1307.3552
A dichotomy in satellite quenching around L* galaxies
Phillips, Wheeler, Boylan-Kolchin, BUllock, COoper, Tollerud
Examine SF properties of bright (~0.1 L*) satellites around isolated ~L* hosts in the local Universe using spectroscopically confirmed systems in SDSS DR7. Selection method aded with N-body sims to avoid groups and clusters. Find that satellites are significantly more likely to be quenched than a stellar mass-matched sample of isolated galaxies. This quenching occurs only for satellites of hosts that are themselves quenched: while SF is unaffected in the satellites of SF hosts, satellites around quiescent hosts are more than twice as likely to be quenched than stellar-mass matched field samples. One implication of this is that whatever shuts down SF in isolated, passive L* galaxies also plays at least an indirect role in quenching SF in their bright satellites. The previously-reportaed tendency for "galactic conformity" in color/morphology may be a by-product of this host-specific quenching dichotomy. The Sersic indices of quenched satellites are statistically identical to those of field galaxies with the same specific SFR, suggesting that environmental and secular quenching give rise to the same morphological structure. By studying the distribution of pairwise velocities between the hosts and satellites, find dynamical evidence that passive host galaxies reside in DM haloes that are ~45% more massive than those of SF host galaxies of the same stellar mass. Emphasize that even around passive hosts, the mere fact that galaxies become satellites does not typically result in SF quenching: find that only ~30% of ~0.1 L* galaxies that fall in from the field are quenched around passive hosts, compared with ~0% around SF hosts.
1307.3555
SN 2000cx and SN 2013bh: extremely rare, nearly twin type Ia supernovae
Silverman, ... Perley, ... Amanullah, ... Blooum, ... Kulkarni, ... Nugent, ... et al
SNIa 2000cs was one of the most peculiar transients ever discovered: While its rise to maximum brightness was typical for SN Ia, its decline was slower, causing standard light curve fitting algorithms to fail; its spectra indicated a high photospheric temperature. 13 years later, SN 2013bh, the first near identical twin of SN 2000cx, was discovered. Obtain optical and NIR photometry and low-resolution optical spectroscopy of this object from discovery until about 1 mo. past r-band maximum brightness. The spectra of both objects indicate the presence of Fe-group elements (CO II, Ni II, Fe II, Fe III, and high-velocity features [HVF] of Ti II), intermediate-mass elements (Si II, Si III, and S II) in addition to separate normal velocity features (~12000 km/s) and HVFs ( ~24000 km/s) of Ca II. Persistent absorption from Fe III and Si III, along with the color evolution, imply relatively high BB temperatures of SNe 2013bh and 2000cx (~12000 K). Both objects lack narrow Na I D absorption and exploded in the outskirts of their host galaxies, indicating that the SN environment was relatively free of interstellar or circumstellar material. This hints that the progenitors of these objects likely came from a relatively old and low-metallicity stellar population and possibly from the merger of two degenerate objects. Models of SN 2000cx, which seem to be directly applicable to SN 2013bh, imply the production of up to ~1 M_sun of Ni-56 and, in order to explain the HVFs of Ca II, (4.3-5.5)e-3 Msun of fast-moving Ca ejecta (which can be explained by primordial material alone).
1307.3577
Sussing merger trees: the merger trees comparison project
Srisawat, et al
Merger trees follow the growth and merger of DM haloes over cosmic history. As well as giving important insights into the growth of cosmic structure, they provide an essential backbone to SAMs of galaxy formation. First in a series to arise from a workshop in which 10 different tree-building algorithms were applied to the same set of halo catalogues and their results compared. Although many of these codes were similar in nature, all algorithms produced distinct results. Main conclusions are that a useful merger-tree code should possess the following features: (i) the use of particle IDs to match haloes between snapshots; (ii) the ability to skip at least one, and preferably more, snapshots in order to recover subhaloes that are temporarily lost during merging; (iii) the ability to cope with (and ideally smooth out) large, temporarily fluctuations in halo mass. Finally, to enable different groups to communicate effectively, defined a common terminology used when discussing merger trees and encourage others to adopt the same language. Specified a minimal output format to record the results.
1307.3705
On the nature of dark matter in the coma cluster
Zioutas et al
The precise observations of the CMB temperature by Planck toward the Coma cluster are not in agreement with X-ray measurements. To reconcile both types of measuring techniques, suggest that unstable DM is the cause of this mismatch. Decaying DM, which gravitationally dominates the galaxy cluster, can affect the estimated hot plasma content, which is then missing in the measured SZ effect from exactly the same place in the sky. THe model independent lifetime of DM decaying entirely to X-rays is estimated to be about 6e24 sec; this lifetime scales down with the fraction of the radiatively decaying DM. In addition, it is shown that the potential of such DM investigations in space is superior to the largest volume Earth-bound DM decay searches. Other clusters might provide additional evidence for or against this suggestion.
1307.3734
Probing the evolution of the substructure frequency in galaxy clusters up to z~1
Weißmann, Böhringer, Chon
The substructure frequency in galaxy clusters, in the past and present epoch, provides means for studying the underlying cosmological model. Using X-ray observations, study the substructure frequency as a function of redshift by quantifying and comparing the fraction of dynamically young clusters at different redshifts up to z=1.08. Especially interested in possible biases due to the inconsistent data quality of the low-z and high-z samples. Morphology estimators, power ratio P3/P0 and center shift w, were used dto quantify the dynamical state of 129 galaxy clusters, taking into account the different observational depth and noise levels of the observations. P3/P0 sensitive to Poisson noise, so essential to use datasets with similar photon statistics. Degrade the high-quality data of the low-z sample to the lo data quality of high-z observations, and found a shallow positive slope that is not significant, indicating a slightly larger fraction of dynamically young objects at higher redshift. The w-z relation shows no significant dependence on the data quality and gives a similar result. Find a similar trend for P3/P0 and w, namely a very mild increase of the disturbed cluster fraction with increasing redshifts; consistent with no evolution.
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