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

2. General Properties of the 6x Working Databases

b. 6x Field Properties - Large Magellanic Cloud (LMC)

i. Sky Coverage and Observation Parameters

Table 1
Target LMC Type galaxy

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

84.2195 -68.9275

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

6 493 659 383

Tile Numbers⁵ 325529-325534, 325537-325736, 326975-327128,
327133-327138, 328134-328260

Approximate Boundaries (J2000 deg)⁶

RA_min RA_max Dec_min Dec_max

58.123 110.324 -78.009 -59.845

**Table 1**
Target	LMC	Type	galaxy
Central Position¹	RA (J2000 deg)	Dec (J2000 deg)
84.2195	-68.9275
Scan Length (deg)	No. of Tiles²	No. of Scans³	Approximate Area (deg²)⁴
6	493	659	383
Tile Numbers⁵	325529-325534, 325537-325736, 326975-327128, 327133-327138, 328134-328260
Approximate Boundaries (J2000 deg)⁶
RA_min	RA_max	Dec_min	Dec_max
58.123	110.324	-78.009	-59.845

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. See Figure 1.

Figure 1 - Sky map showing the distribution of 6x point source catalog sources with K_s<13 mag (red dots) in the 6x LMC field. Figure 2 - Sky map showing the distribution of 6x extended source catalog sources (green dots).

ii. Field-Specific Notes

The 6x LMC observations covered approximately 383 deg² of coverage centered on the Large Magellanic Cloud. The LMC field is the largest of the 2MASS 6x fields.

The numerous features visible in the color-magnitude diagram shown in Figure 5 are associated with various LMC and Galactic stellar populations as described by Nikolaev and Weinberg 2000, ApJ, 542, 804.

The 2MASS 6x LMC 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 LMC, 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 three declination bands of 6° 6x scans. There are coverage gaps in the northwestern corner and eastern center of the field caused by blocks of tiles that were never observed in photometric conditions. 122 of the 492 tiles in the LMC 6x field we scanned two or more times in photometric conditions. Six tiles, 32697, 327005, 327009, 327011-327013 were observed four times, and tiles 325540 and 325653 were scanned five times.

iii. Working Database and Catalog Source Properties

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

Scans 659 493

Atlas Images 15,157 11,339

Point Sources 17,494,177 6,604,666

Extended Sources 171,448 53,002

**Table 2 - 6x WDB and Catalog Statistics**
	Full 6x Working DB¹	6x "Catalog" subset²
Scans	659	493
Atlas Images	15,157	11,339
Point Sources	17,494,177	6,604,666
Extended Sources	171,448	53,002

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. Densities computed in a 32 deg² region centered on α,δ=87.5°,-64.5°, in the northeast quadrant of the galaxy. 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 10⁶ extractions in the point and extended source 6x WDBs in the LMC 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 10⁶ extractions in the point and extended source 6x WDBs in the LMC 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 point source catalog sources with K_s<13 mag (red dots) in the 6x LMC field.	Figure 2 - Sky map showing the distribution of 6x extended source catalog sources (green dots).

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. Densities computed in a 32 deg² region centered on α,δ=87.5°,-64.5°, in the northeast quadrant of the galaxy. 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 10⁶ extractions in the point and extended source 6x WDBs in the LMC 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 10⁶ extractions in the point and extended source 6x WDBs in the LMC 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.