STELLAR SHELLS IN THE ILLUSTRIS SIMULATION Ana-Roxana Pop in - - PowerPoint PPT Presentation

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stellar shells in the illustris simulation
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STELLAR SHELLS IN THE ILLUSTRIS SIMULATION Ana-Roxana Pop in - - PowerPoint PPT Presentation

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STELLAR SHELLS IN THE ILLUSTRIS SIMULATION Ana-Roxana Pop in collabora*on with Lars Hernquist, Annalisa Pillepich, Nicola Amorisco En*re group Satellite forming shells radial velocity x y radial distance Ana-Roxana Pop Stellar Shells in

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SLIDE 1

STELLAR SHELLS IN THE ILLUSTRIS SIMULATION

Ana-Roxana Pop in collabora*on with Lars Hernquist, Annalisa Pillepich, Nicola Amorisco

Satellite forming shells En*re group

radial distance radial velocity

x y

Ana-Roxana Pop Stellar Shells in Illustris Heidelberg - Stellar Halos, July 2018

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SLIDE 2

Hubble DECam coadded image

Ana-Roxana Pop ITC Luncheon, April 2018 Galaxies with Stellar Shells

NGC 474 CFHT/Coelum/MegaCam J.-C. Cullandre & G.A. Anselmi ESO 381-12 NASA, ESA, P. Goudfrooij (STScI)

NS-NS merger - GW170817

  • ccurred in a shell galaxy (NGC 4993)

Credits: NASA, ESA, A. Levan (U. Warwick)

A few famous shells

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 3

Tidal Features in Illustris

INTRODUCTION

  • I. FORMATION
  • II. METALLICITY
  • III. HALO SHAPES

Type II Shells Type I Shells Streams and other ]dal features

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Galaxies with Stellar Shells Pop+2017a, arXiv:1706.06102

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SLIDE 4

Hendel & Johnston 2015

From Shells to Streams

Ana-Roxana Pop Galaxies with stellar shells ITC Luncheon, April 2018 Ana-Roxana Pop ITC Luncheon, April 2018 Galaxies with Stellar Shells

increasing angular momentum

  • f the accreted satellite

SHELLS STREAMS “wrappings” radial orbit more circular orbit

Sanderson & Helmi 2013

Arp 230 (Arp 1966)

Mar]nez-Delgado+2008

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 5

Different Types of Shells

Ana-Roxana Pop Galaxies with stellar shells ITC Luncheon, April 2018 Ana-Roxana Pop ITC Luncheon, April 2018 Galaxies with Stellar Shells

SHELLS radial orbit

Prieur 1988 NGC 474 - Turnbull et al., 1999 NGC 7600 - Turnbull et al., 1999

Type I shells Type II shells

Prieur (1989) and Wilkinson et al. (1987) introduced a system of classifying shells based on their morphology

Prieur 1988

shells aligned with the major axis shells more randomly distributed

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 6

Observed shell galaxy

Shell galaxies in the Illustris simula]on

Ana-Roxana Pop Shell galaxies in Illustris ITC Luncheon, April 2018 Ana-Roxana Pop ITC Luncheon, April 2018 Shell Galaxies in Illustris Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 7

Observed shell galaxy

Shell galaxies in the Illustris simula]on

Ana-Roxana Pop Shell galaxies in Illustris ITC Luncheon, April 2018 Ana-Roxana Pop ITC Luncheon, April 2018 Shell Galaxies in Illustris Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

PART 1 (arXiv:1706.06102) — First study of shell galaxies in a cosmological se^ng (Illustris)

  • What is the frac*on of shells in a cosmological simula*on?
  • How do shells form?

PART 2 (arXiv:1708.01615) — Metallicity of stellar shells PART 3 (paper in progress) — The shape of halos hos*ng shell galaxies

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SLIDE 8

Observed shell galaxy

Shell galaxies in the Illustris simula]on

INTRODUCTION

  • III. HALO SHAPES

Galaxy sample: 220 most massive galaxies in Illustris at z=0,

Two selec]on steps:

Score of 2 Score of 1 Score of 0

Step 1

Visual iden]fica]on Observer M200crit > 6 × 1012 M

Ana-Roxana Pop ITC Luncheon, April 2018 Iden*fying Shell Galaxies in Illustris Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 9

Observed shell galaxy

Shell galaxies in the Illustris simula]on

INTRODUCTION

  • II. METALLICITY
  • III. HALO SHAPES

Galaxy sample: 220 most massive galaxies in Illustris at z=0,

Two selec]on steps: Step 1

Visual iden]fica]on Observer

Step 2

Stellar History Catalogs & tracing the individual satellites forming shells Theorist (s i m u l a t i

