Hierarchical Assembly of Stellar Envelopes in Galaxy Clusters Meng - - PowerPoint PPT Presentation

Hierarchical Assembly of Stellar Envelopes in Galaxy Clusters

Meng Gu (Harvard University)

Collaborators: Charlie Conroy, Gabriel Brammer, David Law, Pieter van Dokkum, Renbin Yan, David Wake, Alexa Villaume, Allison Merritt, Roberto Abraham, Jielai Zhang, Paul Harding, Donald Schneider, Kai Zhang, Anne-Marie Weijmans, Dmitry Bizyaev, Niv Drory

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Scaling Relations of Early-type Galaxies (ETGs)

Thomas et al. 2010

More massive ETGs

Older stellar age More metal rich More alpha-enhanced

1Re 4Re

Cook et al. 2016

• Stellar Envelopes of ETGs

preserve information about the accretion history

• The Illustris simulation
• Mean [Z/H] & surface brightness

profiles do not evolve significantly in the central region

• Accretions flatten[Z/H] & surface

brightness profiles

Fossil Records in the Stellar Envelopes

image credit: the NASA/ESA Hubble Space Telescope

BCG assembly in the center of Abell 3827 (z~0.1)

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33028’45” 30” 15” 00”

• 5956’30”

35” 40” 45” 50” 55”

RA (J2000)

33029’30” 00” 28’30” 00” 27’30”

• 5956’20”

40” 57’00” 20”

RA (J2000)

Abell 3827

N1 N2 N3 N4 N5 N6 N7 N8 N9 N11 N12 N13 N15

10 kpc

z~0.1

• VLT/MUSE datacube
• 13 ETGs in the central 70 kpc of

the cluster.

• Measure stellar populations in the

central R=1kpc

• N1-N4 and N9 will merge within

1Gyr in to a BCG with log(M*/M⊙) ≈ 11.7

BCG assembly in the center of Abell 3827 (z~0.1)

Gu et al. 2018b arXiv 1805.04520

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Conroy & van Dokkum 2012 Conroy et al. 2014, 2018

Absorption (Automated) Line Fitter (alf)

example, S/N=100/Å

6

Full-Spectrum Modeling

• Stellar ages > 1Gyr ; Metallicities from ∼ −2.0 to +0.25
• MIST stellar isochrones, Choi et al. 2016
• MILEs + extended IRTF spectral library, 0.35 to 2.4 µm, Villaume et al. 2017
• Theoretical response functions
• MCMC sampler: emcee, MPI parallelized
• This work: z, σ, age, [Z/H], abundances of Fe, Mg, fixed to Kroupa IMF

33028’45”

• 5956’30”

35” 40” 45” 50” 55” 33029’30” 00” 28’30” 00” 27’30”

• 5956’20”

40” 57’00” 20”

RA (J2000) Dec (J2000)

Abell 3827

N1 N2 N3 N4 N5 N6 N7 N8 N9 N11 N12 N13 N15

10 kpc

z~0.1

• The building blocks of Brightest Cluster

Galaxies (BCGs) in cluster centers have high [α/Fe]

z~0.1

Gu et al. 2018b arXiv 1805.04520

9 10 11 12

log(M⇤/M)

2 4 6 8 10 12 14

Age [Gyr]

this work Conroy et al. 2014

9 10 11 12

log(M⇤/M)

0.0 0.1 0.2 0.3 0.4 0.5

[Mg/Fe]

10 20 30 40 50 60 70

Projected Distance to Cluster Center [kpc]

Coordinated Assembly of BCGs in Cluster Center

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log M∗

[α/Fe] or log Age

Cluster Centers Field

Scaling Relations

log (R/Re)

[α/Fe] or log Age

Coordinated Assembly Random Assembly

Radial Profiles

Coordinated Assembly of BCGs: high [α/Fe] building blocks flat & high [α/Fe] radial profiles flat & old age radial profiles

Coordinated Assembly of BCGs in Cluster Center

Gu et al. 2018b arXiv 1805.04520

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33028’45” 30” 15” 00”

