1510.00718
RHAPSODY-G simulations II - Baryonic growth and metal enrichment in massive galaxy clusters
Martizzi, Hahn, Wu, Evard, Teyssier, Wechsler
Study the evolution of the stellar component and the metallicity of both the ICM and of stars in massive (Mvir~6e14 Msun) simulated galaxy clusters for the RHAPSODY-G suite in detail and compare them to observational results. The simulations were performed with the AMR code RAMSES and include the effect of AGN feedback at the sub-grid level. AGN feedback is required to produce realistic galaxy and cluster properties and plays a role in mixing material in the central regions and regulating SF in the central galaxy. In the low resolution runs with fiducial stellar yields, find that stellar and ICM metallicities are a factor of two lower than in observations, however they tend to converge to the observed values ~0.3 Zsun as the resolution is increased. Find that cool core clusters exhibit steeper metallicity gradients than non-cool core clusters, in qualitative agreement with observations. Verify that the ICM metallicities measured in the simulation can be explained by a simple "regulator" model in which the metallicity is set by a balance of stellar yield and gas accretion. The analytical model also predicts that the metallicities are proportional to the stellar yield. The realists thus indicate that a combination of higher resolution and higher metal yield in AMR simulation would allow the metallicity of simulated clusters to match observed values. Comparison to recent literature highlights that results concerning the metallicity of clusters and cluster galaxies might depend severely on the scheme chosen to solve the hydrodynamics.
NSF report
Impact of declining proposal success rates on scientific productivity
Cushman, Hoeksema, Kouveliotou, Lowenthal, Peterson, Stassun, von Hippel
Over the last decade proposal success rates in the fundamental sciences have dropped significantly. Astronomy and related fields funded by NASA and NSF are no exception. Data across agencies show that this is not principally the result of a decline in proposal merit (the proportion of proposals receiving high ranking is largely unchanged), nor of a shift in proposer demographics (seniority, gender, and institutional affiliation have all remained unchanged), nor of an increase (beyond inflation) in the average requested funding per proposal, nor of an increase in the number of proposals per investigator in any one year. Rather, the statistics are consistent with a scenario in which agency budgets for competed research are flat or decreasing in inflation-adjusted dollars, the overall population of investigators has grown, and a larger proportion of these investigators are resubmitting meritorious but unfunded proposals, likely in response to the decreased success rates. Recent research on the time cost of proposal writing versus that of producing publishable results show that a funding rate of ~6% represents the tipping point below which proposal writing prevents more papers than grants produce. This is close to the success rate experienced by new investigators against an overall average funding rate of 20%, due to treating bias against PIs without recent funding. At this 20% average selection threshold, the opportunity cost is still significant (2-3 papers per successful proposal) even for established researchers. Unfortunately, even an investigator submitting a proposal rated "very good" can expect, with three attempts, only a ~58% chance of funding. A 20% overall funding rate is thus unhealthy for the field, since it precludes stable, long-term support for students, postdocs, or researchers on soft money, and it preferentially discourages young researchers from remaining in the field. Yet, as demonstrated below, we are currently in exactly this situation. Conclude that an aspirational proposal success rate of 30-35% would still provide a healthily competitive environment for researchers, would more fully utilize the scientific capacity of the community's facilities and missions, and provide relief to the funding agencies who face the logistics of alarming volumes of proposals.
1510.01321
Interstellar extinction curve variations toward the inner Milky Way: a challenge to observation cosmology
Nataf, et al
Investigate interstellar extinction curve variations toward ~4 deg2 of the inner MW in VIJKs photometry from the OGLE-III and VVVs surveys, with supporting evidence from diffuse interstellar bands and F435W,F625W photometry. Obtain independent measurements toward ~2000 sightless of A_I, E(V-I), E(I-J), and E(J-Ks), with median precision and accuracy of 2%. Find that the variations in the extinction ratios A_I/E(V-I), E(I-J)/E(V-I) and E(J-Ks)/E(V-I) are large (exceeding 20%), significant, and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how R_V is varied. Furthermore, demonstrate the variations in the shape of the extinction curve has at least 2 degrees of freedom, and not one (e.g., R_V), which is confirmed with a principal component analysis. Derive a median value of <A_V/A_Ks>=13.44, which is ~60% higher than the "standard" value. Show that the Wesenheit magnitude W_I=I-1.61(I-J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, argue that systematic errors in the distance ladder from studies of type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ~100%, and lack sensitivity to extinction curve variations.
1510.01326
Is Draco II one of the faintest dwarf galaxies? First evidence from Keck/DEIMOS spectroscopy
Martin, Geha, et al
Present the first spectroscopic analysis of the faint and compact stellar system Draco II (Dra II, M_V=-2.9±0.8, r_h=19±7 pc), recently discovered in the Pan-STARRS1 3pi survey. The observations, conducted with DEIMOS on the Kick II telescope, reveal a cold velocity peak with 9 member stars at a systemic heliocentric velocity <v_r>=-347.6±1.7 km/s, thereby confirming Dra II is a satellite of the MW. Infer a marginally resolved velocity dispersion with sigma_vr=2.9±2.1 km/s which hints that this system is kinematically hotter than implied from its baryonic mass alone and potential y dark-matter-dominated (log10(M_1/2)=5.5±0.5 and log10((M/L)_(1/2))=2.7±0.6, in Solar units). Furthermore, very weak Calcium triplet lines in the spectra of the high S/N member stars indicate that its metallicity is likely lower than that of the globular cluster NGC 2419 ([Fe/H]<-2.1). Finally, variations in the line strengths of two stars with similar colors and magnitudes suggest the presence of a metallicity spread in Dra II. Taken together, these 3 pieces of evidence lead us to conclude that Dra II is likely to be among the faintest, most compact, and closest dwarf galaxies. However, emphasize that this conclusion needs to be strengthened through a more systematic spectroscopic campaign.
1510.01586
On the segregation of dark matter substructure
van den Bosch, Jiang, Campbell, Behroozi
Present the first comprehensive analysis of the segregation of DM sub haloes in their host halos. Using numerical sims, examine the segregation of 12 different sub halo properties with respect to both orbital energy and halo-centric radius (in real space as well as in projection). Sub haloes are strongly segregated by accretion redshift, which is an outcome of the inside-out assembly of their host halos. Since sub haloes that were accreted earlier have experienced more tidal stripping, sub haloes that have lost a larger fraction of their mass at infall are on more bound orbits. Sub haloes are also strongly segregated in their masses and maximum circular velocities at accretion. Demonstrate that part of this segregation is already imprinted in the infall conditions. For massive sub haloes it is subsequently boosted by dynamical friction, but only during their first radial orbit. The impact of these two effects is counterbalanced, though, by the fact that sub haloes with larger accretion masses are accreted later. Because of tidal stripping, sub haloes reveal little to no segregation by present-day mass or maximum circular velocity, while the corresponding torques cause subhalos on more bound orbits to have smaller spin. There is a weak tendency for sub haloes that formed earlier to be segregated towards the center of their host halo, which is an indirect consequence of the fact hat (sub)halo formation time is correlated with other, strongly segregated properties. Discuss the implications of the results for the segregation of satellite galaxies in galaxy groups and clusters.
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