Identification of heavy element absorption systems in QSO 2000-330

Pergamon Press plc. Printed in Great Britain 0275-1062/88$10.00+.00

Chin.Astron.Astrophys.12 (1988) 13-18 Act.Astrophys.Sin.z (19871 280-286

IDENTIFICATION

OF HEAVY

ELEMENT

ABSORPTION

SYSTEMS

IN QSO 2000-330

GUI Zhen-xing

and CHEN Jian-sheng

Beijing Observatory,Academia Sinica Received 1986 October 28

Keywords: Quasar - absorption lines - line identification

ABSTRACT Using the method of identificationof absorption systems proposed in our previous papers [1,2], we search for heavy element * absorption systems in the spectrum of QSO 2000-330, (ze= 3.78). We found six such systems, za= 3.1881, 3.1913, 3.3334, 3.4419, 1.3441 and 3.3459. The first four agree with the systems A,R,C,D, found by Hunstead et al (1986 [3]), the last two are new.

INTRODUCTION

and comments, [7,8]. The main difference between our and QSO 200-330 was discovered in 1982 by Bahcall's methods is that we replace Monte Peterson et al. [4]. Among quasars with Carlo simulation by calculation of random high-resolution spectra, it has the largest identificationprobabilities, and the main difference between our and Young's methods is redshift (ae= 3.78) so far known. Thus it has a special significance in quasar studies. that our calculation of the random probabilities is more rigorous. Furthermore, we use Hunstead et al. (1986 [3]) published a the theory of statistical testing. Our high resolution absorption spectrum in the method consists of the following steps: 1) The range 4100-5900A, with resolution sl.SA, computer searches for redshift system and gave a list including 280 absorption according to some criteria. 2) Under the same lines. Using the identificationmethods of criteria, we calculate the random identificatBahcall (1968 [5]), of Young et al. (1979 ion probability. 3) The redshift systems 1611,and of others, these authors searched for heavy element absorption systems and found in the search undergo the statistical found four, za = 3.1881, 3.1914, 3.332 and test. 4) A further sieve based on signal-to3.5519. noise ratio is applied. 5) Astrophysical The above search was restricted to the considerationsare applied to let nass only redshift range a= 3.10-3.78; hence they did believable redshift systems. not obtain any systems with z below 3. Also, The list of absorption lines to be previous experience with quasar identificat- identified is the same as TABLE 3 of Ref.[J] ion [7] has shown that different methods of and will not be repeated here. The list of identificationoften give different results. standard lines used is basically the same as Because of these considerations,we decided in [l], except that the hydrogen Balmer lines to use our method [1,2] to re-identify are left out. See TABLE 1. For those lines heavy element absorption systems in this used by Hunstead et al which are not included in TABLE 1, we made additional identifications object. Section 2 gives our procedure and results. in order that our results may be comparable. In the course of identificationwe need to In Section 3, we compare and discuss our and fix the following parameters: Hunstead's results. 1. The maximum allowable discrepancy between the standard line and the absorption line, i.e., thevalue of 6 in Criterion A of 2. PROCESS OF IDENTIFICATIONAND RESULTS Ref. [l]: A detailed description of our method has I(1 + Z&f - l&J < s been given in Refs. [1,2]. Later, one of We took 5= lA, the same as in 131. the authors (CUI) gave further developments 1.

14

CUI + CHEN

‘Table

1

lleferencc Lines Wavclcngth

Ion

(A)

