A First Gaia look at the inner halo* Giuliano Iorio DIFA, - - PowerPoint PPT Presentation

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A First Gaia look at the inner halo* Giuliano Iorio DIFA, - - PowerPoint PPT Presentation

Oct 20, 2022 376 likes •895 views

A First Gaia look at the inner halo* Giuliano Iorio DIFA, University of Bologna IoA, Cambridge Vasily Belokurov, Denis Erkal, Sergey Koposov, Carlo Nipoti, Filippo Fraternali *Iorio et al., 2017, submitted, arXiv:1707.03833 The science of

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Vasily Belokurov, Denis Erkal, Sergey Koposov, Carlo Nipoti, Filippo Fraternali

DIFA, University of Bologna IoA, Cambridge

The science of Gaia and future challenge 01/09/2017 Lund

A First Gaia look at the inner halo*

*Iorio et al., 2017, submitted, arXiv:1707.03833 Giuliano Iorio

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Why study the Halo?

  • Relic of the Galactic formation
  • Trace the Galactic potential

Lightest component

  • f the MW!

Stellar Halo 109 Msun DM Halo 1012 Msun Disc 6x1010 Msun Bulge 1010 Msun

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Why study the Halo?

  • Relic of the Galactic formation
  • Trace the Galactic potential

Lightest component

  • f the MW!

Stellar Halo 109 Msun DM Halo 1012 Msun Disc 6x1010 Msun Bulge 1010 Msun

How?

  • Counting of Halo Tracers: e.g. RRLyrae
  • PopII stars
  • Known absolute magnitude
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Star-counting results, so far:

BHB: Deason+2011

Different tracers:

  • Power Law
  • Oblate

α ≈ 2 − 4

q ≈ 0.4 − 0.8

Only gross agreement and partial sky coverage..

Halo properties:

ρ ∝ m−α

  • K-Giants (e.g. Xue+15)
  • BHB (e.g. Deason+11, Das+16)
  • RRL (e.g. Sesar+10)
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Star-counting results, so far:

BHB: Deason+2011

Different tracers:

Gaia is a formidable all sky variable machine

…. but RRLs available at the end of the missions (>2020)

  • K-Giants (e.g. Xue+15)
  • BHB (e.g. Deason+11, Das+16)
  • RRL (e.g. Sesar+10)
  • Power Law
  • Oblate

q ≈ 0.4 − 0.8

Only gross agreement and partial sky coverage..

Halo properties:

The Gaia Revolution

α ≈ 2 − 4

ρ ∝ m−α

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Exploiting DR1

Photometry in DR1

  • G-band mean mag.
  • Mean Flux in G band
  • Std Flux in G band
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Exploiting DR1

Variable star

Photometry in DR1 Variability in DR1

Non-Variable star

  • G-band mean mag.
  • Mean Flux in G band
  • Std Flux in G band
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SLIDE 8

Exploiting DR1

Photometry in DR1

Variable star Non-Variable star Variable star

  • G-band mean mag.
  • Mean Flux in G band
  • Std Flux in G band

Variability in DR1

Belokurov+17, Deason+17

AMP = log σ FF−1 Nobs

( )

large small

Variable

Non-Variable

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SLIDE 9

Exploiting DR1

AMP alone is not enough… we need a colour! Cross-match with 2MASS!

Variable star

Photometry in DR1 Variability in DR1

Belokurov+17, Deason+17

Variable star

RRLs

AMP = log σ FF−1 Nobs

( )

large small

Variable

Non-Variable

  • G-band mean mag.
  • Mean Flux in G band
  • Std Flux in G band
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Final sample

  • 0.95<J*-G*<-0.4 ‘Colour Cut’

Selection Cuts (Driven by Bona Fide RRLs)

*Magnitude corrected for dust extinction using E(B-V) from Schlegel+98

Map: Gaia+2Mass CRTS RRLs (Drake+13) Stripe82 RRLs (Sesar+10)

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SLIDE 11

Final sample

  • 0.95<J*-G*<-0.4 ‘Colour Cut’

