Daichi Kashino Nagoya

Transcription

1 21 Feb. 2014, Hokkaido Univ. The impact of galactic structure on star formation Properties of star-forming galaxies at z~1.6 revealed by FMOS-COSMOS survey Daichi Kashino Nagoya FMOS-COSMOS team J. Silverman IPMU, G. Rodighiero INAF, A. Renzini INAF N. Arimoto NAOJ, E. Daddi CEA/Saclay, D. Sanders Hawaii, J. Kartaltepe Hawaii J. Zahid Hawaii, M. Onodera ETH, H. McCracken IAP, et al.

2 FMOS-COSMOS Survey New Results Dust properties of high-z SF galaxies Hα-based star-forming main sequence Kashino, Silverman, Rodighiero et al., 2013, ApJL Mass-metallicity relation Zahid, Kashino, Silverman et al., arxiv: submitted to ApJ

3 Outline 1. Introduction Background & Motivation 2. Observation & Data 3. Results & Discussions Dust extinction properties Star-forming main sequence Mass-Metallicity relation 4. Summary

4 Introduction Background & Motivation

5 Introduction Observation & Data Results & Discussions Summary Key questions in galaxy evolution What triggers/prevents star formation activities in galaxies? What is the role of the environment where the galaxy lives? How is the redshift evolution? It is essentially important to disentangle relations between SF and other galactic properties.

6 Introduction Observation & Data Results & Discussions Summary For star-forming galaxies, tight Mstar-SFR relations have been reported. e.g., Noeske+07, Elbaz+07, Daddi+07, Pannella+09, Rodighiero+11 How does the relation evolve with redshift? Does environment impacts on the relation? SFing galaxies standard mode of star formation Star forming main sequence

7 Introduction Observation & Data Results & Discussions Summary Problematic points & Motivation many different SFR indicators are used (e.g., UV, FIR, 24μm) the redshift desert (1.4<z<2.0) For high-z star forming galaxies, Measure SFR based on a well-calibrated indicator Hα emission Beyond z~0.5, Hα is redshifted to the NIR, so one had to rely on other SFR indicators previously...

8 Introduction Observation & Data Results & Discussions Summary Near IR spectrographs on largest ground-based telescopes have been started fully Subaru/FMOS Keck/MOSFIRE VLT/KMOS

9 Introduction Observation & Data Results & Discussions Summary Fiber Multi-Object Spectrograph FMOS can observe 400 galaxies simultaneously Subaru/FMOS 30 diameters Very wide FoV of 30 diameters

10 Introduction Observation & Data Results & Discussions Summary Fiber Multi-Object Spectrograph FMOS can observe 400 galaxies simultaneously Subaru/FMOS FMOS is best suited for our purpose, to survey a lot of Hα emitting galaxies at redshift desert. Hα + [NII], Hβ, [OIII], etc diameters redshift, SFR, dust, metallicity, AGN indicator etc... Very wide FoV of 30 diameters

11 Observation & Data

12 Introduction Observation & Data Results & Discussions Summary #2 #1 #3 #4 COSMOS Field

13 Introduction Observation & Data Results & Discussions Summary Mar Jan. 2013: 12 nights High-resolution mode (R~2200) Exp. time 3-5 hours #2 #3 #1 BzK-selected SFing galaxies #4 OSMOS Field McCracken+10

14 Introduction Observation & Data Results & Discussions Summary Wavelength range Observed spectra H-long ( μm) Hα [NII] J-long ( μm) Hβ [OIII]

15 Results & Discussions

16 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Differential extinctions toward Continuum (stars) and Emission lines (HII regions) Extinction toward Emission lines toward Continuum For nearby starbursts, f = 0.44 Calzetti+00 Is this valid for high-z galaxies? Now different values b/w 0.44 and 1.0 are suggested for high-z e.g. Förster Schreiber+09, Wuyts+11, Mancini+11, Reddy+10, Onodera+10, Pannella+in prep, Wild+11, Price+13

17 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Estimate the factor f Line-Extinction Continuum-Ext. measure the line-extinction from the Balmer decrement (Hα/Hβ), compare it with the continuum-extinction. Stack the individual spectra with Ha detection Observed value Line-extinction Reddening curve Theoretical value

18 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Stacked spectra in three bins of continuum-extinction, which consist of 30 individual spectra each Hβ Hα

19 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Results Line-Extinction Continuum-Ext. based on the Balmer decrement FMOS sample agrees with low-z s, but more attenuated at high mass Line-ext. AHα Continuum-ext.

