Predicting Herschel

1
Predicting Herschel SCUBA2 ConfusionMeasuring
Fluctuations Counts Mattia Vaccari
Alberto Franceschini Giulia Rodighiero
Stefano BertaDepartment of Astronomy -
University of Padova

• A) Summary
• Confusion in Herschel SCUBA2 bands is
  estimated using two complementary criteria
• ISO, Spitzer SCUBA counts are used to
  constrain models of extragalactic populations
• Based on such models the two approaches
  respectively measure 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 bands
• Recommendations for planning Herschel SCUBA2
  extragalactic surveys are outlined

Mattia Vaccari mattia_at_mattiavaccari.net www.mattia
vaccari.net

• B) Confusion at Long Wavelengths with Herschel
  SCUBA2
• Confusion sets a major limit to the sensitivity
  of long-? extragalactic surveys
• 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
  SCUBA2 confusion limits and thus allow a timely
  planning of observations

• C) Modelling ISO, Spitzer SCUBA Observations
• Models by Franceschini et al. 2001 (AA, 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 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

• D) Measuring Confusion with Fluctuations
  Counts
• Fluctuations measure fluctuations in the
  background due to unresolved sources
  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 (AA, 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

MIPS 70 ?m
MIPS 24 ?m

• E) Fluctuations vs. Counts Confusion Limits
• 3 ? Fluctuations are very similar to Counts
  10 bps for PACS but nearer to 20 bps for SPIRE
• This is due to the different slopes of PACS and
  SPIRE counts at and fainter than their 10 bps
  levels
• The availability of multi-? (notably MIPS 24/70
  ?m and/or PACS) data will be invaluable in
  accurately pin-pointing SPIRE SCUBA2 sources in
  order to reach down to 10 bps fluxes in all
  Herschel bands

Channel PACS1 PACS2 PACS3 SPIRE1 SPIRE2 SPIRE3 SC2-S SC2-B
?m 70 110 170 250 350 500 450 850
Beam FWHM 4 .74 6.96 10.76 17.1 24.4 34.6 7.4 13.7
3 ? mJy 0.07047 1.002 7.484 18.12 22.55 20.19 1.967 1.383
10 bps mJy 0.1100 1.263 7.090 14.00 15.23 13.23 1.917 1.302
20 bps mJy 0.3029 2.746 11.82 20.49 21.65 18.31 3.426 2.125
30 bps mJy 0.4887 4.034 15.23 25.40 26.34 21.49 4.604 2.755
40 bps mJy 0.6656 5.110 18.12 29.18 29.93 24.09 5.630 3.253
50 bps mJy 0.8350 6.107 20.45 32.47 33.05 26.18 6.467 3.701
(See C) for Legenda)
Confusion sets in at a flux level determined by
the Beam FWHM line (left below) and the 10 beams
per source line (right below) respectively
Integral Counts
SCUBA2 850
SCUBA2 450
SPIRE 350
PACS 170
PACS 70
(See C) for Legenda)
Differential Counts

• F) Recommendations for Herschel SCUBA2 Survey
  Planning
• Target sensitivities envisaged in Herschel
  SCUBA2 surveys appear to be realistic from a
  confusion stand-point when modelling ISO
  Spitzer SCUBA results
• In particular, reaching the 10 mJy level in all
  SPIRE bands appears to be feasible and thus
  somehow mandatory in order to fulfill Herschels
  potential for extragalactic surveys. Such deep
  SPIRE surveys should be undertaken over sky areas
  where deep Spitzer MIPS 24/70 ?m and/or PACS
  coverage is or will be available, e.g. within the
  most popular Cosmic Windows
• Survey-like exploratory efforts should be
  undertaken at a relatively early time during
  Herschel SCUBA2 operations in order to measure
  actual confusion levels and thus ensure to make
  the most of Herschels 3-year life span and of
  SCUBA2s 2-year 5-year plans.

Herschel Extragalactic GT Survey Wedding Cake
Time (hr) PACS (659) SPIRE (850) Harwit
(10) (Spitzer Depths)
Name Area Field PACSTime SPIRE Time 70 110 170 250 350 500
- deg2 - hr hr mJy mJy mJy mJy mJy mJy
Clusters - - 80 100 - - - - - -
Level 1 0.04 GOODS-S 230 1030 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
Level 4 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

• G) Ongoing Work
• Fitting additional observables (e.g. redshift
  distributions) into refined modelling picture
• Comparing our estimates with results obtained
  using other confusion estimators
• Providing a consensus confusion model suitable
  for survey planning
• Applying techniques to other projects, e.g.
  Akari SPICA FIRM