HSC 狭帯域フィルターを用いた
z~3 の淡い Lyα 放射の研究

Kikuta et al. 2019

Satoshi KIKUTA(NAOJ)
すばる望遠鏡データ解析講習会

2022/11/29

Introduction: Galaxy Formation●●●Galaxies are formed within the cosmic web, a network of dark matter &baryons
Gas accretion along the cosmic web
governs galaxy evolution- “cold-mode accretion”- observationally poorly constrained!
Massive stars, SNe, AGNs inject
energy into ISM/CGM- “feedback”“cold streams”
Dekel+09

Intergalactic
Medium=IGM

Dark MatterGas2eb(IGM

Gas circulation between IGM/CGM
is very important for galaxy evolution––thecos

can be traced with Lyα emission
at high redshift (z>2)
Turned out to be ubiquitous, butvery faint (SB<10-18erg/s/cm2/arcsec2)

To

●micw

●)→

Inter/Circum-galactic medium(IGM/CGM) & Lyα emission

Tumlinson et al., 2017

IFU or deep NB imaging are
powerful tools

UVLyα↑Stacked UV(left) and Lyα(right)
image of LBG @ z=2.65←Their SB profiles (Steidel+11)

so-calledLyα halo!

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Galaxy in Different Environments●●Environmental segregation at z=0 suggests
some processes preferentially work on
galaxies in dense environments
Observations of protoclusters hold the key–At z>2, the local relation reverses–

High gas accretion rate, high merger
rate, etc. may be related to abundantactive populations(starburst, AGN, LAB, ...)

Cappellari+11

SpiralS0(fast rotator)

Alexander & Hickox 12

Elliptical(slow rotator)

galaxy density →4

Observations of Lyα halosaround SF galaxies at z>2●●Diffuse Lyα halo is ubiquitous if we go as deep as<1e-18 erg/s/cm2/arcsec2 – but its origin is still
under debated!
LAH shape and its dependence on various hostproperties should have useful information––

Host UV magnitude, Lyα luminosity, the large-scaleenvironments, etc.
Observations in the literature have not reachedconsensus. More obs. are needed to pin down theorigins and probe the CGM
Leclercq+17
Halo scalelength vs MUV

UV

Lyα

Stacked UV(left) and Lyα(right)
image of LBG @ z=2.65 (Steidel+11)

Matsuda+12:
LAEs in denser environments
have more extended LAHsvs.
Xue+16:No such dependence →Byrohl+21 Simulation

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Origin of Lyα emission in the CGM●Ionizing photon
production rate

Lyα luminosity●HI distribution●●DM halo mass

●DM halo mass

Taken from Momose-san’s slide
See also Momose+16

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Deep HSC imaging for diffuse emission●

Target: Field around a hyperlumious QSO at z=2.84 (HS1549+1919)–Observed with Subaru/HSC (PI: Yuichi Matsuda)G

2.2 hr (20sNB468

6.3 hr (300s ×113 shots) → 26.6 mag (5σ, 1.5” aperture)●–×389 shots) → 27.4 mag (5σ, 1.5” aperture~2×seeing 0.77”)

To avoid saturation of the QSO, exposures need to be short

Large dithering (Ndith=5, Rdith=10’) + PA rotation (30°×N)●Transmission →●reside in massive overdensity (proto-cluster)

To reduce the impact of diffuse ghosts

G band
NB468
Wavelength →Mostardi+137

Data Reduction●

Data reduced using HSC pipeline (hscPipe 4.0.5)–●

raw data: ~1.3TB

With global sky subtraction + ghost mask package +addtionalmask by myself●

https://hsc.mtk.nao.ac.jp/pipedoc/pipedoc_4/j_tips/skysub.html#global-sky●

https://hsc.mtk.nao.ac.jp/pipedoc/pipedoc_4/j_tips/ghost.html

For further analysis, we subtract
the sky with SExtractor witharbitrary sky mesh size–

For point source detection,
we used 64 pixel–

For extended source analyses,
we used 176 pixel (=30”)

8Solutions:

Ignore problematic CCDs●
Define and register “defect”●
Mask problematic regions●–Edit fits mask layer

