Day 535

Thursday.

1310.6031
A rapidly star-forming galaxy 700 Million years after the big bang at z=7.51
Finkelstein et al

Out of several dozen z>7 candidate galaxies observed spectroscopically, only 5 have been confirmed via Lya emission.  The small fraction of confirmed galaxies may indicate that the neutral fraction in the IGM rises quickly at z>6.5, as Lya is resonantly scattered by neutral gas.  However, the small samples and limited depth of previous observations makes these conclusions tentative.  Report here the results of a deep NIR spectroscopic survey of 43 z>6.5 galaxies.  Detect only a single galaxy, confirming that some process is making Lya difficult to detect.  The detected emission line at 1.0343 um is likely to be Lya emission, placing this galaxy at z=7.51, an epoch 700 Myr after BB.  THis galaxy's colors are consistent with significant metal content, implying that galaxies become enriched rapidly.  Measure a surprisingly high SFR of 330 Msun/yr, more than a factor of 100 greater tan seen in MW.  Such a galaxy is unexpected in a survey of their size, suggesting that the early universe may harbor more intense sites of SF than expected.
1310.6037
H$\alpha$ star formation rates of $z$ > 1 galaxy clusters in the IRAC Shallow Cluster Survey
Zeimann et al

HST NIR spectroscopy of 18 galaxy clusters at 1<z<1.5 with WFC3: spectroscopically identify Ha emitters in both the cores of galaxy clusters as well as in field galaxies.  Find a large cluster-to-clutser scatter in the SFR within a projected radius of 500 kpc, and many of the clusters (~60%) have significant levels of SF within a projected radius of 200 kpc.  A stacking analysis reveals that dust reddening in these SF galaxies is positively correlated with stellar mass and may be higher in the field than the cluster at a fixed stellar mass.  This may indicate a lower amount of gas in SF cluster galaxies than in the field population.  Also, Ha equivalent widths of SF galaxies in the cluster environment are still suppressed below the level of the field.  This suppression is most significant for lower mass galaxies (log M* < 10 Msun).  Conclude that environmental effects are still important at 1<z<1.5 for SF galaxies in galaxy clusters with M*<1e10 Msun.
1310.6038
Sufficient observables for large scale structure in galaxy surveys
Carron, Szapudi

Beyond the linear regime, PS and higher order moments of matter field no longer capture all cosmological information encoded in density fluctuations.  While NL transforms have been proposed to extract this information lost to traditional methods, the way to generalize these techniques to discrete processes was unclear; ad hoc extensions had some success.  Pointed out in the past that the log transform approximates extremely well the optimal "sufficient statistics", observables that extract all information from the (continuous) matter field.  Building on these results, generalize optimal transforms to discrete galaxy fields.  Focus calculations on the Poisson sampling of an underlying lognormal density field.  Solve and test the one-point case in detail, and sketch out the sufficient observables for the multi-point case.  Present an accurate approximation to the sufficient observables in terms of the mean and spectrum of a NL transformed field.  Find that the corresponding optimal NL transformation is directly related to the maximum a posteriori Bayesian reconstruction of the underlying continuous field with a lognormal prior as put forward in Kitaura+ 2010.  Thus simple recipes for realizing the sufficient observables can be built on previously proposed algorithms that have been successfully implemented and tested in simulations.

1310.6039
The era of star formation in galaxy clusters
Brodwin et al

Analyze the SF proeprties of 16 IR-selected 1<z<1.5 (spec-z confirmed) from Spitzer/IRAC shallow cluster survey.  Present new spectroscopic confirmation for six of these high-z clusters, 5 of which are at z>1.35.  Using IR luminosities measured with deep Spitzer/MIPS observations at 24 um, along with robust optical+IRAC photometric redshifts and SED-fitted stellar masses, present the dust-obscured SF fractions, SFRs and sSFRs in these clusters as functions of redshift and projected clustercentric radius.  Find that z~1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster SF at earlier times.  Beyond this z, the fraction of SF cluster members increases monotonically toward the cluster centers.  Indeed, the sSFR in the cores of these distant clusters is consistent with field values at similar z, indicating that z>1.4 environment-dependent quenching had not yet been established in ISCS clusters.  Combining these observations with complementary studies showing a rapid increase in the AGN fraction, a stochastic SFH, and a major merging episode at the same epoch in this cluster sample, suggest that the SB activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGN.  The totality of the evidence suggest we are witnessing the final quenching period that brings and end to the era of SF in galaxy clusters and initiates the era of passive evolution.

