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Intergalactic Interactions: A Higgs Centre Workshop on the Intergalactic Medium

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Lecture Theatre (Royal Observatory, Edinburgh)

Lecture Theatre

Royal Observatory, Edinburgh

Blackford Hill Edinburgh
Avery Meiksin (The University of Edinburgh), Einan Gardi (The University of Edinburgh), Luigi Del Debbio (The University of Edinburgh)
Description
The cosmic web contains most of the mass of the Universe. It is revealed through hydrogen and helium absorption lines in the spectra of distant Quasi-Stellar Sources (QSOs), which act as background lightbulbs against which the absorption is measured. The purpose of the workshop is to bring together world-leading experts in the study of the IGM. The topics to be covered include the hydrogen and helium distributions in the IGM, cosmological constraints from the Lyman-alpha forest, the metal content of the IGM and the interaction between galaxies and their circumgalactic gas.
Slides
  • Monday, 24 June
    • 09:15 → 09:30
      Introductory Remarks Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
    • 09:30 → 11:10
      Hydrogen in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      Convener: Avery Meiksin (The University of Edinburgh)
      • 09:30
        Lyman Limit Systems throughout cosmic history 40m
        Speaker: Prof. John O'Meara (Saint Michael's College)
        Slides
      • 10:10
        The fundamental plane of DLAs 30m
        The study of the high redshift universe through quasar absorption lines allows us to measure in great detail the properties of the gas that is responsible for the absorption. Damped Lyα systems, DLAs, the largest of these absorbers, are intimately linked to the predecessors of modern-day galaxies, and their study provide insight into how galaxies form and evolve. In this talk, I will review some of the key parameters we measure for DLAs. I will explain how their distributions and correlations help us understand the properties of the gas surrounding high-redshift galaxies, and how these constrain current galaxy formation models. Furthermore, I will explore if there is any additional constraint besides these distributions and correlations, that can provide further insight into the properties of the absorbing gas. I conclude that indeed such a constraint exist, dubbing it the Fundamental Plane of DLAs.
        Speaker: Mr Marcel Neeleman (UCSD)
        Slides
      • 10:40
        The cosmic neutral hydrogen distribution and its connection to galactic ecosystems 30m
        In this talk, I will show that cosmological simulations of galaxy formation that match the cosmic star formation history are also capable of reproducing the observed HI distribution when they are combined with accurate radiative transfer calculations. I will discuss the impact of different ionizing processes (i.e., the UV background, recombination radiation, collisional ionization and local stellar radiation) on the HI column density distribution over more than 12 billion years of evolution from z = 5 to z = 0. I will also talk about the connection between the so-called Damped Lyα and Lyman limit systems and their host galaxies in the simulations. This talk is based on my recent publications: Rahmati et al. 2013a; 2013b (MNRAS in press) and Rahmati et al. 2013c (in prep.).
        Speaker: Mr Ali Rahmati (Leiden Observatory)
        Slides
    • 11:10 → 11:40
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 11:40 → 12:50
      Hydrogen in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 11:40
        Lyman limit systems and the circumgalactic medium at z~2-3 40m
        Already from the first quasar surveys, it became evident that Lyman limit systems (LLSs) differ from the Lyα forest and are likely associated to galaxies. Recently, this idea has received renewed attention because of the proposed connection between LLSs and the so-called "cold streams" that are postulated to feed star forming galaxies at z>2. In this talk, I will present results from a new survey that has been designed to study the properties of LLSs at z~2.5-3. With the aid of simple analytic models and numerical simulations, I will then discuss the link between LLSs and the circumgalactic medium of galaxies at z~2-3. I will also propose a new experiment to map the optically thick gas around distant galaxies, without the need for large samples of galaxy/LLS associations.
        Speaker: Dr Michele Fumagalli (Carnegie Observatories/Princeton University)
        Slides
      • 12:20
        The Lyα forest flux PDF from BOSS 30m
        The BOSS Lyα forest survey is obtaining Lyα forest sightlines for over 160,000 QSOs at z>2. While the signal-to-noise and resolution is moderate, I will show that it is possible to obtain information on the IGM temperature-density relation by measuring the flux PDF from the BOSS Lyα forest data. I will discuss new methods for continuum-estimation, noise- and metal-modelling that allow us to take a forward modelling approach to compare simulation spectra with the actual BOSS data. I will conclude with preliminary comparisons between the BOSS measurements and simulated spectra.
