Chap.6 Formation and evolution of Local Group galaxies

Transcription

1 Chap.6 Formation and evolution of Local Group galaxies Properties of LG galaxies Formation history of LG galaxies Models to solve missing satellites problem Formation of Andromeda galaxy Future prospects 1

2 6.1 Properties of LG galaxies MW M31 isolated 2

3 Structures of various types of galaxies (Tolstoy+09, ARAA, 47, 371) Ultra Faint Dwarfs (UFDs) dwarf galaxies: Mv > -17 and more spatially extended than globular clusters with gas: dirr, without gas: dsph 3

4 Milky Way & Galactic satellites 4

5 Local Group 5

6 A new, faint and old D=150kpc discovered from SDSS data (Sakamoto & Hasegawa 2006) All stars RGB HB Control field (1 deg distance from the center) (Within a 2.5 radius circle) 6

7 Field of Streams and new satellites in SDSS data (Belokurov et al. 2006) 7

8 Light distribution of star clusters and dsph M31; MWG; Other Nuclear clusters, UCDs, M/L ~ 3 Globular clusters Tidal tails star clusters dsph galaxies Gilmore, Wilkinson, Wyse et al 2007 ApJ

9 HST photometry of LG galaxies 9

10 6.2 Formation history of LG galaxies Leo D=260kpc Low SFR lasting over ~10Gyr Metallicity & Age are degenerated Spectroscopy 10

11 D=138 kpc Buonanno (from HST image) de Boer+2012 (from CTIO image) [Fe/H]=

12 Star formation histories of LG dwarf galaxies Grebel 1997, Reviews in Modern Astronomy, 10, 29 12

13 13

14 Star formation history of dsph galaxies Grebel & Gallagher 2004, ApJ, 610, L89 14

15 HST/WFPC2 results (Weisz et al. 2014) 15

16 α-elements in the stars of dsph galaxies (Venn et al. 2004, AJ, 128, 1177) Halo Retro Thick Thin dsph 16

17 Sculptor Keck/DEIMOS spectroscopic survey by Kirby+09,11 Metallicity Distribution Functions in several dsphs slit mask 17

18 [α/fe] ratios in several classical dsphs (Tolstoy+ 2009) 18

19 List of known UFD galaxies 19

20 C-M diagram for UMaI (Okamoto+08 from Subaru/Suprime Cam) UMaI is as old as 14 Gyr 20

21 HST results by Brown+2012 UFDs are very old systems (as old as M92) Synchronization of SF truncation within ~1 Gyr?

22 Metallicity vs. luminosity relation UFDs appear to show different metallicities 22

23 Kirby+ 08 Assembly of the stars in ultra-faint dwarf galaxies reproduces the MW halo Tolstoy +08 UFDs show similar abundance pattern to the metal-poor MW halo 23

24 Gilmore et al. 2007, ApJ, 663, 948 Dark matter distribution obtained from velocity dispersion profile DM dominated (M/L) = 10 2 ~ 10 3 σ ~ a few to 10 km/s Cuspy or core profile? is yet unclear CDM Car Leo I

25 Mass enclosed within stellar extent (~ 4 x 10 7 M ) in dsph galaxies dsphs are largely dark matter dominated! (old data) 25

26 6.3 Several small-scale issues in ΛCDM theory Moore 10 6 ~10 9 Msun Cumulative number of halos Simulation Local Group galaxies V c / V global 26

27 Impact of reionization on the formation of dwarf galaxies? Bullock, Kravtsov & Weinberg 2000, ApJ, 539, 517 z < z re (reionization): suppression of dwarf formation 27

28 Observed photometric properties of Galactic satellites Tollerud

29 Too big to fail problem Bolyan-Kolchin et al Most massive subhalos in ΛCDM simulation are denser than those in most luminous satellites. 29

30 Anisotropic distribution of satellites Satellites and globular clusters in the Milky Way Satellites in M31 (Ibata et al. 2013) Red marks are confined in the thin plane. View from the M31 center 30

31 6.4 Formation of Andromeda galaxy Andromeda Halo (Ferguson et al. 2002) Northern Spur N205 M32 G1 Clump Stream 31

32 ACS/HST photometry of M31 s halo (using 120 HST orbits) V=28mag V=30mag 32

33 RGB stars with I 0 <24, V 0 < <[Fe/H]<-0.71 Structure of the M31 halo (Tanaka+ 10) Stream field NW 80kpc Stream F Stream E Tip of RGB AGB bump Stream D Stream C stream SE 50kpc 27kpc 50kpc 80kpc Red clump

