Star Formation Activity of
Lyα emitters at z~2
Kusakabe+17 submitted to PASJ
ArXiv: 1707.09373

EAYAM2017 @Ishigaki Island

Haruka Kusakabe (The Univ. of Tokyo)
K. Shimasaku, K. Nakajima, R. Goto, M. Ouchi, T. Hashimoto,
1/19
A. Konno, Y. Harikane, J. Silverman and P. Capakphoto by S. S. Elgueta

Star Formation Activity of
Lyα emitters at z~2
Kusakabe+17 submitted to PASJ
ArXiv: 1707.09373

EAYAM2017 @Ishigaki Island

Haruka Kusakabe (The Univ. of Tokyo)
K. Shimasaku, K. Nakajima, R. Goto, M. Ouchi, T. Hashimoto,
2/19
A. Konno, Y. Harikane, J. Silverman and P. Capakphoto by S. S. Elgueta

Star Formation Activity ofLyα emitters at z~2Kusakabe+17 submitted to PASJ
ArXiv: 1707.09373

EAYAM2017 @Ishigaki Island

Haruka Kusakabe (The Univ. of Tokyo)
K. Shimasaku, K. Nakajima, R. Goto, M. Ouchi, T. Hashimoto,
3/19
A. Konno, Y. Harikane, J. Silverman and P. Capakphoto by S. S. Elgueta

Picture of Galaxy Evolution
GalaxyStar Formation& Merger

Dark matter halo (DMH)

z~0 (The local Universe)”Building block”
・young・low M★
Lyα emitters (LAEs)
High z (The past Universe)
4Picture of Galaxy Evolution
Galaxy①Star formation modeStar Formation& MergerControl・accretion of gas
・star formation feedback

Dark matter halo (DMH)②Stellar to halo mass ratio(SHMR=M★/Mh)
z~0 (The local Universe)”Building block”
・young・low M★
Lyα emitters (LAEs)
High z (The past Universe)
52 Basic Properties of SF Activity① SF mode

starformation

Starburst gals

stellar to halomass ratio② SHMR
Past SF isefﬁcientMS gals (on SFMS)
average relation
low mass=faintcurrent level of SF

past eﬃciency of SF→physical origin & evolutionary path of galaxies

Whatʼs going on LAEs?
Daddi+2007; Rodighiero+2010; Guaita+2010, 2011; Lin+2012; Behroozi+2013; Moster+2013; Tomckzack+2016; Shivaei+2016; Ishilawa+2016, 2017; Hagen+2016; Shimakawa+2017

6/19

Problems① SF mode

starformation② SHMRstellar to halo
mass ratio

individual

Guaita+10HK15

z~2 (~10Gyr ago)

Guaita+10,11

Ø bright objects
Ø poor IRAC (M★)Ø small survey area (Mh)Daddi+2007; Rodighiero+2010; Guaita+2010, 2011; Lin+2012; Behroozi+2013; Moster+2013; Tomckzack+2016; Shivaei+2016; Ishilawa+2016, 2017; Hagen+2016; Shimakawa+2017

7/19

Problems① SF mode?

starformation② SHMRstellar to halo
mass ratio?

Ø bright objects → stacking faint objects
Ø poor IRAC (M★)→ new photometry
Ø small survey area (Mh)→ large area
8/19

Our z~2 LAE Sample
Field

NB mag lim (5σ)

Area (min2)

NBtot<=25.5 (sed)SXDS

25.7~1240

601(93)COSMOS26.1~740

297(47)GOODS-S

26.4~580

51(4)GOODS-N26.1~780299 (56)~1deg2 ~1250~3 G10 ~5 G10

TOTAL
U

NB387

B
Nakajima+2012, 2013;
Konno+2016;
HK+2015, 2017;ﬂux
λMethods① SF mode: stacked SED ﬁt② SHMR: clustering analysis

10/19

① Stacked SED Fit
parameters: SFR, M★, age, E(B-V)
IRAC
ch1, ch2obs. data
B, V, R, I, z,J, H, K,

SMC-like attenuation curve (HK+15)
Bruzual & Charlot 2003 Gordon+2003; Erb+2006; Ono+2010; Nester+2013;
Vargas+2014; Kusakabe+2015