        Speaker: Dr Khee-Gan Lee (MPIA)
        Slides
    • 12:50 → 14:20
      Lunch 1h 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 14:20 → 16:10
      Galaxies, Feedback and the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 14:20
        News on the very local CGM and IGM 40m
        Speaker: Prof. Philipp Richter (University of Potsdam)
        Slides
      • 15:00
        Are metals in the IGM out of equilibrium? 40m
        Speaker: Dr Benjamin Oppenheimer (Leiden University)
        Slides
      • 15:40
        Probing gas infall and outflow in the vicinity of high redshift galaxies 30m
        We present results from the VLT LBG Redshift Survey (VLRS), probing the HI distribution around z ~ 3 galaxies. The VLRS consists of ~ 2,000 galaxy redshifts at z > 2 in the foreground of bright QSOs with pre-existing high-resolution spectra. We have further added to the QSO sample within our survey fields by identifying and observing fainter QSOs with X-Shooter. We present the widest area cross-correlation between galaxies and HI at z ~ 2 - 3, showing the distribution from scales of ~ 100 kpc to 10 Mpc. The overdensity of neutral HI gas around star-forming galaxies extends to scales of 2 - 3 Mpc, whilst the gas profile shows a steady increase in the gas density closer to the galaxies. We present an analysis of the data by incorporating SPH simulations (GIMIC & OWLS), constraining the effects of galaxy and gas dynamics on our measurements.
        Speaker: Dr Richard Bielby (Durham University)
        Slides
    • 16:10 → 16:40
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 16:40 → 17:40
      Galaxies, Feedback and the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 16:40
        Stacking Lyα forest absorbers in the SDSS-III/ BOSS DR9 quasar survey 30m
        We present results from stacking Lyα forest absorbers in the BOSS sample to achieve a variety of goals. Chief among them is the measurement of metals in the intergalactic medium (IGM) associated with the forest using various transitions, including several elements and species only seen using this technique. Metals in the IGM provide a valuable tracer of mechanical feedback - a crucial component of our understanding of galaxy formation and evolution. Surveys of galaxies with low transverse separation from quasar lines of sight and simulations allows us to make inferences on the nature of these absorbers.
        Speaker: Dr Matthew Pieri (ICG, Portsmouth)
      • 17:10
        The distribution of metals in the circumgalactic medium around z ~ 2.4 galaxies in the Keck Baryonic Structure Survey 30m
        We study the distribution of metals spanning a large range of ionization energies (from SiIII to OVI) in the circumgalactic medium, through a sample ~700 star-forming z~2.4 galaxies selected from the Keck Baryonic Structure Survey. Using 15 hyper-luminous background quasars, we search for metals in absorption near galaxies, in order to make 2D metal maps by taking the median optical depth in bins out to 2 pMpc in impact parameter and 5 pMpc (1200 km/s) along the line-of-sight. We find an enhancement in the optical depths of all studied metals in the innermost impact parameter bin (<180 pkpc), and along the line-of-sight up to ~1 pMpc or 240 km/s (assuming pure Hubble flow and depending on the species). Normalizing the optical depth profiles, we do not see any significant difference between the distribution of hydrogen and the metals nor between the metals themselves.
        Speaker: Ms Monica Turner (Leiden Observatory)
  • Tuesday, 25 June
    • 09:30 → 11:20
      Helium in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      Convener: Dr Jamie Bolton (University of Nottingham)
      • 09:30
        Detailed observations of the He II reionization epoch 40m
        The reionization of He II at z~3 was the last major change in the ionization state of the IGM. In addition, the reionization of He II may also aid theoretical understanding of the later stages of hydrogen reionization. In recent years we have dramatically increased the number of He II Gunn-Peterson trough observations. Previously there were only two Gunn-Peterson observations at medium resolution (R>10,000), both with low S/N and one covering only the post-reionization epoch. Such resolution is crucial for gap statistics and other metrics sensitive to the progress of reionization. This year we are tripling the number of such observations to six, which for the first time will allow a statistical understanding of this epoch using higher-resolution techniques. I discuss the first medium-resolution observations of the well-known He II quasar Q0302-003, and preliminary results from a 2013 survey of three newly confirmed He II quasars.
