National Radio Astronomy Observatory EVLA Workshop
Deeper Knowledge Through Confusion
Jim Condon
EVLA Workshop 2008 Dec 17
Outline:
• What can sensitive 1–10 GHz continuum surveys tell us about galaxy evolution?
• Current problems with continuum surveys• EVLA: 5X deeper knowledge through confusion
( ~ 1000 nJy at 1.4 GHz, 600 nJy at 3 GHz, 400 nJy at 6 GHz, and 250 nJy at 10 GHz)
• Unique EVLA contributions as a continuum pathfinder for the SKA
EVLA Workshop 2008 Dec 17
FIR and radio flux densities of star-forming galaxies are correlated so the rescaled FIR (dashed curve) and radio (solid curve) LLFs of star-forming galaxies coincide; FIR and radio trace the same SFRD.
solid curve: 1.4
GHz
dashed curve: FIR
EVLA Workshop 2008 Dec 17
Luminosity Evolution
Local visibility functionyieldscounts normalized by static Euclidean counts
∆ log(L) ~ 1.2 evolutionfor all radio sources <z> ~ 0.8, ∆ log(z) ~ 0.5over wide flux range
stars
AGN
AGN
stars
EVLA Workshop 2008 Dec 17
Condon (1989) and Wilner et al. (2008) models
EVLA Workshop 2008 Dec 17
Evolution of Star Formation: Radio View
EVLA Workshop 2008 Dec 17
Problems with current faint-source counts
Huynh et al. (2005)
P(D)1.4 GHz
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
Deepest counts seem to disagree
EVLA Workshop 2008 Dec 17Isotropy of faint NVSS sources
EVLA Workshop 2008 Dec 17
1.4 GHz source counts in 17 FLS fields
2 is consistent with no clustering (P > 30%)• “Cosmic rms” < 16% (P > 99%)
EVLA Workshop 2008 Dec 17
Faint sources and sky brightness
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
EVLA sensitivity and confusion surveys
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
EVLA confusion surveys as pathfinders for SKA
EVLA Workshop 2008 Dec 17
Ultimate radio survey limits
• confusion:
c~ .03 K (1.4 GHz) instrumental natural• field of view Ω• dynamic range• noise
EVLA Workshop 2008 Dec 17
Summary:
• S ~ 1 Jy surveys at 1.4 GHz can constrain the evolution of the SFRD to z ~ 1.5
• Current surveys disagree below S ~ 100 Jy• EVLA confusion surveys could yield source
counts to S ~ 1 Jy at 1.4 GHz and measure the effective spectral index at this level.
• EVLA confusion surveys will be the deepest pathfinders for SKA continuum surveys, and they will approach the natural confusion limit.
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
X-band surveys
• Small numbers of sources• Spectral-index distributions differ?
EVLA Workshop 2008 Dec 17Isotropy of strong sources
EVLA Workshop 2008 Dec 17
Detecting distant sources and characterizing source populations
EVLA Workshop 2008 Dec 17
The recent SFRD is
proportional to
∫um d log(L) =
1.5 1019 W Hz-1
Mpc-3 at 1.4 GHz
M82
Arp 220
Power-density functions
Vir A
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
The 1.4 GHz sky at 5 arcsec resolution, 23 µJy/beam = 0.6 K rms noise
~1/2 AGN ~1/2 star-
forming galaxies
part of the Spitzer FLS / VLA survey
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