def catl_drop_cols(mockgal_pd):
    """
    Drops certain columns from the galaxy DataFrame

    Parameters
    -----------
    mockgal_pd: pandas DataFrame
        DataFrame containing information for each mock galaxy.
        Includes galaxy properties + group ID

    Returns
    -----------
    gal_pd_mod: pandas DataFrame
        Updated version of the DataFrame containing information for each 
        mock galaxy.

    """
    ## Copies of DataFrames
    gal_pd   = mockgal_pd.copy()
    ## Columns
    gal_cols = ['x','y','z','vx','vy','vz','galid','x_orig','y_orig','z_orig',
                'vel_pec','ra_orig']
    # New object `without` these columns
    gal_pd_mod = gal_pd.loc[:,~gal_pd.columns.isin(gal_cols)].copy()

    return gal_pd_mod