Lecture 21; Nov 08, 2017

High-Redshift Galaxies II- Populations: Galaxy Exotica- Gravitational Lensing- Galaxy Evolution

Reading: Chapter 9 of textbook

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Massive, Active Galaxies at Very High RedshiftDo Massive Galaxies, Supermassive Black Holes, Metals exist very early on?

• SZ effect: no massive (few times 1013 Msun) galaxy clusters at z>1.5 or soÞ density contrasts not high enough yet, cosmic structure formation not

sufficiently “mature” 9-10 billion years ago

Þ At some earlier epochs, halos massive enough to form massive galaxies/ billion solar mass black holes should disappear. How and when?

• Expectations from hierarchical growth: massive galaxies that do exist early on should grow in the highest-density peaks/over-dense regions or even proto-clusters of galaxies. Evidence?

• Also, at some early point timescales become short to have formed significant amounts of metals. The first stars (Pop III) are metal-free, and have to pollute their environments to allow dust, CO etc. to form.

• The most massive halos may be enriched early on. Evidence?

Riechers et al. 2013b, Nature

A dusty massive starburst galaxy found at z=6.34 !!

Detect7 CO lines7 H2O linesH2O+

NH3 (absorption)OHOH+ (absorption)[CI][CII]Hints of others…Þ Highly enriched

Gray line is best existing spectrum of nearby starburstObserved 880 million years after the Big Bang (current age: 13.8 billion yrs)

Lines are associated with gas in star-forming regions

Big Bang today

HFLS3

Riechers et al. 2013b

- Almost as much M* as the Milky Way- Similar total mass, already at z=6.3440x more gas, 2000x higher SFR than MW

~20x higher SFR than extreme nearby starbursts

=> massive galaxies exist at z>6=> already chemically enriched,

>1 billion Msun of dust=> rapid enrichment

at early epochs

• compact(~3.5kpc),highvelocitydispersiongasreservoir:highSFRdrivenbyamajormerger

• RARE:HUDF:~10z~6LBGsperarcmin2Dustystarbursts:oneatz~6knownacrossentiresky!

ALMAHerschel/SPIRE

- idea: z>3.5 galaxy spectral energy distributions peak beyond 500 µmÞ “red” to Herschel telescope, use to ID starbursts at the earliest epochsÞ similar to optical color/dropout techniques, only possible since Herschel

wavelength

250350

500 µm

Flux

den

sity

Spectral Energy Distribution

M100

Cre

dits

: X-

ray:

NASA

/CXC

/SAO

/D.P

atna

ude

et a

l, O

ptic

al: ES

O/V

LT, I

nfra

red:

NASA

/JPL/

Cal

tech

Enrichment of “Typical” Very High z Galaxies?

Untilrecently:nodustorISMdetectionin“normal”galaxybeyondz=3.2(Magdis etal.2012)

ALMAtotherescue:Detectionof[CII]158µmcoolinglineinz=5.3Lyman-breakgalaxy- SFRUV =22Msun/yr – “typical”atz~5(wouldbelowamongclassicalz~3LBGs)- SEDshowslittleevidenceforoldstellarpopulationsorlargequantitiesofdustÞ Even“normal”galaxiesatz>5(1.1billionyearsaftertheBigBang)aresignificantlyenriched

…but:perhapslessthanLBGsatz~3Þ Needtoquantifytheevolution ofmetallicity throughcosmictime Riechers et al. 2014b

§AzTEC-3: Most Distant Massive Starburst Galaxy 2010-13 (1.1 billion years after Big Bang)

Mgas = 5.3 x 1010 (aco/0.8) Msun ~55% Mtotal (20x Milky Way)SFR: ~1100 Msun/yr … or >3 Msun/day (Milky Way: ~2 Msun/yr)

§ Most Distant Galaxy Proto-Cluster:11 star-forming galaxy companions within r~2 Mpc (>10x cosmic average at epoch)

Þ Massive galaxies do appear to grow rapidly in massive halos/density peaks at early epochs

2x2 arcmin2

Riechers, Capak et al. 2010, ApJCapak, Riechers et al. 2011, Nature

Molecular Gas

COSMOS/AzTEC-3 (z=5.3)

ULAS J1120+0641Most distant quasar known; z=7.0852 x 109 Msun SMBHÞ Would be among most massive TODAY!

