Gaps in tidal streams Denis Erkal University of Surrey Stellar - - PowerPoint PPT Presentation

▶
gaps in tidal streams
SMART_READER_LITE
LIVE PREVIEW

Gaps in tidal streams Denis Erkal University of Surrey Stellar - - PowerPoint PPT Presentation

Jul 07, 2023 407 likes •771 views

Gaps in tidal streams Denis Erkal University of Surrey Stellar halos across the cosmos, MPIA, July 4th 2018 Milky Way Substructure Halo mass function Stars No Stars 200 kpc 10 4 10 10 Mass (M ) Aquarius, Springel et al. 2008 Image

slide-1
SLIDE 1

Gaps in tidal streams

Denis Erkal

University of Surrey Stellar halos across the cosmos, MPIA, July 4th 2018

slide-2
SLIDE 2

Milky Way Substructure

Aquarius, Springel et al. 2008

200 kpc Stars No Stars Mass (M) Halo mass function 1010 104

Image credit:ESA/Hubble & NASA

slide-3
SLIDE 3

Tidal Streams from Globular Clusters

Smooth Potential Lumpy Potential

Interaction with substructure

Ibata et al. 2002, Johnston et al. 2002

slide-4
SLIDE 4
slide-5
SLIDE 5

Outline

  • How do gaps grow/evolve?
  • How many gaps are expected in the known

streams around the Milky Way?

  • Gaps in known streams
slide-6
SLIDE 6

Outline

  • How do gaps grow/evolve?
  • How many gaps are expected in the known

streams around the Milky Way?

  • Gaps in known streams
slide-7
SLIDE 7

Analytic Toy Model for Gaps

Setup

  • Stream on circular orbit
  • No position/velocity

dispersion

  • Plummer sphere perturber
  • Arbitrary spherical host

potential

  • Arbitrary impact geometry

Approach

  • Impulse approximation for

velocity kicks

  • Compute resulting orbits at

first order

  • Compute resulting stream

shape

  • Similar to Carlberg 2013,

Yoon, Johnston, Hogg 2011

Stream Perturber

b

Erkal & Belokurov 2015a

slide-8
SLIDE 8

Cartoon of Gap Formation

Orbital Mechanics 101 Gap Formation (also in Space)

Gap!

1) Flyby

ρ ψ ψ ρ

3) Expansion

ρ ψ

4) Gap

ρ ψ

2) Compression

ρ ψ

5) Caustic 1) Flyby

ρ ψ ψ ρ

3) Expansion

ρ ψ

4) Gap

ρ ψ

2) Compression 1) Flyby

ρ ψ ψ ρ

3) Expansion

ρ ψ

2) Compression 1) Flyby

ρ ψ ρ ψ

2) Compression 1) Flyby

ρ ψ

1) Flyby

Tangential Throw Radial Throw

Oscillations!

Earth Earth

aka Football in Space

slide-9
SLIDE 9

N-body example

  • Stream generated by progenitor on circular
  • rbit at 10kpc
  • NFW host potential
  • 108 M Plummer sphere, 250pc scale

radius

  • Direct impact on stream

Density along stream Sky angle (o) Gap density Time in Gyr Gap size (o) Time in Gyr

~1/t ~t1/2 ~t

slide-10
SLIDE 10

Same picture roughly holds for realistic streams

  • Simple model misses two important aspects:
  • Streams are not generally on circular orbits
  • Stream material has a distribution in E,L

Time Time Gap size Gap density ~t1/2 ~1/t

Sanders, Bovy, Erkal 2016

slide-11
SLIDE 11

Outline

  • How do gaps grow/evolve?
  • How many gaps are expected in the known

streams around the Milky Way?

  • Gaps in known streams
slide-12
SLIDE 12

Outline

  • How do gaps grow/evolve?
  • How many gaps are expected in the known

streams around the Milky Way?

  • Gaps in known streams
slide-13
SLIDE 13

Streams around the MW

Pal 5, Odenkirchen et al. 2002 Ibata et al. 2016 Tri/Psc - Bonaca et al. 2012 Martin et al. 2014 GD1, Grillmair & Dinatos 2006

~ 15 globular cluster streams around MW

slide-14
SLIDE 14

Streams around the MW

Shipp + 2018

Streams in DES

slide-15
SLIDE 15

How many subhaloes fly near the stream?

  • Flux through cylinder around stream (same

approach as Yoon et al. 2011, Carlberg 2012)

v

s

z x y

r

|v |dt stream l bmax

Nenc ~ (number density)x(stream length)x(stream age)

  • Also get velocity distribution

Erkal, Belokurov, Bovy, Sanders 2016

slide-16
SLIDE 16

How many subhaloes fly near the stream?

