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The High-Redshift Universe

The High-Redshift Universe

The High-Redshi

Manda Banerji

Royal Society University Research Fellow; Instute of , University of Cambridge The History of the Universe

This talk will cover the redshi range, z ~2-11 (i.e. when the Universe was between 0.5 billion to 3 billion years old). See Vivienne Wild’s talk for evoluon at lower redshis.

From the Epoch of Reionizaon and the First to the Peak Epoch of Galaxy Formaon Measuring redshis: spectra

Redshi esmates based on absorpon and emission line features in a galaxy spectrum.

Revoluonized by large surveys such as the (SDSS)

Redshi, z = (λobs – λrest)/λrest Measuring redshis:

Redshis based on colours of galaxies in a set of broad-band filters.

Considerably cheaper and faster to obtain these measurements compared to galaxy spectra

More common in the high- redshi Universe where spectroscopic samples are sll limited to the brightest sources The Epoch of Reionizaon

The Epoch of Reionizaon is the period in the Universe’s history when the predominantly neutral permeang the intergalacc medium began to be ionized by the first luminous sources of radiaon – i.e. the first , galaxies and (or some combinaon of the above).

Understanding exactly when and how reionizaon happened and what sources were responsible is a very acve area of ongoing research. Peak Epoch of Galaxy Formaon

Cosmic Dawn

Cosmic Noon

Cosmic formaon history from Madau & Dickinson (2014) Supermassive Black-Holes in Galaxies

The of supermassive black holes at the centres of galaxies correlates with the total stellar mass in galaxies.

Supermassive black-hole accreon acvity also peaks at redshis of 1-3 (corresponding to the peak in cosmic star formaon history) – another clue that the growth of galaxies and supermassive black holes is inmately connected Increasing black-hole mass

Increasing stellar mass Magorrian+98, Kormendy & Ho 13 Black-Hole Accreon History

Cosmic star formaon history accreon history

Madau & Dickinson (2014) Baryonic Feedback

Galaxy funcon: Number of galaxies as a funcon of luminosity (or equivalently mass)

When comparing to theorecal models of structure formaon based on cold dark maer we see a deficit of observed galaxies at bright and faint-end. Silk+13

Baryonic feedback effects from accreng black holes and supernovae important at the bright and faint-end respecvely in order to quench the growth of galaxies.

Galaxy Morphologies at Low-z

Only around 10% of local galaxies do not fall into these types and are “peculiar/irregular” The Zoo of High Redshi Galaxies

Submillimeter Galaxies (SMGs) Lyman Break Galaxies (LBGs) BzK Galaxies Lyman Alpha Emiers (LAEs) (Hot) Dust Obscured Galaxies – (DOGs and HotDOGs) Radio Galaxies Distant Galaxies (DRGs) Compact Star-Forming Galaxies (cSFGs)

(Ultra)/(Hyper) Luminous Galaxies Emission Line Galaxies (ELGs) (LIRGs, ULIRGs and HyLIRGs)

Distant/Dusty Star Forming Galaxies (DSFGs) Damped Lyman Alpha Systems Red and Nuggets Acve Galacc Nuclei / Quasars / QSOs H-alpha Emiers Extremely Red Objects (EROs) The Zoo of High Redshi Galaxies

Submillimeter Galaxies (SMGs) Lyman Break Galaxies (LBGs) Spectral BzK Galaxies Distribuon Lyman Alpha Emiers (LAEs) (Hot) Dust Obscured Galaxies – (DOGs and HotDOGs) Radio Galaxies Distant Red Galaxies (DRGs) Compact Star-Forming Galaxies (cSFGs) Luminosity (Ultra)/(Hyper) Luminous Infrared Galaxies Emission Line Galaxies (ELGs) (LIRGs, ULIRGs and HyLIRGs) Funcon

Distant/Dusty Star Forming Galaxies (DSFGs) Damped Lyman Alpha Systems Red and Blue Nuggets Acve Galacc Nuclei / Quasars / QSOs H-alpha Emiers Extremely Red Objects (EROs) Galaxy Spectral Energy Distribuons

X-RAY UV OPTICAL IR RADIO

Mul- observaons of galaxies at all the way from the X-ray to the radio allow us to trace emission from different physical processes in galaxies e.g.

