Search for Optical Identifications in the 5C3-Radio Survey II. Statistical Treatment and Results

On plates of the large Schmidt-telescope of Karl-Schwarzschild-Observatory Tautenburg, taken by F. BÖRNGEN, 139 radio sources of the ₅C₃ area were inspected for possible identifications with optical objects. The results are published in paper I and in the appendix of the present paper II. A detailed analysis of these objects showed a relatively large number of about 65 real identifications up to the utmost plate limit B ≈ 21^m.7, which corresponds to an identification rate of about 47%. The individual reliability of each possible optical identification is estimated (table 6). Apparently the identified objects (see tables 4 and 6) are galaxies, “blue” and “neutral” quasars, and one H II-region of the Andromeda nebula. It is of great cosmological interest that no “red” quasars could be found.     

Revised identifications in the 5C2 survey

In the present paper revised distances of optical objects from radio sources of the 5C2 survey are given. A statistical investigation of the data is given for blue objects and galaxies by the statistical method of the “first neighbour”. The identification rate on blue plates for both the blue objects and galaxies amounts to about 40% out of the total number of 26 identifications. For every blue object and galaxy which are proposed as an identification the statistical reliability is given.     

Search for Optical Identifications in the 5C3-Radio Survey III. Spectroscopic Results

52 possible optical identifications (V ≲ 19.5) of 43 radio sources of the ₅C₃ area have been spectroscopically examined by use of objective prism plates from KARL SCHWARZSCHILD Observatory Tautenburg. The aim was to select objects of special interest for further slit spectrographic investigation. Besides 42 probably ordinary stars and 3 galaxies, five quasar spectra have been found, but only one redshift could be determined. Two further objects probably have unusual spectra.     

Search for Optical Identifications in the 5C1 Radio Survey

Identifications of 5CI radio sources with optical objects are given. The identification rates amount to 44 and 30 per cent up to the limiting magnitude of about 21^m in R and B, respectively. The objects are to about equal parts galaxies, blue starlike objects, and “unclassified objects” (presumably mostly faint galaxies and less pronounced blue objects). For every proposed identification a reliability and for the identification samples the reliability and the completeness are given. Some inaccuracies in the use of a statistical method, proposed in a previous paper, have been removed; two additional means of statistical treatment have been applied to discuss the data.     

Optical identification of iras point sources on the basis of low-dispersion FBS spectra. III

Part three of optically identified point sources from the IRAS Point Source Catalog contains 113 objects. The identifications were based on the Digitized Sky Survey (DSS), the First Byurakan Survey, blue and red maps from the Palomar Sky Survey, and infrared fluxes at 12, 25, 60, and 100 μm in the region of +61° ≤ δ ≤ + 65° and 11^h15^m ≤ α ≤ 18^h35^m with an area of 200 sq. deg. Of the 119 sources in this region, 6 could not be identified owing to the absence of optical counterparts with the given coordinates. For the identified objects we determined their optical coordinates, their departures from the IR coordinates, and their stellar V magnitudes, color indices (CI), and preliminary types. The objects have optical magnitudes in the range of 8ⁿ–21^m. Of the 113 objects, 31 turned out to be stars of spectral types K and M, 1 is a planetary nebula, 2 are candidates to be quasi- stellar objects, and 79 are galaxies. A list of the 48 nonstellar objects is given. The identified galaxies include Seyfert candidates, interacting pairs, galaxies with companions, superassociations, etc. The galaxies are in groups in many cases, and the IR emission may be due to heating of intergalactic matter within a group. Finder charts for these objects from the DSS are given. Translated from Astrofizika, Vol. 41, No. 2, pp. 251–262, April-June, 1998.     

