UKIDSS SciVer Products

E. A. Gonzalez-Solares (IoA, Cambridge)(+CASU)

http://apm15.ast.cam.ac.uk/casudoc/wfcam

http://www.ast.cam.ac.uk/vdfs/UKIDSS SV Meeting – 18/08/05 RoE

Topics

1. Data summary2. Completeness & reliability3. Astrometry accuracy from overlaps4. Flux accuracy from overlaps5. Stacking6. Colour-colour diagrams using other

surveys

Data Summary: coverage

• Using DXS data

• J and K band

• MSB: 25 dithers of 2x2 interleaved frames of 5 s exposure each, i.e., 500 s total exp time.

• High repeatability: up to 20 MSBs of the same pointing

• Lockman and EN1 fields well covered at other wavelengths

Seeing*

*(as measured from the stacked interleaved frames)

Seeing

J band K band

Chip 1 Chip 2

Chip 3 Chip 4

Chip 1 Chip 2

Chip 3 Chip 4

Magnitude limit* (500 s)

*(this is the 5 detection limit in an aperture of 2” radius)

Chip 1 Chip 2

Chip 3 Chip 4

Completeness & Reliability

• Simulations performed using ARTDATA in IRAF• 1000 stars in chip 1 – simulation repeated until good stats• Stacked superframe interleaved 2x2 (i.e. pixel of 0.2 arcsec)• Exposure time 500 s. Seeing ~ 1”• Aperture magnitudes in 2” diameter

• Simulations performed using ARTDATA in IRAF• 1000 stars in chip 1 – simulation repeated until good stats• Stacked superframe interleaved 2x2 (i.e. pixel of 0.2 arcsec)• Exposure time 500s. Seeing ~ 1”• Aperture magnitudes in 2” diameter

Completeness & Reliability

Completeness & Reliability

K band stacked superframe(interleaved)

K band stacked(non interleaved)

Without interleaving -> completeness ~0.3 mags deeper

Completeness & Reliability

Reliability J band Reliability K band

• Completeness measure the fraction of objects found but does not tell us about their measured properties.• Reliability tell us the fraction of objects with correct fluxes in each bin (taking into account flux errors).

• Simulation of a high density field with 20 000 stars• Expect lower level of completeness and reliability

Completeness & Reliability

Star/Galaxy separation

• How good we can classify the objects…• Selected only objects with class_star=-1

Astrometric accuracy

• Astrometric comparison between overlapping MSBs

• Magnitudes K<17

• Overall astrometry accuracy better than 0.04 arcsec

Flux accuracy

• Comparison of fluxes of same objects measured in different MSBs• Only bright (K<17) objects, point-like and extended (from catalogue class)

(poor observing conditions)

Magnitudes good within 3%

Stacking

• Stacking of 80 min of J data and 2 hours of K data• Magnitude limits J=21.7, K=20.8

• DXS aim is K=21 and J=22.5.

Colour Magnitude Diagram

Blue:point-like

Red:Extended

(from catalogueclassification)

Colour Magnitude Diagram

Datasets useful to correlate with

• Optical:– WFS: U, g, r, i, Z – EN01– Subaru: I – EN01– KPNO: U, g, r, i – Lockman– Several deeper imaging over small regions

(including HST).

• Spitzer: 3.5, 4.6,5.8, 8.0, 24, 70, 160 µm

Colours* : K-[3.6] vs J-K*SED models by Polleta et al 2005 (in prep)

Colours : K-[3.6] vs [3.6]-[4.5]