  • n

s) M200crit > 6 × 1012 M

Ana-Roxana Pop ITC Luncheon, April 2018 Iden*fying Shell Galaxies in Illustris Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 10

Satellite forming shells En*re group

radial distance radial velocity

x y

INTRODUCTION

  • I. FORMATION
  • II. METALLICITY
  • III. HALO SHAPES

Ana-Roxana Pop ITC Luncheon, April 2018 Iden*fying Shell Galaxies in Illustris

Step 2

Stellar History Catalogs & tracing the individual satellites forming shells Theorist (s i m u l a t i

  • n

s)

At each important *me in the life*me of a star (forma]on, accre]on, stripping) we save informa*on about the star and its progenitor galaxy.

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 11

We find that the frac]on of shell galaxies increases with stellar and virial mass. In our total sample of 220 galaxies, we find 18% +/- 3% of the galaxies have shells. This es]mate is in overall agreement with the latest observa]ons.

18% shells out of 220 galaxies with

M200crit > 6 × 1012 M

Pop+2017a, arXiv:1706.06102

Shell Galaxies in Illustris

Ana-Roxana Pop ITC Luncheon, April 2018 Shell Galaxies in Illustris Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 12

Hendel & Johnston 2015

The Progenitors of Shell Galaxies

Ana-Roxana Pop Galaxies with stellar shells ITC Luncheon, April 2018 Ana-Roxana Pop ITC Luncheon, April 2018 Galaxies with Stellar Shells

increasing angular momentum

  • f the accreted satellite

SHELLS STREAMS “wrappings” radial orbit more circular orbit

Sanderson & Helmi 2013

Arp 230 (Arp 1966)

Mar]nez-Delgado+2008

however, there are several observa*ons of shells that seem to be the result of major mergers: Schiminovich et al. 1995, Balcells et al. 2001 Goudfrooij et al. 2001, Serra et al. 2006 most studies focused on radial minor mergers

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 13

p<0.0001

PART I - Selec*ng Shell Galaxies in Illustris PART II - Global Proper*es of Shell Galaxies PART III - Shell Progenitors and Their Mergers

The Progenitors of Shell Galaxies

We aim to iden*fy the key parameters that make a satellite likely to form shells in a cosmological segng! Order-zero recipe:

  • 1. radial infall orbit
  • 2. massive satellite
  • 3. accre*on *me 4-8 Gyr ago

We aim to iden*fy the key parameters that make a satellite likely to form shells in a cosmological segng. the satellites forming shells are rela*vely massive compared to the host galaxy!

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Forma*on of Shell Galaxies

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SLIDE 14

p<0.0001

PART I - Selec*ng Shell Galaxies in Illustris PART II - Global Proper*es of Shell Galaxies PART III - Shell Progenitors and Their Mergers

The Progenitors of Shell Galaxies

We aim to iden*fy the key parameters that make a satellite likely to form shells in a cosmological segng! Order-zero recipe:

  • 1. radial infall orbit
  • 2. massive satellite
  • 3. accre*on *me 4-8 Gyr ago

We aim to iden*fy the key parameters that make a satellite likely to form shells in a cosmological segng.

Order-zero recipe:

  • 1. radial infall orbit
  • 2. massive satellite
  • 3. accre*on *me 4-8 Gyr ago

Radial Velocity Ratio (@ t_acc)

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Forma*on of Shell Galaxies

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SLIDE 15

Radial Velocity Ra*o at Accre]on Time

INTRODUCTION

  • I. FORMATION
  • II. METALLICITY
  • III. HALO SHAPES

What type of mergers produce shell galaxies?

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Forma*on of Shell Galaxies Pop+2017a, arXiv:1706.06102

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SLIDE 16

Central Host

R200mean

Small Satellite

Small satellites (stellar mass ra]os ~1:10) can produce shells if they arrive on radial orbits

What type of mergers produce shell galaxies?

Ana-Roxana Pop Forma*on of Shell Galaxies ITC Luncheon, April 2018

Radial Velocity Ratio (@ t_acc)

Stellar Mass Ratio

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Pop+2017a, arXiv:1706.06102

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SLIDE 17

Central Host

R200mean

Small Satellite

Small satellites (stellar mass ra]os ~1:10) can produce shells if they arrive on radial orbits

Massive Satellite

Very massive satellites (stellar mass ra]os > 1:3) have their final infall orbits radialized by dynamical fric]on.

What type of mergers produce shell galaxies?

