Download Initial Results from the Chandra Shallow X

Initial Results from the Chandra
Shallow X-ray Survey in the NDWFS in
Boötes
S. Murray, C. Jones, W. Forman, A. Kenter, A. Vikhlinin,
P. Green, D. Fabricant, G. Fazio - CfA
B. Jannuzi, A. Dey, J. Najita, M. Brown, K. Brand - NOAO
J. Shields, B. McNamara - OhioU
M. Rieke - AzU
C. Kochanek - OSU
Survey Characteristics
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Large contiguous area (9.3 deg2), with arc
second resolution
Well studied optically - NOAO Deep Wide
File Survey (NDWFS)
Accessible for spectroscopic follow up
(MMT-Hectospec, Gemini, Keck, …)
Multiwavelength coverage (SST-IRAC,
VLA-FIRST, GALEX, …)
Centered at =14h 32m =34 06’
Science Objectives
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Complete Flux Limited Contiguous Survey
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Optical Ids
Redshifts
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Large Scale Structure
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Angular and Spatial Correlations
Luminosity Function
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Spectroscopic complete to R < (21-22)
Photometric to R < (24-26)
Classes
Cluster Survey
Mosaic of X-ray Fields
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126 ACIS-I pointings
(ACIS-S2 chip also)
5 ksec exposure
(4287 - 5120 sec)
Fields overlap by
about 1 arc minute
Total of 630 ksec of
Chandra time (about
2 orbits)
March/April 2003
Representative Single Field
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Seq 3602 (N-F57)
Total counts ~3000
Smoothed with 2 arc
second Gaussian
Raw image analyzed
with wavelet detect
31 sources (2 cts)
1 extended source
X-Ray Survey Detection
Results
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Analysis in 0.5-2 keV, 2-7 keV and 0.5-7 kev
bands independently
CIAO Wavedetect using 1,2,4,8 x 2 scales, 2
count (5 x 10-5) threshold yields:
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4578 pt sources (0.5-7 keV)
3352 pt sources (0.5-2 keV)
2008 pt sources (2-7 keV)
42 extended sources (0.5-2 keV)
2942 pt sources (0.5-7 keV) ≥4 counts
1636 pt sources (0.5-7 keV) with 2 and 3 counts
Spurious Sources
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Fully simulate 400
source free fields
using archival ACIS-I
background data
Scale to 126 fields:
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Expect ~22 spurious
for ≥ 4 counts.
Expect ~625 spurious
for ≥ 2 counts.
Extended Sources
•Matched Filter
Analysis - (Vikhlinin 1995)
• 42 Sources (0.5-2
keV)
• Optical follow ups
indicate most are
clusters
• Spectroscopic
redshifts are next
Cosmic Variance on ACIS-I
16’x16’ FOV
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126 Fields, 4767
sources ≥ 2 counts,
0.5-7 keV
Consistent with
Poisson distribution
with mean 36.33
sources per field
2-Point Angular Correlation
• () is the excess probability of finding a source with
± of another source (Peebles, 1980)
• We estimate () according to Landy and Szalay, 1993
• Kenter et al. Poster (43.15 yesterday) for more details
• Solid line is from Vikhlinin 1995 for ROSAT 140 deg2
Log N - Log S
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Use convolution method (Kenter and Murray
2003) to fit survey data with 2 ct threshold. Note
this is differential N(S), not integral N(>S)
Results agree with previous surveys, including
Chandra Deep Fields (e.g., Giaconni 2001)
Source Identifications
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NDWFS - 9 deg2 in Boötes
(Jannuzi and Dey, 1999; Brown et al., 2003)
 Bw (U and B), R, I => 26 mag
 K 19 - 19.5 => mag
 K partial coverage (6 deg2)
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Sub arc second astrometry
Multicolor magnitudes to few hundredths
Can get estimated photometric redshifts for
galaxies, need spectra for AGN
Match to X-ray sources with ≥ 4 counts (need
good positions)
Fraction ≥ 4 Counts Matched
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Solid Curve - R
Dashed Curve - Bw
Dotted Curve - I
Dot-dashed Curve - K
95% have at least
some match within
the X-ray position
uncertainty
X-ray Optical Matches
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Typical match
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Use greater of 1.5” or
3 X-ray position error
R=23.78 m, X=5.24 ct
~50% of X ≥ 4 ct have
R > 22 m match
Accurate X-ray Positions
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Group of possible IDs
One uniquely within
1.5 arc seconds
R=19 m, X=11.26
Might be a group
Empty Field
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X = 12.76
Rlim=25.8
Only 5% of ≥ 4 count
X-ray sources have
no match => ~150,
but only ~20 spurious
expected
May be extremely
absorbed sources
Near Bright Galaxy
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X = 4.18
Bright elliptical
galaxy is 10 arc
seconds offset
Can mask possible
faint candidate
Spectroscopy
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MMT Hectospect Run
4 Nights for NDWFS
676 X-ray selected
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208
175
293
R<19.2
19.2<R<20.0
20.0<R<22.0
Redshifts for 509; 353 AGN,
152 Galaxy (all z<1)
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98 0.0<z<1.0
183 1.0<z<2.0
72
z>2.0
Conclusions
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Survey detects expected numbers of point and
extended sources.
The NDWFS is a good match to the X-ray depth
and identifies most of the sources.
Optical positions can be used for multi-object
spectroscopy to obtain redshifts (4 nights with
MMT-Hectospec in April, a good start > 676
spectra of X-ray selected objects), more in June
X-ray follow up, especially for extended sources.
When complete will provide a true 3D survey
over 9.3 square degrees