled

1n

TabIe

1 data on

seven

presentlv accepted (and two st:.11 suggested) cases

of

multrply

lensed QSO

images.

A

rook

at the lrsted

absolute

magnrtudes

of the

QSOs

shows

that 5 (out ol 7)

accepted cases

are

HLQs. The quasar o957+561,

wrth

Mv

₌

_-28.4,

rs

al.so

quite

luminous, and 2û16+112,

with Mv = -24.8, rs

known

to

show

an

unusually

n"rron emtssron-rrne spectrum. The

results

of

Tab-Le

l

confirm

our

ear.Lv

suggestron

that

a

search

for

recognizabLe slgns

of

gravrtafronai lensing among HLQs would be successful.

Tabre

1

:

Data on

the

seyen accepted (and two suggested) cases

of

quasars being

multiply

lensed

Name no

of

_angular

Iensed

separa-lmages

tron M "v Refs. .Lens tzL/ O957+561 1 1 1 5+080 2O16+112 2237+O31 EsO GL'I ( _{01 42-1 00 )} rsO GLz (1413+117) ESO GL] 1.,4 1.7

J.t

1.7 2.7 2.6 1,5 2

t

4 2 4 2 6n ? 4 2 z = 0.4

0.l:

0. B: 0.04 0.5 '1.52 ? -28.4 -29.7 -24.8 -29.2 -30.2 -29.8 -29.6 1 2 J 4 5 A 7 1635+267 2345+OO7 2.O 2.2 -25.9_-27.1 No No

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aI.,

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(l)

Lawrence

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(5)

Suraej

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aJ..,

(7)

Meytan

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1988.

1984 and Turner

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,

and

Nieto

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1988.

Weymann, 1979.

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Weymann et

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(4)

Huchra

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1987.

(6)

Magarn

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1988.

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Djorgovskr and Spinrad, 1988.

(9)

Weedman

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19Bz

Frgure

1

:

Central

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_of

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for

the

gravitational

(more

_detarls

_are

_gLven

Frgure

₂

_:

_Central

_part

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Iens

sytem ESO GLZ

glven

_in

Magain et

CCD frame

_for

the

=

H1413+117 (more

al.,

19BB).

new

gravttational

details

are

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