The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey
Danica Marsden, Megan Gralla, Tobias A. Marriage, Eric R. Switzer, Bruce Partridge, Marcella Massardi, Gustavo Morales, Graeme Addison, J Richard Bond, Devin Crichton, Sudeep Das, Mark Devlin, Rolando Dunner, Amir Hajian, Matt Hilton, Adam Hincks, John P. Hughes, Kent Irwin, Arthur Kosowsky, Felipe Menanteau, Kavilan Moodley, Michael Niemack, Lyman Page, Erik D. Reese, Benjamin Schmitt, Neelima Sehgal, Jonathan Sievers, Suzanne Staggs, Daniel Swetz, Robert Thornton, Edward Wollack
aa r X i v : . [ a s t r o - ph . C O ] M a r Mon. Not. R. Astron. Soc. , 000–000 (0000) Printed 11 March 2014 (MN L A TEX style file v2.2)
The Atacama Cosmology Telescope: Dusty Star-Forming Galaxiesand Active Galactic Nuclei in the Southern Survey
Danica Marsden , , Megan Gralla , Tobias A. Marriage , Eric R. Switzer ,Bruce Partridge , Marcella Massardi , Gustavo Morales , Graeme Addison ,J. Richard Bond , Devin Crichton , Sudeep Das , Mark Devlin , Rolando D ¨unner ,Amir Hajian , Matt Hilton , Adam Hincks , John P. Hughes , Kent Irwin ,Arthur Kosowsky , Felipe Menanteau , Kavilan Moodley , Michael Niemack ,Lyman Page , Erik D. Reese , Benjamin Schmitt , Neelima Sehgal ,Jonathan Sievers , , , Suzanne Staggs , Daniel Swetz , Robert Thornton ,Edward Wollack Department of Physics, University of California, Santa Barbara, CA 93106, USA Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA, USA 19104 Dept. of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218-2686 NASA/Goddard Space Flight Center, Greenbelt, MD, USA 20771 Department of Physics and Astronomy, Haverford College, 370 Lancaster Avenue, Haverford, PA, USA 19041 INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy Departamento de Astronom´ıa y Astrof´ısica, Facultad de F´ısica, Pontificia Universidad Cat´olica de Chile, Casilla 306, Santiago 22, Chile Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON, Canada M5S 3H8 Berkeley Center for Cosmological Physics, LBL and Department of Physics, University of California, Berkeley, CA, USA 94720 Astrophysics and Cosmology Research Unit, School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Durban, 4041, South Africa Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ USA 08854-8019 NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO, USA 80305 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA 15260 Department of Physics, Cornell University, Ithaca, NY 14853 Jadwin Hall, Princeton University, Princeton, NJ, USA 08544 Physics and Astronomy Department, Stony Brook University, Stony Brook, NY 11794-3800, USA Department of Physics, West Chester University of Pennsylvania, West Chester, PA, USA 19383
11 March 2014
ABSTRACT
We present a catalog of 191 extragalactic sources detected by the Atacama Cosmology Tele-scope (ACT) at 148 GHz and/or 218 GHz in the 2008 Southern survey. Flux densities span 14to 1700 mJy, and we use source spectral indices derived using ACT-only data to divide oursources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei(AGN), and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97% of our sources(166 of the AGN and 19 of the DSFGs) with those in currently available catalogs. Whencombined with flux densities from the Australian Telescope 20 GHz survey and follow-upobservations with the Australia Telescope Compact Array, the synchrotron-dominated popu-lation is seen to exhibit a steepening of the slope of the spectral energy distribution from 20to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source popula-tion has a median spectral index, α − , of 3.7 +0 . − . , and includes both local galaxies andsources with redshift around 6. Dusty sources with no counterpart in existing catalogs likelybelong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies orgalaxy groups. Key words: galaxies: surveys – galaxies: active – millimeter: galaxies c (cid:13) D. W. Marsden et al.
The technologies that enable observations of large numbers ofmillimeter and submillimeter sources were developed relatively re-cently. They open up for study a previously unexplored regime thathas the power to reveal the evolution of underlying galaxy popula-tions over cosmic time, and in particular over epochs of intensestar formation. Instruments such as the Submillimeter CommonUser Bolometer Array (SCUBA, SCUBA-2; Holland et al. 1999,2013) operating at 850 µ m, the Balloon-borne Large Area Submil-limeter Telescope (BLAST; Pascale et al. 2008) operating at 250,350 and 500 µ m, the Large Apex Bolometer Camera (LABOCA;Siringo et al. 2009) operating at 870 µ m, and the AzTEC millime-ter wavelength camera (Wilson et al. 2008) operating at 1.1 and2.1 mm have mapped up to 10 deg of the sky, but greater coveragehas been limited by the large amount of integration time requiredto conduct blind surveys to significant cosmological depth. In-creased sky coverage and sensitivity motivated the construction ofspace-based observatories such as Spitzer (Werner et al. 2004) and
Herschel (Pilbratt et al. 2010), operating in the wavelength regime3–500 µ m and covering up to tens of square degrees. At longerwavelengths, the Wilkinson Microwave Anisotropy Probe ( WMAP ;Wright et al. 2009) covered the whole sky at frequencies up to94 GHz ( λ = 3.2 mm), but observations of unresolved extragalac-tic sources were only complete above 2 Jy due to its large beamsize (roughly 13 ′ at 94 GHz). The Planck space telescope con-tains a high frequency instrument observing at frequencies span-ning 100–857 GHz (Lamarre et al. 2010). At 143 and 217 GHz (2.1and 1.4 mm), the
Planck beam sizes are approximately 7 ′ and 5 ′ re-spectively, allowing for a source catalog that is complete down toflux densities of about 1 Jy. Large-area ( >
100 deg ) ground-basedradio surveys probe with higher resolution than WMAP or Planck ,but only as high in frequency as 20 GHz (e.g., the Australia Tele-scope 20 GHz survey; Murphy et al. 2010). Thus there is a nichefor millimeter wavelength large-scale mapping experiments withspatial resolution superior to that of the space-based observatories.One such experiment is the Atacama Cosmology Telescope(ACT; Swetz et al. 2011). The ACT collaboration released Cos-mic Microwave Backgound (CMB) temperature anisotropy mapsmade with arcminute resolution from its 2008 observing seasonat 148 and 218 GHz (D¨unner et al. 2013). These maps also con-tain galaxies that are luminous at millimeter wavelengths. Mea-surements of the millimeter fluxes of a large sample of sourceshave great potential to discriminate among source populationmodels and reveal new source populations. For example, recentmillimeter surveys (e.g., Vieira et al. 2010; Marriage et al. 2011;Planck Collaboration VII 2013) have yielded source counts that ledto updated source models (Tucci et al. 2011) and the discovery of anew class of high-flux dusty galaxies (this publication; Vieira et al.2010; Negrello et al. 2010).ACT-detected sources at flux densities greater than 20 mJy arepredominantly blazars that have synchrotron-dominated spectralenergy distributions (SEDs). These galaxies are powered by activegalactic nuclei (AGN), central black holes that accrete nearby mat-ter in a process that produces time-variable jets out of the plane ofthe accretion disk; in the case of blazars, the jet direction lies closeto our line of sight. Ejected ionized particles spiraling around mag-netic field lines in the jets create the observed synchrotron emis-sion. The study of blazar SEDs and source counts provides infor-mation about AGN physics (e.g., de Zotti et al. 2010; Tucci et al.2011; Planck Collaboration XV 2011).The second population identified at ACT wavelengths is com- prised of infrared-luminous, dusty star-forming galaxies (DSFGs),which exhibit modified blackbody emission at sub-millimeter tomillimeter wavelengths, diminishing toward longer wavelengths.The observed SED is dominated by thermal emission from dustgrains that have been heated by the prodigious optical and ultravi-olet flux produced by newly formed stars (e.g., Draine 2003, andreferences therein). A fraction of these galaxies may have a signifi-cant non-thermal contribution from AGN at their cores, in additionto the thermal dust emission.Some of these DSFGs are local galaxies ( z ≪ λ = 12–100 µ m)are relatively insensitive to dust with temperatures below 30 K,a significant and largely unexplored component of many nearbygalaxies (Planck Collaboration XVI 2011). Recent results from Herschel (Amblard et al. 2010) and BLAST (Wiebe et al. 2009)have begun to extend our picture of the cold dust in galaxies, butmillimeter-wavelength experiments can, through probing dust innearby galaxies, contribute to establishing a well-calibrated dustSED for typical, low-redshift DSFGs. This in turn has cosmologi-cal ramifications, as current analyses of the first generations of starsand galaxies that fuel the cosmic infrared background (CIB) rely onunderstanding and extrapolating from dust SED templates.High-redshift DSFGs were observed by SCUBA in the firstsystematic survey of these sources, which create a significantfraction of the CIB emission (Blain et al. 2002). Selected at850 µ m, these sources came to be known as submillimeter galax-ies (SMGs). This new population of galaxies subsequently becamea focus of observations (e.g., Weiß et al. 2009; Viero et al. 2009;Austermann et al. 2010) and stacking analyses that resolved moreof the CIB into emission from discrete, dusty star-forming galax-ies (e.g., Dole et al. 2006; Devlin et al. 2009). Though most SMGswill be undetectable by current millimeter survey instruments, anew population of sources that are significantly brighter and rarerthan the submillimeter-selected SMGs and that similarly exhibitdust-dominated spectral indices has been identified at millimeterwavelengths (Vieira et al. 2010). They do not have counterparts inthe IRAS catalog, indicating that they are not members of the stan-dard, local, ultraluminous infrared galaxy (ULIRG) population.These sources have recently been shown to be a new,higher redshift ( z >
3) subpopulation of the progenitor galaxybackground, brought to the fore in millimeter wavelength sur-veys because they are lensed by foreground galaxies or galaxygroups (Negrello et al. 2007; Lima et al. 2010; Negrello et al.2010; Vieira et al. 2013; Hezaveh et al. 2013). Such objects areextremely rare (at submillimeter wavelengths, for example, seeRex et al. 2010; Lupu et al. 2012), but wide area surveys will findmore. The South Pole Telescope (SPT; Carlstrom et al. 2011) hasreported significant numbers of these sources. This population pro-vides an avenue for follow-up research to study the details not onlyof lensed SMGs, but also of the lens systems (e.g., Ikarashi et al.2011; Scott et al. 2011; Lupu et al. 2012; Weiß et al. 2013).In this paper, we report for the first time the discovery ofDSFGs in the ACT data. This is the first multifrequency analysisof the ACT sources and the second report on ACT extragalacticsources. Marriage et al. (2011), hereafter M11, presented a catalogof sources at 148 GHz only from the 455 deg of the 2008 ACTSouthern survey with the best uniformity and coverage. Here weextend those results to include 218 GHz (and updated 148 GHz)flux densities for the same 2008 ACT Southern survey region fromthe new (D¨unner et al. 2013, hereafter D13) data release maps.Gralla et al., in prep. will present sources detected in the ACT c (cid:13) , 000–000 CT-detected Sources at 148 & 218 GHz R.A. (J2000)-56 (cid:0) -54 (cid:0) -52 (cid:0) -50 (cid:0) D e c . ( J ) h h h h h h h -56 (cid:1) -54 (cid:1) -52 (cid:1) -50 (cid:1) D e c . ( J ) Figure 1.