Search for optical identifications in the 5C4 radio survey

With the aid of a statistical approach regarding only the nearest optical object to a given radio position we have found identification rates of nearly 30 per cent up to the blue and red limits of the Palomar Sky Survey prints covering the region of the 5C4 radio survey. Roughly 60 per cent of these identifications are blue starlike objects and therefore possible quasar candidates. The remainig identifications are galaxies. Probabilities for the first neighbours to be an optical counterpart and finding charts for highly reliable objects are given.     

Optical identification of iras point sources. galaxies. v

A fifth list of objects from the BIG (Byurakan-IRAS galaxies) sample is given: 89 galaxies identified with 59 point sources from the IRAS Point Source Catalog. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps from the Palomar Observatory Sky Survey, and infrared fluxes at 12, 25, 60, and 100 mm in the region of+65° ≤ δ ≤69δ and 5^h10^m ≤ α ≤9^h 15^m with an area of 96 deg². For the identified galaxies the optical coordinates, their departures from the IR coordinates, and the stellar V magnitudes, morphological types, angular sizes, and position angles were determined. The objects have optical magnitudes in the range of 14^m. 1-21^m.5 and angular sizes in the range of 2″-47″. The galaxies are mainly spiral in morphology. Compact galaxies and Seyfert candidates, interacting pairs, “mergers,” galaxies with companions and superassociations, groups of galaxies (including compact ones), and others are encountered, which shows the importance of these objects for the study of the relationships among the phenomena of star formation, activity, and interactions. Finder charts from the DSS are given for these objects. New designations and numbering are introduced for galaxies in the studied sample. Translated from Astrofizika, Vol. 43, No. 3, pp. 425-441, July– September, 2000. The NASA/IPAC Extragalactic Database (NED), operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.     

Interacting Galaxies — the X-ray View

We have selected a complete, flux-limited sample of bright point-like sources with absorbed X-ray spectra from the ROSAT All-Sky survey, the ROSAT Hard Survey (RHS). The sample is drawn from the high-galactic latitude sky, |b^II| > ±30°, and avoids the general direction of the Magellanic Clouds and the Virgo Cluster. It comprises a total of 182 objects of which 118 were previosly catalogued objects and 64 were new AGN candidates. Through optical follow-up studies at La Silla, Calar Alto and the 6m Zelentchuk telescope we could identify 56 of the new objects, thus achieving a spectrscopic completeness of 96% of the sample. The selection strategy turned out to be extremely useful. Out of the new identifications, 84% are indeed active galaxies or emission line galaxies. While 14 objects are new BL Lac candidates 33 of the new AGN are Seyfert galaxies with a redshift distribution in the range 0.021–0.63, peaking at around 0.06, i.e. relatively local. Surprisingly, about 40% of the X-ray selected Seyfert galaxies seem to reside in interacting systems. With smaller selection uncertainties this fraction exceeds the number of paired galaxies in optically selected samples and therefore gives strong support to the idea that AGN activity is triggered by interaction.     

Identification and properties of host galaxies of RCR radio sources

FIRST and NVSS radio maps are used to cross identify the radio sources of the RCR catalog, which is based on observational data obtained in several runs of the “Cold” survey, with the SDSS and DPOSS digital optical sky surveys and the 2MASS, LAS UKIDSS, and WISE infrared surveys. Digital images in various filters and the coadded gri-band SDSS images, red and infrared DPOSS images, JHK-band UKIDSS images, and JHK-band 2MASS images are analyzed for the sources with no optical candidates found in the above catalogs. Our choice of optical candidates was based on the data on the structure of the radio source, its photometry, and spectroscopy (where available). We found reliable identifications for 86% of the radio sources; possible counterparts for 8% of the sources, and failed to find any optical counterparts for 6% of the sources because their host objects proved to be fainter than the limiting magnitude of the corresponding surveys. A little over half of all the identifications proved to be galaxies; about one quarter were quasars, and the types of the remaining objects were difficult to determine because of their faintness. A relation between the luminosity and the radioloudness index was derived and used to estimate the 1.4 and 3.94 GHz luminosities for the sources with unknown redshifts. We found 3% and 60% of all the RCR radio sources to be FRI-type objects (L ? 10²⁴ W/Hz at 1.4 GHz) and powerful FRII-type galaxies (L ? 10^26.5 W/Hz), respectively, whereas the rest are sources including objects of the FRI, FRII, and mixed FRI-FRII types. Unlike quasars, galaxies show a trend of decreasing luminosity with decreasing flux density. Note that identification would be quite problematic without the software and resources of the virtual observatory.     

