arXiv 1202.04942012-02-02astro-ph.CO

星系外到z~3的色矢量：对星系性质的依赖

Color Gradients in Galaxies Out to z~3: Dependence on Galaxy Properties

Niraj Welikala, Jean-Paul Kneib

备注：: 13 pages, 7 figures, submitted to ApJ

摘要：

利用HST/ACS观测数据，我们测量了GOODS-South场中z~3和i_{AB} <25.5的3248个星系的颜色梯度，并描述了它们与星系性质（光度、视星等、星系大小、红移和形态类型）的关系。颜色梯度通过半光半径外部（R_{50} <r<2 R_{50}）和内部的v-i颜色的差异来测量。梯度在红移到z~1时几乎没有变化，但在变平之前，梯度从z~1增加到z~2。它也随着视星等的增加而增加，在i_{AB} ~25.5时，中值为0.24等。它有很强的颜色依赖性，最蓝的星系（就观测到的颜色而言）的核心相对于它们的外围更蓝。我们通过堆积星系和测量星系内v-i色的径向变化来探测红移的演化。在低红移（z<0.5）时，星系中心（r< R_{50}）比其外围稍红（1.5 R_{50} <r<2 R_{50}）。z~1和-22.0<M_I<-21.0的星系核比外围平均蓝0.1等。对于z>1，星系的核心越来越蓝，而外围的颜色变化不那么快。在z~2.5和-22.0观察到的颜色梯度可能表明，在z>=2的星系中，强烈的恒星形成集中在它们的中心区域。这些颜色梯度及其对星系性质的依赖性也可能对即将到来的弱透镜宇宙学调查中的剪切测量产生重大影响。

英文摘要：

Using HST/ACS observations, we measure the color gradients of 3248 galaxies in the GOODS-South field out to z~3 and i_{AB}<25.5 and characterize their dependence on galaxy properties (luminosity, apparent magnitude, galaxy size, redshift and morphological type). The color gradient is measured by the difference of v-i color outside (R_{50}<r<2R_{50}) and inside the half light radius. The gradient shows little evolution with redshift up to z~1 but increases from z~1 to z~2 before flattening out. It also increases with apparent magnitude, with a median value of 0.24 magnitudes at i_{AB}~25.5. It has a strong color dependence, with the bluest galaxies (in terms of observed color) having cores that are bluer relative to their outskirts. We probe the redshift evolution by stacking galaxies and measuring the radial variation of v-i color within them. At low redshifts (z<0.5), the centres of galaxies (r<R_{50}) are slightly redder than their outskirts (1.5R_{50}<r<2R_{50}). Galaxies at z~1 and -22.0<M_I<-21.0 are bluer in their cores by 0.1 magnitudes, on average, compared to their outskirts. For z>1, galaxies show increasingly bluer cores while the color of the outskirts does not change as rapidly. At z~2.5 and -22.0<M_I<-21.0, we observe a difference, on average, of 0.4 magnitudes between the centre and the outskirts. The observed color gradients may indicate that strong star formation in galaxies at z>=2 is concentrated in their central regions. These color gradients and their dependence on galaxy properties could also have a significant impact on shear measurements in upcoming weak lensing cosmological surveys.

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