The Intergalactic Medium. & Chemical enrichment. Thomas Nak & Tim Nota

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1 The Intergalactic Medium & Chemical enrichment Thomas Nak & Tim Nota

2 Content Introduction in The IGM Observations using Quasars, Absorption lines & Lyman alpha forest Physical properties of the IGM Reionization of the IGM Chemical enrichment of the IGM

3 Introduction: The IGM Tenuous highly ionized gas consisting primarily of hydrogen and helium Intergalactic clouds are regions not so highly ionized, contain significant amounts of matter. Intergalactic clouds are still too tenuous and highly ionized to give rise to star formation The Intergalactic Medium

4 Observation Tests - searching for neutral hydrogen and helium absorption in the spectra of high-redshift quasars <== - the diffuse X-ray background radiation. - searches for dust reddening of very distant objects.

5 Quasars: Quasi-stellar 0bjects Quasars are Very luminous radio sources, relatively easy to detect at high redshifts ( 16 th magnitude) Emit an excess of ultraviolet light ( blue bumps) Are the most distant visable objects observed Average quasar is 1000 times brighter than the Milky Way An image of 3C 273, one of the first quasars discovered

6 Using Quasars to study the IGM Because quasars are so bright, they can be used are used as background light sources Intervening matter changes spectrum Quasar -Diffuse hydrogen causing decrease of quasar continuum -Intergalactic clouds produce separate absorption lines Result: Absorption pattern leads to physical properties SMALL-SCALE STRUCTURE AT HIGH REDSHIFTINTERSECTING THREE LINES OF SIGHT TO Q Michael Rauch et al

7 Absorption lines Absorption lines found at ultraviolet wavelengths Problem: Earth s atmosphere absorbs ultraviolet wavelengths Doppler effect shifts ultraviolet lines to visible wavelengths Looking at high redshift: Z= (λ obs- λ rest) /(λ rest) Using λ rest = L α, λ obs = 4000Å(violet light) => Z > 2.3

8 Lyman alpha forest Absorption lines in Lα forest mostly come from neutral hydrogen Lα lines Each line corresponds to a different Intergalactic cloud Each line is redshifted by a different proportion Lyman α forest (z<2.523) Lyman Alpha Forest, Encyclopedia of Astronomy & Astrophysics

9 Physical properties of the IGM Limitation: Absorption line studies give only one dimensional information From the absorption line itself - Column density: number of neutral hydrogen atoms per unit area measuring the amount of absorption typical value 10^14 cm -2 - Temperature : Measuring the width of the absorption line Mean value 3 x 10^4 K

10 Physical properties of the IGM Size of intergalactic clouds Using pairs of Lensed quasars & comparing the spectra can restore the missing 2 th dimension The quasar : the first multiply-imaged source discovered Sizes of Mpc From the calculated column density => Mass between 10 7 and 10 8 M solar SMALL-SCALE STRUCTURE AT HIGH REDSHIFT. II. PHYSICAL PROPERTIES OF THE C IV ABSORBING CLOUDS MICHAEL RAUCH et al

11 Physical properties of the IGM At the temperature (3 x 10^4 K) estimated for a typical cloud, self gravity is too week to keep it from dispersing Most absorption systems with column density N > cm -2 also show metal absorption lines

12 Reionization of the IGM Neutral IGM after recombination of hydrogen and helium at z When stars and quasi-stellar objects appear, reionization begins and the IGM temperature rises. Patchy He II reionization and the physical state of the IGM, L. Gleser et al., MNRAS 2005

13 Reionization of the IGM Unclear how the phase of reionization happened. It might not even be a single phase. Ly-α forest observations show most of the hydrogen in the Universe was ionized at z ~ 6. Constraints on the ionization sources of the high-redshift IGM, A. Meiksin, MNRAS 2004

14 Chemical Enrichment Heavy elements (metals) form inside stars. Released in stellar winds or supernova explosions. Practically all stars reside in galaxies. Expectation: zero, or very low, metallicity in the IGM. Metal enrichment of IGM, A. Aguirre et al., APJ 2001

15 Chemical Enrichment Ly-α observations show an IGM metallicity of 1/1000 solar metallicity at z ~ 3. Hot gas in present-day galaxy clusters is enriched to ⅓ ½ solar metallicity. How did all these metals escape their galaxies?

16 Chemical Enrichment Ways for metals to leave their home-galaxy: Dynamical interaction with other galaxies. Supernova-driven winds. Radiation pressure on dust.

17 Dynamical interaction with other galaxies Galaxy mergers. Tidal interactions. Ram-pressure stripping.

18 Supernova-driven winds Galactic-scale winds require: -Multiple supernova explosions. -Overlapping bubbles. Metal-rich gas is blown out of the galaxy.

19 Radiation pressure on dust Photons can deliver their impulse to dust in a galaxy. Outward radiation pressure on a dust grain in a bright galaxy can exceed the gravitational pull, sending the dust grain to a halo or the IGM

20 Summary The intergalactic medium Using quasars to observe the IGM Physical properties of the IGM Reionization of the IGM Chemical enrichment of the IGM