VEXAS: VISTA EXtension to Auxiliary Surveys

Spiniello, C.; Agnello, Adriano

doi:10.1051/0004-6361/201936311

Cited by 5 publications

(4 citation statements)

References 76 publications

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“…The combined information across the optical and infrared, through the SDSS and WISE magnitudes, helps reducing the overlap between different classes in colour-magnitude space. The WISE depth is not a major limiting factor in the sample completeness as long as samples from the SDSS are considered, but it can affect the completeness significantly for deeper surveys (Spiniello & Agnello 2019). In view of performing the classification and photo-z estimation on the DES, and on the Rubin LSST later on, deeper mid-IR data are needed.…”

Section: Discussionmentioning

confidence: 99%

Mixture models for photometric redshifts

Agnello

Gall

2021

A&A

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Context. Determining photometric redshifts (photo-zs) of extragalactic sources to a high accuracy is paramount to measure distances in wide-field cosmological experiments. With only photometric information at hand, photo-zs are prone to systematic uncertainties in the intervening extinction and the unknown underlying spectral-energy distribution of different astrophysical sources, leading to degeneracies in the modern machine learning algorithm that impacts the level of accuracy for photo-z estimates. Aims. Here, we aim to resolve these model degeneracies and obtain a clear separation between intrinsic physical properties of astrophysical sources and extrinsic systematics. Furthermore, we aim to have meaningful estimates of the full photo-z probability distribution, and their uncertainties. Methods. We performed a probabilistic photo-z determination using mixture density networks (MDN). The training data set is composed of optical (griz photometric bands) point-spread-function and model magnitudes and extinction measurements from the SDSS-DR15 and WISE mid-infrared (3.4 μm and 4.6 μm) model magnitudes. We used infinite Gaussian mixture models to classify the objects in our data set as stars, galaxies, or quasars, and to determine the number of MDN components to achieve optimal performance. Results. The fraction of objects that are correctly split into the main classes of stars, galaxies, and quasars is 94%. Furthermore, our method improves the bias of photometric redshift estimation (i.e., the mean Δz = (zp − zs)/(1 + zs)) by one order of magnitude compared to the SDSS photo-z, and it decreases the fraction of 3σ outliers (i.e., 3 × rms(Δz) < Δz). The relative, root-mean-square systematic uncertainty in our resulting photo-zs is down to 1.7% for benchmark samples of low-redshift galaxies (zs < 0.5). Conclusions. We have demonstrated the feasibility of machine-learning-based methods that produce full probability distributions for photo-z estimates with a performance that is competitive with state-of-the art techniques. Our method can be applied to wide-field surveys where extinction can vary significantly across the sky and with sparse spectroscopic calibration samples. The code is publicly available.

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Section: Discussionmentioning

confidence: 99%

Mixture models for photometric redshifts

Agnello

Gall

2021

A&A

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“…WG2100-4452 was discovered 1 by as an extragalactic candidate with astrometric anomalies between the optical and infrared in VEXAS . Its source redshift is 0.920±0.002 and its deflector redshift is 0.203±0.002 (Spiniello et al 2019).…”

Section: Wg2100-4452mentioning

confidence: 96%

“…It has a high UV deficit and "blue" WISE colours, which are more similar to those of known white dwarfs and may explain why it was discovered only once the ESA-Gaia mission pipeline resolved it into multiple source detections. Its source redshift is 3.229±0.004, and the deflector's photometric redshit is 0.22±0.09, as it was too faint to obtain a secure spectroscopic redshift on the 10m SALT follow-up (PI L. Marchetti; Spiniello et al 2019).…”

