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Neutral gas in galaxies: Synergies between ALMA and ASKAP

Neutral gas in galaxies: Synergies between ALMA and ASKAP. Elaine M. Sadler. Outline of this talk. Big picture questions: Gas and galaxy evolution ASKAP: Why an all-sky HI absorption survey? ALMA synergies: CO observations of an HI-selected galaxy sample at 0.5 < z < 1

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Neutral gas in galaxies: Synergies between ALMA and ASKAP

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  1. Neutral gas in galaxies: Synergies between ALMA and ASKAP Elaine M. Sadler

  2. Outline of this talk • Big picture questions: Gas and galaxy evolution • ASKAP: Why an all-sky HI absorption survey? • ALMA synergies: CO observations of an HI-selected galaxy sample at 0.5 < z < 1 • Pathfinder work: An ATCA/CABB search for associated • HI absorption in young radio galaxies

  3. Neutral hydrogen in galaxies HI observations provide a powerful probe of the mass distribution in galaxies (dark matter) and the fuel supply available for new star formation HI gas distribution Stellar light [NGC 4631, Rand 1994]

  4. Cosmic star-formation history ASKAP HI The rate at which new stars form in galaxies has decreased by about a factor of 20 over the past 7-8 billion years (from redshift z~1 to 0). What caused this? A decline in the supply of cold neutral gas in galaxies? We don’t know! (Hopkins & Beacom 2006)

  5. Cosmic HI mass density • Neutral (atomic and molecular) hydrogen is the missing link in our current models of galaxy evolution • We know almost nothing about the HI content of galaxies at 0.2<z<2. • A wide range of models and simulations exist, none of which fit all the data. • Unknown HI/H2 fraction at z > 0.

  6. HI, CO and star formation in nearby galaxies Nearby Sbc spiral galaxy NGC 5055 (Wong & Blitz 2002)

  7. CO in star-forming galaxies at z~1 LJ Tacconi et al.Nature463, 781-784 (2010) doi:10.1038/nature08773

  8. Optical: Damped Ly Absorbers Lyman a forest DLA (Ellison et al. 2001) DLAs: Intervening absorbers with high HI column density (NHI > 2 x 1020 cm-2) can be used to detect and study neutral hydrogen in the very distant universe.Ground-based observations of the Lyman- line are only possible at redshift z > 1.7

  9. Cosmic HI mass density

  10. HI column density distribution Zwaan et al. (2005) Optical DLA surveys at z > 2 do not detect the highest column-density absorbers expected on ~0.1% of sightlines, and “do not trace the majority of star-forming gas in the universe” (Ledoux et al. 2003). Dust obscuration?

  11. Radio: Intervening HI absorption lines Radio 21cm measurements are particularly sensitive to cold HI (TS < 200K) tNHI/Ts.DVfor observed optical depth t Probability of intercepting a DLA system (NHI > 2 x 1020 cm-2) on a random line of sight? dN/dZ=0.055 (1+z)1.11 (Storrie-Lombardi & Wolfe 2000) i.e. ~6% for z=0.7, 300 MHz band Unlike optical, no redshift limit for detecting radio 21cm absorption lines. But do need many targets, wide bandwidth WSRT: Lane et al. 2001, targeted, z = 0.436

  12. FLASH: the First Large Absorption Survey in HI • Key science goals: • To provide the first systematic probe of the neutral hydrogen (HI) content of individual galaxies in the redshift range 0.5 < z < 1.0 • To make tests of current galaxy evolution and mass assembly models in this redshift range, using the observed and predicted distributions of quantities like HI optical depth and line width. Team members:Currently 37 members from 18 institutions in 7 countries Elaine Sadler (Sydney, PI), James Allison (Oxford), Chris Blake (Swinburne), Joss Bland-Hawthorn (Sydney), Robert Braun (ATNF), Matthew Colless (AAO), Rob Crain (Swinburne), Scott Croom (Sydney), Darren Croton (Swinburne), Stephen Curran (UNSW), Jeremy Darling (USA), John Dickey (Tasmania), Michael Drinkwater (Qld), Ron Ekers (ATNF), Sara Ellison (Canada), Bjorn Emonts (ATNF), Ilana Feain (ATNF), Ken Freeman (ANU), Bryan Gaensler (Sydney), Dick Hunstead (Sydney), Helen Johnston (Sydney), Baerbel Koribalski (ATNF), Philip Lah (ANU), Tom Mauch (Oxford), Martin Meyer (UWA), Raffaella Morganti (Netherlands), Tom Oosterloo (Netherlands), Max Pettini (UK), Kevin Pimbblet (Monash), Michael Pracy (Swinburne), Steve Rawlings (Oxford), Tim Robishaw (Sydney), D.J. Saikia (Pune, India), Lister Staveley-Smith (UWA), Matthew Whiting (ATNF), Richard Wilman (Melbourne), Martin Zwaan (ESO)

  13. The advantages of ASKAP • ASKAP’s • Wide field of view • Wide spectral bandwidth • Radio-quiet site • make it possible to carry out the first blind radio survey for HI absorption Only about 400 sightlines have so far been searched for HI absorption in the radio (roughly 200 each with single-dish (blind) and interferometer (targeted) programs). In the ASKAP-FLASH survey, we will target more than 150,000 sightlines to bright background continuum sources, an increase of more than two orders of magnitude over previous work.

  14. Survey parameters Cross-comparison of emission, absorption and stacking measurements at z<0.26 is a new and important aspect of the ASKAP HI surveys

  15. Integrated CO spectra of SF galaxies at z~1 to 2 CO spectral-line detections should require only short integration times with ALMA for HI-selected galaxies out to z=1 LJ Tacconi et al.Nature463, 781-784 (2010) doi:10.1038/nature08773

  16. Associated HI absorption in radio galaxies Nearby galaxy NGC 6868, continuum flux density ~120 mJy at 1.4 GHz. Associated HI absorption at or near the galaxy redshift is particularly common in compact, flat-spectrum radio galaxies (Vermeulen et al. 2003) ATCA: Oosterloo et al., targeted, z = 0.01

  17. ATCA/CABB HI absorption (C2434) • Target sample of 60 nearby (z < 0.08) ‘young’ compact (<0.5 kpc) radio galaxies selected from the AT20G survey. • 30 galaxies so far observed in HI line with ATCA/CABB (Feb and Apr 2011), analysis in progress • Probe distribution and kinematics of gas in innermost regions of AGN • Wideband test data for ASKAP pipeline (Orienti et al. 2006)

  18. HI in PKS 1814-637 ATCA C2434: James Allison ATCA: Morganti et al. 2001

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