UV-excess sources with a red/IR-counterpart: low-mass companions, debris disks and QSO selection

TL;DR

This study cross-matched UV-excess sources with infrared surveys to identify white dwarfs with companions or debris disks, and also selected QSO candidates, revealing a small fraction of white dwarfs with companions and potential IR-bright galaxies.

Contribution

It introduces a method combining UV and IR data to identify white dwarf companions, debris disks, and QSO candidates, with detailed spectral fitting and analysis.

Findings

2-4% of hot white dwarfs have M-dwarf companions

Approximately 2% have lower-mass companions

No clear debris disk candidates found

Abstract

We present the result of the cross-matching between UV-excess sources selected from the UV-excess survey of the Northern Galactic Plane (UVEX) and several infrared surveys (2MASS, UKIDSS and WISE). From the position in the (J-H) vs. (H-K) colour-colour diagram we select UV-excess candidate white dwarfs with an M-dwarf type companion, candidates that might have a lower mass, brown-dwarf type companion, and candidates showing an infrared-excess only in the K-band, which might be due to a debris disk. Grids of reddened DA+dM and sdO+MS/sdB+MS model spectra are fitted to the U,g,r,i,z,J,H,K photometry in order to determine spectral types and estimate temperatures and reddening. From a sample of 964 hot candidate white dwarfs with (g-r)<0.2, the spectral energy distribution fitting shows that ~2-4% of the white dwarfs have an M-dwarf companion, ~2% have a lower-mass companion, and no clear candidates for having a debris disk are found. Additionally, from WISE 6 UV-excess sources are selected as candidate Quasi-Stellar Objects (QSOs). Two UV-excess sources have a WISE IR-excess showing up only in the mid-IR W3 band of WISE, making them candidate Luminous InfraRed Galaxies (LIRGs) or Sbc star-burst galaxies.