Day 781

Friday.

1410.1884
Detection of galactic center source G2 at 3.8 $¥mu$m during periapse passage
Witzel, et al

Report new observations of the GC source G2 from Keck.  G2 is a dusty red object associated with gas that shows tidal interactions as it nears closest approach with the Galaxy's central BH.  Observations, conducted as G2 passed through perhaps, were designed to test the proposal that G2 is a 3 M_earth gas cloud.  Such a cloud should be tidally disrupted during periapse passage.  The data were obtained using the Keck II laser guide star adaptive optics system (LGSAO) and the facility NER camera (NIRC2) through the K' [2.1 um] and L' [3.8 um] broadband filters.  Several results emerge from these observations: 1) G2 has survived its closest approach to the BH as a compact, unresolved source at L'; 2) G2's L' brightness measurements are consistent with those over the last decade; 3) G2's motion continues to be consistent with a keplerian model.  These results rule out G2 as a pure gas cloud and imply that G2 has a central star.  This star has a luminosity of ~30 Lsun and is surrounded by a large (~2.6 AU) optically thick dust shell.  The differences between the L' and Br-gamma observations can be understood with a model in which L' and Br-gamma emission arises primarily from internal and external heating, respectively.  Suggest that G2 is a binary star merger product and will ultimately appear similar to the B-stars that are tightly clustered around the BH (the so-called S-star cluster).

1411.0709
Discovery of O VII line emitting gas in elliptical galaxies
Pinto, ... Zhang, et al

In the cores of ellipticals, clusters and groups of galaxies, the gas has a cooling time shorter than 1 Gyr.  It is possible to probe cooling flows through the detection of Fe XVII and O VII emission lines, but so far O VII was not detected in any individual object.  The Reflection Grating Spectrometers on XMM-Newton are currently the only instruments able to detect O VII in extended objects like elliptical galaxies and galaxy clusters.  Searched for evidence of O VII through all the archival RGS observations of galaxy clusters, groups and ellipticals focusing on those with core temperatures below 1 keV.  Discovered O VII resonance (21.6A) and forbidden (22.1A) lines for the first time in the spectra of individual objects.  O VII was detected at a level higher than three sigma in six elliptical galaxies.  3 of which are members of the Virgo cluster, the other are central dominant galaxies of groups, and most of them show evidence of O VI in UV spectra.  Detect no significant trend between the Fe XVII and O VII resonance-to-forbidden line ratios, possibly due to the limited statistics.  The observed line ratios indicated that the spectra of all these ellipticals are affected by resonance scattering, suggesting low turbulence. Deeper exposures will help to understand whether the Fe XVII and O VII lines are both produced by the same cooling gas or by multi-phase gas.  The O VII luminosities correspond to 0.2-2 Msun/yr that agree with the predictions for ellipticals.  Such weak cooling rates would not be detected in clusters because their spectra are dominated by the emission of hotter gas and due to their larger distance the expected O VII line flux would be undetectable.

1411.1408
Star formation law at z=2.5 inferred from the electron density of ionized gas
Shimakawa, ... Steidel, et al

In 2<z<3, the physical conditions of the ISM in SF galaxies are likely to be different from those in the local Universe because of lower gaseous metallicities and higher gas fractions, and observations suggest higher electron densities, higher ionization parameters, and harder UV radiation fields may be common.  Find that the sSFR and the surface density of SFR (Sigma_SFR) are correlated with the electron density at z=2.5.  The Sigma_SFR - n_e relation is likely to be linked to the global SF law (Kennicutt-Schmidt law) where SF activity is regulated by gas density.  Moreover, discuss the mode and geometry of SF in those galaxies, based on the correlation between sSFR and Sigma_SFR.  Highly SF galaxies (with high sSFR) tend to be characterized by compact dense regions with high values of both n_e and Sigma_SFR.

