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We explore stellar population properties separately in the bulge and the disk of double-component cluster galaxies, to shed light on the formation of lenticular galaxies in dense environments. We study eight low-redshift clusters from the Sydney-AAO Multi-object Integral field Galaxy Survey, using two-dimensional photometric bulge–disk decomposition in the g, r, and i bands to characterize galaxies. For 192 double-component galaxies with M* > 1010M⊙, we estimate the color, age, and metallicity of the bulge and the disk. The analysis of the g − i colors reveals that bulges are redder than their surrounding disks, with a median offset of 0.12 ± 0.02 mag, consistent with previous results. To measure mass-weighted age and metallicity, we investigate three methods: (i) one based on galaxy stellar mass weights for the two components, (ii) one based on flux weights, and (iii) one based on radial separation. The three methods agree in finding 62% of galaxies having bulges that are 2–3 times more metal-rich than the disks. Of the remaining galaxies, 7% have bulges that are more metal-poor than the disks, while for 31%, the bulge and disk metallicities are not significantly different. We observe 23% of galaxies being characterized by bulges older and 34% by bulges younger with respect to the disks. The remaining 43% of galaxies have bulges and disks with statistically indistinguishable ages. Redder bulges tend to be more metal-rich than the disks, suggesting that the redder color in bulges is due to their enhanced metallicity relative to the disks instead of differences in stellar population age. [ABSTRACT FROM AUTHOR]

The Galaxy And Mass Assembly (GAMA) survey furnishes a deep redshift catalog that, when combined with the Wide-field Infrared Survey Explorer (WISE), allows us to explore for the first time the mid-infrared properties of >110, 000 galaxies over 120 deg2 to z ≃ 0.5. In this paper we detail the procedure for producing the matched GAMA-WISE catalog for the G12 and G15 fields, in particular characterizing and measuring resolved sources; the complete catalogs for all three GAMA equatorial fields will be made available through the GAMA public releases. The wealth of multiwavelength photometry and optical spectroscopy allows us to explore empirical relations between optically determined stellar mass (derived from synthetic stellar population models) and 3.4 μm and 4.6 μm WISE measurements. Similarly dust-corrected Hα-derived star formation rates can be compared to 12 μm and 22 μm luminosities to quantify correlations that can be applied to large samples to z < 0.5. To illustrate the applications of these relations, we use the 12 μm star formation prescription to investigate the behavior of specific star formation within the GAMA-WISE sample and underscore the ability of WISE to detect star-forming systems at z ∼ 0.5. Within galaxy groups (determined by a sophisticated friends-of-friends scheme), results suggest that galaxies with a neighbor within 100 h–1 kpc have, on average, lower specific star formation rates than typical GAMA galaxies with the same stellar mass. [ABSTRACT FROM AUTHOR]

The Fermi satellite discovery of the gamma-ray emitting bubbles extending 50° (10 kpc) from the Galactic center has revitalized earlier claims that our Galaxy has undergone an explosive episode in the recent past. We now explore a new constraint on such activity. The Magellanic Stream is a clumpy gaseous structure free of stars trailing behind the Magellanic Clouds, passing over the south Galactic pole (SGP) at a distance of at least 50-100 kpc from the Galactic center. Several groups have detected faint Hα emission along the Magellanic Stream (1.1 ± 0.3 × 10–18 erg cm–2 s–1 arcsec–2) which is a factor of five too bright to have been produced by the Galactic stellar population. The brightest emission is confined to a cone with half angle θ1/2 ≈ 25° roughly centered on the SGP. Time-dependent models of Stream clouds exposed to a flare in ionizing photon flux show that the ionized gas must recombine and cool for a time interval To = 0.6 – 2.9 Myr for the emitted Hα surface brightness to drop to the observed level. A nuclear starburst is ruled out by the low star formation rates across the inner Galaxy, and the non-existence of starburst ionization cones in external galaxies extending more than a few kiloparsecs. Sgr A⋆ is a more likely candidate because it is two orders of magnitude more efficient at converting gas to UV radiation. The central black hole (M• ≈ 4 × 106M☼) can supply the required ionizing luminosity with a fraction of the Eddington accretion rate (fE ∼ 0.03-0.3, depending on uncertain factors, e.g., Stream distance) typical of Seyfert galaxies. In support of nuclear activity, the Hα emission along the Stream has a polar angle dependence peaking close to the SGP. Moreover, it is now generally accepted that the Stream over the SGP must be farther than the Magellanic Clouds. At the lower halo gas densities, shocks become too ineffective and are unlikely to give rise to a polar angle dependence in the Hα emission. Thus it is plausible that the Stream Hα emission arose from a “Seyfert flare” that was active 1-3 Myr ago, consistent with the cosmic ray lifetime in the Fermi bubbles. Sgr A⋆ activity today is greatly suppressed (70-80 dB) relative to the Seyfert outburst. The rapid change over a huge dynamic range in ionizing luminosity argues for a compact UV source with an extremely efficient (presumably magneto-hydrodynamic) “drip line” onto the accretion disk. [ABSTRACT FROM AUTHOR]

