scholarly journals QSO photometric redshifts from SDSS, WISE, and GALEX colours

2020 ◽  
Vol 493 (1) ◽  
pp. L70-L75
Author(s):  
S J Curran
Keyword(s):  
Near Infrared ◽  
Empirical Method ◽  
Machine Learning Techniques ◽  
Radio Sources ◽  
Photometric Redshifts ◽  
Stellar Objects ◽  
Vast Number ◽  
Quasi Stellar Objects ◽  
Continuum Radio ◽  
Non Gaussian

ABSTRACT Machine learning techniques, specifically the k-nearest neighbour algorithm applied to optical band colours, have had some success in predicting photometric redshifts of quasi-stellar objects (QSOs): Although the mean of differences between the spectroscopic and photometric redshifts, Δ$z$, is close to zero, the distribution of these differences remains wide and distinctly non-Gaussian. As per our previous empirical estimate of photometric redshifts, we find that the predictions can be significantly improved by adding colours from other wavebands, namely the near-infrared and ultraviolet. Self-testing this, by using half of the 33 643 strong QSO sample to train the algorithm, results in a significantly narrower spread in Δ$z$ for the remaining half of the sample. Using the whole QSO sample to train the algorithm, the same set of magnitudes return a similar spread in Δ$z$ for a sample of radio sources (quasars). Although the matching coincidence is relatively low (739 of the 3663 sources having photometry in the relevant bands), this is still significantly larger than from the empirical method (2 per cent) and thus may provide a method with which to obtain redshifts for the vast number of continuum radio sources expected to be detected with the next generation of large radio telescopes.

scholarly journals QSO photometric redshifts using machine learning and neural networks

2021 ◽  
Vol 503 (2) ◽  
pp. 2639-2650
Author(s):  
S J Curran ◽  
J P Moss ◽  
Y C Perrott
Keyword(s):  
Machine Learning ◽  
Near Infrared ◽  
Sloan Digital Sky Survey ◽  
Machine Learning Techniques ◽  
Data Sets ◽  
Photometric Redshifts ◽  
Stellar Objects ◽  
Wide Range ◽  
Large Continuum ◽  
Scientific Value

ABSTRACT The scientific value of the next generation of large continuum surveys would be greatly increased if the redshifts of the newly detected sources could be rapidly and reliably estimated. Given the observational expense of obtaining spectroscopic redshifts for the large number of new detections expected, there has been substantial recent work on using machine learning techniques to obtain photometric redshifts. Here, we compare the accuracy of the predicted photometric redshifts obtained from deep learning (DL) with the k-nearest neighbour (kNN) and the decision tree regression (DTR) algorithms. We find using a combination of near-infrared, visible, and ultraviolet magnitudes, trained upon a sample of Sloan Digital Sky Survey quasi-stellar objects, that the kNN and DL algorithms produce the best self-validation result with a standard deviation of σΔz = 0.24 (σΔz(norm) = 0.11). Testing on various subsamples, we find that the DL algorithm generally has lower values of σΔz, in addition to exhibiting a better performance in other measures. Our DL method, which uses an easy to implement off-the-shelf algorithm with neither filtering nor removal of outliers, performs similarly to other, more complex, algorithms, resulting in an accuracy of Δz < 0.1 up to z ∼ 2.5. Applying the DL algorithm trained on our 70 000 strong sample to other independent (radio-selected) data sets, we find σΔz ≤ 0.36 (σΔz(norm) ≤ 0.17) over a wide range of radio flux densities. This indicates much potential in using this method to determine photometric redshifts of quasars detected with the Square Kilometre Array.

scholarly journals THE HIGH A V Quasar Survey: Reddened Quasi-Stellar Objects selected from optical/near-infrared photometry. II.

