A hierarchical model for the ages of Galactic halo white dwarfs

Si, Shijing; Dyk, David A. van; Hippel, Ted von; Robinson, Elliot; Webster, Aaron; Stenning, David C.

doi:10.1093/mnras/stx765

Cited by 10 publications

(9 citation statements)

References 68 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The two objects reported in Gianninas et al (2015), J0301-0044 and J1107+4855, with ages and kinematic characteristics of the halo population, are included in our sample. In Si et al (2017), ten halo white dwarfs were proposed, of which only four are in our 100 pc sample (the two previous ones also included in Gianninas et al 2015 plus J1205+550 and J0346+246), being all four of them identified as halo members by our algorithm. This last object is the well-known and intensively studied ultracool white dwarf WD 0346+246 (J0346+2455) (Hambly et al 1997;Oppenheimer et al 2001;Bergeron 2001).…”

Section: Halo White Dwarf Candidatesmentioning

confidence: 81%

“…As previously stated (see Section 5.2), one of the major drawbacks of the Toomre criterion (and similar ones) is that, when the radial velocities are unknown, the Galactic velocity components are reduced and a significant fraction of low-speed halo members are missed. This fact can be exemplified by the object J1107+4855 which, classified as a halo member not only by us but also by other studies (Harris et al 2006;Gianninas et al 2015;Si et al 2017), is not included in the Kilic et al (2018) sample due to its moderately low motion, Vtan = 167 km s −1 .…”

Section: Halo White Dwarf Candidatesmentioning

confidence: 88%

See 1 more Smart Citation

Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

Torres

Cantero

Rebassa‐Mansergas

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Gaia-DR2 has provided an unprecedented number of white dwarf candidates of our Galaxy. In particular, it is estimated that Gaia-DR2 has observed nearly 400 000 of these objects and close to 18 000 up to 100 pc from the Sun. This large quantity of data requires a thorough analysis in order to uncover their main Galactic population properties, in particular the thin and thick disk and halo components. Taking advantage of recent developments in artificial intelligence techniques, we make use of a detailed Random Forest algorithm to analyse an 8-dimensional space (equatorial coordinates, parallax, proper motion components and photometric magnitudes) of accurate data provided by Gaia-DR2 within 100 pc from the Sun. With the aid of a thorough and robust population synthesis code we simulated the different components of the Galactic white dwarf population to optimize the information extracted from the algorithm for disentangling the different population components. The algorithm is first tested in a known simulated sample achieving an accuracy of 85.3%. Our methodology is thoroughly compared to standard methods based on kinematic criteria demonstrating that our algorithm substantially improves previous approaches. Once trained, the algorithm is then applied to the Gaia-DR2 100 pc white dwarf sample, identifying 12 227 thin disk, 1410 thick disk and 95 halo white dwarf candidates, which represent a proportion of 74:25:1, respectively. Hence, the numerical spatial densities are (3.6 ± 0.4) × 10 −3 pc −3 , (1.2 ± 0.4) × 10 −3 pc −3 and (4.8 ± 0.4) × 10 −5 pc −3 for the thin disk, thick disk and halo components, respectively. The populations thus obtained represent the most complete and volume-limited samples to date of the different components of the Galactic white dwarf population.

show abstract

Section: Halo White Dwarf Candidatesmentioning

confidence: 81%

Section: Halo White Dwarf Candidatesmentioning

confidence: 88%

Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

Torres

Cantero

Rebassa‐Mansergas

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…Statistical analysis of spectroscopy, photometry, and parallaxes can eventually be used to obtain a very accurate estimate of cooling ages (e.g. O'Malley et al 2013;Si et al 2017) for this sample of known white dwarfs.…”

Section: Resultsmentioning

confidence: 99%

Multiband photometry and spectroscopy of an all-sky sample of bright white dwarfs

Raddi

Fusillo

Pala

et al. 2017

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

The upcoming NASA Transiting Exoplanet Survey Satellite (TESS) will obtain spacebased uninterrupted light curves for a large sample of bright white dwarfs distributed across the entire sky, providing a very rich resource for asteroseismological studies and the search for transits from planetary debris. We have compiled an all-sky catalogue of ultraviolet, optical, and infrared photometry as well as proper motions, which we propose as an essential tool for the preliminary identification and characterisation of potential targets. We present data for 1864 known white dwarfs and 305 high-probability white dwarf candidates brighter than 17 mag. We describe the spectroscopic follow-up of 135 stars, of which 82 are white dwarfs and 25 are hot subdwarfs. The new confirmed stars include six pulsating white dwarf candidates (ZZ Cetis), and nine white dwarf binaries with a cool main-sequence companion. We identify one star with a spectroscopic distance of only 25 pc from the Sun. Around the time TESS is launched, we foresee that all white dwarfs in this sample will have trigonometric parallaxes measured by the ESA Gaia mission next year.

show abstract

“…This can be accomplished using the following algorithm. A similar strategy is employed by Si et al (2016) when they use Monte Carlo samples from the posterior distribution of the age of a number of white dwarfs obtained from separate fits as a Metropolis proposal rule for fitting a hierarchical model for all of their ages.…”

Section: A Flux Ratio Testmentioning

confidence: 99%

Detecting Relativistic X-Ray Jets in High-Redshift Quasars

McKeough

Siemiginowska

Cheung

et al. 2016

ApJ

View full text Add to dashboard Cite

We analyze Chandra X-ray images of a sample of 11 quasars that are known to contain kiloparsec scale radio jets. The sample consists of five high-redshift (z ≥ 3.6) flat-spectrum radio quasars, and six intermediate redshift (2.1 < z < 2.9) quasars. The dataset includes four sources with integrated steep radio spectra and seven with flat radio spectra. A total of 25 radio jet features are present in this sample. We apply a Bayesian multi-scale image reconstruction method to detect and measure the X-ray emission from the jets. We compute deviations from a baseline model that does not include the jet, and compare observed X-ray -2 -images with those computed with simulated images where no jet features exist. This allows us to compute p-value upper bounds on the significance that an Xray jet is detected in a pre-determined region of interest. We detected 12 of the features unambiguously, and an additional 6 marginally. We also find residual emission in the cores of 3 quasars and in the background of 1 quasar that suggest the existence of unresolved X-ray jets. The dependence of the X-ray to radio luminosity ratio on redshift is a potential diagnostic of the emission mechanism, since the inverse Compton scattering of cosmic microwave background photons (IC/CMB) is thought to be redshift dependent, whereas in synchrotron models no clear redshift dependence is expected. We find that the high-redshift jets have X-ray to radio flux ratios that are marginally inconsistent with those from lower redshifts, suggesting that either the X-ray emissions is due to the IC/CMB rather than the synchrotron process, or that high redshift jets are qualitatively different.

show abstract

A hierarchical model for the ages of Galactic halo white dwarfs

Cited by 10 publications

References 68 publications

Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

Multiband photometry and spectroscopy of an all-sky sample of bright white dwarfs

Detecting Relativistic X-Ray Jets in High-Redshift Quasars

Contact Info

Product

Resources

About