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The High-Redshift Universe

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The High-Redshift Universe 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 Reionizaon The Epoch of Reionizaon is the period in the Universe’s history when the predominantly neutral hydrogen atoms permeang the intergalac?c medium began to be ionized by the first luminous sources of radiaon – i.e. the first stars, galaxies and quasars (or some combinaon of the above). Understanding exactly when and how reionizaon happened and what sources were responsible is a very ac?ve area of ongoing research. Peak Epoch of Galaxy Formaon Cosmic Dawn Cosmic Noon Cosmic star formaon 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 formaon 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 formaon history Black hole accre?on history Madau & Dickinson (2014) Baryonic Feedback Galaxy luminosity funcon: Number of galaxies as a func?on of luminosity (or equivalently mass) When comparing to theore?cal 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 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 Emihers (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 Emihers 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) Funcon Distant/Dusty Star Forming Galaxies (DSFGs) Damped Lyman Alpha Systems Red and Blue Nuggets Ac.ve Galac.c Nuclei / Quasars / QSOs H-alpha Emihers Extremely Red Objects (EROs) Galaxy Spectral Energy Distribu?ons X-RAY UV OPTICAL IR RADIO Mul?-wavelength observaons 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) • Opcal: more evolved stars and ionized gas, HII regions • IR: re-processed radiaon 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 magnificaon by gravitaonal 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 (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, Nature Detec?on 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 (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- redshis 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 Reionisaon) 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 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 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-ionizaon (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 observaonally: – 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 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 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 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 Distribu?on 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 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 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 Mul?ple, accre?on fuelled by common interac?ng gas supply components ELLIPTICAL: STARBURST: Passive, lihle or Intense star no recent star formaon, dust formaon obscuraon QUASAR: High luminosity Feedback from black hole accre?on onto e.g. Sanders+88; Hopkins+06, 08 shuts off star formaon. 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) populaons e.g.
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