Day 506

Wednesday.

1309.2280
The most luminous z~9-10 galaxy candidates yet found: the luminosity function, cosmic star-formation rate, and the first mass density estimate at 500 Myr
Oesch, ... Smit, ... van Dokkum, ... et al

Discovery of 4 bright (H_160~26-27 AB mag) candidates at z~9-10 in the complete HST CANDELS GOODS-N imaging data, doubling the number of z~10 galaxy candidates, just 500 Myr after the BB.  Sources identified in a search over the full CANDELS-Deep dataset, building on previous analysis of HUDF09/XDF fields and GOODS-S.  3/4 are significantly detected at 4.5-6.2 sigma in the very deep Spitzer/IRAC 4.5 um data.  The brightest of the candidates at z=10.2 pm 0.4 is robustly detected also at 3.6 um, revealing a flat UV SED with a slope beta=-2.0pm0.2, consistent with demonstrated trends with luminosity at high z.  The abundance of these luminous candidates suggests that the LF evolves more significantly in phi* than in L* at z>~8.  Despite the discovery of these luminous candidates, the cosmic SFR density for galaxies with SFR > 0.7 M_sun/yr shows an order-of-magnitude increase in only 170 Myr from z~10 to 8, consistent with previous results.  Based on the IRAC detections, derive galaxy stellar masses at z~10, finding that these luminous objects are typically 1e9 Msun.  This allows for a first estimate of the cosmic stellar mass density at z~10 resulting in log rho* = 4.7 (pm10-20%) Msun/Mpc-3 for galaxies brighter than M_UV~-18.  The remarkable brightness, and hence luminosity, of these z~9-10 candidates highlights the opportunity for deep spectroscopy to determine their redshift and nature, and demonstrates the value of additional search fields to understand SF in the very early universe.

1309.2283
Statistical properties of mass, star formation, chemical content and rotational patterns in early z>9 structures
Biffi, Maio

Study the baryonic, chemical and dynamical properties of a significantly large sample of early proto-galaxies in the first 500 Myr of the universe (z>9), from high-res N-body, hydro, and chemistry simulations including atomic and molecular networks, gas cooling, SF, stellar evolution and metal spreading for Pop III and Pop II-I regimes according to proper stellar yields and lifetimes.  Find that first SF take place in haloes with M_DM>2e6Msun.  Early SF objects have: molecular fractions from x_mol<1e-4 in quiescent structures up to >0.1 in active regions; SFR~1e-8 to 1e-3 Msun/yr, and metallicities in the range 1e-8 to 1e-2 Zsun.  Roughly ~10% of high-z haloes host Pop II-I SF and dominate the cosmic SFR density.  THey usually are bursty objects with mean sSFR around ~10 / Gyr at z~9 and increasing with redshift up to ~100 /Gyr.  Stellar feedback effects alter the baryonic content of the haloes and locally affect their chemical and thermo-dynamical properties, as reflected by the broadening of various physical relations.  The establishment of gaseous, rotationally-supported cores is quite uncommon [no spirals, I guess], weakly related to the large-scale DM behaviour and evolving in an intermittent fashion.  The colder, molecular-rich phase tends to maintain any established rotational motion longer with respect to the hotter, metal-rich component, which is very sensitive to environmental processes.  While the fraction of haloes featuring a significant amount of co-rotating, molecular-rich gas increases with cosmic time (from a few % at z~20 up to ~5-15% at z~9), the chaotic nature of metal-enriched material does not lead to particular trends.

1309.2285
The effect of aberration on partial-sk measurements of the cosmic microwave background temperature power spectrum
Jeong, Chluba, Dai, Kamionkowski, Wang

Our motion relative to the CMB rest frame deflects light rays giving rise to shifts as large as L -> L(1+- beta), where beta = 0.00123 is our velocity on measurements of small-scale (large multipole moment L) CMB fluctuations.  For measurements at L>1000, where the CMB PS varies roughly as C(L)~L^-7, the fractional change to the PS measured on a small sky patch can be as large as Delta C(L)/C(L)~7*beta~1%, larger than the measurement uncertainties in several current experiments.  Present a novel harmonic-space approach to this CMB aberration that improves upon prior work by allowing to (i) go to higher orders in beta, thus extending the validity of the analysis to measurements at L>1/beta~800; and (ii) treat the effects of window functions and pixelization in a more accurate and computationally efficient matter.  Calculate precisely the magnitude of the systematic bias in the PS inferred from current SPT and ACT data, and show that the bias cannot be neglected.  Suggest that the small tension between Planck, ACT, and SPT may be due partially to aberration.  An appendix shows how the nearby constancy of the full-sky PS under aberration follows from unitarity of the aberration kernel.