        Speaker: Dr David Syphers (University of Colorado, Boulder)
      • 10:10
        Toward the beginning of the reionization of intergalactic helium 30m
        From the HST/COS spectra of selected quasars at z~>3.5, we find significant flux blueward of the HeII Lyα wavelength. The absorption profile suggests large "bubbles" of ionized helium embedded in the intergalactic medium. We find that the intensity of He+ ionizing field weakens considerably at z~3, and the reionization of the intergalactic helium started around z=3.5.
        Speaker: Dr Wei Zheng (Johns Hopkins University)
      • 10:40
        Mapping the inside-out morphology of HeII reionization over 800 million years of cosmic time 40m
        The advent of GALEX and HST/COS have revolutionized studies of HeII reionization. In HST Cycle 17 we pioneered an effective strategy to statistically probe the HeII reionization epoch with HST/COS spectroscopy of the UV-brightest quasars. The clear picture emerging from the 13 sightlines probing z<3 is that HeII reionization likely ended at z~2.7. At z>2.7 the large scatter in the mean HeII absorption on scales of ~10 proper Mpc indicates that HeII reionization was highly inhomogeneous and extended. Complementary Keck+VLT spectroscopy of the coeval HI forest maps the underlying density field along the quasar sightline, yielding the first tantalizing evidence for "inside-out" HeII reionization occurring first in overdense regions around quasars. Some of these HeII-reionizing quasars have been identified by us in a dedicated deep imaging and spectroscopic survey for foreground quasars close to HeII sightlines. Currently, we are performing an HST/COS survey for HeII absorption toward 7 newly discovered UV-bright z>3.1 quasars. By doubling the redshift pathlength at z>3 we will obtain the first statistical insight into the early stages of HeII reionization.
        Speaker: Dr Gabor Worseck (Max-Planck-Institut für Astronomie)
    • 11:20 → 11:50
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 11:50 → 13:00
      Helium in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 11:50
        Intensity fluctuations in the HI and HeII Lyα forests 40m
        I will discuss the impact of intensity fluctuations on HI and HeII Lyα forest data. This will include a summary of recent work to measure and model eta fluctuations in the z~2.5 HeII Lyα forest and its implications for the sources of the UV background. In addition, I will summarize what numerical simulations plus radiative transfer predict for the abundance of z>3 HI Lyman-limit systems, and a surprising implication of this modeling for metagalactic radiative transfer. Finally, I will say a few words about the sensitivity of 3D Lyα forest, highlighting the possibility of probing 100Mpc-scale intensity and temperature fluctuations.
        Speaker: Dr Matthew McQuinn (UC Berkeley)
      • 12:30
        The effect of fluctuations on the helium-ionizing background 30m
        The standard cosmological radiative transfer method used to estimate the He II ionizing background assumes a uniform radiation field despite the discrete nature of the (rare) bright quasars that dominate the background. We estimate, for the first time, the effects of fluctuations on the evolving continuum opacity in two ways: by incorporating the complete distribution of ionizing background amplitudes into the standard approach, and by explicitly treating the quasars as discrete -- but isolated -- sources. Our model results in a He II ionization rate that evolves steeply with redshift, which causes rapid evolution in the mean He II optical depth -- as recently observed -- without appealing to the reionization of He II. The observed behavior could instead result from rapid evolution in the mean free path of ionizing photons as the helium in higher column density H I absorbers becomes fully ionized.
        Speaker: Mr Frederick Davies (UCLA)
    • 13:00 → 14:30
      Lunch 1h 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 14:30 → 15:00
      Helium in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 14:30
        Cosmic UV background fluctuations traced by metal ions at the epoch of helium re-ionisation 30m
        The helium reionisation and the cosmic UV background (UVB) at z=3 have been investigated in recent years both theoretically and observationally. Spatial fluctuations of the eta parameter in the Lyα forest show that the He II opacity is “patchy” and a theoretical modelling of the UVB spectral shape is necessary to constrain these fluctuations. Metal ions in the IGM help constraining the UVB spectral shape at the edge of HeI and HeII ionisation potentials. I will show the results of a new radiative transfer (RT) simulation performed with the code CRASH3, accounting for metal ionisation states self consistently with H and He. The importance of the RT effects in shaping the UV background on a scale of 10/h Mpc comoving, is discussed by providing an accurate estimate of the fluctuations in eta, in the IGM temperature and in the column density ratio CIV/SiIV.
