• ZTF Primary Grid on Sky : This shows the layout of the field centers of the primary grid on the sky. The fields are arranged in sets of constant declination. The galactic plane is shown by an orange dashed line, and |b|=5,15,20 degrees are shown by dotted lines. Note that the grid aligns with the galactic plane for Dec<+58, with two fields on either side of the plane to cover |b| < 5 degrees.

• ZTF North Celestial Pole 2: This shows 2 additional fields which cover the north pole cap. One is centered at RA=10 DEC=+87.4 and the other at RA=170 DEC=+87.4. This allows us to observe the north pole region at different times of the year. The offset in RA is helpful in filling in the CCD gaps. The northern most fields were modified in April 2019 to adjust for the 87.5 degree DEC limit.

• ZTF North Celestial Pole 3: This shows all 4 fields which cover the north pole cap from both the primary and secondary grids. These were modified in April 2019 to adjust for the 87.5 degree DEC limit.

ZTF Field selection tool

Tom Barlow has developed a tool to identify FieldIDs for given coordinates. It will also show the position on the ZTF grids.

http://yupana.caltech.edu/cgi-bin/ptf/tb/zoc?begin

ZTF Field Grid

• ZTF_CCD_Layout.tbl: ZTF CCD Layout (ASCII) (as of September 2016). This table gives the corners of all 16 ZTF CCDs in degrees relative to the center of the field. The ZTF field is about 7.46 degrees high in the north-south direction and 7.29 degrees wide in the east-west direction. So the average spacing between fields in the primary grid is 7.2 degrees N-S and 7.0 degrees E-W. The CCDs are about 1.707 degrees on a side, and the gap between CCDs is about 0.186 degrees in the N-S direction and about 0.130 degrees in the E-W direction.

• ZTF_Fields.txt: ZTF Field Data (ASCII) (as of August 29, 2017). The field list is divided into 2 parts: primary (IDs 1 to 879) and secondary (1001 to 1895). The primary grid is set up to cover the entire sky with an average overlap between fields of about 0.26 degrees in Declination and about 0.29 degrees in Right Ascension. (The RA overlap varies significantly with Dec.)

• ZTF_Fields.txt: ZTF Field Data (ASCII) (as of June 9, 2017). The field list is divided into 4 parts: primary (IDs 1 to 879), secondary (1001 to 1893), tertiary (2001 to 2877), and quaternary (3001 to 3893). The primary grid is set up to cover the entire sky with an average overlap between fields of about 0.26 degrees in Declination and about 0.29 degrees in Right Ascension. (The RA overlap varies significantly with Dec.)

• ZTF Primary and Secondary Grid Overlap: This shows the overlap between primary and secondary grid fields. The secondary grid fills the CCD gaps in the primary grid. Slight adjustments were made to some secondary field positions to avoid the N-S CCD gaps aligning with the primary fields.

The gaps in sky coverage (0.8%) in the primary + secondary grids is due to the intersection of N-S and E-W CCD gaps (Primary+Secondary Gaps), these gaps or unavoidable unless the fields were placed very close together.

Uncovered Sky

The primary and secondary grids combined leave about 1% of the sky uncovered. If we combine all 4 grids than only about 0.004% of the sky remains uncovered. Combining the first 3 grids (primary, secondary, and tertiary) leaves about 0.05% of the sky uncovered.

• ZTF_Fields.txt: ZTF Field Data (ASCII). The field list is divided into 4 parts: primary (IDs 1 to 879), secondary (1001 to 1893), tertiary (2001 to 2877), and quaternary (3001 to 3893). The primary grid is set up to cover the entire sky with an average overlap between fields of about 0.26 degrees in Declination and about 0.29 degrees in Right Ascension. (The RA overlap varies significantly with Dec.)

• ZTF_CCD_Layout.tbl: ZTF CCD Layout (ASCII) (as of September 2016). This table gives the corners of all 12 ZTF CCDs in degrees relative to the center of the field. The ZTF field is about 7.46 degrees high in the north-south direction and 7.29 degrees wide in the east-west direction. So the average spacing between fields in the primary grid is 7.2 degrees N-S and 7.0 degrees E-W. The CCDs are about 1.707 degrees on a side, and the gap between CCDs is about 0.186 degrees in the N-S direction and about 0.130 degrees in the E-W direction.