1411.1409
Galactic outflow and diffuse gas properties at z>=1 using different baryonic feedback models
Barai, et al

Measure and quantify properties of galactic outflows and diffuse gas at z>=1 in cosmo hydro sims ("MUPPI", SNe feedback).   At z=2, find outflow velocity and mass outflow rate (Mdot_out) exhibit positive correlations with galaxy mass and with the SFR, but with large scatter.  The outflow mass loading factor (eta) is between 0.2-10.  The comparison Effective model generates a constant outflow velocity, and a negative correlation on eta with halo mass.  The number fraction of galaxies where outflow is detected decreases at lower redshifts, but remains more than 80% over z=1-5.  High SF activity at z~2-4 drives strong outflows, causing the positive and steep correlations of velocity and Mdot_out with SFR.  The outflow velocity correlation with SFR becomes flatter at z=1, and eta displays a negative correlation with halo mass in massive galaxies.  Study demonstrates that both MUPPI and Effective models produce significant outflows at ~1/10 of the viral radius; at the same time shows that the properties of outflows generated can be different from they put speed and mass loading in the Effective model.  MUPPI, using local properties of gas in the sub-resolution recipe, is able to develop galactic outflows whose properties correlate with global galaxy properties, and consistent with observations.

1411.1411
On the origin of near-infrared extragalactic background light anisotropy
Zemcov, Smidt, et al

EBL anistotropy traces variationsi n the total production of photons over cosmic history, and may contain faint, extended components missed in galaxy point source surveys.  IR EBL fluctuations have been attributed to primordial galaxies and BHs at the EOR, or alternately, intra-halo light (IHL) from stars tidally stripped from their parent galaxies at low redshift.  Report new EBL anisotropy measurements from a specialized sounding rocket experiment at 1.1 and 1.6 um.  The observed fluctuations exceed the amplitude from known galaxy populations, are inconsistent with EOR galaxies and BHs, and are largely explained by IHL emission.  The measured fluctuations are associated with an EBL intensity that is comparable to the BG from known galaxies measured through number counts, and therefore a substantial contribution to the energy contained in photons in the cosmos.

1411.1414
Hubble space telescope combined strong and weak lensing analysis of the CLASH sample: mass and magnification models and systematic uncertainties
Zitrin, et al

HST lensing analysis of the CLASH cluster sample.  Identify new multiple-images, improving constraints on cluster inner mass distributions and profiles.  Combine SL constraints with WL shape measurements within HST FOV to jointly constrain the mass distributions.  Analysis performed in two different common parameterizations (light-traces-mass for galaxies and DM; and an analytic, elliptical NFW form for DM), to provide a better assessment of the underlying systematics - which is most important for deep lensing surveys such as CLASH and the Hubble Frontier Fields, especially when studying high-z magnified objects.  Find that the typical (median), relative systematic differences throughout the central FOV are ~40% in the (dimensionless) mass density, kappa, and ~20% in the magnification, mu.  For the Einstein radii, find that all typically agree within 10% between the two models, and Einstein masses agree, typically, within ~15%.  At larger radii, the total projected, 2D integrated mass profiles of the two models within r~2', differ by ~30%.  Stacking the surface-density profiles of the sample from the two methods together, obtain an average slope of d log(Sigma)/d log(r)~-0.64pm0.1, in the radial range [5,350] kpc.  Examine the behavior of the average magnification, surface density, and shear differences between the two models, as a function of both the radius and the best-fit values of these quantities, uncovering some interesting trends.  Lens models are made publicly available.

1411.1424
Optimal redshift weighting for Baron Acoustic Oscillations
Zhu, Padmanabhan, White

Future BAO surveys will cover very large volumes, covering wide ranges in z.  Derive a set of redshift weights to compress the information in the z direction to a small number of modes.  Suggest that such a compression preserves almost all of the signal for most cosmologies, while giving high S/N measurements for each combination.  Present some toy models and simple worked examples.  As an intermediate step, give a precise meaning to the "effective z" of a BAO measurement.

1411.1687
The impact of temperature fluctuations on the large scale clustering f the Ly$\alpha$ forest
Greig, Bolton, Wyithe

Develop SAM for assessing the impact of the large scale IGM temperature fluctuations expected following He II reionization on 3D clustering measurements of the Lya forest.  Methodology builds upon the existing large volume, mock Lya forest survey simulations presented by Greig+2011 by including a prescription for a spatially inhomogeneous ionizing background, temperature fluctuations induced by patchy He II photo-heating and the clustering of quasars.  This approach enables a dynamic range achieved within the SAM substantially larger than currently feasible with computationally expensive, fully numerical simulations.  The results agree well with existing numerical simulations, with large scale temperature fluctuations introducing a scale dependent increase in the spherically averaged 3D Lya forest PS of up to 20-30 % at k~0.02 Mpc-1.  Although these large scale thermal fluctuations will not substantially impact upon the recovery of the BAO scale from existing and forthcoming DE spectroscopic surveys, any complete forward modeling of the broadband term in the Lya correlation function will nonetheless require their inclusion.