Sensitivity maps with source detections at 148 GHz (top) and 218 GHz (bottom), showing the most uniform 455 deg patch of the Southern strip withthe greatest depth of coverage. It lies between right ascension h m and h m , and declination − ◦ ′ and − ◦ ′ . The deepest data correspond toan exposure time of 23.5 minutes per square arcminute and a 1 σ sensitivity of 2.34 mJy at 148 GHz and 3.66 mJy at 218 GHz. White circles or squares markthe locations of ACT sources with a size proportional to the log of the associated source flux density. Circles denote sources designated as AGN, and squaresdenote sources with spectra indicative of DSFGs. Toward the edges of the map, the variation in local noise properties due to uneven coverage is more apparent. Equatorial strip . Mapmaking of the ACT 277 GHz dataset is cur-rently under way.The layout of the paper is as follows. Section 2 describes the2008 season ACT observations and the reduction of raw data intomaps, as well as follow-up observations made with the AustralianTelescope Compact Array (ATCA). Section 3 details our method ofsource extraction. The source catalog, including its astrometric andflux density accuracy, and its estimated completeness and purity, isdiscussed in Section 4. Section 5 compares our catalog with cur-rently available datasets; Section 6 gives the source number counts.Trends observed in the spectral indices of our source populationsare analyzed in Section 7. We conclude in Section 8 with a sum-mary of our results.
The ACT experiment (Swetz et al. 2011) is situated on theslopes of Cerro Toco in the Atacama Desert of Chile at an ele-vation of 5,190 m. ACT’s latitude gives access to both the north-ern and southern celestial hemispheres. Observations occurred si-multaneously in three frequency bands, at 148 GHz (2.0 mm),218 GHz (1.4 mm) and 277 GHz (1.1 mm) with angular resolutionsof roughly 1.4 ′ , 1.0 ′ and 0.9 ′ respectively. Observations of Saturnwere used to determine beam profiles and pointing (Hincks et al.2010; Hasselfield et al. 2013). From 2007 to 2010, ACT targetedtwo survey regions: the Southern strip centered around δ = − . ◦ and the Equatorial strip centered around δ = ◦ . Further informa-tion about the ACT observations can be found in D13. ◦ south latitude, 67.7875 ◦ west longitude. The reduction of raw ACT data into maps is detailed in D13;we will briefly review that process here. Each ACT detector ar-ray (one per frequency band) is composed of 1,024 detectors, witheach detector timestream first analyzed and then kept or rejectedbased on multiple criteria, such as telescope operation, weatherconditions, cosmic ray hits, or other interference. Approximately800 (700) hours of data from the 2008
Southern strip for 148 GHz(218 GHz) remain after these cuts.Maximum likelihood maps of pixels 30 ′′ on a side are pro-duced from the timestream data. From an initial estimate of themaps, source profiles are fit for. We then subtract the timestreammodels for the point sources from the data and re-map. This pre-vents point source power from being aliased into the map, and im-proves the final flux density estimates for S/N > th iteration of the maps used in our study. For148 GHz, the D13 release map is from iteration 1000 of the map-maker, and we use this map both for convenience and in order thatthis study be exactly reproducible using public data. For our studyof source flux densities at 218 GHz, we use iteration 200, whichis more than adequate. Between the map iterations used in thisstudy, the fluxes of the sources change less than . One may askwhether the value to which the measured source flux density hasconverged is accurate. Based on end-to-end simulations in which c (cid:13) , 000–000 D. W. Marsden et al. mock sources are injected into the ACT time streams, we estimatethis accuracy at 3%.The 148 GHz map is calibrated in temperature through crosscomparison of spectra over the range 400 < ℓ < photometric errors for both bands. The profiles of brightpoint sources in the survey maps suggest that the effective beamfor the survey is slightly broader than that measured from Saturn.The survey maps consist of overlapping observations taken overthe entire season, and the observed broadening may be attributedto a night-by-night jitter in the telescope pointing with an rms of5 ± ′′ (Hasselfield et al. 2013). The uncertainty in jitter correctioncorresponds to (148 GHz) and (218 GHz) photometric un-certainties, which are correlated between bands.Finally, for our photometric uncertainty budget we account forthe fact that AGN have a lower effective frequency band center(and thus slightly broader beam) than Saturn, and DSFGs have ahigher effective frequency band center (and thus narrower beam;Swetz et al. 2011, Table 4). We choose effective 148 GHz and218 GHz frequency centers corresponding to halfway between asteep spectrum AGN and a DSFG: 148.65 GHz and 218.6 GHz.This choice introduces a photometric bias of less than 1.5% at148 GHz and 1.1% at 218 GHz, which is positive for DSFGs andnegative for steep spectrum AGN. We fold this photometric biasfrom the source spectrum in with uncertainties due to mapping(3%), WMAP calibration (2%, 2.4%) and beam shape (1.4%, 2.2%)to obtain an overall flux density calibration uncertainty of 4.1% at148 GHz and 4.6% at 218 GHz. As shown in Section 5, the ACTflux densities agree with independent measurements to within thismargin of error.For this study, we have used the most uniform 455 deg of the2008 ACT Southern strip at 148 and 218 GHz. This region, shownin Figure 1, spans declination -56.2 ◦ < δ < -49.0 ◦ and right ascen-sion h m < α < h m . At 148 GHz we use the data publicly released with D13 . Typical white noise levels in this region ofthe map are 30 µ K-arcminute at 148 GHz and 50 µ K-arcminute for218 GHz. As described in Section 3, when matched-filtered withthe ACT beam, this white noise level results in a 1 σ point sourceflux density sensitivity in the best covered regions of σ = 2.34 mJyat 148 GHz and 3.66 mJy at 218 GHz. The sensitivity levels in Fig-ure 1 are proportional to the square root of the number of obser-vations at that map location, N obs , with one observation per 0.005seconds. Then the sensitivity level in a given portion of the map is σ = σ p N obs , max /N obs . Marriage et al. (2011) found that the sample of ACT 148 GHz -detected sources cross-identified with the Australian Telescope20 GHz survey (AT20G; Murphy et al. 2010) is dominated bysources with peaked or falling SEDs using flux densities mea-sured at 5, 20 and 148 GHz. The study also confirmed the find-ings of the AT20G study (Murphy et al. 2010; Massardi, M. et al.2011), namely that this population of radio sources is character-ized, on average, by spectral steepening between 20–30 GHz and148 GHz. However, this sample from M11 was incomplete, biasedin a way that favored sources with negative spectral indices between20 and 148 GHz due to the AT20G survey completeness level of78% above 50 mJy at 20 GHz. ACT-selected sources with 148 GHzflux densities less than 50 mJy and flat or rising spectra may nothave been detected by AT20G. Therefore, in order to complete theM11 20–148 GHz spectral study, a targeted set of measurements offlux densities at 20 GHz was made for the M11 sources that werenot identified with any source in the AT20G catalog within a 30 ′′ search radius.Scheduling and weather constraints permitted us to observe 41of these 48 sources with the 6 ×
22 m antenna array of ATCA over6.5 hours at 20 GHz on November 10, 2010, when the array was inits East-West 750A configuration, with 15 baselines ranging from77 to 3750 m. The primary beam of each array telescope at 20 GHzis 2.3 ′ , with a resolution of 0.5 ′′ possible with the full array in thisconfiguration. The synchrotron-dominated spectra of these sources,as revealed in M11, indicated that they were compact (AGN), andwould be unresolved. For these observations, the two 2 GHz-widefrequency bands of the new ATCA Compact Array BroadbandBackend (CABB; Wilson et al. 2011) digital array correlators wereset to be adjacent by centering them at 19 GHz and 21 GHz. The re-duced average flux densities over the whole bandwidth of the corre-lator corresponds to the “20 GHz” flux density. Good weather con-ditions prevailed throughout the observations, from 07:35:24.9 UTthrough 14:11:54.9 UT. A few data blocks were flagged and re-moved in order to minimize noise and any spurious effects.The primary flux calibrator used for these observations wasPKS B1934-638, and the bandpass calibrator used was PKSB1921-293. The target sources were expected to have flux densi-ties at or just below the AT20G survey limit of 40 mJy. Each targetsource was observed once for 1.5 minutes for an rms noise level of http://lambda.gsfc.nasa.gov/product/act/ (cid:13) , 000–000 CT-detected Sources at 148 & 218 GHz The ATCA follow-up data was reduced using a fully au-tomated, custom, shell script pipeline based on tasks from theMIRIAD aperture synthesis reduction package (Sault et al. 1995).An initial inspection of the data was performed to identify contam-ination or any problems in the data acquisition. Automatic proce-dures were used to identify and flag data for each frequency bandaffected by shadowing or known radio contamination, resulting inless than 1% of the band being flagged and cut. The pipeline thengenerated the calibration solutions for bandpass, flux density ampli-tude and phase based on the calibrators. After checking that resultswere consistent between the two frequency bands, we merged thecalibrated target visibilities before extracting the flux densities toimprove sensitivity.Analyses of the AT20G survey (Murphy et al. 2010) and ofother ATCA projects (Massardi et al. 2011; Bonavera et al. 2011)have shown that the triple correlation technique (Thompson et al.1986) can be effectively used to determine source flux densitiesdown to tenth of mJy scales for point-like sources unaffected bypoor phase stability. This technique is effective for point sourceseven if they are not in the phase center and in the case of low S/N.We manually inspected the 20 GHz deconvolved images, andwherever a source was clearly identifiable we measured its fluxdensity and flux density error at its peak in the image and the rmsof the image pixels in a region unaffected by the source emission.For sources with high S/N, deconvolution techniques were able toreconstruct images, despite the poor uv -coverage of our observa-tions. In the few cases where the source appeared extended withrespect to the synthesized beam we estimated the flux density byintegrating over the source area. In some cases, the image showeda confused field with multiple peaks, primarily due to sidelobes;for these cases we extracted a flux density estimate using the triplecorrelation technique. The flux density errors were obtained fromthe rms of the visibilities of the V Stokes parameter. This assumesthat these objects have negligible circular polarization, which is anoverestimate in the cases where the source is not in the phase cen-ter. The same statistic (V Stokes rms) was used to indicate the noiselevel reached for fields where no source was identified at 20 GHz.Of the 41 ACT sources observed in the follow-up campaign de-scribed here, all had a measured flux density at 20 GHz. The finalresults of this study are included as part of Table 4 with asterisksindicating sources that were part of the follow-up ATCA sample. We use the same matched filtering method as described in M11to produce an estimate of the amplitude of a source at the locationof the source center. In this section we summarize the method withan emphasis on aspects for which this analysis differs from M11.Initially, the data are weighted by the square root of the num-ber of observations per pixel. This method results in a map with anapproximately constant white noise level and a natural apodizationas the number of observations falls off toward the edge of the surveyregion. Using a new procedure, we filter the entire D13 148 GHz re-lease map and corresponding 218 GHz map, both of which extendbeyond the deep 455 deg area of this study, in order to eliminateany potential edge effects. We then use only the 455 deg regionfor source identification.The following filter is applied to the Fourier transform of themap:
148 GHz Filter148 GHz Beam218 GHz Filter218 GHz Beam
Figure 2.