• X-ray: high-energy sources such as accreng black holes and binary stars • UV: accreon disk of supermassive black-hole; young hot OB stars and hot gas (T~105 K) • Opcal: more evolved stars and ionized gas, HII regions • IR: re-processed radiaon from dust heated by the stars / accreng black hole • Microwave/Sub-mm: colder dust, dense molecular gas • Radio: synchrotron emission from remnants & acve galacc nuclei; neutral atomic gas Galaxy Spectral Energy Distribuons The Zoo of High-Redshi Galaxies

• Lyman Break Galaxies (LBGs) & Lyman Alpha Emiers (LAEs) – selected in the rest-frame ultra-violet (young stars) Lyman Break Selecon r-band

i-band

z-band

Dunlop+13 Tradionally selected as ‘drop-outs’: UV photons blue-ward of the Lyman break are absorbed by the intergalacc medium at high redshis -> galaxy undetected at these bluer wavelengths Numbers of Lyman Break Galaxies

Bouwens+15 The LBG Luminosity Funcon

Faint galaxies dominate the counts – these faint galaxies are widely thought to be responsible for reionizing the Universe

Can push even fainter by taking Bouwens+15 advantage of magnificaon by gravitaonal lensing e.g. Livermore+17 The Most Distant “Spectroscopic” Galaxy

Based on detecon of the Lyman break in the rest- frame ultra-violet spectrum (redshied to observed frame near infra-red) this galaxy is at redshi = 11.1!

Oesch+16 A Different Way to Measure a Redshi

Hashimoto+18,

Detecon of the oxygen [OIII] emission line at a rest-frame wavelength of 88 micron, which is redshied into the microwave for this redshi =9.1 galaxy. The Zoo of High-Redshi Galaxies

• Quasars/QSOs – selected in the rest-frame UV (accreng supermassive black holes) Redshi Records

Credit: Richard McMahon Quasars • Powered by accreon on to the supermassive black holes at the centers of galaxies. • On account of their extraordinary luminosies, quasars have tradionally been among the most distant sources known – only recently overtaken by galaxies. • More than half a million quasars now spectroscopically confirmed extending out to the very distant Universe. Distant quasars look remarkably similar to nearby ones.

Broad emission lines originate from high gas Mortlock+11 moving close to the accreng black hole versus LBG Spectrum

Quasars are considerably more luminous compared to the more numerous Lyman Break Galaxies.

Much easier to get high- quality spectra out to high- redshis

Credit: Daniel Mortlock The Most Distant Quasars

Just like LBGs, most distant quasars idenfied as ``drop-outs” in bluer wavebands. But now need to search over >1000 square degrees of sky rather than <1 sq-deg – quasars are rare!

More than 100 redshi > 6 quasars (i.e. in the Epoch of Reionisaon) have now been spectroscopically confirmed – many of these coming in the last ~5 years – advent of very large area but sensive sky surveys where we can find many distant quasars (e.g. Banados+16, 18, Venemans+15,17, Reed+15,17) Quasar The Intergalacc To Earth Medium

Hydrogen absorpon due to galaxy Emission lines from the Quasar Heavy element absorpon

DLA

Lyman limit

Quasars act as “torchlights” in illuminang the distant Universe. Every absorpon line results from from the quasar passing through a cloud of neutral hydrogen. Presence of these absorpon features in high-z quasar spectra (Gunn-Peterson trough) provided some of the first direct evidence for re-ionizaon (e.g. Becker+01). Quasar Host Galaxies

• Quasars outshine their host galaxies by several orders of making it extremely difficult to study the host galaxies observaonally:

– Use high-resoluon imaging from space (e.g. with the Hubble Space ) to separate out the quasar light (unresolved) from the extended host galaxy emission - e.g. Mechtley+16 – it’s sll difficult!

