The Number Density of Old Passively Evolving Galaxies at z = 1 in the Subaru/XMM-Newton Deep Survey Field
The Number Density of Old Passively Evolving Galaxies at z = 1 in the Subaru/XMM-Newton Deep Survey Field
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DOI：
10.1086/496954
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发表时间：
2005-08
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通讯作者：
Toru Yamada;T. Kodama;M. Akiyama;H. Furusawa;I. Iwata;M. Kajisawa;M. Iye;M. Ouchi;K. Sekiguchi-K.
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作者：
Toru Yamada;T. Kodama;M. Akiyama;H. Furusawa;I. Iwata;M. Kajisawa;M. Iye;M. Ouchi;K. Sekiguchi-K.
我们利用在Subaru/XMM-牛顿深度探测(SXDS)场中1.03°2区域探测到的约4000个大而均匀的样本，以很高的统计精度获得了z=1的颜色选择的古老被动演化星系(OPEG)的数目计数和静止帧B带光度函数。我们的选择标准定义在I‘-z’和R-z‘色度平面上，以便在z=0.9-1.1、地层红移Zf=2-10的OPEG被适当地采样，并且最大限度地减少其他种群的污染。极限星等对应于z=0时M*+3星系的光度。我们对99个具有19<；z‘<；22的OPEG候选天体进行了初步红移观测，发现整个样品中至少78%(93个样品中的73个)或95%(77个样品中的73个)的红移确实位于z=0.87到1.12之间，并且它们的大部分光谱显示出连续谱断裂和强烈的Ca、H和K线，表明这些天体确实是由旧恒星群主导的。观察到的红移和颜色之间的关系密切地遵循以一致的方式定义选择标准所使用的模型。我们发现，即使在30‘尺度上，OPEG的表面数密度也是整个样本平均值的10%-30%，而最贫穷的SXDS-South只有最丰富的SXDS-East的65%。然后，我们将我们的结果与z=0时颜色选择或形态选择的早期类型星系的光度函数进行了比较，发现在SXDS区，在z=0时具有~M*星等的旧被动星系的数密度是等效红星系的40%-60%，而形态选择的E/S0星系的数密度是60%-85%，这取决于它们的亮度演化。结果表明，在z=1的情况下，超过一半但不是全部的早期星系已经演化成静止的被动星系。
We obtained the number counts and the rest-frame B-band luminosity function of color-selected old passively evolving galaxies (OPEGs) at z = 1 with very high statistical accuracy using a large and homogeneous sample of about 4000 such objects with z′ < 25 detected in an area of 1.03 deg2 in the Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined on the i′ - z′ and R - z′ color-magnitude plane so that OPEGs at z = 0.9-1.1 with formation redshift zf = 2-10 are properly sampled with minimum contamination by other populations. The limiting magnitude corresponds to the luminosity of galaxies with M* + 3 at z = 0. We made pilot redshift observations for 99 OPEG candidates with 19 < z′ < 22 and found that at least 78% (73 of 93) of the entire sample, or 95% (73 of 77) of those whose redshifts were obtained, indeed lie between z = 0.87 and 1.12, and most of their spectra show a continuum break and strong Ca H and K lines, indicating that these objects are indeed dominated by the old stellar populations. The relationship between the observed redshift and the color closely follows the models used in defining the selection criteria in a consistent manner. We found that the surface number density of OPEGs varies by 10%-30% of the average of the entire sample from field to field even at a 30' scale and that the poorest field, SXDS-South, has only 65% of that of the richest one, SXDS-East. We then compared our results with the luminosity functions of the color- or morphologically selected early-type galaxies at z = 0, taking the evolutionary factor into account, and found that the number density of old passive galaxies with ~M* magnitude at z ~ 1 averaged over the SXDS area is 40%-60% that of equivalently red galaxies and 60%-85% that of morphologically selected E/S0 galaxies at z = 0 depending on their luminosity evolution. It is revealed that more than half, but not all, of the present-day early-type galaxies had already evolved into quiescent passive galaxies at z = 1.