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Wed, 16 Dec 2015 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/19038/ https://edoc.ub.uni-muenchen.de/19038/1/Huber_Markus_B.pdf Huber, Markus B. dd

The work presented here focuses on the investigation and further development of simple mass estimators for early-type galaxies which are suitable for large optical galaxy surveys with poor and/or noisy data. We consider simple and robust methods that provide an anisotropy-independent estimate of the galaxy mass relying on the stellar surface brightness and projected velocity dispersion profiles. Under reasonable assumptions a fundamental mass-anisotropy degeneracy can be circumvented without invoking any additional observational data, although at a special (characteristic) radius only, i.e these approaches do not recover the radial mass distribution. Reliable simple mass estimates at a single radius could be used (i) to cross-calibrate other mass determination methods; (ii) to estimate a non-thermal contribution to the total gas pressure when compared with the X-ray mass estimate at the same radius; (iii) to evaluate a dark matter fraction when compared with the luminous mass estimate; (iv) to derive the slope of the mass profile when combined with the mass estimate from strong lensing; (v) or as a virial mass proxy. Two simple mass estimators have been suggested recently - the local (Churazov et al. 2010) and the global (Wolf et al. 2010) methods - which evaluate mass at a particular radius and are claimed to be weakly dependent on the anisotropy of stellar orbits. One approach (Wolf et al. 2010) uses the total luminosity-weighted velocity dispersion and evaluates the mass at a deprojected half-light radius, i.e. relies on the global properties of a galaxy. In contrast, the Churazov et al. technique uses local properties: logarithmic slopes of the surface brightness and velocity dispersion profiles, and recovers the mass at a radius where the surface brightness declines as R^{-2} (see also Richstone and Tremaine 1984, Gerhard 1993). To test the robustness and accuracy of the methods I applied them to analytic models and to simulated galaxies from a sample of cosmological zoom-simulations which are similar in properties to nearby early-type galaxies. Both local and global simple mass estimates are found to be in good agreement with the true mass at the corresponding characteristic radius. Particularly, for slowly rotating simulated galaxies the local method gives an almost unbiased mass-estimate (when averaged over the sample) with a modest RMS-scatter of 12% (Chapter 2). When applied to massive simulated galaxies with a roughly flat velocity dispersion profile, the global approach on average also provides the almost unbiased mass-estimate, although the RMS-scatter is slightly larger (14-20 %) than for the local estimator (Chapter 4). A noticeable scatter in the determination of the characteristic radius is also expected since the half-light radius depends on the radial range used for the analysis and applied methodology. Next I tested the simple mass estimators on a sample of real early-type galaxies which had previously been analyzed in detail using state-of-the-art dynamical modeling. For this set of galaxies the simple mass estimates are in remarkable agreement with the results of the Schwarzschild modeling despite the fact that some of the considered galaxies are flattened and mildly rotating. When averaged over the sample the simple local method overestimates the best-fit mass from dynamical modeling by 10% with the RMS-scatter 13% between different galaxies. The bias is comparable to measurement uncertainties. Moreover, it is mainly driven by a single galaxy which has been found to be the most compact one in the sample. When this galaxy is excluded from the sample, the bias and the RMS-scatter are both reduced to 6%. The global estimator for the same sample gives the mean deviation 4% with the slightly larger RMS-scatter of 15% (Chapter 4). Given the encouraging results of the tests I apply the local mass estimation method to a sample of five X-ray bright early-type galaxies observed with the 6-m telescope BTA in Russia. Using publicly available Chandra data I derived the X-ray mass profile assuming spherical symmetry and hydrostatic equilibrium of hot gas. A comparison between the X-ray and optical mass estimates allowed me to put constraints on the non-thermal contribution (sample averaged value is 4%) to the total gas pressure arising from, for instance, microturbulent gas motions. Once the X-ray derived circular speed is corrected for the non-thermal contribution, the mismatch between the X-ray circular speed V_c^X and the optical circular velocity for isotropic stellar orbits V_c^{iso} provides a clue to the orbital structure of the galaxy. E.g., at small radii V_c^X > V_c^{iso} would suggest more circular orbits, while at larger radii this would correspond to more radial orbits. For two galaxies in our sample there is a clear indication that at radii larger than the half-light radius stellar orbits become predominantly radial. Finally, the difference between the optical mass-estimate at the characteristic radius and the stellar contribution to the total mass permitted the derivation of a dark-matter fraction. A typical dark matter fraction for our sample of early-type galaxies is 50% for Salpeter IMF and 70% for Kroupa IMF at the radius which is close to the half-light radius (Chapter 3).

