Wednesday. German taxes are so fun to read about, I forgot to read astro-ph last night.
1205.1057
Discovery of super-Li rich red giants in dwarf spheroidal galaxies
Kirby, Fu, Guhathakurta, Deng
Stars destroy Li in their normal evolution, and the convective envelopes of evolved red giants reach temperatures of few 1e6 K, hot enough for the 7Li(p,alpha)4He reaction to burn Li efficiently. Only about 1% of the first-ascenet red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonethless, Li-rich red giants do exist--found 15 Li-rich red giants (14 new) among a sample of 2054 in MW dwarf satellite galaxies. Doubles the sample of metal-poor [Fe/H]<~-0.7, Li-rich red giants, includes the most metal-poor Li-enhanced star known ([Fe/H]=-2.82, A(Li)_NLTE=3.15). Most of these stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. The Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. Consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and seems rare only because it is brief.
1205.01058
A false positive for ocean glint on exoplanets: the latitude-albedo effect
Cowan, Abbot, Voigt
Can we ID liquid water on planet surfaces? Specular reflection (glint) increases the apparent albedo of a planet at crescent phases, but simulated reflected light curves show that glint-like phase variations can appear even if there is no specular reflection in the model. (1) poles are likely covered by highly reflective snow and ice, (2) reflected light from a modest-obliquity planet at crescent phases probes higher latitudes than at gibbous phases (a planet's apparent albedo will naturally increase at crescent phase. The "latitude-albedo effect" will operate even for large obliquities. A necessary pre-condition for properly interpreting reflected phase variations: Using rotational and orbital color variations to map the surfaces of directly imaged planets and estimate their obliquity. This effect severely limits the utility of specular reflection for detecting oceans on exoplanets.
1205.1059
Chaotic exchange of solid material between planetary systems: implications for lithopanspermia
Belbruno, Moro-Martin, Malhotra, Savransky
Examine a low energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. ... Estimate that the order of 3e8 x l(km) could potentially be life-bearing, where l(km) is the depth of the Earth crust in km that was ejected as the result of the early bombardment.
1205.1064
The COSMOS Density Field: A reconstruction using both weak lensing and galaxy distributions
Amara, Lilly, Kovac, Rhodes, Massey, ... et al
Use HST WL measurements with galaxy clustering to reconstruct mass distribution to z=1 in COSMOS field. High resolution in z with galaxies (with spectra); lensing data empirically calibrates mass normalization. Two steps to convert galaxy survey into a density field: first, create a smooth field from the galaxy positions (use: i. gaussian smoothing, ii. convolution with truncated isothermal sphere, iii. fifth nearest neighbor smoothing and iv. a multi-scale entropy method). The second step is toe rescale this density field using a bias prescription. Calculate optimal bias scaling for each method by comparing predictions from the smoothed density field with the measured weak lensing data, on a galaxy-by-galaxy basis. Find the bias to be 2.5 pm 0.25. Also find evidence for a strongly evolving bias, increasing by a factor of ~3.5 between 0<z<0.8. Strong evolution can be explained by the fact that we use a flux limited sample to build the density field.
1205.1066
Detection of ongoing star formation at low levels in nearby elliptical galaxies
Ford, Bregman
Small amounts of star formation in elliptical galaxies (seen in optical line incidies, cooling x-ray gas, and mid-IR dust emission) have been difficult to detect, but using HST WFC3 imaging, have identified individual young stars and star clusters in 4 nearby ellipticials. Orders of magnitude more sensitive than other methods (SF of 1e-5 Msun/yr); SF detected in all galaxies. Observe 2-8e-5 Msun/yr. SFH roughly constant from 0.5-1.5 Gyr, but decreased by a factor of several in the past 0.3 Gyr. Most star clusters have a mass of 1e2 to 1e4 Msun. sSFR of 1e-16 (today) or 1e-14 (average of the past Gyr) cannot build stellar mass of galaxies within the age of the universe, quantifying for the first time the level of quenching they have experienced relative to their average value. No obvious correlation between either the presence or spatial distribution of postulated SF indicators and the SF detected.
