1403.0567
Observations and three-dimensional photoionization modeling of the Wolf-Rayet planetary nebula Abell 48
Danekhar et al
Central star of Abell 48 exhibits spectral features similar to massive N-sequence WR stars. This raises a question whether it is still a planetary nebula or rather a ring nebula of a massive star. Construct a 3d photoionization model of Abell 48, constrained by optical integral field spectroscopy. An analysis of the spatially resolved velocity distributions allowed constraints on the geometry. Use the collision ally excited lines to obtain the nebular physical conditions and ionic abundances of N, O, Ne, S, and Ar wrt H; determine He temperatures and ionic abundances of He and C from the optical recombination lines. Obtain a good fit to the observations for most of the emission-line fluxes in the photoionization model. The ionic abundances deduced from the model are in decent agreement with those derived from empirical analysis. However, obvious discrepancies between He temperatures exists (model overestimates). This could be due to the presence of a small fraction of cold metal-rich structures, which were not included in the model. It is found that the observed nebular line fluxes were best reproduced by using a H-deficient expanding model atmosphere as the ionizing source with an effective temperature of 70k K and a stellar luminosity of 5500 Lsun, which corresponds to a relatively low-mass progenitor star (~3 Msun) rather than a massive Pop I star.
1403.0573
CLASH: extending galaxy strong lensing to small physical scales with distant sources highly-magnified by galaxy cluster members
Grillo et al
Present SL system in which a double source is imaged 5x by 2 early-type galaxies. Take advantage of the multi-band photometry obtained, complemented by spectroscopic followup data. Use photo-z of 3.7 for the source and confirm spectroscopically the membership of the 2 lenses to the galaxy cluster at z=0.44. Exploit the excellent angular resolution of HST images to model the 2 lenses in terms of singular isothermal sphere profiles and derive robust effective velocity dispersions of 97 and 240 km/s. The total mass distribution of the cluster is also well characterized by using only the local information contained in this lensing system, that is located at a projected distance of more than 300 kpc from the cluster luminosity center. According to the best-fitting lensing and composite stellar population models, the source is magnified by a total factor of 50 and has a luminous mass of about 1.0pm0.5 e9 Msun. By combining the total and luminous mass estimates of the 2 lenses, measure luminous over total mass fractions projected within the effective radii of 0.51pm0.21 and 0.80 pm 0.32. With these lenses, extend the analysis of the mass properties of lens early-type galaxies by factors that are about 2 and 3 times smaller than previously done with regard to, respectively, velocity dispersion and luminous mass. The comparison of the total and luminous quantities of the lenses with those of astrophysical objects with different physical scales reveals the potential of studies of this kind for investigating the internal structure of galaxies. These studies, made possible thanks to the CLASH survey, will allow us to go beyond the current limits posed by the available lens samples in the field.
1403.0576
Dark matter as a trigger for periodic comet impacts
Randall, Reece
Periodic crater record on Earth (35 Myr), possibly from Oort cloud comet perturbations as the Solar System passes through the galactic midplane. Show that a smooth dark disk in the galactic mid plane would address the case of the mid-plane passage perturbation. Such a disk is motivated by a novel DM component with dissipative cooling (from an earlier work). Find: the likelihood ratio for such a model relative to one with a constant cratering rate is 3.0, which moderately favors the dark disk model. Analysis furthermore yields a posterior distribution that, based on current crater data, singles out a DM surface density of approximately 10 Msun per square parsec. The geological record thereby motivates a particular model of DM that will be probed in the near future.
1403.0587
Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy"
Faure et al
In an equilibrium axisymmetric galactic disc, the mean galactocentric radial and vertical velocities are expected to be zero everywhere. In recent years, various large spectroscopic surveys have however shown that stars of the MW disc exhibit non-zero mean velocities outside of the Galactic plane in both the Galactocentric radial and vertical velocity components. While radial velocity structures are commonly assumed to be associated with non-axisymmetric components of the potential such as spiral arms or bars, non-zero vertical velocity structures are usually attributed to excitations by external sources such as a passing satellite galaxy or a small dark matter substructure crossing the Galactic disc. Use a 3d test-particl simulation to show that the global stellar response to a spiral perturbation induces both a radial velocity flow and non-zero vertical motions. The resulting structure of the mean velocity field is qualitatively similar to what is observed across the MW disc. Show that such a pattern also naturally emerges from an analytic toy model based on linearized Euler equations. Conclude that an external perturbation of the disc might not be a requirement to explain all of the observed structures in the vertical velocity of stars across the Galactic disc. Non-axisymmetric internal perturbations can also be the source of the observed mean velocity patterns.
