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SXDF-ALMA 2 arcmin2 Deep Survey:Millimeter Line-Emitter SearchNRO-ALMA Science/Development Workshop 2016July 20, 2016Institute of Astronomy, the University of Tokyo D1Yuki Yamaguchi
Today’s outline
• Introduction-Why FIR-to-millimeter emission lines?-Previous studies-Our study
• Observation-Observation field-Observation parameters
• Millimeter line-emitter search-Methods-Results
• Discussion
• Summary
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Introduction
Burgarella + 2013 Walter + 2013
• The evolution of the cosmic SFRD has been studied-Problems
üWhat is the role of dust-obscured star formation at high-z(especially z > 3-4)?
üWhy the cosmic SFRD decline from z ~ 2 to z ~ 0?ØBecause of declining molecular gas mass density?
p Studying dust-obscured star formation activity at high-zand molecular gas mass density in the universevia FIR-to-millimeter lines is one of the promising tools!
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De Looze + 2014
• Star formation activities at high-zè [CII] 158 μm line
-A tracer of SFRs-One of the brightest
FIR fine structure lines
• Molecular gas mass density in the universeèCO rotational transition lines
-A tracer of molecular gas mass in a galaxy
• The evolution of [CII] or CO luminosity functionis critical to understand cosmic star formation history
Introduction “FIR-to-millimeter line”
log L[CII] [L⦿]
log
SFR
[M⦿/y
r]
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Introduction “Previous studies”
Walter + 2014
• Many previous observations are biased
-Follow-up observation of pre-selected sources(e.g., optical/NIR selected galaxies)üBased on stellar mass or star formation properties
è Un-biased searches are needed!
• Un-biased line-emitter searches-Serendipitous detection
üe.g., Tamura + 2014
-CO emitter searches using PdBIüe.g., Walter + 2014
ØDifficult to detect!Velocity [km/s]
Flux
den
sity
[mJy
]
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Introduction “In this study”
• Un-biased millimeter line-emitter search using ALMA-ALMA is more sensitive than PdBI
ü> 3 times (@ Band 6; ~ 1 mm)üMore efficient search
• SXDF-UDS-CANDELS-ALMA deep survey data-Multi-wavelengths properties of line-emitters
üe.g., redshift, stellar mass
-Constraint on line luminosity function
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Observation “Field”
• SXDF-UDS-CANDELS field-We can use deep multi-wavelengths images
üe.g., Subaru, HST, VLT, Spitzer, Herschel, JVLA
-The submm galaxy selected by AzTEC/ASTE(Ikarashi PhD thesis)
-There are many star-forming galaxies (e.g., HAEs)AzTEC 1.1 mm SPIRE (HerMES) IRAC (SEDS; SpUDS) Subaru (SXDS)
1.1 mm
250 μm350 μm500 μm
3.6 μm4.5 μm5.6 μm
BVRc
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Observation “Parameters”• Observation parameters–ALMA Cycle 1 (Band 6; 1.1 mm, 2.0 arcmin2)
• Project ID: 2012.1.00756.S, PI: K. Kohno
–Date: 2014 7/17, 7/18–# of antennas: 30-32–Baseline lengths: 20-650 m–PWV: 0.42-0.55 mm
Credit: NAOJ
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Millimeter line-emitter search “Method”
• We made 3D data cube using CLEAN algorithm- 60 MHz binning (~ 65 km/s @ 275 GHz)- 1σ ~ 0.45-0.70 mJy/beam
• We search for line-emitter candidate with peak S/N > 5using CLUMPFIND (Williams + 1994)
CO(3-2)
CO(4-3)
CO(5-4)
CO(6-5)
CO(7-6)
CO(8-7)
CO(9-8)
CO(10-9)
[CII] 158 µm
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Millimeter line-emitter search “Results”
Speak = 3.8 ± 0.7 mJy/beam (5.4σ) SΔv = 0.53 ± 0.08 Jy km/s (6.6σ)νobs = 273.29 GHzNo continuum counterpart at 1.1 mm
5σline-emitter
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Discussion “Line identification”
• Optical-to-NIR counterpart candidate
-Estimation of photometric redshift using SED fitting
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Discussion “Line identification”
• Optical-to-NIR counterpart candidate
-Estimation of photometric redshift using SED fittingüCO(4-3) emitter @ z = 0.687, if the counterpart is real
ØL’CO(4-3) = (8.3 ± 3.8) × 108 [K km/s pc2]
zphoto = 0.97+0.13-0.40
MW like M82 likeL’CO(1-0)
[K km/s pc2](4.9 ± 2.2)× 108
(0.98 ± 0.44)× 108
Mgas[M¤]
(20 ± 9)× 109
(0.78 ± 0.35)× 109
M★[M¤]
(3.5+5.4-1.0 )
× 108
MWlike:L’CO(4-3) / L’CO(1-0) = 0.17, αCO = 4 M¤ [K km/s pc2]-1M82 like: L’CO(4-3) / L’CO(1-0) = 0.85, αCO = 0.8 M¤ [K km/s pc2]-1
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Discussion “Molecular gas fraction”
• Molecular gas fraction; fgas = Mgas / (Mgas + M★)- fgas = 0.98 (MW), 0.68 (M82)
• We detect gas rich galaxy with M★ ~ 108.5 M¤
- cf. local dwarf galaxies; M★ ~ 108-9 M¤
• Consistent with the relationfrom Kennicutt-Schmidt law(Popping + 2012)
è the relation is alsosupported from gasobservation
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Discussion “Molecular gas fraction”
• Molecular gas fraction; fgas = Mgas / (Mgas + M★)- fgas = 0.98 (MW), 0.68 (M82)
• Comparing with semi-analytic models (SMAs)
-Obreschkow + 2009, Lagos + 2012üExtremely gas rich
• CO search with ALMA
-Gas rich galaxywith small M★üThey have been missed
in previous studies
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Discussion “CO luminosity function”
• Consistent with SAMs-Obreschkow + 2009, Lagos + 2012-Faint end of CO luminosity function is dominated by
main sequence star forming galaxies?
CO(4-3) LF @ z ~ 0.7
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Discussion “[CII] at z = 5.95?”
• If optical/NIR counterpart is not real…
- [CII] 158 μm @ z = 5.95
• How to confirm?-Spectroscopic observation using ALMA!
üCO(5-4) @ z = 0.687 and [NII] 122 μm @ z = 5.95 can beobserved with only single frequency setup (Band 7)
Observed frequency
CO(5-4) at z = 0.687[NII] 122 μm at z = 5.95
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Summary
• We detect a millimeter line-emitter using SXDF-ALMA2 arcmin2 deep survey data
-CO(4-3) @ z = 0.687-Small stellar mass (M★ ~ 108.5 M¤) and
high molecular gas mass fraction (fgas = 0.98, 0.68)- Luminosity function è Consistent with SAMs
• Confirmation of the detected line
- [CII] 158 μm line @ z ~ 5.95 is also bright-Spectroscopic observation using ALMA
üCO(5-4) @ z = 0.687 and [NII] 122 μm @ z = 5.95 can beobserved with only single frequency setup (Band 7)
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