  • Pal 5
  • ~3.4 Gyr old (Kuepper et al. 2015)
  • # density of subhaloes scaled down from Aquarius (Springel et al. 2009)
  • length from observations (Odenkirchen et al. 2002)
  • disk depletes substructure by 3 (D’Onghia et al. 2010, Penarrubia et al.

2010, Sawala et al. 2016) 105-106 M: ~26 within 2 rs 106-107 M: ~10 within 2 rs 107-108 M: ~4 within 2 rs

Ibata et al. 2016 Erkal, Belokurov, Bovy, Sanders 2016

slide-17
SLIDE 17

How many gaps are created?

  • Use gap size and gap depth from model
  • Subhalo properties from VLII (Diemand et al. 2008)
  • Match M-vmax relation with Plummer spheres
  • Know number of interactions, sample properties of flyby, get

distribution of gap properties

Angle along stream Stream density fcut

Erkal, Belokurov, Bovy, Sanders 2016

slide-18
SLIDE 18

Properties of Gaps

  • Distribution of gap sizes for LCDM spectrum from 105-108 M

Gap size Normalized distribution Guides the scale on which to search for gaps

Erkal, Belokurov, Bovy, Sanders 2016

slide-19
SLIDE 19

So… how many gaps?

GD1 0.6 gaps with f < 75% Tri/Psc 1.6 gaps with f < 75%

~3 gaps expected in all three streams

Density threshold Number of gaps deeper than threshold Pal 5 0.7 gaps with f < 75%

Erkal, Belokurov, Bovy, Sanders 2016

slide-20
SLIDE 20

Outline

  • How do gaps grow/evolve?
  • How many gaps are expected in the known

streams around the Milky Way?

  • Gaps in known streams
slide-21
SLIDE 21

Outline

  • How do gaps grow/evolve?
  • How many gaps are expected in the known

streams around the Milky Way?

  • Gaps in known streams
slide-22
SLIDE 22

Gaps in Pal 5

  • Nearby cold/long stream (~ 1km/s dispersion, ~10 kpc long)
  • Progenitor still intact
  • Deep data with CFHT (Ibata et al 2016)
  • Proper motion for progenitor (Fritz & Kallivayalil 2015)
  • Radial velocities along stream (Odenkirchen et al 2009, Kuzma et al

2015)

Belokurov/SDSS

slide-23
SLIDE 23 −5 −4 −3 −2 −1 1 φ2 () Leading Trailing

Fiducial Model

N-body Data 2 4 6 8 Linear Density (arcmin1) epicyclic overdensities 0.0 0.1 0.2 0.3 0.4 w () −80 −60 −40 vr (km/s) −5 −4 −3 −2 −1 1 φ2 () Leading Trailing

Fiducial Model

N-body Data 2 4 6 8 Linear Density (arcmin1) epicyclic overdensities 0.0 0.1 0.2 0.3 0.4 w () −80 −60 −40 vr (km/s)
  • How should unperturbed

stream look?

  • Equal amounts of material

in leading and trailing arm

  • Symmetric density since no

significant distance gradient (Ibata et al 2016)

  • Relatively smooth density

along stream with little small scale structure

  • Epicyclic over densities

near progenitor

Gaps in Pal 5

Erkal, Koposov, Belokurov 2017 Angle along stream Radial velocity Width Density Perp angle Ibata et al 2016

slide-24
SLIDE 24 −5 −4 −3 −2 −1 1 φ2 () Leading Trailing

Fiducial Model

N-body Data 2 4 6 8 Linear Density (arcmin1) epicyclic overdensities 0.0 0.1 0.2 0.3 0.4 w () −80 −60 −40 vr (km/s) −5 −4 −3 −2 −1 1 φ2 () Leading Trailing

Perturbation by subhaloes

N-body Data 2 4 6 8 Linear Density (arcmin1) ∼ 106M flyby ∼ 107.7M flyby 0.0 0.1 0.2 0.3 0.4 w () −80 −60 −40 vr (km/s)
  • 2 gaps
  • ~ 2 degrees (106-107 M)
  • ~ 9 degrees (107-108 M)
  • Observed width is more

uniform

Gaps in Pal 5

Angle along stream Radial velocity Width Density Perp angle Erkal, Koposov, Belokurov 2017 106-107 M ~ 9-18 keV thermal relic WDM Expected 0.7 gaps so ~3x LCDM

slide-25
SLIDE 25
  • Alternative mechanisms
  • GMCs (Amorisco+ 2016): 106-107 M

within solar circle (Rice + 2016), 0.65 gaps expected

  • Globular clusters: < 1/6 rate

expected from subhaloes (Erkal, Koposov, Belokurov 2017)