HI OVI CII (XII

1215.67

1025.72

1031.93

1037.62

1036.34

1334.53

972.54

949.74

1190.42

989.R7

2344.21

977.03

CIV

1548.20

1550.77

NV

1238.81

1242.80

NH

1083.99

915.61

SiII

1260.42

1193.29

SiIIl

1206.51

SiIV

1393.76

Cd

4227.92

1402.77

CaII

393i.78

3969.59

MglI

2i96.35

2803.53

Al11

1670.79

Al111

lY54.72

1062.79

PC1

3720.99

3M61.01

1:c11

23S1.76

26n0.17

1144.95

1:c111

1122.51

3242.92

3073.86

Till

-

ijb4.730

1526.72

2. We took the search window to be 41905859A. The entire redshift range z=O.OO-3.78 3. was to be searched. As in [3], the step size was Az=O.OOOS. 4. The significance level a in the statistical test. We initially took a=O.Ol, in order that the systems obtained may be reliable. During the course, however, we found that in order to recover the systems found in 131, we had to lower the level to a=O.OS. 5. The threshold G in the signal-to-noise ratio sieve. We took G= 3, that is, a system is passed as a candidate system only if the signal-to-noise ratio is greater than 3. 10 candidate systems passed the above statistical test (with a=O.Ol) and the signal-to-noise sieve. They are z -0.6940, 1.3440 2.1405 2.7735 2.7825 2 78-30 2.7855: 2.8655: 2.8660'and 3.3i60: Obviously " the systems za= 2.7825 and 2.7830 can be combined into one at 2.78275 and the systems za= 2.8655 and 2.8660 into one at za= 2.86575. Hence, there wereineffect 8 candidate systems. We now analyse each of them separately. In the identificationresults of the systems z,=2.7735 and 2.78275, Lya absorption line should be uresent but was 4 therefore be not. These two systems ’ 1 procedure. discarded according to tht In the identification result2 \f the system za = 2.1405, only one each of the CIV and SiIV doublets was identified (CIV 1548,

-

25X6.65

2374.46

3230.12

SiV 1393). Hence these identificationsare not reliable. When these lines were discarded, we were left with 3 lines, CII 1334, A1111670 and SiII 1526, and the system of these three lines failed to pass the statistical test. In the identifcation results of the three systems aa= 0.6940, 2.7855, 2.86575, there were many lines mixed up with other systems. We also discarded these for greater reliability. Thus, we were left with two systems, za= 1.3440 and 3.3460. Their mean redshift values are Za = 1.3441 and 3.3459, respectively. The results of identification are given in TABLE 2. If we relax the significance level to a=O.OS, then we would get absorptions systems (za= 3.1881, 3.1913 and 3.3335), close to the systems A,B,C in Ref. [3]. The results for these are given in TABLE 3. Their system D was not found even with a= 0.05. After examination, we discovered that this was due to the three lines HI 1215, 949 and 930 in their system D all corresponding to observed lines with wide absorption troughs (see TABLE 3). At a redshift of 3.5519, the standard lines deviated from the central wavelengths of the corresponding absorption lines by 2.8, 2.0 and l.SA, more than the maximum allowed discrepancy of 1A. Thus they were discarded during the automatic computer search. Then, the other hydrogen Lyman lines were disqualified because of the consideration on the oscillator strengths

qso

The new

‘I’ablc 2

I

Identifications

2000-330

I

NO.

.z, = 1.3441,

15

identified

ayrtcms

Wavelength (A>

S, = 7.4,

I

Width (A>

Comment

U = 2.357

All11

1854.72

25

4347.7

1.9

All11

1862.79

29

4366.2

1.6

Fe11

2382.76

234

5584.5

3.4

Fe11

2344.21

213

5495.6

0.9

Fe11

2374.46

229

5566.7

0.4

I

I, = 3.3459, S, = 3.8, U = 2.381 HI

1215.67

179

5203.5

4.1

HI

1025.72

46

4458.4

1.8

HI

972.54

7

4225.9

3.8

Cl11

977.03

10

4245.9

0.9

NII

1083.99

89

4710.9

2.0

SilI

1260.42

208

5477.6

4.7

Sill

1193.29

161

5185.3

0.9

Sill

1190.42

158

5173.8

0.9

Sill

1304.37

254

5667.8

4.3

Fe11

1144.95

128

4976.3

2.1

FCIII

1122.53

116

4877.5

I.1

Note:

No., given

Wavelength by Hunrtead

last culumn

give

and width

corerpond the observed

cc al.. S, is the signal noise ratio. out the blended line.

(Criterion C of Ref. [l]), and this caused the system to be automatically discarded by the statistical test. By taking the HI 1215, 949, 930 lines as positive identifications, Hunstead et al. must have allowed for the fact that they corresponded to broad absorption lines, and relaxed the condition We agree that this for coincidence. consideration is acceptable and would also obtain the system D. Our results of the identification are also included in TABLE 3. with a= 0.01, we found two Summarizing, new absorption systems, a,=1.3441 and 3.3459; and a reasonable relaxation of the criterion yield the same parameters o and 6, will systems aa=3.1881, 3.1913, 3.3335 and 3.5519 as found by Hunstead et al.