RARE: Only z>7 quasar in 7500 deg2 survey…Þ Need LSST+WFIRST for more?

Early SMBHs: Discovery of a Quasar at z>7

Mortlock et al. 2011

J0840+5624 (z=5.84) J0927+2001 (z=5.77) J1044-0125 (z=5.78)

J1048+4637 (z=6.23) J1148+5251 (z=6.42) J1319+0950 (z=6.13)

J0129-0035 (z=5.78)

J1335+3533 (z=5.90)

J1425+3254 (z=5.89) J2054-0005 (z=6.04)J1429+5447 (z=6.18)

Walter et al. 2003, 2004, Carilli et al. 2007Riechers et al. 2009a, Wang et al. 2010, 2011, 2013

J2310+1855 (z=6.00)

� z>6 QSOs have massive, heavily enriched host galaxies� co-eval formation of SMBHs & hosts at tuniv < 1 Gyr

PdBI 6x15m interferometer

z>6 quasars:

- MBH > 109 Msun

- 1/3: LFIR > 1013 LsunÞ SFR > 1000 Msun/yr

FIR-luminous quasars:- 12/12 detect. in CO- Mgas > 1010 Msun

Wang et al. 2013

• [CII] luminosity of a few 109 Lsun, from the optically most luminous and faint z~6 quasars

• Gas mass fraction: fgas ~ 60%

• [CII] size: ~3.5kpc at z=6: intense star formation over relatively compact regions

Þ z~6 AGN hosts are massive and highly enriched; this also requires massive halos

Þ know only one z~6 dusty massive starburst, but know ~80 z~6 quasars today (1/3 dusty)

Þ still a rare population, but not “singular” – but steep drop towards z~7 (1 quasar known)

+200 km/s

-200 km/s

Discovered via burst of gamma rays (GRB) detected by SWIFT satellite

• GRBs appear associated with star-forming galaxies

• GRBs are believed associated with extraordinary explosions of stars: hypernovae

Þ Where is the hosting galaxy?

GRB090423: an Explosion at z=8.2

Tanvir et al. 2009

(Lack of) GRB host galaxy at z=8.2

Millimeter afterglow/dust in GRB host?

- Riechers et al. 2009 (IRAM 30m):S(250GHz) < 0.96 mJy (3s)[z=6.34 dusty galaxy: 14 mJy]

- Walter et al. 2012 (IRAM PdBI)S(205GHz) <0.22 mJy (3s)

- Berger et al. 2014 (ALMA)S(222GHz) <0.033 mJy (3s)

Þ LIR < 3x1010 Lsun SFRIR <5 Msun/yrÞ UV/optical (HST) SFRUV <1Msun/yrÞ optical/IR (Spitzer): M* <5x107 Msun

Þ very low-mass host galaxy?Þ or “individual” very massive stellar

explosion without a host galaxy?

ULIRG (LIR =1012 Lsun)

Gravitational Lensing

Strong GL as a tool for galaxy evolution:- Randomly probes the same galaxy populations we know- Magnifies sizes and fluxes (conserves surface brightness)Þ Can observe distant galaxies at higher spatial resolutionÞ Can detect faint galaxies much more easily (HFF fields)

Also: sensitive probe of dark matter halos of foreground sources(total galaxy/cluster+halo mass, halo substructure and shape)In galaxy clusters, weak lensing is a powerful statistical probe

lens selections: - radio surveys- optical morphologies- submillimeter fluxes

Gravitational Lensing: Radio Surveys

Predicted by Einstein in 1936, strong GL was first detected in 1979 (z=1.4 QSO SBS 0957+561)- Radio observations played an important role in confirming that this was indeed lensing

- 1990-99: Jodrell Bank VLA Astrometric Survey (JVAS) & Cosmic Lens All-Sky Survey (CLASS)high-resolution radio imaging (VLA/MERLIN/VLBI) of >16000 flat-spectrum radio sources

