Appendix 3. Long Exposure (6X) Images, Scan Databases and Catalogs

2. General Properties of the 6x Working Databases

b. 6x Field Properties - Small Magellanic Cloud (SMC)

i. Sky Coverage and Observation Parameters

Table 1
Target SMC Type galaxy

Central Position¹ RA (J2000 deg) Dec (J2000 deg)

14.1279 -71.9268

Scan Length (deg) No. of Tiles² No. of Scans³ Approximate
Area (deg²)⁴

6 166 225 127

Tile Numbers⁵ 326773-326866, 327980-328051

Approximate Boundaries (J2000 deg)⁶

RA_min RA_max Dec_min Dec_max

359.723 28.273 -78.008 -65.845

**Table 1**
Target	SMC	Type	galaxy
Central Position¹	RA (J2000 deg)	Dec (J2000 deg)
14.1279	-71.9268
Scan Length (deg)	No. of Tiles²	No. of Scans³	Approximate Area (deg²)⁴
6	166	225	127
Tile Numbers⁵	326773-326866, 327980-328051
Approximate Boundaries (J2000 deg)⁶
RA_min	RA_max	Dec_min	Dec_max
359.723	28.273	-78.008	-65.845

Notes to Table 1
1 - Geometric center of area covered by 6x scans. Because of gaps in the scan coverage of some fields, there may not be a scan covering this location. See Figure 1.
2 - Number of unique pre-defined observation areas (tiles) that cover this field.
3 - Number of 6x scans that cover the tiles in this field. The number of scans may exceed the number of tiles because some tiles were observed more than once.
4 - Approximate area is computed from the number of tiles covering this field, accounting for RA and Dec overlap between tiles. It is not the area defined by the approximate field boundaries.
5 - 6° long 6x tiles have the same number and cover the same region as the corresponding tile from the main survey. 1° long 6x tiles are assigned numbers in the range 30000-39999 for northern observatory scans and 333000-349999 for southern observatory scans. 1° long 6x tile numbers do not match tile numbers from the main survey.
6 - Approximate field boundaries define the smallest rectangular region on the sky that encloses all scans of this field. This region may not be completely covered by 6x observations because of gaps in the 6x coverage. Note that the SMC field boundary crosses the 0^h meridian. See Figure 1.

Figure 1 - Sky map showing the distribution of 6x SMC point source WDB extractions brighter than K_s=14.5 mag (red dots). Some tiles may have been observed more than once and have a corresponding higher density of extractions in the WDB. Figure 2 - Sky map showing the distribution of 6x extended source WDB extractions (green dots) in the SMC field.

ii. Field-Specific Notes

The SMC 6x observations provide approximately 127 deg² of contiguous coverage centered on the Small Magellanic Cloud. It is the second largest of the 2MASS 6x fields.

The concentration of of point sources to the west-northwest of the SMC visible in Figure 1 is the globular cluster 47 Tuc. The numerous features visible in the color-magnitude diagram shown in Figure 5 are associated with various SMC and Galactic stellar populations as described by Nikolaev and Weinberg 2000, ApJ, 542, 804.

The 2MASS 6x SMC observations are sensitive enough to detect red giants up to~3.5 magnitudes below the tip of the red giant branch (RGB), improving the precision with which the color distribution and luminosity function of the RGB can be determined. The 6x scans also reach the depth of the AGB-bump in the SMC, which K_s magnitude is an approximate standard candle, and whose color and separation from the RGB tip can be used to probe age and metallicity (e.g. Alves and Sarajedini 1999, ApJ, 511, 225).

The field was covered with two declination bands of 6° 6x scans. Forty-five of the SMC field's 166 tiles were observed more than once. Two tiles, 326826 and 326860 were scanned four times.

iii. Working Database and Catalog Source Properties

Table 2 - 6x WDB and Catalog Statistics
Full 6x Working DB¹ 6x "Catalog" subset²

Scans 225 166

Atlas Images 5,175 3,818

Point Sources 4,265,395 1,153,629

Extended Sources 44,631 16,493

**Table 2 - 6x WDB and Catalog Statistics**
	Full 6x Working DB¹	6x "Catalog" subset²
Scans	225	166
Atlas Images	5,175	3,818
Point Sources	4,265,395	1,153,629
Extended Sources	44,631	16,493

Notes to Table 2
1 - "Full 6x Working DB" refers to the total number of Scans and Atlas Images available from all 6x observations of this field. The "Point Source" and "Extended Source" entries refer to the total number of sources extracted from all observations of this field in the respective 6x Point and Extended Source Working Databases.
2 - "6x Catalog Subset" refers to the subset of all scans covering this field that were selected to constitute a single, unique coverage of the field (A3.6.b), the images from those scans, and the subset of all source extractions from the selected scans that satisfy the "6x-PSC" and "6x-XSC" quality selection criteria described in A3.6.c. The "6x Catalog subset" can be identified in the 6x Scan and Image Metadata tables, and Point and Extended Source WDB tables by selecting entries with "cat=1".

