The optical luminosity function of LOFAR radio-selected quasars at 1.4 ≤ z ≤ 5.0 in the NDWFS-Boötes field

We present an estimate of the optical luminosity function (OLF) of LOFAR radio-selected quasars (RSQs) at 1.4 < z < 5.0 in the 9.3 deg2 NOAO Deep Wide-field survey (NDWFS) of the Boötes field. The selection was based on optical and mid-infrared photometry used to train three different machine learning (ML) algorithms (Random forest, SVM, Bootstrap aggregation). Objects taken as quasars by the ML algorithms are required to be detected at ≥5σ significance in deep radio maps to be classified as candidate quasars. The optical imaging came from the Sloan Digital Sky Survey and the Pan-STARRS1 3π survey; mid-infrared photometry was taken from the Spitzer Deep, Wide-Field Survey; and radio data was obtained from deep LOFAR imaging of the NDWFS-Boötes field. The requirement of a 5σ LOFAR detection allowed us to reduce the stellar contamination in our sample by two orders of magnitude. The sample comprises 130 objects, including both photometrically selected candidate quasars (47) and spectroscopically confirmed quasars (83). The spectral energy distributions calculated using deep photometry available for the NDWFS-Boötes field confirm the validity of the photometrically selected quasars using the ML algorithms as robust candidate quasars. The depth of our LOFAR observations allowed us to detect the radio-emission of quasars that would be otherwise classified as radio-quiet. Around 65% of the quasars in the sample are fainter than M1450 = −24.0, a regime where the OLF of quasars selected through their radio emission, has not been investigated in detail. It has been demonstrated that in cases where mid-infrared wedge-based AGN selection is not possible due to a lack of appropriate data, the selection of quasars using ML algorithms trained with optical and infrared photometry in combination with LOFAR data provides an excellent approach for obtaining samples of quasars. The OLF of RSQs can be described by pure luminosity evolution at z < 2.4, and a combined luminosity and density evolution at z > 2.4. The faint-end slope, α, becomes steeper with increasing redshift. This trend is consistent with previous studies of faint quasars (M1450 ≤ −22.0). We demonstrate that RSQs show an evolution that is very similar to that exhibited by faint quasars. By comparing the spatial density of RSQs with that of the total (radio-detected plus radio-undetected) faint quasar population at similar redshifts, we find that RSQs may compose up to ∼20% of the whole faint quasar population. This fraction, within uncertainties, is constant with redshift. Finally, we discuss how the compactness of the RSQs radio-morphologies and their steep spectral indices could provide valuable insights into how quasar and radio activity are triggered in these systems.

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Effectiveness of WISE colour-based selection techniques to uncover obscured AGN

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314003792 ◽

2013 ◽

Vol 9 (S304) ◽

pp. 209-212

Author(s):

S. Mateos

Keyword(s):

Sloan Digital Sky Survey ◽

Spectral Energy ◽

Wide Field ◽

Mid Infrared ◽

Selection Technique ◽

X Ray ◽

Sky Survey ◽

Two Samples ◽

Optical Surveys

AbstractWe present a highly reliable and efficient mid-infrared colour-based selection technique for luminous active galactic nuclei (AGN) using the Wide-field Infrared Survey Explorer (WISE) survey. Our technique is designed to identify objects with red mid-infrared power-law spectral energy distributions. We studied the dependency of our mid-infrared selection on the AGN intrinsic luminosity and the effectiveness of our technique to uncover obscured AGN missed in X-ray surveys. To do so we used two samples of luminous AGN independently selected in hard X-ray and optical surveys. We used the largest catalogue of 887 [OIII] λ5007-selected type 2 quasars (QSO2s) at z≲0.83 in the literature from the Sloan Digital Sky Survey (SDSS), and the 258 hard (>4.5 keV) X-ray-selected AGN from the Bright Ultrahard XMM-Newton Survey (BUXS). The effectiveness of our mid-infrared selection technique increases with the AGN luminosity. At high luminosities and at least up to z~1 our technique is very effective at identifying both Compton-thin and Compton-thick AGN.

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Transformations from WISE to 2MASS, SDSS and BVI Photometric Systems: II. Transformation Equations for Red-Clump Stars

Publications of the Astronomical Society of Australia ◽

10.1071/as11078 ◽

2012 ◽

Vol 29 (2) ◽

pp. 121-131 ◽

Cited By ~ 5

Author(s):

S. Bilir ◽

S. Karaali ◽

N. D. Dağtekin ◽

Ö. Önal ◽

S. Ak ◽

...