11/19

② Clustering Analysis
sky distribution of the LAEs

ACF amplitude: Aω

Galaxies in more massive DMHs
are more strongly clusteredAω3D correlation ΛCDM model
lengthLandy & Szalay 1993; Simon 2007; Tinker+2010; Ouchi+2010; Khostovan+2017

Mh
12/19

Results① SF mode: M★ vs. SFR② SHMR: Mh vs. M★/Mh

13/19

① SF Mode
z~2
SFMS

individual
Guaita+HK15This work• lie on extrapolations of SFMS:
moderate SF
Daddi+2007; Rodighiero+2010; Guaita+2011;; Tomckzack+2016; Shivaei+2016;
Hagen+2016; Shimakawa+2017

14/19

② Mh vs Ms/Mh (SHMR)
z~2averagerelation

This work
Guaita+• high SHMR~0.02 at Mh~4 1010 M¤
Guaita+2010, 2011; Lin+2012; Behroozi+2013; Moster+2013; Ishilawa+2016, 2017;

15/19

Discussion
moderate SF & high SHMR(i) physical origin of the LAEs
(ii) future of the LAEs

16/19

(i) Physical Origin① SF mode

starformation

keep sSFR
on SFMS② SHMRstellar to halo
mass ratio

SHMR
increases

moderate SF but high SHMR・small spin parameter of DMH
and/or weak feedback (Dutton+10)
・low Mh → low Mgas → low MHI→ Lyα can escape easier
17/19

(ii) LMC Progenitor?
Our LAEsSFH of LMC
SF at z~2 does notsustainat z~0MW-like
1-2 1012M¤
LMC-like
0.2-3 1011M¤
at z~2Similar SFR ~3 M¤/yrSimilar M★~1-3 109M¤
LAEs: unsustainable SF
SFR /gas accretion rate ~1.6

Hamana+2004; Peñarrubia+2015; Wang+2015; Rezaei kh+2014

Take-home message
Stellar and halo properties of z~2 LAEs from 1deg2①moderate SF lying on SFMS②

high Ms/Mh (SHMR)→ (i) small spin parameter and/or weak FB?
(ii) progenitors of LMC-like galaxies→ High-z low-mass galaxies have various evolutionary path
Subaru/HSC enables us to obtain their
Mh more accurately

Thank you
19/19

Appendix

20

③ Mh vs SFR/BAR (BCE )z~2This work

Guaita+• high BCE~1.6+0.6-1.0• high SHMR~0.02+0.07-0.01
at Mh~4.0+5.1-2.9 1010 M¤

Guaita+2010, 2011; Lin+2012; Behroozi+2013; Moster+2013;

averagerelation

21/19

Cosmic Variance in b Measured
at100”:
z~3
narrowband
broadband
narrowband

b!
= 0.5
b!

Calculated using Cohn 06 (see also Kusakabe+17)
Many thanks to Hamana-san and Shimasaku-san
22/19

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 (NBexcess)23

Cosmic Variance in Bias Parameter
Guaita+This work

HSC/SSP

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

24/19

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

ﬁ\ng: y = a * θ^-0.825

Cosmic Variance in b Measured
at100”:
z~3
narrowband
broadband
narrowband

b!
= 0.5
b!

Calculated using Cohn 06 (see also Kusakabe+17)
Many thanks to Hamana-san and Shimasaku-san
26/15

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 relationalso consistent with upper limit of IRX < 2.2 (3σ)• Calzetti: fIVE times higher IRX than those w theSMC curve
Ms and SFR of our LAEs are consistent withthose of previous studies
27→the SMC
curve
isadopted
Bowens+16; HK+15; Shivaei+16;Whitaker+14; Rodighiero+11; Daddi+07

Attenuation Curvefrom IRX-β relation
IRX-β
UV selected galaxies@z~2Meurer(Calzetti)
Takeuchi(updated Calzetti)
SMC(Small Magellanic Cloud)age < 100MyrNG Calzetti✔️ SMC, Takeuchi
similar to young UV galaxies
28

Pettini+98; Meurer+99; Calzetti+00; Takeuchi+12; Reddy+12