英文:
In python how to cross match sources with a given mask?
问题
我有一个数据框，其中记录了遍布天空大部分地区的天文源（星系）的目录。我还有一个 .fits 二进制掩膜，只覆盖天空的某些部分（见下图）。我想要将目录与掩膜进行交叉匹配，以获取仅位于掩膜内的星系。我应该如何实现这一目标，例如使用 healpy？
英文:
I have a dataframe that is a catalogue of astronomical sources (galaxies) spread across most of the sky. I also have a .fits binary mask that covers only some parts of the sky (see below). I want to cross-match the catalogue with the mask to get only the galaxies that fall within the mask. How can I do this, e.g. with healpy?
答案1
得分: 1
以下是翻译好的部分：
一种方法是以下内容：
df_cat = pd.read_csv('file_path_cat.txt', names=['ra', 'dec', 'z', 'flag', 'var1', 'var2'])
nside = 64 #这里的值取决于你使用的掩模，通常包含在掩模的名称中，通常为64、128或512
N = 12*nside**2
# 转换为HEALPix索引并对PS数据进行子采样
indices = hp.ang2pix(nside, df_cat.ra.values, df_cat.dec.values, lonlat=True)
mask = hp.read_map('mask_file_path.fits')
df_cat['sky_mask'] = np.array(mask[indices]).byteswap().newbyteorder()
# 最终，仅保留df_cat中'sky_mask'等于1的源，因为它们位于掩模内
df_cross_matched = df_cat[df_cat.sky_mask==1]
我在以下笔记本中使用了这种方法：'data_exploration_20220825.ipynb' 和 'Joining_and_processing_pyhod_bins_to_one_population.ipynb'
英文:
One way to do this is the following:
df_cat = pd.read_csv('file_path_cat.txt', names=['ra', 'dec', 'z', 'flag', 'var1', 'var2'])
nside = 64 #the value here depends on the mask you are using, it's mostly contained
# in the name of the mask and is usually 64, 128 or 512
N = 12*nside**2
# convert to HEALPix indices and subsample the PS data
indices = hp.ang2pix(nside, df_cat.ra.values, df_cat.dec.values, lonlat=True)
mask = hp.read_map('mask_file_path.fits')
df_cat['sky_mask'] = np.array(mask[indices]).byteswap().newbyteorder()
# eventually, keep only the sources in df_cat with 'sky_mask'==1, since they are within the mask
df_cross_matched = df_cat[df_cat.sky_mask==1]
Notebooks I have used this approach in are data_exploration_20220825.ipynb and Joining_and_processing_pyhod_bins_to_one_population.ipynb
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