  • MW Bar: Rotating bar creates

differential torque along stream (Erkal, Koposov, Belokurov 2017,
 Pearson+2017)

  • MOND can create asymmetries in

tidal streams (Thomas+2018, Wu+2010)

Gaps in Pal 5

−5 −4 −3 −2 −1 1 φ2 ()

Perturbation by Milky Way bar

2 4 6 8 Linear Density 0.0 0.1 0.2 0.3 0.4 w () −80 −60 −40 vr (km/s)

Angle along stream Radial velocity Width Density Perp angle Erkal, Koposov, Belokurov 2017

slide-26
SLIDE 26
  • Alternative statistical approach
  • Measure power spectrum/bispectrum of density

fluctuations (Bovy, Erkal, Sanders 2017)

  • Streams and perturbations generated in action-

angle space (Sanders, Bovy, Erkal 2016)

  • Idea (ABC)
  • Select normalization of LCDM subhaloes
  • Perturb stream with subhalo flybys
  • Keep if power/bispectrum on large scales

matches data

  • Get constraint on LCDM normalization

Gaps in Pal 5

Data Realizations

Bovy, Erkal, Sanders 2017

slide-27
SLIDE 27
  • Tested with N-body streams
  • Pal 5 consistent with 1.5-9 LCDM,


consistent with gap counting

Gaps in Pal 5

Bovy, Erkal, Sanders 2017

N-body inference Pal 5 inference

slide-28
SLIDE 28

Gaps in GD-1

  • 55
  • 50
  • 45
  • 40
  • 35
  • 30
  • 25
  • 20
  • 15
  • 10

ϕ1 (deg)

  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 ∆ϕ2 (deg) 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 N

∆ϕ 15 20 25 30 35 40 45 50

  • 55
  • 50
  • 45
  • 40
  • 35
  • 30
  • 25
  • 20
  • 15
  • 10

density (stars/deg2) ϕ1 (deg)

CFHT data Simulation

Stream


  • n sky

Stream
 density Angle along stream

  • Hard to interpret since no progenitor
  • Wiggles and density variations
  • Still working on interpretation

Angle along stream

de Boer + 2018

slide-29
SLIDE 29

Gaps in GD-1

∆ϕ 15 20 25 30 35 40 45 50

  • 55
  • 50
  • 45
  • 40
  • 35
  • 30
  • 25
  • 20
  • 15
  • 10

density (stars/deg

2

) ϕ1 (deg)

Stream
 density Angle along stream

Price-Whelan & Bonaca 2018

Gaps confirmed with Gaia

de Boer + 2018

3 gaps in GD-1 Wiggles in the stream track, stars off-stream

slide-30
SLIDE 30

Gaps in GD-1

Stream density Stream observables Progenitor disruption creates a gap

Erkal & Gieles in prep.

Angle along stream Angle along stream

slide-31
SLIDE 31

Recovering Subhalo Properties

  • Gap properties depends on 7d parameter

space:

  • Subhalo mass
  • Scale radius
  • 3 velocities
  • Impact parameter
  • Time since impact
  • Can we constrain these from observations of

a gap?

z x y b α (w ,w ,w )

x y z

(0,v ,0)

y

To galaxy center

Stream M,rs

Erkal & Belokurov 2015b

slide-32
SLIDE 32

Stream observables

Angle along stream Distance Declination angle Radial velocity Tangential velocity Vertical velocity Density

  • Analytic model predicts 6d shape of perturbed stream

107 M, rs=250 pc

slide-33
SLIDE 33

Inference with emcee

Mass Velocity rs b time Velocity rs b time

{

107 M, rs=250 pc

LSST Errors

Erkal & Belokurov 2015b

slide-34
SLIDE 34

Observational Strategy

  • Measure density and centroid along stream
  • Look for density variation with accompanying 


wiggle

  • Follow up with radial velocities
  • Develop tools to model gaps in real streams
  • Fit gap!





√ √- Pal 5 GD-1 √ In progress In progress √-

slide-35
SLIDE 35

Conclusions

  • Kicks from subhaloes change orbital periods and create gaps
  • Expect ~1 deep gap per long stream
  • Pal 5 contains 2 gaps and is consistent with ~ 3x LCDM
  • Small gap consistent with 106-107 M subhalo, > 9-18 keV WDM
  • GD-1 has 3 gaps (1 from progenitor?), ~ 3x LCDM
  • Next step: perform inference for observed gaps
  • Can be used for constraints on any DM model