Transcript Predicting Herschel & SCUBA2 Confusion

Extragalactic Confusion Limits
in Herschel Key Programs
Mattia Vaccari & Alberto Franceschini & Giulia Rodighiero & Stefano Berta
Department of Astronomy - University of Padova
Mattia Vaccari
[email protected]
www.mattiavaccari.net
B) Confusion at Long Wavelengths with Herschel
A) Summary
 ISO, Spitzer & SCUBA counts are used to constrain models of extragalactic populations
 Confusion sets a major limit to the sensitivity of long- extragalactic surveys
 Extragalactic confusion in Herschel bands is estimated using 2 complementary criteria
 As IRAS first dramatically showed, the FIR/sub-mm sky is very densely populated
 ISO & Spitzer & SCUBA confirmed this view providing a wealth of additional data
 Great care must be taken in taking stock of current knowledge in order to predict
Herschel confusion limits and thus allow a timely planning of GT & OT KP observations
 The two approaches respectively measure cell-to-cell fluctuations due to unresolved
sources and set a maximum number density for resolved sources
 These two methods provide results which are in good agreement for all Herschel bands
 Currently envisaged sensitivities for Herschel KP surveys are compared with our
D) Measuring Confusion through “Fluctuations” & “Counts”
predictions and opportunities for Herschel OT extragalactic KP surveys are outlined
 “Fluctuations” measure fluctuations in the background due to unresolved sources
C) Modelling ISO, Spitzer & SCUBA Observations
 Models by Franceschini et al. 2001 (A&A, 378) were updated to account for intervened
reanalyses of ISO 15 m data and results from Spitzer MIPS and SCUBA observations
 Models describe available observables (number counts, z-distributions, L-functions,
integrated CIRB levels…), in terms of four populations
 slowly or non-evolving disk galaxies [blue dotted lines]
 type-1 AGNs evolving as shown by UV and X-ray selected quasars & Seyferts
[green long-short dashed lines]
 moderate-luminosity starbursts with peak emission at z ~ 1 [cyan dot-dashed lines]
 ultra-luminous starbursts with peak evolution between z = 2 and z = 4
[red long dashed lines]
(See C) for Legenda)
MIPS 24 m
MIPS 70 m
MIPS 160 m
[Franceschini et al. 1989 (ApJ, 344) ] and set “confusion” at the 3  fluctuation level
 “Counts” measure source counts and set “confusion” where a maximum number of
sources per beam, or rather a minimum number of beams per source (bps), is reached
[Franceschini et al. 2001 (A&A, 378)]
 Roughly speaking, while “Fluctuations” follow the trend of counts fainter than the
confusion limit, “Counts” follow the trend at brighter fluxes than that. The degree of
consistency between the two depends on the slope of counts at and near this flux limit.
E) “Fluctuations” vs. “Counts” Confusion Limits
 3  “Fluctuations” are very close to “Counts” 10 bps for PACS but nearer to 20
bps for SPIRE, due to different count slopes at and fainter than 10/20 bps levels
 The availability of multi- data (e.g. MIPS 24 m for PACS, PACS & SCUBA2 for
SPIRE, etc) will be invaluable in linking various wavelength regimes and accurately
pin-pointing sources in order to reach down to 10 bps levels in all Herschel bands.
See posters by Franceschini on H-COSMOS and by Dunne & Dunlop on H-SCLS
Rodighiero et al. 2006 (MNRAS, 371)
showed that using conventional
deconvolution techniques one can
use IRAC 3.6 m positions to detect
MIPS 24 m sources down to 3  ~
10 bps levels, thus “extrapolating”
by nearly a decade in , as in e.g.
MIPS 24 m vs SPIRE 250 m
…fitting additional Confusion sets in at a flux determined
by the Beam FWHM line (right)
observables into
and the 10 bps line (below)
modeling picture
and applying
techniques to other
instruments, e.g.
Akari & Planck &
SPICA & FIRM.