• ZTF North Celestial Pole 2: This shows 2 additional fields which cover the north pole cap. One is centered at RA=10 DEC=+88 and the other at RA=170 DEC=+88. This allows us to observe the north pole region at different times of the year. The offset in RA is helpful in filling in the CCD gaps.

• ZTF All Four Grids Sky: This shows all four grid patterns on the sky. The tertiary grid is located between the primary grid fields along approximately the same declination. The tertiary declinations are offset slightly to fill in the CCD gaps. The quaternary grid is located between the secondary grid fields and is also offset in declination slightly. The tertiary and quaternary allow us to cover about 86% of the sky with the inner 4 CCDs. They also give more flexibility in choosing fields for particular objects and may also help in TOO field selection.

• ZTF Primary Grid on Sky : This shows the layout of the field centers of the primary grid on the sky. The fields are arranged in sets of constant declination. The galactic plane is shown by an orange dashed line, and |b|=5,15,20 degrees are shown by dotted lines. Note that the grid aligns with the galactic plane for Dec<+58, with two fields on either side of the plane to cover |b| < 5 degrees.

• ZTF Primary and Secondary Grids on Sky: This shows the primary and secondary field centers (red crosses). The secondary grid is also set up in sets of constant declination between the primary grid declination sets. The secondary grid also aligns with the galactic plane with field centers at |b|=0.

• ZTF Primary Grid Overlap: This shows the overlap between adjacent primary grid fields.

• ZTF Primary and Secondary Grid Overlap: This shows the overlap between primary and secondary grid fields. The secondary grid fills the CCD gaps in the primary grid.

• ZTF North Celestial Pole 1: This shows 9 fields surrounding the north pole. The southern edge is at DEC=+80.

• ZTF North Celestial Pole 2: This also shows 2 fields to cover the north pole cap. One is centered at RA=10 DEC=+88 and the other at RA=170 DEC=+88. This allows us to observe the north pole region at different times of the year. The offset is RA is used to fill in the CCD gaps.

• ZTF All Four Grids Sky: This shows all four grid patterns on the sky. The tertiary grid is located between the primary grid fields along approximately the same declination. The tertiary declinations are offset slightly to fill in the CCD gaps. The quaternary grid is located between the secondary grid fields and is also offset in declination slightly. The tertiary and quaternary allow us to cover about 86% of the sky with the inner CCDs. They also give more flexibility in choosing fields for particular objects and may also help in TOO field selection.

Nearby Galaxies

We wish to align the primary grid such that certain nearby large galaxies (M31,M81,M101, etc.) do not overlap the CCD gaps and (preferably) fall within the inner four CCDs. Below are plots of primary ZTF fields which cover selected nearby galaxies:

• M 31
• M 33
• M 51
• M 81 and M 82
• M 85 and M 100
• M 87 (Virgo Cluster)
• M 101

Sky Coverage Statistics

-- TomBarlow - 2 June 2017

Proposed ZTF Field Grid

• ZTF_Fields.txt: ZTF Field Data (ASCII)

The field list is divided into 4 parts: primary (IDs 1 to 879), secondary (1001 to 1893), tertiary (2001 to 2877), and quaternary (3001 to 3892). The primary grid is set up to cover the entire sky with an average overlap of about 0.26 degrees in Declination and about 0.29 degrees in Right Ascension. (The RA overlap varies significantly with Dec.)

• ZTF_CCD_Layout.tbl: ZTF CCD Layout (ASCII) (September 2016)

Given the CCD layout above, the ZTF field is about 7.46 degrees in the north-south direction and 7.29 degrees in the east-west direction. So the average spacing between fields in the primary grid is 7.2 degrees N-S and 7.0 degrees E-W.

Field Grid Aligned to the Galactic Plane

With a small adjustment to the existing ZTF tile grid, it is possible to align the fields so that they fall on (or bracket) the Galactic Plane. This increases the efficiency of programs which focus on the plane. Conversely, this also helps programs which want to focus on extra-galactic fields.

Below are two figures. The first shows a sample of fields in the primary ZTF grid (IDs < 1000) near the Galactic Plane with the original grid pattern and a possible new pattern. The second shows another field sample using the secondary ZTF grid (IDs > 1000).

The orange dashed line is the |b|=0 and the orange dotted lines are |b|=5 degrees.

• ztfmos1.gif: ztf field primary grid

• ztfmos2.gif: ztf field secondary grid

-- TomBarlow - 12 May 2017