Download Deeper Knowledge Through Confusion

National Radio Astronomy Observatory
EVLA Workshop
Deeper Knowledge
Through Confusion
Jim Condon
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 starforming 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.
EVLA Workshop 2008 Dec 17
solid curve: 1.4 GHz
dashed curve: FIR
Luminosity Evolution
Local visibility function
yields
counts normalized by
static Euclidean counts
∆ log(L) ~ 1.2 evolution
for all radio sources
<z> ~ 0.8, ∆ log(z) ~ 0.5
over wide flux range
EVLA Workshop 2008 Dec 17
stars
AGN
stars
AGN
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
P(D)
EVLA Workshop 2008 Dec 17
1.4 GHz
Huynh et al. (2005)
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
Deepest counts seem to disagree
EVLA Workshop 2008 Dec 17
EVLA Workshop 2008 Dec 17
Isotropy of faint NVSS sources
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 17
EVLA Workshop 2008 Dec 17
Isotropy of strong sources
Detecting distant sources and
characterizing source populations
EVLA Workshop 2008 Dec 17
Power-density functions
Vir A
M82
The recent SFRD is
proportional to
∫um d log(L) =
1.5 1019 W Hz-1
Mpc-3 at 1.4 GHz
EVLA Workshop 2008 Dec 17
Arp 220
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 starforming galaxies
part of the Spitzer FLS / VLA survey
EVLA Workshop 2008 Dec 17