sities S3.9 GHz > 200 mJy at declinations 4. â¦â6 ... Note: âextâ means that the galaxy is an extended object. ..... The spectrum is typical of S galaxies. The.
c Pleiades Publishing, Ltd., 2009. ISSN 1063-7729, Astronomy Reports, 2009, Vol. 53, No. 4, pp. 287–294. c V.L. Afanas’ev, S.N. Dodonov, A.V. Moiseev, A.G. Gorshkov, V.K. Konnikova, M.G. Mingaliev, 2009, published in Astronomicheski˘ı Zhurnal, 2009, Original Russian Text Vol. 86, No. 4, pp. 323–330.
Optical Identifications and Spectra of Radio Sources V. L. Afanas’ev1 , S. N. Dodonov1 , A. V. Moiseev1 , A. G. Gorshkov2, V. K. Konnikova2 , and M. G. Mingaliev1, 3 1
Special Astrophysical Observatory, Russian Academy of Sciences, Nizhni ˘ı Arkhyz, Karacha ˘ı-Cherkessian Republic, 357147 Russia 2 Sternberg Astronomical Institute, Moscow University, Universitetski ˘ı pr. 13, Moscow, 119992 Russia 3 Southern Federal University (Rostov University), ul. Bol’shaya Sadovaya 105, Rostov-on-Don, 334006 Russia Received June 20, 2008; in final form, July 2, 2008
Abstract—We present classifications, optical identifications, and radio spectra for eight radio sources from three flux-density-complete samples in the following declination ranges: 4◦ −6◦ (B1950), S3.9 > 200 mJy; 10◦ −12◦ 30 (J2000), S4.85 > 200 mJy; 74◦ −75◦ (J2000), S4.85 > 100 mJy. For all these samples, the right ascensions are 0h −24h and the Galactic latitudes, |b| > 15◦ . Our optical observations at 4000−7500 A˚ were made with the 6-m telescope of the Special Astrophysical Observatory; we also observed at 0.97−21.7 GHz with the RATAN-600 radio telescope of the Special Astrophysical Observatory. We classify four of the objects as quasars and four as galaxies. Five of the radio sources have power-law spectra at 0.97−21.7 GHz, while two objects have flat spectra. The quasar J2358+0430 virtually did not vary during 23 years. PACS numbers: 98.70.Dk, 95.85.Bh DOI: 10.1134/S1063772909040015
1. INTRODUCTION The main goal of our work is to study radio sources (their spectra and variations on time scales from hours to several days) based on three fluxdensity-complete samples, in order to derive cosmological dependences for radio-source parameters (e.g. variability time scales, angular and linear sizes as functions of redshift) and determine their radio luminosity function. We have identified radio sources from all three samples with optical objects down to 21m . One of the samples contains 139 sources of the Zelenchuk 3.9 GHz survey [1] with flux densities S3.9 GHz > 200 mJy at declinations 4◦ −6◦ (B1950), with 68 of these sources having flat spectra, α3.9−7.7 GHz > −0.5 (S ∝ ν α ). These sources have been observed in the radio since 1984. Fifty-six sources were identified with optical objects down to 21m ; 52 objects were classified, and 42 are quasars at redshifts from 0.293 to 3.263. The results from more than 20 years of radio observations of these sources were presented in [2]. The two other samples were extracted from the MGB survey at 4.85 GHz [3]. One of these contains 153 sources with declinations 10◦ − 12◦ 30 (J2000) and flux densities S4.85 GHz > 200 mJy; 83 of these
sources have flat spectra, 72 sources are identified with optical objects, and 70 have been classified. We have observed this sample in the radio since 2000. The radio spectra, optical identifications, and source statistics for the sample are published in [4]. Fiftythree objects with redshifts between 0.331 and 3.610 were identified with quasars. We are continuing our study of the variability of the sample objects on time scales from days to weeks; these results will be published elsewhere. The other sample from the MGB survey contains 63 sources with declinations 74◦ −75◦ (J2000) and flux densities S4.85 GHz > 100 mJy. The spectra of all the sources for epochs 1998 and 2003, along with their optical identifications, were published in [5]. The sample contains 27 flat-spectrum sources; 18 sources were identified with optical objects down to 21m , all of them classified. The right ascensions for all the samples are between 0h and 24h , while the Galactic latitudes are |b| > 15◦ . Classifications and redshifts for a large number of the objects can be found in the 2003 catalog of quasars and active galaxies [6]; other redshifts were taken from the Sloan Digital Sky Survey (SDSS) [7] 287
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Table 1. Coordinates and magnitudes of the objects Difference of coordinates
Radio coordinates (J2000.0)
optical–radio RA h
m
00 52 38.915
Dec s
◦
+74 56 57.73
∆RA
0.009
Source of B
R
(survey)
∆Dec s
0.230
radio coordinates
20.76
17.06
NVSS
0.82
19.77
18.92
NVSS
0.86
19.60
17.01
NVSS
2.07
05 11 58.502
+74 39 19.11
07 42 39.344
+05 07 04.20
–0.07
08 33 18.913
+03 50 32.35
–0.013
–0.15
21.50
19.56
JVAS
11 40 27.693
+12 03 07.44
0.060
1.05
14.79
11.69
NVSS
14 39 04.470
+04 28 27.70
0.048
0.48
18.20
17.52
NVSS
14 25 11.962
+12 10 38.71
ext
ext
21.4
19.6
NVSS
23 58 28.834
+04 30 24.58
0.010
0.50
19.37
19.11
NVSS
Note: “ext” means that the galaxy is an extended object.
or derived from our observations on the 2.1-m telescope of the G. Haro Observatory (Cananea, Mexico) of the National Institute of Astrophysics, Optics, and Electronics and the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO) [8–15]. We present here our optical classifications and radio spectra for eight additional radio sources from these three surveys. 2. OPTICAL OBSERVATIONS We acquired optical spectra of all the sources with the SAO 6-m telescope in 2005–2006 using the multi-mode SCORPIO spectrograph [16]. The spectrograph slit width was 1 ; the detector was an EEV42-40 CCD chip (2048 × 2048 pixels in size, with a readout noise of 2.5 electrons). Most of the spectra were from the VPMG-550G grism, which covered wavelengths of 3650–7550 A˚ and provided a spectral ˚ with the reciprocal dispersion resolution of 8–10 A, ˚ being 1.9 A per pixel. We reduced our observations in the standard way, using software developed in the Laboratory of Spectroscopy and Photometry of Extragalactic Objects of the SAO; a brief description of the applied algorithms can be found in [16]. To relate the spectra to an absolute energy scale, we observed a spectrophotometric standard star on each night. The spectrum of J1425+1210 was taken with the SCORPIO spectrograph, the GR300 grism, and a TK1024 CCD detector (1024 × 1024 pixels, readout ˚ noise 3 el.). The spectral range was 3600–10 000 A, with a reciprocal dispersion of 6 A˚ per pixel and a ˚ resolution of about 20 A.
3. RADIO OBSERVATIONS All our radio observations were performed with the RATAN-600 telescope of the SAO. We obtained the radio spectra presented here in 1995–2007, at 0.97– 21.7 GHz. The exception are two variable sources, which were also observed between 1984 and 1992 at 3.9 and 7.7 GHz and in 1990 at 3.9, 7.7, 4.85, and 11.1 GHz. The characteristics of the beam, parameters of the applied receivers, and flux densities of calibration sources are published in [4, 5, 17]. In 2004, the 3.9 GHz receiver of the RATAN-600 was replaced with a 4.85 GHz receiver. Our reduction techniques are described in [4, 18]. 