– Exploit dust obscuraon towards the quasar to make the host galaxy visible - e.g. Wethers, Banerji+18

– Go to long wavelengths (FIR/mm) where emission from gas and dust from a host galaxy dominates over the quasar light (e.g. Carilli & Walter 2013) Quasars in Mergers Banerji+18

Companion

Quasar Decarli+17, Nature

Evidence is mounng that many of the distant, luminous quasars in the high-redshi Universe oen have gas-rich, dusty companions when we look at them in the far infrared to millimeter wavelengths.

Companions oen not detected at shorter (UV) wavelengths -> heavily obscured by dust which preferenally aenuates bluer light The Zoo of High-Redshi Galaxies

• Submillimeter Galaxies (SMGs) & Distant Star Forming Galaxies (DSFGs) – selected in the far infrared to millimeter (dust emission) DSFGs: Spectral Energy Distribuon

à

Increasing redshi à More star formaon

Colder dust (Wien’s Law) à

Casey+14 Progenitors of today’s most massive structures

This very luminous DSFG at a redshi of 4.3 idenfied by the was revealed by higher resoluon data to be a structure of 14 disnct galaxies all at the same redshi (Miller+18, Nature)

Total SFR is ~6000 M0/yr – a very early example of a massive structure seen in the process of formaon – most of the growth happening is obscured by dust The Link Between DSFGs & Quasars

Dusty starbursts (DSFGs) formed via major mergers

MERGER: Star formaon / black hole Mulple, accreon fuelled by common interacng gas supply components ELLIPTICAL: STARBURST: Passive, lile or Intense star no recent star formaon, dust formaon obscuraon QUASAR: High luminosity Feedback from black hole accreon onto e.g. Sanders+88; Hopkins+06, 08 shuts off star formaon. black hole Evidence for Mergers?

Large proporon of high-redshi DSFGs show Range of morphological types in DSFGs evidence for disturbed morphologies and similar to other less massive galaxy interacons (Kartaltepe+12) populaons e.g. LBGs (Swinbank+10)

No clear consensus. “Merger-ness” is a difficult quanty to measure and prone to lots of observaonal biases e.g. due to dust obscuraon, wavelength at which you are measuring morphology and the presence of an accreng black-hole (AGN) which can hide merger features. Evidence for Feedback?

Redshi Stack of 23 6.42 quasar quasars

Broad, high-velocity wings in gas emission in high-z quasars suggest But extending to larger samples suggests these broad wings are not the presence of significant quasar- driven oulows (Maiolino+12) ubiquitous (Decarli+18)

No clear consensus. “Feedback” is a difficult thing to measure and prone to lots of observaonal biases e.g. due to dust obscuraon, wavelength of measurement etc. The Future

• Astronomy is the most data-rich it has ever been – deluge of imaging data from sensive digital cameras mounted on some of the world’s largest

• New wide-field imaging surveys from the ground opening up discovery space to find the brightest high-redshi galaxies and quasars

• Space-based observaons pushing the froners to find the first galaxies at redshis > 9

• Mul-wavelength follow-up facilies allowing us to build a more complete picture of the spectral energy distribuons of high-z galaxies. Taxonomy à Evoluon

• Mapping different components – stars, gas, dust, metals, oulows – within galaxies to understand the physical condions within them The Large Synopc Survey Telescope

Large Synopc Survey Telescope

• 3200 Megapixel camera • 8.4m diameter primary mirror • Scanning the sky over 10 years starng in 2020-2021 • Will detect 37 billion stars and galaxies • And millions of new quasars including hundreds at redshi > 7 (if they exist!) The James Webb

6.5m diameter mirror in space – almost 3 mes the size of the !

Unparalleled coverage at infrared wavelengths unimpeded by the Earth’s atmosphere

James Webb Space Telescope

The high-quality spectra from JWST for the most distant galaxies will allow us (for the first me) to truly understand the physical condions e.g. star formaon histories, metallicies, ionizaon field strengths in the first galaxies to have formed in the Universe. The Atacama Large Millimeter Array

Atacama Large Millimeter Array

• 66 12-m diameter telescopes operang as one • Variable “zoom” depending on between antennae - 150m to 16km! • Is already enabling us to understand the cool dust and gas content in the most distant galaxies And lots more… The Extremely Large Telescope

The Square Kilometer Array

An excing me to be starng a PhD in Astronomy!

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