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Abell 2744中第一个边缘场星系团:一个z~8候选星系中的4.5μm过剩

The first Frontier Fields cluster: 4.5μm excess in a z~8 galaxy candidate in Abell 2744

N. Laporte, A. Streblyanska, B. Clement, I. Perez-Fournon, D. Schaerer, H. Atek, F. Boone, J. -P. Kneib, E. Egami, P. Martinez-Navajas, R. Marques-Chaves, R. Pello, J. Richard

摘要:

在这封信中,我们提出了第一次分析的z~8星系候选人中发现的哈勃和斯皮策成像数据的阿贝尔2744,作为哈勃前沿领域的遗产计划的一部分。我们应用最常用的方法来选择异常高z星系相结合的非检测和颜色标准,使用7个HST波段。我们在IRAC图像上使用GALFIT来拟合和减去附近明亮光源的污染。的物理性质已推断出从SED拟合使用模板与和没有星云发射。这封信的重点是我们在WFC 3覆盖的4.9弧分$^2$视场内发现的最亮候选物(m $_{F160W}$ =26.2)。在ACS波段和3.6μm处未检测到,而在4.5μm处清晰检测到,深度相当相似。IRAC数据中的这种突变可以用z~8处的强[OIII]+Hβ线来解释,这些线对4.5μm光度测定有贡献。最好的光-z在z~8.0 $^{+0.2}_{-0.5}$,虽然在低红移(z~1.9)的解决方案不能完全排除,但他们强烈不利于SED拟合工作。放大系数相对较小,μ=1.49 $\pm$ 0.02。该天体的恒星形成率为8 - 60 Mo/年,恒星质量为M $_{\star}$ =(2.5-10)x 10 $^{9}$ Mo,大小为r~0.35 $\pm$ 0.15 kpc。该天体是第一个z~8 LBG候选者之一,在3.6μm和4.5μm之间显示出明显的突变,这与第一个光谱证实的星系在类似红移处的IRAC性质一致。由于它的亮度,这个物体的红移可能会被目前8- 10米望远镜的近红外光谱证实。随着新的ACS和斯皮策数据的到来,这个候选者的性质将在未来几个月内被揭示,增加了光学和近红外波长的深度。

英文摘要:

We present in this letter the first analysis of a z~8 galaxy candidate found in the Hubble and Spitzer imaging data of Abell 2744, as part of the Hubble Frontier Fields legacy program. We applied the most commonly-used methods to select exceptionally high-z galaxies by combining non-detection and color-criteria using seven HST bands. We used GALFIT on IRAC images for fitting and subtracting contamination of bright nearby sources. The physical properties have been inferred from SED-fitting using templates with and without nebular emission. This letter is focussed on the brightest candidate we found (m$_{F160W}$=26.2) over the 4.9 arcmin$^2$ field of view covered by the WFC3. It shows a non-detection in the ACS bands and at 3.6μm whereas it is clearly detected at 4.5μm with rather similar depths. This break in the IRAC data could be explained by strong [OIII]+Hβ lines at z~8 which contribute to the 4.5μm photometry. The best photo-z is found at z~8.0$^{+0.2}_{-0.5}$, although solutions at low-redshift (z~1.9) cannot be completely excluded, but they are strongly disfavoured by the SED-fitting work. The amplification factor is relatively small at μ=1.49$\pm$0.02. The Star Formation Rate in this object is ranging from 8 to 60 Mo/yr, the stellar mass is in the order of M$_{\star}$=(2.5-10) x 10$^{9}$Mo and the size is r~0.35$\pm$0.15 kpc. This object is one of the first z~8 LBG candidates showing a clear break between 3.6μm and 4.5μm which is consistent with the IRAC properties of the first spectroscopically confirmed galaxy at a similar redshift. Due to its brightness, the redshift of this object could potentially be confirmed by near infrared spectroscopy with current 8-10m telescopes. The nature of this candidate will be revealed in the coming months with the arrival of new ACS and Spitzer data, increasing the depth at optical and near-IR wavelengths.

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