Antonela Monachesi Universidad de La Serena E. Bell, B. Harmsen, R. - PowerPoint PPT Presentation

Comparing results from the GHOSTS survey and the Auriga simulations Antonela Monachesi Universidad de La Serena E. Bell, B. Harmsen, R. de Jong, D. Radburn-Smith, J. Bailin + GHOSTS team F . Gomez, R. Grand, V. Springel, G. Kau ff mann + Auriga collaboration Stellar halos across the cosmos, Heidelberg, 03-07-2018

Resolved stellar halo measurements It is possible to reach μ ~ 33- 34 mag/arcsec 2 M81; Okamoto et al. (2015) Radburn-Smith et al. (2011) Cen A; Crnojevic et al. (2016) Probe individual galaxies to very low surface brightness. It is possible to quantify substructure. Immune to flat-field/sky background uncertainties and PSF scattered light issue. Allows to constrain the halo stellar population (especially with HST). Limited distance (out to ~10 Mpc), so low statistics + background contamination + small FoV when observing with HST

The Milky Way’s and M31’s stellar halos have similarities but differ greatly from each other Credit: Koposov et al. SDSS MW M31 4-7 10 8 M ◉ 10 10 M ◉ 3-D Power law profile -2.5; r < 20kpc -3.7; r < 150kpc -3.5; r > 20kpc ~Const. [Fe/H] [Fe/H] gradient c/a~0.6 oblate ! prolate Both halos are highly structured e.g., Ivesic+00; Newberg, Yanny+07; Bell+08; Carollo+10, PANDAS; Resolved RGB stars Sesar + 11, Carollo+16; Slater+16; Fernández-Alvar+17; McConnachie + 09; Ibata + 14 Kalirai + 06; Gilbert + 12,14; Ibata +14

GHOSTS survey: HST ACS/WFC3 observations in the outskirts of 18+ nearby disk galaxies. Provide statistics on galaxy stellar outskirts beyond the MW and M31 GHOSTS Survey team: PI: Roelof de Jong (AIP) Jeremy Bailin (UA) Eric Bell (UM) Tom Brown (STScI) James Bullock (UC Irving) Stephane Courteau (Queens) Julianne Dalcanton (UW) Harry Ferguson (STScI) Paul Goudfrooij (STScI) Benjamin Harmsen (UM) Benne Holwerda (UL) Antonela Monachesi (ULS) Chris Purcell (WVU) David Radburn-Smith (FB) Anil Seth (Utah) Jonathan Sick (Queens) David Streich (AIP) In Sung Yang (AIP) de Jong+(2007, 2009), Bailin+(2011), Radburn-Smith+(2011, 2012, 2014), Dan Zucker (Macquarie) Monachesi+(2013, 2014, 2016a), Streich+(2016), Carrillo+(2016) Harmsen, Monachesi+(2017) Bell, Monachesi+(2017), Yang+, in prep.

GHOSTS Sample Overview NGC 0247 NGC 0253 NGC 0891 7 NGC 2403 5 4 5 C G N NGC 3031 NGC 4945 NGC 4244 NGC 4565 NGC 4631 NGC 4736 NGC 5023 IC 5052 G N NGC 5236 NGC 5457 NGC 5907 NGC 7793 NGC 7814

GHOSTS MW-mass Disk Galaxies NGC 0247 NGC 0253 NGC 0891 NGC 2403 NGC 3031 NGC 4945 NGC 4244 NGC 4565 NGC 4631 NGC 4736 NGC 5023 IC 5052 NGC 5236 NGC 5907 NGC 7793 NGC 7814

HST resolves red giant branch stars and measures stellar density and color/metallicity

Projected minor axis stellar halo surface brightness profiles NGC 0247 NGC 0253 NGC 0891 NGC 2403 NGC 3031 NGC 4945 NGC 4244 NGC 4565 NGC 4631 NGC 4736 NGC 5023 IC 5052 NGC 5236 Harmsen, Monachesi et al. (2017) NGC 5907 In general, power law profiles r - α where -2> α >-3.7 over 10 to 70 kpc. NGC 7793 Substructure on top of power law. NGC 7814 Stellar halos appear flattened with 0.4<c/a<0.75 at ~ 25 kpc.