        Speaker: Dr Luca Graziani (Max Planck Institute for Astrophysics - MPA Garching)
        Slides
    • 15:00 → 15:30
      Poster Session Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      slides
    • 15:30 → 16:00
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 16:00 → 17:10
      Hydrogen in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 16:00
        Illuminating the cosmic web with quasar-induced Lyα emission 40m
        I will present the result of a an ongoing, successful program that uses a new approach to directly detect and study cosmic gas in the early Universe: the key idea is to use an external ``source of illumination’’, a bright quasar, to light up with fluorescent Lyα emission dark, proto- galactic clouds and dense streams around galaxies in a large cosmological volume. In the first part of the talk, I will discuss our pilot project based on deep narrow-band imaging on VLT /FORS centered on a z=2.4 hyper-luminous quasar: how we identified and characterized the physical properties of the first sample of high-redshift, “dark” galaxy candidates. In the second part of the talk, I will present the detection of fluorescent emission from the Circumgalactic Medium of star forming galaxies and very recent, spectacular results obtained with Keck/LRIS of the detection of hundred-kpc scale filaments surrounding bright quasars.
        Speaker: Dr Sebastiano Cantalupo (UCSC)
      • 16:40
        On the possible break in the metallicity evolution of DLAs at z ~ 5 30m
        We present chemical abundance measurements for damped Lyα systems (DLAs) at z>4, which show a clear decrease in the metallicity of DLAs with increasing redshift. We find a possible break in the metallicity evolution of DLAs at z>4.7, and showcase our latest results using new Keck ESI and Magellan FIRE spectra. This break may represent a transition in the nature of DLAs, where high redshift cold flows begin to host low HI column density and low metallicity DLAs. Even with the observed break, we show that the metallicity 'floor' of ~1/600 solar continues out to z~5, despite our sensitivity for finding DLAs with much lower metallicities. In addition, we find that the metallicity distribution and the α/Fe ratios of z>2 DLAs are consistent with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of DLA gas.
        Speaker: Dr Marc Rafelski (IPAC (Caltech))
        Slides
  • Wednesday, 26 June
    • 09:30 → 11:30
      Cosmological Constraints from the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      Convener: Prof. Martin White (Higgs Centre Associate)
      • 09:30
        Cosmology with the Lyα forest 40m
        The Baryon Oscillations Spectroscopic Survey of SDSS-III has opened a new era for high-redshift large-scale structure surveys using spectra of intervening absorption. On large scales, the 3D redshift space linear power spectrum can be measured, as modified with two bias parameters for the Lyα forest, for density and peculiar velocity gradient. On small scales, the detailed physics of the intergalactic medium can be probed from the observed 3D and 1D power spectra, comparing them to the predictions of cosmological simulations. Fluctuations in the radiation intensity from ionizing sources also have an impact on the measured power spectra.
        Speaker: Prof. Jordi Miralda-Escudé (ICREA, Barcelona)
        Slides
      • 10:10
        BAO results from BOSS and cosmological implications 40m
        Speaker: Dr Nicolás Busca (Laboratoire AstroParticules Cosmologie - CNRS)
        Slides
      • 10:50
        Measurements of cross-correlations of the Lyα forest with DLAs and quasars from BOSS 40m
        The Baryon Oscillation Spectroscopic Survey (BOSS) uses the SDSS telescope to obtain spectra of 1.5 million galaxies to get a very accurate measurements of the BAO scale at redshift z ~0.5. Roughly a 20% of the fibers of the spectrograph, however, are pointing to high redshift quasars with the idea of detecting the BAO also in the clustering of gas responsible for the Lyα absorption present in the quasars, known as the Lyα forest. In this talk I will present the first results of the survey, highlighting the first large scale measurement of the correlation function (Slosar++ 2011), the first detection of its large scale correlation with Damped Lyα systems (Font-Ribera++ 2012) and with quasars (Font-Ribera++ 2013), and the first detection of the BAO in the Lyα forest (Busca++2013, Slosar++2013).
