MeerKAT吸收线巡天第二批数据发布：宽带连续谱目录与宇宙射电偶极子的测量
The MeerKAT Absorption Line Survey Data Release 2: Wideband continuum catalogues and a measurement of the cosmic radio dipole
AI总结：
本文发布MALS第二批数据，包含391个指向的宽带连续谱目录，并利用该目录在建模并消除赤纬系统性效应后，测得与CMB一致的宇宙射电偶极子，证明了更深更稀疏巡天在偶极子测量中的价值。
摘要：
我们发布了MeerKAT吸收线巡天（MALS）的第二批数据，包含在L波段观测的391个指向的宽带连续谱目录。完整的宽带目录覆盖了4344平方度的天空，深度达到10 μJy beam^-1，包含971,980个源。凭借在巡天深度和天空覆盖范围之间的平衡，MALS DR2覆盖了五个数量级的通量密度，为低至200 μJy的河外射电源族群提供了稳健的视角。利用该目录，我们测量了宇宙射电偶极子，即射电源数量相对于宇宙背景的各向异性，类似于宇宙微波背景（CMB）中发现的偶极子。为此，我们对目录的完整性和噪声特性进行了表征，并表明赤纬相关的系统性效应影响了暗源的数量密度。在MALS目录的偶极子测量中，当我们通过在恢复波束长轴尺寸与每个指向的源数量之间进行线性拟合来建模赤纬系统性效应时，我们恢复了合理的偶极子测量结果。最终结果在方向和幅度上与CMB偶极子一致，这与使用其他厘米波目录进行的许多近期宇宙射电偶极子测量不同，后者通常显示出更大的幅度。该结果证明了在更深、更稀疏的射电巡天中进行偶极子测量的价值，因为探测到的暗源族群可能对测量的偶极子产生了显著影响。
英文摘要：
We present the second data release of the MeerKAT Absorption Line Survey (MALS), consisting of wideband continuum catalogues of 391 pointings observed at L~band. The full wideband catalogue covers 4344 deg$^2$ of sky, reaches a depth of 10 $μ$Jy beam$^{-1}$, and contains 971,980 sources. With its balance between survey depth and sky coverage, MALS DR2 covers five orders of magnitude of flux density, presenting a robust view of the extragalactic radio source population down to 200 $μ$Jy. Using this catalogue, we perform a measurement of the cosmic radio dipole, an anisotropy in the number counts of radio sources with respect to the cosmic background, analogous to the dipole found in the cosmic microwave background (CMB). For this measurement, we present the characterisation of completeness and noise properties of the catalogue, and show that a declination-dependent systematic affects the number density of faint sources. In the dipole measurement on the MALS catalogue, we recover reasonable dipole measurements once we model the declination systematic with a linear fit between the size of the major axis of the restoring beam and the amount of sources of each pointing. The final results are consistent with the CMB dipole in terms of direction and amplitude, unlike many recent measurements of the cosmic radio dipole made with other centimetre wavelength catalogues, which generally show a significantly larger amplitude. This result demonstrates the value of dipole measurements with deeper and more sparse radio surveys, as the population of faint sources probed may have had a significant impact on the measured dipole.
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