

Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Non-negligible fraction of BCGs are not red-and-dead:

I radio emission (Best et al. 2007)

I optical emission-line nebulae (Loubser & Soechting 2013)

I excess UV light (Rafferty, McNamara & Nulsen 2008)

I far-infrared emission from warm dust (Quillen et al. 2008)

I molecular hydrogen (Edge et al. 2002)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

WHY?

Clues in environment:

I BCGs with ‘blue cores’ are only found in cool-core clusters(Cavagnolo et al. 2008)

I and then only if the BCG is located at the cluster centre(Bildfell et al. 2008)

I necessary, but not sufficient criteria for star formation inBCGs

WHY not?

Nearby BCGs exhibit diverse morphologies, stellar populations, andstar formation historiesWe need a framework to explain the physical mechanisms behindSF and quenching in BCGs



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Phases

Figure:

Density Temperature X-ray luminosity Young stellar density

↑



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Sample and data

Gemini spectra (Loubser, Bildfell, Hoekstra, Babul, Mahdavi):

I located close to the centre of cool-core clusters

I 19 BCGs (0.16 < z < 0.30)

I CCCP project: Photometry of the BCGs, Weak lensing(Hoekstra) and X-ray analysis of clusters (Mahdavi)

I Gemini GMOS long-slit spectroscopy

I Data reduced and spatially binned 0 – 5, 5 – 15 kpc

Stellar population analysis:

I full-spectrum fitting (3600 – 4800 A)

I SSPs, Composite (old + young components)

I Presence of < 2 Gyr components, light (mass) contribution



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

(a) A1689 (0 – 5 kpc) (b) A1689 (5 – 15 kpc)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

(c) A1835 (0 – 5 kpc) (d) A1835 (5 – 15 kpc)

(e) MS1455 (0 – 5 kpc) (f) MS1455 (5 – 15 kpc)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

I Vazdekis/MILES models and libraryI Detection of a young (< 2 Gyr) component is robust

Figure: Composite spectra expected for different SFHs with at least oneepisode of star formation during the last Gyr . A single recent burst, andsmall repeated bursts (forming 1 or 5 per cent of the mass).



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Environmental thresholds (regulation of SF andfeedback)

10 100Central entropy

0

0.2

0.4

0.6

0.8

1

1.2

Log

(SSP

age

) Gyr

Figure: SSP ages of the inner 0–5 kpc plotted against central entropy(CCCP X-ray temperature profiles). Four BCGs with young componentsare shown for reference.



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Precipitation-driven feedback model

Figure: Hα detections in BCGs in ACCEPT cluster catalogue (Voit etal. 2015)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Entropy

Figure: MHD Simulations Yuan Li(https://vimeo.com/user24338875/albums)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Figure: MHD Simulations: Li & Bryan (2015)

Figure: MHD Simulations: Prasad, Sharma & Babul (2015)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

(c) A1835 (0 – 5 kpc) (d) A1835 (5 – 15 kpc)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Process description

I The radiative cooling of thermally unstable gas causescondensation and precipitation of cool clouds (hot mediumsurrounding the BCG)

I It fuels star formation and the central supermassive black hole

I The criterion for precipitation: cooling time is ten timesshorter the free-fall time

I The jets of the AGN lift low-entropy gas from the BCG’scentre out to larger radii, it becomes unstable tocondensation and creates filaments of cooler gas



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

UV data – CLASH BCGs

Donahue et al. (2015)

(e) (f)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Phases

Figure:

Density Temperature X-ray luminosity Young stellar density

↑



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Phases: Hot gasObservations on SALT:

I Measuring emission lines of the hot gas nebulae in nearbyBCGs

I → over the entire optical wavelength range

I → with high S/N spatially-resolved observations(∼ 10 000 seconds each for 8 BCGs)

I Dominant excitation mechanisms to be identified(model independent; CLOUDY; MAPPINGS III)

Loubser, Ratsimbazafy, Donahue, Voit

2013-1-RSA OTH-011, 2013-2-RSA OTH-002, 2014-1-RSA OTH-003,

2014-2-SCI-014 (PI: Loubser)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

I Extinction: Hα, Hβ and Hγ

I Ionization diagrams: [OIII]5007/Hβ vs [NII]6584/Hα,[OIII]5007/Hβ vs [SII]6717,6731/Hα, and [OIII]5007/Hβ vs[OI]6300/Hα

I Gas density: [SII]6716/6731

I Gas temperature: [OII]3727/7320+7330 and[SII]4068+4076/6716+6730

I Abundances and metallicity

I He II recombination lines to test for the presence of > 54 eVionizing photons (lack of He II would rule out far UV ionizingsources)

I Ca II diagnostic for calcium in the gas phase (instead ofgrains)

I Shocks: detection of [OIII]4363



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Simultaneous absorption and emission linemeasurements

SALT spectra fitted with MILES stellar library (using GANDALF):

Figure: 2MASXJ1257



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Ionization mechanism

(a) 2MASXJ2319 (b) ESO349



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Ionization mechanism

I Break the degeneracies with many lines/features/auxiliarydata

McDonald et al. (2012)



Ilani Loubser

Introduction

Phases: Young stars

Data



MHD simulations


Phases: Hot gas

Data

Models

Summary

Summary of the results:

I We identify young components (< 2 Gyr) in sample of BCGsinside cool-cores

I We calculate the light (and mass) contribution of the youngcomponents

I Reconstruct the SFHs to determine single or repeated burstsof star formation

I Large variety in stellar population properties in ’cool core’clusters

I corresponds different times in the feedback cycleI Presence and mass fractions of young components agrees

with theoretical entropy thresholdsI observational evidence of precipitation-driven AGN feedback

models

I The young stellar population components are similar intime-scale to the cold-gas structures produced in simulationsof AGN feedback

fuelling (and quenching) star formation in brightest...

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