Matched filters (solid lines) are band pass filters that smooth themap on the scale of the beam (dashed lines) and remove large scale structureassociated with the CMB, other astrophysical signals (e.g., the Sunyaev-Zel’dovich effect) and residual contamination from atmospheric brightnessfluctuations. The beam and filter functions are plotted with unit normaliza-tion at their peak ( θ = 0). The matched filters were binned in radius to bettershow the relevant angular scales. In the analysis, we use two dimensionalfilters to capture the anisotropic character of the noise. Φ( k ) = F k ,k x ( k ) ˜ B ∗ ( k ) | ˜ T other ( k ) | − R ˜ B ∗ ( k ′ ) F k ,k x ( k ′ ) | ˜ T other ( k ′ ) | − ˜ B ( k ′ ) d k ′ , (1)where k = ( k x , k y ) is the angular wave number, and x and y re-fer to the right ascension and declination directions. B ( k ) is theFourier transform of the “effective” instrument beam. As describedin Section 2, the “instantaneous” beam is derived from planet obser-vations (Hasselfield et al. 2013). The “effective beam” in the 2008survey map is broadened by imperfect telescope repointing withmean deviation σ θ = 5 ′′ . This broadening is included in B ( k ) bymultiplying the instantaneous beam transform (released with D13for 148 GHz) by exp( − ℓ σ θ / . ˜ T other is the Fourier transformof all components of the data besides point sources (i.e., atmo-spheric or detector noise, CMB, etc.). The function F k ,k x ( k ) isa high-pass filter that removes undersampled large scale modes be-low k = 1000 and modes with | k x | < B ( k ) is well approximated as azimuthally symmetric, weretain the full two dimensional power spectrum | ˜ T other ( k ′ ) | todownweight anisotropic noise in the maps. The azimuthally-binned148 and 218 GHz real space filters and associated beam profiles areshown in Figure 2.The power spectrum | ˜ T other ( k ′ ) | used in this analysis wasconstructed in a different manner from M11: we used the powerspectrum of the data itself instead of the average of difference(noise) maps and models for the CMB and other contaminating skyemission. This estimate is robust since the total power from the ex-tragalactic source signal is low compared to the CMB, atmosphericnoise, and white noise. To avoid a noisy estimate of the power spec-trum, we smooth the power spectrum | ˜ T other ( k ′ ) | with a Gaus-sian. The exact formulation of the smoothing does not significantlychange the resulting filtered map.Applying the matched filter can cause ringing in the mapsaround the very brightest sources, which impacts source extractionaround other, low S/N, sources. Therefore, we identify sources with c (cid:13) , 000–000 D. W. Marsden et al. -51.5-52.0-52.5-53.0 D e c li n a t i o n ( J )
148 GHz −15−10 −5 0 5 10 15 505152535455565758 R.A. (J2000)-51.5-52.0-52.5-53.0 D e c li n a t i o n ( J )
218 GHz −15−10 −5 0 5 10 15
Figure 3.
Filtered 148 GHz (top) and 218 GHz (bottom) submaps. The datahave been match-filtered such that the grey-scale is in units of flux density(mJy) with white (black) corresponding to -10 mJy (30 mJy). Insets showthe flux density distribution across the data as a grey histogram that has astandard deviation of 2.57 mJy (3.78 mJy) for 148 GHz (218 GHz). Severalsources, both synchrotron and dust dominated, marked as circle and squareoutlines respectively, are apparent as black beam-sized flux excesses. Thewhite extended object in the 148 GHz map, marked by a diamond, is theSunyaev Zel’dovich effect decrement from Abell 3128 NE (ACT-CL J0330-5228).
S/N >
50 in an initial application of the filter, and mask them in themaps. Sources with S/N <
50 are then extracted by match filter-ing these masked maps. Once filtered, groups of map pixels withS/N > ◦ on aside around each source through Fourier space zero-padding (e.g.,Press et al. 2007) to allow for a more precise determination of thesource peak location, and therefore its flux density. Properly cen-tering the detection has the effect of boosting the S/N of typicalS/N = 4.8 sources to >
5. Lastly, to account for the convolution ofsources with the map pixel, which acts as a low pass filter (thesquare pixels become a sinc function in Fourier space), we decon-volve the map pixel window function in the higher resolution map.We find that this method reduces systematic errors associated withpixelization to below 1%. Purity tests (Section 4.3) reveal a signifi-cant number of false detections below S/N of 5.0, due to local noiseand striping artifacts. Therefore we impose a S/N = 5.0 thresholdon sources detected in each map assuming no prior knowledge ofsource location from the other frequency.Once a S/N > The ACT-detected source catalog is given in Table 4. Wefind 169 sources selected at 148 GHz with S/N >
5, spanning twodecades in flux density, from 14 to 1700 mJy. The 218 GHz map in-dependently yielded 133 sources with S/N >
5. The combination ofthese two independent source lists gives a total count of 191, with110 galaxies detected with S/N > α − , between 148 and 218 GHz for each source, are provided.The classification of sources as dust or synchrotron-dominated isbased on the α − spectral index criterion described in Sec-tion 4.2. If the source was cross-identified with an AT20G catalogsource (see Section 5), the AT20G source ID is given. If, instead,the 20 GHz source flux density was measured during the November2010 follow-up campaign (Section 2.3), the 20 GHz ID name hasan asterisk next to it. Sources not cross-identified with one of thecatalogs listed in Section 5 are marked with a “d” superscript.Correlating 148 GHz flux densities between this catalog andthe catalog given in M11, we find an average agreement at the 2%level, with larger scatter for individual sources. This level of consis-tency is expected given changes in calibration, map-making, beamprofile estimates, and deboosting procedure made for this updatedstudy.The reported flux densities are the average over approximatelytwo months of observation for each source, many of which areAGN-driven radio galaxies and thus likely to have varied in thattime. For example, of the three bright sources cross-identified with Planck , in the year between ACT and
Planck observations onesource varied by 20% in flux density whereas another did not varyat all within errors. However, our simultaneous multifrequency ob-servations allow for a consistent internal spectral characterizationbetween ACT bands. In a future study, multiple years of data willbe used to quantify the effects of variability on individual sourcespectra.The following sections provide details and context for the cat-alog values.
Radio interferometers can achieve very precise positional ac-curacy for sources, so ACT-selected sources cross-identified witha robust radio catalog give a good measure of the positional accu-racy of the ACT source detections. The AT20G catalog covers theSouthern sky, and through pointing checks against Very Long Base-line Interferometer (VLBI) measurements of International CelestialReference Frame calibrators, the positional accuracy of AT20G isshown to be accurate to better than 1 ′′ (Murphy et al. 2010). Weexclude nearby extended/resolved sources from this analysis, deter-mined from cross-identification of our sources with currently avail-able catalogs, as distant point-like sources will present a clearerpicture of the overall accuracy of our pointing.We compared the positions of the 34 ACT sources withS/N >
16 to positions of associated sources in the AT20G cat-alog using a search radius of half the ACT 148 GHz beam (0.7 ′ ).Figure 4 shows the offsets in location between the AT20G right as-cension (RA) and declination (Dec) and the ACT-derived positions c (cid:13) , 000–000 CT-detected Sources at 148 & 218 GHz Table 1.
Astrometric Pointing Accuracy148 GHz 218 GHzMean RA Offset ( ′′ ) 0.6 ± ± ′′ ) − . ± ± ′′ ) 2.1 3.5RMS in Dec Offset ( ′′ ) 1.8 3.4 (cid:2) (cid:2) (cid:2) (cid:2) (cid:2) (cid:2) D e c li n a t i o n ( " ) Figure 4.
