Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos

We study the population of satellite galaxies formed in a suite of N-body/gasdynamical simulations of galaxy formation in a LCDM universe. We find little spatial or kinematic bias between the dark matter and the satellite population. The velocity dispersion of the satellites is a good indicator of the virial velocity of the halo: \sigma_{sat}/V_{vir}=0.9 +/- 0.2. Applied to the Milky Way and M31 this gives V_{vir}^{MW}=109 +/- 22$ km/s and V_{vir}^{M31} = 138 +/- 35 km/s, respectively, substantially lower than the rotation speed of their disk components. The detailed kinematics of simulated satellites and dark matter are also in good agreement. By contrast, the stellar halo of the simulated galaxies is kinematically and spatially distinct from the population of surviving satellites. This is because the survival of a satellite depends on mass and on time of accretion; surviving satellites are biased toward low-mass systems that have been recently accreted by the galaxy. Our results support recent proposals for the origin of the systematic differences between stars in the Galactic halo and in Galactic satellites: the elusive ``building blocks'' of the Milky Way stellar halo were on average more massive, and were accreted (and disrupted) earlier than the population of dwarfs that has survived self-bound until the present.Comment: 13 pages, 11 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

Cosmic M\'enage \`a Trois: The Origin of Satellite Galaxies On Extreme Orbits

We examine the orbits of satellite galaxies identified in a suite of N-body/gasdynamical simulations of the formation of $L_*$ galaxies in a LCDM universe. Most satellites follow conventional orbits; after turning around, they accrete into their host halo and settle on orbits whose apocentric radii are steadily eroded by dynamical friction. However, a number of outliers are also present, we find that ~1/3 of satellites identified at $z=0$ are on unorthodox orbits, with apocenters that exceed their turnaround radii. This population of satellites on extreme orbits consists typically of the faint member of a satellite pair that has been ejected onto a highly-energetic orbit during its first approach to the primary. Since the concurrent accretion of multiple satellite systems is a defining feature of hierarchical models of galaxy formation, we speculate that this three-body ejection mechanism may be the origin of (i) some of the newly discovered high-speed satellites around M31 (such as Andromeda XIV); (ii) some of the distant fast-receding Local Group members, such as Leo I; and (iii) the oddly isolated dwarf spheroidals Cetus and Tucana in the outskirts of the Local Group. Our results suggest that care must be exercised when using the orbits of the most weakly bound satellites to place constraints on the total mass of the Local Group.Comment: 10 pages, 6 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

Polycyclic Aromatic Hydrocarbon in the Central Region of the Seyfert 2 Galaxy NGC1808

We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC 1808, obtained with the Gemini's Thermal-Region Camera Spectrograph (T-ReCS) at a spatial resolution of 26 pc. The high spatial resolution allowed us to detect bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and 11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2 S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar to Peeters's A class, with the line peak shifted towards the blue. The differences in the PAH line profiles also suggests that the molecules in the region located 26 pc NE of the nucleus are more in the neutral than in the ionised state, while at 26 pc SW of the nucleus, the molecules are mainly in ionised state. After removal of the underlying galaxy contribution, the nuclear spectrum can be represented by a Nenkova's clumpy torus model, indicating that the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud distribution of sigma = 70degree, observer's view angle i = 90degree, and an outer radius of R0 = 0.55 pc. The derived column density along the line of sight is NH = 1.5 x 10^24 cm-2, which is sufficient to block the hard radiation from the active nucleus, and would explain the presence of PAH molecules near to the NGC 1808's active nucleus.Comment: Accepted by MNRAS 2012 December

High Spatial Resolution of the Mid-Infrared Emission of Compton-Thick Seyfert 2 Galaxy Mrk3

Mid-infrared (MIR) spectra observed with Gemini/Michelle were used to study the nuclear region of the Compton-thick Seyfert 2 (Sy 2) galaxy Mrk 3 at a spatial resolution of $\sim$200 pc. No polycyclic aromatic hydrocarbons (PAHs) emission bands were detected in the N-band spectrum of Mrk 3. However, intense [Ar III] 8.99 $\mu$m, [S IV] 10.5 $\mu$m and [Ne II] 12.8 $\mu$m ionic emission-lines, as well as silicate absorption feature at 9.7$\mu$m have been found in the nuclear extraction ($\sim$200 pc). We also present subarcsecond-resolution Michelle N-band image of Mrk 3 which resolves its circumnuclear region. This diffuse MIR emission shows up as a wings towards East-West direction closely aligned with the S-shaped of the Narrow Line Region (NLR) observed at optical [O III]$\lambda$5007\AA image with Hubble/FOC. The nuclear continuum spectrum can be well represented by a theoretical torus spectral energy distribution (SED), suggesting that the nucleus of Mrk 3 may host a dusty toroidal structure predicted by the unified model of active galactic nucleus (AGN). In addition, the hydrogen column density (N$_H\,=\,4.8^{+3.3}_{-3.1}\times\,10^{23}$ cm$^{-2}$) estimated with a torus model for Mrk 3 is consistent with the value derived from X-ray spectroscopy. The torus model geometry of Mrk 3 is similar to that of NGC 3281, both Compton-thick galaxies, confirmed through fitting the 9.7$\mu$m silicate band profile. This results might provide further evidence that the silicate-rich dust can be associated with the AGN torus and may also be responsible for the absorption observed at X-ray wavelengths in those galaxies.Comment: 11 pages, 6 figure

Satellite Galaxies and Fossil Groups in the Millennium Simulation

We use a semianalytic galaxy catalogue constructed from the Millennium Simulation to study the satellites of isolated galaxies in the LCDM cosmogony. This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites) allows the characterization, with minimal statistical uncertainty, of the dynamical properties of satellite/primary galaxy systems in a LCDM universe. We find that, overall, the satellite population traces the dark matter rather well: its spatial distribution and kinematics may be approximated by an NFW profile with a mildly anisotropic velocity distribution. Their spatial distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg'' effect that reflects the misalignment between the major axis and angular momentum of the host halo. The isolation criteria for our primaries picks not only galaxies in sparse environments, but also a number of primaries at the centre of ''fossil'' groups. We find that the abundance and luminosity function of these unusual systems are in reasonable agreement with the few available observational constraints. We recover the expected L_{host} \sigma_{sat}^3 relation for LCDM models for truly-isolated primaries. Less strict primary selection, however, leads to substantial modification of the scaling relation. Our analysis also highlights a number of difficulties afflicting studies that rely on blind stacking of satellite systems to constrain the mean halo mass of the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

A novel printed 3-electrode system for the electrochemical detection of sulfadiazine

We thank the financial support of 3C´s – Cellulose and Cork in the Control of antibiotics in aquaculture (PTDC/AAG-TEC/5400/2014 and POCI-01-0145-FEDER-016637), to FEDER, through COMPETE2020, POCI, and FCT (Fundação para a Ciência e a Tecnologia I.P.).info:eu-repo/semantics/publishedVersio

Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms

In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein modes; yet only for the Eu and Sr systems is there a large dip in the thermal conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here we argue that it is the off-center displacement that is crucial for understanding this unexplained difference in behavior. It enhances the coupling between the "rattler" motion and the lattice phonons for the Eu and Sr systems, and turns on/off another scattering mechanism (for 1K < T < 20K) produced by the presence/absence of off-center sites. The random occupation of different off-center sites produces a high density of symmetry-breaking defects which scatters phonons. It may also be important for improving our understanding of other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened arguments regarding need for additional phonon scattering mechanis