Okayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

KOOLS-IFU followup observations of extremely strong
emission line galaxies discovered with Subaru/HSC
Kiyoto Yabe (UT/Kavli IPMU)
Collaborators: Yuichi Harikane, Takashi Kojima, Yoshiaki Ono, Masami Ouchi,
Takatoshi Shibuya, Yi-Kuan Chiang (ICRR), Masao Hayashi, Kazuya Matsubayashi,
Masayuki Tanaka (NAOJ), Ikuru Iwata, Yuko Kakazu, Chien-Hsiu Lee, Ichi Tanaka(Subaru), Rhythm Shimakawa (UCSC), Kazuhiro Shimasaku (Tokyo), Tohru Nagao(Ehime), Daichi Kashino (ETH Zurich), Ai Lei Sun, Yoshiki Toba (ASIAA), Jenny Greene,
Michael Strauss (Princeton), Marcin Sawicki (St. Mary’s)

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to scale our N2-based oxygen abundance estimates to those exOkayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)
pected from the theoretical calibration (their Table 3). In doing
so, we obtained a mean difference of 0.23 dex, which is notenough to explain the largest offset in O/H shown in Figure 1.
■ Low-mass galaxies with strong emissionWelinesconclude that GPs are genuine metal-poor galaxies with low
Important to understand the formationand evolution
extinction
values. galaxies in the early phase

Background:‣ Diﬃcult to examine in details at very high redshift‣ Examine similar galaxies at lower redshift
3.2. N/O Ratios and Metallicity‣■ Narrow/Intermediate band excess galaxiesTheat z<1(e.g., Kakazu+07,16)
nitrogen-to-oxygen
ratio Ly+14,
is a powerful
evolutionary

indicator
in galaxies(Pilyuginal. 2004;
Mollá et al. 2006).
■ Broad band excess galaxies in SDSS sample
so-called"GreenPeaet(GP)"(Cardamone+09)
We havethe relation between the N/O ratio andLow stellar mass and high star-formation
rateinvestigated(SFR)
the oxygen abundance for the sample of GPs, LBAs, andHigh [OIII]/Hβ emission line ratio
the SFGs taken from the SDSS in Figure 2. For the SFGs,
Metal poor
we found a positive trend with an increasing scatter toward■ Deep and wide Subaru/Hyper Suprime Cam(HSC)
datacan reflecting
provide us
galaxysampleatthe metal-richregimebothprimaryand secondary
production
nitrogen inlinethecomparedsame metallicity
lowhigher redshift with lower stellar mass andstrongerofemission
to therange.
SDSSAtGPs‣‣‣

metallicities the trend flattens out, possibly a consequence ofnitrogen being of primary origin, coming mainly from massive

L2u
Ttdu
u
2w
sfa
Nb
Gs(txies

galaF
S
la
ormrm
nonal
SF
esxi

laga

GPs

g+r+i
Izotov+16
Cardamone+09

Figure 3. M⋆ vs. O/H (left) and M⋆ vs. N/O (right). Symbols stand for the same type
Amorin+10in the M⋆ –Z plane, green and black lines indicating second-order polynomial fits to theOkayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

Subaru Hyper Suprime-Cam (HSC):
M31 in one shot

Wide field (1.5 deg diameter) optical imagerof Subaru 8.3m Telescope3

Okayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

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Sample selection:■ HSC SSP data (planned)
HSC-Wide: ~1400 deg2, rlimit~26 AB
HSC-Deep: ~27 deg2, rlimit~27 AB
HSC-UltraDeep: ~3 deg2, rlimit~28 AB
All 5 broad-band data will be available■ Internal data release (S16a) is used
HSC-Wide coverage: ~300 deg2
■ Broad band excess by strong emission lines
Similar techniques to SDSS GPs
Tentative selection criteria are usedi-band excess from r-i vs. i-z (iGPs)
z-band excess from i-z vs. z-y (zGPs)
z<26 AB (for iGPs) and y<26 AB (for zGPs)■ The rest-frame emission line equivalent widthof EWrest > a few x 100 Å■ Very compact (almost point sources)‣‣‣‣‣‣‣‣‣‣

z=22.1r+i+zExtremely strongemission line galaxies

y=24.4i+z+yy=23.5i+z+y

y=24.0i+z+yOkayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

5Spectroscopic observation:■ Spectroscopic observation
Gemini/GMOS-S (in Gemini Fast Turnaround program)
R150_G5326 (R~700), λ=5000-10000Å, MOS mode
Total on-source exposure time of each object is 3600 sec.
40 objects were observed in total■ Detected multiple emission lines from 19 objects at z=0.3-0.85■ A weak [OIII]λ4363 emission line is detected significantly from 4 objects■ [OIII]λ5007 EWrest is 100 Å - 2000 Å (extremely strong emission line)‣‣‣‣

Extremely strongemission line galaxies~2000 Å~100 ÅOkayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

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Stellar mass and star formation rate:■ Stellar mass is derived from SED fittings using broad-band photometry after subtracting thecontribution from the emission lines■ Dust extinction is derived from Balmer decrements using Hβ, Hγ, Hδ if possible■ Star formation rate (SFR) is derived from the extinction corrected Hβ luminosityStellar mass - SFR diagram■ Stellar mass vs. SFR diagram (socalled main sequence of galaxies)■ Our sample shows higher SFR byup to 1000x compared to normal
star-forming galaxies at the similar
redshiftOkayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