Þ Identified 22 multiply-imaged gravitationally-lensed radio AGN at high redshiftÞ Many are lensed type-1 quasars, some are type-2 AGNÞ Clear breakthrough, but limited success rateÞ To date (2017), a fair number of the optically-faint sources do not have redshifts…

Gravitational Lensing: Optical Surveys

- Late 1990s/early 2000s: rigorous high-resolution HST follow-up of radio lenses and optically-IDed quasars (e.g., CfA-Arizona Space Telescope LEns Survey; CASTLES) revealed ~100 lenses and ~20 quasar pairs. More recently, ground-based adaptive optics (e.g., Keck/NIRC2).

- a handsome sample, but still biased toward AGN

- Lensed galaxies: serendipitous discoveries (they are much more common), searches, e.g., in SDSS (seeing-limited, so biased towards larger separations, and shallow), and targeted galaxy cluster surveys have today revealed 100s of lensed galaxies that are not quasars/radio AGN

Also (since 2014) Lensed SN in Galaxies

Dec 2010-Mar 2011

10-20 Nov 2014

difference

Sp1149 lensed galaxy imagesNov 3-20, 2014: SN in spiral arm of z=1.491 galaxy lensed by Hubble Frontier Field galaxy cluster

Rare lensing configuration where entire galaxy is stretched widely (magnified by a factor of 72)

Galaxy is quadruply lensed by cluster, SN is quadruply lensed (~30x) by intervening early-type galaxy in cluster

Kelly et al. 2014 (submitted Nov 21)

Days since Nov 3, 2014

Observed Counts500µm

Wardlow ea. 2013

Until ~2010, the largest submm surveys were 10s to maybe 100 arcmin2 on the sky(limited detector sizes, challenging atmosphere)

Large-area (>100-1000deg2) Herschel/SPIRE 250/350/500µm surveys since 2010 have found an extended bright tail in the submm counts, too rare to be seen previously (also: SPT 1.4mm)

Most are nearby star-forming galaxies (SDSS) or radio blazars sloping down (e.g., 20cm FIRST)

The remaining, very rare sources (<1deg-2) look like optically faint dusty sources at high z (=SMGs?)

Problem: SMGs are already very luminous, up to LFIR >1013 Lsun and “maximum starbursts”, and the likely progenitors of most massive galaxies today

Þ More far-IR-luminous galaxies should not exist…Oliver ea. 2012

HerMES 7deg2 FLS field250 350 500 µm

SPIRE surveys:

HerMES110 deg2

HeLMS270 deg2

HeRS70 deg2

H-ATLAS550 deg2

Þ very submm-bright starbursts, but never studied in detail before- completely new way of finding lenses, just requires a flux limit (i.e., no morph. bias)- past identifications of SMG redshifts, imaging etc. very slow due to sensitivity

Þ a factor10 in lensing saves a factor of 100 in observing time: ALMA science on a budget

These are (dominantly) strongly lensed SMGs:

• high redshift � high efficiency for lensing• steep counts � strong magnification biasBlain 1996; Negrello et al. 2007, 2010

Observed Counts500µm

Wardlow ea. 2013

Introduce extended bright tail to counts,But: rare -- <1deg-2 on the sky(intrinsic population: 0.05 arcmin-2

& need alignment with massive foreground galaxy)

Þ Large-area (>100-1000deg2) Herschel/SPIRE 250/350/500µm surveys ideal to find new population of rare, strongly lensed SMGs

Riechers ea. 2008

The High-Redshift “Galaxy Zoo”

e.g., Franx et al. 2003, Daddi et al. 2004, Reddy et al. 2006, Papovich et al. 2006, Chapman et al. 2004, Grazian et al. 2007, Dey et al. 2008

6

Source Counts & Galaxy Evolution

In a homogenous, Euclidean universe in which there is no evolution and the LF is constant, we expect the number of sources to increase as N(> S) µ S-3/2

This is not what is observed Þ evolving universe

(and LF)

• The counts clearly lie ABOVE the no-evolution model

Galaxies do evolve!

