The meaning of WISE colours – I. The Galaxy and its satellites

Nikutta, Robert; Hunt-Walker, Nicholas; Nenkova, Maia; Ivezić, Željko; Elitzur, Moshe

doi:10.1093/mnras/stu1087

Cited by 74 publications

(77 citation statements)

References 61 publications

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“…Quasar templates, both with and without reddening, show a poor fit to the spectrum of object CQ095924.4+020842.6. The photometry at MIR wavelengths disagrees with typical quasar MIR colors (Nikutta et al 2014) as well. Because several stellar absorption lines at z = 0.05 are detected in the spectrum, we can identify a low-redshift quiescent galaxy as contribution to the SED.…”

Section: Spectroscopic Analysismentioning

confidence: 58%

Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

Heintz

Fynbo

Møller

et al. 2016

A&A

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The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high A V quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21% +9 −5 of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39% +9 −8 reddened quasars defined by having A V > 0.1, and 21% +9 −5 of the sample having E(B − V) > 0.1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g − r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J < 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys.

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Section: Spectroscopic Analysismentioning

confidence: 58%

Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

Heintz

Fynbo

Møller

et al. 2016

A&A

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“…Given that most QSOs are eliminated, as they do not have light curves that resemble RR Lyr, and adding in a check with NED, the contamination rate of QSOs within the sample selected for spectroscopy can be kept very low and can, as described above, be expected to fall with time as the survey time coverage increases. WISE colors (Wright et al 2010) can also be used to cut down the fraction of QSO contamination (Nikutta et al 2014) due to the difference in spectral slope between a power law and a (hot) thermal spectrum, but they are of limited use for such distant objects, as they are often so faint that only the W1 color is given in the WISE catalog.…”

Section: Contaminants In the Sample Of Candidate Rr Lyr Starsmentioning

confidence: 99%

The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility*

Cohen

Sesar

Bahnolzer³

et al. 2017

ApJ

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RR Lyrae stars are ideal massless tracers that can be used to study the total mass and dark matter content of the outer halo of the Milky Way (MW). This is because they are easy to find in the light-curve databases of large stellar surveys and their distances can be determined with only knowledge of the light curve. We present here a sample of 112RR Lyr stars beyond 50 kpc in the outer halo of the MW, excluding the Sgr streams, for which we have obtained moderate-resolution spectra with Deimos on the Keck II Telescope. Four of these have distances exceeding 100 kpc. These were selected from a much larger set of 447candidate RR Lyr stars that were datamined using machine-learning techniques applied to the light curves of variable stars in the Palomar Transient Facility database. The observed radial velocities taken at the phase of the variable corresponding to the time of observation were converted to systemic radial velocities in the Galactic standard of rest. From our sample of 112RR Lyr stars we determine the radial velocity dispersion in the outer halo of the MW to be ∼90 km s −1 at 50kpc, falling to about 65 km s −1 near 100kpc once a small number of major outliers are removed. With reasonable estimates of the completeness of our sample of 447candidates and assuming a spherical halo, we find that the stellar density in the outer halo declines as r 4 -.

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“…More recently, Ferraro et al (2015) have defined their own colour cuts to identify galaxies and quasars from the WISE database; however, this left positiondependent contamination visible in all-sky maps. Nikutta et al (2014) have explored WISE colours of Galactic and other nearby sources, while Mateos et al (2012) have used the XMM-Newton survey to define a WISE colour-based selection of luminous AGN. The latter criterion has recently been applied to the all-sky WISE data by Secrest et al (2015) to select a sample of 1.4 million AGN candidates.…”

Section: Introductionmentioning

confidence: 99%

Towards automatic classification of all WISE sources

Kurcz

Bilicki

Solarz

et al. 2016

A&A

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Context. The Wide-field Infrared Survey Explorer (WISE) has detected hundreds of millions of sources over the entire sky. Classifying them reliably is, however, a challenging task owing to degeneracies in WISE multicolour space and low levels of detection in its two longest-wavelength bandpasses. Simple colour cuts are often not sufficient; for satisfactory levels of completeness and purity, more sophisticated classification methods are needed. Aims. Here we aim to obtain comprehensive and reliable star, galaxy, and quasar catalogues based on automatic source classification in full-sky WISE data. This means that the final classification will employ only parameters available from WISE itself, in particular those which are reliably measured for the majority of sources. Methods. For the automatic classification we applied a supervised machine learning algorithm, support vector machines (SVM). It requires a training sample with relevant classes already identified, and we chose to use the SDSS spectroscopic dataset (DR10) for that purpose. We tested the performance of two kernels used by the classifier, and determined the minimum number of sources in the training set required to achieve stable classification, as well as the minimum dimension of the parameter space. We also tested SVM classification accuracy as a function of extinction and apparent magnitude. Thus, the calibrated classifier was finally applied to all-sky WISE data, flux-limited to 16 mag (Vega) in the 3.4 µm channel. Results. By calibrating on the test data drawn from SDSS, we first established that a polynomial kernel is preferred over a radial one for this particular dataset. Next, using three classification parameters (W1 magnitude, W1 − W2 colour, and a differential aperture magnitude) we obtained very good classification efficiency in all the tests. At the bright end, the completeness for stars and galaxies reaches ∼95%, deteriorating to ∼80% at W1 = 16 mag, while for quasars it stays at a level of ∼95% independently of magnitude. Similar numbers are obtained for purity. Application of the classifier to full-sky WISE data and appropriate a posteriori cleaning allowed us to obtain catalogues of star and galaxy candidates that appear reliable. However, the sources flagged by the classifier as "quasars" are in fact dominated by dusty galaxies; they also exhibit contamination from sources located mainly at low ecliptic latitudes, consistent with solar system objects.

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The meaning of WISE colours – I. The Galaxy and its satellites

Cited by 74 publications

References 61 publications

Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility*

Towards automatic classification of all WISE sources

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