Extracted Source Counts and Statistics

Figure 3 - Full 6x point and extended source Working Database source counts as a function of magnitude. Point source counts are shown by the red line and extended source counts are the blue shaded region. The default magnitudes are used for point sources, and the K_s=20 mag arcsec^-2 elliptical isophotal magnitudes are used for extended sources. Figure 4 - Differential source densities as a function of magnitude for the 6x Point and Extended Catalogs compared with those for the All-Sky PSC and XSC. 6x PSC and XSC counts are shown by the red and blue lines, respectively. All-Sky PSC and XSC counts are shown in the grey and cyan shaded regions.

Photometric Properties

Figure 5 - Color-magnitude diagram for extractions in the point and extended source 6x WDBs in the SMC field. Point sources are shown as small red dots and extended sources as larger green dots. The black contours trace the density of point sources. The horizontal discontinuity in the point source distribution near K_s~10.5 mag in the color-magnitude diagram is caused by the sensitivity gap between the 51 ms R1 and 7.8 s R2-R1 exposures in the 6x data. Figure 6 - Color-color diagram for extractions in the point and extended source 6x WDBs in the SMC field. Point sources are shown as small red dots and extended sources as larger green dots. The black contours trace the density of point sources.

Figure 7 - Differences between 6x and main survey point source photometry plotted as a function of 6x source default magnitude. Black contours trace the density of individual sources that are shown as light grey points. The large blue points and error bars show the trimmed average and RMS of the 6x-survey magnitude differences for all sources in 0.25 magnitude wide bins. Figure 8 - Differences between 6x and main survey extended source photometry in 7" circular apertures ([jhk]_m_7) plotted as a function of 6x extended source magnitude. Black contours trace the density of individual sources that are shown as light grey points. The large blue points and error bars show the trimmed average and RMS of the 6x-survey magnitude differences for all sources in 0.25 magnitude wide bins.

[Last updated: 2008 February 15; by R. Cutri]

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Figure 1 - Sky map showing the distribution of 6x SMC point source WDB extractions brighter than K_s=14.5 mag (red dots). Some tiles may have been observed more than once and have a corresponding higher density of extractions in the WDB.	Figure 2 - Sky map showing the distribution of 6x extended source WDB extractions (green dots) in the SMC field.

Extracted Source Counts and Statistics

Figure 3 - Full 6x point and extended source Working Database source counts as a function of magnitude. Point source counts are shown by the red line and extended source counts are the blue shaded region. The default magnitudes are used for point sources, and the K_s=20 mag arcsec^-2 elliptical isophotal magnitudes are used for extended sources.	Figure 4 - Differential source densities as a function of magnitude for the 6x Point and Extended Catalogs compared with those for the All-Sky PSC and XSC. 6x PSC and XSC counts are shown by the red and blue lines, respectively. All-Sky PSC and XSC counts are shown in the grey and cyan shaded regions.

Photometric Properties

Figure 5 - Color-magnitude diagram for extractions in the point and extended source 6x WDBs in the SMC field. Point sources are shown as small red dots and extended sources as larger green dots. The black contours trace the density of point sources. The horizontal discontinuity in the point source distribution near K_s~10.5 mag in the color-magnitude diagram is caused by the sensitivity gap between the 51 ms R1 and 7.8 s R2-R1 exposures in the 6x data.	Figure 6 - Color-color diagram for extractions in the point and extended source 6x WDBs in the SMC field. Point sources are shown as small red dots and extended sources as larger green dots. The black contours trace the density of point sources.

Figure 7 - Differences between 6x and main survey point source photometry plotted as a function of 6x source default magnitude. Black contours trace the density of individual sources that are shown as light grey points. The large blue points and error bars show the trimmed average and RMS of the 6x-survey magnitude differences for all sources in 0.25 magnitude wide bins.	Figure 8 - Differences between 6x and main survey extended source photometry in 7" circular apertures ([jhk]_m_7) plotted as a function of 6x extended source magnitude. Black contours trace the density of individual sources that are shown as light grey points. The large blue points and error bars show the trimmed average and RMS of the 6x-survey magnitude differences for all sources in 0.25 magnitude wide bins.