RAVE, the unbiased magnitude limited survey of southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the Ca II infrared triplet (IRT) range, which is a known indicator of chromospheric activity. Our previous work classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here, we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-local thermal equilibrium profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5 Å wide interval and their sum EWIRT for ∼44,000 candidate active dwarf stars with signal-to-noise ratio >20, with no cuts on the basis of the source of their emission flux. From these, ∼14,000 show a detectable chromospheric flux with at least a 2σ confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and, in some cases, radial velocities of active stars derived from automatic pipelines suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity, and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre-main-sequence cases. The catalog will be made publicly available with the next RAVE public data releases. [ABSTRACT FROM AUTHOR]

We present a combined optical and X-ray analysis of the rich cluster ABELL 1882 (A1882) with the aim of identifying merging substructure and understanding the recent assembly history of this system. Our optical data consist of spectra drawn from the Galaxy and Mass Assembly survey, which lends itself to this kind of detailed study thanks to its depth and high spectroscopic completeness. We use 283 spectroscopically confirmed cluster members to detect and characterize substructure. We complement the optical data with X-ray data taken with both Chandra and XMM. Our analysis reveals that A1882 harbors two main components, A1882A and A1882B, which have a projected separation of ~2 Mpc and a line of sight velocity difference of vlos ~ -428-139+187 km s-1. The primary system, A1882A, has velocity dispersion σv = 500-26+23 km s-1 and Chandra (XMM) temperature kT = 3.57 ± 0.17 keV (3.31-0.27+0.28 keV) while the secondary, A1882B, has sv = 457-101+108 km s-1 and Chandra (XMM) temperature kT = 2.39 ± 0.28 keV (2.12 ± 0.20 keV). The optical and X-ray estimates for the masses of the two systems are consistent within the uncertainties and indicate that there is twice as much mass in A1882A (M500 = 1.5-1.9 × 1014 M⊙) when compared with A1882B (M500 = 0.8-1.0 × 1014 M⊙). We interpret the A1882A/A1882B system as being observed prior to a core passage. Supporting this interpretation is the large projected separation of A1882A and A1882B and the dearth of evidence for a recent (<2 Gyr) major interaction in the X-ray data. Two-body analyses indicate that A1882A and A1882B form a bound system with bound incoming solutions strongly favored.We compute blue fractions of fb = 0.28±0.09 and 0.18±0.07 for the spectroscopically confirmed member galaxies within r500 of the centers of A1882A and A1882B, respectively. These blue fractions do not differ significantly from the blue fraction measured from an ensemble of 20 clusters with similar mass and redshift. [ABSTRACT FROM AUTHOR]