Source Counts: Proxy for Luminosity Function

Evolution in counts of LBGs observed, what is physical cause of evolution?

- primary evolution is a shift in mag M* (0.7 mag in 0.7 Gyr over 4<z<6)

- change in shape of LF less secure (but a=-1.7 is very steep)

- evolution can be explained by models driven by halo mergers

z = 4,5,6,7

Stark, Loeb & Ellis 2007, Bouwens et al. 2007

For similarly-luminous LBGs, those at z~5 are younger and less massive than at z~3

Þ Witnessing stellar mass buildup with cosmic time

Verma et al. (2007)

Stellar Masses & Ages: Comparing z~5 & z~3 LBGsz~5

z~5z~3 z~3

Star formation history of the universeThe Madau-Lilly Plot describes the SFR of the Universe within a comovingvolume element as a function of redshift. Madau et al. 1996, MNRAS, 283, 1388.

Note that heavy element production tracks the star formation rate Steidel et al. 1999, ApJ, 519, 1

Star formation rate density

• The rate of star formation in galaxies was much higher in the past than it is today. (30-100 times)

• About half the stellar mass in the universe today were built up at z=1-3(“epoch of galaxy assembly”)

• The SFR density then declines towards very high z

Main Issues in Assembling the Cosmic Star Formation History

• Different redshifts: different technique for finding galaxies and different SFR estimates

• Correction for dust extinction

• Which fraction of <SFR> comes from faint but numerous galaxies (extrapolating the LF)?– Count the effect of the UV photons

on the IGM (next week)

reionization

today�suniverse

quasar/galaxybuild-up

�dark ages�

cosmic star formationhistory of the universe

big bangrecombination

z~6-150.3-1 Gyr

z~15-10000.0003-0.3 Gyr

z<~6>1 Gyr

z~013.8 Gyr

z~10000.0003 Gyr

?

First galaxies

“Epoch of galaxy assembly”

Present day

Volume density of star formation in galaxies as f(cosmic time)

Stellar LightStars+Dust

Star Formation in Galaxies at High Redshift:

- A few billion years ago, galaxies in the universe formed ~30x more stars than today (making up the stars we see now)

- The most intensely starbursts at high z form 10-30x more stars than the most extreme examples today

sites of star formation enshrouded by dust, absorbing a fraction of the stellar light (which is re-radiated in the rest-frame far-infrared)

Bouwens

et al. 2011

How important is this in general?~50% of starlight from galaxies in the Universe received at Earth is absorbed by dustSome (very distant) dusty galaxies are not seen in deep Hubble images at allÞ To understand the cosmic history of star formation in galaxies, dust is important

Cosmic Infrared Background

• COBE detected a cosmic IR background (CIB) in 1996, suggesting the existence of a population of dusty galaxies at high redshift.

• Multiple groups have used SCUBA/MAMBO (850µm/1.2mm) to search for the sources making up this background.

• But they cannot be resolved easily (need higher resolution)

Blain et al. 2002, PhRep, 369, 111

Lagache et al. 2005 ARA&A

Dole et al. 2006, A&A, 451, 417

CIB vs. Galaxy SED

Lyman limitUV lightyoung, hot stars

Stellar bumpold stars

Dust bumpre-processed stellar light

Stellar light deficiencyabsorbed by dust

COB/CIB: Integrated over all galaxies

Lagache et al. 2005 ARA&A

Highly star-forming galaxies:

- Brighter- Lower

Optical/IR ratio

ÞDustier

Þ Important for CIB

Passive red galaxies:

- Fainter

- Higher Optical/IR ratio

?

First galaxies

“Epoch of galaxy assembly”

Present day

CIB vs. Star Formation HistoryThe dust-obscured fraction of star formation in the universe is significant!UV/optical studies miss substantial fraction of cosmic star formationÞNew phenomenon: distant, very IR-luminous (observed-frame submm) galaxies

The (sub)mm is a key wavelength regime to understand galaxy evolution!