Constraining Galactic Halos with the SZ-effect by Naureen Goheer, University of Cape Town based on a collaboration with Kavilan Moodley (UKZN)

Galaxy morphology spirals much better understood, focus on them rich in gas and dust 90% 10% far less evidence for young stars, gas, or dust

Optical part of Spiral Galaxies two visible components ~ 90 % of the visible mass: spiral arms (stars + gas&dust) < 10% of visible mass: Bulge (stars)

“invisible” matter component: Halo Stellar Halo, < 1% of stars visible part Dark Matter Halo some indirect observational evidence for the existence of Halo baryonic non-baryonic

DM Halo and Observations some indirect observational evidence for the existence of Halo through kinematic tracers, e.g: disk galaxy rotation curves , satellite galaxies and globular clusters, hot gas (also around ellipticals) confirm existence of halo radial extents and total masses of these halos remains poorly constrained one possible new way of constraining amount of dark baryons is the SZ-effect

DM Halo and Theory might account for missing baryons (only 20% of mean baryonic density has been observed) DM halo required by most models of galaxy formation galaxy formation still not understood – have no accepted model of galaxy formation, thus no accepted halo model expect different halo dynamics depending on whether the galaxy at hand is starburst or quiescent; smooth halo or filaments

CMB Anisotropies Secondary Anisotropies –effects due to structure formation (nonlinear structure evolution) –gravitational effects (lensing) –scattering effects SZ-effect: scattering of CMB photons on hot gas Primary Anisotropies: early effects at the last scattering surface and large scale Sachs-Wolfe effect.

The Sunyaev Zel'dovich (SZ) effect secondary anisotropies due to (up-)scattering of CMB photons with hot gas (keV) along the line of sight (at the centre of clusters etc.) thermal: due to the thermal velocities of the electrons in the gas kinematic: due to the bulk velocity of gaseous object

CMB=black body distinct spectral signature allows us to distinguish signal from other sources lower intensity at no effect at higher intensity at scattering of CMB photons on e- in hot gas net effect photons pick up energy and get shifted to higher frequencies distortion of black body spectrum

Thermal SZ-effect: Central decrement empirically: number density of e- highest in the center and falls off radially central decrement dl frequency dependence Comptonization parameter =gas pressure along the line of sight thermal SZ depends on temperature and number of electrons in gas mass of object purely classical treatment must include relativistic effects when (e.g. in clusters)

high central decrement for clusters (higher temperature and mass) integrated effect (over entire object) high central decrement for clusters (higher temperature and mass) much smaller central decrement due to much lower mass and lower temperature in galaxies integrate over angular size dl observable integrated effect (if halo is massive and hot enough) use integrated effect to constrain electron number density and thus the dark baryons in halo of nearby galaxies assuming that non-baryonic DM scales like dark baryons, this constrains the total DM content of halo BUT

other observational constraints spectroscopy: can only test for specific isotopes using X-rays: observe Bremstrahlung etc.

SZ-effect versus X-rays X-ray luminosity: SZ-flux: electron temperature central electron density for extended halos with low central density, X-rays observations are less sensitive than SZ-observations!

Summary and Future outlook 80% of the predicted baryons have not been observed some of them might hide in the hot halos of galaxies very difficult to directly measure the halo content the integrated thermal SZ-effect can be used to directly measure baryonic matter content of halo the new Atacama Telescope (ACT) will have high enough sensitivity to get a clear signal (better than PLANCK)

discarded slides

models of galaxy formation explain different halo scenarios: halos can be smooth or filled with filaments (mention models of galaxy formation) halo content: O VI (observed using x-rays, show example pics) what can we learn about models of galaxy formation

Whats nice about SZE? 1) Ofcourse, the distinct spectral signature 2) Measures the total thermal content of the cluster 3) More or less redshift independent 4) Less susceptible to messy cluster substructure, core physics (prop to density and not density squared as in XRays)

Note that at   GHz, the maximum change in intensity due to the kinematic effect coincides with the null of the thermal effect. This, in principle, allows one to separate the two effects. The magnitude of the thermal effect for a hot, dense cluster is , and for reasonable cluster velocities the kinematic effect is an order of magnitude smaller.

OR Primary Anisotropies :early effects at the last scattering surface and large scale Sachs-Wolfe effect. Secondary Anisotropies: secondary contributions through nonlinear structure evolution, star formation, and radiative feedback from the small scales to the large .

CMB Anisotropies Secondary Anisotropies contributions through nonlinear structure evolution, star formation, and radiative feedback from the small scales to the large . SZ-effect: scattering of CMB photons on hot gas Primary Anisotropies: early effects at the last scattering surface and large scale Sachs-Wolfe effect.

The SZ-effect Thermal Sunyaev-Zel’dovich effect: Inverse Compton scattering of the CMB by hot electrons in the intracluster gas of a cluster of galaxies distorts the black body spectrum of the CMB. Low frequency photons will be shifted to high frequencies. Kinetic Sunyaev-Zel’dovich effect: The peculiar velocities of clusters produces anisotropies via a Doppler effect to shift the temperature without distorting the spectral form. Its effect is proportional to the product of velocity and optical depth.