RGS observations of cool gas in cluster cores Jeremy Sanders Institute of Astronomy University of Cambridge A.C. Fabian, J. Peterson, S.W. Allen, R.G. Morris, J. Graham, R.M. Johnstone Sanders et al, 2008, MNRAS, 385, 1186 Sanders et al, in prep

Cooling in cluster cores Many cluster cores have steeply peaked X-ray surface brightness profiles, i.e. short mean radiative cooling times. Suppose there is a luminosity L emitted from within a cooling region r cool To offset radiation lost through cooling, if the cluster is in steady state and there is no heating, there should be a mass deposition rate of Measured values from SB profiles gave values of s solar masses per year – a “cooling flow” luminosity of region is: - radiation of thermal energy - PdV work done on gas entering r cool

Lack of cool X-ray emitting gas see also Peterson et al 01, 03, Kaastra et al 01, 03, Tamura et al 01,... Spectra imply less than 10% of cooling rates expected from luminosity profiles Only significant gas down to 1/2 to 1/3 of outer temperature AGN heating? Fe XVII lines (indicating temperature ~ 0.7 keV) missing de Plaa et al 2A

The Centaurus cluster Inner core of the Centaurus cluster 200 ks Chandra observation RGB image Sanders & Fabian (2002, 2006) Fabian, Sanders et al (2005) 10 kpc

Centaurus temperature map Temperature (keV) Crawford et al 2005 Chandra 200ks observation 200 ks Chandra observation Projected temperature in Centaurus varies from 3.7 keV in outskirts to 0.7 keV in the cool plume

Centaurus cross dispersion image wavelength 1D image With the RGS spectrometer we get a spectrum of the cluster as a function of one spatial dimension. 150 ks total XMM exposure

Inner 160 arcsec width (30 kpc) Central inner 60 arcsec (13 kpc) arcsec (13-30 kpc)

Ionisation equilibrium Values taken from Mazzotta et al 1998 By measuring the distribution of ionisation states of metals we can find the gas temperature, or distribution of gas temperature

Inner 60 arcsec width (16 kpc) strong missing

Line ratios — constraints on kT Implies average temperature of gas 3.5 to 5.2 × 10 6 K Ratio of flux of emission lines and compared to CHIANTI model

Spectral fitting limits on gas kT Multi temperature model (components fixed in temperature but varying in emission measure) Cooling flow model (mass deposition in absence of heating) Factor of 10 in temperature > factor of 10 in mass deposition

Spectral fitting limits on gas kT Multi temperature model (components fixed in temperature but varying in emission measure) Cooling flow model (mass deposition in absence of heating) Factor of 10 in temperature > factor of 10 in mass deposition t cool ~ 10 7 yr!

New RGS spectra 156ks 138ks

HCG 62 O VIII Fe XVII 156 ks HCG 62 is a compact group of galaxies Prominent radio bubbles with ~10 57 erg energy content Temperature varies in spatially resolved studies from 1.5 to 0.7 keV (Morita et al 2006) High abundance arc (Gu et al 2007)

HCG 62: temperature distribution 8 component VAPEC model Shows clear break in temperature distribution at 0.6 keV Emission measure drops by more than an order of magnitude Lower temperature consistent with CCD results from Chandra/XMM (Morita et al 2006)

HCG 62: mass deposition rate 8 component VMCFLOW cooling flow model in steps of temperature In the absence of cooling, there is a very sharp drop in mass deposition rate at 0.6 keV, by at least an order of magnitude t cool ~ 3×10 8 yr

Conclusions Varied behaviour of cool cores observed by RGS  Wide range in temperature in Centaurus (factor 10)  Narrow range in HCG 62 (factor 2) Both show strong variation in emission measure with temperature Implies there is always close feedback It is important to study a wide range of clusters with deep observations with XMM We have a deep Abell 1835 observation soon  Star formation in this object ~ mass deposition rate (100 Solar masses/year)

Sound waves in Centaurus Fourier high-pass-filtered image Sanders & Fabian (submitted)

Centaurus SB profiles and residuals λ ~ 9 kpc

Power calculation Use deprojection factor to convert from ripple amplitude to intrinsic pressure ampl. Assuming spherical waves, this implies 9×10 42 erg s -1 sound wave power at r=30 kpc, where t cool =3.3 Gyr 9 kpc wavelength implies 10 7 yr period (similar to Perseus) Luminosity emitted within 30 kpc is 1.3×10 43 erg s -1 Using period and energy of radio bubbles, implies power of 2×10 43 erg s -1

HCG 62: extra absorption 8 component VMCFLOW cooling flow model in steps of temperature Extra column density of 5×10 20 cm -2 added into model for three lowest temperature components

HCG 62: ignoring OVII 8 component VMCFLOW cooling flow model in steps of temperature Only fitting spectrum from 7 to 20 A

Very coolest gas Very coolest X-ray gas at 0.35 keV has a mean radiative cooling time of only ~10 7 yr

Line profiles

Emission measure maps Best fitting smoothing sizes from RGS line widths

Centaurus temperature and metals 25 kpc

Centaurus in different elements Sanders & Fabian (2006)

Significant amount from Type II supernovae (~30%) Therefore large amount of star formation in the Centaurus cluster Either massive initial burst Continuous ~5 M  /yr Likely to have been undisturbed for ~ 8 Gyr Close heating/cooling balance Sanders & Fabian (2006) Supernova fractions