We study dwarf satellite galaxy quenching using observations from the Geha et al. (2012) NSA/SDSS catalog together with ΛCDM cosmological simulations to facilitate selection and interpretation. We show that fewer than 30% of dwarfs (M 10 8.5−9.5 M ) identified as satellites within massive host halos (M host 10 12.5−14 M ) are quenched, in spite of the expectation from simulations that half of them should have been accreted more than 6 Gyr ago. We conclude that whatever the action triggering environmental quenching of dwarf satellites, the process must be highly inefficient. We investigate a series of simple, one-parameter quenching models in order to understand what is required to explain the low quenched fraction and conclude that either the quenching timescale is very long (> 9.5 Gyr, a "slow starvation" scenario) or that the environmental trigger is not well matched to accretion within the virial volume. We discuss these results in light of the fact that most of the low mass dwarf satellites in the Local Group are quenched, a seeming contradiction that could point to a characteristic mass scale for satellite quenching.

We examine the star formation properties of bright (∼ 0.1 L * ) satellites around isolated ∼ L * hosts in the local Universe using spectroscopically confirmed systems in the Sloan Digital Sky Survey DR7. Our selection method is carefully designed with the aid of N -body simulations to avoid groups and clusters. We find that satellites are significantly more likely to be quenched than a stellar mass-matched sample of isolated galaxies. Remarkably, this quenching occurs only for satellites of hosts that are themselves quenched: while star formation is unaffected in the satellites of star-forming 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 star formation in isolated, passive L * galaxies also plays at least an indirect role in quenching star formation in their bright satellites. The previously-reported tendency for "galactic conformity" in colour/morphology may be a by-product of this host-specific quenching dichotomy. The Sérsic indices of quenched satellites are statistically identical to those of field galaxies with the same specific star formation rates, 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, we find dynamical evidence that passive host galaxies reside in dark matter haloes that are ∼ 45% more massive than those of star-forming host galaxies of the same stellar mass. We emphasize that even around passive hosts, the mere fact that galaxies become satellites does not typically result in star formation quenching: we find that only ∼ 30% of ∼ 0.1L * galaxies that fall in from the field are quenched around passive hosts, compared with ∼ 0% around star forming hosts.

We present a multi-wavelength catalog in the Subaru-XMM Deep Field (SXDF) as part of the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH). We include the newly acquired optical data from the Hyper-Suprime Cam Subaru Strategic Program, accompanied by IRAC coverage from the SPLASH survey. All available optical and near-infrared data is homogenized and resampled on a common astrometric reference frame. Source detection is done using a multi-wavelength detection image including the u-band to recover the bluest objects. We measure multiwavelength photometry and compute photometric redshifts as well as physical properties for ∼1.17 million objects over ∼4.2 deg 2 with ∼800,000 objects in the 2.4 deg 2 HSC-UltraDeep coverage. Using the available spectroscopic redshifts from various surveys over the range of 0 < z < 6, we verify the performance of the photometric redshifts and we find a normalized median absolute deviation of 0.023 and outlier fraction of 3.2%. The SPLASH-SXDF catalog is a valuable, publicly available a) resource, perfectly suited for studying galaxies in the early universe and tracing their evolution through cosmic time.

We combine COBE DMR measurements of cosmic microwave background (CMB) anisotropy with a recent measurement of the mass power spectrum at redshift z \ 2.5 from Lya forest data to derive constraints on cosmological parameters and test the inÑationary cold dark matter (CDM) scenario of structure formation. By treating the inÑationary spectral index n as a free parameter, we are able to Ðnd successful Ðts to the COBE and Lya forest constraints in models with and without massive neu-) m \ 1 trinos and in models with and without a cosmological constant. Within each class of model, the low-) m combination of COBE and the Lya forest P(k) constrains a parameter combination of the form with di †erent indices for each case. This new constraint breaks some of the degeneracies in ) m hanb) b c, cosmological parameter determinations from other measurements of large-scale structure and CMB anisotropy. The Lya forest P(k) provides the Ðrst measurement of the slope of the linear mass power spectrum on DMpc scales, l \ [2.25^0.18, and it conÐrms a basic prediction of the inÑationary CDM scenario : an approximately scale invariant spectrum of primeval Ñuctuations (n B 1) modulated by a transfer function that bends P(k) toward kn~4 on small scales. Considering additional observational data, we Ðnd that COBE-normalized, models that match the Lya forest P(k) do not match the ) m \ 1 observed masses of rich galaxy clusters, and that models with a cosmological constant provide low-) m the best overall Ðt to the available data, even without the direct evidence for cosmic acceleration from Type Ia supernovae. With our Ðducial parameter choices, the Ñat, models that match COBE and low-) m the Lya forest P(k) also match recent measurements of small-scale CMB anisotropy. Modest improvements in the Lya forest P(k) measurement could greatly restrict the allowable region of parameter space for CDM models, constrain the contribution of tensor Ñuctuations to CMB anisotropy, and achieve a more stringent test of the current consensus model of structure formation.

We compare the dynamics of satellite galaxies in the Sloan Digital Sky Survey to simple models in order to test the hypothesis that a large fraction of satellites co-rotate in coherent planes. We confirm the previously-reported excess of co-rotating satellite pairs located near diametric opposition with respect to their host, but show that this signal is unlikely to be due to rotating discs (or planes) of satellites. In particular, no overabundance of co-rotating satellites pairs is observed within ∼ 20 • − 50 • of direct opposition, as would be expected for planar distributions inclined relative to the lineof-sight. Instead, the excess co-rotation for satellite pairs within ∼ 10 • of opposition is consistent with random noise associated with undersampling of an underlying isotropic velocity distribution. Based upon the observed dynamics of the luminous satellite population, we conclude that at most 10% of isolated hosts harbor co-rotating satellite planes (as traced by bright satellites).