VISTA Hemisphere Survey(VHS) The State of the Survey
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Transcript of VISTA Hemisphere Survey(VHS) The State of the Survey
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Richard McMahon Ins.tute of Astronomy (IOA)
Kavli Ins.tute for Cosmology (KICC) University of Cambridge
VISTA Hemisphere Survey(VHS) The State of the Survey
IOA, 2012 Sep 12 1
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VISTA Surveys summary
Survey Area (deg2)
Depths Measure (mag)
Depth (mag)
VHS 18, 000 5σ, AB J=21.2 Ks=20.0
1. VHS-‐DES 4500 5σ, AB J=21.6 H=21.0 Ks=20.4
2. VHS ATLAS 5000 5σ, AB Y=21.2 J=21.2 H=20.6 Ks=20.0
3. VHS-‐GPS 8000 5σ, AB J=21.2 Ks=20.0
VIKING 1,500 5α, AB Z=23.1 Y=22.3 J=22.1 H=21.5 Ks=21.2
VVV 520 5σ, Vega Z=21.9 Y=21.2 J=20.2 H=18.2 Ks=18.1
VMC 184 10σ, Vega Y=21.9 J=21.4 Ks=20.3
VIDEO 15 5σ, AB Z=25.7 Y=24.6 J=24.5 H=24.0 Ks=23.5
Ultra-‐VISTA 0.70 5σ, AB NB=26.0 Y=26.7 J=26.6 H=26.1 Ks=25.6
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VHS and other Large Area VISTA Surveys
Survey Area (deg2)
Depths Measure (mag)
Depth (mag)
VHS 18, 000 5σ, AB J=21.2 Ks=20.0
1. VHS-‐DES 4500 5σ, AB J=21.6 (H=21.0) Ks=20.4
2. VHS ATLAS 5000 5σ, AB Y=21.2 J=21.2 (H=20.6) Ks=20.0
3. VHS-‐GPS 8000 5σ, AB J=21.2 Ks=20.0
VIKING 1,500 5α, AB Z=23.1 Y=22.3 J=22.1 H=21.5 Ks=21.2
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VISTA Summary Visible and Infrared Survey Telescope for Astronomy (VISTA) • LocaTon: ESO, Paranal, Chile • Aperture: 4.1 m diameter f/1 primary • Field of view: 1.65 degree diameter • InstrumentaTon: VIRCAM ― 8k x 8k
mosaic near-‐infrared camera • Detectors: 16 x 2k x 2k pixel
(Raytheon VIRGO HgCdTe); 67 megapixels
• Wavelength range: 0.84–2.5 microns • Pixel scale: 0.34 arcseconds/pixel
• Surveys start: April 2010
Sparse filled mosaic 90%, 42% spacing IOA, 2012 Sep 12 4
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VISTA Focal Plane • 16 Raytheon VIRGO 2k × 2k
detectors • 67 Million pixels • 4 × 4 sparse array • Spacings 90% & 42% of a
detector • 0.34” pixels
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IR camera field sizes:
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IR focal plane: • 16 arrays, 64 Mpix = 0.60 deg2 on-pixels , 0.34 arcsec/pix.
- 6 offset pawprints gives 1.5 x 1.0 deg2 `tile' , every pixel covered by ≥ 2 pawprints.
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VISTA Tile • 6 poin.ngs or paw-‐prints are required to give a con.guous ‘.le’ • 0.60deg2 of sky coverage per poin.ng
• 1.017 deg x 1.475deg = 1.501 deg2 sky is covered (by a minimum of 2 pixels) as shown in light green in the exposure .me map below for a filled .le.
