Thursday.
Special topics
Citizen scientists discover gravitational lens at record speed
Symmetrymagazine.org
55k citizen scientists went to Spacewarps.org, and over 72 hours make 6 million image classifications on CFHT and VISTA survey areas, searching for gravitational lensing in the IR. Found handful of new GLs, including one confirmed system that was followed up immediately by eMerlin (radio telescope).
1401.2984
Observations of environmental quenching in groups in the 11 Gyr since z=2.5: different quenching for central and satellite galaxies
Tal, Dekel, Oesch, … van Dokkum, … Rix, … et al
Direct observational evidence for SF quenching in galaxy groups in 0<z<2.5. Utilize a large sample of 6000 groups selected by fixed cumulative number density from 3 photometric catalogs, to follow the evolving quiescent fractions of central and satellite galaxies over ~11 Gyr. At z~0, central galaxies in the sample range in M* from MW/M31 analogs (6.5e10 Msun) to nearby massive ellipticals (1.5e11 Msun). Satellite galaxies in the same groups reach masses as low as twice that of the LMC (6.5e9 Msun). Using statistical BG subtraction, measure the average rest-frame colors of galaxies in groups and calculate the evolving quiescent fractions of centrals and satellites over 7 z bins. Analysis shows clear evidence for SF quenching in group halos, with a different quenching onset for centrals and their satellite galaxies. Using halo mass estimates for central galaxies, find that SF shuts off in centrals when typical halo masses reach between 1e12 and 1e13 Msun, consistent with predictions from the halo quenching model. In contrast, satellite galaxies in the same groups most likely undergo quenching by environmental processes, whose onset is delayed wrt their central galaxy. Although SF is suppressed in all galaxies over time, the processes that govern quenching are different for centrals and satellites. While mass plays an important role in determining the SF activity of central galaxies, quenching in satellite galaxies is dominated by the environment in which they reside.
1401.2990
Possible origin of the G2 cloud from the tidal disruption of a known giant star by Sgr A*
Guillochon, Loeb, MacLeod, Ramirez-Ruiz
Propose that G2 formed out the debris stream produced by removal of mass from the outer envelope of a nearby giant star. Perform hydrodynamical simulations of the returning tidal debris stream with cooling, and find that the stream condenses into clumps that fall to Sgr A* approximately once per decade. Propose that one of these clumps is the observed G2 cloud, with the rest of the stream being detectable at lower Br-gamma emissivity along a trajectory that would trace from G2 to the star that was partially disrupted. By simultaneously fitting the orbits of S2, G2, and ~2000 candidate stars, and by fixing the orbital plane of each candidate star to G2 (as is expected for a tidal disruption), find that the late-type star S1-34 has an orbit that is compatible with the notion that it was tidally disrupted to produce G2. If S1-34 is indeed the star that was disrupted, it last encountered Sgr A* in the late 18th century, and will likely be disrupted again in several hundred years. However, while S1-34's orbit is compatible with the giant disruption scenario given its measured position and proper motion, its radial velocity is currently unknown. If S1-34's radial velocity is measured to be compatible with a disrupted orbit, it would strongly suggest that a tidal disruption of S1-34 produced G2.
1401.2998
A theory for the excitation of CO in star forming galaxies
Narayanan, Krumholz
Necessary to deduce molecular gas masses from observations of CO emission. Find: while the shape of the spectral line energy distribution is ultimately determined by difficult-to-observe quantities such as the gas density, temperature, and optical depth distributions, all of these quantities are well-correlated with the galaxy's mean SFR surface density (Sigma_SFR), which is observable. Use this result to develop a model for the CO SLED in terms of Sigma_SFR, and show that this model quantitatively reproduces the SLEDs of galaxies over a dynamic range of ~200 in SFR surface density, at 0<z<6. This model should make it possible to significantly reduce the uncertainty in deducing molecular gas masses from observations of high-J CO emission.
1401.2999
Dust reverberation mapping in the era of big optical surveys and its use as a standard ruler in cosmology
Hoenig
The time lag between optical and NIR flux variability can be taken as a means to determine the sublimation radius of the dusty "torus" around SMBHs in AGN. Show that data from big optical survey telescopes (LSST) can be used to measure dust sublimation radii as well. Uses Wein tail of the hot dust emission as it reaches into the optical and can be reliably recovered with high-quality photometry. Simulations show that dust sublimation radii for a large sample of AGN can be reliably established out to 0.1<z<0.2 with LSST. Propose to use AGN dust time lags as "standard rulers" for cosmology.
1401.3001
Optical galaxy clusters in the Deep Lens Survey
Ascaso, Wittman, Dawson
882 optically selected galaxy clusters in DLS, selected with the Bayesian Cluster Finder, 0.1<z<1.2, M200>=1.2e14 Msun. Verify with other optical, WL, X-ray and spectra surveys which overlap the DLS footprint. Spectro redshift good at z>0.25, richness estimates consistent with available dynamical mass estimates (from SHeLS), optical mass maps correlate to 3sigma with WL mass maps, and MF derived consistent with CDM. Investigate correlation with BCG properties and host cluster properties with a broader range in z (0.25<z<0.8) and mass (>=2.4e14Msun) than in previous work. Find that the slope of the BCG magnitude-redshift relation throughout this z range is consistent with that found at lower z. This result supports an extrapolation to higher redshift of passive evolution of the BCG within the hierarchical scenario.
1401.3162
A simple model linking galaxy and dark matter evolution
Birrer, Lilly, Amara, Paranjape, Refregier
Construct a simple phenomenological model for the evolving galaxy population by incorporating pre-defined baryonic prescriptions into a DM hierarchical merger tree. Specifically, the model is based on the simple gas-regulator model introduced by Lilly+2013 coupled with the empirical quenching rules of Peng+2010,2012. The simplest model does well in reproducing, without adjustable parameters, observables including the MS sSFR-mass relation, the faint end slope of the galaxy mass function and the shape of the SF and passive MS. Model also qualitatively reproduces the evolution of the MS sSFR and SFRD SFR density relations, the M_s-M_h stellar-to-halo mass relation and the SFR-M_h relation. SHort points: ratio of quenched to SF galaxies around Ms is not high enough, and evolution of sSFR and SFRD not steep enough, Ms-Mh relation not quite peaked enough Deficiencies related and they can be simultaneously solved by allowing galaxies to re-ingest some of the gas previously expelled in winds, in a mass-dependent and epoch-dependent way, allowing the model to reduce any inherent tendency to saturate their SF efficiency. Emphasizes how efficient galaxies around M* are in converting baryons into stars and highlights an apparent coincidence that quenching occurs just at the point when galaxies are rapidly approaching the maximum possible efficiency of converting baryons into stars. [if it weren't for quenching, would the SF efficiency be higher?]
1401.3317
The data release of the Sloan digital sky survey-II supernova survey
Sako, et al
As the title says, 10k variable and transient sources along Stripe 82 (300 deg sq) along the celestial equator. Spectra on 889 transients from BOSS spectrograph; photometric classification show 4607 transients likely to be, or spectroscopically confirmed, SNe. 677 SNIa candidates, determine Omega_m=0.315pm0.093 and a non-zero cosmological constant at 5.7 sigma.
1401.3741
Enduring quests-daring visions (NASA astrophysics in the next three decades)
Kouveliotou et al
First decade: JWST, WFIRST, Euclid, Gaia, and more. Second decade: Gravitational wave surveyor, CMB polarization surveyor, Far IR surveyor, LUVOIR surveyor, X-ray surveyor. Third decade: Gravitational wave mapper, cosmic dawn mapper (radio), ExoEarth mapper, Black Hole mapper.
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