Section: Wg0214-2105mentioning

confidence: 99%

STRIDES: automated uniform models for 30 quadruply imaged quasars

Schmidt

Treu

Birrer

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Gravitational time delays provide a powerful one step measurement of H0, independent of all other probes. One key ingredient in time delay cosmography are high accuracy lens models. Those are currently expensive to obtain, both, in terms of computing and investigator time (105 − 6 CPU hours and ∼0.5–1 year, respectively). Major improvements in modeling speed are therefore necessary to exploit the large number of lenses that are forecast to be discovered over the current decade. In order to bypass this roadblock, we develop an automated modeling pipeline and apply it to a sample of 31 lens systems, observed by the Hubble Space Telescope in multiple bands. Our automated pipeline can derive models for 30/31 lenses with few hours of human time and <100 CPU hours of computing time for a typical system. For each lens, we provide measurements of key parameters and predictions of magnification as well as time delays for the multiple images. We characterize the cosmography-readiness of our models using the stability of differences in Fermat potential (proportional to time delay) w.r.t. modeling choices. We find that for 10/30 lenses our models are cosmography or nearly cosmography grade (<3 per cent and 3-5 per cent variations). For 6/30 lenses the models are close to cosmography grade (5-10 per cent). These results utilize informative priors and will need to be confirmed by further analysis. However, they are also likely to improve by extending the pipeline modeling sequence and options. In conclusion, we show that uniform cosmography grade modeling of large strong lens samples is within reach.

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“…We have also looked for counterparts in the near-infrared VISTA Hemisphere Survey, which has a target depth is 20.6, 19.8, and 18.5 magnitudes for the J, H, and K bands, respectively (Spiniello & Agnello 2019). Again, no clear counterparts are seen at the position of the pulsar.…”

Section: Position and Proper Motionmentioning

confidence: 99%

The eccentric millisecond pulsar, PSR J0955−6150

Serylak

Krishnan

Freire

et al. 2022

A&A

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Context. PSR J0955−6150 is a member of an enigmatic class of eccentric millisecond pulsar (MSP) and helium white dwarf (He WD) systems (eMSPs), whose binary evolution is poorly understood and believed to be strikingly different to that of traditional MSP+He WD systems in circular orbits. Aims. Measuring the masses of the stars in this system is important for testing the different hypotheses for the formation of eMSPs. Methods. We carried out timing observations of this pulsar with the Parkes radio telescope using the 20 cm multibeam and ultra-wide bandwidth low-frequency (UWL) receivers, and the L-band receiver of the MeerKAT radio telescope. The pulse profiles were flux and polarisation calibrated, and a rotating-vector model (RVM) was fitted to the position angle of the linear polarisation of the combined MeerKAT data. Pulse times of arrival (ToAs) were obtained from these using standard pulsar analysis techniques and analysed using the TEMPO2 timing software. Results. Our observations reveal a strong frequency evolution of this MSP’s intensity, with a flux density spectral index (α) of −3.13(2). The improved sensitivity of MeerKAT resulted in a greater than tenfold improvement in the timing precision obtained compared to our older Parkes observations. This, combined with the eight-year timing baseline, has allowed precise measurements of a very small proper motion and three orbital post-Keplerian parameters, namely the rate of advance of periastron, ω̇ = 0.00152(1) deg yr−1, and the orthometric Shapiro delay parameters, h3 = 0.89(7) μs and ς = 0.88(2). Assuming general relativity, we obtain Mp = 1.71(2) M⊙ for the mass of the pulsar and Mc = 0.254(2) M⊙ for the mass of the companion; the orbital inclination is 83.2(4) degrees. Crucially, assuming that the position angle of the linear polarisation follows the RVM, we find that the spin axis has a misalignment relative to the orbital angular momentum of > 4.8deg at 99% confidence level. Conclusions. While the value of Mp falls well within the wide range observed in eMSPs, Mc is significantly smaller than expected from several formation hypotheses proposed, which are therefore unlikely to be correct and can be ruled out; Mc is also significantly different from the expected value for an ideal low mass X-ray binary evolution scenario. If the misalignment between the spin axis of the pulsar and the orbital angular momentum is to be believed, it suggests that the unknown process that created the orbital eccentricity of the binary was also capable of changing its orbital orientation, an important evidence for understanding the origin of eMSPs.

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VEXAS: VISTA EXtension to Auxiliary Surveys

Cited by 5 publications

References 76 publications

Mixture models for photometric redshifts

Mixture models for photometric redshifts

STRIDES: automated uniform models for 30 quadruply imaged quasars

The eccentric millisecond pulsar, PSR J0955−6150

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