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arXiv 1005.3076astro-ph.GAastro-ph.IM
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Herschel Hi-GAL图像卷云噪声的直接估计

Direct Estimate of Cirrus Noise in Herschel Hi-GAL Images

P. G. Martin, M. -A. Miville-Deschenes, A. Roy, J. -P. Bernard, S. Molinari, N. Billot, C. Brunt, L. Calzoletti, A. M. DiGiorgio, D. Elia, F. Faustini, G. Jonca… 展开作者

P. G. Martin, M. -A. Miville-Deschenes, A. Roy, J. -P. Bernard, S. Molinari, N. Billot, C. Brunt, L. Calzoletti, A. M. DiGiorgio, D. Elia, F. Faustini, G. Joncas, J. C. Mottram, P. Natoli, A. Noriega-Crespo, R. Paladini, J. F. Robitaille, F. Strafella, A. Traficante, M. Veneziani

摘要:

在银河平面和许多恒星形成区域的赫歇尔图像中,限制我们提取微弱致密源的能力的一个主要因素是卷云混淆噪声,操作上定义为“由于表面亮度波动背景中的混淆而导致的测光测量中预期的统计误差”。提取的源的通量密度的直方图显示出一个独特的模糊端截止值,低于该截止值,星表就不完整,通量密度变得不可靠。这种经验截止应密切相关的卷云噪声估计,我们表明,这是情况。我们直接计算卷云噪声,无论是从已被删除的明亮的源的赫歇尔图像和模拟图像的卷云具有统计上相似的波动。我们连接这些直接估计与功率谱分析,已被广泛用于预测卷云噪声,并提供洞察它如何取决于各种统计特性和光度操作参数。我们报告的多波长功率谱的弥漫银河尘埃排放的高GAL观测在70至500微米内的银河平面领域在l= 30度和l= 59度。我们发现功率谱的指数约为-3。在250微米处,功率谱的幅度大致随着地图的中值亮度的平方而增加,因此预期的卷云噪声与中值亮度成线性比例。通常,由于较低的角分辨率和卷云的功率谱向较低的空间频率上升的组合,在较长的波长处混淆噪声将是更严重的问题,但是光度计信噪比还将取决于源与卷云相比的相对光谱能量分布。

英文摘要:

In Herschel images of the Galactic plane and many star forming regions, a major factor limiting our ability to extract faint compact sources is cirrus confusion noise, operationally defined as the "statistical error to be expected in photometric measurements due to confusion in a background of fluctuating surface brightness". The histogram of the flux densities of extracted sources shows a distinctive faint-end cutoff below which the catalog suffers from incompleteness and the flux densities become unreliable. This empirical cutoff should be closely related to the estimated cirrus noise and we show that this is the case. We compute the cirrus noise directly, both on Herschel images from which the bright sources have been removed and on simulated images of cirrus with statistically similar fluctuations. We connect these direct estimates with those from power spectrum analysis, which has been used extensively to predict the cirrus noise and provides insight into how it depends on various statistical properties and photometric operational parameters. We report multi-wavelength power spectra of diffuse Galactic dust emission from Hi-GAL observations at 70 to 500 microns within Galactic plane fields at l= 30 degrees and l= 59 degrees. We find that the exponent of the power spectrum is about -3. At 250 microns, the amplitude of the power spectrum increases roughly as the square of the median brightness of the map and so the expected cirrus noise scales linearly with the median brightness. Generally, the confusion noise will be a worse problem at longer wavelengths, because of the combination of lower angular resolution and the rising power spectrum of cirrus toward lower spatial frequencies, but the photometric signal to noise will also depend on the relative spectral energy distribution of the source compared to the cirrus.

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