Decrypting the Universe with LOFAR

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Decrypting the Universe with LOFAR
Philip Best Institute for Astronomy, Edinburgh
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Overview

• Introduction to LOFAR
• Instrument description status
• European LOFAR
• LOFAR science
• Brief overview of the science case
• Epoch of Reionisation with LOFAR
• LOFAR extragalactic surveys
• Radio-loud AGN feedback with LOFAR
• (time permitting)
• Conclusions

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LOFAR The Low Frequency Array

• Low frequency radio array, 30-80 and 120-240 MHz
• Being built in Netherlands other European
  countries
• Software telescope thousands of all-sky
  dipoles.

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LOFAR The Low Frequency Array

• Low frequency radio array, 30-80 and 120-240 MHz
• Being built in Netherlands other European
  countries
• Software telescope thousands of all-sky
  dipoles.
• Original design 77 stations spread across
  Netherlands
• Recent re-scope 36-50 Dutch stations (
  international)
• 96 low and 48 high-band antennae per station
• Beam-forming of 8 beams at each station
• Imaged area limited by correlator computer
• 10 SKA Pathfinder at low frequencies
• Core station 1 operational. Completion 2009.

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Latest CS-1 commissioning results
3x24h, 16 dipoles 38 - 59 MHz Noise level 1
Jy Confusion-limited
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E-LOFAR

• LOFAR may be extended around many European
  countries
• Germany (GLOW) 6-10 stations
• UK (LOFAR-UK) 1-4 stations
• http//www.lofar-uk.org
• France (FLOW) 1 station
• Italy, Poland, Sweden serious consideration
• Ukraine, Austria, Ireland,
  Lithuania, Bulgaria
  some discussion
• E-LOFAR stations will increase baselines from
  100km to
• 1000km, improving resolution to sub-arcsec at
  200MHz
• International stations will be larger (96
  low-band and 96
• high-band antennae) to assist with calibration

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LOFAR Science Goals

• LOFAR has incredibly wide-ranging science goals
• Epoch of Reionisation
• Detect through 21cm hyperfine transition
• Deepest extragalactic radio surveys
• 2p sr at 15,30,60,120,200MHz to unparalleled
  depths
• Radio AGN and star-forming galaxies
• Transient objects
• Supernovae, pulsars, GRBs, etc all-sky monitor
• Cosmic Rays
• Solar solar-terrestrial physics
• Solar flares, solar wind, Earths ionosphere etc
• Galactic surveys and Cosmic Magnetism

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LOFAR the Epoch of Reionisation

• 21cm hyperfine transition (1 0S1/2 and 1 1S1/2
  states).
• Ratio of upper to lower state occupancy is
• 
  T 0.068K
• 
  Ts spin temp.
• Coupling to CMB means TsTCMB, so absorption and
  re-emission at same rate and no net signal.
• But, scattering of Ly-a photons from first
  sources decouples spin temp Wouthuysen-Field
  effect and produces a signal
• Signal then disappears as Universe is ionised.

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LOFAR EoR signal

• For Ts gtgt TCMB, brightness temperature
  differential (dT) depends only on overdensity
  neutral fraction, so can be constructed from
  simulations.
• However, in practice many complication, e.g.
• Signal extremely faint (weeks-months observing)
• EoR signal in 80-120 MHz gap?
• Foreground subtraction?

Credit Mellema
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Challenge removing foregrounds
From Jelic Zaroubi (2007)
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Alternative approach 21cm forest

• A simulated radio spectrum of a radio galaxy at
• z12 (left) and z8 (right) Carilli (2005)

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LOFAR Extra-galactic surveys

• First-pass survey design (for 77-station Dutch
  LOFAR)
• Freq. Angular Sky 3s flux Source
  No Time
• resol. cover limit
  density sources needed
• (MHz) () (mJy)
  (arcmin-2) (bm yrs)
• 15 50.3 2p sr 4.7 0.2
  1.3x107 0.28
• 30 25.2 2p sr 1.0 0.7
  5.4x107 0.88
• 60 12.6 2p sr 1.0 0.3
  2.2x107 2.24
• 120 6.3 2p sr 0.043 11.6
  8.6x108 8.56
• 200 3.8 250?2 0.014 32.2
  3.0x107 2.44
• Surveys reach confusion limit at 15, 30, 120 and
  200 MHz.
• International baselines will increase resolution
  lower the
• confusion limit, so surveys are being modified
• Likely 2p shallower survey at 200MHz, plus few sq
  deg deeper

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LOFAR compared to other radio surveys
Credit Morganti
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LOFAR Survey Science