        Speaker: Dr Andreu Font-Ribera (University of Zurich)
        Slides
    • 11:30 → 12:00
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 12:00 → 13:50
      Cosmological Constraints from the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 12:00
        Using the IGM to measure the coldness of cold dark matter 40m
        I will present new measurements of cold dark matter coldness by using a set of high resolution quasar spectra.
        Speaker: Dr Matteo Viel (INAF)
        Slides
      • 12:40
        Lyα forest statistics 40m
        I will present some recent results on IGM simulations, including statistics of strong absorbers, and the effect of WDM.
        Speaker: Dr Tom Theuns (Durham University)
      • 13:20
        Precision measures of the primordial deuterium abundance 30m
        We are currently in an exciting era of precision cosmology. With the release of the cosmic microwave background data recorded by the Planck satellite, we are now in a position to accurately test the standard model of Big Bang Nucleosynthesis. In this talk, I will present a new, precise measure of the primordial abundance of deuterium - the most accurate measurement to date - derived from a redshift ~3 metal-poor damped Lyα system. In light of this new measurement, we have performed a careful reanalysis of the best systems where the primordial deuterium abundance can be estimated. These precise measures, when analysed in conjunction with the Planck data, now place strong limits on the effective number of neutrino species in the early Universe, and offers new insight into physics beyond the standard model. I will also discuss our ongoing survey to obtain new precision measures of the primordial deuterium abundance.
        Speaker: Dr Ryan Cooke (UC Santa Cruz)
        Slides
    • 13:50 → 15:20
      Lunch 1h 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 19:30 → 21:30
      Workshop Dinner 2h Rainy Hall (New College, University of Edinburgh)

      Rainy Hall

      New College, University of Edinburgh

      Mound Place Edinburgh EH1 2LX

      Doors open 19.15pm.
      Map: http://www.ed.ac.uk/schools-departments/divinity/map

  • Thursday, 27 June
    • 09:30 → 11:15
      Galaxies, Feedback and the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      Convener: Dr Joseph Hennawi (MPIA)
      • 09:30
        The unchanging circumgalactic medium over the past 11 billion years 40m
        I will review observations of the circumgalactic medium at low and high redshifts based on absorption spectroscopy, and present new resolved velocity maps of the CGM at intermediate redshifts.
        Speaker: Prof. Hsiao-Wen Chen (The University of Chicago)
      • 10:10
        HST COS and STIS observations of gaseous galaxy halos 35m
        The Science Team for the Cosmic Origins Spectrograph (COS) has conducted a modest-sized survey of QSOs near very low-z galaxies to characterize gaseous galaxy halos. We have found that high (~100%) covering factors in Lyα absorption extend at least out to the virial radius for L>0.1L* galaxies. Standard photo-ionization modeling of these absorbers finds cloud sizes of 1—30 kpc, masses of 10^(1-8) solar masses and total filling factors of 3—5%. The total mass in warm photo-ionized clouds approaches 10^10 solar masses, comparable to the mass of galaxy disks. This leaves ~50% of spiral galaxy baryons ``missing’’. Dwarfs (L<0.1L*) have smaller covering factors and cloud masses (<5% baryon fraction). Constant cloud pressures as a function of impact parameter and, in a few cases, broad, shallow Lyα absorption suggests the presence of a hot (T≈10^6 K) gas in spiral groups that could account for the remainder of the missing baryons.
        Speaker: Prof. John Stocke (CASA, U. of Colorado)
        Slides
      • 10:45
        Near-field cosmology results from the Cosmic Origins Spectrograph 30m
        The Cosmic Origins Spectrograph on HST has been in operation for nearly four years and has accumulated a library of ~400 AGN sight lines. Many of these are suitable for probing the low-redshift IGM for HI (Lyα forest) and metal-ion absorbers. The result is an unprecedented view of the local (z<1) IGM several times larger and more sensitive than previous surveys. I will present initial results from the COS IGM absorber survey: correlations between IGM absorbers and galaxies/large-scale structure, the current state of the baryon census, evidence for evolution in the IGM since z=0.5, and work on the physical scales of IGM absorbers.
