Powering the intra-cluster filaments in cool-core clusters of galaxies

NGC 1275

Perseus-Pisces Supercluster, 75 Mpc, mass ~8×1015 Msun

Perseus Cluster, 75 Mpc, 500 galaxies, M~2×1015 Msun

NGC 1275

H I, He I recombination, low ionization lines, [N I]

Inverted ionization ratios

Unlike any starlight-ionized nebulae Hatch+ in

preparation

(Å)

[O II]

H I [N I]

H I

H I [O I] [S II]

H I + [N II]

He I

Strong H2 lines in IR

Johnstone et al 2007, MNRAS, 382, 1246

H2 H2

CO lines: Mmolecule ~ 1011 Msun

Salome et al 2006, A&A, 454, 4376

CO 1-0

Astronomical context

Atomic, molecular gas

~70 pc wide, 6 kpc long

B~100 mG for magnetic support

~70 km/s turbulence

Surrounded by ~5 keV gas with nT~3×106 cm-3 K

Fabian+ 2008 Nature

Spectrum of a non-equilibrium gas

Detailed microphysics

Energetic radiation & particles interact with gas

Ejected electrons heats, excite & ionize gas

Ionization drives chemistry

Full spectrum predicted

–Detailed chemistry, grain physics

Cloudy

Follows the detailed microphysics, with minimum compromise

All stages of ionization of the lightest 30 elements, 100+ molecules

2.7 K ≤ T ≤ 1010 K

10-10 ≤ n ≤ 1020 cm-3

Continuously maintained

Fully open source, at www.nublado.org

Ryan Porter, Peter van Hoof, Robin Williams

ν f

ν [

erg

cm

-2 s

-1]

10−3

0.01

0.1

1

10

100 1000

ν f

ν [e

rg c

m-2 s

-1]

10−4

10−3

0.01

0.1

1

10

100

Wavelength (μm)

1 10 100 1000

The big questions

What powers emission from the filaments?

How is the strange optical spectrum produced?

– Inverted ionization ratios, strong [N I] emission

–Strong molecular emission, including H2, CO, and HCN

–Unlike anything seen in H II regions or planetary nebulae

Filaments trace feedback between massive black hole in central galaxy and the intracluster medium. How and why?

Three possible energy sources

Starlight

–Photoionization as in HII regions or planetary nebulae

Heat deposition

– dissipative MHD waves

– shocks

Ionizing particles entering molecular gas

– Intracluster medium (5 keV)

– radio lobes (MeV)

– or produced in situ

And ionization/recombination processes

Starlight

–Valence shell photoionization

–Radiative/dielectronic recombination

Heat deposition

–Collisional ionization

–Radiative/dielectronic recombination

Ionizing particles

– primary impact ionization

– secondary impact ionization, excitation, heating

– charge exchange recombination

Ionizing particles entering …

Ionized gas

–Heat

Atomic/molecular gas

–Shower of suprathermal electrons

–Secondary excitation and ionization

– less heating

–Rich ion-molecule chemistry

Energetic photons have same effects

AIRES, U Chicago

These three processes produce very different ionization ratios

Photons vs particles

Photons vs particles

Photoionization – RR&DR electron recombination rates ~10-13 cm3 s-1,

photoionization cross sections few megabarns

Photons vs particles

Ionizing particles – O, N ionization strongly coupled to H by resonant

charge exchange

Thermal vs ionizing particles

Thermal vs ionizing particles

Recombination by

CX, RR, DR Electron impact

ionization with

Boltzmann factors

The curious ionization ratios are produced by ionizing

particles entering molecular gas

Observed / predicted spectrum

wavelength (microns)

1 10

pre

dic

ted / o

bse

rve

d

0.1

1

10

H I, [N I],

He I, [O I],

[N II], [S II] H2 H2, [Ne II]

Ferland+ 2009MNRAS.392.1475F

Predicted spectrum

Optical/UV spectrum

Radio

X-ray

Conclusions

Filaments powered by penetration of surrounding hot gas (Fabian+ 2011)

Suprathermal ionization followed by charge transfer recombination accounts for odd spectrum

Grains must be present to sustain the rich chemistry

–Galactic origin rather than condensation from hot gas?

Composition within factor of two of ISM

Large mass deduced from CO confirmed

Large reservoirs of undetectable gas likely

Ferland et al, 2008MNRAS.386L..72F, 2009MNRAS.392.1475F