4. RADIO AND OPTICAL COORDINATES Columns 1 and 2 of Table 1 contain the J2000 coordinates of the studied objects from the NRAO VLA Sky Survey (NVSS) catalog at 1.4 GHz [19]. The rms error of the NVSS coordinates is about 0.03s in right ascension (0.11s for declinations of 74◦ ) and 0.56 in declination. The radio coordinates of J0833+0350 were retrieved from the Jodrell Bank–VLA Astrometric Survey (JVAS) catalog at 8.4 GHz [20]. Columns 3 and 4 of Table 1 contain the differences between the optical coordinates of the objects from the USNO astrometric survey [21] and their radio coordinates; all the detected differences are within 2σ. Columns 5, 6 present the B and R magnitudes from the USNO survey, and column 7 references to the surveys that were the sources of the given coordinates. The galaxy J1425+1210 is substantially extended, making it difficult to compare its optical and radio coordinates. ASTRONOMY REPORTS Vol. 53 No. 4
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Table 2. Data for optical observations Object name
Spectral lines
Wavelength, A˚
z
Object type
Date
Texp , min
1
2
3
4
5
6
7
CaII∗
3933/4440
0.135
G
2005.12.06
20
CaII∗
3968/4465
Hβ∗
4861/5517
MgI∗
5170/5868
NaI∗
5893/6689
CIII]
1909/4687
1.455
QSO
2005.04.17
20
MgII
2798/6870
[OII]
3727/4320
0.160
G
2005.12.01
10
CaII∗
3933/4560
CaII∗
3968/4600
[OIII]
4950/5742
[OIII]
5007/5808
MgI∗
5170/6000
NaI∗
5893/6836
[OIII]
2321/4420
0.905
QSO
2005.11.25
20
MgII
2798/5330
[OII]
3727/7100
Hδ∗
4104/4445
0.083
G
2005.04.17
20
Hβ∗
4861/5264
MgI∗
5170/5600
NaI∗
5893/6382
Hα
6563/8125
NeV
3426/3968
0.158
G
2002.04.06
20
MgI
5175/5995
NaI∗
5893/6820
CIII]
1909/4211
1.206
QSO
2005.04.17
30
MgII
2798/6172
Lα
1216/4004
2.294
QSO
2006.07.25
10
NV
1240/4085
SiV + OIII
1400/4610
CIV
1549/5102
CIII]
1909/6288
J0052 + 7456
J0511 + 7439
J0742 + 0507
J0833 + 0350
J1140 + 1203
J1425 + 1210
J1439 + 0428
J2358 + 0430
Note: Column 3 presents the wavelength in the object’s rest frame and the observed wavelength. In column 5, G denotes galaxy and QSO denotes quasar.
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0.5
(a)
J0052 + 7456 G z = 0.135
0.4 NaI
0.3 0.2
Hβ
MgI
0.1 CaII
0 0.5
J0511 + 7439 G z = 1.455
0.4
(b)
ëIII]
0.3
MgII
0.2 0.1
Flux, 10–16 erg/cm2 s Å
0 0.8
J0742 + 0507 G z = 0.160
[OIII]
[OII]
(c)
0.6 0.4 0.2
MgI
NaI
CaII
0 0.4
J0833 + 0350 G z = 0.905
0.3
MgII
(d)
[OIII]
0.2
[OII]
0.1 0 Hα
(e)
1.5 Hβ NaI
MgI
1.0 0.5
Hδ
J1140 + 1203 G z = 0.083
0 4000
5000
6000 Wavelength, Å
7000
Fig. 1. The optical spectra of the objects identified with the radio sources J0052+7456, J0511+7439, J0742+0507, J0833+0350, and J1140+1203, taken with the 6-m SAO telescope.
5. RESULTS The optical spectra of the objects are shown in Figs. 1 and 2, and Table 2 presents descriptions of these spectra. The columns of Table 2 contain (1) the object’s name, (2) the lines present in the spectrum,
(3) the wavelengths of the lines in the object’s rest frame and as observed, (4) the object’s redshift, (5) the object’s type, (6) the observation date, and (7) the exposure time in minutes. Lines marked with ASTRONOMY REPORTS Vol. 53 No. 4
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2.0 (‡)
J1425 + 1210 G z = 0.158 1.5 1.0
[NeV]
NaI
MgI
0.5
Flux, 10–16 erg/cm2 s Å
0
4000
5000
6000
CIII]
70000 (b)
MgII
0.3 0.2 0.1
J1439 + 0428 G z = 1.206 0
1.5
4000
5000
6000
Lyα
70000
J2358 + 0430 G z = 2.294
(c)
CIV
1.0 0.5
NV
SiV + OIII
CIII]
0 4000
5000
6000 Wavelength, Å
70000
Fig. 2. Same as Fig. 1 for the radio sources J1425+1210, J1439+0428, and J2358+0430.
asterisks were observed in absorption, while all other lines were observed in emission. The radio spectra and light curves for the variable sources are shown in Fig. 3. The open squares are flux densities from the Texas survey at 0.365 GHz [22] or from WENSS survey at 0.325 GHz [23]. Below, we present a description of the optical spectrum, classification of the optical counterpart, and characteristics of the radio spectra for each source.
