Galaxy Evolution Workshop 2019 @ Kavli IPMU

Extended star-forming region within star-forming
galaxies in a dense proto-cluster core at z=2.53
based on Suzuki et al. 2019, PASJ

Tomoko Suzuki (Tohoku Univ. / NAOJ)
Y. Minowa, Y. Koyama (Subaru Telescope)
T. Kodama (Tohoku Univ.), M. Hayashi (NAOJ), R. Shimakawa,I. Tanaka (Subaru Telescope), K.-i. Tadaki (NAOJ)

Structural growth of star-forming galaxies at high-zz ~ 1 SFGs

• Inside-out growth(e.g., Trujillo+06; Nelson+16)

Hα > ContinuumStar-forming region is more extended
than the stellar continuum
Nelson et al. (2016)• Wet compactionz ~ 2 massive SFGs

(e.g., Zolotov+15; Tacchella+16)

Induced by- Violent disk instability of gas-rich disk
- Gas-rich major merger

Gas

Centrally concentrated star formation
SFRTacchella et al. (2016)

Environmental dependence?
• Different mode of gas accretion(e.g., Dekel+09; van de Voort+11)
Gas accretion is important to keep
gas-rich unstable diskslog(Halo mass/Msun)

In high-density environments…
Tgas
Tgas
van de Voort+11• Higher merger frequency

Overzier+16(e.g., Lotz+13; Hine+16)→ Relative dominance of the compaction event may change?
Investigate the spatial distribution of SF region for galaxies inhigh-density environments

Our project: AO+NB imaging for high-z galaxies• co-PIs: Y. Minowa and Y. Koyama• Observation
Imaging with Subaru/IRCS+AO188 and NB filter- Spatially resolve line-emitting region- 0.1-0.2 arcsec resolution

Hα emitter at z = 2.5

MOIRCS NB2315

IRCS+AO188 NB2315→ 1-2 kpc @ z~2PSF• Targets
NB-selected Hα emitters at z = 2-2.5- General field: UDS, COSMOS (Minowa et al.)- Proto-cluster field: USS1558 (This work), PKS1138

USS1558: a proto-cluster at z=2.53• A high-density region around a radiogalaxy at z=2.53 (Kajisawa+06)

RG• Deep MOIRCS NB observation→ 107 Hα emitters(Hayashi+16; Shimakawa+18)• IRCS+AO188 observation- May 2013, 2014 (PI: Y. Koyama)
IRCS
FoV
Shimakawa et al. (2017)- The densest group of HAEs
→ proto-cluster core

Targets on M*-SFR diagram

RG

Tomczak+2016IRCS
FoV
Shimakawa et al. (2017)

11 HAEs with M* > 109.5 Msun

→ “Normal” star-forming galaxies
around the main sequenceObtained spatially resolved images
IRCS/K’ IRCS/NB2315-K’ HST/IF814W(~ 6000Å)(Hα+[NII])(~2300Å)• Achieved PSF size
0.25’’ → 2.5 kpc @z=2.5• K’ image = Stellar continuum→ Stellar mass
• NB-K’ image = Hα+[NII]→ Star-forming region• HST/ACS images are available(Hayashi+)• Stacking analyses- High-mass (> 1010 Msun)- Low-mass (< 1010 Msun)

4.3 × 4.3 arcsec2

Radially dependent dust extinction for Hα
Locally calibrated relation by Koyama et al. (2015)
observed SFR ratio

SFRUV→ HST/IF814W

AHα (mag)< 1.2 kpc 1.2-3.0 kpc 3.0-4.8 kpc

High-mass

1.11

0.78

0.68

Low-mass

0.52

0.47

0.41

Higher AHa at the center (e.g., Nelson+16; Tacchella+18)

Extended star-forming region of massive SFGs
High-mass sub-sample
1010Msun< M* <= 1011.1 Msun

SFR(Hα)M*R1/2(M*) = 3.32 +0.21−0.19 kpc
R1/2(SFR) = 4.04±0.19 kpc

Low-mass sub-sample
109.5Msun < M* < 1010 Msun

SFR(Hα)M*

R1/2(M*) = 3.63 +0.60−0.50 kpc
R1/2(SFR) = 3.81±0.42 kpc

Star-forming region is further extended than underlying
stellar structure

Field galaxies at similar redshifts
Minowa et al.
- 20 Hα emitters in the general fields (UDS+COSMOS)- Three NB filters (z~2.2 and 2.5)
- Distribute around the main sequence at the epochTargets

Comparison with the field galaxies at z = 2-2.5

Open symbols:
assume constant AHα• No clear environmental dependence for massive SFGs
• Structural growth is mainly driven by internal secular
processes in both environments

SummaryWe conducted the AO-assisted K’+NB imaging observation withSubaru/IRCS+AO188 for the Hα emitters in the dense protocluster core at z =2.53●

Spatially resolve the Hα-emitting region within galaxies at z > 2●More extended star-forming region than stellar structure forthe massive SFGs in the proto-cluster core

●No clear environmental dependence of the spatial extent ofstar-forming region●Structural growth of massive SFGs at z=2-2.5 is likely
dominated by the internal secular processes both in the generalfields and the proto-cluster core.

Future prospects● Star-forming region highly obscured by dust

: High angular resolution observation of dust emission with ALMAz~2 star-forming galaxies (Tadaki+17)

Compact dust emission within
an extended stellar structure● Internal structures for a larger number of individual galaxies: ULTIMATE-Subaru(GLAO+Wide-field imager)

https://ultimate.naoj.org/overview.html