The High-Redshi Universe
Manda Banerji
Royal Society University Research Fellow; Ins tute of Astronomy, 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 galaxy evolu on at lower redshi s.
From the Epoch of Reioniza on and the First Galaxies to the Peak Epoch of Galaxy Forma on Measuring redshi s: spectra
Redshi es mates based on absorp on and emission line features in a galaxy spectrum.
Revolu onized by large surveys such as the Sloan Digital Sky Survey (SDSS)
Redshi , z = (λobs – λrest)/λrest Measuring redshi s: photometry
Redshi s 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 s ll limited to the brightest sources The Epoch of Reioniza on
The Epoch of Reioniza on is the period in the Universe’s history when the predominantly neutral hydrogen atoms permea ng the intergalac c medium began to be ionized by the first luminous sources of radia on – i.e. the first stars, galaxies and quasars (or some combina on of the above).
Understanding exactly when and how reioniza on happened and what sources were responsible is a very ac ve area of ongoing research. Peak Epoch of Galaxy Forma on
Cosmic Dawn
Cosmic Noon
Cosmic star forma on history from Madau & Dickinson (2014) Supermassive Black-Holes in Galaxies
The mass of supermassive black holes at the centres of galaxies correlates with the total stellar mass in galaxies.
Supermassive black-hole accre on ac vity also peaks at redshi s of 1-3 (corresponding to the peak in cosmic star forma on history) – another clue that the growth of galaxies and supermassive black holes is in mately connected Increasing black-hole mass
Increasing stellar mass Magorrian+98, Kormendy & Ho 13 Black-Hole Accre on History
Cosmic star forma on history Black hole accre on history
Madau & Dickinson (2014) Baryonic Feedback
Galaxy luminosity func on: Number of galaxies as a func on of luminosity (or equivalently mass)
When comparing to theore cal models of structure forma on based on cold dark ma er we see a deficit of observed galaxies at bright and faint-end. Silk+13
Baryonic feedback effects from accre ng black holes and supernovae important at the bright and faint-end respec vely 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 Emi ers (LAEs) (Hot) Dust Obscured Galaxies – (DOGs and HotDOGs) Radio Galaxies Distant Red Galaxies (DRGs) Compact Star-Forming Galaxies (cSFGs)
(Ultra)/(Hyper) Luminous Infrared Galaxies Emission Line Galaxies (ELGs) (LIRGs, ULIRGs and HyLIRGs)
Distant/Dusty Star Forming Galaxies (DSFGs) Damped Lyman Alpha Systems Red and Blue Nuggets Ac ve Galac c Nuclei / Quasars / QSOs H-alpha Emi ers Extremely Red Objects (EROs) The Zoo of High Redshi Galaxies
Submillimeter Galaxies (SMGs) Lyman Break Galaxies (LBGs) Spectral Energy BzK Galaxies Distribu on Lyman Alpha Emi ers (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) Func on
Distant/Dusty Star Forming Galaxies (DSFGs) Damped Lyman Alpha Systems Red and Blue Nuggets Ac ve Galac c Nuclei / Quasars / QSOs H-alpha Emi ers Extremely Red Objects (EROs) Galaxy Spectral Energy Distribu ons
X-RAY UV OPTICAL IR RADIO
Mul -wavelength observa ons of galaxies at wavelengths 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 accre ng black holes and binary stars • UV: accre on disk of supermassive black-hole; young hot OB stars and hot gas (T~105 K) • Op cal: more evolved stars and ionized gas, HII regions • IR: re-processed radia on from dust heated by the stars / accre ng black hole • Microwave/Sub-mm: colder dust, dense molecular gas • Radio: synchrotron emission from supernova remnants & ac ve galac c nuclei; neutral atomic gas Galaxy Spectral Energy Distribu ons The Zoo of High-Redshi Galaxies
• Lyman Break Galaxies (LBGs) & Lyman Alpha Emi ers (LAEs) – selected in the rest-frame ultra-violet (young stars) Lyman Break Selec on r-band
i-band
z-band
Dunlop+13 Tradi onally selected as ‘drop-outs’: UV photons blue-ward of the Lyman break are absorbed by the intergalac c medium at high redshi s -> galaxy undetected at these bluer wavelengths Numbers of Lyman Break Galaxies
Bouwens+15 The LBG Luminosity Func on
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 magnifica on by gravita onal lensing e.g. Livermore+17 The Most Distant “Spectroscopic” Galaxy
Based on detec on of the Lyman break in the rest- frame ultra-violet spectrum (redshi ed to observed frame near infra-red) this galaxy is at redshi = 11.1!
