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A Survey for Large Separation Lensing Among 9100 FIRST Quasars
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ract e carried out a survey for gravitationally-lensed objects, sources in the FIRST 20cm radio survey, that have point-like l counterparts in the digitizations of the POSS. From the tics of ongoing surveys that search for quasars among FIRST s, we estimate that there are about 9100 quasars in this sample. nd 15 gravitational lenses candidates. Spectroscopy se candidates shows that none of the pairs are lensed quasars. ets an upper limit of 3.3x10 -4 (95% CL) on the lensing fraction s survey. Our procedure is novel in that our exhaustive for lensed objects does not require prior identification of the s in the sample as such. Characterization of the FIRST-selected population will enable using our result to constrain the mass ties of clusters. The Sample Selection Process We selected FIRST radio sources (White et al. 1997) from the FIRST cataloge (1999, July 21 version) that have an optical counterpart in the APM catalog (McMahon & Irwin 1992), with positional coincidence smaller than 2.”5 in both the O and E bands, with color index O-E<2 mag., and that are point like as detected by the APM classification algorithm, at least on one of the O or E POSS-I/UKST plates. In this sample, there are 12,576 quasars candidates, with the above criteria. Based on recent result from the FBQS and FFQS (White et al. 2000; Brotherton, 1999 - private communication), we estimates that there are about 9100 quasars in our sample out of the 12,576 candidates. Among all the quasars candidates defined by the above criteria, we selected all the pairs of radio-optical quasars candidates with separation between 5” to 30” for follow-up observations. Analysis A detailed interpretation of the results requires good knowledge (1) the joint radio-optical luminosity function, to quantify doub magnification bias. The magnification bias reflects the over- (or representation of lensed objects in our survey, compared to purel geometrical cross-section calculations. (2) the redshift distribution of the quasars in our sample, to qu the probed pathlength. (1) Using the faint-end number counts distribution of radio-optic quasars detected both in the 20cm band (Richards 2000) and in the optical (Liu et al. 1999; Impey & Petry 2000), we derived a lower to our survey double-flux magnification-bias. We find that the magnification bias is B~1-2. (2) From multi-color photometry, the median redshift of the quasa in our sample is about 1.4 (Rix - private communication). The expected optical-depth for large-separation (>5”) lensing i in the range 10 -5 -10 -2 (Bartelmann et al. 1995; Maoz et al. 1997; Wambsganss et al. 1998; Li & Ostriker 2000; Wyithe et al. 2000). In light of these wide-ranging predictions, empirical constraints in order. Preliminary Results We estimated the expected probability for lensing in our sample, using: (i) the estimated magnification bias; (ii) the source redshift distribution; (iii) the completeness fac due to the range of separation probed in our survey (i.e., 5”-30” and assuming, (iv) the Girardi et al. (1998) cluster mass functi redshift; (v) SIS lens model; (vi) 0 =0.3, 0 =0.7 cosmology. We get the expected probability for lenseing in our sample, of We conclude that our non-detection is consistent with this simple However, our 95% CL observational upper limit of 3.3x10 -4 does rul very concentrated cluster mass profiles (Maoz et al. 1997). This limits are also in conflict with the Wambsganss et al. (1998 simulations: scaling their results to our typical source redshift can reject their =1 CDM model with 99% CL. Observations We obtained spectra for all candidates. The spectra were obtained using the TWIN double- channel spectrograph on the Calar-Alto 3.5m telescope. The spectra for one pair, was obtained using the Keck-II 10m telescope with the LRIS spectrograph. Our observations show that none of the candidates turned up by our selection process is a gravitationally lensed quasar. Therefore, we sets an upper limit of 3.3x10 -4 (95% CL) on the lensing fraction in our sample. 1- School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel-Aviv 69978, Israel 2-Max-Planck-Institut fr Astronomie, Knigstuhl 17, D-69117 Heidelberg, Germany 3-Centro Astronomico Hispano-Aleman, Apdo 511, E-04080 Almeria, Spain 4-Racah Institute of Physics, The Hebrew Universitym Jerusalem 91904, Israel 1,2 2 1 3 4 Quasars candidates position in Aitoff projection. Spectra of candidate pairs. Vertical axis is counts in arbitrary units and horizontal axis is wavelength in angstrom. Additive shifts have been applied to some of the spectra for display purposes.
