Galaxy Clusters with XEUS Silvano Molendi Stefano Borgani Stefano Ettori
Cosmic Vision Under the Cosmic Vision theme "The Universe taking shape" Investigation of galaxy clusters is declared to be amongst the top priority science goals for XEUS
Questions 1.How does XEUS address the scientific goals 2.What happens in the event of a factor of ~2 descoping
Clusters Simplified view cluster may be divided in 2 regions: 1. An inner one, often dominated by a cool core where feedback mechanisms play an important role 2. An outer one where the virialization process is taking place.
XEUS XEUS is much better at collecting photons than previous experiments not that much better at characterizing lower contrast regions SB_sou/SB_bkg better only by a factor of a few NFI migh be able to extend measures of x-ray emission to larger radii
Cores At larger distances we will have less details, however data quality will be more than enough to study how these regions evolve through cosmic time. These results will help us understand issus in structure formation from downsizing to
Physics and mass distribution of evolving clusters Characterization of dynamical, therm dynam and chemical properties of cluster from the local universe to z~1 On regions extending out to 1/3 ~ 1/2 of virial radius Measurements will provide valuable information to help us understand how clusters evolve through cosmic time Caveat: objects will not be discovered by XEUS, have to come from other experiments SZ surveys, X-ray surveys etc.
Where does the limit come from? z=1, L bol =7.7e43 erg/s, kt=2kev R<0.25R 180 100ks with NFI 0.2R 180 <R<0.3R 180 R 500 500 ~ ½ R 180 ~ ½ R vir
The Background
The Background Fe L Si K S K
NFI leading instrument Thorough Background characterization is mandatory!
Cores Background is the major limitation at large radii no such problem exists for cores XEUS will do a great job on cluster cores, particularly cool cores, both in the local universe and at higher redshifts Combination of huge throughput with almost Chandra like spatial resolution and few ev spectral resolution will provide impressive results
Cores NFI will open up the field of dynamic studies (bulk motions/turbulence/viscosity) Chemical structure Thermo-dynamics
Chemical and thermal properties of first clusters Very little is known of these objects today what do the first clusters look like? what are the their dynamic, thermodynamic, chemical properties, do they host cool cores?
How does a z=2 cluster look like? The spider-web galaxy: the assembly of a BCG @ z=2.16 (Miley et al. 06)? 40 kpc
Chemical and thermal properties of first clusters From simulations Borgani Saro Fabjan estimate that a M vir ~1.3e14 M sol @ z=0 @ z=2.1 M 500 ~2.3e13 M sol, R 500 ~500 kpc, Lx[0.5-2] ~7e43 cgs, Tsl(< r500 ) ~ 1.7 kev Z Fe 0.3 Z sol Estimates of T, Z should be possible, much depends on SB distribution Fe ~
Descoping Most critical component is the telescope Difficulty in getting both the large throughput and the high angular resolution at the same time What happens if we loose a factor of 2 in Eff.Area or PSF?
Effective area vs resolution trade-off Eff.. area reduction 5m 2 -> 3m 2 reduction in focal length 35m -> 25m (keep instrumental bkg down) increase in FOV loss is not irreparable, can be compensated by increase of exp time moreover loss in eff area in part compensated by increase of FOV (larger region of cluster can be imaged)
Effective area vs resolution trade-off Angular resolution hard limit is somewhere btwn 5-10 arcsec, Dictated by request of detecting and characterizing cluster from formation epoch to present date (8kpc = 1arcsec @ z=2) z
What if the descoping is more severe This is not XEUS anymore! Do we want to go ahead with that? Adjusting scientific goals from current XEUS science goals is not the way to go Thorough review of science goals would be mandatory
What if the descoping is more severe Very much depends on the nature and on the severity of the descoping. If, for example, the effective area had to be reduced to within a factor of ~5 of XMM-Newton area, say <2m 2 or less, than a thorough redisign of the mission would be inevitable. Various options for clusters, however it is probably premature to discuss them now
Summary XEUS will address a number of highly important issues on evolving cluster and on the formation process out to z~2. Measures will extend to 1/3 ~ 1/2 R vir, perhaps more if bkg characterization is given high priority Major advance on core regions. Moderate descoping is not a showstopper More significant descoping,, this is not XEUS anymore, a thorough reconsideration of science case.