Keyword(s):

Field Survey ◽

Sloan Digital Sky Survey ◽

Wide Field ◽

Experiment Data ◽

The Third ◽

Final Sample ◽

Sky Survey ◽

Data Release ◽

Red Clump ◽

Absolute Magnitudes

AbstractWe present colour transformations for the conversion of Wide-Field Survey Explorer W1, W2, and W3 magnitudes to the Johnson–Cousins BVIc, Sloan Digital Sky Survey gri, and Two Micron All Sky Survey JHKs photometric systems, for red clump (RC) stars. RC stars were selected from the Third Radial Velocity Experiment Data Release. The apparent magnitudes were collected by matching the coordinates of this sample with different photometric catalogues. The final sample (355 RC stars) was used to obtain metallicitydependent and free-of-metallicity transformations. These transformations combined with known absolute magnitudes at shorter wavelengths can be used in space density determinations for the Galactic (thin and thick) discs at distances larger than the ones evaluated with JHKs photometry alone, hence providing a powerful tool in the analysis of Galactic structure.

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The Optical/Near-IR Colours of Red Quasars

Publications of the Astronomical Society of Australia ◽

10.1071/as00056 ◽

2000 ◽

Vol 17 (1) ◽

pp. 56-71 ◽

Cited By ~ 58

Author(s):

Paul J. Francis ◽

Matthew T. Whiting ◽

Rachel L. Webster

Keyword(s):

Power Law ◽

High Redshift ◽

Sloan Digital Sky Survey ◽

Spectral Energy ◽

Spectral Energy Distributions ◽

Energy Distributions ◽

Red Power ◽

Near Ir ◽

Sky Survey ◽

Ir Photometry

AbstractWe present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fv∝v0 to Fv∝v−2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19·6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band.

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The optically selected 1.4-GHz quasar luminosity function below 1 mJy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa112 ◽

2020 ◽

Vol 492 (4) ◽

pp. 5297-5312 ◽

Cited By ~ 1

Author(s):

Eliab Malefahlo ◽

Mario G Santos ◽

Matt J Jarvis ◽

Sarah V White ◽

Jonathan T L Zwart

Keyword(s):

Luminosity Function ◽

Significant Contribution ◽

Detection Threshold ◽

Simulated Data ◽

Sloan Digital Sky Survey ◽

Radio Luminosity ◽

Host Galaxies ◽

Star Forming ◽

Sky Survey ◽

Radio Luminosity Function

ABSTRACT We present the radio luminosity function (RLF) of optically selected quasars below 1 mJy, constructed by applying a Bayesian-fitting stacking technique to objects well below the nominal radio flux density limit. We test the technique using simulated data, confirming that we can reconstruct the RLF over three orders of magnitude below the typical 5σ detection threshold. We apply our method to 1.4-GHz flux densities from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey, extracted at the positions of optical quasars from the Sloan Digital Sky Survey over seven redshift bins up to z = 2.15, and measure the RLF down to two orders of magnitude below the FIRST detection threshold. In the lowest redshift bin (0.2 < z < 0.45), we find that our measured RLF agrees well with deeper data from the literature. The RLF for the radio-loud quasars flattens below $\log _{10}[L_{1.4}/{\rm W\, Hz}^{-1}] \approx 25.5$ and becomes steeper again below $\log _{10}[L_{1.4}/{\rm W\, Hz}^{-1}] \approx 24.8$, where radio-quiet quasars start to emerge. The radio luminosity where radio-quiet quasars emerge coincides with the luminosity where star-forming galaxies are expected to start dominating the radio source counts. This implies that there could be a significant contribution from star formation in the host galaxies, but additional data are required to investigate this further. The higher redshift bins show a similar behaviour to the lowest z bin, implying that the same physical process may be responsible.

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Chemical abundances of Seyfert 2 AGNs – II. N2 metallicity calibration based on SDSS

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa193 ◽

2020 ◽

Vol 492 (4) ◽

pp. 5675-5683 ◽

Cited By ~ 3

Author(s):

S P Carvalho ◽

O L Dors ◽

M V Cardaci ◽

G F Hägele ◽

A C Krabbe ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Sloan Digital Sky Survey ◽

Spectral Energy ◽

Chemical Abundances ◽

Data Set ◽

Line Intensity Ratio ◽

Sky Survey ◽

Empirical Calibration ◽

Semi Empirical ◽

Photoionization Model

ABSTRACT We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 active galactic nuclei and the N2 = log([N ii]λ6584/H α) emission-line intensity ratio. This calibration was derived through the [O iii]λ5007/[O ii]λ3727 versus N2 diagram containing observational data and photoionization model results obtained with the cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift $z \: \lesssim 0.4$) taken from the Sloan Digital Sky Survey DR7 data set. The obtained Z–N2 relation is valid for the range $0.3 \: \lesssim \: (Z/{\rm Z}_{\odot }) \: \lesssim \: 2.0$ that corresponds to $-0.7 \: \lesssim \: ({\rm N}2) \: \lesssim \: 0.6$. The effects of varying the ionization parameter (U), electron density and the slope of the spectral energy distribution on the Z estimations are of the order of the uncertainty produced by the error measurements of N2. This result indicates the large reliability of our Z –N2 calibration. A relation between U and the [O iii]/[O ii] line ratio, almost independent of other nebular parameter, was obtained.