• 5956’30”

35” 40” 45” 50” 55”

RA (J2000)

10 kpc

17 18 19 20 21 22 23 24 25 26 Surface Brightness in r-band [mag/arcsec2] 33029’30” 00” 28’30” 00” 27’30”

• 5956’20”

40” 57’00” 20”

RA (J2000) Dec (J2000)

Abell 3827

N1 N2 N3 N4 N5 N6 N7 N8 N9 N11 N12 N13 N15

10 kpc

14 kpc

Radial Trends of Stellar Population Properties

Gu et al. 2018b arXiv 1805.04520

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Gu et al. 2018b arXiv 1805.04520

100 200 300 400

σ [km/s]

6 8 10 12 14

Age [Gyr]

10−1 100 101

Radius [kpc]

−0.6 −0.4 −0.2

0.0 0.2

[Fe/H]

N1 N2 N3 N4 N9 van Dokkum+17

10−1 100 101

Radius [kpc]

0.0 0.1 0.2 0.3 0.4 0.5

[Mg/Fe]

10

Radial Trends of Stellar Population Properties

Beyond 100 kpc

Massive Ellipticals from center to ~ 35kpc

• NGC 4889
• NGC 4874
• NGC 4860
• NGC 4839
• NGC 4841A

3 Dwarf Ellipticals 3 UDGs (Gu et al. 2018a) 3 bundles on ICL

3 IFU bundles on the sky 1/3 time on nod Exposures

image credit: The Dragonfly Telephoto Array

Ancillary Deep Coma Project 6 MaNGA plates

SDSS IV/MaNGA: ICL in the Coma Cluster

Gu et al. 2018c in prep.

• Three 127-fiber IFU bundles on the ICL with 13.5 hrs total exposure time
• IFU diameter ~32’’
• wavelength coverage: 3622 − 10354Å
• spectral resolution: 1560 − 2650

100kpc 150kpc 180kpc

• ~ 100 kpc from NGC4889
• S/N4500-5000Å=21/Å
• σ ~ 700 km/s
• Age ~12.7 Gyr
• [Fe/H] ~ -0.7 dex

Best-Fit Spectrum of ICL1

Gu et al. 2018c in prep.

• Recession velocities are close to two BCGs
• Velocity dispersion profiles rise to ~700km/s at 100-200 kpc

Stars in the ICL

Gu et al. 2018c in prep.

• [Fe/H]:
• Declining radial profiles
• [Fe/H] ~ -0.1 in the center
• [Fe/H] ~ -0.4 at 20-35 kpc
• Comparable or more metal poor

than stellar envelopes at 10-30 kpc

• Stellar Age:
• > 10 Gyr within 20 kpc
• > 5 Gyr within 35 kpc
• ICL have similar ages

Age and Metallicity of Stars in the ICL

Gu et al. 2018c in prep.

• Stars in the ICL are similar to the current dwarf ellipticals (~109 Msun)
• Compare age and [Fe/H] of ICL to the dwarf ETGs in Coma

Age and Metallicity of Stars in the ICL

Gu et al. 2018c in prep.

• Stars in the ICL are similar to the current dwarf ellipticals (~109 Msun).
• The two BCGs have richer accretion histories than average.
• Compare age and [Fe/H] of ICL to the dwarf ETGs in Coma

Age and Metallicity of Stars in the ICL

Gu et al. 2018c in prep.

Summary

• The cluster center shapes the [α/Fe]–σ⋆ and [α/Fe]–M∗ relations

differently than other environments.

• Coordinated assembly of BCGs: their building blocks are different from

the general low mass populations by their high [α/Fe].

• Age, [Fe/H] and σ radial profiles extended to 200 kpc. They are

consistent with the coordinated assembly picture.

• Age and [Fe/H] in the ICL are similar to the outskirts of massive ETGs

and dwarf ellipticals.

Next Steps

• Stellar Population of the ICL across z=0.1-0.5 using integrated field

spectroscopy (e.g. MUSE)

• The Stellar Initial Mass Function in the Coma ETGs