The Magellanic System includes some of the nearest examples of galaxies disturbed by galaxy interactions. These interactions have redistributed much of their gas into the halos of the Milky Way (MW) and the Magellanic Clouds. We present Wisconsin Hα Mapper kinematically resolved observations of the warm ionized gas in the Magellanic Bridge over the velocity range of +100 to +300 km s-1 in the local standard of rest reference frame. These observations include the first full Hα intensity map and the corresponding intensity-weighted mean velocity map of the Magellanic Bridge across (l, b) = (281. ° 5,-30. ° 0) to (302. ° 5,-46. ° 7). Using the Hα emission from the Small Magellanic Cloud (SMC)-Tail and the Bridge, we estimate that the mass of the ionized material is between (0.7-1.7) × 108M☉, compared to 3.3 × 108M☉ for the neutral mass over the same region. The diffuse Bridge is significantly more ionized than the SMC-Tail, with an ionization fraction of 36%-52% compared to 5%-24% for the Tail. The Hα emission has a complex multiple-component structure with a velocity distribution that could trace the sources of ionization or distinct ionized structures. We find that incident radiation from the extragalactic background and the MW alone are insufficient to produced the observed ionization in the Magellanic Bridge and present a model for the escape fraction of the ionizing photons from both the SMC and Large Magellanic Cloud (LMC). With this model, we place an upper limit of 4.0% for the average escape fraction of ionizing photons from the LMC and an upper limit of 5.5% for the SMC. These results, combined with the findings of a half a dozen other studies for dwarf galaxies in different environments, provide compelling evidence that only a small percentage of the ionizing photons escape from dwarf galaxies in the present epoch to influence their surroundings. [ABSTRACT FROM AUTHOR]

A 45 deg² radio continuum imaging campaign of the nearest radio galaxy, Centaurus A, is reported. Using the Australia Telescope Compact Array and the Parkes 64 m radio telescope at 1.4 GHz, the spatial resolution of the resultant image is ~.600 pc (~50′), resolving the ≳500 kpc giant radio lobes with approximately five times better physical resolution compared to any previous image, and making this the most detailed radio continuum image of any radio galaxy to date. In this paper, we present these new data and discuss briefly some of the most interesting morphological features that we have discovered in the images. The two giant outer lobes are highly structured and considerably distinct. The southern part of the giant northern lobe naturally extends out from the northern middle lobe with uniformly north-streaming emission. The well known northern loop is resolved into a series of semi-regular shells with a spacing of approximately 25 kpc. The northern part of the giant northern lobe also contains identifiable filaments and partial ring structures. As seen in previous single-dish images at lower angular resolution, the giant southern lobe is not physically connected to the core at radio wavelengths. Almost the entirety of the giant southern lobe is resolved into a largely chaotic and mottled structure which appears considerably different (morphologically) to the diffuse regularity of the northern lobe. We report the discovery of a vertex and a vortex near the western boundary of the southern lobe, two striking, high surface brightness features that are named based on their morphology and not their dynamics (which are presently unknown). The vortex and vertex are modeled as reaccelerated lobe emission due to shocks from the active galactic nucleus itself or from the passage of a dwarf elliptical galaxy through the lobe. Preliminary polarimetric and spectral index studies support a plasma reacceleration model and could explain the origin of the Faraday rotation structure detected in the southern lobe. In addition, there are a series of low surface brightness wisps detected around the edges of both the giant lobes. [ABSTRACT FROM AUTHOR]

We investigate the kinematic parameters of the Milky Way disk using the Radial Velocity Experiment (RAVE) and Geneva-Copenhagen Survey (GCS) stellar surveys. We do this by fitting a kinematic model to the data and taking the selection function of the data into account. For stars in the GCS we use all phase-space coordinates, but for RAVE stars we use only (ℓ, b, vlos). Using the Markov Chain Monte Carlo technique, we investigate the full posterior distributions of the parameters given the data. We investigate the age-velocity dispersion relation for the three kinematic components (σR, σϕ, σz), the radial dependence of the velocity dispersions, the solar peculiar motion (U☼, V☼, W☼), the circular speed Θ0 at the Sun, and the fall of mean azimuthal motion with height above the midplane. We confirm that the Besançon-style Gaussian model accurately fits the GCS data but fails to match the details of the more spatially extended RAVE survey. In particular, the Shu distribution function (DF) handles noncircular orbits more accurately and provides a better fit to the kinematic data. The Gaussian DF not only fits the data poorly but systematically underestimates the fall of velocity dispersion with radius. The radial scale length of the velocity dispersion profile of the thick disk was found to be smaller than that of the thin disk. We find that correlations exist between a number of parameters, which highlights the importance of doing joint fits. The large size of the RAVE survey allows us to get precise values for most parameters. However, large systematic uncertainties remain, especially in V☼ and Θ0. We find that, for an extended sample of stars, Θ0 is underestimated by as much as 10% if the vertical dependence of the mean azimuthal motion is neglected. Using a simple model for vertical dependence of kinematics, we find that it is possible to match the Sgr A* proper motion without any need for V☼ being larger than that estimated locally by surveys like GCS. [ABSTRACT FROM AUTHOR]

