LOFARLOFAR

Low Frequency Radio ArrayLow Frequency Radio Array

Veres Péter

Structure of the presentationStructure of the presentation IntroductionIntroduction Technical dataTechnical data Low Frequency Sky Low Frequency Sky

SurveysSurveys Z>>6 Radio GalaxiesZ>>6 Radio Galaxies Mpc Radio GalaxiesMpc Radio Galaxies Radio HaloesRadio Haloes Low Frequency VariablesLow Frequency Variables Large –Scale StructureLarge –Scale Structure Global Reionization of the Global Reionization of the

UniverseUniverse

Thermal & Nonthermal Thermal & Nonthermal EmissionEmission

Compact Sources in Nearby Compact Sources in Nearby GalaxiesGalaxies

Polarization @ Low Polarization @ Low FrequenciesFrequencies

HII Regions with Low HII Regions with Low FrequecyFrequecy

Supernova RemnantsSupernova Remnants (Extrasolar) Planets(Extrasolar) Planets

IntroductionIntroduction

Netherlands Foundation for Research in AstronomyNetherlands Foundation for Research in Astronomy

Inventory of scientific programmes using a LOFARInventory of scientific programmes using a LOFAR

Hierarchical array of fixed elements operating at:Hierarchical array of fixed elements operating at:10 - 300MHz10 - 300MHz

Existing LFRTs: Existing LFRTs: GMRTGMRT in India and in India and VLAVLA in th US in th US

LOFARLOFAR will provide: will provide:GreaterGreater sensitivity sensitivity

GreaterGreater spatial resolution spatial resolution

GreaterGreater frequency range frequency range

Greater Greater freq. coverage & agilityfreq. coverage & agility

In generalIn general

Multi beaming capability at full strengthMulti beaming capability at full strengthHigh speed data processingHigh speed data processingExtreme agility in frequency & pointingExtreme agility in frequency & pointing Ionospheric compensationIonospheric compensationAdvanced computational techniquesAdvanced computational techniques

In generalIn general

Low Frequency Sky Low Frequency Sky SurveysSurveys

At 20-100 MHz the sky is virtually unexploredAt 20-100 MHz the sky is virtually unexploredExpected from LOFARExpected from LOFAR::• distant (z>6) radio galaxiesdistant (z>6) radio galaxies• extended (Mpc sized) and powerful galaxies @ z>1extended (Mpc sized) and powerful galaxies @ z>1• radio halos associated with X-ray clustersradio halos associated with X-ray clusters• Low Frequency Variables & constraints on LSS of Low Frequency Variables & constraints on LSS of the Universe with TPCFthe Universe with TPCF• new galaxies in the neighborhoodnew galaxies in the neighborhood

Mpc-Sized Radio Galaxies @ z>1Mpc-Sized Radio Galaxies @ z>1

Giant Radio Galaxies (GRG) Giant Radio Galaxies (GRG) •projected linear dimensions >1 Mpcprojected linear dimensions >1 Mpc•3C 236>5.7 Mpc3C 236>5.7 Mpc•expand well out of their clusters into the expand well out of their clusters into the IGM probe of IGMIGM probe of IGM•verify AGN endstage theoriesverify AGN endstage theories•many of these large sources are quasars ()many of these large sources are quasars ()

WNB 2147+816

z=0.15

linear size : 3.7 Mpc

Radio HaloesRadio HaloesThings to know about RHThings to know about RH extended radio emitting plasma ~1 Mpcextended radio emitting plasma ~1 MpcMostly present in clusters that:Mostly present in clusters that: are extremely richare extremely rich few spiral galaxies (~10%)few spiral galaxies (~10%) large velocity dispersion (~1000 km/s)large velocity dispersion (~1000 km/s) large X-ray luminositylarge X-ray luminosity Large core radii (>0.3 Mpc)Large core radii (>0.3 Mpc)ExplanationExplanation: a massive merger going on in the cluster, distorting its : a massive merger going on in the cluster, distorting its

morphologymorphologyThings sought:Things sought:Few radio haloes are catalogued (~10) because of low surface density. Few radio haloes are catalogued (~10) because of low surface density. LOFAR will provide large samples: study of merging activity associated LOFAR will provide large samples: study of merging activity associated

with still forming clustreswith still forming clustresLOFAR is expected to find a few hundreds galaxies with radio haloesLOFAR is expected to find a few hundreds galaxies with radio haloes