Astrometric accuracy of the ACT source detections. The 34 filledblack circles are the positional offsets of ACT sources with S/N > for the sources as they were detected in the 148 GHz (black points)and 218 GHz (blue points) maps. The results are also summarizedin Table 1. The large overlaid errorbars are centered on the meanoffsets, and extend as far as the rms of the offsets. For sources withlower S/N, the ACT location rms with respect to AT20G positionbecomes inflated by the effect of noise in the maps. Therefore thecatalog uses coordinates derived from the 148 GHz map since thereis a higher level of noise present in the 218 GHz map. Flux densities derived from the ACT maps have systematicuncertainties arising from five effects: the overall calibration un-certainty, the mapmaker, errors in the assumed source profile, errorin the assumed source spectrum, and flux boosting of lower signif-icance candidates. The first four potential sources of flux densityerror were discussed in Section 2. Here we will discuss the lastsource of flux density error.The differential counts of the sources selected in our sam-ple fall steeply with increasing flux (Table 2, Figure 6). With noprior information about the source flux, the most likely scenario isthat the measured flux is the sum of a dimmer intrinsic flux and apositive noise fluctuation. We use the two-band Bayesian methoddeveloped in Crawford et al. (2010), and report the 16, 50, and84 percentiles ( enclosed, equivalent to σ ) of the posterior flux and spectral index distributions. For the source count priorsin this calculation we use the sum of the models of de Zotti et al.(2010) for radio sources (using the Tucci et al. 2011 model re-sults in flux differences of < σ ) and B´ethermin et al. (2011)for dust-dominated sources. Following Vieira et al. (2010), we takea flat prior on the spectral index between − and , consistentwith the expected range for our populations. The two-band like-lihood includes negligible correlation between bands and is consis-tent with background astrophysical emission rather than correlatedatmospheric emission.The source populations in 148 and 218 GHz naturally splitinto sources having their emission dominated by synchrotron (cen-tered on α = -0.6) or thermal dust (centered on α = 3.7; see Fig-ure 7, bottom panel). We use the threshold spectral index α = 1.66(Vieira et al. 2010) to divide these populations in terms of their pos-terior spectral index populations, with P ( α > > P ( α > < α ± ( S/N ) / p S/N − . For sourcesin the range 20–25 mJy, this is a correction of 0.5% at 148 GHzand 1.5% at 218 GHz. We have confirmed through simulations withsynthetic sources implanted in the ACT data that this positional de-boosting results in unbiased flux densities. Furthermore, we havecompared raw flux densities from the matched filter to flux den-sities from the ACT data at the positions of ATCA counterparts,when available. The latter should not be boosted due to maximiz-ing the flux over position in RA and Dec. As expected, we find thatpositional deboosting accounts for the ratio between the raw fluxdensities and the flux densities derived using ATCA counterpart lo-cations.As a final consistency check, we note that for the sources ob-served by both ACT and Planck , flux densities are consistent atthe ≈ The number of false detections at each frequency was esti-mated by running the detection algorithm on an inverted (nega-tive temperature) map in which we masked the sources and, in thecase of the 148 GHz map (for which the Sunyaev-Zel’dovich effectwas non-zero), all ACT-detected and optically confirmed clustersof galaxies. With this approach, no spurious detections are foundin the 148 GHz data down to a S/N of 5. In the 218 GHz data, fourspurious detections at S/N c (cid:13) , 000–000 D. W. Marsden et al.
Table 2.
Number Counts, Purity, and Completeness a .148 GHz 218 GHzFlux Range (Jy) N Purity Completeness N Purity Completeness N bsync N cdust ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± a The number of sources at each frequency with S/N = 5 over 455 deg . Errors on number count are simplyPoisson. See Figure 6 for a graph of purity/completeness-corrected differential source counts. b Counts of synchrotron-dominated sources are taken relative to the 148 GHz flux density. c Counts of dust-dominated sources are binned according to their 218 GHz flux density. ings from source cross-identification (Section 5). At 148 GHz, onlyone 5 σ source, ACT-S J023600-530237, is not cross-identifiedwith other catalogs. At 218 GHz, five 5 σ sources, ACT-S J024430-541605, ACT-S J035034-524801, ACT-S J062747-512614, ACT-S J063715-500414 and ACT-S J065207-551605, are not cross-identified with other catalogs, although we expect some of theseto be real DSFGs, a hypothesis which will be tested through futurefollow-up observations.In order to estimate completeness of the catalog for each band,we added 100 synthetic sources of a single flux density to the455 deg region of the ACT maps used in this study. The map filter-ing and source detection algorithm (Section 3) were run, and the re-sulting catalog checked for inclusion of the input sources. This pro-cedure was repeated in each band in intervals of 10 mJy in syntheticsource flux density in the range 10–100 mJy. The completeness ateach flux density was interpolated to estimate the completeness influx density bins given in Table 2. To further characterize ACT sources, we consider cross-identifications with other catalogs. Given the number of ACT-detected sources and the ACT beam size, around 1 out of 10,000sources randomly placed in the 455 deg area considered herewould coincide with an ACT source. Figure 5 shows the ACTsources located in flux density space, and cross-identifications fromsome overlapping catalogs with extragalactic source detections inthe southern hemisphere discussed in this section. The synchrotron-dominated sources occupy points near the power law S ν ∝ ν α with spectral index α = -0.6. Dust-dominated sources will followa line closer to α = 3.7, and are generally associated with sourcesdetected with S/N > S [mJy] S [ m J y ] S/N = 5.0 (cid:3) = 1.66IRASATCASUMSSSPTPlanck
Figure 5.
The ACT sources cross-identified in flux density space. Sourceshave been selected with S/N > S ν ∝ ν α with α = 1.66 for the dashed line, distinguishing the α = − . (dash-dot)synchrotron-dominated source population from the α = 3.7 (dash-dot-dot)dust-dominated source population. individual follow-up studies (e.g., Ikarashi et al. 2011; Scott et al.2011; Lupu et al. 2012; Weiß et al. 2013). Of our 191 sources, many have cross-identifications withseveral catalogs. One hundred seventy-four are identified withsources in the 0.84 GHz Sydney University Molonglo Sky Sur-vey (SUMSS; Mauch et al. 2003), and 122 of those cross-identifiedsources also belong to the 4.85 GHz Parkes-MIT-NRAO (PMN)survey radio catalog (Wright et al. 1994). Fourteen sources werecross-identified with the Infrared Astronomical Satellite (IRAS; c (cid:13) , 000–000 CT-detected Sources at 148 & 218 GHz Helou et al. 1988) at 12–100 µ m. Sources were also identified withone or both of the Australian Telescope 20 GHz survey (AT20G;Murphy et al. 2010) and the 1.4/2.0 mm SPT (Vieira et al. 2010)catalogs. Two of the remaining 8 unmatched sources were observedduring the November 2010 ATCA follow-up campaign (Sec-tion 2.3). This leaves 6 sources (ACT-S J023600-530237, ACT-S J024430-541605, ACT-S J035034-524801, ACT-S J062747-512614, ACT-S J063715-500414 and ACT-S J065207-551605)with no identification in any of the available catalogs, all but one ofwhich have dust-dominated spectra. The single unidentified sourcewith a synchrotron spectrum, ACT-S J023600-530237, falls nearour S/N = 5 threshold at 148 GHz and could be a false detection.A NASA/IPAC Extragalactic Database (NED) search using aradius of 2 ′ cross-identified 3 sources from the ACT catalog withgalaxy clusters: Abell S0250, Abell 3391 and S´ersic 037/01. In-creasing the search radius to 3 ′ adds Abell 3128 and Abell 3395 tothis list. Simulations of the microwave sky suggest that only ≈ The AT20G survey, carried out from 2004 to 2008 at 20 GHzwith follow-up at 5 and 8 GHz, covered 6.1 sr of the Southern skyto a flux density limit of 40 mJy at 20 GHz (Murphy et al. 2010).Of our sources, 115 match sources in the AT20G catalog, listed inTable 4, all of which we classify as synchrotron-dominated. Giventhe AT20G completeness limit and the predominance of flat spectrafor our 148 GHz-selected sources (Section 7), faint ACT sourcesmay not have matches in AT20G. We received time on the AustraliaTelescope Compact Array to measure flux densities for sources inthe earlier M11 catalog that did not appear in AT20G, the results ofwhich are described in Sections 2.3 and 7.
The
Planck satellite team has released two sets of all-sky cata-logs in nine frequency channels, including two very close to thoseused by ACT. The first set of catalogs made up the Early ReleaseCompact Source Catalog (ERCSC; Planck Collaboration XIII2011). Very recently, a deeper catalog based on 1.6 complete
Planck surveys has been released, the Planck Catalog of CompactSources (PCCS; Planck Collaboration XXVIII 2013). At 143 and217 GHz, the
Planck beam sizes are approximately 7 ′ and 5 ′ re-spectively. Like WMAP, Planck makes great gains by observingthe entire sky simultaneously at several frequencies, thus captur-ing all bright sources. On the other hand, due to their large beamsizes, these experiments detect only the brightest sources. In thecase of the PCCS, the detection threshold at 143 and 217 GHz is ≈
400 mJy; at lower flux densities the catalog completeness dropswell below 80%. In the area treated in this study,
Planck detects 3of the brightest ACT sources.For a more complete comparison with the PCCS, we exam-ined all bright ACT sources, combining the Equatorial and South-ern regions mapped by ACT. Almost 50 matches were found inthis wider comparison. At 148 GHz, the agreement of ACT fluxdensities and the PCCS flux densities, properly color-corrected and(slightly) extrapolated to match ACT’s central frequency, is excel-lent, at the 1-2% level, despite scatter introduced by source variabil-ity. At 218 GHz, source variability plays at least as large a role, andPCCS flux densities are ≈
5% higher than ACT’s. If we remove a couple of the most variable sources, however, the agreement of the218 GHz flux density scales improves to ≈ Planck fluxes are on average slightly higher. Agreement at the ≈ The SPT study of compact sources (Vieira et al. 2010) wasbased on observations of a square patch of sky of 87 deg centeredat 05 h right ascension, having only fractional ACT overlap. Nev-ertheless, 2,304 of the 3,496 SPT candidate sources (those withS/N > > > ±
5% level at 148 GHz and 3 ±
7% at 218 GHz, with ACTflux densities typically higher than those of SPT. At low flux, theACT and SPT measurements of individual sources agree withintheir errors. However, at fluxes above 30 mJy, individual sourcesmay disagree at several sigma. We understand the discrepancy tobe due to variability in radio sources, which is deferred to a futurepublication.Recently, using spectroscopic follow-up observations withthe Atacama Large Millimeter/submillimeter Array (ALMA),Vieira et al. (2013) and Weiß et al. (2013), derived robust red-shifts for about 18 of the SPT-detected dust-dominated sourcesfrom a larger sky area than in Vieira et al. (2010). One of thesesources, found to be at redshift 5.66, matches ACT-S J034640-520505 which otherwise had no cross-identification. A second pre-viously unmatched source, ACT-S J002707-500713, was imagedwith ALMA at 870 µ m, is resolved at the 0.5 ′′ scale, likely dueto gravitational lensing, but awaits spectroscopic follow-up. Fourother ACT dust-dominated sources that were cross-identified withthe Vieira et al. (2010) catalog now also have robust redshifts. ACT-S J055139-505800 is at redshift 2.123, ACT-S J053250-504709 isat redshift 3.399, ACT-S J052903-543650 is a source at redshift3.369, with a lens at redshift 0.140, and ACT-S J053817-503058has a redshift of 2.782, and a lens at a redshift of 0.404. It is likelythat the few ACT dust-dominated sources which lie outside the SPTfootprint are also lensed DSFGs. Given the ACT beam size, a normal galaxy will be unresolvedat redshifts z > z ≪ c (cid:13) , 000–000 D. W. Marsden et al. synchrotron-dominated spectra, both of which are nearby galax-ies. The twelve that show spectra dominated by dust re-emissionare Galactic sources, in the Magellanic clouds, or are knownnearby star-forming galaxies. For example, for two local resolvedgalaxies particularly bright at ACT frequencies, NGC1566 (ACT-S J041959-545622), a Seyfert two-arm spiral, and IC1954 (ACT-SJ033133-515352), a late-type spiral with a short central bar, ACTobserves a higher 218 GHz flux density than at 148 GHz or 20 GHz,confirming the dust-dominated nature of their spectra.
