Day 617

Saturday.  Sunday.

1402.1165
Dancing in the dark: galactic properties trace spin swings along the cosmic web
Dubois et al

Investigate alignment between the spin of galaxies and large-scale cosmic filaments above z=1, using large-scale hydro cosmo sims.  Analysis of more than 150k galaxies with morphological diversity in a 100 Mpc/h comoving box size shows that the spin of low-mass, rotation-dominated, blue, SF galaxies is preferentially aligned with their neighboring filaments.  High-mass, dispersion-dominated, red, quiescent galaxies tend to have a spin perpendicular to nearby filaments.  The orientation of the spin of massive galaxies is provided by galaxy mergers which are significant in the mass build up of high-mass galaxies.  Find the the stellar mass transition from alignment to misalignment happens around 3.1e10 Msun.  This is consistent with earlier findings of DM mass transition for the orientation of the spin of haloes 5.1e11 Msun at the same redshift.  With these numerical evidence, advocate a scenario in which galaxies form in the vorticity-rich neighborhood of filaments, and migrate towards the nodes of the cosmic web as they convert their orbital angular momentum into spin.  The signature of this process can be traced to the physical and morphological properties of galaxies, as measured relative to the cosmic web.  Argue that a strong source of feedback such as AGN is mandatory to quench in situ SF in massive galaxies.  It allows mergers to play their key role by reducing post-merger gas inflows and, therefore, keeping galaxy spins misaligned with cosmic filaments.  It also promotes diversity amongst galaxy properties.

1402.1168
What is the physical origin of strong Lya emission? II. Gas kinematics and distribution of Lya Emitters
Shibuya et al

Present statistical study of velocities if Lya, interstellar (IS) absorption, and nebular lines and gas covering fraction for Lya emitters (LAEs) at z~2.  Make a sample of 22 LAEs with a large Lya EW of >50A based on deep observations, in conjunction with spectra data taken and from literature.  Estimate the average velocity offset of Lya from a systemic z determined with nebular lines to be dv_Lya=234pm9 km/s.  Using a KS test, confirm the previous claim of Hashimoto+2013 that the average dv_Lya of LAEs is smaller than that of LBGs.  Data successfully identify blue-shifted multiple IS absorption ones in the UV continua of four LAEs on an individual basis.  The average velocity offset is IS absorption lines from a systemic redshift is dv_IS=204pm27 km/s, indicating LAE's gas outflow with a velocity comparable to typical LBGs.  Thus, the ratio, R^Lya_IS = dv_Lya/dv_IS of LAEs, is around unity, suggestive of low impacts on Lya transmission by resonant scattering of neutral hydrogen in the IS medium.  Find an anti-correlation between Lya EW and the covering fraction, f_c, estimated from the depth of absorption lines, where f_c is an indicator of average neutral hydrogen column density, N_HI.  The results of the study support the idea that N_HI is a key quantity determining Lya emissivity.

1402.1172
ZENS IV. Similar morphological changes associated with Mass- and environment-quenching, and the relative importance of bulge growth versus the fading of disks
Carollo et al

Study the dependence of the quenched satellite fraction and of the morphological mix of these quenched satellites, on three different environmental parameters: group halo mass, halo-centric distance and large-scale structure over-density.  The fraction of quenched satellites is independent of halo mass and the surrounding large-scale overdensity, but increases towards the centers of the haloes, as previously found.  The morphological mix is, however, constant with radial position, indicating that the well-known morphology-density relation results form the increasing fraction of quenched galaxies towards the centers of haloes.  The constancy of the morphological outcome suggests that mass-quenching and satellite quenching have the same effect on the morphologies of the galaxies.  The quenched satellites have larger B/T and smaller half-light radii than the SF satellites.  These are mostly due to differences in the disks.  The bulges in quenched satellites have very similar luminosity's and surface brightness profiles, and any mass growth of the bulges associated with quenching cannot greatly change these quantities.  The quenched disks are fainter and have smaller scale lengths than in SF satellites.  This can be explained either by a differential fading of the disks or if disks were generally smaller in the past, both of which are expected in an inside-out growth of disks.  At least at low z, the structure of massive quenched satellites is produced by processes that operate before quenching takes place.  A comparison with SAMs argues for a reduction in the efficiency of group haloes in quenching their disk satellites and for mechanisms to increase the B/T of low mass quenched satellites.

