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NEUTRAL HYDROGEN Frank Briggs RSAA and ATNF z=8 z=0 damped Lyman-a abs-lines 21cm Line Studies (HIPASS) Quasar Absorption lines Lyman a forest Metal lines 20 DLA -2 N >2x10 cm HI Wavelength (Angstroms) Quasar (all DLAs have metal lines) HI D.L.A. SiII CII OI/SiII SiIV SiII FeII AlII CIV …bathe HI cloud in photoionizing radiation… Photons DE > 13.6 eV …bathe HI cloud in photoionizing radiation… ?? minimum thickness of skin before becomes self-shielding ?? …bathe HI cloud in photoionizing radiation… optical depth t > 1 for DE ~ 13.6 eV photons 17 -2 N >3x10 cm HI note: t < 1 … transparent… hard to heat! Energy Levels in Hydrogen Optically thick in at the Lyman limit continuum Energy E=0 transitions from ground state are absorbed Ground State Photons DE > 13.6 eV are absorbed Energy Levels in Hydrogen Optically thick in the Lyman continuum Energy E=0 BUT HI layer is transparent to all other wavelengths shorter than the Lyman limit Ground State Ionization by ambient starlight with l > 912 Angstrom Energy E=0 Ground State H He C N O Na Mg Al Si Ca Ti Cr Mn Fe Zn Quasar Absorption lines Lyman a forest Metal lines DLA Wavelength (Angstroms) Quasar Absorption lines Lyman a forest DLA LL Metal lines Quasar Absorption lines thoroughly developed statistics !!! for Lyman a and metal lines… (whatever is common… is most likely to intervene by chance) (ordinary Galaxies Relative interception cross sections … DLA Z=3 Ly break galaxy CIV MgII/ Lyman limit (CII, FeII, SiII, …) HI Column density distribution function Petijean etal 1993 -10 Number of interceptions Nin = NH (n / nH) N HI to N+dN HI range: f(N) dN -15 Log f(NHI) Ionization fraction > 1-3 ? LL~10 t Lya forest IGM -20 12 14 per unit z DLA CIV Log NHI 18 20 22 HI Column density distribution function Petijean etal 1993 -10 -3/2 f(N)dN ~ N dN /unit Z -15 Log f(NHI) M ~ N f(N)dN HI -20 M /Log Interv ~ N HI DLA 2 f(N) +1/2 ~N 12 14 Log NHI 18 20 22 Relative interception cross sections … What are these things??? DLA Z=3 Ly break galaxy (tough to image)pin CIV MgII/ Lyman limit (CII, FeII, SiII, …) nearby Neutral gas disks analogs to high Z DLAs ??? Optical + Radio Extended, low-column density gas = analog of LymanLimit/MgII CIV is the lower density material ?? Square Kilometre Array ARRAY Simple antenna “elements” “Station” “Array” Sensivity depends on collecting area Angular resolution ~ l/D D Sensivity depends on collecting area Angular resolution ~ l/D D ESO VLTI ALMA VLA 6th ATNF Synthesis Imaging Workshop “Synthesis Imaging from Centimetre to Millimetre Wavelengths” 12-16 May 2003 at Narrabri NSW www.atnf.csiro.au/synthesis ARRAY Simple antenna “elements” “Station” “Array” “Magic Carpet” SKA Design Eggs on Legs 3C196-G1 z = 0.437 HST image (Ridgway & Stockton) 3” Cohen et al Double Lobed Radio Source Radio spectrum at 988 MHz Westerbork (Briggs, deBruyn, Vermeulen) 300 km/s source centroid as fnct of Frequency map emission ? SKA map absorption ? new GMRT Kanekar & Chengalur 988 MHz high redshift radio galaxies TNR J1402-1510 TNR J2254+1857 Radio galaxy spectra No UV continuum No DLA absorption lines Molonglo Telescope: SKAMP III • frequency coverage • sensitivity • RFI rejection VLBI to resolve source Cosmic Evolution Indicators Redshift cosmic density Wg of Neutral Gas extent of metal-rich gaseous halos co-moving number density of bright Quasars Cosmic Star Formation Rate history: the Madau Plot 0 0 1 1 2 2 3 3 4 4 5 5 0 1 2 3 4 5 Cosmic Evolution Indicators Passive relaxation 1420 frequency Redshift 500 250 MHz Violent accretion If neutral fraction nHI > -3 ~ 10 nHI +nHII Cut off from view of optical wavelengths !!! Gnedin’s simulation of Reionization: http://casa.colorado.edu/~gnedin/GALLERY/ log(Neutral fraction) log(density) log(mean intensity of ionizing flux) log T .…. ionized…… re-ionized re-re-ionized MAP MAP Result Z = 17 + 4 ??? Rules out WDM 70 MHz ………………..180 MHz Global Signal… 20 mK “The Z=20 Expt” JR, FB, et al Passband filters (from load scan) and RFI (from sky scan) LOFAR and SKA … distributed star formation Quasar 10 arcmin SUMMARY: still plenty to do !