1310.6040
The evolution of dust-obscured star formation activity in galaxy clusters relative to the field over the last 9 billion years
Alberts, ... Lin, ... et al

Compare the SF activity in cluster galaxies to the field from z=0.3-1.5 using Herschel SPIRE 250 um imaging.  Utilize 274 clusters from IRAC Shallow Cluster Survey selected as rest-frame NIR overdensities over the 9 sq deg Bootesfield.  This analysis allows us to quantify the evolution of SF in lusters over a long redshift baseline without bias against active cluster systems.  Using a stacking analylsis, determine the average SFRs and sSFRs (sSFR = SFR/M*) of stellar mass-limited (M>1.3e10 Msun), statistical samples of cluster and field galaxies, probing both the SF and quiescent populations.  Find a clear indication that the average SF in cluster galaxies is evolving more rapidly than in the field.  Additionally, see enhanced SF above the field level at z~1.4 in the cluster outskirts (r>0.5 Mpc).  These general trends in the cluster cores and outskirts are driven by the lower mass galaxies in our sample.  Blue cluster galaxies have systematically lower sSFRs than blue field galaxies, but otherwise show no strong differential evolution wrt the field over the redshift range.  This suggests that the cluster environments is bothe suppressing the SF in blue galaxies on long time-scales and rapidly transitioning some fraction of blue galaxies to the quiescent galaxy population on short time-scales.  Argue that results are consistent with both strangulation and ram pressure stripping acting in these clusters, with merger activity occurring in the cluster outskirts.

1310.6042
The rapid decline in metallicity of damped Ly-$\alpha$ systems at $z\sim5$
Rafelski, ... Prochaska, et al

PResent evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at z>4.7 down to <Z>=-2.03pm0.10, which is 6 sigma deviant from that predicted by a linear fit to the data at lower redshifts.  This measurement is made possible by the chemical abundance measurements of 8 new damped Lya (DLA) systems at z>4.7 observed with the Echellette Spectrograph and Imager on the Keck II telescope, doubling the number of measurements at z>4.7 to 16.  The sudden decrease in metallicity is possibly due to the lower UV radiation field and higher density at high z increasing the neutral fraction of gas inside haloes, such as cold flows.  This would result in a new population of presumably lower metallicity DLAs, with an increased contribution to the DLA population at higher z resulting in a reduced mean metallicity.  While the comoving metal mass density of DLAs, rho_metals (z)_DLA, is flat out to z~4.3, there is evidence of a possible decrease at z>4.7.  Such a decrease is expected, as otherwise most of the metals from SF galaxies would reside in DLAs by z~6.  While the metallicity is decreasing at high z, the contribution of DLAs to the total metal budget of the universe increases with redshift, with DLAs at z~4.3 accounting for ~20% as many metals as produced by Lyman break galaxies.

1310.6044
Counter-orbiting planets were flipped over by a coplanar outer object
Li, Naoz, Kocsis, Loeb

Some massive exoplanets with close-in orbits, so-called hot Jupiters, are observed to orbit in exactly the opposite direction to the spin of their host star.  True (not projected) ~180 degree misalignment cannot be well explained with previously proposed physical processes.  Here, present a mechanism that can naturally lead to these counter-orbiting systems.  The gravitational influence of an outer eccentric object in a coplanar orbit increases the initial eccentricity of the planet to high values.  The planet's orbit then suddenly flips by ~180 degree, rolling over its major axis.  The ~180 degree flip criterion and timescale are given by simple analytic expressions that depend on the initial orbital parameters.  With tidal dissipation, this mechanism naturally leads to the observed counter-orbiting systems.  

1310.6046
PyGFit: a tool for extracting PSF matched photometry
Mancone, Gonzalez, Moustakas, Price

PyGFit, a program designed to measure PSF-matched photometry from images with disparate pixel scales and PSF sizes.  While PyGFit has a number of uses, its primary purpose is to extract robust SEDs from crowded images.  It does this by fitting blended source in crowded, low resolution images with models generated from a higher resolution image.  This approach minimizes the impact of crowding and also yields consistently measured fluxes in different filters, minimizing systematic uncertainty in the final SEDs.  Present an example of applying PyGFit to real data and perform simulations to test its fidelity.  The uncertainty in the best-fit flux rises sharply as a function of nearest-neightbor distance for objects with a neighbor within 60% of the PSF size.  Similarly, the uncertainty increases quickly for objects blended with a neighbor more than four times brighter.  For all other objects the fidelity of PyGFit's results depends only on flux, and the uncertainty is primarily limited by sky noise.

1310.6148
A dearth of dark matter in strong gravitational lenses
Sanders

Show that the dynamical masses of the SLACS sample of strong gravitational lenses are consistent with the stellar masses determined from population synthesis models using the Salpeter IMF.  This is true in the context of both Newtonian and modified Newtonian dynamics, and is in agreement with the expectation of MOND that there should be little classical discrepancy within the high surface brightness regions probed by SL.  There is also dynamical evidence from this sample supporting the claim that the mass-to-light ratio of the stellar component increases with the velocity dispersion.

1310.6175
Spherical collapse and halo mass function in the symmetron model
Taddei, Catena, Pietroni

Study the gravitational clustering of spherically symmetric overdensities and the statistics of the resulting DM haloes in the "symmetron model", in which a new long range force is mediated by a Z_2 symmetric scalar field.  Depending on the initial radius of the overdensity, identify two distinct regimes: for small initial radii, the symmetron mediated force affects the spherical collapse at all redshifts; for initial radii larger than some critical size this force vanishes before collapse because of the symmetron screening mechanism.  In both cases overdensities collapse earlier than in the LCDM and statistically tend to form more massive dark matter haloes.  Regarding the halo-mass function of these objects, observe order one departures from standard LCDM predictions.  The formalism developed here can be easily applied to other models where fifth-forces participate to the dynamics of the gravitational collapse.