11.4.5. astroML.datasets.fetch_dr7_quasar

astroML.datasets.fetch_dr7_quasar(data_home=None, download_if_missing=True)[source]

Loader for SDSS DR7 quasar catalog

Parameters
data_homeoptional, default=None

Specify another download and cache folder for the datasets. By default all scikit learn data is stored in ‘~/astroML_data’ subfolders.

download_if_missingoptional, default=True

If False, raise a IOError if the data is not locally available instead of trying to download the data from the source site.

Returns
datandarray, shape = (105783,)

numpy record array containing the quasar catalog

Notes

Not all available data is extracted and saved. The extracted columns are:

sdssID, RA, DEC, redshift, mag_u, err_u, mag_g, err_g, mag_r, err_r, mag_i, err_i, mag_z, err_z, mag_J, err_J, mag_H, err_H, mag_K, err_K, specobjid

many of the objects are missing 2mass photometry.

More information at http://www.sdss.org/dr7/products/value_added/qsocat_dr7.html

Examples

>>> from astroML.datasets import fetch_dr7_quasar
>>> data = fetch_dr7_quasar()  # doctest: +IGNORE_OUTPUT
>>> u_g = data['mag_u'] - data['mag_g']
>>> u_g[:3]  # first three u-g colors
array([-0.07699966,  0.03600121,  0.10900116], dtype=float32)