3.

DISCUSSIONS

The a, = 1.3441 System TABLE 2 shows 1. that it contains the identifications of 5 absorption lines. But at this redshift, just 5 standards and no other fall inside the observational window. Therefore, the identification of this system cannot be That Hunstead et al. did not find denied. this was because they did not search the We can predict that redshift range below 3. if the observational window is extended to

liner.

(B SilI

1260)

No. is the number of a observed (I is the U value for statistical C/-test.

line The

the blue end, then we shall find the CIV resonance doublet. The a, = 3.3459 System. This is a 2. system of absorption lines of medium degree of ionization. HI 972 and SiII 1304 may possibly be blends. Obviously Hunstead. et this one. al. overlooked The aa = 3.1881 System is completely 3. the same as System A of Ref. [3]. 4. The aa = 3.1913 System is basically the same as System B of Ref. [3]. Hunstead et al. did not include Fe111 i122 in their list of identifications, probably because it is blended with the HI 1025 line in their Lyman system of aa= 3.5866, while the corresponding absorption line had a small equivalent width (1.4A). On the other hand, we didnothave the NII 1083 they identified. This is because the coincidence error between this line and the observed absorption line No. 64 at 4547.5A was as much as 4A, far exceeding the adopted maximum. 5. The a, = 3.3335 and 3.5519 Systems correspond to Systems C and D of Ref. 131. In both, we identified two more lines (CIII 977 and NII 1083) than Hunstead et al. did. The two heavy-element absorption systems newly identified in this paper should be reliable, for they were obtained under the more stringent condition, a=O.Ol. The three systems close to their Systems A, B and C

16

CUI

Table

3

The

Identifications

systems

+ CHEN

idcntitied

NO.

by

SI=5.3,

et

al.

(1986).

Wavelength

Width

(A)

(A)

I Z‘ =3.1881,

Hunstead

U=l.866

(System

A

Comment

z,=3.Itlfil)

HI

1215.67

146

5084.2

39.4

(B

HI

1216)

HI

1025.72

18

4296.5

10.8

(B

HI

1026)

(C

Sill

1260)

(A

HI

1215)

(A

HI

1026)

CII

1334.53

235

5588.6

2.1

Cl1

1036.34

23

4338.9

3.6

NI

1199.97

13x

5026.4

I.7

NII

1083.99

63

4540.1

0.7

01

1302.17

203

5453.6

3.5

01

1039.23

26

4352.4

0.9

Sill

1304.37

205

5462.6

1.1

Sill

1260.42

178

5279.1

1.6

Sill

1193.29

132

4997.9

1.4

Sill

1190.42

130

4985.6

1.3

Sill1

1206.51

144

5052.1

1 .o

Fe11

1144.95

105

4794.5

2.5

Z, =

3.1913,

S, =

5.3,

U =

1.866

(System

B za =

3.1914)

HI

1215.67

146

5084.2

39.4

I-II

1025.72

18

4296.5

10.8

Cl1

1334.53

237

5593.7

2.3

CII

1036.34

24

4343.5

2.3

NI

1134.66

98

4755.6

3.6

NI

1199.97

139

502A .7

1.9

01

1302.17

204

5458.2

3.6

01

1039.23

27

4357.2

2.4

Sill

1304.37

206

5466.9

1.0

Sill

1260.42

179

5283.5

4.1

Sill

1193.29

133

5001.7

1.8

Sill

1190.42

131

4989.6

1.1

Sill1

1206.51

145

5056 ..S

3.3

SiIV

1393.76

279

5841.6

0.5

FCII

1144.95

106

4800.5

5.1

Fe111

1122.53

X8

4704.6

1.4

I.

=

3.3335,

S,=

1.5,

U =

2.085

(System

C Z, =

111

1215.67

175

5267.8

5.0

1025.72

44

4445.8

10.0

HI

972.54

5

4215.6

6.0

Cl1

1334.53

275

5782.7

1.7

Cl1

1036.34

52

4490.5

1.7

977.03

Y

4235.2

8.2

1083.99

87

4698.2

6.6

01

1302.17

249

5642.9

1.1

01

1039.23

54

4503.4

2.9.