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A Survey for Large Separation Lensing Among 9100 FIRST Quasars. 1,2. 2. 4. 1. 3. 1- School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel-Aviv 69978, Israel 2-Max-Planck-Institut fr Astronomie, K צ nigstuhl 17, D-69117 Heidelberg, Germany - PowerPoint PPT Presentation
Transcript of A Survey for Large Separation Lensing Among 9100 FIRST Quasars
AbstractWe have carried out a survey for gravitationally-lensed objects,among sources in the FIRST 20cm radio survey, that have point-likeoptical counterparts in the digitizations of the POSS. From thestatistics of ongoing surveys that search for quasars among FIRSTsources, we estimate that there are about 9100 quasars in this sample.We found 15 gravitational lenses candidates. Spectroscopyof these candidates shows that none of the pairs are lensed quasars.This sets an upper limit of 3.3x10-4 (95% CL) on the lensing fractionin this survey. Our procedure is novel in that our exhaustivesearch for lensed objects does not require prior identification of thequasars in the sample as such. Characterization of the FIRST-selectedquasar population will enable using our result to constrain the massproperties of clusters.
The Sample Selection ProcessWe selected FIRST radio sources (White et al. 1997) from theFIRST cataloge (1999, July 21 version) that have an opticalcounterpart in the APM catalog (McMahon & Irwin 1992), withpositional coincidence smaller than 2.”5 in both the O and E bands,with color index O-E<2 mag., and that are point like as detectedby the APM classification algorithm, at least on one of the O or EPOSS-I/UKST plates. In this sample, there are 12,576 quasarscandidates, with the above criteria. Based on recent result fromthe FBQS and FFQS (White et al. 2000; Brotherton, 1999 - privatecommunication), we estimates that there are about 9100 quasarsin our sample out of the 12,576 candidates.Among all the quasars candidates defined by the above criteria, weselected all the pairs of radio-optical quasars candidates withseparation between 5” to 30” for follow-up observations.
AnalysisA detailed interpretation of the results requires good knowledge of(1) the joint radio-optical luminosity function, to quantify double-flux magnification bias. The magnification bias reflects the over- (or under)representation of lensed objects in our survey, compared to purelygeometrical cross-section calculations.(2) the redshift distribution of the quasars in our sample, to quantifythe probed pathlength.
(1) Using the faint-end number counts distribution of radio-opticalquasars detected both in the 20cm band (Richards 2000) and in theoptical (Liu et al. 1999; Impey & Petry 2000), we derived a lower limitto our survey double-flux magnification-bias. We find that themagnification bias is B~1-2.(2) From multi-color photometry, the median redshift of the quasarsin our sample is about 1.4 (Rix - private communication).
The expected optical-depth for large-separation (>5”) lensing isin the range 10-5-10-2 (Bartelmann et al. 1995; Maoz et al. 1997;Wambsganss et al. 1998; Li & Ostriker 2000; Wyithe et al. 2000).In light of these wide-ranging predictions, empirical constraints seemsin order.
Preliminary ResultsWe estimated the expected probability for lensing in our sample,using: (i) the estimated magnification bias;(ii) the source redshift distribution; (iii) the completeness factor (0.66)due to the range of separation probed in our survey (i.e., 5”-30”);and assuming, (iv) the Girardi et al. (1998) cluster mass function for allredshift; (v) SIS lens model; (vi) 0=0.3, 0=0.7 cosmology.We get the expected probability for lenseing in our sample, of ~2x10-4.We conclude that our non-detection is consistent with this simple model.
However, our 95% CL observational upper limit of 3.3x10-4 does rule outvery concentrated cluster mass profiles (Maoz et al. 1997).This limits are also in conflict with the Wambsganss et al. (1998)simulations: scaling their results to our typical source redshift, wecan reject their =1 CDM model with 99% CL.
ObservationsWe obtained spectra for all candidates. The spectrawere obtained using the TWIN double-channelspectrograph on the Calar-Alto 3.5m telescope.The spectra for one pair, was obtained using theKeck-II 10m telescope with the LRIS spectrograph.
Our observations show that none of the candidatesturned up by our selection process is a gravitationally lensed quasar. Therefore, we sets an upper limit of3.3x10-4 (95% CL) on the lensing fraction in our sample.
1- School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel-Aviv 69978, Israel
2-Max-Planck-Institut fr Astronomie, Kצnigstuhl 17, D-69117 Heidelberg, Germany
3-Centro Astronomico Hispano-Aleman, Apdo 511, E-04080 Almeria, Spain
4-Racah Institute of Physics, The Hebrew Universitym Jerusalem 91904, Israel
1,2 2 1 34
Quasars candidates position in Aitoff projection.
Spectra of candidate pairs. Vertical axis is counts in arbitraryunits and horizontal axis is wavelength in angstrom. Additiveshifts have been applied to some of the spectra for displaypurposes.