Relative Exposure Time dark green = 1 light green = 2, magenta = 3 red = 4 yellow = 6
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VHS Components • VHS Galac.c Plane (VHS-‐GP)
– 5< |b| <30 – 8200deg2 – J(60sec); K(60sec)
• VHS-‐ATLAS (VST-‐ATLAS PI: Shanks) – 5000deg2 – Y(60sec), J(60sec), H(60sec), K(60sec)
• Changed April 2012 to Y(120sec), J(60sec), H(0sec), K(60sec) • VHS-‐Dark Energy Survey (VHS-‐DES)
– 4500deg2 ( excludes 500deg2 from VIKING footprint) – J (120sec), H(120sec), K(120sec)
• Changed April 2012 to J(240sec), H(0sec), K(120sec)
9 IOA, 2012 Sep 12
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VISTA Surveys Processing Status
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VHS observa.ons status on July 1st
IOA, 2012 Sep 12 11
Each Observing Block(OB) = 1.5deg2
~5500 deg2 observed
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Next Public Release (upto 2011 Sep 30)
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5 deg x 5 deg patch:
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VHS-‐ATLAS NGP Stellar density distribu.on
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Sergey Koposov, Eduardo Gonzalez
J-K > 0.9
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Period 87 QC
April 2011 – Sep 2011
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VHS-‐ATLAS Tiles: Limi.ng magnitude 5sigma (stars)
IOA, 2012 Sep 12 20
Band Measured (Vega)
Y 20.08
J 19.66
H 18.74
Ks 18.00
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IOA, 2012 Sep 12 21
VHS-‐ATLAS Pawprints: Limi.ng magnitude 5sigma (stars)
Band Measured (Vega)
Y 19.81
J 19.43
H 18.57
Ks 17.84
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SPT-CLJ0546 (z=1.06)
Dark Energy Survey Collaboration Meeting Portsmouth, June 2011 Manda Banerji
Ks~18.5 (10σ AB)
Stellar mass analysis currently ongoing for both clusters (Banerji, Stroe, McMahon, Mohr et al.)
IOA, 2012 Sep 12 22
Ks~18.9 (10σ AB)
1’
SPT-CLJ0528 (z=0.76)
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Future
• Image quality on processed Tiles 0.1” worse than Pawprints and will be effec.ng depth – Could be due to sampling – Need to run further mosaicing and stacking tests
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Changes to observing strategy
• Y/J depths were 0.5 mag shallower than proposal
• ESO response was that no extra .me could be allocated especially since overheads were also 50% higher than planned
• Agreed that .me could be moved from H to Y for VHS-‐ATLAS and from H to J for VHS-‐DES
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Astrometry Quality Assurance • Early independent tests on Pawprint data at the IAC showed
that VHS Astrometry reliable to 0.1”; both random and systama.cs errors
• Recently has been revisited by McMahon, Koposov and Gonzalez looking at Tles. Found that Tile astrometry is reliable at the 0.1” level BUT below 0.1” there are two systema.c effects – as a func.on of posi.on on sky due to reference stars proper mo.ons – as a func.on in the focal plan due to WCS transforma.on
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VHS and Absolute Astrometry Comparison with ICRS Radio Reference Frame
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Comparison of SDSS with ICRS
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Comparison of UKIDSS LAS with ICRS
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Absolute Astrometry Uncertain.es
Survey (n) sigma (StaTsTcal) SystemaTc uncertainty
RA Dec RA Dec
VHS (563) 0.11 0.09 -‐0.011±0.005” -‐0.051±0.004”
SDSS (2308) 0.05” 0.05” 0.006±0.001” -‐0.003±0.001”
UKIDSS (599) 0.10” 0.09” -‐0.031±0.004” -‐0.068±0.004”
IOA, 2012 Sep 12 29
• Note random error will depend on the signal to noise of the object • sigma = FWHM/ (S/N)
• Systema.c is consistent with expected proper mo.ons of 2MASS stars due to the 10 year difference in epoch between 2MASS and VHS. Note this systema.c error varies depending on direc.on in sky due to Solar mo.on with respect to average 2MASS reference star
• Proper mo.ons will be included in a future CASU processing based on UCAC4 or PPMXL
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VHS versus 2MASS Astrometry VDFS end to end self-‐consistency check: CASU-‐WFAU
IOA, 2012 Sep 12 30
J: rms=0.17, 0.15: median=0.004, 0.002 Ks: rms=0.17, 0.15: median=0.004, 0.002
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VHS versus 2MASS Astrometry VDFS end to end self-‐consistency check: CASU-‐WFAU
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• Spa.al systema.c across the focal plane
• Median: 0.044” • Due to FITS World
Coordinate System (WCS) numerical issue in mosaicking of .les.
• Now fixed for future Tile data
• Does not effect pawprint data
• Exis.ng Tile data might be fixed later
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The Dark Energy Survey (US, UK, Spain, Brasil, Germany, Switzerland collabora.on)
• Telescope; upgraded CTIO 3.9m • 525 nights over 5 years • Star.ng late 2012 • First light scheduled for late Sep, 2012 • Mul.ple pass survey so coverage of 5000deg2 in first full observing season
• Field of view • 2.3deg diameter; 3.0deg2
• Very red sensi.ve CCDs • QE; 90% at 900nm; 50% at 1µm
• g, r, i, z, Y wavebands
DECam Focal Plane
62 2kx4k Image CCDs: 520 MPix 8 2kx2k focus, alignment CCDs
4 2kx2k guide CCDs 0.27” per pixel
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DES Imager Installation August 30, 2012
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THE END
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EXTRA SLIDES
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