2015 ◽  
Vol 217 (1) ◽  
pp. 5 ◽  
Author(s):  
J.-K. Krogager ◽  
S. Geier ◽  
J. P. U. Fynbo ◽  
B. P. Venemans ◽  
C. Ledoux ◽  
...  
Keyword(s):  
Near Infrared ◽  
Infrared Photometry ◽  
Stellar Objects ◽  
Quasi Stellar Objects

scholarly journals Quasi-stellar object redshift estimates from optical, near-infrared, and ultraviolet colours

2019 ◽  
Vol 629 ◽  
pp. A56 ◽  
Author(s):  
S. J. Curran ◽  
J. P. Moss
Keyword(s):  
Active Galactic Nuclei ◽  
Rest Frame ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Additional Contribution ◽  
Stellar Objects ◽  
Simple Estimate ◽  
Photometric Redshift ◽  
Wide Range ◽  
Quasi Stellar Objects

A simple estimate of the photometric redshift would prove invaluable to forthcoming continuum surveys on the next generation of large radio telescopes, as well as mitigating the existing bias towards the most optically bright sources. While there is a well-known correlation between the near-infrared K-band magnitude and redshift for galaxies, we find the K − z relation to break down for samples dominated by quasi-stellar objects. We hypothesise that this is due to the additional contribution to the near-infrared flux by the active galactic nucleus, and, as such, the K-band magnitude can only provide a lower limit to the redshift in the case of active galactic nuclei, which will dominate the radio surveys. From a large optical dataset, we find a tight relationship between the rest-frame (U − K)/(W2 − FUV) colour ratio and spectroscopic redshift over a sample of 17 000 sources, spanning z ≈ 0.1−5. Using the observed-frame ratios of (U − K)/(W2 − FUV) for redshifts of z ≲ 1, (I − W2)/(W3 − U) for 1 ≲ z ≲ 3, and (I − W2.5)/(W4 − R) for z ≳ 3, where W2.5 is the λ = 8.0 μm magnitude and the appropriate redshift ranges are estimated from the W2 (4.5 μm) magnitude, we find this to be a robust photometric redshift estimator for quasars. We suggest that the rest-frame U − K colour traces the excess flux from the AGN over this wide range of redshifts, although the W2 − FUV colour is required to break the degeneracy.

scholarly journals Radio Emission from Compact Objects

1972 ◽  
Vol 44 ◽  
pp. 190-213
Author(s):  
K. I. Kellermann
Keyword(s):  
Angular Size ◽  
Brightness Distribution ◽  
Compact Objects ◽  
Radio Sources ◽  
Stellar Objects ◽  
Large Intensity ◽  
Quasi Stellar Objects ◽  
One Year ◽  
Ngc 1275 ◽  
Compact Sources

Compact radio stars are associated with both galaxies and quasi-stellar objects; and there appears to be no way to distinguish between the radio galaxies and the quasi-stellar radio sources from their radio properties alone.The compact radio sources are opaque at the longer radio wavelengths and have spectra that are either peaked or complex. They have a complex brightness distribution and often contain components less than 0.001 arc sec in size.Many of the compact sources show large intensity variations and in NGC 1275 there is evidence for a change in the angular size during one year.

scholarly journals Detecting the highest redshift (z > 8) quasi-stellar objects in a wide, near-infrared slitless spectroscopic survey

2012 ◽  
Vol 420 (2) ◽  
pp. 1764-1778 ◽  
Author(s):  
Nathan Roche ◽  
Paolo Franzetti ◽  
Bianca Garilli ◽  
Giovanni Zamorani ◽  
Andrea Cimatti ◽  
...  
Keyword(s):  
Near Infrared ◽  
Stellar Objects ◽  
Quasi Stellar Objects

scholarly journals The Parkes 2700 MHz Survey (Tenth Part). Supplementary Catalogue for the Declination Zone +4° to +25°

1975 ◽  
Vol 28 (2) ◽  
pp. 239
Author(s):  
AJ Shimmins ◽  
JG Bolton ◽  
JV Wall
Keyword(s):  
Flux Density ◽  
Galactic Plane ◽  
Radio Sources ◽  
Stellar Objects ◽  
Quasi Stellar Objects