Of the 24 ACT dust-dominated sources in the catalog pre-sented here, 18 of these are cross-identified with either IRAS(12 sources) and/or SPT (9 sources, including the recent ALMAobservations). ACT-S J051506-534420, ACT-S J053311-523827,and ACT-S J055115-533435 were cross-identified with both cata-logs. Ten of the dust-dominated sources are cross-identified withsources in the SUMSS catalog, bringing the total for cross-identified sources to 19. The remaining 5 sources, ACT-S J024430-541605, ACT-S J035034-524801, ACT-S J062747-512614, ACT-S J063715-500414 and ACT-S J065207-551605, have no match-ing counterpart, and signal-to-noise at 218 GHz in the range5.27 < S/N < ≈ µ m samples from the Herschel
HerMES survey have lensing candidate densitiesof 0.14 ± − and 0.31 ± − , respectively(Wardlow et al. 2013). An analogous sample from Herschel ’sH-ATLAS survey is 0.35 ± − (Negrello et al. 2010). Inthe same bands as presented here, SPT finds 0.25 ± − lensing candidates (Mocanu et al. 2013). This suggests that ≈ The completeness-corrected differential number counts forACT sources based on the data in Table 2 are plotted in Figure6. For comparison, completeness-corrected number counts fromVieira et al. (2010) and Planck Collaboration XIII (2011) are plot-ted as well. The ACT data fill in the flux density gap between theSPT and
Planck catalogs at these frequencies, caused by the differ-ences between experiments in sky coverage and sensitivity to pointsources. The effect of calibration error is to shift the flux bins by ±
2% ( ± Planck total counts at 148 GHzand synchrotron-dominated source counts at 218 GHz are best fitby the recently developed Tucci et al. (2011) C2Ex radio sourcemodel. This model divides the ∼ flat- or steep-spectrum blazar pop-ulation into BL Lac objects, with a region close to the AGN coredominating the observed emission ( Planck analysis finds that the de Zotti et al. (2005) model is consistent with their countsat frequencies up to 100 GHz, but over-predicts the counts at higherfrequencies in the flux density region of ≈ ≈ ≈ Source spectral energy distributions (SEDs) can be used to dif-ferentiate source types by their dominant emission mechanisms.Assuming the commonly used simple power law model S ( ν ) ∝ ν α , a negative α is indicative of sources dominated by synchrotronemission, such as radio galaxies. Sources with free-free emissiondominating will have an index close to 0. The high-redshift SMGpopulation will have spectra dominated by re-emission of theirprodigious optical and UV flux by the surrounding dust in a grey-body spectrum, with indices expected to be greater than 2 and moretypically 3-4.We can divide the ACT source population according to sev-eral broad spectral groups: classical steep (and steepening) spec-trum sources, sources that peak within the frequency range underconsideration, and sources that show flat, rising or upturned spec-tra. The ACT catalog is dominated by synchrotron-dominatedblazers, which have variable flux densities. This variation in fluxdensity is not periodic. For any single source, then, inferences aboutits spectrum will depend on the epoch of observation, although notbiased one way or the other. For the catalog as an ensemble, how-ever, a spectral study may give rise to insights about the averagespectral behavior of the galaxy populations.Table 3 summarizes the median spectral indices between pairsof frequencies for various subsets of the ACT data. In obtainingthe spectral indices we compare the deboosted flux densities fromACT with the raw flux densities from AT20G. The whole sampleincludes data from the 20 GHz ATCA follow-up observations takenin November 2010 (Section 2.3).Figure 7 shows the 5–20 GHz, 20–148 GHz and 148–218 GHzcolor-magnitude diagrams. The radio-selected AGN (black points)are predominantly characterized by steepening of the spectra, withonly a few characterized by extremely flat or inverted spectra. There c (cid:13) , 000–000 CT-detected Sources at 148 & 218 GHz De Zotti (2005)Toffolatti radio (1998)Tucci C2Ex (2011)Toffolatti fIR (1998)Lima (2010)Bethermin (2011)Cai (2013) -2 -1 S [Jy] S d N / dS [ J y / s r ] ACTSPTPlanck
Figure 6.
Differential number counts of ACT-selected sources. Derived from Table 2 and corrected for completeness, the ACT differential source counts areplotted together with models of radio and infrared source populations. The Planck Collaboration VII (2013) data points and the SPT data points of Vieira et al.(2010) are also plotted, both of which are consistent with ACT counts. The ACT and Planck points have Poissonian errors (1 σ ), whereas the SPT pointsinclude measurement and independent calibration errors. The fIR models on this scale predicts number counts too low to be seen at 148 GHz. The ACT dataare consistent with being dominated by radio sources at both frequencies. Table 3.
Median Spectral Indices.Spectral Index Synchrotron (all) a Synchrotron (S >
50 mJy) Synchrotron (S <
50 mJy) Dust-dominated α − -0.15 +0 . − . -0.07 +0 . − . -0.21 +0 . − . ... α − -0.42 +0 . − . -0.36 +0 . − . -0.43 +0 . − . ... α − -0.55 +0 . − . -0.60 +0 . − . -0.51 +0 . − . +0 . − . a Quoted errors are the 68% confidence levels of the distribution. is a clear trend towards more negative median spectral index withincreasing frequency. Magenta points, showing rising spectra be-tween 148 and 218 GHz, denote sources ACT-classified as spec-trally dust dominated. They do not show up in the top two plots,indicating that these sources have flux densities falling below thedetection threshold of the AT20G catalog.The average spectral indices between AT20G and ACT fre-quencies indicates an underlying source population made up ofFlat-Spectrum Radio Quasars (FSRQ), a type of blazar, with AGNjet pointed along our line of sight (de Zotti et al. 2010). Ejectedmaterial flows through several shocked regions in the jet which lo-cally enhance the radiation (Marscher & Gear 1985; Valtaoja et al.1992). The observed spectral flatness is the superposition ofmany components with different turnover frequencies. At frequen-cies greater than approximately 100 GHz, however, Marriage et al.(2011), Vieira et al. (2010), and Planck Collaboration XIII (2011)observe a steepening of the spectrum ( α − ≈ -0.6) that un-til now had not been conclusively shown (Tucci et al. 2011). Thischange is possibly due to electron energy losses in the jet (“elec- tron ageing”) or the transition to the optically thin regime in theextended radio lobes. The underlying physical mechanisms havebeen contested for more than a decade and remain the subject ofongoing study, (e.g., Nieppola et al. 2008; Ghisellini & Tavecchio2008; Sambruna et al. 2010).All but one of the synchrotron-dominated ACT detectionswith flux density >
50 mJy have cross-identifications in AT20G.Below this flux density, the mean spectral indices of the populationof ACT-AT20G cross-identified sources are biased toward the neg-ative by the incompleteness of the AT20G catalog below 100 mJyat 5 GHz and below 40 mJy at 20 GHz. It is therefore illustrative tofurther divide this subpopulation according to 148 GHz flux den-sity. Figure 8, a radio color-magnitude diagram, plots spectral in-dex α − against 148 GHz source flux density. Black and greypoints identify the M11 sources that were cross-identified with theAT20G catalog. Black points are for sources with flux densities >
50 mJy, which represented a complete sample. Grey points de-note the fainter, incomplete sample. The blue points were obtained c (cid:13) , 000–000 D. W. Marsden et al. (cid:4) (cid:4) (cid:4) (cid:5) (cid:6) (cid:4) (cid:4) (cid:5) (cid:6) log(148 GHz Flux Density [mJy]) (cid:7) (cid:7) (cid:5) (cid:6) dustsync (cid:8) =1.66 Figure 7.
Color-magnitude diagrams comparing the 5–20 GHz (top), 20–148 GHz (middle), and 148–218 GHz (bottom) spectral indices for ACT-ATCA cross-identified sources. The synchrotron-dominated radio galaxypopulation is dominated by sources which have consistently falling SEDstowards higher frequencies. by calculating the spectral index for the previously unmatched,lower flux density subsample, followed up with ATCA (see Ta-ble 4 for AT2G0 source IDs with an asterisk). The population rep-resented by the blue points fills in the picture remarkably for thefainter (below 50mJy flux density at 148 GHz, below 40 mJy at20 GHz) population, especially in the region with spectral indexof approximately zero.The unbiased S >
50 mJy sample has a 20–148 GHz me-dian spectral index of -0.36 +0 . − . . For the S <
50 mJy subsampleprior to follow-up with ATCA (grey points only), the 20–148 GHzspectral index was α − = -0.52 +0 . − . . However, with the addi-tion of the synchrotron-classified ACT-selected sources with 2010ATCA follow-up data (grey and blue points), the full sample has20–148 GHz spectral index α − = -0.42 +0 . − . . This supportsthe hypothesis that the lower flux contingent is probing the samepopulation of synchrotron-dominated sources (blazers), and thatthere isn’t much evolution of their spectral index with flux. Thefull dataset suggests that the increased scatter at lower fluxes is dueto variability (which will have a larger relative effect on the fluxes)and decreased S/N from flux error.For our dust-dominated sources, we find a median spec-tral index of α − = +0 . − . . For sources detected above5 σ at both 150 and 220 GHz, SPT derives α − = ± ± α P − = ± -2 -1
148 GHz Flux Density [Jy] (cid:9) (cid:9) (cid:10) (cid:11) S > 50mJy M11S < 50mJy M11ATCA follow-up
Figure 8.