We present a study of the chemical abundances of solar neighborhood stars associated with dynamical structures in the Milky Way's (thick) disk. These stars were identified as an overdensity in the eccentricity range 0.3 < ε < 0.5 in the Copenhagen-Geneva Survey by Helmi et al. We find that stars with these dynamical characteristics do not constitute a homogeneous population. A relatively sharp transition in dynamical and chemical properties appears to occur at a metallicity of [Fe/H] ∼ –0.4. Stars with [Fe/H] > –0.4 have mostly lower eccentricities, smaller vertical velocity dispersions, are α-enhanced, and define a rather narrow sequence in [α/Fe] versus [Fe/H], clearly distinct from that of the thin disk. Stars with [Fe/H] < –0.4 have a range of eccentricities, are hotter vertically, and depict a larger spread in [α/Fe]. We also found tentative evidence of a substructure possibly associated with the disruption of a metal-rich star cluster. The differences between these populations of stars is also present in, e.g., [Zn/Fe], [Ni/Fe], and [SmII/Fe], suggesting a real physical distinction. [ABSTRACT FROM AUTHOR]

The M82 “cap” is a gas cloud at a projected radius of 11.6 kpc along the minor axis of this well-known superwind source. The cap has been detected in optical line emission and X-ray emission and therefore provides an important probe of the wind energetics. In order to investigate the ionization source of the cap, we observed it with the Kyoto3DII Fabry-Perot instrument mounted on the Subaru Telescope. Deep continuum, Hα, [N II]λ6583/Hα, and [S II]λλ6716,6731/Hα maps were obtained with subarcsecond resolution. The superior spatial resolution compared to earlier studies reveals a number of bright Hα emitting clouds within the cap. The emission line widths (≲ 100 km s–1 FWHM) and line ratios in the newly identified knots are most reasonably explained by slow to moderate shocks velocities (vshock = 40-80 km s–1) driven by a fast wind into dense clouds. The momentum input from the M82 nuclear starburst region is enough to produce the observed shock. Consequently, earlier claims of photoionization by the central starburst are ruled out because they cannot explain the observed fluxes of the densest knots unless the UV escape fraction is very high (fesc > 60%), i.e., an order of magnitude higher than observed in dwarf galaxies to date. Using these results, we discuss the evolutionary history of the M82 superwind. Future UV/X-ray surveys are expected to confirm that the temperature of the gas is consistent with our moderate shock model. [ABSTRACT FROM AUTHOR]

Near the minor axis of the Galactic bulge, at latitudes b < –5°, the red giant clump stars are split into two components along the line of sight. We investigate this split using the three fields from the ARGOS survey that lie on the minor axis at (l, b) = (0°, –5°), (0°, –7.°5), (0°, –10°). The separation is evident for stars with [Fe/H] > – 0.5 in the two higher-latitude fields, but not in the field at b = –5°. Stars with [Fe/H] < – 0.5 do not show the split. We compare the spatial distribution and kinematics of the clump stars with predictions from an evolutionary N-body model of a bulge that grew from a disk via bar-related instabilities. The density distribution of the peanut-shaped model is depressed near its minor axis. This produces a bimodal distribution of stars along the line of sight through the bulge near its minor axis, very much as seen in our observations. The observed and modeled kinematics of the two groups of stars are also similar. We conclude that the split red clump of the bulge is probably a generic feature of boxy/peanut bulges that grew from disks, and that the disk from which the bulge grew had relatively few stars with [Fe/H] < – 0.5. [ABSTRACT FROM AUTHOR]