Ana-Roxana Pop Forma*on of Shell Galaxies ITC Luncheon, April 2018

Central Host

R200mean

Radial Velocity Ratio (@ t_acc)

Stellar Mass Ratio

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Pop+2017a, arXiv:1706.06102

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SLIDE 18

What type of mergers produce shell galaxies?

Ana-Roxana Pop Forma*on of Shell Galaxies ITC Luncheon, April 2018

Radial Velocity Ratio (@ t_acc)

Stellar Mass Ratio

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

Remember Nicola “the younger” talk on Monday! Msat/Mhost - 1/6 Msat/Mhost - 1/40

Amorisco 2017a

higher mass ra]o (close to major mergers) more efficient

  • rbit radializa]on

Pop+2017a, arXiv:1706.06102

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SLIDE 19

Pop et al. 2018, in prepara]on Ana-Roxana Pop Metallici*es of Stellar Shells ITC Luncheon, April 2018

Metallici]es of Stellar Shells

Stellar shells formed due to rela*vely major mergers can be more metal rich than host stars at similar radii.

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Pop+2017b, arXiv:1708.01615

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SLIDE 20

Pop et al. 2018, in prepara]on Pop+2017b, arXiv:1708.01615 Ana-Roxana Pop Metallici*es of Stellar Shells ITC Luncheon, April 2018

Metallici]es of Stellar Shells

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 21

Pop et al. 2018, in prepara]on Pop+2017b, arXiv:1708.01615 Ana-Roxana Pop Metallici*es of Stellar Shells ITC Luncheon, April 2018

Metallici]es of Stellar Shells

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

See Erin’s talk on observed HSC shells arXiv:1805.05970

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SLIDE 22

INTRODUCTION

  • I. FORMATION
  • II. METALLICITY
  • III. HALO SHAPES

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018 Metallici*es of Stellar Shells 1 : 1.3 1 : 1.6 1 : 6 1 : 2 1 : 4 1 : 4.3 1 : 1.3 1 : 2.5 1 : 4 Stellar Mass Ra]o — Pop+2017b, arXiv:1708.01615

Metallici]es of Stellar Shells

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SLIDE 23

Pop et al. 2018, in prepara]on

Compe*ng effects: outer shells correspond to the first stars stripped -> metal-poor stars BUT for ~major mergers, outer shells contain metal-rich stars which are deposited at large effec*ve radii, where the host galaxy is metal-poor.

Ana-Roxana Pop Metallici*es of Stellar Shells ITC Luncheon, April 2018 Pop+2017b, arXiv:1708.01615

Metallici]es of Stellar Shells

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 24

10 out of 39 shell galaxies in our sample have mul*ple shell-forming progenitors.

Pop et al. 2018, in prepara]on

In some cases, there is a significant difference in the metallicity of shells formed from the two different progenitors

  • > metallicity measurements can be used to iden*fy systems with mul*ple progenitors.

Ana-Roxana Pop Metallici*es of Stellar Shells ITC Luncheon, April 2018 Pop+2017b, arXiv:1708.01615

Metallici]es of Stellar Shells

Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

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SLIDE 25

Halo Shapes of Shell Galaxies

Pop+2018, in prepara]on Ana-Roxana Pop Halo Shapes of Shell Galaxies ITC Luncheon, April 2018 Ana-Roxana Pop Heidelberg - Stellar Halos, July 2018

Preliminary results Email me at ana-roxana.pop@cfa.harvard.edu to discuss results presented in the talk about the stellar and dark marer halo shapes of shell galaxies.

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SLIDE 26
  • In Illustris, at redshio z = 0, 18% +/- 3% of galaxies with have shells.

The frac*on of shells is higher for more massive galaxies.

  • Shells in massive hosts form through mergers between about 1:10 - 1:1 in stellar mass ra]o,

with the progenitors being accreted on radial orbits between 4-8 Gyrs ago.

  • Dynamical fric]on is more effec*ve at radializing the orbits of massive satellites, while

smaller ones need to be accreted on very radial orbits.

  • Outer shells are ooen *mes more metal-rich than the surrounding stellar material in the host

halo at similar radii. Can poten*ally use metallicity measurements to dis*nguish between different shell-forming progenitors in the same system.

  • Type I shells are predominantly found in prolate halos.

M200crit > 6 × 1012 M

Most shell galaxies are prolate. Especially Type I shells! Outer shells are osen metal-rich (compared to host stars at same radius) shells in massive galaxies form through mergers 1:10 - 1:1 in stellar mass ra]o

  • n radial orbits, 4 - 8 Gyrs ago

Conclusions

P S O

T

b/a c/a