Radio color-magnitude diagram using 20–148 GHz spectral in-dices for ACT-AT20G cross-identified sources. The data are divided be-tween flux densities at 50 mJy at 148 GHz. The low flux sample was in-complete and suffered from selection bias that favored sources with morenegative spectral indices. Data from the ATCA follow-up study for the M11ACT 148 GHz sources not cross-identified with AT20G are shown as greensquares. The high flux sample, denoted with black points, has a medianspectral index -0.37. Prior to ATCA follow-up observations, the lower fluxACT sources cross-identified with the AT20G catalog (grey crosses) hada median spectral index of -0.52. Including the follow-up data, the morecomplete lower flux sample has a median spectral index of -0.43. for Poisson-distributed sources, and α C − = ± β = α − = ≈
30K dust made from graphite and silicate grains(Draine & Lee 1984). We leave a more rigorous analysis involvingredshifted greybodies, where the RJ limit is not as good an approx-imation, and the implications for star formation, to future work.
We have described the extragalactic source population at 148and 218 GHz found in a 455 deg region of the ACT 2008 South-ern strip , centered on declination -52.5 ◦ . This updates the ACT148 GHz catalog by using the data released with D¨unner et al.(2013), extends the results in Marriage et al. (2011) to two bands,and treats noise as more local, which in turn yields a higher S/N.We detect 191 sources above S/N = 5 in at least one of the ACT148 and 218 GHz frequency bands, spanning flux densities 14–1700 mJy (Table 4). Known redshifts are as high as ≈
6, with mea-surements ongoing. The catalog is estimated to be 100% pure and96.8% complete above 30 mJy at 148 GHz, and 97.7% pure and80.2% complete above 30 mJy at 218 GHz. We have confirmed fluxrecovery of the pipeline, and jointly deboosted the flux densities inboth bands.The multifrequency nature of our observations allows for in- c (cid:13) , 000–000 CT-detected Sources at 148 & 218 GHz ternal classification of sources into three broad classes of sourcesbased on their spectra: synchrotron-dominated sources (the vastmajority of which are cross-identified with radio catalogs), low-redshift dust-dominated sources with IRAS counterparts (typicallyULIRGs), and dust-dominated sources also observed by SPT orwith no cross-identification, either shown or assumed to be highredshift star-forming galaxies. This last class, only recently ob-served at millimeter wavelengths, has many of the properties ex-pected of the progenitor population of massive, modern-day, el-liptical galaxies, background SMGs whose flux has been magni-fied through gravitational lensing by a foreground galaxy or galaxygroup. This interpretation, bolstered by population synthesis anal-yses (e.g. Thomas et al. 2005), is being validated with follow-upobservations.A comparison with other catalogs shows that 97% of ACT-detected sources correspond to sources detected at lower or higherfrequencies. The 148 GHz source counts are fit reasonably wellby the C2Ex radio model of Tucci et al. (2011), the most cur-rent model for radio sources. According to the analysis of theaverage spectral indices derived from the combined AT20G andACT datasets, the ACT data support the case for a spectral steep-ening toward higher frequencies above 100 GHz for AGN. TheACT dust-dominated source population has a median spectral in-dex, α − , of 3.7 +0 . − . . Properly linking these sources into thebroader context of galaxy formation and evolution is of cosmolog-ical interest, and a goal of future work.The analysis presented here uses only the 2008 data of ACT’s Southern strip , representing only 1/6 th of the data ACT obtainedbetween 2007 and 2010. In future work, we will extend our anal-ysis of the source population to include the full dataset integratingboth the southern and equatorial regions observed by ACT. TheACT Equatorial strip overlaps with deep Sloan Digital Sky SurveyStripe 82 observations (Annis et al. 2011). Thus as well as increas-ing the sky coverage and number counts for the ACT sources, futurework (Gralla et al. in prep.) will include joint analyses with opticaldata.
ACKNOWLEDGMENTS
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S. e. a., 2009,ApJS, 180, 283 c (cid:13) , 000–000 rXiv:1306.2288v2 [astro-ph.CO] 10 Mar 2014 Table 4: ACT High Significance 148 GHz and 218 GHz Extragalactic Source CatalogID and Coordinates 148 GHz 218 GHz Spectral Index 20 GHzACT ID RA (J2000) Dec S/N S a m S db S/N S b m S db α m α db Type ATCA ID c S m hh:mm:ss dd:mm:ss (mJy) (mJy) (mJy) (mJy) (mJy)ACT-S J001849 − . −
51 : 15 : 06 . +5 . − . +5 . − . -0.8 -0.8 +0 . − . sync J001849 − ± − . −
49 : 29 : 53 . +7 . − . +9 . − . -0.3 -0.4 +0 . − . sync ... ...ACT-S J002233 − . −
51 : 53 : 26 . +4 . − . +5 . − . +0 . − . sync J002233 − ± − . −
54 : 27 : 44 . +3 . − . +4 . − . -0.0 0.0 +0 . − . sync J002511 − ± − . −
50 : 07 : 13 . +5 . − . +7 . − . +1 . − . dust ... ...ACT-S J003134 − . −
51 : 43 : 17 . +4 . − . +5 . − . -0.6 -0.6 +0 . − . sync J003134 − ± − . −
53 : 07 : 36 . +3 . − . +4 . − . -0.2 -0.3 +0 . − . sync J003735 − ± − . −
50 : 06 : 30 . +5 . − . +6 . − . -0.8 -0.8 +0 . − . sync ... ...ACT-S J004905 − . −
55 : 21 : 12 . +4 . − . +6 . − . -0.4 -0.4 +0 . − . sync J004905 − ± − . −
54 : 02 : 42 . +3 . − . +3 . − . -1.8 -1.8 +0 . − . sync J004950 − ∗ ± − . −
55 : 44 : 45 . +4 . − . +5 . − . -1.2 -1.2 +1 . − . sync ... ...ACT-S J005240 − . −
53 : 11 : 32 . +3 . − . +4 . − . -0.7 -0.8 +0 . − . sync J005242 − ∗ ± − . −
49 : 47 : 25 . +5 . − . +7 . − . -0.8 -0.9 +0 . − . sync J005243 − ± − . −
52 : 41 : 56 . +3 . − . +4 . − . -0.5 -0.5 +0 . − . sync J005604 − ∗ ± − . −
53 : 18 : 48 . +3 . − . +4 . − . -1.1 -1.2 +0 . − . sync J005622 − ∗ ± − . −
52 : 14 : 25 . +3 . − . +4 . − . -0.5 -0.5 +0 . − . sync J005705 − ± − . −
52 : 19 : 30 . +3 . − . +4 . − . -1.1 -1.1 +0 . − . sync J005855 − ± − . −
51 : 09 : 17 . +3 . − . +4 . − . -0.5 -0.5 +0 . − . sync J010306 − ± − . −
51 : 35 : 50 . +3 . − . +5 . − . +0 . − . sync J010329 − ± − . −
53 : 29 : 45 . +3 . − . +4 . − . -0.8 -0.8 +0 . − . sync J011323 − ± − . −
54 : 46 : 39 . +3 . − . +4 . − . +0 . − . sync ... ...ACT-S J011829 − . −
51 : 15 : 27 . +3 . − . +5 . − . +0 . − . sync J011828 − ∗ ± − . −
53 : 57 : 18 . +5 . − . +6 . − . -0.5 -0.5 +0 . − . sync J011950 − ± − . −
51 : 13 : 15 . +6 . − . +7 . − . -0.5 -0.5 +0 . − . sync J012457 − ± − . −
51 : 03 : 13 . +3 . − . +4 . − . -0.2 -0.2 +0 . − . sync J012624 − ± − . −
51 : 36 : 46 . +3 . − . +4 . − . -0.2 -0.2 +0 . − . sync J012756 − ± − . −
