Lyman Break Galaxies Dr Elizabeth Stanway (E.R.Stanway@Bristol.ac.uk) Current Topics Lyman Break Galaxies Dr Elizabeth Stanway (E.R.Stanway@Bristol.ac.uk) Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Topic Summary Star Forming Galaxies and the Lyman- Line Lyman Break Galaxies at z<4 Lyman Break Galaxies at z>4 The Star Formation History of the Universe and Reionisation This course will be assessed through a 1 hour examination including mathematical and essay questions Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Recommended Reading Steidel, Pettini & Hamilton, 1995, AJ, 110, 2519 Carilli & Blain, 2002, ApJ, 569, 605 Verma et al, 2007, MNRAS, 377, 1024 Bouwens et al, 2007, ApJ, 670, 928 Stanway et al, 2008, ApJ, 687, L1 Current Topics: Lyman Break Galaxies - Elizabeth Stanway

A few definitions … In these lectures LBG = Lyman Break Galaxy LAE = Lyman Alpha Emitter HST = Hubble Space Telescope Gyr = 1 Billion Years (Myr = 1 million yrs) z = redshift Z = metallicity z’ or zAB are broadband filters Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The History of High-z studies Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The History of High-z studies Practical limits starting to be important The highest redshift galaxy has been increasing steadily in distance for ~20 yrs Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The History of High-z studies Universe 1Gyr old Universe 1/8 current age Universe 1/4 current age Universe half current age Now: Universe 13.7 Gyr Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The History of High-z studies Z=3 => age about 2 Gyr z=3 LBGs Universe 1/8 current age ~ 2 Billion years after the Big Bang Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Why Push So Far Back? We are now starting to probe the last major phase transition in the universe - reionisation We’re within a few generations of the earliest galaxies forming Unevolved galaxies are simpler - easier to understand - and so help shape theory Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Why Push So Far Back? Lyman break galaxies are star-forming so directly measure how exciting a place the universe is Lyman break galaxies are relatively bright and so easy to study Lyman break galaxies are relatively easy to find Current Topics: Lyman Break Galaxies - Elizabeth Stanway

But Why is it so difficult? Redshift equation: (obs)=em) * (1+z) => Distant galaxies are very RED The night sky is also very red => the sky background is much higher for high-z galaxies Flux Wavelength Current Topics: Lyman Break Galaxies - Elizabeth Stanway

