Galaxy Formation
Probed with Lyα
Imaging with aNarrowband Filter
Satoshi Kikuta (Center for Computational Sciences)
Collaborators: Yuichi Matsuda, Renyue Cen, et al.
15 June 2020
TCHoU members meeting
202006151

Galaxy Formation
Galaxies are formed within the cosmic web, a networkof dark matter & baryons
Gas accretion along the cosmic web
governs galaxy evolution- “cold mode accretion” scenario

Intergalactic
Medium=IGM“cold streams”

Dekel+09
Introduction

Dark Matter
20200615

Gas2

Feedback Mechanisms
Massive stars, supernovae, and AGNs (active supermassive black holes) inject energy back into ISM/CGM
These feedback mechanisms are the cause of lower SFE
in lower/higher mass halos

w/ feedback

w/o feedback

Hopkins+12

Introduction

Silk+12202006153

Role of Environment
Galaxy properties depend on their environments
Observations of protoclusters hold the key- At z>2, the local relation reverses- Enhanced inflow and merger rate should be related

SpiralS0merger

Elliptical
Alexander & Hickox 2012

Introduction

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4

Cappellari et al. 2011

To/ In thec(IG terg osmM) ala ic
cti wecm b→edium

Circumgalactic/Intergalactic Medium(CGM/IGM)©Tumlinson, Peeples, and Werk,“The Circumgalactic Medium”, ARAA, 2017

Introduction

20200615※No clear demarcation
between CGM and IGM
5

Background QSO spectra✓sensitive to low NHI gas
× one dimensional
sparse background sources...

“Down the barrel” spectra✓trace inflow/outflow...

Emission line maps

✓morphology information
× emissions very faint...
★Narrow-band technique©Tumlinson, Peeples, andWerk, ARAA, 2017

Introduction

Ouchi+03

20200615

Lyman alpha blobs
6or LABs Matsuda+11Lyα Halos around SF Galaxies
Diffuse Lyα halo is ubiquitous
if we go as deep as<<10-18erg/s/cm2/arcsec2
UV

Lyαα

LAH dependence on environments may
Stacked UV(left) and Lyα(right)
cause environmental segregation

image of LBG @ z=2.65 (Steidel+11)

Matsuda+12:
LAEs in denser environments have more
extended LAHs
vs.
Xue+16:
No such dependence →Introduction

20200615

7Extreme Cases●●

Lyα blobs (LABs)– Mostly found in dense environments

Typical extent:> 100 kpc !!

QSO nebulaeMatsuda+11– Bright QSOs at z~3 almost always have associated Lyα nebulae(Borisova+16)

Ionizing radiation likely help detection
But, most nebulae do not havecold stream-like morphology~400kpc

Key targets to understandthe cosmic web and cold accretion

Cantalupo+14

Introduction

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ArrigoniBattaia+18~300kpc
9

Our Work
Central questions:
1. Does filamentary IGM gas and the cold-mode accretion reallyexist around massive halos at cosmic noon?
2. Is there a difference in the CGM as a function of environment?
●To tackle these problems, we– Search for traces of the cosmic web and cold-mode accretionaround the core of a protocluster at z=2.84– Probe environmental dependence of LAHs with numerous LAEs

residing in various environments from voids to protoclusters

Introduction

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10

1. Lyα View arounda Hyperluminous Quasar
at a Node of the Cosmic Web(Kikuta et al. 2019, PASJ, 71, L2)

2020061511

Subaru Observation
Hyperlumious QSO at z=2.84: HS1549+1919–L1450(νLν @ λ=1450A)LνLν @ λ=1450A) @ λ=1450A)=1.5×1014 L⦿ , MBH=4.6×109 M⦿
33※L⦿=3.8×10 erg/s(Trainor & Steidel 2012)–

reside in massive overdensity (proto-cluster)–

Deep imaging & spectroscopic data available at the center–

Observed with Subaru Hyper Suprime-Cam (HSC)★←HS1549

Mostardi+13

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Redshift

May+1812

Observation: HS1549+1919
Hyper Suprime-Cam(HSC) Observation (S16A-110, PI: Yuichi Matsuda)
FoV= 1.5 deg diameter = 42 pMpc/165 cMpc @ z=2.84
G
2.2 hr (389 shots) → 27.4 mag (5σ, 1.5” aperture=2×seeing FWHM 0.77”)
NB468 6.3 hr (113 shots) → 26.6 mag (5σ, 1.5” aperture)

Transmission →Data reduced using HSC pipeline (hscpipe 4.0.5)
G band
NB468

Wavelength →NB

Spectrum of Lyman
α emitter = LAE
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13LAE Detection
LAE selection criteria:
NB < 26.57(5σ)
G – NB > max{0.5, 0.1+4σ(G-NB)}(rest EWLyα >12Å)

G-NB468

Source detection & photometry
with Source Extractor (Bertin & Arnouts 96)

