1The Lyα Forest Revisted• It’s the cosmic web.• Contains most of the baryons at high redshift.• Contains 30% of baryons at z = 0.When did galaxy formation occur?Age of U.(Gyr)0.000180.18≤ 0.480.481.20≤ 2.19≤ 3.345.935.93Ned Wright’s Cosmology Calculator2Bias• CDM simulations Îaccurate predictions of CDM structure.• Problems describing baryon response.– Observations Î preference for galaxies to form in denser regions.Dark matter Baryons (for b = 2.5)in CDM simulation Îfrom observations, where σ8= variance of mass distr. in 8h-1Mpc co-moving sphere.• So arbitrary assumptions are needed to describe theobservable galaxies.The Hubble Deep FieldNorthern field:• 10 days, 150 orbits– WFPC2 camera– 5.3 arcmin2• 5000 objects– 20 stars– rest are galaxiesSouthern field:• 70 hours•QSO in center3Photometric RedshiftszSpec= 1.355zSpec= 0.089zSpec= 0.475www.ifa.hawaii.edu/~cowie/tts/tts.html• Pioneered by Loh & Spillar 1986• Used with HDF and most deep surveys since.• Reasonable redshift accuracy. • Reasonable ability to classify galaxies.• Only need a few broad-band images, not spectra.Hubble Ultra Deep FieldAdvanced Camera for Surveys• 3 x 3 arcmin2• 11.3 days exposure.NICMOS• 2.4 x 2.4 arcmin2• 4.5 days exposure4Other deep surveys:• Chandra Deep Fields– North (Centered on HDF North)– South (New location; no QSO; but HUDF now centered here)• GOODS (Great Observatories Origins Deep Survey)– Less deep survey, but over wider area– Incorporates HST, Chandra, Spitzer, XMM Newton + ground-based observations.– Fields centered at:• Hubble Deep Field North (same as CDF North)• Chandra Deep Field South (same as HUDF)Basic idea behind galaxy formation -objects start small and grow by mergingAbraham & van den Bergh (2001)Do galaxiesform this way? Does star formationoccur before,during or aftermass assembly?When and howdo Hubble Types form?From a talk by Chris Conselice5From the HST PR dept:Star formation rate as a function of timeMeasured from• Blue light (O star continuum)•Hα emission (H II regions)“Madau diagram”6Galaxy Formation Gravity Î Material Falls to CenterQuasar = gas falling into massive black hole.Most Quasars Lived and Died Long AgoNumber of Quasars per unit volumeRate at which stars are formed in galaxies.Now= 14 billion yrsFormation of universeÅ timeConclusion: Quasars are events in young galaxies.Out of gas7Sidetrack: The Black Hole at the the Galactic CenterVelocities of stars in very center Î 1 million Mblack hole at position of Sagittarius A*Infrared observations over 6 years.Follows complete orbits to within 60AU from black hole.The Gunn – Peterson Effect• Expect Ly continuum absorption from Inter-Galactic Medium to completely block all radiation with λ < 912Å• Why doesn’t it?Ly break912Å13.6 evLyα1216ÅHydrogen absorption spectrumWavelength ÎFlux ÎLyα1216ÅLy break912Å13.6 evIGM is ionized.Re-ionized.Large columndensity8The dark agesWhen did re-ionization occur?• We see QSOs at z ~ 6 with Gunn-Peterson absorption.• But WMAP finds z =10.9 (420 Myr) for re-ionization– From polarization of CMB.Î patchy re-ionization?z=6.28z=5.80z=5.82z=5.99Neutral H fraction ÎContinuum disappears at Lyα (1215Å)+2.7-2.3z = 7 galaxy?Gravitationally lensed galaxy observed at Keck by Ellis et al.Ly 1215 break?Lens simulation9Z ~ 10 galaxies?Conjugate causticsKeck NIRSPEC slit positionsExpected (rest frame) spectrumHST broadband images show no continuum emission.6 possible Lyαemission lines (circled)z ~ 8.5 – 10.42 best bets are z ~
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