AnalysisA detailed interpretation of the results requires good knowledge of(1) the joint radio-optical luminosity function, to quantify double-flux magnification bias. The magnification bias reflects the over- (or under)representation of lensed objects in our survey, compared to purelygeometrical cross-section calculations.(2) the redshift distribution of the quasars in our sample, to quantifythe probed pathlength.
(1) Using the faint-end number counts distribution of radio-opticalquasars detected both in the 20cm band (Richards 2000) and in theoptical (Liu et al. 1999; Impey & Petry 2000), we derived a lower limitto our survey double-flux magnification-bias. We find that themagnification bias is B~1-2.(2) From multi-color photometry, the median redshift of the quasarsin our sample is about 1.4 (Rix - private communication).
The expected optical-depth for large-separation (>5”) lensing isin the range 10-5-10-2 (Bartelmann et al. 1995; Maoz et al. 1997;Wambsganss et al. 1998; Li & Ostriker 2000; Wyithe et al. 2000).In light of these wide-ranging predictions, empirical constraints seemsin order.
Priliminary Results(1) We estimated the expected probability for lensing in our sample,using: (i) the estimated magnification bias;(ii) the source redshift distribution; (iii) the completeness factor (0.66)due to the range of separation probed in our survey (i.e., 5”-30”);and assuming, (iv) the Girardi et al. (1998) cluster mass function for allredshift; (v) SIS lens model; (vi) 0=0.3, 0=0.7 cosmology.We get the expected probability for lenseing in our sample, of ~2x10 -4.Therefore, with this simple model and our 95% CL observationalupper limit of 3.3x10-4 for the lensing probability in our sample,it is not possible to constrain the parameter space.
(2) Based on Wambsganss et al. (1998) simulations, and scaling theirresults to our typical source redshift, we can reject their =1 CDM modelwith 99% CL.
The Sample Selection ProcessWe selected FIRST radio sources (White et al. 1997) from theFIRST cataloge (1999, July 21 version) that have an opticalcounterpart in the APM catalog (McMahon & Irwin 1992), withpositional coincidence smaller than 2.”5 in both the O and E bands,with color index O-E<2 mag., and that are point like as detectedby the APM classification algorithm, at least on one of the O or EPOSS-I/UKST plates. In this sample, there are 12,576 quasarscandidates, with the above criteria. Based on recent result fromthe FBQS and FFQS (White et al. 2000; Brotherton, 1999 - privatecommunication), we estimates that there are about 9100 quasarsin our sample out of the 12,576 candidates.Among all the quasars candidates defined by the above criteria, weselected all the pairs of radio-optical quasars candidates withseparation between 5” to 30” for follow-up observations.
ObservationsWe obtained spectra for all candidates. The spectrawere obtained using the TWIN double-channelspectrograph on the Calar-Alto 3.5m telescope.The spectra for one pair, was obtained using theKeck-II 10m telescope with the LRIS spectrograph.
Our observations show that none of the candidatesturned up by our selection process is a gravitationally lensed quasar. Therefore, we sets an upper limit of3.3x10-4 (95% CL) on the lensing fraction in our sample.
AnalysisA detailed interpretation of the results requires good knowledge of(1) the joint radio-optical luminosity function, to quantify double-flux magnification bias. The magnification bias reflects the over- (or under)representation of lensed objects in our survey, compared to purelygeometrical cross-section calculations; and (2) the redshift distributionof the quasars in our sample, to quantify the probed pathlength.
(1) Using the faint-end number counts distribution of radio-opticalquasars detected both in the 20cm band (Richards 2000) and in theoptical (Liu et al. 1999; Impey & Petry 2000), we derived a lower limitto our survey double-flux magnification-bias. We find that themagnification bias is larger than unity.(2) The median redshift of the quasars in our sample is about 1.4(Rix - private communication)
Priliminary Results(1) Starting with the 3.3x10-4 (95% CL) upper limit on the probabilityfor lensing in our survey, and using: (i) the magnification bias lowerlimit; (ii) our quasars redshift distribution; (iii) the completenessfactor (0.66) due to the range of separation probed in our survey(i.e., 5”-30”); and assuming, (iv) the Girardi et al. (1998) clustersmass function; (v) SIS lens model; (vi) 0=0.3, 0=0.7 cosmology.We get a lower limit for the expected probability for lensed quasars in oursample, of > 1.3x10-4.
(2) Based on Wambsganss et al. (1998) simulations, and scaling theirresults to our typical source redshift, we can reject the CDM model with99% CL.
