Studying Galaxy Studying Galaxy Clusters Clusters

with Astro-Hwith Astro-H

Silvano MolendiSilvano Molendi

IASF-Milano/INAFIASF-Milano/INAF

Largest gravitationally bound structures in the

local universe.

Subject of intense research

a)as cosmological tools

b)interesting structures

a) and b) are of course connected as some

understanding of the structures is required

to use clusters as cosmological tools.

ICM in Galaxy ClustersICM in Galaxy Clusters

Setting the contextSetting the context

• The ICM is tenuous, typical densities 10-4 to a few 10-2 cm-3

• hot, temperatures from 107 to 108 K (1-10 keV)

• highly ionized: H, He completely ionized heavier elements partially ionized

• Chemically enriched, heavy elements such as O, Si and Fe are present in almost solar proportions

Basic properties of the ICM

X-ray emission

Thermal bremsstrhalung + line emission

Setting the contextSetting the context

Basic properties of the ICM

X-ray emission form clusters is extended

ASTRO-H ASTRO-H ASTRO-H will carry the first micro-calorimeter

We have had high resolution spectroscopy in X-ray for more than decade now, so is ASTRO-H

really going to be a major step forward?

The large improvement in collecting area at Fe K line will afford considerable insight for many

astrophysical sources.

However, for extended sources, for which high res. spectroscopy has been possible only in the

most limited sense, SXS will produce a true quantum leap

The importance of The importance of motion motion

Show movies

Disclaimer Disclaimer

• Many things can and will be done, in this presentation I will cover some of the most important.

• Not an exhaustive presentation.

Motions in the ICM Motions in the ICM

Indirect evidence of motions is now abundant

Shocks in the ICM

Markevitch & Vikhlinin (2007)

Bullet cluster

Best example of shock

Core of sub-structure already

gone through cluster

From RH conditions and density jump

Mach number ~ 3

Vshock ~ 4700 km/s

Motions in the ICM Motions in the ICM

Shocks now seen in a few systems point to mildly supersonic gas motions

These are rare systems, one of the reasons is

the shocks occur exactly in the plane of the sky

There are likely similar systems seen at different angles (e.g. A576 Dupke+07) these

will be accesible with SXS

Motions in cores Motions in cores

Indirect evidence of gas motions in the cores of many “relaxed” (Cool Core)

systems

Core of Perseus cluster

Highly structuredEnhanced emissionCavities

Fabian+03

Radio Bubbles

Cavities coincide with radio lobes associated to the AGN at the center

Fabian+03

Ripples and weak shocks

• Radio cavities expand and rise buoyantly, in doing so they set the ICM in motion, generating ripples and weak shocks

Fabian+03

Cold FrontsCold Fronts

• CF are contact discontinuities (SB jumps) discovered by Chandra (Markevitch & Vikhlinin 2007)

• Found in merging systems where they mark dense subcluster cores that have survived a merger

Ghizzardi, Rossetti &SM 2010

Cold FrontsCold Fronts

•Found in non merging systems were they result from the displacement of lowest entropy gas from the bottom of the potential well.•Small pressure jump across the CF point to subsonic motions•Search for cold fronts in a representative sample of nearby systems shows that ALL relaxed clusters host at least 1 CF

Ghizzardi, Rossetti &SM 2010

• Indirect evidence for ubiquitous subsonic gas motion in cluster cool cores

• Subsonic motions are quite likely one of the defining traits of these systems, (the reason this statement is seldom made is that we have, thus far, lacked direct observations of gas motions)

• Open questions are: what is the kinetic energy vs. thermal

energy? is the flow laminar or turbulent? what is the viscosity of the ICM?• Indirect evidence for mildly supersonic motion

in a few systems, typically those were shock is propagating in the plane of the sky.

Gas Motions in clusters Gas Motions in clusters

• A 6eV resol @ Fe Kα line corresponds to a velocity resolution of 300 km/s

SXS on ASTRO-H SXS on ASTRO-H

• The sound speed in the ICM is cs = (5/3·p/ρ)1/2 = 1460 km/s·(kT/8 keV) 1/2

ASTRO-H well suited to measure subsonic motions in ICM

• Most important line is the Fe Kα

• For most T He-like Fe Kα is the most prominent

Fe He-like KFe He-like Kαα

Different regions with Δv=200km/s

Laminar flow Laminar flow

Turbulent flow Turbulent flow

Region with vTurb=200km/s

• Some line broadening may be present even if turbulence is completely absent (limited angular resolution & line of sight effects)

• The combination of high spectral resolution and moderate angular resolution should allow us to distinguish between flows dominated by laminar and turbulent motions.

• Intermediate cases will be more difficult but not impossible to characterize.

Laminar vs Turbulent flow Laminar vs Turbulent flow

• XMM-Newton Grating (Peterson+01 ) and CCD data (SM & Pizzolato 01) falsified the cooling-flow model that predicted strong multi-phaseness of ICM in cluster cores (temperatures from a few keV down to 0.1 keV).

• Evidence, in some instances, of suppression of conduction, presence of multi-temperature structure:

ICM Thermo-dynamic ICM Thermo-dynamic structure structure

1. suppression of conduction across cold fronts e.g. A3667, Ettori & Fabian 2001

2. presence of blobs/filaments of cooler gas in the radio arms of M87 (SM 2002, etc.)

The limited spectral resolution of CCDs and spatial resolution of gratings does not allow us to address the issue of moderate multi-phaseness in the ICM at large

ICM Thermo-dynamic ICM Thermo-dynamic structure structure

SXS will change this

ICM Spectra at CCD ICM Spectra at CCD resolution resolution

―1 keV―2 keV―4 keV―8 keV

―1 keV―2 keV―4 keV―8 keV

ICM Spectra at SXS ICM Spectra at SXS resolution resolution

Fe L-shell emission Fe L-shell emission

T up to 3keV

Ar KAr Kαα line emission line emission

He-like H-like

Ratio of H to He-like

2keV <T < 8keV

Fe KFe Kαα line emission line emission

He-like H-like

Ratio of H to He-like

2keV <T < 10keV

•The relative intensity of Fe L-shell lines and the ratio of H-like Kalpha to He-like Kalpha lines for O,Mg,Si,S,Ar,Ca & Fe are all dependent upon temperature and can be used to provide independent estimates of T and assess presence of even modest multiphase-ness.•As for the study of line broadening some apparent multi-T will be present even if the gas is single phase (limited angular resolution & line of sight effects), however these effects can be accounted for

ICM Thermo-dynamic ICM Thermo-dynamic structure structure

The SXS will produce a quantum leap in our understanding of the ICM

It will:

Summary Summary

directly detect motions within the ICM for the first time

characterized the thermodynamic structure of the ICM

improve our understanding of metals in the ICM

•The relative intensity of Fe L-shell lines and the ratio of H-like Kalpha to He-like Kalpha lines for O,Mg,Si,S,Ar,Ca & Fe are all dependent upon temperature and can be used to provide independent estimates of T and assess presence of even modest multiphase-ness.•As for the study of line broadening some apparent multi-T be present even if turbulence is the gas is single phase (limited angular resolution & line of sight effects), however these effects can be accounted for

NuSTAR NuSTAR

10 arcsec (FWHM)

13 x 13 arcmin

1 keV @ 60 keV 0.5 keV @ 6 keV

< 48 h

•Launched on June 13th in LEO •First Light on June 28th

NuSTAR NuSTAR

• Thus far everything has gone well• Mast deployment successful• Instruments functioning within expectations