TheGalacticDisk and Halo in the. Carlos Allende Prieto Instituto de Astrofísica de Canarias

Transcription

1 TheGalacticDisk and Halo in the GaiaEra Carlos Allende Prieto Instituto de Astrofísica de Canarias

2 Introduction Hierarchical galaxy formation Galaxy disks Doubledisks seenin manydisk galaxies observed edge-on (image credit: 2MASS, shown by Bournaud et al. 2009) Alsopresentin themilkyway

3 Starcounts 2MASS (Cabrera-Lavers et al. 2003) Thin/thick scaleheights 269 +/- 13 pc and /- 52, respectively Scale-lengths of 2000 and 3100 pc SDSS (Juricet al. 2008) Scale-heights 300 pc and 900 pc Scale-lengths 2600 pc and 3600 pc

4 Agesand abundances Thick disk stars tend to be significantly older and more metal-poor than thin disk stars Seenin individual local turn-off stars Alsoseenin the turn-off colors of in-situ stars Reddyet al. 2006

5 Kinematicsand abundances Thethickdisks lagsbehindthethindisk in rotation speed Fuhrmann 1998 Reddyet al. 2006

6 Vertical velocitydispersion A larger vertical velocity dispersion corresponds to a larger scale-height Thethindisk starsshow a strongcorrelation between velocity dispersion and age with a smooth transition suggesting the thick disk may have formed thin Nordstrom et al. 2004

7 Chemistry The two disks show distinct but overlapping metallicity distributions(as it happens with kinematics) Butthetwodisks are mostdifferentwhen looked at in abundance space Fuhrmann 1998 Prochaska et al Bensbyet al Reddyet al. 2006

8 Intermediate[α/Fe] stars Haywood et al Feuillet et al. 2016

9 New more distantsamples SDSS-SEGUE RAVE APOGEE Gaia-ESO LAMOST GALAH 4MOST, WEAVE, DESI + Gaia

10 Revealinga largerscale-lengthforthethindisk thanthethickdisk (Bensbyet al. 2011, Chenget al. 2012, Bovy et al. 2012, Anderset al. 2014) Thiscan bein contrastwithstarcounts determinations due to flaring Radial abundancegradientclearin thethindisk (a tenthof a dexper kpc) notpresentin thethick disk stars(seenas a functionof agein Nordstrom et al. 2004, in situ in Allende Prieto et al. 2006, now obvious in APOGEE and GES observations)

11 Haydenet al [α/fe] as a functionof R

12 CorrelationbetweenV and [Fe/H] Spagnaet al. (2010) Lee et al. (2011) Adibekyan et al. (2013) Recio-Blanco et al. (2014) Kordopatis et al. (2016) Adibekyan et al. 2013

13 GaiaDR1 TGAS Gaiaprovidesglobal astrometryand spectrophotometryoverthewholeskyto20th mag(1e12 sources), and radial velocitiesto16th mag DR1 public last september, includes positions for the full sample, but parallaxes and proper motionsonlyforthestarsin Tycho-2 (TGAS, 2.5e6 sources) CombinedwithAPOGEE, 3D positions, motionsand chemistry for thousands of stars

14 TGAS-APOGEE Allende Prieto, Kawata, Cropper 2016

15 TGAS-APOGEE

16 CorrelationbetweenV and [Fe/H]

17 CorrelationbetweenV and [Fe/H] data Model(D. Kawata) Allende Prieto, Kawata, Cropper 2016

18 Spread in abundanceratios Large abundance spread expected among the firststars formed afteroneorfew supernovae Abundancespread reduces as thenumberof supernovae increases A measureof thespread in abundanceratios putscontraintsonsupernova ratesand therefore star formation rates

19 Cosmic scatter in the disk Nissen 2015

20 Cosmic scatter in the disk Nissen 2015

21 Cosmic scatter in the disk [Fe/H] Age (Gyr) Nissen 2015

22 Abundanceratio spread overlarger scales Bertran de Lis et al APOGEE data

23 Abundanceratio spread overlarger scales O/Fe spread in thindisk O/Fe spread in thick disk APOGEE data Bertrande Lis et al. 2016

24 Modelsof formationforthethickdisk Accretion/merger: stars(unlikely), gas Secular evolution: orbital migration(unlikely) Secular evolution: thick disk forms first (maybeas a thindisk thatlaterfattensup), then thin disk forms after injection of fresh (metal-poor) gas

25 The formation of the Milky Way halo Monolithic collapse (Eggen, Linden-Bell, Sandage 1962) vs. accretion (Early and Zinn 1978) Streams and echoes (Yannyet al. 2009; Schlaufman et al. 2012; Grillmair 2017) Chemistry of extremely metal-poor stars (Cayrel et al. 2004)

26 The formation of the Milky Way halo Accretion seems to have left a clear signature in the outer halo Bell et al. (2008)

27 The double halo SDSS/SEGUE (Carollo et al. 2008) Photometry (de Jonget al. 2012) Spectroscopy in situ(fernandez-alvaret al. 2015, 2016)

28 [α/fe] Inner vs. outer parts (Fernandez-Alvaret al. 2015)

29 [α/fe] Inner vs. outer parts (Fernandez-Alvaret al. 2015) Split in the inner halo (Nissen& Schuster 2010)

30 [α/fe] APOGEE data (Hayes et al. 2017; Fernandez- Alvaret al. 2017)

31 [α/fe] APOGEE data (Hayes et al. 2017; Fernandez- Alvaret al. 2017)

32 Summary TheMilkyWayhas a doubledisk wichis distinct in kinematics, age, and chemistry from the thin disk There appears to be a connection between Thereappearstobea connectionbetween thetwodisks, starsin boththatshare properties, e.g. have the same age, yet they are clearlyin oneorother chemicalgroup

33 Summary II We find evidence of both chemical evolution in the halo and accretion at early times There is chemical distinction between the inner and outermost parts of the halo at about kpc The split in [α/fe] found in the local (inner) halo population is likely related to the metal-weak thick disk Gaia DR2 + ground-based spectroscopic surveys are a gigantic step for the study of the disk and the halo