第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

Search for extremely strong emission line galaxies
at z < 1 using Subaru/HSC
Kiyoto Yabe (UT/Kavli IPMU)
Collaborators: Takashi Kojima, Yoshiaki Ono, Takatoshi Shibuya, Yuichi Harikane,
Yi-Kuan Chiang, Masami Ouchi (ICRR), Masao Hayashi, Kazuya Matsubayashi,
Masayuki Tanaka (NAOJ), Ikuru Iwata, Yuko Kakazu, Chien-Hsiu Lee, Ichi Tanaka(Subaru), Rhythm Shimakawa (UCSC/Subaru), 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)

1LBAs), and the MPA–JHUtoscale
ourN2-based
oxygenabundance
estimates
tothoseex第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)
2using spectral energy distrib
pected from the theoretical calibration (their Table 3). In doing
Thus, stellar masses are eso, we obtained a mean difference of 0.23 dex, which is not
typical dispersion of ∼0.2
enough to explain the largest offset in O/H shown in Figure 1.
der Wel et al. 2006). This
■ Properties of galaxies
at veryhigh
We conclude
that GPs
areredshift
genuine metal-poor galaxies with low
uncertainties of 0.3 dex quextinction
values.
Important to understand the early phase of the galaxy formation andevolution
uncertainties
in their star fo2009).
Observationally diﬃcult 3.2.
dueN/Oto their
Ratiosfaintness
and Metallicity
In the M⋆ –Z plane, SDS
Examine similar galaxies at lower redshift
The nitrogen-to-oxygen ratio is a powerful evolutionary
which flattens toward highe■ Galaxy populations
atz<0.3suchas"GreenPeas(GPs)"(Cardamone+09)
andindicator in galaxies (Pilyugin et al. 2004; Mollá et al. 2006).
scatter atlower masses, inrecently found "BlueberryGalaxies(Yang+17)
We have investigatedthe (BGs)"
relation between
the N/O ratio andfor local galaxies (e.g., Tre
the oxygenabundance
for the sample
GPs, LBAs,
LBAs increase their m
Low stellar massand highstar-formation
rateof(SFR): Highand
specificand
SFR
SFGs taken
Nevertheless, GPs lie mor
Very strong theemission
linesfrom the SDSS in Figure 2. For the SFGs,
we found a positive trend with an increasing scatter toward
below the MZR of SDSS
High [OIII]/Hβratio
theemission
metal-rich line
regimereflecting both primary and secondary
GPs are systematically mor
Metal poor production of nitrogen in the same metallicity range. At low
similar shift in the MZR has(log(M⋆ ) " 10) LBAs (HooCompact metallicities the trend flattens out, possibly a consequence ofnitrogen being of primary origin, coming mainly from massive
this work). In terms of stella

Background:‣‣‣‣‣‣‣‣■ Low-z analogue to primordial galaxies?
rmnoalaxie
gFSlnormasalSDSS-GP

SF

Cardamone+09

metallicity

esxi

laga

BPT diagram

GPsg+r+istellar mass

Izotov+16

Figure 3. M⋆ vs. O/H (left)
and M⋆ vs. N/O (right). Symbols stand for the same type of objects as described in Figure 2Amorin+10
in the M⋆ –Z plane, green and black lines indicating second-order polynomial fits to the GPs and SFGs, respectively, have

第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

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Background:"very low-z""very high-z"
CR7 (LAE@z=6.6)

SDSS-BGs
g+r+i
SDSS-GPs?
z+NB921+yg+r+i■ Missing link between very high-z(such as LAEs) and very low-z (GPs and BGs)
■ Narrow/Intermediate band excess galaxies at z<1 (e.g., Kakazu+07, Ly+14, 16)■ The sample size of (especially extreme) objects is limited■ Systematic search of lower stellar mass and stronger emission line galaxies atz>0.3 with deep and wide Subaru/Hyper Suprime Cam (HSC) data

第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

4Sample selection:■ Detecting broad-band excessdue to strong emission lines
Similar technique to theSDSS GPs (with strong [OIII]emission line)
HSC 5 broad-band filters(g, r, i, z, y)r-band excess (rGPs@z~0.3)
i-band excess (iGPs@z~0.6)
z-band excess (zGPs@z~0.8)■ More quantitatively, two-color
diagrams are used to detect thebroad-band excess (see next)

HCS filter set with GP template‣‣‣‣‣(SDSS-BG)

r-band excess: rGPs(SDSS-GP)

i-band excess: iGPs

z-band excess: zGPs

g+r+i
SDSS-GPs

g+r+i
SDSS-BGs第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

5Sample selection:■ HSC SSP internal data release (S17a)
HSC-Wide: ~500 deg2, rlimit~26 AB
HSC-Deep: ~27 deg2, rlimit~27 AB
HSC-UltraDeep: ~3 deg2, rlimit~28 AB■ Broad-band excess by strong emission lines
r-excess from g-r vs. r-i (rGPs@z~0.3)
i-excess from r-i vs. i-z (iGPs@z~0.6)
z-excess from i-z vs. z-y (zGPs@z~0.8)■ The expected EWrest > 100 Å■ The number density = ~20 deg-2 (EW>1000Å)
to ~400 deg-2 (EW>100 Å)■ Very compact appearance‣‣‣‣‣‣