7Oxygen abundance:■ The "direct" method for gas phase metallicity measurements if [OIII]λ4363 is detectedElectron temperature measured from [OIII]λ4363/[OIII]λ5007
We follow Izotov+06 for the "direct" method■ The "strong line" method if [OIII]λ4363 is not detected
KK04 (Kobulnicky&Kewley04; theoretical approach) is used (R23 indicator)~0.3-0.7 dex overestimated compared to the "direct" method --> correction■ The oxygen abundance of our sample: 7.3 (extremely metal poor) < 12+log(O/H) < 8.3■ The mass-metallicity relation (MZR) is the extension of the MZR of the SDSS GPs towards
lower stellar mass
■ The fundamental metallicity relation (FMR; SFR dependence of the MZR) is in roughagreement with the local (SDSS) FMR‣‣‣‣

mass-metallicity relation
SDSSSDSS GPs

fundamental metallicity relation
SDSS

Okayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

8Ionization state:■ Ionization diagnostics by using emission line ratios
R23 index (metallicity) vs. O32 index (ionization parameter)
Our sample is very high [OIII]λ5007/[OII]λ3727 ratio, which is comparable or higher thanthat of the SDSS GPs and other emission line galaxies at the similar redshift
The high [OIII]λ5007/[OII]λ3727 is originated from high ionization parameter
The high ionization parameter of our sample may be due to high SF activity?

‣‣‣‣

low-Z

metallicit

yhigh-Z

SDSS

R23

O32

O32

ionization p

CLOUDY
photoionization
modelarameter

high-q

low-q
SDSS

R23

Solid: SB99
Dashed: BPASSv2

Okayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

9Follow up observations with 3.8m KOOLS-IFU:■ A normal way of follow-up observations may be:
Find out interesting objects by using small/middle-class telescopes
Observe them by using larger telescopes■ We take an opposite strategy to observe interesting objects (strong emission line galaxies)
found with an 8m-class telescope (Subaru) and a wide FoV camera (HSC) by using a smaller
telescope (3.8m telescope)■ Optical instruments of large telescope are very competitive■ The advantage of our sample is that they are very bright emission line galaxies■ Because they are "rare" objects with very low density (~1 deg-2 for extremely strong emission
line galaxies) on the sky, we do not need MOS‣‣Okayama 3.8m

Subaru 8.3m

Follow-upOkayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

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Follow up observations with 3.8m KOOLS-IFU:■ Specification of 3.8m/KOOLS-IFUIFU unit with 127 fibers (but our targets are basically point sources)
Wavelength coverage: 4000 - 9000 ÅResolution: R~400-1600
Sensitivity: ~3×10-16 erg s-1 cm-2 (1 hour, S/N=5)■ Simulated spectrum of a bright zGP at z=0.6■ We will plan to use No.2 grism (λ=5000-9000Å, R~700)■ We will detect [OII]λ3727 (S/N~7), Hβ (S/N~6), [OIII]λ5007 (S/N~55) in 2-hour exposure■ In 10 nights, we will observe 30 objects in total (25% overheads are assumed), which expands
our sample of extremely strong emission line galaxies by a factor of ~10‣‣‣‣

Gemini/GMOS-S
1-hour exposure

3.8m/KOOLS-IFU
2-hour exposure(simulated)Okayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

11Follow up observations with 3.8m KOOLS-IFU:■ Specification of 3.8m/KOOLS-IFUIFU unit with 127 fibers (but our targets are basically point sources)
Wavelength coverage: 4000 - 9000 ÅResolution: R~400-1600
Sensitivity: ~3×10-16 erg s-1 cm-2 (1 hour, S/N=5)■ Simulated spectrum of a bright zGP at z=0.6■ We will plan to use No.2 grism (λ=5000-9000Å, R~700)■ We will detect [OII]λ3727 (S/N~7), Hβ (S/N~6), [OIII]λ5007 (S/N~55) in 2-hour exposure■ In 10 nights, we will observe 30 objects in total (25% overheads are assumed), which expands
our sample of extremely strong emission line galaxies by a factor of ~10‣‣‣‣[OII]3727Gemini/GMOS-S
S/N~71-hour exposure

Hγ, [OIII]4363

non-detection ...

Hβ, [OIII]4959,5007
S/N~6S/N~55

3.8m/KOOLS-IFU
2-hour exposure(simulated)Okayama Users Meeting 2017 @NAOJ, 2017/09/04, Kiyoto Yabe (Kavli IPMU)

Summary:■ Extremely strong emission line galaxies discovered by using Subaru/HSC■ Follow up observation by using Gemini/GMOS-S to examine detailed properties
Very low-mass and high SFR
Metal poor comparable to local extremely metal poor galaxies
High [OIII]λ5007/Hβ and [OIII]λ5007/[OII]λ3727 indicating high ionization parameter■ Because they are very bright, these galaxies will be a good target for 3.8m/KOOLS-IFU■ We expect to detect some lines ([OII]λ3727, Hβ, [OIII]λ4959,5007) in 2-hour exposure■ We can expand our existing sample by a factor of ~10‣‣‣12