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

 Large contiguous area (9.3 deg 2 ), with arc second resolution
 Well studied optically - NOAO Deep Wide
File Survey (NDWFS)
 Accessible for spectroscopic follow up
(MMTHectospec, Gemini, Keck, …)
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Multiwavelength coverage (SST-IRAC,
VLAFIRST, GALEX, …)
Centered at

=14 h 32 m

=34
 06’

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Complete Flux Limited Contiguous Survey
 Optical Ids
 Redshifts
 Spectroscopic complete to R < (21-22)
 Photometric to R < (24-26)
Large Scale Structure
 Angular and Spatial Correlations
Luminosity Function
 Classes
Cluster Survey

 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

 Seq 3602 (N-F57)
 Total counts ~3000
 Smoothed with 2 arc second Gaussian
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Raw image analyzed with wavelet detect
31 sources (

2 cts)
 1 extended source

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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:
 4578 pt sources (0.5-7 keV)
 3352 pt sources (0.5-2 keV)
 2008 pt sources (2-7 keV)
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 42 extended sources (0.5-2 keV)
2942 pt sources (0.57 keV) ≥4 counts
 1636 pt sources (0.5-7 keV) with 2 and 3 counts

 Fully simulate 400 source free fields using archival ACIS-I background data
 Scale to 126 fields:
 Expect ~22 spurious for ≥ 4 counts.
 Expect ~625 spurious for ≥ 2 counts.

•Matched Filter
Analysis -
(Vikhlinin 1995)
• 42 Sources (0.5-2 keV)
• Optical follow ups indicate most are clusters
• Spectroscopic redshifts are next

 126 Fields, 4767 sources ≥ 2 counts,
0.5-7 keV
 Consistent with
Poisson distribution with mean 36.33 sources per field

• 
(

) 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 deg 2

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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)

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NDWFS - 9 deg 2 in Boötes
(Jannuzi and Dey, 1999; Brown et al., 2003)
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B w
(U and B), R, I => 26 mag
K 19 - 19.5 => mag
K partial coverage (6 deg 2 )
Sub arc second astrometry
Multicolor magnitudes to few hundredths
Can get estimated photometric redshifts for galaxies, need spectra for AGN
Match to Xray sources with ≥ 4 counts (need good positions)

 Solid Curve - R
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Dashed Curve - B w
Dotted Curve - I
 Dot-dashed Curve - K
 95% have at least some match within the X-ray position uncertainty

 Typical match

Use greater of 1.5” or
3

X-ray position error
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R=23.78 m, X=5.24 ct
~50% of X ≥ 4 ct have
R > 22 m match

 Group of possible IDs
 One uniquely within
1.5 arc seconds
 R=19 m, X=11.26
 Might be a group

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X = 12.76
R lim
=25.8
Only 5% of ≥ 4 count
X-ray sources have no match => ~150, but only ~20 spurious expected
May be extremely absorbed sources

 X = 4.18
 Bright elliptical galaxy is 10 arc seconds offset
 Can mask possible faint candidate

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MMT Hectospect Run
4 Nights for NDWFS
676 X-ray selected
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208 R<19.2
175 19.2<R<20.0
293 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

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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