LAB selection criteria:
criteria above(isomag)+ ALyα,iso>16arcsec2

NB468→ 3490 LAEs and 76 LABs foundFalse-color
image
R: G
G: NB
B: GLAB

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LABLAB

14

LAE Distribution●●●Filamentary structure
Overdensity at the centersuggests Mhalo of the protocluster
will become 1015M◉ at z=0
LABs are distributed along thestructure & clearly prefer denser
environments

KS-test p-value: 0.00173※δgal=n/nave-1

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Kikuta+1915

Lyα View around the QSO-Overabundance of LABs
-Alignment of LABs with the LSS-Tail & Filament+ LAE□ LAB

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16

Summary (1)●We found that the HS1549 protocluster corresponds to theintersection of ~100 cMpc-scale structure.
●●

Significant overdensity of LABs and their apparentalignment with that of the large-scale structure are foundnear the protocluster core.
Discovery of a candidate of gaseous filament along thecosmic web–

Might be facilitated by the HLQSO irradiation–

Significant step toward direct test of cold accretion
scenario!

–

Follow-up observation scheduled (tomorrow!!)
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17

2. Lyα Halos around LAEs
across Environments

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18

Grouping & Stacking LAEs●●

●Group LAEs according tovarious properties→ Stack them (median)& examine their Lyα SBprofiles
Large sample size →very high sensitivity
achieved (~1e-19 erg/s/cm2/arcsec2)
Note the correlations
between quantities
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19

Grouping & Stacking LAEs●●●

Group LAEs according tovarious properties→ Stack them (median)& examine their Lyα SB
profilesLarge sample size →very high sensitivity
achieved (~1e-19 erg/s/cm2/arcsec2)
Note the correlations
between quantities
20200615

20

Grouping & Stacking LAEs●●●Group LAEs according tovarious properties→ Stack them (median)& examine their Lyα SBprofiles
Large sample size →very high sensitivity
achieved (~1e-19 erg/s/cm2/arcsec2)
Note the correlations
between quantities
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21

Stacking Analyses●

Use cutout Lyα images of LAEs (sky mesh size=30”)●

Mask continuum source & unmask a target of interest●

stack Lyα & continuum images with IRAF imcombine

Continuum

Masked Lyα
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22

Uncertainties●Sky noise behaves well (noise ∝ N-1/2; Fig 3.4)

●Slight difference in shapes of PSFs are noted●``Non-LAE’’ sample is constructed to check total systematics
LAE

non-LAE

Lyα

Cont20200615

23

Fig 3.920200615

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Fig 3.1020200615

25

Results of Stacking
LAHs are detected for all subsamples
Obviously, brighter (in both UV/Lyα)
LAEs have larger LAHs
High EWLyα,0 LAEs have compact LAHs

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Results of Stacking
No systematic trend is observed for environments anddistance from the QSO, though protocluster LAHs are large
Gray shade … 5th and 95th percentile of the stacked Lyα SB
distribution of 700 randomly selected LAEs

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27

LAH Dependence on Galaxy Properties
Hard to discuss trend beyond >30 pkpc due
to low S/NTrend of UV bright LAEs having larger LAHs
is consistent with previous studies(Momose+14), while the trend for LLyα is not
Trend for EW are likely made by correlation
with UV mag and/or fluorescence

Radius [pkpc]

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Origin of the Large LAH of Protocluster LAE
Protocluster LAEs are brighter in UV and this may be thecause of larger LAHs
→ Our simulation suggests NOOverlap of LAEs also cannot explain
the trend
UV magnitude bin

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Origin of the Large LAH of Protocluster LAE
Diffuse Lyα emission around the core may boost the signal→ further divide LAEs with δ>2.5 into two and stack again→ The result suggests the extent is madeby the diffuse Lyα emission
Almost no dependence on environments
outside of the protocluster

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30

LAH dependence on environments
In the HS1549 field, a likely cause of large LAHs is diffuseemission around the protocluster core
All studies which reported such large LAHs are targeted atprotoclusters at z=2-3, which could have diffuse Lyα emission→ No dependence on environments out of protoclusters
Matsuda+12: SSA22

Steidel+11: SSA22,HS1549, HS1700

20200615

Umehata+1931

Highlights
●

●

●

●

●

Our target protoclusters are found to be at the intersection of afilamentary structure.
Significant overdensity of LABs and their apparent alignment withthat of the large-scale structure are found near the protocluster core.
We detect huge Lyα emitting structure around the core of the HS1549protocluster. Especially, we discovered a candidate of cold streams
at the node of the cosmic web.
LAHs of LAEs across environments are investigated with the samedatasets, finding almost no dependence on environments.
Large LAHs observed are likely due to diffuse Lyα emission thatpermeates the core of protoclusters at cosmic noon. Suchprotoclusters are good places to search for cold streams.
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32

Conclusion●Does the cosmic web gas and cold-mode accretion
really exist in massive halos at cosmic noon?
– Maybe yes, this should be confirmed with future IFS

observations.
– Our method worked well for increasing candidates of such

filament.
●Is there a difference in the CGM as a function ofenvironment?
– No, except for protocluster LAEs – their CGM traced by

LAHs are likely to be affected by diffuse Lyα emission.
–2020061533