SKA Continuum Deep Field Surveys Amit Vishwas April 7, 2010
The Square Kilometer Array The Next Generation Radio Telescope Spread over a long baseline ~1000 kms Large Effective Area: but only a fraction of (km) 2 Tentative design and deployment Precursor Designs & Studies underway
Why Radio? Radio frequencies are insensitive to obstruction by Dust Sources exist at a nearly all radio flux densities From Nuclear to Star forming Allows observations at a range of z Range of z allows studies at different periods in history
Current Surveys FIRST 97, NVSS 98 VLA, US @ 1400MHz SUMSS 99 MOST, Australia @ 843 MHz These surveys cover 1000 s o of the sky to mjy limits Involve large amount of observing time Deeper surveys cover lesser area VLA HDF Observations 00 0.35 sq. deg w/ 0.04mJy (5σ-level) ATESP 01: 26 sq.deg w/0.4mjy (5σ-level)
Continuum Fields Extragalactic Radio Sources Cover a wide range of luminosity 10 19-10 28 Watts/Hz from normal spirals to Radio loud QSOs Intermediate in luminosity powerful FRI radio galaxies, the radio quiet quasars, and galaxies with active star formation. The nature of individual radio sources may be classified on the basis of their: luminosity optical counterpart observed radio morphology spectral features radio spectral index observed characteristics in variability other wavelength bands
What SKA can see The SKA is proposed to have a significantly larger area Capable of going down to μ-jy for large area surveys nano-jy for small area surveys To determine how the sky could look like at these low flux densities Simulated HDF size field for 20 cm using SKA (5σ-level) 100 nano-jy
Simulating the Radio Source Sky Based on number density predictions Models of evolution of the RLF Allows to predict Typical Source Distributions Natural Confusion limits Flux density limits Assumptions: All sources 3 Populations FRI, FRII, Starforming Galaxies LRLF and evolution of each known
Large Area survey to overcome Cosmic Variance
SKA will have a huge dynamic range The floor is set by natural confusion and Noise 1Msec observation to reach nano-jy levels FoV: Size of a single pixel N FoV : Number of pixels N sa : Number of Subarrays B: Bandwidth, T sys : System Temperature m: threshold S/N A e : Effective area of entire array f c : fraction of A e used in the survey
Target #1 - AGNs The SKA can map a census of AGN sources over the sky at different epochs (z) Aid study of: AGN Lifecycle : Evolution & Relation b/w different populations Relation b/w AGN Activity and Star formation Power range (10 2-10 28 Watts/Hz) suggests a continuum of nuclear activity in radio frequencies
Target #1 - AGNs Most populations of moderate radio luminosity objects overlap Such a survey would help comparative studies with Galaxy Redshift surveys & Large area radio surveys At Low luminosity long time observations (noise errors) At high luminosities too few to look at (sparse space density) Current surveys are flux density limited Luminosity z degeneracy: SKA can overcome that! (at z>1, only high power AGNs) Study strong Cosmic Evolution b/w z = 1 to z = 5
Target #1 - AGNs Most populations of moderate radio luminosity objects overlap Such a survey would help comparative studies with Galaxy Redshift surveys & Large area radio surveys At Low luminosity long time observations (noise errors) At high luminosities too few to look at (sparse space density) Current surveys are flux density limited Luminosity z degeneracy: SKA can overcome that! (at z>1, only high power AGNs)
Predictions Important Consideration: Confusion Rate fraction of sources which overlap each other on the plane of the sky (at a given sensitivity) FRI & FRII population extend to z > 5 and upto z ~ 8
Baseline Requirements At Full Sensitivity : estimation of 40 sources/arc min Resolution: 0.05 @ 1.4GHz, (>)1000 km baseline for array Resolution should be comparable to counterparts in other wavelengths (JWST(?)) to be able to compare results. Simultaneous Wide-band observations Monitor time variability and study the mechanisms driving the variations
Baseline Requirements
Lets do it tomorrow NOT POSSIBLE (tomorrow, or lets speculate 2015-ish) Mid-SKA : RSST (v/s LSST) Radio Synoptic Survey Telescope 0.4 1.4 Ghz High G/T ~ 20000 m 2 /K Wide FoV: Optimize Survey Speed, A e v/s T sys Technology Constraints: 2.5 25TB/sec compare that to VLA: 250MB/sec Data flow of ~100-1000TB/day : Even Google can t help (today) Processing requirements: Area: 10x Arecibo(305m), cant make 10 more Arecibos (?) Area: 2700x VLA(25m), Processing cost 10 4 x VLA Area: 12000x (12m), Processing cost 10 5 x VLA
Others things down the pipeline RSST : major science surveys using SKA CHILDS & BiG CHILDS: Cosmological HI Large Deep Survey Spectroscopic observations, cosmological studies DeCOS: Deep Continuum Surveys TraMP: Transient Monitoring Program
References Jackson, C (2004), New Astronomy Reviews Kellermann, K.I, Deep radio Source surveys with the SKA Cordes, J.M., SKA Memo 97 Myers, et al., CHILDS & BiG CHILDS Blake, et al., SKA Weak Lensing Condon, J, Sensitive Continuum Surveys with the SKA: Goals & Challenges, SKA Workshop, Feb 2009