In Greimel et al (2021), we present a method (HaGrid) for interrogating Hα and r image data in order to extract from them candidate ionized ISM pointings for use in the WEAVE spectroscopic survey (Jin et al, 2023). The list generated via HaGrid can be downloaded from here.
The list is supplied in fits format and is a table of 187,541 rows and 45 columns. A feature of the supplied data is that an estimate of the surface brightness in erg cm-2 s-1 arcsec-2, based on the image photometric zero points. For details of the table columns, refer to the table below.
| Column name | Description | |
|---|---|---|
| id | Unique name for selected position of form "run number"-"CCD"-nnn, where nnn is a serial integer starting from 0, rising to a maximum of 200 (per CCD). | |
| ra | ICRS right ascension (decimal degrees, Gaia DR2 reference frame) | |
| dec | ICRS declination (decimal degrees, Gaia DR2 reference frame) | |
| l | Galactic longitude (degrees) | |
| b | Galactic latitude (degrees) | |
| Ha_xpeak | x pixel on frame at Hα narrowband peak | |
| Ha_ypeak | y pixel on frame at Hα narrowband peak | |
| Ha_peak_count | Hα narrowband count at peak | |
| Ha_peak_variance | Variance on Hα peak count | |
| Ha_sky_used | Adopted sky count for Hα narrowband frame. Either the median estimated for the frame or the mean of this direct estimate and an estimate predicted from matched r frame (see Greimel et al 2021 for details). | |
| Ha_sky_median | The median sky count for Hα frame | |
| Ha_sky_variance | The sky variance for Hα frame | |
| Ha_CASU_sky | Pipeline sky estimate for Hα frame | |
| Ha_CASU_skynoise | Pipeline sky noise estimate for Hα frame | |
| Ha_photzp | Photometric zero point for Hα frame (mag.) | |
| Ha_net_count | Peak Hα count for position less the sky count | |
| Ha_mag | Hα narrowband magnitude per arcsec-2 at position | |
| Ha_S | Hα narrowband surface brightness at position (erg cm-2 s-1 arcsec-2) | |
| r_count | Counts in the companion r band frame at the same sky position as Hα peak | |
| r_variance | Variance on the r count | |
| r_sky_median | Median sky count for the companion r frame | |
| r_sky_variance | Sky variance for companion r frame | |
| r_CASU_sky | Pipeline sky estimate for companion r frame | |
| r_CASU_skynoise | Pipeline sky noise estimate for companion r frame | |
| r_photzp | Photometric zero point for companion r frame (mag.) | |
| r_factor | Mostly 4, sometimes 12. This is the ratio between the Hα and companion r frame exposure times. | |
| r_net_count | Count in the r frame less sky, at the position of the Hα peak. | |
| r_mag | Companion r frame magnitude per arcsec-2, at the position of the Hα peak | |
| Hα_sky_prediction | Sky count prediction, based on companion r frame sky, of Hα narrowband sky (important in highly nebulous regions) | |
| Hα_star_prediction | Count prediction, based on companion r frame net count at position, of Hα narrowband peak for the case of a continuum source (i.e. a star) | |
| sp_masked_fraction | Fraction of 25x25 superpixel that was masked (less than 0.5 always) | |
| sigma | Error on the distance between the Hα net count, as a function of the corresponding r net count, and the nebular trend line. (See figure 10 in Greimel et al. 2021) | |
| nsigma | The distance between the Hα net count and the nebular trend line in units of sigma. | |
| star_sigma | Error on the distance between the Hα net count, as a function of the corresponding r net count, and the stellar trend line. (See figure 10 in Greimel et al, submitted.) | |
| star_nsigma | The distance between the Hα net count and the stellar trend line in units of star_sigma. | |
| fieldid | Field identifier, of form nnnn or nnnno where nnnn is a 4-digit integer and o, when appended, indicates a field offset pointing. | |
| run | Run number, always starts with "r" | |
| CCD | CCD number (1, 2, 3 or 4) | |
| utstart | UT at beginning of Hα narrowband eposure | |
| moon_phase | Moon phase at time of Hα exposure expressed as a fraction (0.0 is new moon) | |
| moon_separation | Angular distance to moon from telescope pointing (degrees) | |
| moon_altitude | Height of moon above horizon at time of Hα exposure (degrees) | |
| uni_cal | True if frames passed through IGAPS uniform calibration; false if pipeline calibrated only | |
| qcgrade | Quality grade assigned to r, i, Hα exposure set in building the IGAPS catalogue (A++ best, D worst). See Monguio et al 2020 for details. | |
| qcproblems | Note on nature of quality control problems picked up |