Evolution of Lyman-alpha Halos

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  • resonant scattering, atom struck by lya photon will emit another lya photon
    mean-free path in wings >> mfp in line core
    short mfp greatly increases dust-absorption cross-section
    two wings lead to double-peaked profile
    ratio of wings affected by motion, eg, infall tends to give momentum to outward propagating photons, favors blue peak





  • bulk motion on large scales (hubble flow or decoupling) leads to escape over a range of radii
    outflows from dusty starbursts or infall on forming starburst



    here’s some examples:
  • Gas at temperatures which peak in the UV redshifts into the optical band (along with Lya)
    While Lya has its problems, still a good tracer because H is everywhere and energies aren’t too high


  • here’s some examples:
    not the first, but well-studied
    fades into background





  • no radio galaxies!
    similar size and luminosity to radio sources


  • three basic scenarios: infall, outflow or in situ SF
    infall may contain lower metallicity gas than either other 2 scenarios




  • morphology of lya is one way to differentiate the scenarios
    here is a case...


  • many scenarios can lead to decrease in line luminosity, however combined with morf may not be totally degenerate
    I purposely didn’t label either axis because we only have data at a few discrete redshifts
    but, spatial average could increase as more numerous smaller halos begin to collapse, for the infall-driven case
    so need data over a range of redshifts... UV at low-z -->
  • need wavelength coverage to extended redshift range --> space-based UV


  • five radio galaxies, four of five detected
    modeled a simple power-law continuum bracketed the empirical slopes for AGN and SF galaxies, no preferred slope
    lines less than ~5000 km/s are unresolved
    for sources apart from 3c265 hard to tell the difference between extended emission and the core of a halo and a purely-galactic emission region


  • are there bright halos?
    a “fiducial” model, the rough scale and surface-brightness of the high-z population


  • lower-z radio galaxies are not necessarily the descendants of high-z RGs, but...
    they are also massive galaxies
    if there are bright halos at z~1 they don’t seem to be around RGs
  • Evolution of Lyman-alpha Halos