        Speaker: Dr Charles Danforth (University of Colorado)
    • 11:15 → 11:45
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 11:45 → 12:45
      Galaxies, Feedback and the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 11:45
        Mapping metals in the circumgalactic medium at z~2.5 30m
        I will present observations of the distribution and covering fraction of metal-enriched gas around star-forming galaxies at redshift ~2.5. Using high resolution spectra of background quasars at impact parameters from ~70 to 300 kpc from foreground galaxies, we have measured precise column densities from both cool ~10^4 K and hotter ~10^5 K gas. We compare our results to those for star-forming galaxies at redshifts < 0.5, and to complementary measurements made at z~2.5 using composite, lower resolution spectra of galaxy pairs. Finally we discuss the implications for the extent of the metal-enriched CGM at z~2.5 and for its evolution to the present day.
        Speaker: Dr Neil Crighton (MPIA)
        Slides
      • 12:15
        On the connection between the IGM and galaxies at z < 1 30m
        I will present observational results on the large-scale connection between the Intergalactic medium (IGM) and galaxies at z<1. I will focus on a statistical approach to this problem by measuring the gas-galaxy 2-point cross-correlation, and comparing it with both the galaxy-galaxy and the gas-gas auto-correlations, as a function of different absorber/galaxy properties. These results come from one of the largest samples of HI absorption lines and galaxies in the same volume obtained from deep spectroscopic galaxy surveys (VLT/VIMOS, Gemini/GMOS, Keck/DEIMOS) around QSOs having high resolution UV spectroscopy (HST/COS, HST/FOS). I will also present results from a complementary study on HI absorption systems found within and around galaxy voids at z<0.1.
        Speaker: Mr Nicolas Tejos (Durham University)
        Slides
    • 12:45 → 14:15
      Lunch 1h 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 14:15 → 15:55
      Hydrogen in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 14:15
        New measurements of the galaxy ionizing emissivity in the post-reionization epoch 40m
        Reconciling our current constraints on hydrogen reionization with what we know about high-redshift galaxy populations points to interesting galaxy physics at early times. For example, in order to emit enough ionizing photons to complete reionization by z=6, it appears that faint sources must make a larger than expected contribution to the ionizing budget at z > 6, or else reionization galaxies must have different stellar populations and/or ionizing escape fractions than their lower-redshift counterparts. In this talk I will describe how careful measurements of the physical conditions in the IGM in the post-reionization epoch are providing unique insight into the properties of high-redshift galaxies. Specifically, new measurements of the ionizing UV background over 2 < z < 5 derived from measurements of the temperature and opacity of the IGM, combined with galaxy luminosity functions over the same redshift interval, are delivering new information on whether reionization at z > 6 is consistent with the ionizing emissivity of lower-redshift galaxies, and how the evolution in galaxy properties that enables reionization to occur continues to substantially lower redshifts.
        Speaker: Dr George Becker (University of Cambridge)
        Slides
      • 14:55
        The IGM thermal history down to z ~ 3.5: A new curvature measurement 30m
        The HeII reionization is expected to leave a “footprint” on the thermal history of the IGM: a peak in the temperature evolution at the mean density. So far no clear evidence for this mark has been found and recently it has been suggested that new volumetric heating processes, from blazar emission, could dominate the photo-heating at z<3. These processes would obscure the peak due to the HeII reionization preventing any constraint on this event. We present an extension of the IGM temperature measurements down to the optical limit of the HI Lyα forest at z≃1.5. This is the regime where the different models of thermal histories diverge most strongly. Applying the curvature method, we investigated the thermal history of the IGM at z<3 with precision comparable to the higher redshifts results. We will show the measurements obtained and we will discuss their consistency with the different heating models.