Public web page is
also in the works!
z-distribution
MIPS 24 m
SCUBA 850 m
Integral Counts
PACS 70
PACS 170
What extragalactic OT KP surveys can we ask of Herschel?
From a confusion
point of view, rich
opportunities exist
to extend GT KP
mid- & large-area
planned surveys
(~ 1 deg2 or larger)
to deeper levels,
and particularly so
on the PACS side
3  ~ 10 bps
20 bps
10 bps
3  ~ 20 bps
Opp. Area
An Herschel Survey of Surveys (SOS)
www.mattiavaccari.net/herschel/sos
Herschel Extragalactic GT Survey Wedding Cake
(See C) for Legenda)
Channel
PACS1
PACS2
PACS3
SPIRE1
SPIRE2
SPIRE3
m
70
110
170
250
350
500
Beam FWHM 4 .74”
0.07047
3  [mJy]
10 bps [mJy] 0.1100
6.96”
1.002
1.263
10.76”
7.484
7.090
17.1”
18.12
14.00
24.4”
22.55
15.23
34.6”
20.19
13.23
20 bps [mJy]
30 bps [mJy]
40 bps [mJy]
50 bps [mJy]
2.746
4.034
5.110
6.107
11.82
15.23
18.12
20.45
20.49
25.40
29.18
32.47
21.65
26.34
29.93
33.05
18.31
21.49
24.09
26.18
0.3029
0.4887
0.6656
0.8350
F) Recommendations for Herschel GT & OT KP Planning
 From a confusion point of view, target sensitivities envisaged in Herschel GT
Time (hr) : PACS (659) SPIRE (850) Harwit (10) (Spitzer Depths)
Name
Area
Field
PACS
Time
-
deg^2
-
hr
hr
mJy
mJy
mJy
mJy
mJy
mJy
Clusters
-
-
80
100
-
-
-
-
-
-
Level 1
0.04
GOODS-S
230
10+30
1.0
1.0
1.0
3.3
4.0
4.6
Level 2
0.04
GOODS-N
27
10
2.0
2.8
3.0
6.7
8.1
9.2
Level 3
0.25
GOODS-S
34
25
2.2
6.2
6.7
10.5
12.7
14.5
0.25
Groth Strip
34
25
2.2
6.2
6.7
10.5
12.7
14.5
0.25
Lockman
34
25
2.2
6.2
6.7
10.5
12.7
14.5
2
COSMOS
110
50
6.0
9.8
10.5
21.1
25.5
29.1
2
XMM-LSS
110
50
18
9.8
10.5
21.1
25.5
29.1
Level 5
10
Spitzer
185
200
18
16.9
18.0
23.6
28.5
32.5
Level 6
50
Spitzer
-
150
18
-
120
61
74
84
Level 4
SPIRE 350
SPIRE
Time
70
110
170
250
350
500
KP surveys appear to be realistic when modeling ISO & Spitzer & SCUBA results.
 Opportunities exist to go deeper (see posters by Franceschini on H-COSMOS
and by Dunne & Dunlop on H-SCLS) and wider (see posters by De Zotti on SPIRE
LAS and by Serjeant on H-SASSy) over medium- and large-size areas.
 In particular, judging from Spitzer results, reaching the 3  ~ 10 bps levels in all
PACS & SPIRE bands over larger areas than planned in GT KP surveys appears to
be feasible and thus somehow mandatory in order to fulfill Herschel’s potential for
extragalactic surveys. Such deep OT KP surveys should be undertaken over sky
areas where deep Spitzer MIPS 24 m and/or SCUBA2 coverage is or will soon be
available, e.g. within the most popular “Cosmic Windows”.
 Survey-like ultra-deep exploratory efforts should be undertaken at a relatively
early time during Herschel operations in order to determine actual confusion levels
and test deconvolution techniques in a timely manner, thus ensuring to make the
most of Herschel’s 3-year life span.