9LAE/LAB Detection●●

LAE selection criteria (2.815<z<2.887):– NB < 26.57(5σ)– G – NB > max{0.5, 0.1+4σ(G-NB)}(rest EWLyα >12Å)
LAB (Lyα blob)selection criteria:– criteria above(in isophotal mag) +Lyα 2σ isophotal area>16 arcsec2 inthe smoothed Lyα image(gaussian with σ=3 pixel)★Narrow-band techniqueTransmission →Source detection & photometry withSource Extractor (Bertin & Arnouts 96)

NB468
Wavelength →→ 3490 LAEs and 76 LABs found

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Distribution of LAEs & LABs●●

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

KS-test p-value:0.00173※δgal=n/nave-1, n is the number of LAEs
within a 1.8’ aperture at a given point□ LAB
Kikuta+1912

Diffuse Lyα emission from protocluster core

Diffuse emission down to1e-18 erg/s/cm2/arcsec2(white contour)

Kikuta+19+ LAE□ LAB 13

Physical Origin of Extended Lyα Emission●Lyα photons are emitted from excited/ionizedhydrogen atoms–Photoionization (>13.6eV, 921nm)→ Recombination–

N=2→1, 10.2eV, 1216nm–Collision
Cantalupo+14

Yoshida+16

Momose+1614

Diffuse Emission from Protocluster Coreat Cosmic Noon

●

●

●

There are so many AGNs around the central
part of the protocluster core

Kikuta+19, HS1549@z=2.8

Abundant cool gas & active source (provideionizing radiation) can boost the Lyα emission
from the filamentary structure
New direct way to test galaxy formation theory!

Umehata+19: SSA22@z=3.1

Erb+11, HS1700@z=2.3

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Detection of an SMG at the tip of the “filament”(preliminary)●●interesting diffuse LAB with filamentary shape,pinpointing the HLQSO – may trace the coldstreams?
To know the origin, we conducted Keck/KCWIobservations–●

Achieved S/N is not high due to weather, but wetentatively detect a double-peaked Lyα line

A sub-mm source detected at the tip by ourALMA observations–Spec-z not obtained yet...

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Stacking Analyses●Use cutout Lyα images of LAEs (sky mesh size=30”) with continuum sources masked●Stack Lyα & continuum images with IRAF imcombine●Sky noise is estimated with “sky cutouts”; behaves well (∝ ~N -1/2)●PSFs of NB/g-band images are measured with bright point sources→“average face”
of Japanese menLyα

Cont.

–

Central part: objects with CLASS_STAR> 0.95 and 18 < g < 22–Outer part: stars with 13 < gSDSS < 15 from SDSS DR14 catalog–

These are connected at r = 20 pixels following a method described in Infante-Sainz et al. (2019)17Stacking Analyses“Non-LAE” sample is constructed to check total
systematics (see Momose+14)–Detect diffuse Lyα emission down to ~10 -20
erg/s/cm2/arcsec2

LAE non-LAE
Lyα●

Stack randomly selected objects with similar NB
mag & FWHM and check if they are extended=64 pixel

Cont.

●

Sufficiently large sky mesh size is crucial!!
orange: Lyα, blue: Cont.
Solid: LAE, dashed: non-LAE

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LAH Dependence on Various Properties●●●Divide LAEs into 5 groups according to theirphotometric properties“Projected distance from the HLQSO” is used
to test whether QSO radiation affects theLAHs
Note the correlations between quantities※overdensity δ=n/nave-1, n is the number of LAEs
within a 1.8’ aperture at a given point

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Fitting exponential functions●SB radial profiles are fit with the following functions:–2-component exponential: PSF*(C1×exp(-r/r1))–

1-component exponential: PSF*(C1×exp(-r/r1)+C2×exp(-r/r2) )–Power-law: PSF*(C1×r -α) as suggested by a model in Kakiichi &Dijkstra 2018

MUSE#6905@z=3.10
Leclercq+17

LyαUV
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Data 2-comp 1-comp PL▽: 1-sigma upper limit21

Results of Stacking: UV, LLyα, EW●

LAHs are detected for all subsamples●Bright/low-EW LAEs tend to have larger LAHs

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Data 2-comp 1-comp EW profile

Gray: scaled Lyα S
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Fitting exponential functions●●●

2-comp exp. functions are needed for Lyα SB profiles,while 1-comp exp. functions are enough for UV in most cases
Bright (in Lyα/UV) / low-EW LAEs require the UV 2ndcomponent●
This is the first robust detection at high-redshift
Power-law sometimes fails to capture the transition from 1st to2nd component

