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Register a new userLuminous Satellites of Early-Type Galaxies I: Spatial Distribution
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Anna Mercedes Nierenberg
Publication date
2011
fields
Physics
and research's language is
English
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We study the spatial distribution of faint satellites of intermediate redshift (0.1<z<0.8), early-type galaxies, selected from the GOODS fields. We combine high resolution HST images and state-of-the-art host subtraction techniques to detect satellites of unprecedented faintness and proximity to intermediate redshift host galaxies (up to 5.5 magnitudes fainter and as close as 0.5/2.5 kpc to the host centers). We model the spatial distribution of objects near the hosts as a combination of an isotropic, homogenous background/foreground population and a satellite population with a power law radial profile and an elliptical angular distribution. We detect a significant population of satellites, Ns =1.7 (+0.9,-0.8) that is comparable to the number of Milky Way satellites with similar host-satellite contrast.The average projected radial profile of the satellite distribution is isothermal, gamma_p= -1.0(+0.3,-0.4), which is consistent with the observed central mass density profile of massive early-type galaxies. Furthermore, the satellite distribution is highly anisotropic (isotropy is ruled out at a >99.99% confidence level). Defining phi to be the offset between the major axis of the satellite spatial distribution and the major axis of the host light profile, we find a maximum posterior probability of phi = 0 and |phi| less than 42 degrees at the 68% confidence level. The alignment of the satellite distribution with the light of the host is consistent with simulations, assuming that light traces mass for the host galaxy as observed for lens galaxies. The anisotropy of the satellite population enhances its ability to produce the flux ratio anomalies observed in gravitationally lensed quasars.
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We have made a careful selection of a large complete volume-limited sample (1209) of projected close pairs (7<r_p<50 kpc) of luminous early-type galaxies (M_r<-21.5) in the local universe (z<0.12) from the SDSS data. 249 (21%) of them show interaction features, which suggests that about 0.8% of the galaxies are merging. We derived a comoving volume merger rate of ~(1.0+/-0.4)times 10^{-5} Mpc^{-3} Gyr^{-1} for luminous early-type galaxies. This is a direct observational determination of the merger rate of luminous galaxies in the local universe. We also obtained the chirp mass distribution of supermassive black hole (SMBH) binary following log[Phi(log M /M_{odot})]=(21.7+/-4.2)-(3.0+/-0.5)log M/M_{odot}. With less assumptions than previous works, we estimated the strain amplitude of the gravitational wave (GW) background from coalescence of SMBH binaries at frequency 10^{-9}-10^{-7} Hz.
X-ray luminosity, temperature, gas mass, total mass, and their scaling relations are derived for 94 early-type galaxies using archival $Chandra$ X-ray Observatory observations. Consistent with earlier studies, the scaling relations, $L_X propto T^{4.5pm0.2}$, $M propto T^{2.4pm0.2}$, and $L_X propto M^{2.8pm0.3}$, are significantly steeper than expected from self similarity. This steepening indicates that their atmospheres are heated above the level expected from gravitational infall alone. Energetic feedback from nuclear black holes and supernova explosions are likely heating agents. The tight $L_X - T$ correlation for low-luminosities systems (i.e., below 10$^{40}$ erg/s) are at variance with hydrodynamical simulations which generally predict higher temperatures for low luminosity galaxies. We also investigate the relationship between total mass and pressure, $Y_X = M_g times T$, finding $M propto Y_{X}^{0.45pm0.04}$. We explore the gas mass to total mass fraction in early-type galaxies and find a range of $0.1-1.0%$. We find no correlation between the gas-to-total mass fraction with temperature or total mass. Higher stellar velocity dispersions and higher metallicities are found in hotter, brighter, and more massive atmospheres. X-ray core radii derived from $beta$-model fitting are used to characterize the degree of core and cuspiness of hot atmospheres.
We analyze $Chandra$ observations of the hot atmospheres of 40 early spiral and elliptical galaxies. Using new temperature, density, cooling time, and mass profiles, we explore relationships between their hot atmospheres and cold molecular gas. Molecular gas mass correlates with atmospheric gas mass and density over four decades from central galaxies in clusters to normal giant ellipticals and early spirals. The mass and density relations follow power laws: $M_{rm mol} propto M_{rm X}^{1.4pm0.1}$ and $M_{rm mol} propto n_{rm e}^{1.8pm0.3}$, respectively, at 10 kpc. The ratio of molecular gas to atmospheric gas within a 10 kpc radius lies between $3%$ and $10%$ for early-type galaxies and between $3%$ and $50%$ for central galaxies in clusters. Early-type galaxies have detectable levels of molecular gas when their atmospheric cooling times falls below $sim rm Gyr$ at a radius of 10 kpc. A similar trend is found in central cluster galaxies. We find no relationship between the ratio of the cooling time to free fall time, $t_{rm c}/t_{rm ff}$, and the presence or absence of molecular clouds in early-type galaxies. The data are consistent with much of the molecular gas in early-type galaxies having condensed from their hot atmospheres.
The spatial distribution of Milky Way (MW) subhaloes provides an important set of observables for testing cosmological models. These include the radial distribution of luminous satellites, planar configurations, and the abundance of dark subhaloes whose existence or absence is key to distinguishing amongst dark matter models. We use the COCO $N$-body simulations of cold dark matter (CDM) and 3.3keV thermal relic warm dark matter (WDM) to predict the satellite spatial distribution. We demonstrate that the radial distributions of CDM and 3.3keV-WDM luminous satellites are identical if the minimum pre-infall halo mass to form a galaxy is $>10^{8.5}$$mathrm{M}_{odot}$ The distribution of dark subhaloes is significantly more concentrated in WDM due to the absence of low mass, recently accreted substructures that typically inhabit the outer parts of a MW halo in CDM. We show that subhaloes of mass $[10^{7},10^{8}]$$mathrm{M}_{odot}$ and within 30kpc of the centre are the stripped remnants of larger haloes in both models. Therefore their abundance in WDM is $3times$ higher than one would anticipate from the overall WDM subhalo population. We estimate that differences between CDM and WDM concentration--mass relations can be probed for subhalo--stream impact parameters $<2$kpc. Finally, we find that the impact of WDM on planes of satellites is likely negligible. Precise predictions will require further work with high resolution, self-consistent hydrodynamical simulations.
We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation (epsilon > 0.2) and intermediate to high luminosities (M_z<-19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, we find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and where the present day major axis is an indicator of the preferred merging axis.
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