Selection Cuts (Driven by Bona Fide RRLs)

  • 0.4<Amp<-0.7 ‘AMP Cut’

*Magnitude corrected for dust extinction using E(B-V) from Schlegel+98

Iorio+17 (arXiv:1707.03833)

Contamination analysis using Stripe82

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Final sample

  • 0.95<J*-G*<-0.4 ‘Colour Cut’

Selection Cuts (Driven by Bona Fide RRLs)

  • 0.4<Amp<-0.7 ‘AMP Cut’
  • G*<17.1 ‘Uniform completeness’

Not so complete… ….but we don’t care

Completeness analysis using Stripe82

*Magnitude corrected for dust extinction using E(B-V) from Schlegel+98

Iorio+17 (arXiv:1707.03833)

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Final sample

  • 0.95<J*-G*<-0.4 ‘Colour Cut’

Selection Cuts (Driven by Bona Fide RRLs)

*Magnitude corrected for dust extinction using E(B-V) from Schlegel+98

  • 0.4<Amp<-0.7 ‘AMP Cut’
  • G*<17.1 ‘Uniform completeness’
  • |b|>10°

85% of the stars has E(B-V)<0.25 1% of the stars has E(B-V)>0.8

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(l,b,G)

D⊙(MG)

(Xg,Yg,Zg)

From sky to physical coordinates

Final sample

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(l,b,G)

D⊙(MG)

(Xg,Yg,Zg)

From sky to physical coordinates

  • Little spread around median

Iorio+17 (arXiv:1707.03833)

< MG >= 0.53 < σ M G >= 0.09

Final sample

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SLIDE 16

(l,b,G)

D⊙(MG)

(Xg,Yg,Zg)

From sky to physical coordinates

  • Little spread around median
  • MG distribution almost constant with b

Final sample

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(l,b,G)

D⊙(MG)

(Xg,Yg,Zg)

From sky to physical coordinates

  • Little spread around median
  • MG distribution almost constant with b

MG=0.53 for all the stars

Final sample

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Final sample

about 22000 stars Contamination < 10% Completeness 20%

D⊙ ≈ 0.5 − 20 kpc fV

tot ≈ 50%

Sampled Vol. fraction:

Previous works < 20% (e.g. Deason+11)

DG ≈1− 28 kpc

Properties

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Final sample

about 22000 stars Contamination < 10% Completeness 20%

D⊙ ≈ 0.5 − 20 kpc fV

tot ≈ 50%

Sampled Vol. fraction:

Previous works < 20% (e.g. Deason+11)

DG ≈1− 28 kpc

Sky distribution Properties

Iorio+17 (arXiv:1707.03833)

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Exploring the Halo

Density in the RZ plane

  • Disky at low Z
  • Ellipsoidal at high Z

Iorio+17 (arXiv:1707.03833)

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Exploring the Halo

Density profile Assumption: Density stratified on ellipsoids

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

m [kpc]

Iorio+17 (arXiv:1707.03833)

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Exploring the Halo

Flattening

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

θ

m

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Exploring the Halo

Flattening

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

θ

m

Mock sample: qtrue=0.5 ptrue=1

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Exploring the Halo

Flattening

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

m [kpc] m [kpc]

θ

m

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m [kpc] m [kpc]

Exploring the Halo

Flattening

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

θ

m

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m [kpc] m [kpc]

Exploring the Halo

Flattening

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

θ

m

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SLIDE 27

Exploring the Halo

Flattening

ρ = ρ(m) m= x2 + p−2y2 + q−2z2

θ

m

Direct evidence of a change of flattening

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Exploring the Halo

MCMC Likelihood sampling

  • about half of RRLs in our sample
  • No due to disc cont. (Rd=2.6, zd=0.2)

Maybe Monoceros (e.g. Juric+08)

  • r related to Gaia DR1 problems

at low latitude

m [kpc]

  • Exclude the disky structure |θ |> 20!
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Exploring the Halo

  • about half of RRLs in our sample
  • No due to disc cont. (Rd=2.6, zd=0.2)

Maybe Monoceros (e.g. Juric+08)

  • r related to Gaia DR1 problems

at low latitude MCMC Likelihood sampling

m [kpc]

  • Exclude the disky structure |θ |> 20!
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SLIDE 30

Exploring the Halo

  • Exclude the disky structure
  • Halo model

|θ |> 20!

