A) Summary Confusion in Herschel & SCUBA2 bands is estimated using two complementary criteria

1. 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@mattiavaccari.net www.mattiavaccari.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 (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 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 (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 Predicting Herschel & SCUBA2 ConfusionMeasuring “Fluctuations” & “Counts”Mattia Vaccari & Alberto Franceschini & Giulia Rodighiero & Stefano BertaDepartment of Astronomy - University of Padova 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 (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 PACS 70 PACS 170 SPIRE 350 SCUBA2 450 SCUBA2 850 (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 Herschel’s 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 Herschel’s 3-year life span and of SCUBA2’s 2-year & 5-year plans. Herschel Extragalactic GT Survey Wedding Cake Time (hr) : PACS (659)SPIRE (850) Harwit (10)(Spitzer Depths) • 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