[en] We demonstrate that the space formed by the star formation rate (SFR), gas-phase metallicity (Z), and stellar mass (M _*) can be reduced to a plane, as first proposed by Lara-López et al. We study three different approaches to find the best representation of this 3D space, using a principal component analysis (PCA), a regression fit, and binning of the data. The PCA shows that this 3D space can be adequately represented in only two dimensions, i.e., a plane. We find that the plane that minimizes the χ² for all variables, and hence provides the best representation of the data, corresponds to a regression fit to the stellar mass as a function of SFR and Z, M _*= f(Z, SFR). We find that the distribution resulting from the median values in bins for our data gives the highest χ². We also show that the empirical calibrations to the oxygen abundance used to derive the Fundamental Metallicity Relation have important limitations, which contribute to the apparent inconsistencies. The main problem is that these empirical calibrations do not consider the ionization degree of the gas. Furthermore, the use of the N2 index to estimate oxygen abundances cannot be applied for 12 + log(O/H) ∼> 8.8 because of the saturation of the [N II] λ6584 line in the high-metallicity regime. Finally, we provide an update of the Fundamental Plane derived by Lara-López et al.

[en] We report on the results of a visual search for galaxy-scale strong gravitational lenses over 650 arcmin² of HST/ACS (F606W and F814W) imaging in the DEEP2-Extended Groth Strip (EGS). In addition to a previously-known Einstein Cross also found by our search (the 'Cross', HSTJ141735+52264, z_lens = 0.8106, z_source = 3.40), we identify two new strong galaxy-galaxy lenses with multiple extended arcs. The first, HSTJ141820+52361 (the 'Dewdrop'; z_lens = 0.5798), lenses two distinct extended sources into two pairs of arcs (z_source = 0.9818), while the second, HSTJ141833+52435 (the 'Anchor'; z_lens = 0.4625), produces a single pair of arcs (z_lens not yet known). Four less convincing arc/counter-arc and two-image lens candidates are also found and presented for completeness. Lenses are found in a both underdense and overdense local environments, as characterized by a robust measure, 1+(delta)₃, a normalized density that uses the distance to the third nearest neighbor. All three definite lenses are fit reasonably well by simple singular isothermal ellipsoid models including external shear, giving χ_ν² values close to unity. These shears are much greater than those implied by a simple consideration of the three-dimensional convergence and shear from galaxies along the line of sight, where each galaxy is approximated by a singular isothermal sphere halo truncated at 200 h^-1 kpc. This shows how a realistic treatment of galaxies and the large scale structure they are embedded in is necessary, and that simply characterizing the very-local environment may be insufficient

[en] We present a 250 ks Chandra observation of the cluster merger A2034 with the aim of understanding the nature of a sharp edge previously characterized as a cold front. The new data reveal that the edge is coherent over a larger opening angle and is significantly more bow-shock-shaped than previously thought. Within ∼27° about the axis of symmetry of the edge, the density, temperature, and pressure drop abruptly by factors of 1.83_−0.08^+0.09, 1.85_−0.41^+0.41, and 3.4_−0.7^+0.8, respectively. This is inconsistent with the pressure equilibrium expected of a cold front and we conclude that the edge is a shock front. We measure a Mach number M=1.59_−0.07^+0.06 and corresponding shock velocity v _shock ≅ 2057 km s^–1. Using spectra collected at the MMT with the Hectospec multi-object spectrograph, we identify 328 spectroscopically confirmed cluster members. Significantly, we find a local peak in the projected galaxy density associated with a bright cluster galaxy that is located just ahead of the nose of the shock. The data are consistent with a merger viewed within ∼23° of the plane of the sky. The merging subclusters are now moving apart along a north-south axis approximately 0.3 Gyr after a small impact parameter core passage. The gas core of the secondary subcluster, which was driving the shock, appears to have been disrupted by the merger. Without a driving 'piston,' we speculate that the shock is dying. Finally, we propose that the diffuse radio emission near the shock is due to the revival of pre-existing radio plasma that has been overrun by the shock.

[en] High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to study aspects of the early universe, including the cosmic star formation rate (SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z ≅ 6.7 and GRB 090423 at z ≅ 8.1, and more than four years of Swift observations, we first confirm that the GRB rate does not trace the SFR in an unbiased way. Correcting for this, we find that the implied SFR to beyond z = 8 is consistent with Lyman Break Galaxy-based measurements after accounting for unseen galaxies at the faint end of the UV luminosity function. We show that this provides support for the integrated star formation in the range 6 ∼< z ∼< 8 to have been alone sufficient to reionize the universe.

