TY - JOUR
T1 - Faint, moving objects in the hubble deep field
T2 - Components of the dark halo?
AU - Ibata, Rodrigo A.
AU - Richer, Harvey B.
AU - Gilliland, Ronald L.
AU - Scott, Douglas
N1 - Funding Information:
The research of H. B. R. and D. S. is supported in part by the Natural Sciences and Engineering Research Council of Canada. R. L. G. is supported under grant GO-6473.01-95A from STScI.
PY - 1999/10/20
Y1 - 1999/10/20
N2 - The deepest optical image of the sky, the Hubble Deep Field, obtained with the Hubble Space Telescope in 1995 December, has been compared to a similar image taken in 1997 December. Two very faint, blue, isolated, and unresolved objects are found to display a substantial apparent proper motion, 23 ± 5 and 26 ± 5 mas yr-1 ; a further three objects at the detection limit of the second-epoch observations may also be moving. Galactic-structure models predict a general absence of stars in the color-magnitude range in which these objects are found. However, these observations are consistent with recently developed models of old white dwarfs with hydrogen atmospheres, whose color, contrary to previous expectations, has been shown to be blue. If these apparently moving objects are indeed old white dwarfs with hydrogen atmospheres and masses near 0.5 M⊙, they have ages of approximately 12 Gyr and a local mass density that is sufficient, within the large uncertainties arising from the small size of the sample, to account for the entire missing Galactic dynamical mass.
AB - The deepest optical image of the sky, the Hubble Deep Field, obtained with the Hubble Space Telescope in 1995 December, has been compared to a similar image taken in 1997 December. Two very faint, blue, isolated, and unresolved objects are found to display a substantial apparent proper motion, 23 ± 5 and 26 ± 5 mas yr-1 ; a further three objects at the detection limit of the second-epoch observations may also be moving. Galactic-structure models predict a general absence of stars in the color-magnitude range in which these objects are found. However, these observations are consistent with recently developed models of old white dwarfs with hydrogen atmospheres, whose color, contrary to previous expectations, has been shown to be blue. If these apparently moving objects are indeed old white dwarfs with hydrogen atmospheres and masses near 0.5 M⊙, they have ages of approximately 12 Gyr and a local mass density that is sufficient, within the large uncertainties arising from the small size of the sample, to account for the entire missing Galactic dynamical mass.
UR - http://www.scopus.com/inward/record.url?scp=0033589193&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0033589193&partnerID=8YFLogxK
U2 - 10.1086/312310
DO - 10.1086/312310
M3 - Article
AN - SCOPUS:0033589193
SN - 0004-637X
VL - 524
SP - L95-L97
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 PART 2
ER -