HST & Resolved Stellar Popula3ons

Transcription

1 HST & Resolved Stellar Popula3ons

2 Resolved stellar popula3ons provides a powerful tool to follow galaxy evolu3on consistently and directly in terms of physical parameters such as age (star forma3on history), chemical composi3on, enrichment history, IMF, environment and dynamical history of the system Tolstoy 2003

3 Topics: Proper Mo3ons of Local Group Members & orbit determina3on (near field cosmology) Internal Structure of galaxies Star Forma3on Histories Stellar halos (next week)

4 What is Near Field Cosmology Tes3ng predic3ons from various cosmological models using observa3ons of LOCAL galaxies Understanding our place in the universe: PuSng our local environment in context within these cosmological models.

5 Orbit Determination Depends On 3D V? Vr, Vtan Host Gravita+onal Poten+al? ρ(r, t) 3D r?

6 V tan --> Proper Motion The proper motion of an object is the measurement of its angular change in position on the sky over time." Size = Distance * Angular change Barnard s Star: Highest proper motion of any star visible from the Earth. True motion: 140 km/s Credit: Steve Quirk

7 HSTPROMO The HST Proper Motion Collaboration ( Characteristic velocity accuracy necessary 10 km/s at 70 kpc (Milky Way halo/satellite dynamics) Corresponding PM accuracy 30 μas / yr (~ speed of human hair growth at distance of the Moon) Observations Ground-based: NO VLBI: LIMITED (some water masers, M33, M31) GAIA: FUTURE (but not crowded or faint) HST: YES (0.006 HST ACS/WFC pixels in 10 yr)

8 The Orbits of the MW & M31 TOTAL Velocity???? Velocity TOWARDS US (BLUE SHIFT)

9 First Proper Motion Measurement of M31 Sohn µas/yr errors, 5yr

10 The impending MW-M31 collision V rad = /- 4.4 km/s Indirect arguments had placed V tan < 60 km/s, Theoretical arguments, V tan < 200 kms V tan = 17 +/- 34 km/s (van der Marel, Fardal, Besla+ 2012) First Passage occurs Gyr from now Pericenter distance = kpc Merger = No chance of missing us Gyr from now! (van der Marel, Besla )

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12 Our Galaxy in a Cosmological Context The Most Energetic Satellite: Leo I Leo I R MW = 260 kpc Vr, gal = /- 2.8 km/s The inclusion of Leo I as a bound satellite increases the MW halo mass by 25-30% (Kochanek et al Watkins et al. 2010) Ferris, Na3onal Geographic, Dec 2011

13 HST Proper Motions of Leo I WFC3/ACS, 5 yr baseline PM accuracy ~30 µas/yr Sohn, Besla V tan = / km/s Orbit is not radial V tot = / km/s Leo I mass: Walker Lv = 3.4 x 10 6 L M tot (< 0.93 kpc) ~ 8.9 x 10 7 M

14 The Escape Speed of the MW K + U = 0 à ve = sqrt ( 2* U/m) If the MW is modeled as an NFW profile and its mass is : then at 260 kpc ve = 182 km/s < v Leo I 1.5 x then at 260 kpc ve = 222 km/s 2 x then at 260 kpc ve = 256 km/s

15 Leo I: Cosmological Analogs Boylan- Kolchin, Bullock, Sohn, Besla & van der Marel Aquarius Halos (Springel et al. 2008) WMAP- 1 Cosmology M vir > M Otherwise Leo I is less bound than almost all subhalos. Rare to find an unbound satellite

16 Orbit of Leo I If M MW < M Leo I is unbound to the MW. (V esc is 182 km/s) M MW = 1.5 x M R peri = 91 +/- 36 kpc t peri = / Gyr ago t infall = 2.33+/ Gyr ago SFH: t SFR_last ~ 0.5 Gyr ago t burst_last ~ 2 Gyr ago (Smecker- Hane+ 2010) Implies t Quenching ~ 1.5 Gyr t peri t infall

17 Galaxy Structure with Resolved Stellar Popula3ons

18 Carlos Milovic F. - PixInsight Team " Biomedical Imaging Center - PUC" The Magellanic Clouds are not 'oddities' of Nature, but typical of a definite stage of the barred spiral sequence " characterized by a specific kind of asymmetry " - de Vaucouleurs & Freeman 1972" SB(s)m

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20 The first measure of a galac3c rota3on curve using proper mo3ons van der Marel & Kallivayalil 2014 First 3me the rota3on curve has been measured using PM rota3on field for any galaxy

21 Mass of the LMC: Rotation Curve Vcirc = / km/s Baryonic Tully Fisher M(8.7 kpc) = (1.7 +/- 0.7) x M (LMC is dark matter dominated) van der Marel & Kallivayalil 2014

22 ACS Nearby Galaxy Survey Treasury: ANGST PI Dalcanton, Skillman, Weisz Imaging survey of all galaxies outside the Local Group (< 4 Mpc ) 69 galaxies, 14 mill stars Dalcanton+ 2009

23 ANGST Will Measure: {1} the star forma3on history (SFH) of a >100 Mpc 3 volume of the Universe with a 3me resolu3on of Δlog t =0.25; {2} correla3ons between spa3ally resolved SFHs and environment; {3} the structure and proper3es of thick disks and stellar halos; {4} the color distribu3ons, sizes, and specific frequencies of globular and disk clusters as a func3on of galaxy mass and environment.

24 PHAT Central science drivers are to: - understand high- mass varia3ons in the stellar IMF as a func3on of SFR intensity and metallicity; - capture the spa3ally- resolved star forma3on history of M31; - study a vast sample of stellar clusters with a range of ages and metallici3es. These are central to understanding: - stellar evolu3on and clustered star forma3on; - constraining ISM energe3cs; - understanding the counterparts and environments of transient objects {novae, SNe, variable stars, x- ray sources, etc.}

25 Star Forma3on Histories

26 Tolstoy+2009 dsph dtrans dirr

27 Ultra Faint Dwarfs Uniformly old. Relics of reioniza3on. (Near field cosmology) Brown , 2013

28 ANGST : SFHs of 60 Dwarf galaxies (- 8 >M B > - 18) 1 < d< 4 Mpc (Weisz+2011)

29 Cumula3ve SFHs & Dwarf Type dsphs - 10 < Mb < Weisz 2011 Dis3nct morphological types might not have emerged un3l within the last few Gyr

30 Starbursting Dwarfs: Blue Compact Dwarfs Most metal poor Strong outflows, Most of metals lost Lee : 11HUGS Tolstoy 2009 Only 6% of dwarfs are experiencing a starburst today Bursts are only responsible for 1/4 of all stars formed in dwarfs

31 Star Formation Histories of the Clouds: Spatially Resolved Weisz et al. 2013: The early SFH of both galaxies was quiescent --- in contrast to all other satellites about MW.

32 The HST effect: ACS NGC resolves 346: sparkling SF in the SMC stars in NGC346 (SMC) (Nota et al. 2005) 3 Myr 4.5 Gyr pre-ms Nota et al 2005, Sabbi et al 2007 Talk by Aloisi