The Galaxy—Halo Connection
Across Cosmic History
石川 将吾 (NAOJ/CfCA)
第４回 銀河進化研究会, 2017年６月８日
Reference: Ishikawa et al. (2017), ApJ, 841, 8

Co-Investigators
Nobunari Kashikawa, Jun Toshikawa, Masayuki Tanaka,
Takashi Hamana, Yuu Niino, Kohei Ichikawa, andHisakazu Uchiyama

Introduction

Introduction

Stellar-to-halo Mass Ratio (SHMR)Star-formation efficiency as a function of DMH mass
~ Mstar/Mhalo
Pivot halo mass

SHMR (Mstar/Mhalo)

SN feedback?

AGN feedback?
Numerical simulation
Satellite formation? predicts z=0-8Star-formation issuppressed at themassive/less-massiveend

Behroozi+13

Dark Matter Halo Mass [Msun]

DMH masses withpeak SHMR (pivothalo masses) arealmost unchanged

Introduction

Stellar-to-halo Mass Ratio (SHMR)
SHMR is well constrained
in low-z Universe- Pivot halo mass is
consistent with the model- Massive end becomes flat
due to satellite galaxies

Coupon+15

SHMR (Mstar/Mhalo)

Why High-z?

Observation
Observation(Central+Satellite)(Central+Satellite)

Central gals.

Satellite gals.
Model prediction
DMH mass [Msun]...But SHMR at high-z have not been well studies!
- DMH mass estimation in high-z is difficult
Large number of high-z galaxy samples are required- Galaxy stellar mass estimation in high-z is difficult
Deep (and wide) multi-wavelength imaging data are required

Stellar Mass Estimation

Imaging Data
Construct large LBG samples at z~3, 4, 5
Optical data: CFHT Legacy Survey Deep Field
Optical 5-band survey (u, g, r, i, z-band)
Deep imaging data（i<27.3mag, 3sigma, AB）

Wide survey area (1.0 deg x 4 fields)

Selected LBG samplesz~3: 63,563 z~4: 47,760 z~5: 9,477
NIR data: WIRCam Deep Survey
NIR 3-band survey (J, H, K-band)
Covered ~half area of the CFHTLS
Deep imaging data（K<24.5mag, 3sigma, AB）

SED fitting

Stellar Mass Estimation

Consistency of Stellar Masses
We estimate stellar masses of LBGs in two ways
- Main sequence of star-forming galaxies- SED fitting technique

Stellar mass shows nearly a
one-to-one correspondence

We adopt the MS relation to use- all of the selected LBGs
- faint LBGs

Dark Matter Halo Mass Estimation

Angular Correlation Function
Statistical measurement of the galaxy clustering
Angular correlation function (ACF) ( )  DD  /  RR θ<DD>: the number of galaxy pairs<RR>: the number of random pairs
with separation angle θStrong galaxy clustering -> larger values of w(θ)
Large number of galaxy samples are required to measure
ACFs with good S/N...

Dark Matter Halo Mass Estimation

Halo Occupation Distribution
ACF is composed of two components (1-halo/2-halo term)

2-halo term

1-halo term

Predict ACFs assuming the relation b/w galaxies and DMHs
Halo Occupation Distribution (HOD) modelResults and discussion- Clustering/HOD analyses- Dark matter halo mass

- Satellite fraction- Stellar-to-halo mass ratio

Results and Discussion

Clustering Analyses
We compute ACFs at z=3, 4, 5 as a function of galaxy
stellar mass
- Massive galaxies show the strong clustering- High-z galaxies show the strong clustering at fixed a stellar mass

Results and Discussion

Clustering Analyses
We compute ACFs at z=3, 4, 5 as a function of galaxy
stellar mass
- Massive galaxies show the strong clustering- High-z galaxies show the strong clustering at fixed a stellar mass
- the HOD model well represents observed ACFs

Results and Discussion

Dark Matter Halo Mass
DMH masses as a function of galaxy stellar mass
We derive DMH masses with wide stellar mass range and small errors
Our DMH mass estimation is consistent with previous studies

LBGs reside in DMHs with masses of 1012 Msun

Results and Discussion

Satellite Fraction
We compute a fraction of satellite galaxies as a functionof stellar mass

Satellite fraction

This work(3<z<5)
Literature(0.9<z<2.5)
We firstly calculate the fraction ofsatellite galaxies in high-z
Satellite galaxies are rarely formed
in high-z Universelog(Mstar/Msun)

The number of satellite galaxy
drastically evolves from z=3 to z=1

Results and Discussion

Stellar-to-halo Mass Ratio
Our stellar-to-halo mass ratios at z=3-5...
are consistent with the model prediction (Behroozi+13)
show significant evolution from z=0 (gray solid line)
firstly capture pivot halo masses at z>3

Results and Discussion

Stellar-to-halo Mass Ratio in Low-z

SHMR (Mstar/Mhalo)

We also compute precise stellar-to-halo mass ratios at
0.3<z<1.4 using the excellent dataset of the HSC SSP

DMH mass [Msun/h]Caution: These results arederived using S15b Catalogue

Results and Discussion

Redshift Evolution of Pivot Halo Mass
Pivot halo mass shows small increasing trend with cosmic time at z>3
At z<2, pivot halo mass decreases with decreasing redshift (downsizing)log(Pivot halo mass/Msun)

Galaxies are efficiently formed within DMH with mass of 1012 Msun

Highlights
 We construct large galaxy samples at z=3, 4, and 5, and carry out
precise clustering analyses . Clustering strength monotonicallyincrease with increasing galaxy stellar mass and redshift.

 LBGs are hosted in DMHs with masses of 1011.7-12.8 h-1Msun, whichis consistent with results of previous studies. Our analyses showthat satellite fraction of LBGs is less than 4%, indicating thatsatellite galaxies rarely form in high-z Universe.
 The observed SHMRs at z=3-5 are in good agreement with themodel prediction.
 We find the pivot halo mass is almost unchanged around 10 12 Msun
at 0<z<5. Our study provides observationally evidence that galaxy
formation is ubiquitously most efficient near a DMH mass of Mh ~1012 Msun over cosmic time.