Stellar to Halo Mass Ratioand Gas Conversion
Efﬁciency of LAEs at z~2(Kusakabe+17 in prep )2017/6/8
第4回銀河進化研究会@大阪大学

Haruka Kusakabe
K. Shimasaku, K. Nakajima, R. Goto, M. Ouchi,
T. Hashimoto, A. Konno Y. Ono, Y. Harikane and J. Silverman

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3 Key Properties of SF in galaxies①star formation mode (SF mode)②stellar to halo mass ratio (SHMR)③baryon conversion efﬁciency (BCE)2

①SF Mode (Ms vs SFR)
z~2
individualstack(Guaita+)

SFMS

UV+IR stack w/ SMC-curve(HK15)

Ø SF mode of LAEs: burst or moderate SF?
ü problems:

・individual → only bright objects
・individual /stack → no or shallow IRAC photometry
ü UV + FIR stack w/ SMC-curve: moderate SF・only one ﬁeld, no clustering result3② SHMR (Mh vs Ms)
z~2

averagerelation

Guaita+Ø lie on or below the average relation?
ü problems:・small sample size 250→ large statistics error
・small area 0.3 deg2→large cosmic variance4③ Mh vs BCE = SFR/BAR
z~2
average relation
Guaita+Ø lie on the average relation? (but with calzetti)
ü problems:・small sample size 250→ large statistics error
・small area 0.3 deg2→cosmic variance5This Study・SF mode, SHMR, and BCE of z~2 LAEs
FIeldArea(min2)

NB maglim (5σ)

Number of objects
AllNBtot<=25.5 (sed ﬁt)

SXDS

~1240

25.7

603

601(93)COSMOS

~740

26.1

619

297(47)GOODS-S~580

26.4

269

51(4)

GOODS-N~780

26.1

950

299 (56)

TOTAL~1deg2~3 G10~2440~1250~5 G10

Nakajima+2012, 2013; Kusakabe;2015; Konno+2016

・dark matter halo masses: clustering analyses
・stellar properties: SED ﬁtting

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Methods
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Stacked SED Fit
assumed model:IRAC
ch1, ch2
obs. data
B, V, R, I, z,J, H, K,・BC03 with nebularemission (Ono+10)
・constant SFH
・Z=0.2Zsun(Nakajima+12)
・fesc(ion)=0.2(Nester+09)
・the SMC-likeattenuation curve(Kusakabe+15)

derived parameters: SFR, Ms, age, E(B-V)

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Clustering Analysis
 ACF observation:

Landy & Szalay+93
error: poisson
Khostovan+17

 ACF model: β=0.8,ﬁtting range=40”-1000”

 bias factorhalo mass:Tinker+109Bias Factor
Guaita+Thiswork

 No signiﬁcant dependence on L(Lya) limit
 at NBtot = 25.5 mag
b=1.21+0.18-0.16

Mh=2.6+6.6-2.4

1010M¤

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Results
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①SF Modez~2
individualSFMS

This work
Guaita+UV+IR

 our LAEs have Ms ~1 109 M¤ & SFR~3 M¤/yr lie on extrapolations of SFMS: moderate SF12

②Mh vs Ms (SHMR)
z~2

averagerelation
This work
Guaita+ lie slightly above extrapolated average relation
 possibly high SHMR~0.01-0.1

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③ Mh vs BCE = SFR/BARz~2This workaverage relation
Guaita+• BCE~2.1 1.9• higher than extrapolated average relation

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Discussion
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Physical Origin of LAEs
(1) moderate SF but possibly high SHMR + high BCE
low Mh → low Mgas? → low MHI? → Lyα can escape(2) low duty cycle: ~1.6% in Mh=1010-1011M¤
low LAE fraction: ~14% in Ms=108.5-109.5M¤
・How to reproduce (1) & (2)? small spin parameter of DMH
and/or weak feed back (Dutton+10)
keep sSFR
on SFMS

increase
SHMR

increase
BCE

Tomczak+13; Ricciardelli+11; Dutton+1016

Future of LAEs

Guaita+MW-like
1-2 1012M¤
LMC-like
0.2-3 1011M¤

This work

Peñarrubia+15; Wang+15; hamana+04

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Cosmic Variance
Guaita+This work