5.1. J0052+7456 ˚ ˚ and NaI 5893 A˚ abHβ 4861 A, MgI 5170 A, sorption lines can be reliably identified in the optical spectrum (Fig. 1a). We classify the object as an Etype galaxy at a redshift of z = 0.135. The source has a power-law spectrum at 0.325– 21.7 GHz (Fig. 3a), S = 1000ν −0.63 mJy (frequency in GHz), and a constant flux density. The source may be polarized; the 3.9-GHz flux density is below the power-law spectrum because the angle between the electric polarization vector of the receiver at 3.9 GHz ASTRONOMY REPORTS
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and the vertical was 90◦ , whereas this angle was zero for the other detectors.
5.2. J0511+7439 Our optical spectrum (Fig. 1b) is fairly noisy, but we can identify two broad emission lines, CIII] 1909 A˚ and MgII 2798 A˚ , at the redshift z = 1.455. We classify this object as a quasar. The standard quasar spectrum shows no lines of considerable strength in this redshift range apart from these two lines. The source has a power-law spectrum at 0.325– 11.1 GHz (Fig. 3b), S = 604ν −0.87 mJy, and a constant flux density. 5.3. J0742+0507 The optical spectrum is displayed in Fig. 1c. ˚ [OIII] 4950 A, ˚ and 5007 A˚ Strong [OII] 3727 A, emission lines, as well as MgI 5170 A˚ and NaI 5893 A˚ absorption lines were identified in the spectrum, which is typical of a Seyfert 2 galaxy. The redshift of the object is z = 0.160.
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(‡)
(b) 1
1
0.1 J0052 + 7456 G z = 1.455
0.1
J0511 + 7439 G z = 1.455
10 ν, GHz
1
10 ν, GHz
1
(c)
(d)
1
1
0.1
0.1 J0742 + 0507 G z = 0.160
10 ν, GHz
1
S, Jy
J1439 + 0428 G z = 1.206
10 ν, GHz
1 1
0.7 0.6 0.5 0.4 0.3 0.2 0.1
J0833 + 0350 G z = 0.905
(f)
J0833 + 0350 G z = 0.905
07.1999 05.2004
07.1996
1979
0.4
(e)
1985
1991
1997
J2358 + 0430 G z = 2.294
2003 Years
0.1
(g)
10 ν, GHz
1 J2358 + 0430 G z = 2.294
(h)
0.3 05.1997
0.2 02.2006
0.1 0 1979
1985
1991
1997
2003 Years
0.1
1
10 ν, GHz
Fig. 3. Spectra of the radio sources J0052+7456, J0511+7439, J0742+0507, J0833+0350, J1439+0428, and J2358+0430 obtained with the SAO RATAN-600 radio telescope.
The source is extended in the radio. The flux densities fell off at frequencies above 7.7 GHz; the 0.365– 7.7 GHz spectrum can be approximated with a power law, S = 883ν −0.84 mJy (Fig. 3c).
5.4. J0833+0350 ˚ MgII 2798 A, ˚ and [OIII]+CII 2321, 2326 A, [OII] 3727 A˚ emission lines were detected in the ASTRONOMY REPORTS Vol. 53 No. 4
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optical spectrum. We identify this object with a quasar at z = 0.905. The source has a complex spectrum and variable flux density in the radio. Figure 3e displays its light curve at 7.7 GHz (filled circles) and 3.9 GHz (open circles) between 1980 and 2008. Figure 3f presents spectra obtained in 1996 (triangles), 1999 (filled circles), and 2004 (open circles). In 1996, the source was at its minimum activity and had a flat spectrum at 0.365–21.7 GHz. The development of a flare can be seen in 1999. The 2.3–21.7 GHz spectrum can be successfully approximated with a logarithmic parabola with its maximum near 15 GHz. In 2004, the flare maximum moved towards lower frequencies. The source’s variability index for all the years covered by our observations is 0.31, where the variability index is defined as (Smax − σmax ) − (Smin + σmin ) , V = (Smax − σmax ) + (Smin + σmin ) where Smax and Smin are the maximum and minimum recorded flux densities and σmax and σmin are their rms errors at 3.9 and 7.7 GHz. The apparent angular size of the source determined from its flare in 1991–1992 is 0.08 milliarcseconds (mas) at 7.7 GHz; the inferred brightness temperature is Tb = 1.5 × 1012 K.