Oesch+16 A Different Way to Measure a Redshi
Hashimoto+18, Nature
Detec on of the oxygen [OIII] emission line at a rest-frame wavelength of 88 micron, which is redshi ed into the microwave for this redshi =9.1 galaxy. The Zoo of High-Redshi Galaxies
• Quasars/QSOs – selected in the rest-frame UV (accre ng supermassive black holes) Redshi Records
Credit: Richard McMahon Quasars • Powered by accre on on to the supermassive black holes at the centers of galaxies. • On account of their extraordinary luminosi es, quasars have tradi onally 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 velocity gas Mortlock+11 moving close to the accre ng black hole Quasar 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- redshi s
Credit: Daniel Mortlock The Most Distant Quasars
Just like LBGs, most distant quasars iden fied 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 Reionisa on) have now been spectroscopically confirmed – many of these coming in the last ~5 years – advent of very large area but sensi ve sky surveys where we can find many distant quasars (e.g. Banados+16, 18, Venemans+15,17, Reed+15,17) Quasar The Intergalac c To Earth Medium
Hydrogen absorp on due to galaxy Emission lines from the Quasar Heavy element absorp on
DLA
Lyman limit
Quasars act as “torchlights” in illumina ng the distant Universe. Every absorp on line results from light from the quasar passing through a cloud of neutral hydrogen. Presence of these absorp on features in high-z quasar spectra (Gunn-Peterson trough) provided some of the first direct evidence for re-ioniza on (e.g. Becker+01). Quasar Host Galaxies
• Quasars outshine their host galaxies by several orders of magnitude making it extremely difficult to study the host galaxies observa onally:
– Use high-resolu on imaging from space (e.g. with the Hubble Space Telescope) to separate out the quasar light (unresolved) from the extended host galaxy emission - e.g. Mechtley+16 – it’s s ll difficult!
– Exploit dust obscura on 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 moun ng that many of the distant, luminous quasars in the high-redshi Universe o en have gas-rich, dusty companions when we look at them in the far infrared to millimeter wavelengths.
Companions o en not detected at shorter (UV) wavelengths -> heavily obscured by dust which preferen ally a enuates 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 Distribu on
à
Increasing redshi à More star forma on
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 iden fied by the South Pole Telescope was revealed by higher resolu on data to be a structure of 14 dis nct 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 forma on – most of the growth happening is obscured by dust The Link Between DSFGs & Quasars
Dusty starbursts (DSFGs) formed via major mergers
MERGER: Star forma on / black hole Mul ple, accre on fuelled by common interac ng gas supply components ELLIPTICAL: STARBURST: Passive, li le or Intense star no recent star forma on, dust forma on obscura on QUASAR: High luminosity Feedback from black hole accre on onto e.g. Sanders+88; Hopkins+06, 08 shuts off star forma on. black hole Evidence for Mergers?
Large propor on of high-redshi DSFGs show Range of morphological types in DSFGs evidence for disturbed morphologies and similar to other less massive galaxy interac ons (Kartaltepe+12) popula ons e.g. LBGs (Swinbank+10)
No clear consensus. “Merger-ness” is a difficult quan ty to measure and prone to lots of observa onal biases e.g. due to dust obscura on, wavelength at which you are measuring morphology and the presence of an accre ng 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 ou lows (Maiolino+12) ubiquitous (Decarli+18)
No clear consensus. “Feedback” is a difficult thing to measure and prone to lots of observa onal biases e.g. due to dust obscura on, wavelength of measurement etc. The Future
• Astronomy is the most data-rich it has ever been – deluge of imaging data from sensi ve digital cameras mounted on some of the world’s largest telescopes
• New wide-field imaging surveys from the ground opening up discovery space to find the brightest high-redshi galaxies and quasars
• Space-based observa ons pushing the fron ers to find the first galaxies at redshi s > 9
• Mul -wavelength follow-up facili es allowing us to build a more complete picture of the spectral energy distribu ons of high-z galaxies. Taxonomy à Evolu on
• Mapping different components – stars, gas, dust, metals, ou lows – within galaxies to understand the physical condi ons within them The Large Synop c Survey Telescope
Large Synop c Survey Telescope
• 3200 Megapixel camera • 8.4m diameter primary mirror • Scanning the sky over 10 years star ng 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 Space Telescope
6.5m diameter mirror in space – almost 3 mes the size of the Hubble Space Telescope!
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 condi ons e.g. star forma on histories, metallici es, ioniza on 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 opera ng as one • Variable “zoom” depending on distance 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 Euclid
The Square Kilometer Array
An exci ng me to be star ng a PhD in Astronomy!