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Extragalactic Confusion Limits in Herschel Key Programs Mattia Vaccari & Alberto Franceschini & Giulia Rodighiero & Stefano Berta Department of Astronomy.

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Presentation on theme: "Extragalactic Confusion Limits in Herschel Key Programs Mattia Vaccari & Alberto Franceschini & Giulia Rodighiero & Stefano Berta Department of Astronomy."— Presentation transcript:

1 Extragalactic Confusion Limits in Herschel Key Programs Mattia Vaccari & Alberto Franceschini & Giulia Rodighiero & Stefano Berta Department of Astronomy - University of Padova A) Summary ISO, Spitzer & SCUBA counts are used to constrain models of extragalactic populations ISO, Spitzer & SCUBA counts are used to constrain models of extragalactic populations Extragalactic confusion in Herschel bands is estimated using 2 complementary criteria Extragalactic confusion in Herschel bands is estimated using 2 complementary criteria The two approaches respectively measure cell-to-cell fluctuations due to unresolved sources and set a maximum number density for resolved sources 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 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 predictions and opportunities for Herschel OT extragalactic KP surveys are outlined Currently envisaged sensitivities for Herschel KP surveys are compared with our predictions and opportunities for Herschel OT extragalactic KP surveys are outlined Mattia Vaccari 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 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. 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 See posters by Franceschini on H-COSMOS and by Dunne & Dunlop on H-SCLS B) Confusion at Long Wavelengths with Herschel Confusion sets a major limit to the sensitivity of long- extragalactic surveys 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 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 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 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 D) Measuring Confusion through “Fluctuations” & “Counts” “Fluctuations” measure fluctuations in the background due to unresolved sources [Franceschini et al (ApJ, 344) ] and set “confusion” at the 3  fluctuation level “Fluctuations” measure fluctuations in the background due to unresolved sources [Franceschini et al (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 (A&A, 378)] “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 (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. 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. F) Recommendations for Herschel GT & OT KP Planning From a confusion point of view, target sensitivities envisaged in Herschel GT KP surveys appear to be realistic when modeling ISO & Spitzer & SCUBA results. From a confusion point of view, target sensitivities envisaged in Herschel GT 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. 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”. 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. 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. ChannelPACS1PACS2PACS3SPIRE1SPIRE2SPIRE3 mmmm Beam FWHM 4.74” 6.96”10.76”17.1”24.4”34.6” 3  [mJy] bps [mJy] bps [mJy] bps [mJy] bps [mJy] bps [mJy] C) Modelling ISO, Spitzer & SCUBA Observations Models by Franceschini et al (A&A, 378) were updated to account for intervened reanalyses of ISO 15  m data and results from Spitzer MIPS and SCUBA observations Models by Franceschini et al (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 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] 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] 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] 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] ultra-luminous starbursts with peak evolution between z = 2 and z = 4 [red long dashed lines]NameAreaField PACS Time SPIRE Time deg^2-hrhrmJymJymJymJymJymJy Clusters Level GOODS-S Level GOODS-N Level GOODS-S Groth Strip Lockman Level 4 2COSMOS XMM-LSS Level 5 10Spitzer Level 6 50Spitzer Time (hr) : PACS (659) SPIRE (850) Harwit (10) (Spitzer Depths) Herschel Extragalactic GT Survey Wedding Cake Confusion sets in at a flux determined by the Beam FWHM line (right) and the 10 bps line (below) SPIRE 350 PACS 170 PACS 70 (See C) for Legenda) Integral Counts Rodighiero et al (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 MIPS 24  m MIPS 70  m MIPS 160  m SCUBA 850  m z-distribution MIPS 24  m (See C) for Legenda) …fitting additional observables into modeling picture and applying techniques to other instruments, e.g. Akari & Planck & SPICA & FIRM. Public web page is also in the works! An Herschel Survey of Surveys (SOS) 3  ~ 10 bps 3  ~ 10 bps 3  ~ 20 bps 3  ~ 20 bps 10 bps 10 bps 20 bps 20 bps From a confusion point of view, rich opportunities exist to extend GT KP mid- & large-area planned surveys (~ 1 deg 2 or larger) to deeper levels, and particularly so on the PACS side Opp. Area What extragalactic OT KP surveys can we ask of Herschel?


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