RGB colors in old populations reflect their metallicities

Minor axis stellar halo Color/Metallicity profiles NGC 0247 NGC 0253 NGC 0891 NGC 2403 NGC 3031 [Fe/H] (dex) NGC 4945 NGC 4244 NGC 4565 NGC 4631 NGC 4736 NGC 5023 IC 5052 NGC 5236 NGC 5907 Monachesi et al. 2013, 2016a NGC 7793 Steep metallicity gradients in half halos, very weak or NGC 7814 absent in the other half

Milky Way mass disk galaxies have a broad range of stellar halo masses and properties an order of magnitude range metallicities Harmsen, Monachesi et al. , 2017 X15 scatter in stellar x30 range in stellar halo mass halo mass fraction Poner plot del paper Large variation in density slopes Significant variation in [Fe/H] gradients The Milky Way and M31 are at the extremes of these correlations See also next talk by In Sung Yang and Dragonfly results (Merritt et al. 2016)

The stellar halo metallicity and mass correlation reflects the properties of the dominant accreted satellites. Larger halos accrete more massive satellites Harmsen, Monachesi et al. , 2017 We can use stellar halo mass or metallicity to quantify dominant merger See talk by Eric Bell See also Deason et al. 2016, Bell&Monachesi et al. 2017, D´Souza&Bell 2017, Amorisco 2017a

The Auriga simulations: 30 Milky Way-mass halos Halos of (1-2)x10 12 M Sun Fully cosmological hydrodynamical simulations of very high resolution + statistics Grand et al. (2017) m(dm)~ 2x10 5 M SUN m(g) ~ 5x10 4 M SUN Auriga Core team: PI: Volker Spingel (HITS-MPA) David Campbell (Durham) Carlos Frenk (Durham) Facundo Gomez (ULS) Robert Grand (HITS) Adrian Jenkins (Durham) Federico Marinacci (MIT) Rudiger Pakmor (HITS) Christine Simpson (HITS) Simon White (MPA) V-band surface brightness maps of stellar halos, Monachesi et al. (2018)

Some of the Auriga stellar halo metallicity and age profiles along different directions Stellar halos have diverse median ages and metallicities, even the accreted-only component, and are composed of a mixture of populations at each radius Monachesi et al. 2018, arXiv:1804.07798

Projected minor axis surface brightness and color profiles Auriga vs. observations Monachesi et al. 2018, arXiv:1804.07798 Results from observations in general agree better with accreted-only stellar halos, except M31 which shows a prominent and metal-rich halo

The Auriga simulations reproduce the diversity found in observed stellar halos of Milky Way-mass galaxies Accreted-only component This broad range in properties is driven by diversity in merger history Monachesi et al. 2018, arXiv:1804.07798, See also Harmsen et al. 2017, Bell et al. 2017

Too massive in-situ stellar halos in Auriga sims compared with observations (and in general in all hydro simulations) Accreted + in-situ halo Monachesi et al. 2018, arXiv:1804.07798, See also Harmsen et al. 2017, Bell et al. 2017

Larger gradients are found when fewer significant progenitors built up the stellar halo 2 -1.8 0 Au2 Au9 Projected power law density slope Projected power law density slope -2.2 [Fe/H] slope (10 -3 dex/kpc) [Fe/H] slope (10 -3 dex/kpc) -2 0 Au3 Au10 -2.4 -2 -2.2 Au4 Au12 -2.6 -2 -4 Au5 -2.8 Au13 -2.4 -4 -3 Au6 Au14 -2.6 -6 -3.2 Au7 Au15 -6 -2.8 -3.4 -8 Au8 Au16 Accreted Accreted All halo -8 -3 -3.6 5 10 15 5 10 15 5 10 15 # significant progenitors # significant progenitors # significant progenitors # significant progenitors # significant progenitors: Number of satellites that make up 90% of the stellar halo Halo metallicity gradients and density profiles may quantify the degree of dominance of the largest accretion Monachesi et al. 2018, arXiv:1804.07798

Summary All GHOSTS MW-mass disc galaxies have extended stellar halos Milky Way-mass disc galaxies have diverse stellar halo properties (Monachesi+ 2013, 2016a, Harmsen+2017) A tight stellar halo mass — [Fe/H] (minor axis) relation is discovered empirically, confirming an accretion origin of stellar halos. Larger halos are formed from few larger satellites (Harmsen+2017; see also Deason+2016, D’Souza & Bell 2018, Monachesi+2018) New hydrodynamical simulations of high resolution, Auriga, lead to a good agreement with the data (Importance of a careful and fair comparison) Too high in-situ stellar halo masses (Monachesi+2016b, Monachesi+2018) Gradients may better quantify the merger history (Monachesi+2018)

Bright Future for stellar halo studies Expand de sample of individual galaxies studied to ~20 Mpc and obtain panoramic maps of many more galaxies. Excellent to sample diversity in halos as well as in galaxy types ELT, Chile, 2024 LSST, Chile, 2023 TMT , Hawaii, 2027 From Ben Williams´talk JWST, 2021? GMT , Chile, 2023 WFIRST, 2020?