1403.0588
Fossil groups origins III. Characterization of the sample and observational properties of fossil systems
Zarattini et al
Fossil systems are group- or cluster-sized objects whose luminosity is dominated by a very massive central galaxy. In the current CDM scenario, these objects formed hierarchically at an early epoch of the Universe and then slowly evolved until the present day. This is the reason why they are called fossils. Began an observational program to characterize a sample of 34 fossil group candidates spanning a broad range of physical properties. Deep r-band images were taken for each candidate and optical spectroscopic observations were obtained for 1200 galaxies. This new dataset was completed with SDSS DR7 archival data to obtain robust cluster membership and global properties of each fossil group candidate. For each system, recomputed the magnitude gaps between the two brightest galaxies and the first and fourth galaxies within 0.5 R200. Consider fossil systems those with m_12>2 mag or m_14>2.5 mag. Find that 15 candidates turned out to be fossil systems. Their observational properties agree with those of non-fossil systems. Both follow the same correlations, but fossils are always extreme cases. In particular, they host the brightest central galaxies and the fraction of total galaxy light enclosed in the central galaxy is larger in fossil than in non-fossil systems. Finally, confirm the existence of genuine fossil clusters. Combining results with others in the literature, favor the merging scenario in which fossil systems formed due to mergers of L* galaxies. The large magnitude gap is a consequence of the extreme merger ratio within fossil systems and therefore it is an evolutionary effect. Moreover, suggest that at least one candidate in the sample could represent a transitional fossil stage.
1403.0590
Fossil groups origins IV. The relation between optical and X-ray lumionsities
Girardi et al
… Fossil and normal systems [in this comparison] span the same redshift range 0<z<0.5 and have the same Lx distribution. For each fossil and normal system, homogeneously compute Lopt in the r-band within the characteristics cluster radius, using SDSS DR7. Sample the Lx-Lopt relation over 2 orders of magnitude in Lx. Analysis shows that fossil systems are not statistically distinguishable from the normal systems both through the 2d KS test and the fit of the Lx-Lopt relation. THe optical luminosity of the galaxy system does strongly correlate with the X-ray luminosity of the hot gas component, independently of whether the system is fossil or not. Conclude that results are consistent with the classical "merging scenario" of the brightest galaxy formed via merger/cannibalism of other group galaxies, with conservation of the optical light. Find no evidence for a peculiar state of the hot intracluster medium.
1403.0608
The Atacama Cosmology Telescope: cross correlation with Planck maps
Louis et al
Find excellent agreement between the two datasets at 143 and 217 GHz, quantified using the variance of the residuals between the ACT PS and the ACTxPlanck cross-spectra. Use these X-correlations to calibrate the ACT data to 0.7 and 2% precision respectively. Find no evidence for anisotropy in the calibration parameter. Compare the Planck 353 GHz PS with the measured amplitudes of dust and CIB of ACT data at 148 and 218 Ghz. Also compare planet and point source measurements from the two experiments.
1403.0732
Diffuse Ly$\alpha$ halos around galaxies at $z=2.2-6.6$: implications for galaxy formation and cosmic reionization
Momose et al
Present diffuse Lya halos (LAHs) identified in the composite Subaru narrowband images of 100-3600 Lya emitters (LAEs) at z=2.2, 3.1, 3.7, 5.7, and 6.6. First, examine potential artifacts mimicking LAHs that include a large-scale PSF made by instrumental and atmospheric effects. Based on critical testing with composite images of non-LAE samples whose narrowband-magnitude and source-size distributions are the same as the LAE samples, confirm that no artifacts can produce a diffuse extended feature similar to the LAHs defined here. Then measure the scale lengths of exponential profile for the LAHs estimated from the z=2.2-6.6 LAE samples of L_Lya>2e42 erg/s. Obtain the scale lengths of 5-10 kpc at z=2.2-5.7, and find no evolution of scale lengths in this redshift range beyond the measurement uncertainties. Combining this result and the previously-known UV-continuum size evolution, infer that the ratio of LAH to UV-continuum sizes is nearly constant at z=2.2-5.7. On the other hand, the scale length of the z=6.6 LAH is larger than 5-10 kpc, and there is a hint the the scale lengths of LAHs would increase from z=5.7 to 6.6. This may be a signature of increasing fraction of neutral H scattering Lya photons, due to cosmic reionization, although larger data are needed for a definitive conclusion.
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