NII

(HI

1215

z =

3.346)

3.3332)

Hl

Cl11

)

(D

Cl11

(D

HI

926)

977)

(D

HI

930)

17

QSO 2000-330

Table Wwelength (A)

NO. .z, = 3.3335,

S, = 1.5,

U = 2.085

(System

Width (A)

1037.62

53

4496.2

2.3

OVl

1031.93

48

4470.8

4.2

SilI

1304.37

251

5650.8

8.0

Sill

1260.42

205

5462.6

1.1

Sill

1193.2’)

157

5170.6

0.3

Sill

1190.42

154

5157.9

1.2

Sill1

1206.51

165

5228.1

2.5

Frill

1122.53

114

4865.0

0.5

(System

Comment

C z, = 3.3332)

OVI

Z‘ = 3.5519

3 (contd.)

(A Sill 1304)

D Z‘ = 3.5519)

Hl

1215.67

222

5530.R

15 .G

111

1025.72

nr

4669.3

7.4

tll

972.54

41

4426.4

5.4

Ii1

949.74

21

4325 .I

9.6

HI

937.M

14

4268.4

4.2

Ill

Y30.75

8

4235.2

8.2

(C CIlI 977)

III

926.23

5

4215.6

6 .O

(C Hl.972)

i-11

923.15

3

4201 .9

3.7

I-11

920.96

1

4191.7

5.0

c-11

1036.34

90

4717.5

0.7

(:I11

977.0;

44

4445.S

10.0

Nil

1083.99

121

4933.3

1.2

01

1039.23

93

4730.1

0.5

Sill

1260.42

267

5738.4

2.8

Sill

1193.29

200

5431.3

2 .Y

5111

1190.42

198

5418.4

3.1

Sill

989.87

55

4506.4

2.9

Sill1

1206.51

212

5492.7

2.0

Fell

1144.95

163

5211.8

3.6

Note:

The same as ‘l‘z~blr 2.

were obtained under the less stringent condition a=O.OS, and should be regarded as Particularly System C, probable systems. with its rather small signal-to-noise ratio see TABLE 3) cannot be so reliable. (1.3, out certain Hunstead et al. also pointed unreasonableness in System C, for example, the identification of OVI was suspect. As failure at regards System D, our initial detecting it even at a=O.OS has been From the quality of the explained above. it should be regarded as a actual results, reliable system, for as many as 9 of the hydrogen Lyman lines were included. The lesson from the identification of System D the value of d specifying the is this: maximum discrepancy between the standard and the observed lines should be made to vary in accordance with the character of the The problem of automatic absorption line.

(C HI 1025)

adjustment of 6 correct calculation of the random probabilities in that case is being investigated. The identification and study of the absorption systems of QSO 2000-330 are only From the present work, we believe beginning. that other systems will yet be discovered. Our method of identification tends to be conservative, for we put a high premium on so we cannot be sure that we reliability, Of course, have not missed some systems. more and better observed spectra bri,rging more information will always be welcome.

18

CUI + CHEN

REFERENCES CUI Zhen-xing, CHEN Jian-sheng and TANG Xiao-yang, Chin.Astron.Astrophys. 7 (1983) 216-223 = Act.Astrophys.Sin. 3 (1983) 122-133. PI CHEN Jian-sheng, CUI-Zhen-xing, BIAN Yu-lin et al., Chin.Astron. Astrophys. 7 (1983) 280-287 = Act.Astrophys.Sin.3 (1983) 189-201. [31 Hunstead, R.W., Murdoch, H.S., Peterson, B.A., Blades, J.C., Jauncey, D.L., Wright, A.E., Pettini, M., and Savage, A., Astrophys. J., 305 (1986), 496. Peterson, B.A., Savage, A., Jauncey, D.L. and Wright, A.E., Astrophys. [41 J. (letters) 260 (1982), 127. Bahcall, J.N., Astrophys. J., 153 (1968), 679. / Young, P.J., Sargent, W.L.W., Boksenberg, A., Carswell, R.F., and Whelan, J.A., Astrophys. J., 229 (1979), 891. 171 CUI Zhen-xing, Chin.Astron.Astrphys.11 (1987) 291-296 = Act.Astrophys. Sin. 7 (1987) 194-202. CUI Zhen-xing, to be published in Tianwenxue Jinzhan I"Advances in PI Astronomy"!. [II