Presentation on theme: "Decrypting the Universe with LOFAR Philip Best Institute for Astronomy, Edinburgh."— Presentation transcript:
Decrypting the Universe with LOFAR Philip Best Institute for Astronomy, Edinburgh
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
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.
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.
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
LOFAR Science Goals LOFAR has incredibly wide-ranging science goals: –Epoch of Reionisation Detect through 21cm hyperfine transition –Deepest extragalactic radio surveys 2π 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, Earth’s ionosphere etc –Galactic surveys and Cosmic Magnetism
LOFAR & the Epoch of Reionisation 21cm hyperfine transition (1 0 S 1/2 and 1 1 S 1/2 states). Ratio of upper to lower state occupancy is T * = 0.068K T s = spin temp. Coupling to CMB means T s =T CMB, so absorption and re- emission at same rate and no net signal. But, scattering of Ly-α photons from first sources decouples spin temp [Wouthuysen-Field effect] and produces a signal Signal then disappears as Universe is ionised.
LOFAR EoR signal For T s >> T CMB, brightness temperature differential (δT) 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
Challenge: removing foregrounds From Jelic & Zaroubi (2007)
Alternative approach: 21cm forest A simulated radio spectrum of a radio galaxy at z=12 (left) and z=8 (right): Carilli (2005)
LOFAR Extra-galactic surveys First-pass survey design (for 77-station Dutch LOFAR): Freq. Angular Sky 3σ flux Source No Time resol. cover limit density sources needed (MHz) (“) (mJy) (arcmin -2 ) (bm yrs) 15 50.3 2π sr 4.7 0.2 1.3x10 7 0.28 30 25.2 2π sr 1.0 0.7 5.4x10 7 0.88 60 12.6 2π sr 1.0 0.3 2.2x10 7 2.24 120 6.3 2π sr 0.043 11.6 8.6x10 8 8.56 200 3.8 250□ 2 0.014 32.2 3.0x10 7 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 2π shallower survey at 200MHz, plus few sq deg deeper
LOFAR compared to other radio surveys Credit: Morganti
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 LOFAR’s 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
Star-forming gals with LOFAR LOFAR will detect >10 8 SF gals and will be sensitive to gals with SFR > 10 M sun /yr out to z>2 and SFR > 100 M sun /yr out to z>8. Main science goals: comparison with multi-λ 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)
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
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
AGN and galaxy formation The local galaxy luminosity function (data points, from 2dFGRS) compared to that predicted if light follows mass in the dark matter haloes. 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 & ionising background ??? Radio AGN Supernovae
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 f radio-loud is a very strong function of mass: f radio-loud M * 2.5
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
Radio feedback in the local Universe Assume f radio-loud gives duty cycle of recurrent activity Use observations of radio source bubbles/cavities in nearby clusters to convert L rad to L mechanical
Radio feedback in the local Universe Assume f radio-loud gives duty cycle of recurrent activity Use observations of radio source bubbles/cavities in nearby clusters to convert L rad to L mechanical 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!
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 z=2 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 < z < 2 requires about 60 square degrees. PanSTARRS Medium Deep Survey will provide this.
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