The Spitzer Source List

Harry Teplitz, Peter Capak, Tim Brooke, Sachin Shenoy, Carolyn
Brinkworth, Vandana Desai,Iﬀat Khan, Russ Laher
IntroducMon

Requirements

Abstract
The Spitzer Science Center will produce a source list (SL) of photometry fora large subset of imaging data in the Spitzer Heritage Archive (SHA). The list
will enable a large range of science projects. The primary requirement on
the SL is very high reliability, with areal coverage, completeness and limiMng
depth being secondary consideraMons. The SHA at the NASA Infrared
Science Archive (IRSA) will serve the SL as an enhanced data product. TheSL will include data from the four channels of IRAC (3‐8 microns) and the 24
micron channel of MIPS. The Source List will include image products(mosaics) and photometric data for Spitzer observaMons of about 1500
square degrees and include around 30 million sources. We describe theplans and Mmeline for development of the Spitzer Source List. We
demonstrate the veriﬁcaMon of the Source List pipeline using Spitzer Legacy
catalogs at "truth tables". Finally, we discuss the range of use cases whichwill be supported.

INTRO•We plan to make a Source List for the Spitzer Heritage Archive, not asource catalog•We present the plans for generaMng a list of ﬂuxes of compact sources•Our goal is to have a lights‐out pipeline for processing..
•Final product to be easily searchable, highly documented, list for archiveusers•Must minimize misuse of the list

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ExtragalacMc– SL shall meet reliability level achieved by Legacy teams– Maximum of 0.01% spurious sources
GalacMc, without structured background– SL shall meet reliability level achieved by Legacy teams– Maximum of 0.05% spurious sources when detected at 10 sigma in two bands
GalacMc, with structure in the background– Maximum of 0.2% spurious sources when detected at 10 sigma in two bands
MIPS‐only ﬁelds (about half of MIPS data)– ExtragalacVc: 0.05%– GalacVc, low BG: 0.1% (appx, sVll under study)– GalacVc, structured BG: 0.25% (appx, sVll under study)
GalacMc with high crowding– Under study– In the worst case, these ﬁelds will have to be rejectedValidaMon
Comparison to SWIRE•Low coverage, xgal legacy survey (test area 0.2 sq. deg.)•We can solve this case•spurious source rate is < 0.01% (area limited number)•Completeness is 80‐90% relaMve to legacy catalog•Some diﬀerences remain (phot. scamer, diﬀ bg sub, SWIRE required ch1+ch2)•Source list to be publically available at IRSA in April 2011

Spitzer Science CenterNASA Infrared Science Archive

Source list, not source catalog
 Need high reliability, but don’t have to be complete Mask signiﬁcant area and when in doubt reject quesMonable sources
Limit to common SNR threshold (10 sigma)
Only point‐ and compact‐sources (FWHM < 2 x PSF)
No requirement on completeness– 80‐90% complete compared to Legacy surveys at 10σ– 50‐70% compared to deeper, Legacy‐survey full catalogs (e.g. c2d “class A+B”
sources down to 5σ),Use only subset of the archive to make list feasible
 Avoid extended sources (local galaxies, etc); very low galacMc laMtude
 Minimum AOR requirements (e.g depth of coverage)
 No 16,70,160 micron data
Use‐case speciﬁc namelists for mosaic and photometry
Need to make super (mulM‐AOR) mosaics
Both APEX and SExtractor in the source list pipeline– SExtractor Aperture photometry for IRAC
 Report single aperture ﬂux and FWHM
– PRF ﬁsng for MIPS
Merge source ﬂuxes for each object into single list row entry (Bandmerge)

SWIRE

Source List P/LComparison to c2d•Typical galacMc, legacy survey (test area 0.4 sq. deg. In Perseus)•We can solve this case•spurious source rate is < 0.1% (area limited number)•Completeness is 80‐90% w.r.t. to legacy catalog “class A”•Some diﬀerences remain (photometry diﬀers by ~15%; c2d used DOphot)
c2d

Source List P/LDistribuMonof Spitzer
observaMonson the sky
IRAC only
MIPS only
BothIRAC+MIPS: 600 sq. degrees; 2/3 at |b|<20
 IRAC only: 350 sq. degrees; 2/3 at |b|<20
 MIPS only: 650 sq. degrees; 1/2 at |b|<20
>= 30e6 galaxies in ch1
 >= 3e6 galaxies in ch4
 >= 1e6 galaxies in MIPS