Lyα

UV24

Results of Fitting●Lyα/UV 1st components correlate with MUV, LLyα, EW–Brighter LAEs have larger cores●

Lyα 2nd component behaves stochastically●Protocluster sample (δ>2.5) stands out

Lyα
UV25

Relation between scalelengths
r1,UV, r1, Lyα, r2, Lyα●Correlation found only for r1,UV - r1,Lyα–●r2,Lyα is difficult to predict

Commonly used assumption of r1,UV = r1,Lya is not valid (gray line: 1:1 rel.)–Caution: small value for r1,UV may be just due to nondetection incontinuum images

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Discussion:
Origin of the Large LAH in PCs●Overlapping of galaxies or UV brightness of the PC LAEs cannot fully explain the large LAH●We further divide the PC sample into near/far from the QSO sample●–Far sample no longer has a very large LAH–

Near sample shows an even larger LAH

Diffuse emission around the PC core may be the cause–

Related to abundant cool gas irradiated by active membersin the PC corenear QSO

Steidel+11: SSA22,HS1700, HS1549

Umehata+19: SSA22

far from QSO
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Discovery of “UV Halos” and Its Implicationto Low-Mass Galaxy Evolution●Comparison with the TNG100 run of the IllustrisTNGsimulation–●

make median stacked SFR surface density profiles of FOF (friends-offriends) halos at z = 3

The UV-brightest subsample has a similar shape as the SFR surface
density profiles of TNG galaxies with 1 < SFR < 10 and 10 < SFR <100 subsamples–Given the similarity of the profiles, the UV halo of the UV-brightest LAEs
would be also due to satellite galaxies–On average, they have 1.9 and 2.3 satellites, with median DM halo
masses of 3.3×109 M⊙ and 4.4×109 M⊙–the UV halo may be comprised of a few satellite galaxies, not by an
intrinsically diffuse stellar halo, unlike local mature galaxies–Such satellites have 0.01 < SFR < 0.1 – detectable with JWST?

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Insights into the Origin of LAHs●●

First detection of the UV 2nd component (r < 40 pkpc) offers direct
evidence for a contribution from satellite SF–

Agree with recent simulation results (Byrohl+20, Mitchell+20, Lake+15)–

Can be tested with JWST by seeing if “Hα halos” exist or not

To determine the origin of LAH at larger radii, deeper obs. & comparison withstate-of-the-art simulations are needed–

Current simulations still cannot treat all relevant physics–

Fluorescent Lyα emission may contribute significantly at outer regions
within protocluster cores at cosmic noon and/or near bright QSOs

Figure from Momose+16+(d) fluorescence

Byrohl+20(TNG50)

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Summary●

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The HS1549 protocluster corresponds to the intersection of ~100cMpc-scalestructure. “Cold stream”-like structure is discovered near its core.
Sensitivity close to 1e-20 erg/s/cm 2/arcsec2 is necessary for safe argument (atz~3) of LAHs – NB stacking with Subaru/HSC is still a powerful tool in theera of sensitive IFUs!
Lyα SB profiles are well fit with 2-component exponential functions with r 2,Lyα~10
pkpc
r1,Lyα and r1,UV correlate, but r2,Lyα does not correlate with any photometric property –insufficient S/N?
Very large r2,Lyα in the PC suggest the importance of “fluorescence” as a LAH origin
under some situations
We found “UV halos” around bright/low-EW LAEs–

demonstrates satellite SF as important contributor–

Comprised of a few low-mass satellites?

To determine the origin of LAH at larger radii, deeper obs. & comparison withstate-of-the-art simulations are needed31

Take home messages for HSC research●

やりたいことを念頭に観測戦略を立てる–●

データ整約、解析も目的に応じて適切なものを選ぶ––●

ディザリング、一枚あたり露出時間、観測効率、 etc

アーカイブ画像を使う場合、観測条件や解析過程がやりたいサイエンスと照らして適切かをチェックする
例 : スカイ引きのメッシュサイズが目標天体に対して十分大きいか

画像の質は必ず自分の目で確かめる–

カタログには人工信号が混入している可能性あり–

データが巨大な近年では機械学習で人工信号を除くなどの例も●32