• Surveys will be dominated by star-forming
  galaxies, not traditional radio-loud AGN
• Will detect essentially all radio-loud AGN in the
  Universe, and a large fraction of radio-quiet AGN

• Figure the L-z relation for radio sources in
  LOFARs 200MHz survey, per sq deg (credit Matt
  Jarvis)
• White FR2s (per 100 sq deg)
• Blue FR1s (low power RL-AGN)
• Pink Radio-quiet quasars
• Yellow Star-forming galaxies

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Star-forming gals with LOFAR

• LOFAR will detect gt108 SF gals
• and will be sensitive to gals with
• SFR gt 10 Msun/yr out to zgt2 and
• SFR gt 100 Msun/yr out to zgt8.
• Main science goals
• comparison with multi-? surveys (SF history)
• clustering of high-z SF gals
• evolution of the FIR/radio correlation
• detailed studies of nearby SF galaxies

The flux-redshift relation at different freqs for
star-forming gals. White bands indicate regions
above confusion limit (from Dutch LOFAR science
case)
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LOFAR AGN Survey Science

• Detecting the highest redshift radio sources
• Epoch of Reionisation
• Early formation of massive galaxies clusters

Figure (de Breuck et al 2000) ultra-steep
spectrum selection of the highest redshift radio
sources. Combine radio-selection with deep
near-IR imaging
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LOFAR AGN Survey Science

• Detecting the highest redshift radio sources
• Epoch of Reionisation
• Early formation of massive galaxies clusters
• Studying AGN feedback on galaxy formation
• Energy content of radio lobes through low-energy
  e-
• Evolution of the mass-radio relation
• Radio source growth evolution
• Cluster radio sources intracluster magnetic
  fields
• Strong and weak lensing studies
• Target selection for BAO spectroscopic studies
• Exploration of new parameter space. SETI?
• etc

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AGN and galaxy formation

• Galaxy formation models have
• historically had problems
• explaining the most massive gals
• Galaxies grow too massive
• Blue colours due to ongoing SF
• Too few massive gals at high-z.
• Missing physics AGN feedback?
• The current idea is that energy
• input from recurrent radio-loud
• AGN activity turns off gas cooling
• in massive haloes

Supernovae
Supernovae ionising background
???
Radio AGN
The local galaxy luminosity function (data
points, from 2dFGRS) compared to that predicted
if light follows mass in the dark matter haloes.
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Radio feedback in the local Universe
Best et al 2005a, 2005b, 2006

• Cross-matched SDSS spectroscopic sample with NVSS
  and FIRST radio samples
• Derived fraction of gals hosting radio-loud AGN
  as a function of stellar mass
• fradio-loud is a very strong
• function of mass
• fradio-loud ? M2.5

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Radio feedback in the local Universe
Best et al 2005a, 2005b, 2006

• Cross-matched SDSS spectroscopic sample with NVSS
  and FIRST radio samples
• Derived fraction of gals hosting radio-loud AGN
  as a function of stellar mass
• Split into mass bins and
• examine radio LF
• Shape of the RLF is
• independent of mass

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Radio feedback in the local Universe

• Assume fradio-loud gives duty cycle of recurrent
  activity
• Use observations of radio source bubbles/cavities
  in nearby clusters to convert Lrad to Lmechanical

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Radio feedback in the local Universe

• Assume fradio-loud gives duty cycle of recurrent
  activity
• Use observations of radio source bubbles/cavities
  in nearby clusters to convert Lrad to Lmechanical
• Compare time-averaged
  radio-AGN heating rates
  with bolometric
  cooling
  rates of hot X-ray haloes
• Heating from radio-loud
• AGN balances gas cooling
• for elliptical galaxies of
• all masses!

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Cosmic evolution of radio-AGN feedback

• Massive ellipticals mostly form at high redshift
  how
• important is this radio-AGN feedback mode then?
• To repeat this analysis to the same effective
  depth at z2 requires a survey with 6 ?Jy rms
  noise at 200 MHz.
• LOFAR will provide this.
• The critical requirement is then spectroscopic
  redshifts
• or accurate photometric redshifts
• To match the volume of the SDSS studies over 1.5
  lt z lt 2 requires about 60 square degrees.
• PanSTARRS Medium Deep Survey will provide this.

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Summary

• The LOFAR telescope will be operating in 2 years
• It is becoming a truly European venture
• It will impact on a broad range of astrophysics,
  from solar-system studies to the high redshift
  Universe and cosmology
• Its novel design means that it will be a great
  pathfinder, both technologically and
  scientifically, for the Square Kilometre Array