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Subject
- x-ray sources[remove]1,419
- photometry344
- surveys285
- active galactic nuclei283
- galaxies249
- redshifted226
- optical astronomy209
- infrared photometry191
- galaxy clusters178
- astronomical object identification132
- radio astronomy119
- open star clusters115
- quasars115
- infrared sources103
- radio sources100
- pre-main sequence stars95
- gamma-ray astronomy89
- wide-band photometry89
- spectroscopy85
- infrared astronomy80