5.5. J1140+1203 Five lines can be identified in the optical spectrum ˚ Hβ 4861 A, ˚ MgI 5170 A, ˚ (Fig. 1e): Hδ 4104 A, and NaI 5893 A˚ in absorption, and Hα 6563 A˚ in emission. The spectrum is typical of S galaxies. The object’s redshift is z = 0.083. A spectrum of the same object was obtained in the SDSS, where its redshift is given as z = 0.0835. According to the Texas survey, the source is double; we have obtained the integrated flux densities at 0.97, 2.3, and 3.9 GHz. Underestimated flux densities were derived at the higher frequencies.
5.6. J1425+1210 The optical spectrum is presented in Fig. 2a. Two ˚ and two emission lines, [NeV] 3346 and 3426 A, ˚ ˚ are absorption lines, MgI 5175 A and NaI 5893 A, clearly distinguished. The Hα 6563 A˚ line exactly coincides with the atmospheric water absorption line. We classify the object as a galaxy with redshift z = 0.158. In the radio, this source is extended for essentially any beam width. ASTRONOMY REPORTS
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5.7. J1439+0427 Figure 2b shows the optical spectrum. We identi˚ at the fied two lines, CIII] 1909 A˚ and MgII 2798 A, redshift z = 1.206. At such redshifts, the presence of only these two lines in the studied range is characteristic of quasars. The radio spectrum at 0.365–21.7 GHz range (Fig. 3d) can be successfully approximated with a power law, S = 683ν −0.77 mJy. 5.8. J2358+0430 Only emission lines are present in the optical spectrum, the strongest of them being Lα 1216 A˚ and ˚ weaker lines are also observed: NV CIV 1549 A; ˚ SiV+OII 1399 A, ˚ and [CIII] 1909 A. ˚ The 1240 A, spectrum is typical of distant quasars, and the object’s redshift is z = 2.294. The spectrum is shown in Fig 2c. The radio source is slightly variable in flux density. Its variability index between 1982 and 2007 at 7.7 GHz was V = 0.09, and the source’s spectrum is complex. We display the light curve of the source in Fig. 3g; Fig. 3h shows the source’s spectrum for May 1997 and February 2006. 6. CONCLUSIONS We have obtained optical spectra of eight radio sources. We have identified four of these with quasars; J0511+7439 (z = 1.455) and J1439+0428 (z = 1.206) have power-law spectra at 0.365–21.7 GHz, with the spectral indices α = 0.87 and 0.77, respectively. J0833+0359 (z = 0.905) displayed a variability index of V = 0.31 at 3.9 and 7.7 GHz over 23 years of observations. The angular size of a source undergoing a flare with its maximum in 1992 is 0.08 mas. J2358+0430 (z = 2.294) experienced only insignificant variability over 25 years, without any appreciable flares. Four of the sources were identified with galaxies. J0052+7456 (z = 0.135) has a power-law spectrum at 0.365–2.3 GHz, with the spectral index α = −0.63; the offset point at 3.9 GHz shows that the source is probably polarized. Its optical counterpart has a set of absorption lines typical of E galaxies. J0742+0507 (z = 0.160) is extended to the RATAN600 beam at frequencies above 3.9 GHz. It has a power-law spectrum at 0.365–3.9 GHz, with the spectral index α = 0.84. Its optical counterpart is a Seyfert 2 galaxy. According to the Texas survey, J1140+1203 (z = 0.083) is double, and we simultaneously detect both sources at low frequencies. In the optical, this is an S galaxy. J1425+1210 is extended at all frequencies.
