Spectra and Polarisation In Cutouts of Extragalactic sources from RACS First Data Release (SPICE-RACS-DR1): Full data deposit

*NOTICE* June 2024: We have discovered an error in the flux density of Stokes Q and U in this data release. Full details are provided in a corrigendum in PASA (see link below). If you are reading this notice the catalogue, spectra and images in this collection have now been corrected. Additionally, the data in the linked 'cut' CASDA collection have been also corrected. Users of the old data can apply their own correction by multiplying Stokes Q and U by 2 for correct results. However, we recommend using the provided updated products. Users can confirm they are using updated files by inspecting the HISTORY card in the FITS headers.

Spectra and Polarisation In Cutouts of Extragalactic sources from RACS (SPICE-RACS) is a project to derive an all-Southern-sky, linear polarisation map from the Rapid ASKAP Continuum Survey (RACS). Through this project, we will derive the following products:
- Cutout image cubes in Stokes I, Q, and U around every source detected in total intensity as a function of frequency
- Polarisation spectra as a function of frequency and Faraday depth for every component detected in total intensity
- A catalogue summarising the polarisation properties, including rotation measure (RM), for every component.

This collection represents the entirety ('full' subset, 105912 components) of the data presented in SPICE-RACS-DR1 (Thomson et al. 2023). The subset of 24680 components ('cut') for which a reliable polynomial fit could be derived for the Stokes I spectra that were extracted are also available in the linked CASDA collection. The individual spectra and cubelets files are divided into sub-directories named by their Field ID from the RACS DR1 (Hale et al. 2021) catalogue.

Our final data products are as follows:

spice-racs.dr1.corrected.{cut,full}.xml:

- Our component catalogue in VOTable format for the first (cut) and second (full) sets of components described above. The former is included with this deposit.

{source_id}.cutout.{image,weights}.*.fits:

- Image and weights cube cutout in Stokes I, Q, and U cutout around a RACS-low source identified by ‘source_id’. The data dimensions are J2000 right ascension and declination, Stokes parameter, and frequency.

{cat_id}_polspec.fits:

- Polarisation spectra extracted on the position of the RACS-low component identified by ‘cat_id’ in POLSPECTRA format. Each table contains a single row, corresponding to the component.

spice_racs_dr1_polspec_{cut,full}.tar:
- A tarball containing all of the POLSPECTRA for the 'cut' and second 'full' sets of components described above. These are available in the linked collections.

Recommended catalogue subsets:
Our 'full' catalogue contains extracted polarisation data for all 105912 Stokes I components detected in our DR1 region. It is important to note that the majority of these do not have reliably detected polarised emission. When using this catalogue please use the provided flags, and uncertainty/quality metrics to derive a subset suitable for your science goals. If you're unsure where to start, these are our recommended basic subsets:

- 'goodI' : Where our Stokes I model is reliable -- channel_flag and stokesI_fit_flag are False (this produces the 'cut' catalogue from the 'full').
- 'goodL': Where we have a reliable detection of polarised signal, but not necessarily a reliable RM -- goodI plus leakage_flag is False and snr_polint >= 5.
- 'goodRM': Where the RM is reliable -- goodL plus snr_flag is False.

*注意* 2024年6月更新：我们发现本次数据发布中的斯托克斯Q（Stokes Q）与斯托克斯U（Stokes U）通量密度存在错误。详细说明已发表于《澳大利亚天文学会出版物》（PASA）的勘误表中（详见下方链接）。若您正在阅读本公告，则本数据集内的星表、光谱与图像均已完成修正。此外，链接中的“精简版”（cut）CASDA数据集也已同步修正。使用旧版数据的用户可自行校正：将斯托克斯Q与U的数值乘以2即可得到正确结果，但我们推荐使用官方提供的更新版产品。用户可通过检查FITS文件头中的HISTORY卡片，确认当前使用的是否为更新后的文件。

**来自RACS的河外源切片光谱与偏振（SPICE-RACS, Spectra and Polarisation In Cutouts of Extragalactic sources from RACS）** 项目旨在基于快速ASKAP连续谱巡天（RACS, Rapid ASKAP Continuum Survey）构建全南天线性偏振地图。通过本项目，我们将产出以下数据产品：
- 针对总强度探测到的所有源，生成其斯托克斯I（Stokes I）、Q（Stokes Q）与U（Stokes U）波段的切片图像立方体，维度包含频率函数
- 针对总强度探测到的所有成分，生成其随频率与法拉第深度变化的偏振光谱
- 一份星表，汇总所有成分的偏振特性，包括旋转量度（rotation measure, RM）。

本数据集包含SPICE-RACS-DR1（Thomson等人，2023）发布的全部数据（即“完整子集”，共105912个成分）。另有24680个成分的“精简子集”（cut）：这些成分可通过提取的斯托克斯I光谱得到可靠的多项式拟合结果，该子集已收录于关联的CASDA数据集中。单个光谱与小立方体文件按RACS DR1（Hale等人，2021）星表中的场编号（Field ID）划分至不同子目录中。

我们的最终数据产品如下：
1. `spice-racs.dr1.corrected.{cut,full}.xml`：
上述两组成分（精简版与完整版）的VOTable格式成分星表。其中精简版星表已包含于本次提交的数据中。
2. `{source_id}.cutout.{image,weights}.*.fits`：
以`source_id`标识的RACS-low源为中心的斯托克斯I、Q、U波段图像与权重立方体切片。数据维度为J2000坐标系下的赤经、赤纬、斯托克斯参数与频率。
3. `{cat_id}_polspec.fits`：
以`cat_id`标识的RACS-low成分位置处提取的偏振光谱，采用POLSPECTRA格式存储。每张表格仅包含一行，对应单个成分。
4. `spice_racs_dr1_polspec_{cut,full}.tar`：
包含上述两组成分（精简版与完整版）全部POLSPECTRA格式文件的tar压缩包。相关文件可在关联数据集中获取。

**推荐星表子集**
本次发布的“完整”星表包含DR1巡天区域内探测到的全部105912个斯托克斯I成分的偏振提取数据，但其中绝大多数并未可靠探测到偏振辐射。使用该星表时，请结合提供的标记与不确定度/质量指标，筛选出符合您科学目标的子集。若您不确定如何入手，以下是我们推荐的基础子集：
- `goodI`：斯托克斯I模型可靠的样本——即`channel_flag`与`stokesI_fit_flag`均为False（该筛选条件可从“完整子集”中得到“精简子集”）。
- `goodL`：偏振信号可靠探测，但旋转量度未必可靠的样本——在`goodI`的基础上，额外要求`leakage_flag`为False且`snr_polint ≥5`。
- `goodRM`：旋转量度可靠的样本——在`goodL`的基础上，额外要求`snr_flag`为False。