TY - JOUR
T1 - Galaxy formation in the reionization epoch as hinted by wide field camera 3 observations of the hubble ultra deep field
AU - Yan, Hao Jing
AU - Windhorst, Rogier
AU - Hathi, Nimish P.
AU - Cohen, Seth H.
AU - Ryan, Russell E.
AU - O'Connell, Robert W.
AU - McCarthy, Patrick J.
PY - 2010/9
Y1 - 2010/9
N2 - We present a large sample of candidate galaxies at z ≈ 7 - 10, selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3 that was recently installed on the Hubble Space Telescope. Our sample is composed of 20 z850-dropouts (four new discoveries), 15 Y 105-dropouts (nine new discoveries) and 20 J125-dropouts (all new discoveries). The surface densities of the z850-dropouts are close to what was predicted by earlier studies, however, those of the Y 105- and J125-dropouts are quite unexpected. While no Y105- or J125-dropouts have been found at AB ≤ 28:0 mag, their surface densities seem to increase sharply at fainter levels. While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed, the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z ̃ 7 to 10. Motivated by such steep increases, we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈ 8 and 10. As compared to their counterpart at z ≈ 7, here L* decreases by a factor of ̃ 6:5 and * increases by a factor of 17-90. Although such parameters are not yet demanded by the existing observations, they are allowed and seem to agree with the data better than other alternatives. If these luminosity functions are still valid beyond our current detection limit, this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10, which, while seemingly exotic, would naturally fit in the picture of the cosmic hydrogen reionization. These early galaxies could easily account for the ionizing photon budget required by the reionization, and they would imply that the global star formation rate density might start from a very high value at z ≈ 10, rapidly reach the minimum at z ≈ 7, and start to rise again towards z ≈ 6. In this scenario, the majority of the stellar mass that the universe assembled through the reionization epoch seems still undetected by current observations at z ≈ 6.
AB - We present a large sample of candidate galaxies at z ≈ 7 - 10, selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3 that was recently installed on the Hubble Space Telescope. Our sample is composed of 20 z850-dropouts (four new discoveries), 15 Y 105-dropouts (nine new discoveries) and 20 J125-dropouts (all new discoveries). The surface densities of the z850-dropouts are close to what was predicted by earlier studies, however, those of the Y 105- and J125-dropouts are quite unexpected. While no Y105- or J125-dropouts have been found at AB ≤ 28:0 mag, their surface densities seem to increase sharply at fainter levels. While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed, the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z ̃ 7 to 10. Motivated by such steep increases, we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈ 8 and 10. As compared to their counterpart at z ≈ 7, here L* decreases by a factor of ̃ 6:5 and * increases by a factor of 17-90. Although such parameters are not yet demanded by the existing observations, they are allowed and seem to agree with the data better than other alternatives. If these luminosity functions are still valid beyond our current detection limit, this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10, which, while seemingly exotic, would naturally fit in the picture of the cosmic hydrogen reionization. These early galaxies could easily account for the ionizing photon budget required by the reionization, and they would imply that the global star formation rate density might start from a very high value at z ≈ 10, rapidly reach the minimum at z ≈ 7, and start to rise again towards z ≈ 6. In this scenario, the majority of the stellar mass that the universe assembled through the reionization epoch seems still undetected by current observations at z ≈ 6.
KW - Cosmology
KW - Early universe-galaxies
KW - Evolution-galaxies
KW - Galaxies
KW - Luminosity function
KW - Mass function-infrared
KW - Observations-cosmology
UR - http://www.scopus.com/inward/record.url?scp=77958497588&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77958497588&partnerID=8YFLogxK
U2 - 10.1088/1674-4527/10/9/003
DO - 10.1088/1674-4527/10/9/003
M3 - Article
AN - SCOPUS:77958497588
SN - 1674-4527
VL - 10
SP - 867
EP - 904
JO - Research in Astronomy and Astrophysics
JF - Research in Astronomy and Astrophysics
IS - 9
ER -