1402.1215
Design for minimum energy in starship and interstellar communication
Messerschmitt

The design of an interstellar digital communication system at radio wavelengths and interstellar distances is considered, with application to communication with starship and extraterrestrial civilizations.  The distances involved are large, resulting in a need for large transmitted power and/or large antennas.  In light of a fundamental tradeoff between wider signal bandwidth and lower signal energy per bit delivered to the receiver, the design uses unconstrained bandwidth and thus minimizes delivered energy.  One major challenge for communication with civilizations is the initially uncoordinated design and, if the distances are greater, new impairments introduced by the ISM.  Unconstrained bandwidth results in a simpler design, helping overcome the absence of coordination.  An implicit coordination strategy is proposed based on approaching the fundamental limit on energy delivered to the receiver in the face of jointly observable impairments due to the ISM (dispersion, scattering, and scintillation) and motion.  It is shown that the CMB is the only fundamental limitation on delivered energy per bit, as the remaining impairments can be circumvented by appropriate signal design and technology.  A simple design that represents information by the sparse location of bundles of energy in time and frequency can approach that fundamental energy limit as signal bandwidth grows.  Individual energy bundles should fall in an interstellar coherence hole, which is a time-duration and bandwidth limitation on waveforms rendering them impervious to medium and motion impairments.

1402.1342
The cross-correlation of MgII absorption and galaxies in BOSS
Pérez-Ràfols, Miralda-Escudé, et al

Use the DR11 galaxy sample of BOSS and DR7 quasar spectra.  The X-corr is measured by stacking quasar absorption spectra shifted to the redshift of galaxies that are within a certain impact parameter bin of the quasar, after dividing by a quasar continuum model. This results in an average MgII equivalent width as a function of impact parameter from a galaxy, ranging from 50 kpc to more than 10 Mpc in proper units, which includes all MgII absorbers.  Show that special care needs to be taken to use an unbiased quasar continuum estimator, to avoid systematic errors in the measurement of the mean stacked MgII EW.  The measured X-corr follows the expected shape of the galaxy correlation function, although measurement errors are large.  Use the X-corr amplitude to derive the bias factor of MgII absorbers, finding b_MgII=1.20pm0.19, where the error accounts only for the statistical uncertainty in measuring the mean EW.  This result indicates that MgII absorbers at z~0.5 are spatially distributed on large scales similarly to galaxies with L~L*.  

1402.1456
Dusty star-forming galaxies at high redshift
Casey, Narayanan, Cooray

[review] FIR and submillimeter wavelength surveys have established the important role of dusty, SF galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe.  The brightness of these galaxies have IR luminosities >1e13 Lsun with implied SFRs of 1000s of Msun per year.  They represent the most intense starbursts in the universe, yet many are completely optically obscured.  Their easy detection at submm wavelengths is due to dust heated by UV radiation of newly forming stars.  When summed up, all of the dusty, SF galaxies in the universe produce an IR radiation field that has an equal energy density as the direct starlight emission from all galaxies visible at UV and optical wavelengths.  The bulk of this IR extragalactic BG light emanates from galaxies as diverse as gas-rich disks to mergers of intense SB galaxies.  Major advances in FIR instrumentation in recent years, both space-based and ground-based, has led to the detection of nearly a million DSFGs, yet the understanding of the underlying astrophysics that govern the star and end of the dusty SB phase is still in nascent stage.  This review is aimed at summarizing the current status of DSFG studies, focusing especially on the detailed characterization of the best-understood subset (sub millimeter galaxies, who were summarized in the last review of this field over a decade ago, Blain+2002), but also the selection and characterization of more recently discovered DSFG populations.  Review DSFG population statistics, their physical properties including dust, gas and stellar contents, their environments, and current theoretical models related to the formation and evolution of these galaxies.