1202.0550
Simulating the evolution of disc galaxies in a group environment. I. the influence of the global tidal field
Villalobos, De Lucia, Borgani, Murante
Study evolution of disc galaxy within the global tidal field in numerical simulations. Both disc and group are multi-component, collisionless, N-body systems (DM and stars). [gas?] In simulations, evolution of disc followed as their orbits sink towards the group center, under the effect of dynamical friction. Explore: prograde and retrograde orbits, orbital eccentricities, disc inclination, role of central bulge in discs, internal disc kinematics, and galaxy-to-group mass ratios. Find: significant disc transformations occur only after the mean density of the group, measured within the orbit of the galaxy, exceeds ~0.3-1 times the central mean density of the galaxy. The morphological evolution of discs is found to be strongly dependent on the initial inclination of the disc wrt the orbital plane. Discs on face-on and retrograde orbits are shown to retain longer their disc structures and kinematics, in comparison to prograde discs. [interesting.] Suggests after interacting with the global tidal field alone, a significant fraction of disc galaxies should be found in the central regions of groups. Prominent central bulges are not produced, and pre-existing bulges are not enhanced in discs after the interaction with the group. Assuming that most S0 are formed in group environments, implies that prominent bulges should be formed mostly by young stars, created only after a galaxy has been accreted by a group. [why?] Contrary to some current implementations of tidal stripping in semi-analytical models of galaxy evolution, find that more massive galaxies suffer more tidal stripping. [why?]
1202.0551
Spin-down of radio millisecond pulsars at Genesis
Tauris
Millisecond pulsars are old NSs that have been spun up via accretion of mass from a binary companion star. An important issue for understanding the physics of the early spin evolution of millisecond pulsars is the impact of the expanding magnetosphere during the terminal stages of the mass-transfer process. Report binary stellar evolution calculations that show the braking torque acting on a NS, when the companion star decouples from its Roche-lobe, is able to dissipate >50% of the rotational energy of the pulsar. This may explain the apparent difference in observed spin distributions between x-ray and radio millisecond pulsars and help account for the noticable age discrepancy with their young WD companions.
1202.0552
Vertical structure of a SNe-driven turbulent magnetized ISM
Hill, Joung, Mac Low, Benjamin, Haffner, Klingenberg, Waagan
Stellar feedback drives the circulation of matter from the disk to the halo of galaxies. Perform 3d MHD sims of a vertical column of the ISM with initial conditions typical of the solar circle in which SNe drive turbulence and determine the vertical stratification of the medium. Find: majority (~90%) of the mass is contained in thermally-stable temperatuare regimes of cold molecular and atomic gas at T<200K or warm atomic and ionized at 5k < T < 1e4.2 K, with strong peaks on probability distribution functions of T in both the cold and warm regimes. The 200-1e4.2 K gas fills 50-60% of the volume near the plane, with hotter gas associated with SNe remnants (30-40%) and cold clouds (<10%) embedded within. At |z| ~1-2 kpc, transition-temperature 1e5K gas accounts for most of the mass and volume, while hot gas dominates at |z| > 3kpc. The magnetic field in the models has no significant impact on the scale heights of gas in each temperature regime; the magnetic tension force is approximately equal to and opposite the magnetic pressure, so the addition of the field does not significantly affect the vertical support of the gas. The addition of a magnetic field does reduce the fraction of gas in the cold (<200K) regime with a corresponding increase in the fraction of warm (1e4K) gas. However, models lack rotational shear and this have no large-scale dynamo, which reduces the role of the field in the models compared to reality. The SNe drive oscillations in the vertical distribution of halo gas, with the period of the oscillations ranging from ~30 Myr in the T<200K gas to ~100 Myr in the 1e6 K gas, in line with predictions by Walters & Cox.
* didn't know there were vertical outflow oscillations in the distribution of gas in... disk gals?
1202.0553
The effects of primordial non-gaussianity on giant-arc statistics: a scale dependent example
D'Aloisio, Natarajan
Have quantified the impact of primordial non-Gaussianity on the probability of giant-arc formation, focusing on the local form of non-Gaussianity and found that it can have only a modest effect given the most recent constraints from CMB measurements. Present new calculations here using parameterization of scale-dependent non-G in which the primordial power bispectrum has the equilateral shape and the effective f_NL parameter depends on scale. Find that non-G of this type can yield a larger effect on the giant-arc abundance compared to the local form due to both the scale dependence and the relatively weaker constraints from CMB measurements. In contrast to the maximum ~40% effect previously found for the local form, find that the predicted giant-arc abundance for the scale-dependent equilateral form can differ by a factor of a few with respect to the Guassian case.
