Monday.
1303.7228
How well can we really estimate the stellar masses of galaxies from broadband photometry?
Mitchell, Lacey, Baugh, Cole
The estimated stellar masses of galaxies are widely used to characterize how the galaxy population evolves over cosmic time. Explore how galaxy stellar masses, estimated by fitting broad-band SEDs with stellar population models, can be biased as a result of commonly adopted assumptions for the SF and chemical enrichment histories, recycled fractions and dust attenuation curves of galaxies. Apply the observational technique of broad-band SED fitting to model galaxy SEDs calculated by the theoretical galaxy formation model GALFORM, isolating the effect of each of these assumptions. Find: (1) averaged over the entire galaxy population, the common assumption of exponentially declining SFH does not adversely affect stellar mass estimation. Show: (2) fixing the metallicity in SED fitting or using sparsely sampled metallicity grids can introduce mass dependent systematics into stellar mass estimates. Find that (3) the common assumption of a star-dust geometry corresponding to a uniform foreground dust screen can cause the stellar masses of dusty model galaxies to be significantly underestimated. Show: (4) stellar mass functions recovered by applying SED fitting to model galaxies at high z can differ significantly in both shape and normalization from the intrinsic mass functions predicted by a given model. Given these differences, methodology of using stellar masses estimated from model galaxy SEDs offers a new, self-consistent way to compare model predictions with observations.
1303.7231
Galaxy evolution near groups and clusters: ejected satellites and the spatial extent of environmental quenching
Wetzel, Tinker, Conroy, van den Bosch
Satellite galaxies within groups/clusters are more likely to exhibit quiescent SFR than central/field galaxies, but enhanced quiescent likelihood extends to galaxies that are several virial radii beyond groups/clusters. Use SDSS DR7 group/cluster catalog: show that this enhancement has two causes. (1) massive haloes are clustered, so neighboring haloes that host their own satellite galaxies boost the observed quiescent fraction out to large distances. (2) central/field galaxies exhibit a strongly enhanced quiescent fraction out to 2.5 virial radii (with some enhancement out to 5 virial radii) beyond groups/clusters. Show that this enhancement for central galaxies can be explained by 'ejected' satellite galaxies that orbit beyond their host halo's virial radius. Use cosmo N-body sim, examine the orbital histories of ejected satellites, showing that they extend out to 2.5 virial radii beyond their host halo and compose up to 40% of all central galaxies out to this distance. After ejection, these satellites typically orbit for several Gyr beyond the virial radius before falling back in, during which time they (continue to) lose significant halo mass. Show that a model in which ejected satellites experience the same SFR evolution and quenching as satellites within a host halo can explain all environmental dependence of galaxy quenching beyond a host halo's virial radius. The strong halo mass stripping of ejected satellites also reduces the average halo masses of galaxies near massive groups/clusters, an effect that is potentially observable via weak lensing. Overall, the SFRs/colors and stellar/halo masses of ejected satellites present challenges for the standard halo model for galaxy occupation and highlight the importance of environmental history in galaxy evolution.
1303.7233
Stability analysis for cosmic-ray heating of cool cores in galaxy clusters
Fujita, Kimura, Ohira
Heating of cool cores in galaxy clusters by CR from AGNs. The CRs steram with Alfven waves in the ICM and heat the ICM. Assume heating and radiative cooling balanced; boundary conditions set by cluster observations. Find steady state solutions if B-fields are strong enough and the association between the B-fields and the ICM is relatively weak. Confirm analytical global stability with numerical simulations. Follow evolution of profiles for 100 Gyr. Find: the profiles do not evolve on time scales much larger than cluster lifetimes. CR heating is a promising mechanism to solve the "cooling flow problem".
1303.7239
The fundamental plane of damped Lyman alpha systems
Neeleman, Wolfe, Prochaska, Rafelski
Use 100 HI-selected DLA system sample; present evidence that the scatter in the well-studied correlation between the z and metallicity of a DLA is largely due to the existence of mass-metallicity relationship at each z. To describe the fundamental relations that exist between z, metallicity and M, use a fundamental plane description. M represented by velocity width dv_90 (velocity interval containing 90% of the integrated optical depth, traces DM halo). Improvements over M-metallicity correlation and metallicity-z correlation: (1) fundamental equation reduces the scatter around both relationships by 20%. (2) confirms that the DM haloes that host DLAs satisfy a mass-metallicity relation at each z between 2 and 5.
1303.7266
Reactive desorption and radiative association as possible drivers of complex molecule formation in the cold interstellar medium
Vasyunin, Herbst
Discovery of terrestrial-type organic species (e.g., methyl formate and dimethyl ether) in the cold interstellar gas proves that the formation of organic matter in the Galaxy begins at a much earlier stage of SF than was thought before. Previous "warm-up" scenario (organic molecules are formed via diffusive chemistry on surfaces of interstellar grains starting at 30K, and then release to the gas at higher temperatures during later stages of SF) cannot explain the abundance. Investigate alternative scenario: complex organic species formed via a sequence of gas-phase reactions between precursor species formed on grain surfaces, and then ejected into the gas via efficient reactive desorption (non-thermal desorption as a result of conversion of the exothermicity of chemical reactions) into the ejection of products from the surface. Mixed results.
1303.7269
TPZ: photometric redshift PDFs and ancillary information by using prediction trees and random forests
Kind, Brunner
Publicly available Photo-z code, parallel and machine learning algorithm that generates photo-z PDFs by using prediction trees and random forest techniques, TPZ. TPZ incorporates measurement errors into the calculation while also dealing efficiently with missing values in the data [improvement for training-set method?]. Implementation of this algorithm provides supplementary information regarding the data being analyzed, including unbiased estimates of the accuracy of the technique without resorting to a validation data set, identification of poor photometric redshift areas within the parameter space occupied by the spectroscopic training data [this is nice], a quantification of the relative importance of the variables used to construct the PDF, and a robust identification of outliers. This extra information can be used to optimally target new spectroscopic observations and to improve the overall efficacy of the redshift estimation. Test TPZ on SDSS main galaxy sample, and from the DEEP2 survey, obtaining excellent results in each case [what training set sample was used?]. Also tested implementation by participating in the PHAT1 project, finding that TPZ performs comparable to if not better than other empirical photometric redshift algorithms. Discuss the various parameters that control the operation of TPZ, the specific limitation of this approach, and an application of photometric redshift PDFs.
1303.7314
Cosmic rays and climate change over the past 1000 million years
Sloan, Wolfendale
Galactic cosmic ray (GCR) has been postulated by others to vary cyclically with a peak to valley ratio of 3:1, as the Solar System moves from the Spiral Arm to the Inter-Arm regions of the Galaxy. These intensities have been correlated with global temperatures and used to support the hypothesis of GCR induced climate change. Show that the model used to deduce such a large ratio of Arm to Interarm GCR intensity requires unlikely values of some of the GCR parameters, particularly the diffusion length in the interstellar medium, if, as seems likely to be the case, the diffusion is homogeneous. Comparison is made with the existing gamma ray astronomy data and this also indicates that the ratio is not large. The variation in the intensity is probably of order 10-20% and should be no more than 30% as the SS moves between these two regions, unless the conventional parameters of the GCR are incorrect. In addition, show that the variation of the GCR intensity, as the trajectory of the SS oscillates about the Galactic plane, is too small to account for the extinctions of species as has been postulated unless, again, conventional assumptions about the GCR parameters are not correct. [paper not submitted anywhere?]
1303.7433
Unidentified moving objects in the next generation time domain surveys
Davenport
Present a simple parameterized model of the detectability of UFOs with LSST.
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