53 : 29 : 36 . +2 . − . +4 . − . +0 . − . sync J012759 − ∗ ± − . −
52 : 55 : 20 . +2 . − . +3 . − . +0 . − . sync J012834 − ± − . −
54 : 57 : 14 . +3 . − . +3 . − . -1.6 -1.4 +1 . − . sync J013108 − ∗ ± − . −
52 : 00 : 06 . +7 . − . +7 . − . -0.8 -0.8 +0 . − . sync J013305 − ± − . −
55 : 26 : 15 . +4 . − . +5 . − . -0.2 -0.2 +0 . − . sync J013408 − ± − . −
51 : 49 : 36 . +2 . − . +3 . − . -0.3 -0.3 +0 . − . sync J013540 − ± − . −
52 : 44 : 17 . +3 . − . +4 . − . -0.8 -0.8 +0 . − . sync J013548 − ± − . −
54 : 39 : 46 . +3 . − . +4 . − . -0.9 -0.9 +0 . − . sync J013726 − ∗ ± − . −
52 : 17 : 45 . +3 . − . +4 . − . -1.1 -1.2 +0 . − . sync J013949 − ± − . −
52 : 02 : 36 . +3 . − . +4 . − . -0.5 -0.5 +0 . − . sync J014648 − ± − . −
52 : 45 : 50 . +2 . − . +4 . − . +0 . − . dust ... ...ACT-S J015358 − . −
54 : 06 : 50 . +3 . − . +4 . − . -0.5 -0.5 +0 . − . sync J015358 − ± − . −
51 : 07 : 52 . +5 . − . +6 . − . -0.7 -0.7 +0 . − . sync J015419 − ± − . −
51 : 25 : 44 . +3 . − . +2 . − . -3.8 -2.2 +0 . − . sync J015557 − ± a m S db S/N S b m S db α m α db Type ATCA ID c S m hh:mm:ss dd:mm:ss (mJy) (mJy) (mJy) (mJy) (mJy)ACT-S J015649 − . −
54 : 39 : 48 . +3 . − . +4 . − . -1.7 -1.7 +0 . − . sync J015649 − ± − . −
50 : 04 : 19 . +4 . − . +5 . − . +0 . − . sync J015817 − ± − . −
53 : 08 : 57 . +2 . − . +3 . − . -1.7 -1.8 +0 . − . sync J015913 − ± − . −
55 : 02 : 58 . +3 . − . +4 . − . -0.1 -0.1 +0 . − . sync J020454 − ∗ ± − . −
53 : 45 : 36 . +2 . − . +3 . − . -0.7 -0.8 +0 . − . sync J020647 − ± − . −
52 : 29 : 26 . +2 . − . +4 . − . -0.1 -0.1 +0 . − . sync J020916 − ∗ ± − . −
51 : 01 : 03 . +48 . − . +48 . − . -0.5 -0.5 +0 . − . sync J021046 − ± − . −
50 : 04 : 12 . +4 . − . +4 . − . -1.4 -1.2 +1 . − . sync J021240 − ∗ ± − . −
51 : 04 : 37 . +3 . − . +4 . − . -0.8 -0.8 +1 . − . sync J021518 − ∗ ± − . −
52 : 00 : 09 . +2 . − . +4 . − . -0.5 -0.5 +0 . − . sync J021603 − ± − . −
55 : 03 : 50 . +3 . − . +4 . − . -1.0 -1.1 +0 . − . sync J021834 − ± − . −
51 : 06 : 33 . +3 . − . +4 . − . -1.4 -1.5 +0 . − . sync J022215 − ± − . −
53 : 47 : 42 . +4 . − . +5 . − . -0.7 -0.7 +0 . − . sync J022330 − ± − . −
52 : 25 : 52 . +2 . − . +4 . − . -0.7 -0.8 +0 . − . sync J022529 − ± − . −
49 : 01 : 26 . +6 . − . +8 . − . -0.6 -0.7 +0 . − . sync ... ...ACT-S J022820 − . −
55 : 37 : 38 . +4 . − . +5 . − . -0.0 -0.0 +0 . − . sync J022820 − ± − . −
55 : 46 : 05 . +5 . − . +6 . − . -0.7 -0.7 +0 . − . sync J022821 − ± − . −
54 : 03 : 25 . +10 . − . +10 . − . -0.6 -0.6 +0 . − . sync J022912 − ± − . −
52 : 32 : 25 . +2 . − . +4 . − . -0.6 -0.6 +0 . − . sync J022925 − ± − . −
53 : 56 : 35 . +2 . − . +3 . − . -0.6 -0.6 +0 . − . sync J023246 − ∗ ± − . −
50 : 30 : 21 . +3 . − . +3 . − . -2.3 -1.8 +1 . − . sync J023356 − ± − d
02 : 36 : 00 . −
53 : 02 : 37 . +2 . − . +3 . − . -1.2 -1.0 +1 . − . sync ... ...ACT-S J023923 − . −
51 : 08 : 22 . +2 . − . +4 . − . -0.1 -0.1 +0 . − . sync J023923 − ∗ ± − . −
54 : 29 : 32 . +3 . − . +4 . − . -0.1 -0.1 +0 . − . sync J024040 − ± − . −
49 : 24 : 47 . +4 . − . +6 . − . -0.6 -0.6 +0 . − . sync J024136 − ± − . −
53 : 45 : 46 . +2 . − . +3 . − . +0 . − . sync J024155 − ∗ ± − . −
51 : 05 : 16 . +3 . − . +4 . − . -0.7 -0.7 +0 . − . sync J024313 − ± − . −
53 : 28 : 03 . +2 . − . +3 . − . -0.1 -0.2 +0 . − . sync ... ...ACT-S J024430 − d
02 : 44 : 30 . −
54 : 16 : 05 . +2 . − . +4 . − . +1 . − . dust ... ...ACT-S J024509 − . −
55 : 44 : 19 . +2 . − . +6 . − . +0 . − . dust ... ...ACT-S J024540 − . −
52 : 57 : 58 . +2 . − . +3 . − . +0 . − . sync J024539 − ∗ ± − . −
49 : 53 : 54 . +4 . − . +5 . − . -2.0 -2.0 +0 . − . sync J024614 − ± − . −
55 : 27 : 39 . +3 . − . +6 . − . +1 . − . dust ... ...ACT-S J024647 − . −
50 : 26 : 08 . +3 . − . +5 . − . +0 . − . sync ... ...ACT-S J024948 − . −
55 : 56 : 27 . +4 . − . +5 . − . +0 . − . sync J024948 − ± − . −
52 : 08 : 12 . +2 . − . +3 . − . -0.3 -0.3 +0 . − . sync J025109 − ∗ ± − . −
51 : 45 : 60 . +2 . − . +3 . − . -1.0 -1.0 +1 . − . sync J025201 − ∗ ± − . −
54 : 41 : 52 . +23 . − . +23 . − . -0.6 -0.6 +0 . − . sync J025329 − ± − . −
49 : 53 : 21 . +3 . − . +6 . − . +0 . − . dust ... ...ACT-S J025629 − . −
52 : 27 : 24 . +2 . − . +3 . − . +0 . − . sync ... ...ACT-S J025839 − . −
50 : 52 : 03 . +4 . − . +5 . − . -0.8 -0.8 +0 . − . sync J025838 − ± − . −
53 : 32 : 01 . +2 . − . +4 . − . +0 . − . sync J025847 − ∗ ± a m S db S/N S b m S db α m α db Type ATCA ID c S m hh:mm:ss dd:mm:ss (mJy) (mJy) (mJy) (mJy) (mJy)ACT-S J030056 − . −
51 : 02 : 36 . +3 . − . +4 . − . -0.7 -0.7 +0 . − . sync J030055 − ± − . −
52 : 56 : 04 . +2 . − . +4 . − . -0.7 -0.7 +0 . − . sync J030132 − ∗ ± − . −
52 : 34 : 31 . +3 . − . +4 . − . -0.5 -0.5 +0 . − . sync J030328 − ± − . −
55 : 28 : 06 . +4 . − . +6 . − . -0.1 -0.1 +0 . − . sync J030616 − ± − . −
53 : 20 : 03 . +2 . − . +4 . − . +0 . − . dust ... ...ACT-S J031207 − . −
55 : 41 : 37 . +4 . − . +6 . − . -0.6 -0.6 +0 . − . sync J031207 − ± − . −
51 : 04 : 32 . +4 . − . +5 . − . -0.3 -0.3 +0 . − . sync J031425 − ± − . −
53 : 31 : 48 . +3 . − . +4 . − . -1.3 -1.3 +0 . − . sync J031823 − ∗ ± − . −
50 : 00 : 27 . +4 . − . +5 . − . -1.1 -1.2 +0 . − . sync J031910 − ∗ ± − . −
53 : 54 : 22 . +2 . − . +3 . − . -0.1 -0.1 +0 . − . sync J032210 − ∗ ± − . −
50 : 42 : 32 . +3 . − . +4 . − . -1.2 -1.3 +0 . − . sync J032212 − ∗ ± − . −
52 : 26 : 32 . +3 . − . +4 . − . -0.2 -0.2 +0 . − . sync J032327 − ± − . −
52 : 47 : 10 . +2 . − . +4 . − . +0 . − . dust ... ...ACT-S J032650 − . −
53 : 37 : 02 . +2 . − . +4 . − . -0.4 -0.4 +0 . − . sync J032650 − ± − . −
50 : 35 : 17 . +3 . − . +4 . − . -0.4 -0.5 +0 . − . sync J033002 − ± − . −
52 : 41 : 42 . +2 . − . +4 . − . -0.0 -0.1 +0 . − . sync J033114 − ± − . −
52 : 58 : 29 . +2 . − . +4 . − . +0 . − . sync J033126 − ± − . −
51 : 53 : 55 . +2 . − . +4 . − . +0 . − . dust ... ...ACT-S J033444 − . −
52 : 18 : 52 . +2 . − . +3 . − . -0.2 -0.2 +0 . − . sync J033443 − ∗ ± − . −
54 : 30 : 29 . +3 . − . +4 . − . -1.5 -1.5 +0 . − . sync J033553 − ± − . −
51 : 51 : 46 . +2 . − . +2 . − . -3.5 -2.2 +0 . − . sync J034154 − ∗ ± − . −
52 : 41 : 16 . +2 . − . +3 . − . -1.3 -1.4 +0 . − . sync J034349 − ± − . −
52 : 05 : 05 . +2 . − . +4 . − . +0 . − . dust ... ...ACT-S J034940 − . −
54 : 01 : 09 . +3 . − . +4 . − . +0 . − . sync J034941 − ± − d
03 : 50 : 34 . −
52 : 48 : 01 . +1 . − . +5 . − . +1 . − . dust ... ...ACT-S J035128 − . −
51 : 42 : 56 . +4 . − . +5 . − . -0.5 -0.5 +0 . − . sync J035128 − ± − . −
49 : 55 : 49 . +4 . − . +6 . − . -0.6 -0.7 +0 . − . sync J035700 − ± − . −
54 : 34 : 05 . +3 . − . +5 . − . +0 . − . sync J035842 − ∗ ± − . −
