Day 721

Wednesday.

1408.2511
The FUV to Near-IR morphologies of luminous infrared galaxies in the GOALS sample
Petty, et al

Compare the morphologies of 20 LIRGs in the FUV, B, I and H bands, using Gini (G) and M20 parameters to quantitatively estimate the distribution and concentration of flux as a function of wavelength.  HST images provide an average spatial resolution of ~80 pc.  While the LIRGs can be reliably classified as mergers across the entire range of wavelengths studied here, there is a clear shift toward more negative M20 (more bulge-dominated) and a less significant decrease in G values at longer wavelengths.  Find no correlation between the derived FUV G-M20 parameters and the global measures of the IR to FUV flux ratio, IRX.  Given the fine resolution in the HST data, this suggests either that the UV morphology and IRX are correlated on very small scales, or that the regions emitting the bulk of the IR emission emit almost no FUV light.  Use the multi-wavelength data to simulate how merging LIRGs would appear from z~0.5-3 in deep optical and NIR images such as the HUDF, and use these simulations to measure the G-M20 at these redshfits.  Simulations indicate a noticeable decrease in G, which flattens at z>=2 by as much as 40%, resulting in mis-classifying the LIRGs as disk-like, even in the rest-frame FUV.  The higher redshift values of M20 for the GOALS sources do not appear to change more than about 10% from the values at z~0.  The change in G-M20 is caused by the surface brightness dimming of extended tidal features and asymmetries, and also the decreased spatial resolution which reduced the number of individual clumps identified.  This effect, seen as early as z~0.5, could easily lead to an underestimate of the number of merging galaxies at high-redshift in the rest-frame FUV.

1408.2526
The first billion years project: gamma-ray bursts at z>5
Elliott, et al

LGRBs have been suggested as close tracers of the underlying SFR in the universe.  They could potentially be used to probe the cosmic SFH with high accuracy due to their high luminosities.  Utilise two cosmological simulations from the First Billion Years project to investigate the systematic biases between the CSFH and the LGRB rate at z>5.  Populate LGRBs using a Monte-Carlo technique and a sub-selection based on environmental metallicity, progenitor stellar mass and ante.  Using a physically motivated LGRB progenitor model, demonstrate that the LGRB rate should trace the CSFH to high redshifts z>5.  The measured LGRB rate suggests that LGRBs have opening angles of 0.1 degrees, although the degeneracy with the progenitor model cannot rule out an underlying bias.  Demonstrate that proxies that relate the LGRB rate with global LGRB host properties do not reflect the underlying LGRB environment, and are in fact a result of the host galaxy's spatial properties, such that LGRBs can easily exist in galaxies of solar metallicity. However, find a sub-class to host galaxies that have low stellar mass and are metal-rich, to the extent that their metallicity dispersions would not allow low-metallicity environments.  Detection of a host galaxy with this set of global properties would directly reflect the progenitor's environment without information on the progenitor's environment itself.  Predict that 10% of LGRBs per year are associated with this subset of host galaxies.  The forbidden line emission of these galaxies would be bright enough to be detected by instruments mounted on JWST.  Such a discovery would place strong constraints on the collapsar model and suggest other avenues to be investigated, e.g., binary progenitor models.  
1408.2543
Cupid is doomed: an analysis of the stability of the inner Uranian satellites
French, Showalter

Cupid and Belinda are the first satellite to cross orbits, and they do so on a time scale of 1e3-1e7 years.  Cressida and Desdemona are next, in 1e5 to 1e7 years.  Show that the crossing times are highly sensitive to ICs and that Cupid's instability is related to its resonant interactions with Belinda.  Show that a previously discovered power law, which relates orbit crossing time to satellite mass, is valid across a wide range of masses.  Generalize the power law to handle two unstable orbital pairs with overlapping lifetimes and show that it can be used to extend the time span of studies of orbital stability in a computationally efficient manner.  Results suggest that the current Uranian satellite system is in transition and that the moons will continue to collide and reaccrete for the foreseeable future.

1408.2553
Quenching of star formation in SDSS groups: centrals, satellites and galactic conformity
Knobel, Lilly, Woo, Kovac

Re-examine the fraction of low-z SDSS satellite and centrals in which SF has been quenched, using the environment quenching efficiency formalism that separates out the dependence of stellar mass.  Show that the centrals of the groups containing the satellites are responding to the environment in the same way as their satellites, and that the well known differences between satellite and the general set of centrals arises because the latter are overwhelmingly dominated by isolated galaxies.  The widespread concept of "satellite quenching" as the cause of environmental effects in the galaxy population can therefore be generalized to "group quenching".  Then explore the dependence of the quenching efficiency of satellites on overdensity, group-centric distance, halo mass, the stellar mass of the satellite, and the stellar mass and sSFR of its central, trying to isolate the effect of these often interdependent variables.  Emphasize the importance of the central sSFR in the quenching efficiency of the associated satellites, and develop the meaning of this "galactic conformity" effect in a probabilistic description of the quenching of galaxies.  Show that conformity is strong, and that it varies strongly across parameter space.  Several arguments then suggest that environmental quenching and mass quenching may be different manifestations of the same underlying process.  These include the fact that mass quenching of galaxies is associated with the same halo masses that apparently see the onset of environmental effects in the satellites.  The marked difference in the apparent mass dependencies of environment quenching and mass quenching which produces distinctive signatures in the mass functions of centrals and satellites will arise naturally, since the distribution of the environmental variables are essentially independent of the stellar mass of the satellite.