20 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Discussion f~0.8: greater than 0.44, close to 1.0 Extinctions toward Continuum and Emission lines from HII regions are more similar to each other What pictures does this indicate?

21 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Speculations for the similar continuum/line-extinction Light from young stars in HII reg. might contribute largely to the continuum Dust might distribute more smoothly birth-cloud dust Nearby SF galaxy e.g., Price+13 High-z SF galaxy Contribution of young star s light Small Large diffuse dust Contrast of dust distribution Strong Weak

22 Results & Introduction Discussions Dust Observation extinction & / Data Star-forming Results main & sequence Discussions / MZ relation Summary Summary Speculations for the similar continuum/line-extinction Evolution of the differential scale-height structure surface Differential heights for different components e.g., Wild+04, Older stars Continuum Gas, Dust Young stars, star-forming regions bottom e.g., Tuffs+04, Emission lines Continuums from stars near the surface are less attenuated Continuum-extinction < Line-extinction

23 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Speculations for the similar continuum/line-extinction Evolution of the differential scale-height structure e.g., Wild+04, If the scale-height of older stars is smaller, Continuum-extinction becomes more similar to the line-extinction. surface Older stars Gas, Dust Young stars, star-forming regions bottom This picture implies that the differential scale-height structure evolves with the galaxy age.

24 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Speculations for the similar continuum/line-extinction Evolution of the differential scale-height structure e.g., Wild+04, If the scale-height of older stars is smaller, Continuum-/Line-extinctions are similar to each other. Older stars Gas/Dust Note: These are very speculative pictures. More detailed studies are needed! e.g., time evolution of extinction law, internal galactic structures,... Young stars, star-forming regions This picture implies that the differential scale-height structure evolves with the galaxy age.

25 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Star forming main sequence at z~1.6 Slope logsfr at M sun 11Gyr ago x20 higher Daddi+07 Zahid+12 Elbaz+07 Today

26 Results & Discussions Dust extinction / Star-forming main sequence / MZ relation Summary Metallicity Indicates how the galaxy grow can measured from [NII]/Hα High-z galaxies might be younger, so their metallicities might be small... Hα [NII] FMOS (HR) can separate the two lines completely.

27 Results & Introduction Discussions Dust Observation extinction & / Data Star-forming Results main & sequence Discussions / MZ relation Summary Summary Mass-Metallicity relation based on [NII]/Hα Massive galaxies might have evolved more fully at this era local relation (SDSS) FMOS sample z~1.6 Small galaxies will keep SF, and grow from now

28 Results & Introduction Discussions Dust Observation extinction & / Data Star-forming Results main & sequence Discussions / MZ relation Summary Summary Mass-Metallicity relation based on [NII]/Hα Massive galaxies might have evolved more fully local relation (SDSS) Down-sizing scenario Large galaxy Grow up rapidly and stop SF earlier Small galaxy keep SF for long-time and grow up gradually z~1.6 (10Gyr ago) Small galaxies will keep SF, and grow from now

29 Introduction Observation & Data Results & Discussions Summary Summary Dust extinction in high-z galaxies dissimilar to that of local universe might indicate evolution of dust distribution and/or scale-height structure Star-forming main sequence at z~1.6 measured based on Hα first x20 higher relative to the local relation Time evolution of MZ relation measured based on [NII]/Hα indicate that massive galaxies have already fully-matured 10 Gyrs ago support the down-sizing idea