T. Jarrett, IPAC
(980519)
Using 2MASS data it is now possible to compute galaxy counts (for Ks < 14) with areal coverage that dwarfs (to greatly understate it) previous imaging surveys. E.g., The tiny subsample of northern RTB fields, including 971205n, 971110n, 971116n, 980114n and 980125n covers over 180 square degrees. The counts for these fields are given below, including a comparison between high glat fields and low glat fields. These results should be representative of the survey in whole.
The raw galaxy counts have been normalized by the area (sq. degrees) and the mag bin interval (counts per deg**2 per mag). The sqrt(n) error bar are indicated by dashed lines for the bar graphs. The mags are derived from fixed circular R=7" aperures. As a comparison, the K-band galaxy counts of Glazebrook et al (MNRAS, 266, 65) are indicated on the Ks plot. The counts of Glazebrook et al. are identical to those of Cowie (1991) and Jenkins & Reid (1991) for K <= 16. Note that the 2MASS galaxy counts and the Glazebrook et al counts are in very good agreement for the field (mostly non-cluster galaxies).
Caveat: The counts reflect all real (confirmed by eye) galaxies extracted by GALWORKS. No effort has been made to optimize reliability (which would have slightly decreased completeness).
Individual RTB fields: Low Stellar Density Regions
Cluster RTB fields
Individual RTB fields: Mid/High Stellar Density Regions
Combined RTB fields
Comments
In comparison to the deep K-band counts of Glazebrook et al, 2MASS is evidently complete up to Ks = 14, but thereafter drops to the basement. For J and H, the bar histograms suggest that completeness limits are around J = 14.8 to 15.0, and H = 14.3 to 14.5.
For the mid to high density fields, the combined results show that the completeness begins to fade at K = 13 to 13.25. In the 13.0 to 13.5 mag bin, the counts are down by 30% compared to Glazebrook.
