Kavli Affiliate: Masahiro Takada
| First 5 Authors: Tian Qiu, Masahiro Takada, Naoki Yasuda, Akira Tokiwa, Kazumi Kashiyama
| Summary:
We present 5,080 white dwarf (WD) candidates selected from stars matching
between the multi-band imaging datasets of the Subaru Hyper Suprime-Cam (HSC)
Survey and the Sloan Digital Sky Survey (SDSS) in the Stripe82 region covering
about 165~deg$^2$. We select WD candidates from the “reduced proper motion”
diagram by combining the apparent magnitude in the range $i=19$ — 24 and the
proper motion measured from the datasets among a baseline of $sim$ 14~years.
We refine the WD candidates by fitting blackbody and template WD atmosphere
models to HSC photometries for each candidate, enabling the estimation of
distance and tangential velocity ($v_{rm t}$). The deep HSC data allow us to
identify low-temperature ($<4000$~K) and faint WD candidates down to absolute
magnitude, $M_{rm bol}simeq 17$. We evaluate the selection function of our WD
candidates using a mock catalogue of spatial and kinematic distributions of WDs
in the (thin and thick) disc and halo regions based on a Galactic model. We
construct samples of disc and halo WD candidates by selecting WDs with
tangential velocity, $40<v_{rm t}/[{rm km}~{rm s}^{-1}]<80$ and $200<v_{rm
t}/[{rm km}~{rm s}^{-1}]<500$, respectively. The total number densities of
the disc and halo WDs are $(9.33 pm 0.89) times 10^{-3}$~pc$^{-3}$ and $(6.34
pm 2.90) times 10^{-4}$~pc$^{-3}$. Our luminosity functions (LF) extend down
to fainter absolute magnitudes compared with previous work. The faint WDs could
represent the oldest generation of building blocks over the past $sim$10
billion years of the assembly history of our Milky Way.
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