Day 395

Tuesday.

1303.5787
Effect of a high opacity on the light curves of radioactively powered transients from compact object mergers
Barnes, Kasen

Coalescence of compact objects are a promising astrophysical sources of GW signals.  The ejection of r-process material from such mergers may lead to a radioactively-powered EM counterpart which, if discovered, would enhance the science return of a GW detection.  Very little is known about the optical properties of heavy r-process elements; previous light curve models have adopted opacities similar to those of Fe group elements.  Report that the presence of heavier elements, particularly the lanthanides, increase the ejecta opacity by several orders of magnitude.  Include these higher opacities in time dependent, multi-wavelength radiative transport calculations to predict the broadband light curves of one-dimensional models over a range of parameters (eject masses from 0.001 to 0.1 Msun and velocities from 0.1 to 0.3c).  Find that the higher opacities lead to much longer duration light curves which can last a week or more.  The emission is shifted toward to IR bands due to strong optical line blanketing, and the colors at later times are representative of a BB near the recombination temperature of the lanthanides (T~2500K).  Further consider the case in which a second mass outflow, composed of 56Ni, is ejected from a disk wind, and show that the net result is a distinctive 2 component spectral energy distribution, with a bright optical peak due to 56Ni and an IR peak due to r-process ejecta.  Briefly consider the prospects for detection and identification of these transients.

1303.5788
Opacities and spectra of the r-process ejecta from neutron star mergers
Kasen, Badnell, Barnes

Material ejected during (or immediately following) the merger of 2 NSs may assemble into heavy elements by the r-process.  Subsequent decay of the nuclei can power EM emission similar to, but significantly dimmer than, and ordinary SNe.  Predictions of the transient light curves and spectra, however, have suffered from the uncertain optical properties of heavy ions.  Consider the opacity of expanding r-process material, argue that it tis dominated by the line transitions from those ions with the most complex valence electron structure, namely the lanthanides.  For a few representative ions, run atomic structure models to calculate radiative data for ~1e7 lines.  Find: resulting r-process opacities are orders of magnitude larger than that of ordinary (i.e., Fe-rich) SNe ejecta.  Radiative transport calculations using these new opacities indicate that the transient emission should be dimmer and redder than previously thought.  The spectra appear pseudo-BB, with broad absorption features, and peak in the IR (~1um).  Uncertainties in opacities needed to quantify their impact on the spectral predictions.    Implications for observational strategies for studies of radioactively powered EM counterparts to compact object mergers.

1303.5987
The chemical evolution of star-forming galaxies over the last 11 billion years
Zahid, Geller, Kewley, Hwang, Fabricant, Kurtz

Measure the stellar mass-metallicity relation at 5 epochs out to z~2.3.  Quantify evolution in the shape of mass-metallicity relation as a function of redshift; the mass-metallicity relation flattens at late times.  Empirical upper limit to the gas-phase O abundance in SF galaxies that is independent of z.  From examination of the mass-metllicity relation and its observed scatter, show that the flattening at late times is a consequence of evolution in the stellar mass where galaxies enrich to this empirical upper metallicity limit; there is also evolution in the fraction of galaxies at a fixed stellar mass that enrich to this limit.  The stellar mass where metallicities begin to saturate is ~0.7 dex smaller in the local universe than it is at z~0.8.  These observations provide a benchmark for theoretical and observational studies of the chemical evolution of SF galaxies.

1303.6109
A candidate z~8 galaxy lensed by a foreground z~1.7 group
Barone-Nugent, Wyithe, Trenti, Treu, Oesch, Bradley, Schmidt

As the title says.  Find in pure-parallel HST as part of BoRG survey.  A Y-dropout galaxy with m=25.9 which appears to be SL by a FG group with a photo-z~1.7, which would be the highest-z deflector discovered to date.  Multiple evidence: (1) the z~8 dropout is close in project to the FG group, (2) it is lightly elongated tangentially in the direction of the putative critical curve, (3) a possible counter image marginally detected, (4) the Y-dropout is not clustered (intrinsically fainter than it appears---i.e., magnified) [clustered?].  SIE deflector model with Sersic SB (with index 0.92) appears to work.  Magnification factor of 3.7.  Lens group mass of 1e12 Msun, M/L_B=30 Msun/Lsun within the Einstein radius.  If confirmed, the system provides a unique opportunity to obtain spectroscopy of a typical z~8 galaxy, and an absolute measure of mass for a galaxy at z~1.7.  Qualitatively consistent with theoretical expectation that 10% of z~8 galaxies with L>2L* are significantly magnified.

1303.6110
Resolving the molecular gas around the lensed quasar RXJ0911.4+0551
Anh, ... Kneib, ... et al

High angular resolution observations of CO(7-6) line and mm continuum in the host galaxy of the gravitationally lensed (z~2.8) quasar.  Resolves molecular disk of the source; 1pm0.2 kpc disk radius, inclination of 70 deg (observed in CO).  Continuum is more compact, only marginally resolved by observations.  Relatively low mass, a scaled-down version of the QSOs usually found at high-z.  ...

1303.6158
Reconciling extremely different concentration-mass relations
Meneghetti, Rasia

Concentration estimates are sensitive to the largely different radial scales probed by a particular measurement method.