Orientation of extragalactic radio sources relative to the elliptical galaxies associated with them

The relative orientations of the optical and radio axes of radio galaxies are analyzed using data for 271 objects. It is found that the radio axes correlate with the minor axes of the optical galaxies for more elongated radio galaxies (K > 2.5, where K is the ratio of the lengths of the major and minor axes of the radio image) and for radio galaxies of the class FRII, whereas for less elongated radio galaxies (K < 2.5) and radio galaxies of the class FRI the radio axes correlate with the major axes of the optical galaxy. In both cases the correlation turns out to be more significant when the radio galaxies are classified in terms of their elongation than when they are classified in terms of the Fanaroff-Riley criterion. The classification in terms of elongation of the radio image can therefore be of interest for understanding overall problems associated with the mechanism of formation and evolution of radio galaxies. A theoretical foundation for such a classification may be the alternative mechanism of formation of radio galaxies from relativistic plasma ejected from the central part of the optical galaxy and moving in its large-scale, dipole magnetic field. Translated from Astrofizika, Vol. 42, No. 3, pp. 365–371, July–September, 1999.     

Optical Identifications of IRAS Point Sources. Galaxies. VI

A sixth list of objects from the BIG (Byurakan—IRAS galaxies) sample is given: 87 galaxies identified with 60 point sources from the IRAS Point Source Catalog. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps from the Palomar Observatory Sky Survey, and infrared fluxes at 12, 25, 60, and 100 µm in the region of +65° +69° and 9^h15^m 14^h00^m with an area of 111 deg². We determined the optical coordinates of the identified galaxies, their departures from the IR coordinates, and their V magnitudes, morphological types, angular sizes, and position angles. The objects have optical magnitudes in the range of 12 ^m .5-21 ^m .5 and angular sizes in the range of 2-29. Finder charts from the DSS are given for these objects.     

On the efficiency of the Ultra Steep Spectrum technique in finding high-z radiogalaxies

In the last three decades, the Ultra Steep Spectrum technique has been exploited by many groups since it was demonstrated that radio sources with very steep spectra (<−1.0; S ∝ ν) are good tracers of high-z radio galaxies (HzRGs; z>2). Though more than 150 HzRGs have been discovered up to now with this technique, little is known about its real effectiveness, as most of the ongoing searches still have incomplete follow-up programs. By selecting a new appropriate sample of USS sources from the MRC survey, the true searching efficiency of the USS technique has been quantitatively demonstrated for the first time in this paper. Moreover, it was compared with that of an optical search of HzRGs based on a simple cut of the galaxies r-band magnitude distribution. When no bias other than the radio-spectrum steepness is applied, the USS technique may be up to four times more efficient in selecting HzRGs with respect to an optical search. Nevertheless, when the search is limited to objects fainter than the POSS-II plates (r21), the USS technique is still 2.5 times more efficient (ε_USS=0.52 vs. ε_OPT=0.19). For an optical search to reach a comparable efficiency it is necessary to select objects fainter than r=23, but this implies that about half of the HzRGs are lost because of the imposed magnitude bias. The advantage of the USS technique is that a 0.5 search efficiency is already reached at the POSS-II plates limit, where all the optical identification work is done without telescopes. However, this technique has the drawback that up to 40% of the HzRGs of the sample are lost simply because of the applied spectral index bias. Interestingly, the introduction of a strong angular-size bias such as θ<15″ can double the searching efficiency irrespectively of the adopted technique, but only in the case that no optical bias has been introduced first.     