[en] In this second of a series of papers on spatially resolved star formation, we investigate the impact of the density-morphology relation of galaxies on the spatial variation of star formation (SF) and its dependence on environment. We find that while a density-morphology relation is present for the sample, it cannot solely explain the observed suppression of SF in galaxies in high-density environments. We also find that early-type and late-type galaxies exhibit distinct radial star formation rate (SFR) distributions, with early types having an SFR distribution that extends further relative to the galaxy scale length, compared to late types at all densities. We find that a suppression of SF in the highest density environments is found in the highest star-forming galaxies for both galaxy types. This suppression occurs in the innermost regions in late types (r ≤ 0.125 Petrosian radii), and further out in radius in early types (0.125 Petrosian radii < r ≤ 0.25 Petrosian radii). When the full sample is considered no clear suppression of SF is detected, indicating that the environmental trends are driven only by the highest SF galaxies. We demonstrate that the density-morphology relation alone cannot account for the suppression of SF in the highest density environments. This points to an environmentally governed evolutionary mechanism that affects the SF in the innermost regions in both early- and late-type galaxies. We suggest that this is a natural consequence of the 'downsizing' of SF in galaxies.

[en] We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13 fused fiber bundles (hexabundles) across a one-degree field of view allowing simultaneous spatially resolved spectroscopy of 13 galaxies. During the first SAMI commissioning run, targeting a single galaxy field, one object (ESO 185-G031) was found to have extended minor axis emission with ionization and kinematic properties consistent with a large-scale galactic wind. The importance of this result is twofold: (1) fiber bundle spectrographs are able to identify low surface brightness emission arising from extranuclear activity and (2) such activity may be more common than presently assumed because conventional multi-object spectrographs use single-aperture fibers and spectra from these are nearly always dominated by nuclear emission. These early results demonstrate the extraordinary potential of multi-object hexabundle spectroscopy in future galaxy surveys.

[en] Strong gravitational lenses are a rare and instructive type of astronomical object. Identification has long relied on serendipity, but different strategies—such as mixed spectroscopy of multiple galaxies along the line of sight, machine-learning algorithms, and citizen science—have been employed to identify these objects as new imaging surveys become available. We report on the comparison between spectroscopic, machine-learning, and citizen-science identification of galaxy–galaxy lens candidates from independently constructed lens catalogs in the common survey area of the equatorial fields of the Galaxy and Mass Assembly survey. In these, we have the opportunity to compare high completeness spectroscopic identifications against high-fidelity imaging from the Kilo Degree Survey used for both machine-learning and citizen-science lens searches. We find that the three methods—spectroscopy, machine learning, and citizen science—identify 47, 47, and 13 candidates, respectively, in the 180 square degrees surveyed. These identifications barely overlap, with only two identified by both citizen science and machine learning. We have traced this discrepancy to inherent differences in the selection functions of each of the three methods, either within their parent samples (i.e., citizen science focuses on low redshift) or inherent to the method (i.e., machine learning is limited by its training sample and prefers well-separated features, while spectroscopy requires sufficient flux from lensed features to lie within the fiber). These differences manifest as separate samples in estimated Einstein radius, lens stellar mass, and lens redshift. The combined sample implies a lens candidate sky density of ∼0.59 deg⁻² and can inform the construction of a training set spanning a wider mass–redshift space. A combined approach and refinement of automated searches would result in a more complete sample of galaxy–galaxy lens candidates for future surveys.

[en] We cross-match the two currently largest all-sky photometric catalogs—mid-infrared Wide-field Infrared Survey Explorer and SuperCOSMOS scans of UKST/POSS-II photographic plates—to obtain a new galaxy sample that covers 3π steradians. In order to characterize and purify the extragalactic data set, we use external GAMA and Sloan Digital Sky Survey spectroscopic information to define quasar and star loci in multicolor space, aiding the removal of contamination from our extended source catalog. After appropriate data cleaning, we obtain a deep wide-angle galaxy sample that is approximately 95% pure and 90% complete at high Galactic latitudes. The catalog contains close to 20 million galaxies over almost 70% of the sky, outside the Zone of Avoidance and other confused regions, with a mean surface density of more than 650 sources per square degree. Using multiwavelength information from two optical and two mid-IR photometric bands, we derive photometric redshifts for all the galaxies in the catalog, using the ANNz framework trained on the final GAMA-II spectroscopic data. Our sample has a median redshift of $z_{\mathrm{m}\mathrm{e}\mathrm{d}}=0.2$, with a broad $dN/dz$ reaching up to z > 0.4. The photometric redshifts have a mean bias of $|\mathrm{\delta <!--\; ??\; -->}z|\sim <!--\; ???\; -->{10}^{-<!--\; ???\; -->3}$, a normalized scatter of σ _z = 0.033, and less than 3% outliers beyond 3σ _z. Comparison with external data sets shows no significant variation of photo-z quality with sky position. Together with the overall statistics, we also provide a more detailed analysis of photometric redshift accuracy as a function of magnitudes and colors. The final catalog is appropriate for “all-sky” three-dimensional (3D) cosmology to unprecedented depths, in particular through cross-correlations with other large-area surveys. It should also be useful for source preselection and identification in forthcoming surveys, such as TAIPAN or WALLABY.