deeper knowledge through confusion

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