        Speaker: Ms Elisa Boera (Swinburne University)
        Slides
      • 15:25
        Measuring the Jeans scale of the IGM with close quasar pairs 30m
        The small scale structure of the IGM, quantified by the Jeans filtering scale, has fundamental cosmological implications. On the one hand, it provides a thermal record of the heat injected by UV photons during cosmic reionization events, and its value thus constrains the thermal and reionization history of the Universe. On the other hand, it sets the minimum mass scale for gravitational collapse from the IGM, and hence plays a pivotal role in galaxy formation. Unfortunately, it is extremely challenging to measure from the standard technique of analyzing purely longitudinal Lyα forest spectra, because thermal broadening is highly degenerate with the Jeans filtering. However, it can be directly measured by characterizing the coherence of Lyα forest absorption in close quasar pair spectra whose small separations ~ 100 kpc resolve the Jeans scale. We have developed a novel technique to directly measure the Jeans filtering based on analyzing the probability distribution of phase angle differences of homologous Fourier modes in close quasar pair spectra. A Bayesian formalism is introduced based on this new method, which combined with MCMC simulations, allows us to characterize the precision of a hypothetical Jeans scale measurement and explore degeneracies with other parameters governing the temperature density relation of the IGM (T0,gamma). A large grid (500) of thermal models is generated by combining a large dark matter simulation with a semi-analytical model of the Lyα forest. Our full parameter study indicates that a realistic sample of 20 close quasar pair spectra can measure the Jeans scale to 5% precision, fully independent of the temperature-density relation of the IGM. We will provide a progress report on our very recent effort to use this new technique to make the first measurement of the Jeans scale with real quasar pair spectra.
        Speaker: Mr Alberto Rorai (Max Planck Institute for Astronomy - Heidelberg)
        Slides
    • 15:55 → 16:25
      Coffee/Tea Break 30m Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
    • 16:25 → 17:25
      Helium in the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 16:25
        Inhomogeneous He II reionization and the implications for the intergalactic medium 30m
        Recent HeII Lyα forest observations from 2.0 < z < 3.4 show large fluctuations in the optical depth at z > 2.7. These results point to a fluctuating HeII-ionizing background, possibly due to the end of helium reionization. We present a fast, semi-numeric procedure to approximate detailed cosmological simulations. Spanning a large parameter space, we find order-of-magnitude fluctuations in the HeII ionization rate in the post-reionization regime that increase during reionization. As in previous studies, we show that the rarity of quasars and the inhomogeneous intergalactic medium induce order unity fluctuations in the mean HeII Lyα optical depth even after reionization, even when averaged over large segments (~10 − 100 Mpc in length). We then compare to the latest observations, demonstrating that ongoing reionization readily explains the large fluctuations in the Lyα forest transmission, and examine the possibility of using the quasar proximity effect to probe the HeII-ionizing background.
        Speaker: Dr Keri Dixon (University of Sussex)
        Slides
      • 16:55
        The imprint of inhomogeneous HeII reionization on the HI and HeII Lyα forest 30m
        I will present results on the topology of HeII reionization obtained from AMR hydrodynamic simulations of the intergalactic medium post-processed with the radiative transfer code RADAMESH. Ionizing radiation is propagated from a realistic population of active galactic nuclei considering different scenarios for the time evolution of the ionizing sources. During the early phases of the reionization the temperature distribution presents a clear bimodality and cannot be described by a simple effective equation of state. When helium reionization is complete, the IGM is characterized by a polytropic equation of state appreciably flatter than at the onset of the reionization process, with a wider dispersion around the mean value. By extracting synthetic Lyα absorption spectra from the simulations, I will provide evidence that the Doppler b parameters and the curvature statistics of HI absorption spectra contain information about the bimodal temperature distribution of the IGM during the early phases of HeII reionization.
        Speaker: Mr Michele Compostella (Argelander Institute for Astronomy, Bonn)
        Slides
  • Friday, 28 June
    • 09:30 → 10:40
      Galaxies, Feedback and the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      Convener: Prof. Joop Schaye (Leiden Observatory)
      • 09:30
        Cold accretion, hot feedback and the bimodal metallicity distribution in the circumgalactic medium of galaxies at z < 1 40m
        Theoretical studies have raised a number of important questions about the roles of gas inflows (accretion) and outflows (feedback) in galaxy evolution. Unfortunately, galactic gas flows are likely to have low densities and hence are difficult to observe with most techniques. However, QSO absorption lines provide sensitive observational probes of galactic flows, and the recent deployment of the Cosmic Origins Spectrograph on HST has greatly expanded this capability by opening access to QSO absorbers in the low-z Universe (where the absorber-galaxy connections can really be studied in detail). This talk will present results from several large HST+COS programs to study galactic flows and missing baryons, including (1) statistical comparisons of the gaseous halos of star-forming galaxies vs. early-type (red and dead) galaxies (2) unambiguous evidence of massive (and escaping) galactic winds from poststarburst galaxies, (3) observations of cool and pristine (low-metallicity) gas in the halos of high-metallicity star-forming galaxies, and (4) first results on the physical conditions of circumgalactic gases.