Optical identification of IRAS point sources on the basis of low-dispersion FBS spectra. IV

A fourth list of optically identified point sources from the IRAS Point Source Catalog, containing 34 nonstellar objects, is given. The identifications were made on the basis of the Digitized Sky Survey (DSS), the First Byurakan Survey, blue and red maps from the Palomar Sky Survey (FBS), and infrared fluxes at 12, 25, 60, and 100 μm in the region of +61° ≤ δ ≤ 65° and 11^h15^m ≤ α ≤ 18^h35^m with an area of 200 sq. deg. For the identified objects we determined their optical coordinates, their departures from the IR coordinates, their stellar V magnitudes, color indices CI, and preliminary types. The optical magnitudes of the objects are in the range 12^m.5-27^m. The identified galaxies include Seyfert candidates, interacting pairs, galaxies with companions, superassociations, etc. The galaxies are encountered in groups in many cases, and the IR emission may be due to heating of intergalactic matter within a group. Finder charts from the DDS are given for these objects. Translated from Astrofizika, Vol. 41, No. 3, pp. 359–366, July–September, 1998.     

A comparison catalogue ofHii-regions

For complete information about the apparent distribution ofHii-regions along the whole galactic equator a Catalogue of 698 known emission nebulae is given on the basis of 13 lists and catalogues of these objects. The main catalogue used for the northern sky was that of Sharpless (1959) including 313 objects while the coverage of the southern sky can be characterized by a greater number of smaller catalogues represented in the first place by that of Rodgerset al. (1960) and that of Gum (1955). ForHii-regions, only optical data were taken into account.Where several authors describe the complex of nebulosities a more detailed specification of objects is preferred. The objects in the Catalogue are listed according to their right ascensions for 1950. As only three catalogues applied here give also the objects out of the belt ±15° around the galactic equator, the Catalogue is divided into two parts. The first (main) part contains 667 objects lying within this belt, the second contains 31 objects lying outside it. A Summary Table listing the objects from the two parts according to their galactic longitudes involving, in addition, the 50-yrs precession for every object is also added.An attempt was made not to repeat contingent errors present in the source-catalogues. The maps of the POSS were often used. Coincidences with SNR and planetaries were sought for independently of identifications given in the source-catalogues. The list of objects from the source-catalogues ofHii-regions excluded as SNR, planetaries and galaxies is also given.Astrophysics and Space Science Review Paper.     

A search for the submillimetre counterparts to Lyman break galaxies

We have carried out targeted submillimetre observations as part of a programme to explore the connection between the rest-frame ultraviolet and far-infrared properties of star-forming galaxies at high redshift, which is currently poorly understood. On the one hand, the Lyman break technique is very effective at selecting     galaxies. On the other, 'blank-field' imaging in the submillimetre seems to turn up sources routinely, amongst which some are star-forming galaxies at similar redshifts. Already much work has been done searching for optical identifications of objects detected using the SCUBA instrument. Here we have taken the opposite approach, performing submillimetre photometry for a sample of Lyman break galaxies, the ultraviolet properties of which imply high star formation rates. The total signal from our Lyman break sample is undetected in the submillimetre, at an rms level of ∼0.5 mJy, which implies that the population of Lyman break galaxies does not constitute a large part of the recently detected blank-field submillimetre sources. However, our one detection suggests that with reasonable SCUBA integrations we might expect to detect those few Lyman break galaxies that are far-infrared brightest.     