    1. 1. Evolution of Lyman-α Halos CAS Seminar 19 May 2009 Andrew Zirm
    2. 2. Talk Summary Production and Radiative Transfer of Lyman-α The Halo Phenomenon Observational Summary Energetics and Lifetimes Possible origins Observations at z~1 Possible Evolutionary Scenarios What have we learned? What do we do now? Andrew W. Zirm CAS Seminar 19 May 2009
    3. 3. “How Do We Know Things?” Andrew W. Zirm CAS Seminar 19 May 2009
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    8. 8. “How Do We Know Things?” Books Internet Google Wikipedia Wolfram Alpha? Andrew W. Zirm CAS Seminar 19 May 2009
    9. 9. “How Do We Know Things?” Books Internet Google Wikipedia Wolfram Alpha? Andrew W. Zirm CAS Seminar 19 May 2009
    10. 10. “How Do We Know Things?” Books Internet Google Wikipedia Wolfram Alpha? Andrew W. Zirm CAS Seminar 19 May 2009
    11. 11. Production and Propagation of Lyman-α n=2 to 1, 10.2 eV, 1216A Resonant Scattering leads to diffusion of photons out of the cloud amplifies absorption by dust Shifts to the wings allows photons to escape more λ easily due to bulk motions of the gas Easily Quenched by dust both in the galaxy and in the surrounding medium Inherently double-peaked motion favors red or blue peak Andrew W. Zirm CAS Seminar 19 May 2009
    12. 12. What is a Lyman-α Halo? Line luminosities in excess of 1044 erg/s Diameters of ~ 100 kpc or more No observed continuum high equivalent-width emission Lack of observations of other emission lines Often contain bright sub-mm source Lyman-α emission implies bulk/differential motions are present Extremely short cooling times imply an ionization source and/or gas replenishment Seemingly rare, at least in the narrow redshift ranges probed so far Andrew W. Zirm CAS Seminar 19 May 2009
    13. 13. Importance of Halos Tracer of Gas X-rays not detectable at z>1.5 or so Tracer of Large Scale Structure “Cosmic Web” Cooling of LSS shock-heated material Identify Protoclusters Tracer of Massive Galaxies outflows from enshrouded starbursts shocked gas by massive halos recently quenched AGN? Source of ionization? short cooling times imply replenishment of gas or steady ionization source Andrew W. Zirm CAS Seminar 19 May 2009
    14. 14. Lyman-α Halos around Radio Galaxies z ≥ 1.8 Lyα visible from the ground Surrounding powerful radio galaxies Sizes of 100 kpc or more Line Luminosities of > 1044 High equivalent-width No other emission-lines Outside radio source Lack of correspondence between radio and line emission Reuland et al. 2003 No collimation Andrew W. Zirm CAS Seminar 19 May 2009
    15. 15. Lyman-α Halos in Protoclusters Rare objects associated with LSS formation some evidence for outflows (IFU data) dusty central source in some cases (bright SCUBA source) smaller “blobs” may be powered by AGN (see Geach et al. 2009) Other “blobs” also in protoclusters? e.g., Dey et al. 2005 Steidel et al. 2000 Andrew W. Zirm CAS Seminar 19 May 2009
    16. 16. Origin of Halos cooling via Lyα (Pristine) infalling gas heating via accretion shock for massive DM halos Processed outflows cold flows AGN or SNe driven In situ star-formation photoionization and shocks possibly static cloud SNe and AGN driven wind metal-enriched local IGM stars forming in infalling gas sharp spatial cutoff? photoionization from stars should produce: stellar continuum Hα, other lines metals dispersed Andrew W. Zirm CAS Seminar 19 May 2009
    17. 17. Using Morphology as a Clue to Halo Origin TNJ1338-1942 at z=4.11 Deep ACS imaging incl. Lyα in the r-band “Wedge” morphology suggests outflow Apex of wedge does not coincide with radio core Axis of wedge is ⊥ to radio axis If SNe-driven, would take 107 years to create halo No UV continuum Zirm et al. 2005 Andrew W. Zirm CAS Seminar 19 May 2009
    18. 18. Using Evolution as a Clue to Halo Origin Fate of the gas cooling and forming stars fueling AGN L hydrostatic equilibrium at high T X-ray halo/ICM z Evolution of Ionization AGN turns off L: individual halo line luminosity SFR declines rapidly L: spatially averaged line luminosity Complete Surveys how common are halos? how do they cluster? Andrew W. Zirm CAS Seminar 19 May 2009
    19. 19. Observing Lyman-α at z~1 with STIS Peak of NUV throughput coincides with redshifted Lyman-α (around 2400Å) Prism provides low-resolution spectroscopy over small FOV Slitless mode Andrew W. Zirm CAS Seminar 19 May 2009
    20. 20. STIS Prism Data I Targeted 5 radio galaxies and 5 galaxy clusters around z~1 Very low background Only radio galaxies detected 4 of 5 RGs detected both in direct and prism data used direct image to model 2D spectrograms line emission is spectrally unresolved Aperture Photometry isophotal areas in continuum-subtracted image masked CIVλ1549 emission for 3C265 (not extended) Andrew W. Zirm CAS Seminar 19 May 2009
    21. 21. STIS Prism Data I Targeted 5 radio galaxies and 5 galaxy clusters around z~1 Very low background Only radio galaxies detected 4 of 5 RGs detected both in direct and prism data used direct image to model 2D spectrograms line emission is spectrally unresolved Aperture Photometry isophotal areas in continuum-subtracted image Raw Data Line Emission masked CIVλ1549 emission for 3C265 (not extended) Andrew W. Zirm CAS Seminar 19 May 2009
    22. 22. STIS Prism Data II Targeted 5 radio galaxies and 5 galaxy clusters around z~1 Very low background Only radio galaxies detected both in direct and prism data used direct image to model 2D spectrograms Fiducial “high-z” model King model profile rc = 50 kpc LLyα=1044 erg/s Lack of luminous halos of the type seen at z > 1.8 Andrew W. Zirm CAS Seminar 19 May 2009
    23. 23. STIS Prism Data II Targeted 5 radio galaxies and 5 galaxy clusters around z~1 Very low background Only radio galaxies detected both in direct and prism data used direct image to model 2D spectrograms Fiducial “high-z” model King model profile rc = 50 kpc LLyα=1044 erg/s Lack of luminous halos of the type seen at z > 1.8 Andrew W. Zirm CAS Seminar 19 May 2009
    24. 24. Luminosity Evolution of Extended Lyman-α No large luminous halos at z~1 (around RGs) Luminosity associated with UV continuum, aligned light Two “by eye” evolutionary lines: L ∝ (1+z)5 and (1+z)2.3 Possible different evolutionary tracks for galaxy-scale halos versus LSS halos Large circles: Radio Galaxy halos Small squares: “Blobs” Stars: This Sample Andrew W. Zirm CAS Seminar 19 May 2009
    25. 25. (Lack of) Correlation with Other Properties Stellar Mass Radio Power Andrew W. Zirm CAS Seminar 19 May 2009
    26. 26. Surface-Brightness profiles Generally steeper and smaller profiles than at high-z For 3C265, the emission is clearly not symmetric about the center (see next slide) Andrew W. Zirm CAS Seminar 19 May 2009
    27. 27. 3C 265: The Best Case UV continuum morphology closely traces the Lyman-α SB profile steeply declines from center Some relatively constant SB features Line emission driven by aligned light? Andrew W. Zirm CAS Seminar 19 May 2009
    28. 28. Ionization Source Evolution? Comparison of ionizing flux extrapolated from X-ray core measurements and Lyman-α flux z > 1.8 X-rays are insufficient, while at z~1 they may be sufficient Assuming one ionizing photon translates to one Lyα photon New dominant physical mechanism? Andrew W. Zirm CAS Seminar 19 May 2009
    29. 29. Evolutionary Scenario infalling gas is shocked and cools via Lyman-α on a large scale additional line emission from subsequent AGN and star formation gas is used-up in star formation and AGN extended line emission later powered solely by star-formation in “aligned” light, lighting up the residue of galaxy formation Lyman-α especially prominent at crossings of “cosmic web”, i.e., protoclusters process repeats itself at lower mass scales Andrew W. Zirm CAS Seminar 19 May 2009
    30. 30. Conclusions Space-based NUV imaging works! No “high-z” type halos around radio galaxies (or clusters) at z~1 Change in physical process driving emission OR change in location of brightest halos? Lyman-α emission moved to smaller halos still with infalling gas? Use line emission as a “calorimeter” via its morphology and luminosity Andrew W. Zirm CAS Seminar 19 May 2009
    31. 31. Future Work UV imaging and spectroscopy with HST/WFC3 (yipee!) one grism and several narrow-band filters in the NUV survey of more clusters and radio galaxies Wide-field Ground-based surveys narrow-band filters on the VST telescope at Paranal tunable-filters on 4-meter telescopes (also in NIR) Other emission lines? Hα perhaps Andrew W. Zirm CAS Seminar 19 May 2009

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