Low-Frequency VariablesLow-Frequency Variables

Things to know about LFR:Things to know about LFR:• deeply burried inside the host galaxydeeply burried inside the host galaxy• size less than a few tenths of arcsecssize less than a few tenths of arcsecs• the cause: Refractive Interstellar Scintilationthe cause: Refractive Interstellar Scintilation• only present at low frequenciesonly present at low frequenciesThings to expectThings to expect• if the LFVs turn out to be high redshift objects they if the LFVs turn out to be high redshift objects they

define a clean sample of galaxiesdefine a clean sample of galaxies• if they are as small as we think they’re very if they are as small as we think they’re very

young, we can obtain data abut how strong radio young, we can obtain data abut how strong radio sources formsources form

• perhaps they’re confined in dense ISM perhaps they’re confined in dense ISM might explain why is ISM so densemight explain why is ISM so dense

Large-Scale StructureLarge-Scale Structure

Things known:Things known: at z~1 there were a hundred times more at z~1 there were a hundred times more

galaxies than is todaygalaxies than is today evidence of anisotropies of radio sourcesevidence of anisotropies of radio sources

e.g. bright sources seem to be more e.g. bright sources seem to be more concentrated than fainter ones (but we don’t concentrated than fainter ones (but we don’t know why)know why)

Expected from LOFAR:Expected from LOFAR:• cleaner sample of intrinsically bright, not cleaner sample of intrinsically bright, not

because of Doppler boostingbecause of Doppler boosting

Global Reionization of the UniverseGlobal Reionization of the UniverseWhat we know:What we know:• the epopch of galaxy formation lies somewhere between the epopch of galaxy formation lies somewhere between

z=5-10z=5-10• protogalaxy contenders are very abundent (one per protogalaxy contenders are very abundent (one per

square minute) (search for high –z quasars takes very square minute) (search for high –z quasars takes very long optical time)long optical time)

• at z>5 (today’s record) the 21cm line is shifted below at z>5 (today’s record) the 21cm line is shifted below 230MHz230MHz

What is thought, expected:What is thought, expected:• Individual structures around the reionization era aren’t Individual structures around the reionization era aren’t

massive enough to detect with e.g. SKAmassive enough to detect with e.g. SKA• Reionization edge may be detectable (Shaver) Reionization edge may be detectable (Shaver)

Consequence: direct measurement of th e baryon Consequence: direct measurement of th e baryon content of the Univese. For this a full range (110-content of the Univese. For this a full range (110-250MHz) is needed250MHz) is needed

• LOFAR is perfectly suitable for this job. Expected LOFAR is perfectly suitable for this job. Expected integration time is one dayintegration time is one day

Thermal & Nonthermal Emission in Thermal & Nonthermal Emission in Nearby GalaxiesNearby Galaxies

BasicsBasics:: Continuum emission from galaxies give off information Continuum emission from galaxies give off information

about their ISMabout their ISM @ low frequencies synchrotron is th dominating @ low frequencies synchrotron is th dominating

mechanismmechanism In the 20-300 MHz range we expect to see th e old In the 20-300 MHz range we expect to see th e old

population of relativistic electrons coming from SNRspopulation of relativistic electrons coming from SNRs With LOFAR separation of thermal and non-thermal With LOFAR separation of thermal and non-thermal

emission will be possibleemission will be possible Spectral index variation across galaxies clues to Spectral index variation across galaxies clues to

relativistic electron production & evolutionrelativistic electron production & evolution Thermal component dominates above 300 MHzThermal component dominates above 300 MHzImportanceImportance: least biased view of star formation: least biased view of star formation

Compact Sources in Nearby Compact Sources in Nearby GalaxiesGalaxies

• LOFAR may be used to search for LOFAR may be used to search for compact non-thermal sources in the compact non-thermal sources in the neighbouring galaxiesneighbouring galaxies

• Possibly SNRs but there’s a chance for Possibly SNRs but there’s a chance for detexting pulsars as welldetexting pulsars as well

• Search for low frequency nuclear emission Search for low frequency nuclear emission is also an issue (e.g. in the center of the is also an issue (e.g. in the center of the MW & M31). Their nature is uncertainMW & M31). Their nature is uncertain

Radio Polarization @ Low Radio Polarization @ Low FrequenciesFrequencies

The polarization offers insight into:The polarization offers insight into:Galactic magnetic fieldGalactic magnetic fieldplasma turbulence plasma turbulence ionized components at ionized components at anyany temperature temperature

MechanismMechanism: Faraday rotation: Faraday rotation

Low Frequency Recombination Line Low Frequency Recombination Line Observations of Galactic HII RegionsObservations of Galactic HII Regions