But Why is it so difficult? Distance Modulus equation: m = M - 5 log (dL/10pc) Luminosity Distance equation: dL = (1+z) * c/H0 * At z=1, dL=6634 Mpc At z=3, dL=25840 Mpc At z=5, dL=47590 Mpc => Distant galaxies are very FAINT 44 magnitudes of dimming at z=1 47 magnitudes of dimming at z=3 48 magnitudes of dimming at z=5 Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Depth vs Area? The Luminosity Function (LF) of a galaxy population relates number of objects seen to volume/area observed Most galaxies follow a Schecter (1973) function: N(L) dA  (L/L*)e-(L/L*) dA When L<<L*, this approximates a power law: N(L) dA  LdA => Increasing area of observation leads to increase in galaxy sample BUT: since the power law is steep, increasing the depth usually increase sample size more quickly Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Building a Galaxy Every galaxy is made of stars Lower mass stars live longer More massive stars are more luminous => burn more quickly TMS~10Gyr*(M/M) -2.5 M Blue Red Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Building a Galaxy TMS~10Gyr*(M/M) -2.5 30 Myr TMS~10Gyr*(M/M) -2.5 Old galaxies are dominated by A-M stars and have 4000A breaks Young galaxies are dominated by short-lived O and B stars and are UV-bright 300 Myr 10 Gyr 15 Gyr Blue Red Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Types of Galaxy SED Old/Red Old galaxies are dominated by A-M stars and have 4000Å breaks Young galaxies are dominated by short-lived O and B stars and are UV-bright Younger galaxies also show strong emission lines, powered by star formation. Young/Blue Rest-UV Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Hydrogen Emission Lines Flux from star formation excites electrons in atoms The most abundant atom in the universe is Hydrogen As an electron relaxes from an excited state, it emits a photon Each transition emits at a particular wavelength The easiest transition to excite is Lyman- The Balmer series emerges in the optical and so is known as ‘Hydrogen-’ etc for historical reasons Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Hydrogen Emission Lines OIII The Balmer Series and Oxygen lines dominate the optical spectrum of a star forming galaxy OII H H H H The Lyman series emerges in the ultraviolet. The Lyman- emission line can emit up to 1% of the galaxy’s bolometric flux, but …. Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Hydrogen Emission Lines OIII The Balmer Series and Oxygen lines dominate the optical spectrum of a star forming galaxy OII H H H H The Lyman series emerges in the ultraviolet. The Lyman- emission line can emit up to 1% of the galaxy’s bolometric flux, but …. Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Hydrogen Emission Lines Ly Å OIII OII H H H Ly H The Lyman series emerges in the ultraviolet. The Lyman- emission line can emit up to 1% of the galaxy’s bolometric flux, but …. Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Asymmetric Lyman- Line Low z The Lyman- line is intrinsically symmetric Higher z At high-z the line always appears asymmetric and broadened Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Asymmetric Lyman- Line Star formation drives galaxy-scale winds (Adelberger et al 2003) Lyman- is resonantly scattered by the winds Blue Wing is scattered by outflowing galactic winds Red wing is broadened by back-scattered light Wind v = 0 v = +300 km/s v = -300 km/s Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Asymmetric Lyman- Line v/c = z/(1+z) => 300km/s wind broadens line by about 5Å FWHM at z=3 Blue Wing is scattered by outflowing galactic winds Red wing is broadened by back-scattered light Wind v = 0 v = +300 km/s v = -300 km/s Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest … Lyman-a is also seen in absorption wherever there are clouds of hydrogen Source Observer z=0 z* Ly Åz*) Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest … Lyman-a is also seen in absorption wherever there are clouds of hydrogen Source Observer z=0 z1 z* Ly Å z1) Åz*) Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest … Lyman-a is also seen in absorption wherever there are clouds of hydrogen Source Observer z=0 z4 z3 z2 z1 z* Ly Å z3) Å z1) Åz*) Å z4) Å z2) Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest At low z almost all of a galaxy’s Lyman continuum flux reaches us Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest Above z=3, the fraction of galaxy flux reaching us declines rapidly Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest Beyond z=5.5, <1% of the galaxy’s flux gets through the IGM Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman- Forest Low z Higher z Lyman- Forest Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Dominated by O and B stars Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Dominated by O and B stars Bright in the ultraviolet Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Dominated by O and B stars Bright in the ultraviolet Drive strong galactic winds Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Dominated by O and B stars Bright in the ultraviolet Drive strong galactic winds They have key observable characteristics: Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Dominated by O and B stars Bright in the ultraviolet Drive strong galactic winds They have key observable characteristics: They have asymmetric Lyman- emission lines Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Properties of High-z Galaxies Young galaxies at high-z are: Dominated by O and B stars Bright in the ultraviolet Drive strong galactic winds They have key observable characteristics: They have asymmetric Lyman- emission lines Flux is suppressed shortward of Lyman- Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman Break Technique The Steidel, Pettini & Hamilton (1995) Lyman Break Method At z=3, about 50% of the Lyman continuum is transmitted This leads to a ‘break’ in the spectrum So consider what would happen if you place filters either side of the Lyman- and Lyman limit breaks… Lyman Continuum Ionising Radiation UV Continuum Lyman-α Break 912Å Break Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Lyman Break Technique Red If the filters bracket the breaks, then the galaxies show extreme colours Blue Red Current Topics: Lyman Break Galaxies - Elizabeth Stanway

The Dropout Technique At z>4, the Lyman forest absorption reaches near 100%  only one break is detected A source will be detected in filters above the break but ‘drop-out’ of filters below it V-drops  z > 4.5 R-drops  z > 5. I-drops  z > 5.8 Starburst at z=6 f-2.0 For galaxies at 5.6<z<7.0, i'- z'>1.3 Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Narrow Band Surveys A magnitude is the average flux in a filter Sky Emission A magnitude is the average flux in a filter If half the filter is suppressed by Ly-a forest, the galaxy appears faint Narrow Band Broad Band If an emission line fills the filter, the galaxy will seem bright By comparing flux in a narrow band with flux in a broadband, you can detect objects with strong line emission Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Narrow Band Surveys But what line have you detected? Could be: OIII at 5007A OII at 3727A Lyman- at 1216A Need spectroscopic follow-up Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Lecture Summary (I) Building a sample of high z galaxies gives vital information on the state of the early universe It requires the right balance between depth and area - because the LF is steep, depth is usually preferred Starburst galaxies are UV-bright, dominated by hot, young massive stars They have a rich spectrum of emission lines, dominated by: oxygen and Balmer series lines in the optical Lyman series lines in the ultraviolet Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Lecture Summary (II) Lyman- is characteristically asymmetric due to galaxy-scale outflows Absorption by the intervening IGM suppresses flux shortwards of Lyman- The degree of suppression increases with redshift A few percent at z=1 50% at z=3 More than 99% by z=5.5 This leads to a characteristic spectral break Current Topics: Lyman Break Galaxies - Elizabeth Stanway

Lecture Summary (III) Galaxies at high-z are selected by: Narrow band surveys Selecting for presence of strong emission lines Uses improved background between skylines Prone to contamination Lyman break galaxy surveys Selecting on the presence of a 912A or 1216A break Based on broad-band photometry Current Topics: Lyman Break Galaxies - Elizabeth Stanway