Beyond 12+log(O/H)=7:
Search for extremely metal-poor galaxies
with HSC, PFS, and TMT
Tohru Nagao (Ehime U.)
Metallicity Measurements for Galaxies
Extremely Metal-Poor Galaxies (XMPGs)
Best Synergy: The HSC NB Dataset & PFS
Observational Strategy

NAOJ Mitaka, 10 Dec. 2010
PFS Science Workshop

Why Metallicity?

The Mass-Metallicity Relation in Galaxies

12+log(O/H)...suggesting theimportance of galactic
outﬂows (superwinds)

Gas-phase metallicity ofSDSS 53000 galaxies
at z~0.1
Tremonti et al. (2004)
log ( Mstar/Msun )The Mass-Metallicity Relation at Low-M
Lee et al. (2006)
SDSS

Extremely Metal-Poor Galaxies

XMPG
The M-Z relation extends
for 6 dex in stellar mass !!
(12+log(O/H)<7.6: XMPGs)

Chemical Properties of XMPGs: C
Pettini et al. (2008)
Garnett+99log (C/O)

12+log(O/H)=7.6log (C/O)

Red: DLAs
Black: Galactic stars

XMPG
7.0

7.5

8.0

8.5

9.0

12+log(O/H)

Enhanced C at low-Zgas??

Relation with CEMP stars?
High C-yield in PopIII stars??
(Cooke et al. 2011)
Relation with high L[CII]157um/LFIRat high-z (i.e., low-Zgas)?
(Maiolino, Nagao, et al. 2009)12+logO/H < 7.612+logO/H < 7.6(XMPGs)(XMPGs)log Fe/O

log N/O

Chemical Properties of XMPGs: N and Fe

higher Feabundance?
7.6<12+logO/H<8.2

log N/O

log Fe/O

7.6<12+logO/H<8.2

Large EW(Hb) objects show
smaller N/O and Fe/O ratios

12+logO/H > 8.2...but, how about XMPGs?

log N/O

log Fe/O

12+logO/H > 8.2

Time delay of N enrichment &Gradual grain destruction

oldyoung

EWrest(Hβ) (A)old EWrest(Hβ) (A)youngIzotov+06

XMPG Search: The Case of SDSS
Izotov et al. (2006):
Only 6 XMPGs in SDSS DR3 sample(~50000 galaxies !!!)
 success rate: ~0.01%...
# Izotov+: 136 [OIII]4363 detected, 6 XMPGs# literature:120 [OIII]4363 detected, 19 XMPGs

XMPG

Why is the search of XPMGs diﬃcult?

Nagao+06

Black: SDSS galaxies (Tremonti+04)
Green: SDSS low-Zgas sample (Izotov+06)
Red: Compiled from literature (Nagao+06)

XMPG Optical Spectrum

Fricke et al. (2001)

XMPG: Tol 1214-227
12+log(O/H)=7.52
Most of photons areemission lines, NOT
continuum emission!!
Broad-band selection(such as SDSS data)
fails to ﬁnd XMPGs...

x100[OIII]4363

Pre-selection with narrow-band data
should be the right way for XMPG search!

XMPG Search: The Case of NB Survey
Keck/DEIMOS ~1hr exposure[OIII]4363

V-bandR-band

NB912-band

I-bandz-bandKakazu et al. (2007)
NB816 & NB912, ~0.5 deg2
Selection criteria:
N816<25 & I-N816>0.8
N912<25 & z-N912>1.0
both corresponds to EWobs>100A[OII]3727, Hb, [OIII]5007, or Ha

Photometric sample of strong NB: 542
Targets for spectroscopic runs:
161[OIII]4363-detected objects:
17
Extremely metal-poor galaxies:
10
Success rate of the NB XMPG survey: 10/161 ~ 6%
XMPG number density: 542 x (10/161) x (1/0.5) ~ 67 deg-2
Target number density: 542 x (1/0.5) ~ 1000 deg-2

XMPG Search: The Case of HSCNB+PFS
HSC Ultradeep (3.5deg2)
NB526: mlim=26.8
NB717: mlim=26.4
NB816: mlim=26.6
NB921: mlim=26.4
NB973: mlim=25.0

HSC Deep (~28 deg2 ??)NB816: mlim=25.3
NB921: mlim=24.9

Depth: OK !!
30 deg2 for NB<25

XMPG survey with PFS~at 0.05 < z < 1.0~6hour/FoV x 18FoV = >15nights

Requirements to PFS~lambda coverage:
3900 - 9800A for O/H(3900 -13000A for N/H)
~lambda resolution: R=2000-3000~ﬁber number: >2000/FoV

Synergy with TMT~For detailed chemical composition
such as C, Fe, Cl, ...

 2000 XMPGs (among 3e4 obj.)

HSC for candidate selection
PFS for XMPG identiﬁcation
TMT for abundance studies

Summary
Extremely metal-poor galaxies: very early stage of chemical evolution~ abundance ratios tell us various info on early galaxy evolution~ only <50 XMPGs ever known
New XMPG survey by focusing on NB-selected galaxies at z<1~ to obtain statistical sample of XMPGs~ to go beyond 12+log(O/H)=7 (the current record is ~7.1)
for the study of possible “primordial” galaxies at z<1
Observational strategy:~ HSC: providing unique targets with NB (NB<25mag, 30deg2)~ PFS: identifying ~1000 XMPGs by detecting faint [OIII]4363
and measuring O, N, S, Ne elemental abundance ratios~ TMT: analyzing abundance ratios of C, Fe, Cl, Ar, ...
Requirements to PFS:
~ λ coverage: 3900A < λ < 9800A (or up to 1.3um for N/O)
~ λ resolution: R~2000-3000

Appendix

Metal-Poor Blue Compact Dwarf Galaxies
I Zw 18 (Aloisi et al. 1999)

247 reliable stars

10”

HST/WFPC2 F555W 6600sec

12+log(O/H)=7.2 (Zgas=0.02Zsun)

Presence of faint RGB/AGB stars

A Local “Primordial” Galaxy?

0.5-1 Gyr old (not primordial...)Gas-Phase Elemental Abundance Ratios

Izotov+06

Eﬀective Yield as a Function of Galaxy Mass
Tremonti et al. (2004)

Z= y ln(μgas-1) for closed-box
 yeﬀ: eﬀective yield strong superwind at low-M