HSC/SSP

cosmic variance
~31%

~17%

~3%

 ﬁrst estimation of cosmic variance of bias~(ωgals/ωmatter)0.5
assuming that CV comes from ﬂuctuation of ωmatter

 HSC SSP: ~ 27 deg2 →1σ of cosmic variance ~3%<< ﬁtting & contami fraction error

18SummaryStellar and halo properties are derived
by ~1250 LAEs at z~2 from 1deg2 ﬁeld

l average bias = 1.21+0.18-0.16 with Mh=4.0+8.6-3.0 1010M¤
・large cosmic variance in each sub sample
・smaller than Guaita+10 based on 0.3 deg2 area

l average LAEs form star moderately lying on SFMS
l eﬃcient mass assembly as opposed to their low Mh・possibly high SHMR・high BCEl They are progenitors of LMC-like galaxies (not of MW)l HSC enables us to constrain Mh of LAEs robustly

19Appendix
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SamplesFIeldArea(min^2)

NB mag lim Number of # w NBtot<=25.5mag(5σ, mag)samples(#) (# for SED ﬁtting)

SXDS

~1240

25.7, 2” ap

603

601(93)COSMOS~740

26.1, 2”ap619

297(47)GOODS-S~580

26.4, 2” ap

269

51(4)

GOODS-N~780

26.1, 3” ap

950

299 (56)

TOTAL~1deg2

~2440

~1250
Nakajima+12, 13,
Kusakabe+15,
Konno+16

ﬁve cumulative samples
NB<=25.0, <=25.3, <=25.5,<=25.8, <=26.3

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SED ﬁtting(fesc=0.2)

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SED ﬁtting(fesc=0.2)

23SED ﬁtting(fesc=0.2)

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compared with the previous work
IRX-β(Calzetti curve) Meurer+99
SFMS at z~2
COSMOSCOSMOSSXDSGOODS-S

individual LAEs
(NB & HST, S17)
individual LAEs
(spec or NB& HST, H16)

Assuming the Calzetti curve and IRX-β relation

 Our LAEs lie similary to the previous work

Shivaei+16;Whitaker+14; Rodighiero+11; Daddi+07; Kusakabe+15;
Hagen+16; Shimakawa+16

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Ms vs SFR (fesc=1)
fesc =1 fixed(no nebular lines and continuum)

fesc =0.2 fixed(0.8*Nlyc translate into nebula)

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Stacked SED ﬁt
SXDS(Calzetti)

SXDS(SMC)

NBtot>=25.5mag

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L(TIR)/L(UV)

Ms vs IRX: prefer SMC
Open: Calzetti
ﬁlled: SMC
consensus
relationship

IRX(HK15)
Calzetti + IRX-β

 SMC: our LAEs lie on the consensus relation

also consistent with upper limit of IRX < 2.2 (3σ)

 Calzetti: fIVE times higher IRX than those w the SMC curve
Ms and SFR of our LAEs are consistent with those ofprevious studies→the SMC curve is adopted
Bowens+16; HK+15; Shivaei+16;Whitaker+14; Rodighiero+11; Daddi+07

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Sky distribution

SXDS: 1240arcmin^2, 0.2”/pix

COSMOS: 740arcmin^2, 0.15”/pix29

Sky distribution

GOODS-S: 580arcmin^2, 0.267”/pix

GOODS-N: 780arcmin^2, 0.3”/pix

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Clustering Analysis

 ACF observation: Landy & Szalay+93(error: poisson)

 ACF model: β=0.8, ﬁtting range=40”-1000”
 bias factor-halo mass: Tinker+10
 左だけ、右 文章

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ACF

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ACF

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Bias factor
cumulative NB cut sub samples

fc=0-20%1042

 large cosmic variance > statistics errors ?
 No signiﬁcant dependence on L(Lya) limit
 No signiﬁcant dependence on EW (NB excess)34

Cosmic Varianceassumption: bint is constantCV originate from variation of ωDM(ﬁeld)
k: FT θP2(K): FT ω(θ) (Kohn 2009)
Ω: area size(->Hamana-sanʼs code)

fitting: y = a * θ^-0.8

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③ Ms vs BCE = SFR/BARz~2This work
average relationG+• BCE~2.1 1.9• higher than that of extrapolated B13 relation

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