What we know about the ionized ISM:What we know about the ionized ISM: from optical and radio samples: T=5000 to 15000Kfrom optical and radio samples: T=5000 to 15000KWhat we would like to see:What we would like to see: cool ionized gas sampled by low frequecy radio cool ionized gas sampled by low frequecy radio

recombination lines (20-100MHz)recombination lines (20-100MHz) n=400-700(alpha)n=400-700(alpha) n=500-750(beta)n=500-750(beta) atoms are ~20 microns and very sensitive to their atoms are ~20 microns and very sensitive to their

surroundings – probes of ambient physical conditionssurroundings – probes of ambient physical conditions probably carbon, not hydrogenprobably carbon, not hydrogen

Supernova Remnants and PulsarsSupernova Remnants and PulsarsContinuum imaging and spectral indicesContinuum imaging and spectral indices

What we know:What we know: SNR are responsable for the SNR are responsable for the

Galactic cosmic rays and most Galactic cosmic rays and most of the synchrotron radiationof the synchrotron radiation

models constructed agree with models constructed agree with observations alpha=-0.5 (-0.3 observations alpha=-0.5 (-0.3 thru -0.8)thru -0.8)

same spectral index same spectral index everywhere (ENIGMA)everywhere (ENIGMA)

What is needed:What is needed: high resolution SNR images high resolution SNR images

over a wide Freq. range (wide over a wide Freq. range (wide range = more precise alpha)range = more precise alpha)

filaments vs. smooth filaments vs. smooth component problemcomponent problem

IC 443IC 443

JupiterJupiter

Things known:Things known: Jupiter produces decametric bursts at Jupiter produces decametric bursts at

frequencies up to 40 MHz (cause: rotation, frequencies up to 40 MHz (cause: rotation, placement & Io )placement & Io )

size of source : less than 500 kmsize of source : less than 500 km process: unknownprocess: unknown highly circularly polarized suggesting cyclotron highly circularly polarized suggesting cyclotron

emissionemissionWhat is expected?What is expected? the resolution of 1/10 D (Jup) enables to track the resolution of 1/10 D (Jup) enables to track

the sourcethe source

Extrasolar PlanetsExtrasolar Planets

What is known about exoplanets?What is known about exoplanets? Jupier sized (if we’re lucky)Jupier sized (if we’re lucky) d<1 A.U.d<1 A.U. their observation is possibly selection bias?their observation is possibly selection bias?How does Radio Astronomy fit in?How does Radio Astronomy fit in?• as seen at Jupiter (Jupiter has Io within its as seen at Jupiter (Jupiter has Io within its

magnetosphere)magnetosphere)• detection of decameter bursts offers lower mass planets detection of decameter bursts offers lower mass planets

at any distances form their parent starat any distances form their parent star• Sun’s interference: sporadic bursts can be detached Sun’s interference: sporadic bursts can be detached

from the signal from the signal • chances: 0.4 mJ @ 1pc or 4 microJ @ 10 pc (marginal)chances: 0.4 mJ @ 1pc or 4 microJ @ 10 pc (marginal)

SummarySummary

Science TaxonomyScience Taxonomy

LOFAR Science is being categorized according to the Science Taxonomy. The LOFAR Science is being categorized according to the Science Taxonomy. The main categories, together with the initial point of contact (SCB Member) are:main categories, together with the initial point of contact (SCB Member) are:

100 : Cosmological Studies (Reionization) - Ger de Bruyn (ASTRON) 100 : Cosmological Studies (Reionization) - Ger de Bruyn (ASTRON) 200 : Extragalactic Surveys - Huub Röttgering (Leiden) 200 : Extragalactic Surveys - Huub Röttgering (Leiden) 300 : Acceleration, Turbulence & Propagation in the ISM - Jim Cordes 300 : Acceleration, Turbulence & Propagation in the ISM - Jim Cordes

(Cornell) (Cornell) 400 : Targeted Extragalactic Observations - Frazer Owen (NRAO) 400 : Targeted Extragalactic Observations - Frazer Owen (NRAO) 500 : Galactic Surveys - Bryan Gaensler (Harvard) 500 : Galactic Surveys - Bryan Gaensler (Harvard) 600 : Transients - Rob Fender (Amsterdam) and Colin Lonsdale (Haystack) 600 : Transients - Rob Fender (Amsterdam) and Colin Lonsdale (Haystack) 700 : Solar System - Namir Kassim (NRL) 700 : Solar System - Namir Kassim (NRL) 800 : Ionosphere - Namir Kassim (NRL) 800 : Ionosphere - Namir Kassim (NRL) 900 : Active Observations - Namir Kassim (NRL) 900 : Active Observations - Namir Kassim (NRL)

THE ENDTHE END