1309.2300
The stellar number density distribution in the local Solar neighborhood is North-South asymmetric
Yanny, Gardner

Study the number density distribution of a sample of K and M dwarf stars, matched North and South of the Galactic plane within a distance of 2 kpc from the sun, using observations from SDSS DR9.  Determine distances using the photometric parallax method [what's that?], and in this context systematic effects exist which could potentially impact the determination of the number density profile with height from the Galactic plane -- and ultimately affect a number density North-South asymmetry [what is the Sun's location from the center of the galactic plane?].  They include: (i) the calibration of the various photometric parallax relations, (ii) the ability to separate dwarfs from giants in the sample, (iii) the role of stellar population differences such as age and metallicity, (iv) the ability to determine the offset of the sun from the Galactic plane, and (v) the correction for reddening from dust in the Galactic plane, though the stars are at high Galactic latitudes.  Find the various analyzed systematic effects to have a negligible impact on the observed asymmetry, and using a new and larger sample of stars, confirm and refine the earlier discovery of Widrow+  of a significant Galactic N-S asymmetry in the stellar number density distribution.

1309.2301
The effect of baryonic streaming motions on the formation of the first supermassive black holes
Tanaka, Li, Haiman

Observations of quasars at z>6 reveal that 1e9 Msun SMBHs had already formed when the Universe was <0.9 Gyr old.  One hypothesis for the origins of these SMBHs is that they grew from the remnants of the first generation of massive stars, which formed in low-mass (~1e5 to 1e6 Msun) DM minihalos at z>20.  This is the regime where baryonic streaming motions- the relative velocities of baryons with respect to DM in the early Universe-most strongly inhibit SF by suppressing gas infall and cooling.  Investigate the impact of this effect on the growth of the first SMBHs using a suite of high-fidelity, ellipsoidal-collapse MC merger-tree simulations.  Find that the suppression of seed BH formation by the streaming motions significantly reduces the number density of the most massive BHs at z>15, but the residual effect at lower redshifts is essentially negligible.  The streaming motions can reduce by a factor of few the number density of the most luminous quasars at z~10-11, where such objects could be detected by JWST.  Conclude, with minor theoretical caveats, that baryonic streaming motions are unlikely to pose a significant additional obstacle to the formation of the observed high-z quasar SMBHs.  Nor do they appreciably affect the heating and reionization histories of the Universe o the merger rates of nuclear BHs in the mass and redshift ranges of interest for proposed gravitational-wave detectors.

1309.2427
The evolution of the number density of compact galaxies
Poggianti, et al

Compare the number density of compact (small size) massive galaxies at low and high redshift using Padova Millennium Galaxy and Group Catalog (PM2GC) at z=0.03-0.11 and the CANDELS results from Barro+ at z=1-2.  The number density of local compact galaxies with luminosity weighted (LW) ages compatible with being already passive at high redshift is compared wit the density of compact passive galaxies observed at high-z.  Results place an upper limit of a factor ~2 to the evolution of the number density and are inconsistent with a significant size evolution for most of the compact galaxies observed at high-z.  The evolution may be instead significant (up to a factor 5) for the most extreme, ultracompact galaxies.  Considering all compact galaxies, regardless of LW age and SF activity, a minority of local compact galaxies (<=1/3) might have formed at z<1.  Finally, show that the secular decrease of the galaxy stellar mass due to simple stellar evolution may in some cases be a non-negligible factor in the context of the evolution of the mass-size relation, and caution that passive evolution in mass should be taken into account when comparing samples at different redshifts.

1309.2474
Weak lensing reconstruction through cosmic magnification. II. improved power spectrum determination and map-making
Yang, Zang, Zhang, Yu

The existence of galaxy intrinsic clustering severely hampers the WL reconstruction from cosmic magnification.  In paper I, proposed a minimal variance estimator to overcome this problem.  By utilizing the different dependences of cosmic magnification and galaxy intrinsic clustering on galaxy flux, demonstrated that the otherwise overwhelming galaxy intrinsic clustering can be significantly suppressed such that lensing maps can be reconstructed with promising accuracy.  This procedure relies heavily on the accuracy of determining the galaxy bias from the same data.  Paper I adopts an iterative approach, which degrades toward high z.  The current paper presents an alternative method, improving over paper I.  Prove that the measured galaxy clustering between flux bins allows for simultaneous determination of the lensing PS and the flux dependence of galaxy bias, at this redshift bin.  Compared to paper I, the new approach is not only more straightforward, but also more robust.  Identifies an ambiguity in determining the galaxy bias and further discovers a mathematically robust way to suppress this ambiguity to non-negligible level (~0.1%).  The accurately determined galaxy bias can then be applied to the minimal variance estimator proposed in paper I to improve the lensing mapmaking.  The gain at high z is significant.  These maps can be used to measure other statistics, such as cluster finding and peak statistics.  Furthermore, by including galaxy clustering measurement between different redshift bins, can also determine the lensing cross PS between these bins, up to a small and correctable multiplicative factor.

1309.2587
Extended ionized gas in z=0.4 cluster
Yagi, et al

From Ha imaging, discovered 9 candidates of extended ionized gas (EIG) from galaxies in Abell 851 cluster at z=0.4.  The parent galaxies are SF or post-starburst spiral galaxies, and 5 of them are spectroscopically confirmed members.  The spectrum of the brightest parent galaxy of the extended emission shows a post-starburst signature, and resembles the Ha stripped galaxies found in the Coma cluster.  In another z=0.39 cluster, no EIGs were found.  Implies that a cluster mass might be a key parameter to make EIGs.