55 : 20 : 21 . +4 . − . +5 . − . -0.8 -0.8 +0 . − . sync J040400 − ± − . −
54 : 05 : 55 . +2 . − . +4 . − . +0 . − . dust ... ...ACT-S J040622 − . −
50 : 35 : 01 . +3 . − . +4 . − . -1.2 -1.1 +1 . − . sync J040621 − ∗ ± − . −
51 : 49 : 21 . +3 . − . +4 . − . -0.6 -0.6 +0 . − . sync J041137 − ± − . −
56 : 00 : 53 . +4 . − . +6 . − . +0 . − . sync J041247 − ± − . −
53 : 31 : 55 . +3 . − . +4 . − . -0.1 -0.1 +0 . − . sync J041313 − ± − . −
56 : 03 : 49 . +3 . − . +7 . − . +0 . − . dust ... ...ACT-S J042000 − . −
54 : 56 : 22 . +3 . − . +6 . − . +0 . − . dust ... ...ACT-S J042504 − . −
53 : 31 : 59 . +5 . − . +6 . − . -0.3 -0.3 +0 . − . sync J042504 − ± − . −
50 : 05 : 30 . +6 . − . +7 . − . -0.7 -0.8 +0 . − . sync J042842 − ± − . −
54 : 30 : 05 . +3 . − . +5 . − . +0 . − . sync J042852 − ± − . −
53 : 49 : 43 . +3 . − . +4 . − . -0.6 -0.6 +0 . − . sync J042908 − ± − . −
51 : 09 : 27 . +4 . − . +5 . − . -0.8 -0.8 +0 . − . sync J043221 − ± − . −
52 : 16 : 39 . +2 . − . +4 . − . -0.2 -0.2 +0 . − . sync J043652 − ± a m S db S/N S b m S db α m α db Type ATCA ID c S m hh:mm:ss dd:mm:ss (mJy) (mJy) (mJy) (mJy) (mJy)ACT-S J044116 − . −
54 : 38 : 49 . +3 . − . +5 . − . +0 . − . sync J044115 − ∗ ± − . −
51 : 54 : 54 . +3 . − . +5 . − . -0.5 -0.5 +0 . − . sync J044158 − ± − . −
52 : 34 : 25 . +2 . − . +4 . − . -1.0 -1.0 +0 . − . sync J044506 − ∗ ± − . −
51 : 02 : 57 . +3 . − . +4 . − . -1.4 -1.2 +1 . − . sync J044706 − ∗ ± − . −
51 : 50 : 58 . +2 . − . +4 . − . -0.8 -0.9 +0 . − . sync J044748 − ± − . −
50 : 41 : 38 . +3 . − . +4 . − . -0.5 -0.6 +0 . − . sync J044822 − ± − . −
53 : 46 : 57 . +2 . − . +3 . − . -1.7 -1.7 +0 . − . sync J045032 − ∗ ± − . −
49 : 36 : 30 . +4 . − . +7 . − . -0.4 -0.4 +0 . − . sync J045102 − ± − . −
53 : 06 : 37 . +2 . − . +4 . − . -0.8 -0.9 +0 . − . sync J045238 − ± − . −
55 : 31 : 15 . +4 . − . +6 . − . -0.0 -0.0 +0 . − . sync J045503 − ± − . −
53 : 02 : 37 . +2 . − . +4 . − . -0.6 -0.6 +0 . − . sync J045558 − ± − . −
53 : 21 : 25 . +2 . − . +4 . − . -0.3 -0.3 +0 . − . sync J050019 − ± − . −
50 : 23 : 11 . +4 . − . +6 . − . -0.8 -0.8 +0 . − . sync J050401 − ± − . −
51 : 56 : 02 . +3 . − . +4 . − . -0.7 -0.8 +0 . − . sync J050747 − ± − . −
50 : 55 : 49 . +3 . − . +5 . − . +0 . − . sync J051355 − ± − . −
53 : 44 : 20 . +1 . − . +4 . − . +0 . − . dust ... ...ACT-S J051812 − . −
51 : 43 : 58 . +3 . − . +4 . − . +0 . − . sync J051811 − ± − . −
50 : 05 : 45 . +4 . − . +5 . − . -1.3 -1.1 +1 . − . sync ... ...ACT-S J052046 − . −
55 : 08 : 23 . +3 . − . +4 . − . +0 . − . sync J052045 − ± − . −
49 : 13 : 01 . +6 . − . +9 . − . -0.8 -0.9 +1 . − . sync ... ...ACT-S J052317 − . −
53 : 08 : 33 . +3 . − . +4 . − . -1.3 -1.4 +0 . − . sync J052318 − ± − . −
54 : 26 : 09 . +3 . − . +4 . − . -1.0 -1.1 +0 . − . sync J052743 − ± − . −
54 : 36 : 50 . +2 . − . +5 . − . +0 . − . dust ... ...ACT-S J053117 − . −
55 : 04 : 25 . +4 . − . +5 . − . -0.6 -0.6 +0 . − . sync J053115 − ∗ ± − . −
53 : 10 : 33 . +3 . − . +4 . − . -0.1 -0.1 +0 . − . sync J053208 − ± − . −
50 : 47 : 09 . +2 . − . +6 . − . +0 . − . dust ... ...ACT-S J053311 − . −
52 : 38 : 27 . +1 . − . +4 . − . +0 . − . dust ... ...ACT-S J053323 − . −
55 : 49 : 35 . +4 . − . +7 . − . -0.5 -0.5 +0 . − . sync J053324 − ± − . −
54 : 39 : 06 . +3 . − . +5 . − . -0.1 -0.1 +0 . − . sync J053458 − ± − . −
50 : 30 : 58 . +2 . − . +6 . − . +0 . − . dust ... ...ACT-S J053909 − . −
55 : 10 : 55 . +4 . − . +6 . − . +0 . − . sync J053909 − ± − . −
53 : 03 : 48 . +3 . − . +4 . − . +0 . − . sync J054025 − ± − . −
53 : 56 : 26 . +3 . − . +3 . − . -2.0 -1.7 +1 . − . sync J054029 − ± − . −
54 : 18 : 21 . +13 . − . +12 . − . -0.6 -0.6 +0 . − . sync J054045 − ± − . −
51 : 42 : 56 . +3 . − . +5 . − . -0.3 -0.3 +0 . − . sync J054223 − ± − . −
52 : 18 : 36 . +3 . − . +4 . − . +0 . − . sync J054833 − ∗ ± − . −
52 : 46 : 26 . +6 . − . +6 . − . -0.6 -0.6 +0 . − . sync J054943 − ± − . −
53 : 04 : 54 . +3 . − . +4 . − . -0.1 -0.2 +0 . − . sync J055049 − ∗ ± − . −
53 : 34 : 35 . +2 . − . +5 . − . +1 . − . dust ... ...ACT-S J055139 − . −
50 : 58 : 00 . +2 . − . +6 . − . +0 . − . dust ... ...ACT-S J055152 − . −
55 : 26 : 28 . +4 . − . +5 . − . -0.2 -0.2 +0 . − . sync J055152 − ± − . −
53 : 49 : 26 . +3 . − . +4 . − . -0.8 -0.8 +1 . − . sync ... ...D and Coordinates 148 GHz 218 GHz Spectral Index 20 GHzACT ID RA (J2000) Dec S/N S a m S db S/N S b m S db α m α db Type ATCA ID c S m hh:mm:ss dd:mm:ss (mJy) (mJy) (mJy) (mJy) (mJy)ACT-S J055811 − . −
50 : 29 : 52 . +4 . − . +6 . − . -0.3 -0.3 +0 . − . sync J055811 − ± − . −
50 : 26 : 46 . +4 . − . +5 . − . -0.9 -1.0 +0 . − . sync J055947 − ± − . −
54 : 25 : 08 . +3 . − . +5 . − . -0.1 -0.1 +0 . − . sync J060212 − ± − . −
52 : 57 : 43 . +3 . − . +4 . − . -0.4 -0.4 +0 . − . sync J060749 − ± − . −
54 : 56 : 43 . +5 . − . +7 . − . -0.5 -0.5 +0 . − . sync J060849 − ± − . −
49 : 26 : 04 . +5 . − . +7 . − . +0 . − . sync ... ...ACT-S J061714 − . −
53 : 06 : 08 . +3 . − . +4 . − . -0.4 -0.4 +0 . − . sync J061716 − ∗ ± − . −
54 : 27 : 16 . +3 . − . +5 . − . -1.0 -1.0 +0 . − . sync J061955 − ± − . −
52 : 41 : 33 . +4 . − . +6 . − . -0.5 -0.5 +0 . − . sync J062143 − ± − . −
54 : 38 : 52 . +5 . − . +6 . − . -0.8 -0.8 +0 . − . sync J062552 − ± − . −
53 : 41 : 30 . +3 . − . +5 . − . -0.7 -0.7 +0 . − . sync J062620 − ± − . −
54 : 32 : 31 . +4 . − . +5 . − . -0.1 -0.1 +0 . − . sync J062648 − ± − d
06 : 27 : 47 . −
51 : 26 : 14 . +3 . − . +6 . − . +1 . − . dust ... ...ACT-S J063159 − . −
54 : 04 : 53 . +3 . − . +5 . − . +0 . − . sync J063201 − ± − d
06 : 37 : 15 . −
50 : 04 : 14 . +3 . − . +8 . − . +0 . − . dust ... ...ACT-S J063739 − . −
50 : 07 : 33 . +5 . − . +6 . − . -0.9 -1.0 +0 . − . sync J063738 − ± − . −
52 : 02 : 24 . +3 . − . +4 . − . -1.3 -1.3 +0 . − . sync J064107 − ∗ ± − . −
55 : 51 : 06 . +5 . − . +6 . − . -1.8 -1.5 +1 . − . sync J064150 − ∗ ± − . −
53 : 58 : 45 . +4 . − . +5 . − . -0.4 -0.4 +0 . − . sync J064320 − ± − . −
54 : 51 : 11 . +4 . − . +5 . − . -1.2 -1.3 +0 . − . sync J064629 − ± − . −
50 : 17 : 58 . +5 . − . +7 . − . -0.3 -0.3 +0 . − . sync ... ...ACT-S J065207 − d
06 : 52 : 07 . −
55 : 16 : 05 . +4 . − . +7 . − . +1 . − . dust ... ...ACT-S J065518 − . −
49 : 51 : 56 . +6 . − . +10 . − . +0 . − . sync J065518 − ± − . −
55 : 14 : 20 . +5 . − . +6 . − . +0 . − . sync J070412 − ± − . −
50 : 22 : 33 . +6 . − . +5 . − . -3.2 -2.3 +0 . − . sync J070700 − ± a Flux density as measured directly from the ACT 148 GHz map. b Flux density as measured directly from the ACT 218 GHz map. c AT20G or an asterisk denotes the November 2010 follow-up observations catalog. dd