1205.1082
Detection of a radio bridge in Abell 3667
Carretti, Brown, ... et al
Detection of a radio bridge of unpolarized synchrotron emission connecting the NW relic of the galaxy cluster Abell 3667 to its central regions. Emission further aligned with a diffuse X-ray bridge, and represents the most compelling direct evidence for an association between intracluster medium turbulence and diffuse synchrotron emission. Conclude: synchrotron bridge is related to the post-shock turbulence wake trailing a shock front. The origin of the relativistic electrons still unknown; the turbulent re-acceleration model provides a natural explanation for the large-scale emission. The bridge magnetic field intensity is 0.5-0.6 uG. Further detect diffuse emission coincident with the central regions of the cluster for the first time.
1205.1124
Swift follow-up observations of candidate gravitational-wave transient events
Evans, et al (>800 authors!)
Present the first multi-wavelength follow-up observations of two candidate gravitational-wave transient events recorded by LIGO and Virgo in 2009-2010 science run. Events detected were observed by Swift. Image transient detection used (but consistent with BG). Selected GW events show no evidence of an astrophysical origin; one of them consistent with BG and the other was a test (part of a "challenge"). Demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement going EM and GW observations could bring. ... [bah, boring! no real results]
1205.1194
Galactic annihilation emission from nucleosynthesis positrons
Martin, Strong, Jean, Alexis, Diehl
The Galaxy hosts a widespread population of low-energy positrons, as seen in gamma-ray telescopes through annihilation emission from the bulge region, with a fainter contribution from the inner disk. Exact origin of these particles currently unknown. Estimate the contribution to the annihilation signal of positrons generated in the decay of radioactive 26Al, 56Ni and 44Ti. Adapt GALPROP propagation code to simulate the transport and annihilation of radioactivity positron in a model of our Galaxy. Using plausible source spatial distributions, explore several possible propagation scenarios to account for the large uncertainties in the transport of 1MeV positrons in the ISM. In high-diffusion ballistic case, up to 40% escape the Galaxy. This affects bulge positrons more than disk positrons (disk positrons mostly injected in the dense molecular ring. Nucleosynthesis positrons alone cannot account for the observed annihilation emission in the frame of the model. Additional component is needed to eeelain the strong bulge contribution, and the latter is very likely concentrated in the central regions if positrons have initial energy in the 100keV-1MeV range.
1205.1332
Low Metallicity ISM: excess submillimetre emission and CO-free H2 gas
Madden et al
Excess emission often found in low metallicity ISM of dwarfs in FIR/submm regions than the more metal-rich galaxies. Excess found beginning or beyond 500mu. The SEDs of the lowest meatllicity galaxies give very low dust masses and excessively low values of dust to gas ratio (DGR), inconsistent with the amount of metals expected to be captured into dust. These results rely on accurately quantifying the total molecular gas reservoir, which is uncertain in low metallicity galaxies due to the difficulty in detecting CO(1-0) emission. Dwarf galaxies show an exceptionally high CII/CO(1-0) ratio which may be indicative of a significant reservoir of 'CO-free' molecular gas residing in the pohotodissociated envelope, and not traced by the small CO cores.
1205.1401
Composite reverberation mapping
Fine, Shanks, Croom, Green, Kelly, Berge, Chornock, Burgett, Magnier, Price
Reverberation mapping: one of the best techniques for studying the inner regions of QSOs. Besed on cross-correlating continuum and emission-line light curves. New time-resolved optical surveys will produce well sampled light curves for many thousands of QSOs. Explore the potential of stacking samples to produce composite cross-correlations for groups of objects that have well sampled continuum light curves, but only a few (~2) emission-line measurements. Explores multiplexing capability of multi-object spectrographs to significantly reduce the observational expense of revelation mapping, in particular at high redshift (0.5 to 2.5). Demonstrate the technique using simulated QSO light curves (biases from stacking studied). Show: stacked X-corr have smaller amplitude peaks compared to well sampled correlation functions as the mean flux of the emission light curve is poorly constrained. But the position of the peak remains intact. ....
1205.1493
Intensity mapping of lyman-alpha emission during the epoch of reionization
Silva, Santos, Gong, Cooray
Absolute intensity and anisotropies of Lya field present during the epoch of reionization. Consider both galaxy and IGM emission, take into account all of the contributions to the production of Lya photons: recombinations, collisions, continuum emission from stars and scattering of Lyman-n photons in the IGM. Find emission from individual galaxies dominates over the IGM (at z~7-10), a level well below the extragalactic BG intensity from starlight emission from galaxies; unlikely that the Lya background during reionization can be established by an experiment aiming at an absolute BG light measurement. Instead consider Lya intensity mapping for anisotropy power spectrum measurements. a few Mpc scale fluctuations can be measured.
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