TY - JOUR
T1 - A mass threshold in the number density of passive galaxies at z ∼ 2
AU - Sommariva, V.
AU - Fontana, A.
AU - Lamastra, A.
AU - Santini, P.
AU - Dunlop, J. S.
AU - Nonino, M.
AU - Castellano, M.
AU - Ferguson, H.
AU - McLure, R. J.
AU - Galametz, A.
AU - Giavalisco, M.
AU - Grazian, A.
AU - Lu, Y.
AU - Menci, N.
AU - Merson, A.
AU - Paris, D.
AU - Pentericci, L.
AU - Somerville, R.
AU - Targett, T.
AU - Koekemoer, A. M.
N1 - Funding Information:
We thank the referee, David Wilman, for a very useful report. The authors are grateful to the E.S.O. staff for their support during the Hawk-I observations. J.S.D. acknowledges the support of the Royal Society via a Wolfson Research Merit award, and also the support of the European Research Council via the award of an Advanced Grant. R.J.M. acknowledges the support of the European Research Council via the award of a Consolidator grant. A.F. and J.S.D. acknowledge the contribution of the EC FP7 SPACE project ASTRODEEP (Ref.No: 312725). This work is based in part on observations (program GO-12060) made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc, under NASA contract NAS5-26555. This work is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Program based in part on the data collected in the ESO programs 60.A-9284, 181.A0717, LP 186.A-0898 and 085.A-0961.
Funding Information:
Acknowledgements. We thank the referee, David Wilman, for a very useful report. The authors are grateful to the E.S.O. staff for their support during the Hawk-I observations. J.S.D. acknowledges the support of the Royal Society via a Wolfson Research Merit award, and also the support of the European Research Council via the award of an Advanced Grant. R.J.M. acknowledges the support of the European Research Council via the award of a Consolidator grant. A.F. and J.S.D. acknowledge the contribution of the EC FP7 SPACE project ASTRODEEP (Ref.No: 312725). This work is based in part on observations (program GO-12060) made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc, under NASA contract NAS5-26555. This work is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Program based in part on the data collected in the ESO programs 60.A-9284, 181.A0717, LP 186.A-0898 and 085.A-0961.
Publisher Copyright:
© ESO 2014.
PY - 2014
Y1 - 2014
N2 - The process that quenched star formation in galaxies at intermediate and high redshifts is still the subject of considerable debate. One way to investigate this puzzling issue is to study the number density of quiescent galaxies at z ≃ 2 and its dependence on mass. Here we present the results of a new study based on very deep Ks-band imaging (with the HAWK-I instrument on the VLT) of two HST CANDELS fields (the UKIDSS Ultra-deep survey (UDS) field and GOODS-South). The new HAWK-I data (taken as part of the HUGS VLT Large Program) reach detection limits of Ks > 26 (AB mag). We have combined this imaging with the other ground-based and HST data in the CANDELS fields to select a sample of passively-evolving galaxies in the redshift range 1.4 < z < 2.5 (via the pBzK color-based selection criterion). Thanks to the depth and wide area coverage of our imaging, we have been able to extend the selection of quiescent galaxies to a magnitude fainter than previous analyses. Through extensive simulations we demonstrate, for the first time, that the observed turnover in the number of quiescent galaxies at K > 22 is not due to incompleteness, but is real. This has enabled us to establish unambiguously that the number counts of quiescent galaxies at z - 2 flatten and slightly decline at magnitudes fainter than Ks ∼ 22 (AB mag.), in contrast to the number density of star-forming galaxies, which continues to rise to fainter magnitudes. We show that this trend corresponds to a stellar mass threshold M∗ ≃ 1010.8 M⊙ below which the mechanism that halts the star formation in high-redshift galaxies seems to be inefficient. We also show that, while pBzK galaxies at K < 23 are in the redshift range 1.4 < z < 2.5, as expected, at K > 23 a higher redshift population of z ≃ 3 pBzK galaxies is detected and dominates the counts at the faintest magnitudes. Finally, we compare the observed pBzK number counts with those of quiescent galaxies extracted from four different semi-analytic models. We find that only two of these models reproduce the observed trend in the number counts, even qualitatively, and that none of the models provides a statistically acceptable description of the number density of quiescent galaxies at these redshifts. We conclude that the mass function of quiescent galaxies as a function of redshift continues to present a key and demanding challenge for proposed models of galaxy formation and evolution.
AB - The process that quenched star formation in galaxies at intermediate and high redshifts is still the subject of considerable debate. One way to investigate this puzzling issue is to study the number density of quiescent galaxies at z ≃ 2 and its dependence on mass. Here we present the results of a new study based on very deep Ks-band imaging (with the HAWK-I instrument on the VLT) of two HST CANDELS fields (the UKIDSS Ultra-deep survey (UDS) field and GOODS-South). The new HAWK-I data (taken as part of the HUGS VLT Large Program) reach detection limits of Ks > 26 (AB mag). We have combined this imaging with the other ground-based and HST data in the CANDELS fields to select a sample of passively-evolving galaxies in the redshift range 1.4 < z < 2.5 (via the pBzK color-based selection criterion). Thanks to the depth and wide area coverage of our imaging, we have been able to extend the selection of quiescent galaxies to a magnitude fainter than previous analyses. Through extensive simulations we demonstrate, for the first time, that the observed turnover in the number of quiescent galaxies at K > 22 is not due to incompleteness, but is real. This has enabled us to establish unambiguously that the number counts of quiescent galaxies at z - 2 flatten and slightly decline at magnitudes fainter than Ks ∼ 22 (AB mag.), in contrast to the number density of star-forming galaxies, which continues to rise to fainter magnitudes. We show that this trend corresponds to a stellar mass threshold M∗ ≃ 1010.8 M⊙ below which the mechanism that halts the star formation in high-redshift galaxies seems to be inefficient. We also show that, while pBzK galaxies at K < 23 are in the redshift range 1.4 < z < 2.5, as expected, at K > 23 a higher redshift population of z ≃ 3 pBzK galaxies is detected and dominates the counts at the faintest magnitudes. Finally, we compare the observed pBzK number counts with those of quiescent galaxies extracted from four different semi-analytic models. We find that only two of these models reproduce the observed trend in the number counts, even qualitatively, and that none of the models provides a statistically acceptable description of the number density of quiescent galaxies at these redshifts. We conclude that the mass function of quiescent galaxies as a function of redshift continues to present a key and demanding challenge for proposed models of galaxy formation and evolution.
KW - Galaxies: High-redshift
KW - Galaxy: Fundamental parameters
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U2 - 10.1051/0004-6361/201322301
DO - 10.1051/0004-6361/201322301
M3 - Article
AN - SCOPUS:85006323947
SN - 0004-6361
VL - 571
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A99
ER -