Red=SWIRE
sources
Blue=source list
extended

SWIRE only
are mostlyRed=c2d
Blue=source list

Pipeline
Source List Inputs
Use‐case speciﬁc namelists for mosaic and photometry• IRAC, GalacMc low bg, GalacMc high bg; xgal: shallow, medium, deep
• MIPS, GalacMc and extragalacMc• Deﬁne GalacMc = ExMncMon E(B‐V)>0.2; or as in abstract••

Mosaicking and Source ExtracMon•Super (mulM‐AOR) mosaics for each PID (Some broken into smaller mosaics tofacilitate processing; max 1 sq. deg.)•Polled Legacy teams for best pracMces:GOODS, COSMOS, SWIRE, MIPSGAL, NOAO Deep/Wide, etc.
•Use some version of Overlap•Outlier RejecMon:
Dual outlier + Box + Temporal for coverage <10Box and Temporal outlier for coverage >=10Higher thresholds used for GalacMc case•Source ExtracMon with APEX and Sextractor
SExtractor extended source masks (see below)
SExtractor Aperture photometry for IRAC
PRF ﬁfng for MIPS
Deblending available in both packages•IniMal extracMon of many sources, then exclude based on masks and shapeparameters•Bandmerge the list
Match to closest object by posiMon, report if mulMple possiblematches exist within posiMonal errors•Require two‐band detecMon in GalacMc cases to reduce spurious sources

Masking
SExtractor extended source mask for each ﬁeld to exclude:• Non‐compact galaxies• Extended background structure• Deﬁnes 0.5sigma isophote
Mask regions around bright stars• 2MASS stars• Bright, red stars idenVﬁed by pixel ﬂuxes in BCDs
• include muxbleed spikes

Reject Spurious Sources Exclude sources that are too compact or too extended– Cosmic rays are too compact; galaxies and false detecVons withinextended emission are too extended– IRAC: Peak pixel ﬂux divided by aperture ﬂux– MIPS Central ﬂux (1 PSF) divided by extracted ﬂux– Reject sources with FWHM inconsistent with point source (>2xPSF)
 Reject source if peak pixel is not within posiMonal uncertainty (0.9 arcsec) ofthe centroid

ArMfact RejecMonIRAC•
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Science Use Cases A user would like to know the ﬂux(es) of individual sources selectedat other wavelengths– Measuring the 24um ﬂux for a list of SDSS quasars– Search for Exo‐Zodiacal dust around main sequence stars– MIPS/IRAC ﬂuxes of UV‐selected starbursts
 A user would like to select objects by color and/or ﬂux– Select obscured quasars– Search for z>5 galaxies– Search for Y, L, T dwarf stars– IdenVfy “Missing” evolved stars– Search for galaxy clusters at z>1
 A user would like to download photometry for a set of objects to do
SED ﬁfng– Line of sight exVncVon curves– Photometric redshi[sSource List (COSMOS)

Lacy et al. (FLS)MIPS

Scamered light:• masked in cBCDs
Muxbleed:• improved in cBCDs; can be masked
False splifng of bright stars:• Bright star mask
Unsplit close pairs:• reject as extended or centroid shi[Cosmic rays:• reject as too compact
CR on top of real source:• Rare; reject as too compact if CR isbright enoughFalsely split extended objects• use SExtractor isophote mask
Structured background emission detected asobject:• isophote mask, reject as too extended• Rarely survives two‐band match••••••

Cosmic rays
• almost never a problem due tohigher coverage
Latent images• mask with new module
False detecMon in airy rings• Increase size of bright star mask?
• Could add iteraVve APEX QA
Structured background emission• SVll under study• Mask more area?
• Add APEX QA following MIPS‐GAL
False detecMon at edges• MaskAsteroids/moving objects• Compare median/mean mosaics

Products•

SL misses source instructureded bg

Mosaics• IRAC data corrected by CBCD pipeline• MIPS data corrected for Latents, Jailbars and delta‐ﬂat• Will produce super‐mosaics crossing AORs and PIDs
• Average images• Median images• Coverage maps
• Uncertainty maps
• IRAC color correcMon maps
Source list
• Will only include compact sources• Extended sources masked to reduce arVfacts and objects with poor
photometry due to confusion• Regions of extended emission have higher S/N cut• The list is not complete, but is robust and cuts are quanVﬁed

We reproduce the selecMon of the AGN “wedge” in IRAC color‐color plot (Lacyet al. 2004, 2007)

NOTEResults remain limited in ﬁelds with highly structured backgrounds.
Few spurious sources are selected but completeness is compromised.