The Carina Nebula Complex is known to be an active star-formation region. This work presents a large catalogue of point-like sources assembled from archive data of the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope. This catalogue covers a region of 2.3 deg × 3.0 deg, which makes it the most extendended mid-infrared survey undertaken of the Carina Nebula Complex to date. From the catalogue a subsample of candidate young stellar objects is extracted utilising the fact that young stellar objects exhibit typical mid-infrared excesses. These catalogues are employed to characterise the young stellar population of the Carina Nebula Complex. Using them, it was possible to identify three new extended green objects and five compact green objects and find the probable sources for 28 further objects connected with jets emitted from young stars, such as molecular hydrogen emission-line objects and Herbig-Haro jets. For 17 of them, observational data from the near-infrared (from HAWK-I and 2MASS) to the far-infrared (from the Herschel Space Observatory) could be collected and their spectral energy distributions fitted. From the fit parameters, stellar characteristics such as stellar and disk masses could be estimated. No young stellar objects with masses above 10 M_sol could be evidenced, pointing towards an intermediate-mass population currently forming. It could be shown that the Gum 31 region on the outer periphery of the Carina Nebula Complex is not only part of the complex but also an important centre of star formation. A large sample of candidate young stellar object was obtained from the WISE All-Sky Data Release, which allowed a detailed comparison with both the candidate young stellar objects from the IRAC catalogue and those identified from Herschel observations. Evidence could be found that two modes of triggered star formation are going on in the HII region: Young stellar objects are found in and in front of dust pillars, which is an indicator of radiative triggering, and a ‘collect and collapse’ model of the region was shown to produce results in agreement with the observations. An objective and large-scale search for clusters of young stellar objects in the complex was performed using a nearest-neighbour algorithm. This search derived 22 clusters not described before. Nine of those are new detections in the fields of previous studies of clusters while the majority are found in fields surveyed for clusters for the first time here. Clusters are also found in agreement with previous studies where study fields overlap, thus corroborating the validity of the study. It is found that ∼40% of the young stellar objects in the Carina Nebula Complex occur in clusters while up to 60% are part of a distributed population. A total population for the 2.3 deg × 3.0 deg study field of ∼200 000 young stars is estimated.

Studies have suggested that there is a strong correlation between the masses of nuclear star clusters (NSCs) and their host galaxies, a correlation which is said to be an extension of the well-known correlations between supermassive black holes (SMBHs) and their host galaxies. But careful analysis of disk galaxies-including 2D bulge/disk/bar decompositions-shows that while SMBHs correlate with the stellar mass of the bulge component of galaxies, the masses of NSCs correlate much better with the total galaxy stellar mass. In addition, the mass ratio M-NSC/M-star,M- tot for NSCs in spirals (at least those with Hubble types Sc and later) is typically an order of magnitude smaller than the mass ratio M-BH/M-star,M- bul of SMBHs. The absence of a universal ``central massive object'' correlation argues against common formation and growth mechanisms for both SMBHs and NSCs. We also discuss evidence for a break in the NSC-host galaxy correlation, galaxies with Hubble types earlier than Sbc appear to host systematically more massive NSCs than do types Sc and later.

Observational constraints on the average radial distribution profile of AGN in distant galaxy clusters can provide important clues on the triggering mechanisms of AGN activity in dense environments and are essential for a completeness evaluation of cluster selection techniques in the X-ray and mm wavebands. The aim of this work is a statistical study with XMM-Newton of the presence and distribution of X-ray AGN in the large-scale structure environments of 22 X-ray luminous galaxy clusters in the redshift range 0.9 < z less than or similar to 1.6 compiled by the XMM-Newton Distant Cluster Project (XDCP). To this end, the X-ray point source lists from detections in the soft band (0.35-2.4 keV) and full band (0.3-7.5 keV) were stacked in cluster-centric coordinates and compared to average background number counts extracted from three independent control fields in the same observations. A significant full-band (soft-band) excess of similar to 78 (67) X-ray point sources is found in the cluster fields within an angular distance of 8' (4 Mpc) at a statistical confidence level of 4.0 sigma (4.2 sigma), corresponding to an average number of detected excess AGN per cluster environment of 3.5 +/- 0.9 (3.0 +/- 0.7). The data point towards a rising radial profile in the cluster region (r < 1Mpc) of predominantly low-luminosity AGN with an average detected excess of about one point source per system, with a tentative preferred occurrence along the main cluster elongation axis. A second statistically significant overdensity of brighter soft-band-detected AGN is found at cluster-centric distances of 4'-6' (2-3 Mpc), corresponding to about three times the average cluster radius R-200 of the systems. If confirmed, these results would support the idea of two different physical triggering mechanisms of X-ray AGN activity in dependence of the radially changing large-scale structure environment of the distant clusters. For high-z cluster studies at lower spatial resolution with the upcoming eROSITA all-sky X-ray survey, the results suggest that cluster-associated X-ray AGN may impose a bias in the spectral analysis of high-z systems, while their detection and flux measurements in the soft band may not be significantly affected.