1202.0554
Cuspy no more: how outflows affect the central dark matter and baryon distribution in LCDM galaxies
Governato, Zolotov, Pontzen, Christensen, Oh, Brooks, Quinn, Shen, Wadsley
Examine the evolution of the inner DM and baryonic density profile of a new sample of simulated field galaxies using fully cosmological, LCDM, high resolution SPH+N-body sims; includes explicit H2 and metal cooling, SF and SNe driven gas outflows. Starting at highg z, repeated gas outflows following bursty SF transfer energy to the DM component and significantly flatten the originaly 'cuspy' central DM mass profile of galaxies with present day stellar masses in the 1e4.5-98 Msun range. At z=0, the central slope of the DM density profile of our galaxies (measured at 0.3-0.7 kpc from center) is well fitted by rho_DM propto r^alpha, with alpha ~= -0.5 + 0.35 log_10 (M*/1e8 Msun) where M* is the stellar mass of the galaxy and 4 < log (M_star/Msun) < 8.4. These values imply DM profiels flatter than those obtained in DM-only simulations and in close agreement with those inferred in galaxies from the TINGS and LITTLE THINGS survey. Only in very small halos, where by z=0 star formation has converted less than ~0.03% of the original baryon abundance into stars, outflows do not flatten the original cuspy DM profile out to radii resolved by our simulations. The mass (DM and baryonic) measured within the inner 500pc of each simulated galaxy remains nearly constant over 4 orders of magnitudes in stellar mass for Mstar < 1e9 Msun. Consistent with estimates for faint LG dwarfs and field galaxies. Addresses one of the outstanding problems of CDM model.
1202.0555
In situ formation of SgrA* stars via disk fragmentation: parent cloud properties and thermodynamics
Mapelli, Hayfield, Mayer, Wadsley
Formation of massive young stars surrounding SgrA* is still an open question. In this paper, simulate the infall of a turbulent molecular cloud towards the GC. Adopt two different cloud masses (4e4 and 1e5 Msun). 4 isothermal gas runs, plus one with radiative cooling. In all simulations, molecular cloud is tidally disrupted, spirals towards the GC, and forms a small, dense and eccentric disk around SgrA*. With high res sims, follow the fragmentation of the gas disk. Satar candidates form in a ring at 0.1-0.4 pc from the SMBH and have moderately eccentric orbits (0.2-0.4), in good agreement with the observations. The mass function of star candidates is top-heavy only if the local gas temperature is high (>100K) during the star formation and if the parent cloud is sufficiently massive (>1e5 Msun). This, this study indicates that the infall of a massive molecular cloud is a viable scenario for the formation of massive stars around SgrA*, provided that the gas temperature is kept sufficiently high (>100K).
1202.0557
Global models of runaway accretion in WD debris disks
Metzger, Rafikov, Bochkarev
Growing sample of WDs with metal-enriched atmospheres are accompanied by excess IR emission, indicating that they are encircled by a compact dusty disk of solid debris. Such 'WD debris disks' are thought to originate from the tidal disruption of asteroids or other minor bodies, but the precise mechanism(s) responsible for transporting matter to the WD surface remains unclear, especially in those systems with the highest inferred metal accretion rates dM_Z/dt ~ 1e8-10 g/s. Present global time-dependent calculations of the coupled evolution of the gaseous and solid components of WD debris disks. Solids transported inwards (initially due to PR drag) sublimate at tens of WD radii, producing a source of gas that accretes onto the WD surface and viscously spreads outwards in radius, where it overlaps with the solid disk. If the aerodynamic coupling between the solids and gaseous disks is sufficiently strong (and/or the gas viscosity sufficiently weak), then gas builds up near the sublimation radius faster than it can viscously spread away. Since the rate of drag-induced solid accretion increases with gas density, this results in a runaway accretion process, during which the WD accretion rate reaches values orders of magnitude higher than can be achieved by PR drag alone. Explore the evolution of WD debris disks across a wide range of physical conditions and calculate the predicted distribution of observed accretion rates, finding reasonable agreement with the current sample. Although the conditions necessary for runaway accretion are at best marginally satisfied given the minimal level of aerodynamic drag between circular gaseous and solid disks, the presence of other stronger forms of solid-gas coupling--such as would result if the gaseous disk is only mildly eccentric--substantially increase the likelihood of runaway accretion.