The peaks and gaps in the redshift distributions of active galactic nuclei and quasars

The distributionsf(z) of the redshifts for active galaxies (Seyfert galaxies, radio galaxies, and quasars) have been studied. Some statistically-significant maxima and minima are observed in the distributionsf(z) for these objects. The significance of peaks and gaps increases for the brighter objects, for which the samples are more complete. The clustering of the Seyfert galaxies is significantly different from that of the nearby normal galaxies. The distributionf(z) for the radio galaxies is similar to the analogous distribution for the galaxy clusters. Three of the five peaks in the distributionf(z) for the radio quasars may be caused by the selection effects. Two peaks within the intervalsz (0.5, 0.7) and (1.0, 1.1) are probably real. The corresponding scales of the QSO clustering along the line-of-sight are about 100h ^–1 Mpc (h is the Hubble constant in the units of 75 km s^–1 Mpc^–1). The possibility of some global quasi-periodical cycles for the processes of activity is discussed. The period of a cycle for the Seyfert and radio galaxies is about 1×10⁸ years that corresponds to the distances of about 30h ^–1 Mpc between the shells.     

Polar-ring galaxies: New candidates and statistics

We present the results of our observational study of two candidates for polar-ring galaxies (PRGs). Both objects, A2330-3751 and SDSS J000911.57-003654.7, are giant edge-on galaxies with large-scale structures resembling polar rings observed along their minor axes. The optical diameter of the putative ring reaches 60 kpc in A2330-3751 and 18 kpc in SDSS J000911.57-003654.7. To estimate the space density of PRGs, we have constructed their luminosity function in the range of B-band absolute magnitudes from −17_· ^m 5 to −21_· ^m 5. We have found that ∼10⁻³ of the nearby galaxies exhibit polar structures. Polar rings around early-type (E/S0) galaxies are encountered approximately a factor of 3 more frequently than those around spiral ones. According to our estimates, ∼20–30 PRGs in which large-scale rings are seen almost face-on must be observed among relatively bright galaxies (B ≤ 15 ^m ).     

Optical Identifications of IRAS Point Sources. Galaxies. VIII

A list of objects of the BIG (Byurakan-IRAS galaxies) sample is given: 89 galaxies identified with 55 point sources from the IRAS Point Source Catalog. The identifications were based on the Digital Sky Survey (DSS), the First Byurakan Survey, blue and red maps of the Palomar Observatory Sky Survey, and infrared fluxes at wavelengths of 12, 25, 60, and 100 mm in the region of +61° +65° and 05^h30^m 18^h 00^m with an area of 340 deg² (additional IR sources were identified). The optical coordinates of the identified galaxies, their departure from the IR coordinates, the V stellar magnitude, morphological type, angular size, and position angle were determined. The objects have optical magnitudes in the range of 12 ^m .5 - 21 ^m .5 and angular sizes in the range of 3 - 43. Finder charts for these objects from the DSS are given.     

Optical identification of iras point sources on the basis of low-dispersion FBS spectra. II

The second portion of optically identified point sources from the IRAS Point Source Catalog contains 104 objects. The identifications were made on the basis of the Digitized Sky Survey (DSS), the First Byurakan Survey (FBS), blue and red maps of the Palomar Survey (POSS), and infrared fluxes at wavelengths of 12, 25, 60, and 100 fim in the region of +61 ° ≤ δ ≤ +65°and 50^h30^m ≤ α ≤ 11^h15^m with an area of 157 sq. deg. Of the 114 sources in this region, 10 could not be identified because of the absence of the corresponding optical counterparts with the given coordinates. For the identified objects we determined their optical coordinates, their departure from the IR coordinates, the stellar V magnitudes, the color indices CI, and the preliminary types. The objects have optical magnitudes in the range of 8ⁿ–21^m. Of the 104 objects, 46 turned out to be stars of spectral types K and M, 1 is a planetary nebula, 3 are QSO candidates, and 54 are galaxies. In the present work we give a list of the 58 nonstellar objects. The identified galaxies include Seyfert candidates, interacting pairs, galaxies with companions and superassociations, etc. Finder charts for these objects from the DSS are given. Translated from Astrofizika, Vol. 40, No. 4, pp. 581–593, October-December, 1997.