34 (Photometric) metallicity distribution of Giant Southern Stream 34

35 Surface luminosity distribution along minor axis NW Tanaka SE

36 Important features in CM diagram RGB bump (RGBb) Evolutionary pause when the H-burning shell crosses a discontinuity left by the convective envelope Tip of RGB (TRGB) He-burning ignition through the He flash Nearly constant I-band mag standard candle 843±48kpc, 855±48kpc > D=770kpc Red Clump (RC) Clustered feature of red HB (He coreburning) stars being metal-rich / young age AGB bump (AGBb) Clustered feature of AGB stars at the beginning of He shell-burning evolution Luminosities of RGBb, RC, & AGBb depend on age. age distribution 36

37 Alves & Sarajedini 1999 AGBb RGBb HB Fainter for Z M Age indicator 37

38 Age calibration for giant stream Mean Age ~ 7.1 Gyr Tanaka+10 38

39 Halo formation model (Bullock & Johnston 2005) merging tree + semi-analytic galaxy formation Halo realization 1 39

40 Gilbert et al Observed surface brightness µ vs. [Fe/H] for each halo substructure higher µ, more metal-rich colder, more metal-rich lower µ, larger dispersion in [Fe/H] These are caused by more massive progenitors with higher [Fe/H] Simulated relations for each substructure 40

41 6.5 Future prospects Near-field cosmology: next decade SDSSIII SEGUE-2 APOGEE 2008~2014 Spec. of many Galactic stars Subaru HSC, PFS, GLAO 2013~ Imag. and spec. of ancient stars in LG TMT WFOS HROS NIRES 2022~ Spec. of many ancient stars in LU Gaia 2013~ 2020 Accurate astrometry of Galactic stars Towards understanding galaxy formation

42 HSC (Hyper Suprime Cam) Prime focus FOV: 1.77 sq deg (1.5 deg diameter) Pixel scale: 0.17/pix Filters: grizy + several NB Operation: 2013~ International collaboration: Japan, Princeton, Taiwan

43 HSC Wide-field FoV is essential for mapping stars

44 Near-field cosmology with HSC Wide-field survey of the MW outer halo (g, r, i) ~ 26 mag over ~1400 deg 2 i.e. fully utilizing SSP wide-field survey data Color-magnitude diagram for old MS + RGB stars in the outer halo (r = kpc) Discovery of new ultra-faint dsphs and halo stellar streams Wide- & deep-field survey of the M31/M33 halo and Galactic dwarf satellites Use NB515 filter (CW: 5145 A, BW: 80 A) Separate true halo RGBs (g < 25) with (g, r, i) + NB515 imaging The survey will be PI-led projects

45 Search for new Galactic satellites Unexplored region Single LSST: r lim = 24.5 Co-added LSST: r lim =27.5 Subaru/HSC (wide-f. survey): r lim ~26

46 Deep imaging (reaching HB) Both (g, i) available g only Shallow imaging (RGB only) Both (g, i) available i only + NB515 available HSC imaging of the M31 halo (Chiba et al.) kpc kpc

47 NB515 filter for HSC NB515 (CW: 515 nm, FWHM: 8nm) (from S15A) Separation of RGB stars in M31 halo + MW satellites from the foreground MW dwarfs Aug 28, 2013 Test w. S-Cam (by Mikito Tanaka) RGBs dwarfs

48 Led by IPMU (U. of Tokyo) + NAOJ/Subaru community + Caltech/JPL, Princeton, JHU, LAM, UK, Brazil, Taiwan, & Chinese consortium PFS (Prime Focus Spectrograph) Prime focus FOV: 1.3 deg in diameter 2400 fiber positioners λ: 380~1,300 nm (3 channels: Blue, Red, IR) R: ~3,000 (LR) 5,000 (MR) First light: 2018

49 Proposed PFS (R=5000 mode) pointings for three Galactic dsphs Previous [α/fe] measurements with DEIMOS (Kirby+) Tidal radius r t ~ 71 Previous RV measurements with MMFS (Walker+) PFS pointing Tidal radius r t ~ 76 Tidal radius r t ~ 160

50 TMT (Thirty Meter Telescope) WFOS, IRIS, IRMS, HROS, NIRES etc. R~5,000 for m V <26 mag R~50,000 for m V <21 mag First light: 2028~? Goal: ultimate understanding of galaxy formation based on resolved stars in the local universe