Halo recipes

  • Density
  • Single Power Law
  • Double Power Law
  • Broken Power Law
  • Core Power Law
  • Einasto
  • Spherical
  • Axisymmetric
  • Triaxial
  • Tilted
  • Off-set
  • Varyng q
  • Shape

MCMC Likelihood sampling

m [kpc]

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Exploring the Halo

MCMC Likelihood sampling - Main results

  • No strong evidence of deviation from a SPL ρ ∝ m−2.95
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Exploring the Halo

MCMC Likelihood sampling - Main results

  • No strong evidence of deviation from a SPL
  • Triaxial: flattening along Z (q=0.6), elongation along Y(p=1.3)

ρ ∝ m−2.95

22°

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Exploring the Halo

  • No strong evidence of deviation from a SPL
  • Triaxial: flattening along Z (q=0.6), elongation along Y(p=1.3)
  • q increasing with m

MCMC Likelihood sampling - Main results

m

ρ ∝ m−2.95

Iorio+17 (arXiv:1707.03833)

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MCMC Likelihood sampling - Main results

  • No strong evidence of deviation from a SPL
  • Triaxial: flattening along Z (q=0.6), elongation along Y(p=1.3)
  • q increasing with m
  • No significant off-set (doffset) wrt GC or tilt wrt G. plane

tilt < 6°

doffset = 0.43± 0.07 kpc

Xoffset = 0.39 ± 0.05 kpc

Compatible with uncertainties in Sun dist. wrt GC

McMillan+10

ρ ∝ m−2.95

Exploring the Halo

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Conclusions

First analysis of RRLs in the inner halo (Rg<28 kpc) using Gaia data*:

Thank you for your attention!

  • Density is a Single Power Law
  • The halo is Triaxial and highly flattened along Z
  • Flattening changes with radius becoming more spherical

GAIA DR2 expected for April 2018

  • Release of Gaia colors!
  • Get rid of 2MASS

Extend this analysis up to 90 kpc!

ρ ∝ m−2.95 (q ≈ 0.6)

*Iorio et al., 2017, submitted, arXiv:1707.03833

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EXTRA

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ρ = m−2.95

p = 1.25

q = 0.56 → 0.82

Iorio+17 (arXiv:1707.03833)

MCMC Likelihood sampling - Main results

Exploring the Halo

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SLIDE 38

Iorio+17 (arXiv:1707.03833)

ρ = m−2.95

p = 1.25

q = 0.56 → 0.82

MCMC Likelihood sampling - Main results

Exploring the Halo

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Map: Gaia+2Mass CRTS RRLs (Drake+13) Stripe82 RRLs (Sesar+10)

Iorio+17 (arXi

CRTS RRLs (Drake+13) Stripe82 RRLs (Sesar+10)

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Exploring the Halo

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G distribution

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Z distribution

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  • Extended disky feature
  • It contains about half of RRLs in our sample
  • It cannot be explained (entirely) by the Galactic disc

ρ

It could be Monoceros (e.g. Juric+08) or related to Gaia DR1 problems at low latitude

Structures

Structures - Low Latitude

(Juric+08)

Data Disc+ halo model

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  • Extended disky feature
  • It contains about half of RRLs in our sample
  • It cannot be explained (entirely) by the Galactic disc

It could be Monoceros (e.g. Juric+08) or related to Gaia DR1 problems at low latitude

Structures

Structures - Low Latitude

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Structures - High Latitude

  • Overdensity at very high-latitude

Structures

It is likely related to the Virgo Overdensity (Bell+08) Yg Yg Xg

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Z-Slab

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Rz Residuals

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Flattening: previous works

m [kpc]

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Dens models

m [kpc] m [kpc]

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Metallicity distribution

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Corner Plot