        Speaker: Prof. Todd Tripp (University of Massachusetts)
        Slides
      • 10:10
        Metals and gas in the circumgalactic medium of distant galaxies 30m
        Quasar absorption lines offer powerful probes to study the circumgalactic medium and the intergalactic medium. The gas-rich damped Lyα (DLA) and sub-DLA absorbers allow an especially detailed study of metals, gas, and dust in the circum-galactic medium. Most past studies of chemical composition of the absorbers focused on DLAs, rather than sub-DLAs. But recent studies by our team and others have indicated that at redshifts 0.6 < z < 1.5, sub-DLAs may be more metal-rich than DLAs, and may have evolved faster. We will discuss our new Magellan and HST spectroscopic observations of sub-damped Lyα absorbers at z > 2 as well as z < 0.6, and the implications for cosmic chemical evolution models. We will also discuss results obtained from imaging and/or integral field spectroscopy of some DLA/sub-DLAs to investigate the gas kinematics and spatial distribution of metals in the circumgalactic medium in these distant galaxies.
        Speaker: Prof. Varsha Kulkarni (University of South Carolina)
        Slides
    • 10:40 → 11:10
      Coffee/Tea Break 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
    • 11:10 → 12:30
      Galaxies, Feedback and the IGM Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
      • 11:10
        The circumgalactic medium in high resolution, zoom-in simulations: A test of stellar feedback, galactic outflows and cold streams 40m
        I will present results on the kinematics, thermal and ionization state and spatial distribution of metal-enriched gas in the circumgalactic medium (CGM) of galaxies of different mass scales, using two suites of very high resolution cosmological hydrodynamic “zoom-in” simulations from Milky Way-like scales to (“Eris”) down to dwarf galaxies. The runs adopt a blastwave scheme for supernova feedback that produces large-scale galactic outflows, a star formation recipe based on a high gas density threshold, metal-dependent radiative cooling, and a model for the diffusion of metals and thermal energy. The effect of the local UV radiation field is added in post-processing. The star formation and feedback models are able to produce simulated galaxies with various properties consistent with observations. At redshift 2-3, the CGM of Eris contains multiple phases having a wide range of physical conditions, and the synthetic spectra produce interstellar absorption line strengths of Lyα, CII, CIV, SiII, and SiIV as a function of galactocentric impact parameter that are in broad agreement with those observed at high-redshift. The fraction of sightlines within one virial radius that intercept optically thick material is 27%, in agreement with recent observations by Rudie et al. 2012. Such optically thick absorption is shown to trace inflowing "cold" streams that penetrate deep inside the virial radius. The streams, enriched to metallicities above 0.01 solar by previous episodes of star formation in the main host and in nearby dwarfs, give origin to strong CII absorption with a covering factor of 22% within the virial radius. In the simulation of dwarf galaxies, the field dwarfs appear to have very large mass loading factors (several tens to hundred) and eject about 90% of their metals by redshift 0. Metals propagates into the underdense intergalactic medium, reaching ~ 15 times the virial radius of the host, with little of them recycled back onto the halo. I will briefly discuss how the observed CGM properties depend on radiative cooling, mixing of metals and the stellar UV radiation.
        Speaker: Dr Sijing Shen (University of California, Santa Cruz)
        Slides
      • 11:50
        The First Billion Years simulations: galactic outflows and metal enrichment 40m
        Speaker: Dr Claudio Dalla Vecchia (MPE)
        Slides
    • 12:30 → 12:45
      Concluding Remarks Lecture Theatre

      Lecture Theatre

      Royal Observatory, Edinburgh

      Blackford Hill Edinburgh
    • 12:45 → 14:15
      Lunch 1h 30m Stobie Room

      Stobie Room

      Royal Observatory, Edinburgh
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