1507.02282
The impact of baryonic physics on the structure of dark matter haloes: the view from the FIRE cosmological simulations
Chan, ... Hopkins, ... Faucher-Giguère, Quataert
Study the distribution of CDM in cosmo zoom-in simulations from the Feedback in Realistic Environments (FIRE) project, for a range of halo mass (2e9-12 Msun) and stellar mass (1e4-11 Msun). The FIRE simulations incorporate explicit stellar feedback within the multi-phase ISM. Find that stelar feedback, without any "fine-tuned" parameters, can greatly alleviate small-scale problems in CDM. Feedback causes bursts of SF and outflows, altering the DM distribution. As a result, the inner slope of the DM halo profile "alpha" shows a strong mass dependence: profiles are shallow at M_h~1e10-11 Msun and steepen at higher/lower masses. The resulting core sizes and slopes are consistent with observations. This is broadly consistent with previous work using simpler feedback schemes, but find steeper mass dependence of "alpha,", and relatively late growth of core. Because the star formation efficiency is strongly halo mass dependent, a rapid change in the central slope occurs at M_h~1e10 Msun, as sufficient feedback energy becomes available to perturb the DM. Show that large cores are not established during the period of rapid growth of haloes because of ongoing DM mass accumulation. Instead, cores require several bursts of star formation after the rapid buildup has completed. The same effects dramatically reduce circular velocities in the inner kpc of massive dwarfs; this could be sufficient to explain the "Too Big to Fail" problem without invoking non-standard DM. Finally, study baryonic contraction in MW-size halos. The net result of stellar feedback and baryonic contraction is to produce DM profiles slightly shallower than the NFW profile, as required by the normalization of the TF relation.
1507.02396
Linking galaxies to dark matter haloes at $z\sim1$: dependence of galaxy clustering on stellar mass and specific star formation rate
Kim, ... Merson, et al
Study the dependence of angular 2PCF on M* and sSFR of M*>1e10 Msun galaxies at z~1. The data from UKIDSS DXS and CFHTS covering 8.2 deg2 sample scales larger than 100 Mpc/h at z~1, allowing investigation of the correlation between clustering, M* and SF through halo modeling. Based on HODs of M* threshold samples, derive HODs for M* binned galaxies, and then calculate the M*/Mhalo ratio. The ratio for central galaxies shows a peak at Mhalo~1e12 Msun/h, and satellites predominantly contribute to the total stellar mass in cluster environments with M*/Mhalo values of 0.01-0.02. Using SF galaxies split by sSFR, find that MS galaxies (log sSFR/yr ~ -9) are mainly central galaxies in ~1e12.5 Msun/h haloes with the lowest clustering amplitude, while lower sSFR galaxies consistent of a mixture of both central and satellite galaxies where those with the lowest M* are predominantly satellite influenced by their environment. Considering the lowest Mhalo samples in each M* bin, massive central galaxies reside in more massive haloes with lower sSFRs than low mass ones, indicating SF central galaxies evolve from a low M*-high sSFR to a high M*-low sSFR regime. Also find that the most rapidly star-forming galaxies (low sSFR/yr> -8.5) are in more massive haloes than MS ones, possibly implying galaxy mergers in dense environments are driving the active SF. These results support the conclusion that the majority of SF galaxies follow secular evolution through the sustained but decreasing formation of stars.
1507.02657
The population of galaxy-galaxy strong lenses in forthcoming optical imaging surveys
Collett
Ongoing and future imaging surveys represent significant improvements in depth, area and seeing compared to current data-sets. These improvements offer the opportunity to discover up to 3 orders of magnitude more gg strong lenses than are currently known. In this work, forecast the number of lenses discoverable in forthcoming surveys and simulate their properties. Generate a population of statistically realistic strong lenses and simulate observations of this population for the DES, LSST and Euclid surveys. Verify the model against the galaxy-scale lens search of the CFHTLS, predicting 250 discoverable lenses compared to 220 found by Gavazzi+2014. The predicted Einstein radius distribution is also remarkably similar to that found by Sonnenfeld+2013. For future surveys, find that, assuming Poisson limited lens galaxy subtraction, searches in DES, LSST and Euclid datasets should discover 2.4k, 120k, and 170k gg strong lenses respectively. Finders using blue minus red (g-i) difference imaging for lens subtraction can discover 1.3k and 62k lenses in DES and LSST. The uncertainties on the model are dominated by the high z source population which typically gives fractional errors on the discoverable lens number at the tens of percent level. Find that doubling the S/N ratio required for a lens to be detectable, approximately halves the number of detectable lenses in each survey, indicating the importance of understanding the selection function and sensitivity of future lens finders in interpreting strong lens statistics. Make population forecasting and simulated observation codes publicly available so that the selection function of strong lens finders can easily be calibrated.
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