z=22.1

r+i+zi - z color

z-band excess (zGP) selectionz - y color

y=24.4i+z+y

y=23.5i+z+y

y=24.0i+z+y第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

6

Follow-up spectroscopic observation:■ Follow-up spectroscopic observations are on going
Filler targets in several Subaru/FOCAS observations
Main sample in Gemini/GMOS-S observation
Main sample in the coming Subaru/FOCAS observation in July
■ Spectroscopic redshift confirmation for ~100 objects at z=0.3-0.85■ Detection rate is higher for objects far from the selection criteria‣‣‣

spec- z distribution

two-color diagram for zGPs
filled: confirmed
open: non-detection

第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

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Follow-up spectroscopic observation:■ Very high [OIII]λ5007 equivalent width (EW)
EWrest range from 100 Å to 3000 ÅIn agreement with model predictions■ A weak [OIII]λ4363 emission line isdetected significantly from 5 objects‣‣An example of the GMOS-S spectra in 1 hourintegration

EW([OIII]) vs. excess color
black line: prediction using
SDSS-GP template

We will show some results
obtained with Gemini/GMOS-S第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

8Stellar mass and star formation rate:■ Stellar mass: from SED fittings
after subtracting the contribution
from the emission lines■ Dust extinction: from Balmer
decrements using Hβ, Hγ, Hδ (ifpossible)■ Star formation rate (SFR): fromthe extinction corrected Hβluminosity■ Very low stellar mass
■ Very high SFR (up to 1000x
higher than normal galaxies)

Stellar mass - SFR diagram第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

9AGN emission line ratio diagnostics:■ BPT diagnostics cannot be used because no [NII]/Hα ratio is available■ Stellar mass vs. [OIII]/Hβ (MEx) diagram (e.g., Juneau+14)

Mass Excitation (MEx) diagram
AGN-S

F separation

SDSS■ Our sample is basically within
SFG region on the MEx diagram■ Our sample shows smaller stellar
mass and higher [OIII]/Hβ ratio
than normal SDSS galaxies atz~0.1 and comparable [OIII]/Hβratio to the SDSS GPs and BGs第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

10Metallicity (oxygen abundance):■ The "direct" method if [OIII]λ4363 is detected"Te" measured from [OIII]λ4363/[OIII]λ5007
Following Izotov+06 method■ The "strong line" method if [OIII]λ4363 is not detected
KK04 (Kobulnicky&Kewley04) is used (R23 indicator)~0.3-0.7 dex overestimated compared to the "direct" method --> "correction"■ 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■ The fundamental metallicity relation (FMR; SFR dependence of the MZR) is in roughagreement with the local (SDSS) FMR

‣
‣
‣
‣

mass-metallicity relation

fundamental metallicity relation

SDSSSDSS

metallicity

metallicity

SDSS GPs第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

11Ionization state:■ Ionization diagnostics
R23 index (metallicity sensitive) vs. O32 index (ionization parameter sensitive)‣■ Very high [OIII]λ5007/[OII]λ3727
Comparable or higher than thatof the SDSS GPs and otheremission line galaxies at thesimilar redshift
Comparable to the LAEs atz=2-4‣

R23 ([OIII]+[OII]/Hβ) vs. O32 ([OIII]/[OII])O32‣

SSSDR23

第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

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Ionization state:■ Ionization diagnostics
R23 index (metallicity sensitive) vs. O32 index (ionization parameter sensitive)‣■ Very high [OIII]λ5007/[OII]λ3727
Comparable or higher than thatof the SDSS GPs and otheremission line galaxies at thesimilar redshift
Comparable to the LAEs atz=2-4‣

R23 ([OIII]+[OII]/Hβ) vs. O32 ([OIII]/[OII])‣eteraramionization p‣‣‣q = 7.0 - 8.5
dashed: SB99
solid: BPASSv2

O32■ Comparison to photoionization
models using CLOUDY (c17.00)
Explained by models with very
high ionization parameters
Some cannot be explained by
the normal models
Harder ionizing spectra may berequired?

high-q0.07ZsunR230.1Zsun
0.2Zsunlow-q

0.4ZsunSSSD

第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

13What is the ionization source?:■ Weak HeII λ4686 emission line is detected in the stacked spectra■ What is the origin of HeII λ4686 ?
Wolf-Rayet (WR) or very hot O-star?
Contamination of weak AGN?
High-Mass X-ray Binary?
Shock by SNe / galactic wind?
■ Models with very hot WR (Jaskot & Oey 13) can explain the observed [OIII]/[OII] and HeII4686/Hβ emission line ratio■ Contribution of WR stars is large‣‣‣‣

Jaskot & Oey 13
HeII 4686
Our sample

HeII/HβSDSS
extreme GPs

O32第5回 銀河進化研究会@愛媛大学 (Kiyoto Yabe, Kavli IPMU)

Summary:■ Systematic Search for extremely strong emission line galaxies with Subaru/HSC■ Follow-up spectroscopy using Subaru/FOCAS Gemini/GMOS-S is ongoing
multiple emission lines from ~100 objects at z=0.3-0.85
EWrest([OIII]λ5007) = 100 - 3000 Å[OIII]λ4363 detections from 5 objects■ From our GMOS-S run, we found the following:
Very low-mass and high SFR (i.e., very high sSFR)
Possibility of AGN is low
Metal poor comparable to local extremely metal poor galaxies
High [OIII]λ5007/Hβ and [OIII]λ5007/[OII]λ3727: high ionization parameter
Possibility of a large contribution from WR stars to the obtained line ratio‣‣‣‣‣‣‣‣

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