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ACKNOWLEDGMENTS This study was supported by the Russian Foundation for Basic Research (project no. 06-02-16667) and the Basic Research Program of the Presidium of the Russian Academy of Sciences “The Origin and Evolution of Stars and Galaxies.” The authors wish to thank A.N. Burenkov, S.S. Kaisin, and V.P. Mikhailov for their assistance during the observations of the sources J0052+7456, J0833+0350, and J1425+1210. REFERENCES 1. V. R. Amirkhanyan, A. G. Gorshkov, A. A. Kapustkin, et al., Catalog of Radio Sources in the Zelenchuk Sky Survey at Declinations from 0 to +14◦ (Mosc. State Univ., Moscow, 1989) [in Russian]. 2. A. G. Gorshkov, V. K. Konnikova, and M. G. Mingaliev, Astron. Zh. 85, 314 (2008) [Astron. Rep. 52, 278 (2008)]. 3. P. C. Gregory, W. K. Scott, K. Douglas, and J. J. Condon, Astrophys. J., Suppl. Ser. 103, 427 (1996). 4. A. G. Gorshkov, V. K. Konnikova, and M. G. Mingaliev, Astron. Zh. 80, 978 (2003) [Astron. Rep. 47, 903 (2003)]. 5. A. G. Gorshkov, V. K. Konnikova, and M. G. Mingaliev, Astron. Zh. 83, 241 (2006) [Astron. Rep. 50, 210 (2006)]. 6. M. P. Veron-Cetty and P. Veron, Astron. Astrophys. 412, 399 (2003). 7. The Sloan Digital Sky Survey, http://www.sdss.org. 8. A. G. Gorshkov and V. K. Konnikova, Pis’ma Astron. Zh. 19, 136 (1993) [Astron. Lett. 19, 55 (1993)]. 9. V. Chavushyan, R. Mukhika, A. G. Gorshkov, et al., Pis’ma Astron. Zh. 26, 403 (2000) [Astron. Lett. 26, 339 (2000)].
10. V. Chavushyan, R. Mukhika, A. G. Gorshkov, et al., Astron. Zh. 78, 99 (2001) [Astron. Rep. 45, 79 (2001)]. 11. V. Chavushyan, R. Mukhika, Kh. R. Valdes, et al., Astron. Zh. 79, 771 (2002) [Astron. Rep. 46, 697 (2002)]. 12. V. L. Afanas’ev, S. N. Dodonov, A. V. Moiseev, et al., Astron. Zh. 80, 499 (2003) [Astron. Rep. 47, 458 (2003)]. 13. V. L. Afanas’ev, S. N. Dodonov, A. V. Moiseev, et al., Pis’ma Astron. Zh. 29, 656 (2003) [Astron. Lett. 29, 579 (2003)]. 14. V. L. Afanas’ev, S. N. Dodonov, A. V. Moiseev, et al., Astron. Zh. 82, 420 (2005) [Astron. Rep. 49, 374 (2005)]. 15. V. L. Afanas’ev, S. N. Dodonov, A. V. Moiseev, et al., Astron. Zh. 83, 291 (2006) [Astron. Rep. 50, 255 (2006)]. 16. V. L. Afanas’ev and A. V. Moiseev, Pis’ma Astron. Zh. 31, 214 (2005) [Astron. Lett. 31, 194 (2005)]. 17. A. M. Botashev, A. G. Gorshkov, V. K. Konnikova, and M. G. Mingaliev, Astron. Zh. 76, 723 (1999) [Astron. Rep. 43, 631 (1999)]. 18. A. G. Gorshkov and O. I. Khromov, Astrofiz. Issled. (Izv. Spetsial’n. Astrofiz. Observ.) 14, 15 (1981). 19. P. C. Gregory, W. K. Scott, K. Douglas, and J. J. Condon, Astrophys. J., Suppl. Ser. 103, 427 (1996). 20. I. W. A. Browne, Mon. Not. R. Astron. Soc. 293, 257 (1998). 21. D. Monet, A. Bird, B. Canzian, et al., USNO-SA1.0 (US Naval Observatory, Washington, DC, 1996). 22. J. N. Douglas, Astron. J. 111, 1945 (1996). 23. R. B. Rengelink, Y. Tang, A. G. de Bruyn, et al., Astron. Astrophys., Suppl. Ser. 124, 259 (1997).
Translated by N. Samus’
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