A catalogue of lSI radio sources is presented covering the declination zone +4� to +25� and all right ascensions, omitting two regions within approximately 10� of the galactic plane (R.A. 05h30'" to 07ho()m and R.A. lShOO'" to 2Oh30"'). The catalogue was compiled from a 'fast' finding survey at 2700 MHz aimed at detecting sources stronger than o� 5 Jy. Subsequently, measurements of accurate flux density and position were made on all the sources which were not in the Parkes 40S MHz catalogue and on a few sources in the 40S MHz catalogue for which only data of low accuracy were available. The' positions of sources were determined to an accuracy of 10" arc r.m.s. in both coordinates. Flux densities for most of the sources were also measured at 5009 MHz. Identifications are suggested for 17 galaxies and 62 quasi-stellar objects.

scholarly journals Further Identifications Of Radio Sources Between Declinations 0° And 20°

1966 ◽  
Vol 19 (3) ◽  
pp. 471 ◽  
Keyword(s):  
Radio Sources ◽  
Stellar Objects ◽  
Sky Survey ◽  
Position Data ◽  
Quasi Stellar Objects

Clarke, Bolton, and Shimmins (1966) have recently suggested identifications for 138 of the radio sources listed in the Parkes catalogue for declinations 0� to +20� (Day, Shimmins, Ekers, and Cole 1966). The identifications were made from inspection of the Palomar Sky Survey plates in areas 2' arc square centred on the catalogue positions. In general, identifications were suggested only for galaxies or possible quasi-stellar objects brighter than 17m . 5, in order to avoid the possibility of chance coincidences. Where objects fainter than 17m . 5 were suggested, position data of higher accuracy were available, due principally to unpublished measurements by Shimmins, Clarke, and Ekers with the 210 ft telescope.

scholarly journals Accurate Positions and Some Optical Identifications for 255 Radio Sources Between Declinations +20° and ?33°

1969 ◽  
Vol 22 (2) ◽  
pp. 237 ◽  
Author(s):  
Jeannette K Merkelijn
Keyword(s):  
Radio Sources ◽  
Stellar Objects ◽  
Quasi Stellar Objects ◽  
Optical Identifications

Accurate positions have been measured at 2700 MHz for 255 sources from the Parkes catalogue between declinations +20� and -33�. The estimated accuracy in both coordinates is approximately 15N arc. For 103 of the sources, identifications are suggested using the accurate positions. Sixty-two of the sources are identified with galaxies and 41 with quasi-stellar objects.

scholarly journals New Optical Identifications from the Parkes 2700 MHz Resurvey of the ± 4° Declination Zone

1982 ◽  
Vol 35 (2) ◽  
pp. 207 ◽  
Author(s):  
Ann Savage ◽  
JG Bolton ◽  
Jenny Trett
Keyword(s):  
Radio Sources ◽  
Stellar Objects ◽  
Sky Survey ◽  
Quasi Stellar Objects ◽  
Optical Identifications

Identifications are suggested for 59 radio sources from the resurvey of declination zone �4�, 27 with galaxies and 32 with stellar objects; 19 of the latter are confirmed as quasi-stellar objects (QSOs). The identifications were made from the Palomar Sky Survey prints plus supplementary plates taken with the Palomar and U.K. Schmidt telescopes and the Anglo-Australian 3�9 m telescope.

scholarly journals Observations of the Linear Polarization of Radio Sources at 6 cm Wavelength

1968 ◽  
Vol 21 (4) ◽  
pp. 493 ◽  
Author(s):  
D Morris ◽  
JB Whiteoak
Keyword(s):  
Linear Polarization ◽  
High Frequency ◽  
Wavelength Dependence ◽  
Radio Galaxies ◽  
Short Wave ◽  
Radio Sources ◽  
Polarization Data ◽  
Stellar Objects ◽  
Quasi Stellar Objects

The polarizations of 45 sources have been measured at 6 cm wavelength and have been compared with values obtained at longer wavelengths. The resulting wavelength dependence has been studied in relation to the spectra of the sources. For the quasi. stellar objects in particular, polarization features at short wave� lengths are associated with the young components of the source which radiate at high frequency. However, it is not possible to distinguish between radio galaxies and quasi-stellar objects solely on the basis of polarization data.

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