1202.0560
Dwarf galaxy sized monopoles as dark matter?
Evslin, Gudnason
As the title says.
1202.0581
Surface brightness fluctuations as primary and secondary distance indicators
Blakeslee
The surface brightness fluctuations (SBF) method measures the variance in a galaxy's light distribution arising from fluctuations in the numbers and luminosities of individual stars per resolution element. Once calibrated for stellar population effects, SBF measurements with HST provide distances to early-type galaxies with unrivaled precision. Optical SBF data from HST for the Virgo and Fornax clusters give the relative distances of these nearby fiducial clusters with 2% precision and constrain their internal structures. Observations in hand will allow to tie the Coma cluster, the standard of comparison for distant cluster studies, into the same precise relative distance scale. The SBF method can be calibrated in an absolute sense either empirically from Cepheids or theoretically from stellar population models. The agreement between the model and empirical zero points has improved dramatically, providing an independent confirmation of the Cepheid distance scale. SBF is still brighter in the near-IR, and an ongoing program to calibrate the method for the F110W and F160W passbands of the WFC3 IR channel will enable accurate distance derivation whenever a large early-type galaxy or bulge is observed in these passbands at distances reaching well out into the Hubble flow.
* a new (to me) cosmological distance measure
1202.0610
Modelling high z Lyman-alpha emitters
Garel, Blaizot, Guidedoni, Schaerer, Verhamme, Hayes
Present a new model for high-z LAEs in the cosmological context which takes in to account the resonant scattering of Lya photons through expanding gas. Implement gas outflow model for each galaxy based on simple scaling arguments. Coupling of Lya transfer through expanding or static dusty shells of gas allows us to derive the Lya escape fractions and profiles. The predicted distribution of Lya photons escape fractions shows that galaxies with a low star formation rate have a f_esc of the order of unity, suggesting that, Lya may be used to trace the SFR assuming a given conversion law. In galaxies forming stars intensely, the escape fraction spans the whole range from 0 to 1. The model is able to get a good match to the UV and Lya luminosity function data at 3<z<5. Find in good agreement with both the bright Lya data and the faint population observed by Rauch+2008 at z=3. Most of the Lya profiles of LAEs are redshifted by the diffusion in the outflow which suppresses IGM absorption. The bulk of the observed Lya EW distribution is recovered by the model, but fail to obtain the very large values sometimes detected. Predictions for stellar masses and UV LFs of LAEs show a satisfactory agreement with observational estimates. The UV brightest galaxies are found to show only low Lya EWs in the model, as it is reported by many observations of high redshift LAEs. Interpret this effect as the joint consequence of old stellar populations hosted by UV-bright galaxies, and high HI column densities that are predicted for these objects, which quench preferentially resonant Lya photos via dust extinction.
1202. 0640
The correlation function of galaxy clusters and detection of BAOs
Hong, Han, Wen, Sun, Zhan
Calculate correlation function of 14k galaxy clusters of z<0.4 selected from the cluster catalog. The correlation function can be fitted with a power-law model xi(r)=(r/R_0)^gamma on the scales of 10 Mpc/h < r < 50 Mpc/h, with a larger correlation length of R_0 = 18.84 pm 0.27 Mpc/h for clusters with a richness of R >15 and a smaller length of R_0=16.15 pm 0.13 Mpc/h for clusters with a richness of R > 5. The power law index of gamma=2.1 is found to be almost the same for all cluster subsamples. A pronounced BAO peak is detected at r~110 Mpc/h with a significance of 1.9 sigma. By analyzing the correlation function in the range of 10Mpc/h<r<200 Mpc/h, find the constraints on distance parameters are D_v(0.276)=1077pm55 Mpc and h=0.73 pm 0.039, which are consistent with WMAP7. However, the BAO signal from the cluster sample is stronger than expected, and leads to a rather low matter density Omega_M h^2=0.093 pm 0.0077, which deviates from WMAP7 by more than 3 sigma. The correlation function of the GMBCG cluster sample is also calculated and the detection of the BAO feature is confirmed.
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