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Extreme ionised outflows are more common when the radio emission is compact in AGN host galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936408 ◽

2019 ◽

Vol 631 ◽

pp. A132 ◽

Cited By ~ 4

Author(s):

S. J. Molyneux ◽

C. M. Harrison ◽

M. E. Jarvis

Keyword(s):

Radio Emission ◽

Emission Line ◽

Sloan Digital Sky Survey ◽

Line Profiles ◽

Host Galaxies ◽

Gas Kinematics ◽

Radio Jets ◽

Sky Survey ◽

Compact Sources

Using a sample of 2922 z < 0.2, spectroscopically identified active galactic nuclei (AGN), we explore the relationship between radio size and the prevalence of extreme ionised outflows, as traced using broad [O III] emission-line profiles in spectra obtained by the Sloan Digital Sky Survey (SDSS). To classify radio sources as compact or extended, we combined a machine-learning technique for morphological classification with size measurements from two-dimensional Gaussian models to data from all-sky radio surveys. We find that the two populations have statistically different [O III] emission-line profiles; the compact sources tend to have the most extreme gas kinematics. When the radio emission is confined within 3″ (i.e. within the spectroscopic fibre or ≲5 kpc at the median redshift), the chance of observing broad [O III] emission-line components, which are indicative of very high velocity outflows and have a full width at half-maximum > 1000 km s−1, is twice as high. This difference is greatest for the highest radio luminosity bin of log[L1.4 GHz/W Hz−1] = 23.5−24.5 where the AGN dominate the radio emission; specifically, > 1000 km s−1 components are almost four times as likely to occur when the radio emission is compact in this subsample. Our follow-up ≈0.3″–1″ resolution radio observations for a subset of targets in this luminosity range reveal that radio jets and lobes are prevalent, and suggest that compact jets might be responsible for the stronger outflows in the wider sample. Our results are limited by the available relatively shallow all-sky radio surveys, but forthcoming surveys will provide a more complete picture of the connection between radio emission and outflows. Overall, our results add to the growing body of evidence that ionised outflows and compact radio emission in highly accreting “radiative” AGN are closely connected, possibly as a result of young or weak radio jets.

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The Extremely Luminous Quasar Survey in the Sloan Digital Sky Survey Footprint. III. The South Galactic Cap Sample and the Quasar Luminosity Function at Cosmic Noon

The Astrophysical Journal ◽

10.3847/1538-4357/aaf86c ◽

2019 ◽

Vol 871 (2) ◽

pp. 258 ◽

Cited By ~ 7

Author(s):

Jan-Torge Schindler ◽

Xiaohui Fan ◽

Ian D. McGreer ◽

Jinyi Yang ◽

Feige Wang ◽

...

Keyword(s):

Luminosity Function ◽

Sloan Digital Sky Survey ◽

The South ◽

Sky Survey

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A hot white dwarf luminosity function from the Sloan Digital Sky Survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/200912094 ◽

2009 ◽

Vol 508 (1) ◽

pp. 339-344 ◽

Cited By ~ 25

Author(s):

J. Krzesinski ◽

S. J. Kleinman ◽

A. Nitta ◽

S. Hügelmeyer ◽

S. Dreizler ◽

...

Keyword(s):

White Dwarf ◽

Luminosity Function ◽

Sloan Digital Sky Survey ◽

Sky Survey

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Stellar Populations in M31 from Broad-band Photometry

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311022770 ◽

2010 ◽

Vol 6 (S277) ◽

pp. 199-202

Author(s):

Antti Tamm ◽

Elmo Tempel ◽

Peeter Tenjes ◽

Taavi Tuvikene

Keyword(s):

Complex Structure ◽

Broad Band ◽

Far Infrared ◽

Stellar Populations ◽

Sloan Digital Sky Survey ◽

Spectral Energy ◽

3 Dimensional ◽

Sky Survey ◽

The Galaxy ◽

M 31

AbstractDue to its proximity, size, complex structure and high inclination angle, M31 offers an excellent opportunity for studying galactic structures outside the Milky Way and for drawing implications for their cosmological origin. We have studied the stellar populations of M 31 using the Sloan Digital Sky Survey (SDSS) photometry and the Spitzer far-infrared (FIR) mappings of dust. Combining these data, we have constructed a 3-dimensional model of the galaxy, laying constraints on the intrinsic (dust-free) properties of the galaxy and its stellar populations: their apparent and intrinsic luminosities, luminosity distributions, colours, shapes and sizes. We have interpreted the derived spectral energy distributions with synthetic stellar populations created with the Starburst99 software, in order to constrain the ages and masses of the stellar components.

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