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Extragalactic very-high-energy (VHE; E > 100 GeV) sources are unique objects to study the most powerful particle accelerators in nature, as active galactic nuclei are likely sources of ultra-high-energy cosmic rays. BL Lacertae blazars are the most frequent extragalactic objects found in the VHE gamma-ray catalogs. It is very difficult to estimate their redshifts, considering they have no strong enough optical spectral features, hence ∼20% of them have unknown or poorly constrained redshifts. KUV 00311–1938 is a VHE BL Lacertae blazar, with an uncertain redshift in the range of 0.5 < z < 0.98. We have obtained deep spectroscopy using Gemini and the GTC telescopes of KUV 00311–1938 and its surroundings with high signal-to-noise ratio in 2016–2017. The lack of features did not allow us to determine the spectroscopic redshift of KUV 00311–1938; nevertheless, we obtain a lower limit of z ≳ 0.475. We determined the redshifts of 41 galaxies observed in the field-of-view of the blazar and through a population study, identified three pairs and four groups consisting of 3 or 4 members with redshifts in the range z = 0.1468–0.4756. Due to the absence of a large group of galaxies, we could not associate KUV 00311–1938 with any of the groups detected. [ABSTRACT FROM AUTHOR]

We study the behaviour of the dynamical and stellar mass inside the effective radius of early-type galaxies (ETGs) as a function of environment considering Newtonian dynamics, different surface-brightness profiles, different initial mass functions (IMF), and different redshift ranges. We use several samples of ETGs – ranging from 19 000 to 98 000 objects – from the ninth data release of the Sloan Digital Sky Survey. We assume that any difference between the dynamical and stellar mass is due to dark matter and/or a non-universal IMF. The main results, considering samples in the redshift range 0.0024 ≤  z  ≤ 0.35, are as follows: (i) the amount of dark matter inside ETGs depends on the environment; (ii) ETGs in low-density environments span a wider dark matter range than ETGs in dense environments; (iii) the amount of dark matter inside ETGs in the most dense environments will be less than approximately 55–75 per cent of the dynamical mass; (iv) the accurate value of this upper limit depends on the impact of the IMF on the stellar mass estimation; (v) in the case of an ETG sample which is approximately complete for log(MVirial/MSun) > 10.5 and in the redshift range 0.04 ≤  z  ≤ 0.08, we find that the amount of dark matter in the most dense environments will be less than approximately 60–65 per cent of the dynamical mass. [ABSTRACT FROM AUTHOR]

Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with 0.01 < z < 0.05, $\log ({\it M}_{\star }/{\it M}_{{\odot }})>9.5$ and projected axial ratio b/a > 0.32. We explore their structural properties, environments, emission lines, and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines are most likely caused by dust-star geometry, we find evidence for three different pathways through the post-starburst phase, with most events occurring in intermediate-density environments: (1) a significant disruptive event, such as a gas-rich major merger, causing a starburst and growth of a spheroidal component, followed by quenching of the star formation (70 per cent of post-starburst galaxies at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ and 60 per cent at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$ ); (2) at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ , stochastic star formation in blue-sequence galaxies, causing a weak burst and subsequent return to the blue sequence (30 per cent); (3) at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$ , cyclic evolution of quiescent galaxies which gradually move towards the high-mass end of the red sequence through weak starbursts, possibly as a result of a merger with a smaller gas-rich companion (40 per cent). Our analysis suggests that active galactic nuclei (AGNs) are 'on' for $50\hbox{ per cent}$ of the duration of the post-starburst phase, meaning that traditional samples of post-starburst galaxies with strict emission-line cuts will be at least $50\hbox{ per cent}$ incomplete due to the exclusion of narrow-line AGNs. [ABSTRACT FROM AUTHOR]

In this Paper, we describe how we use stellar dynamics information to constrain the shape of the stellar initial mass function (IMF) in a sample of 27 early-type galaxies from the CALIFA survey.We obtain dynamical and stellar mass-to-light ratios, ♈dyn and ♈*, over a homogenous aperture of 0.5 Re.We use the constraint♈dyn ♈* to test two IMF shapes within the framework of the extended MILES stellar population models. We rule out a single power-law IMF shape for 75 per cent of the galaxies in our sample. Conversely, we find that a double power-law IMF shape with a varying high-mass end slope is compatible (within 1σ) with 95 per cent of the galaxies. We also show that dynamical and stellar IMF mismatch factors give consistent results for the systematic variation of the IMF in these galaxies. [ABSTRACT FROM AUTHOR]

We present a new morphological indicator designed for automated recognition of galaxies with faint asymmetric tidal features suggestive of an ongoing or past merger. We use the new indicator, together with pre-existing diagnostics of galaxy structure to study the role of galaxy mergers in inducing (post-) starburst spectral signatures in local galaxies, and investigate whether (post-) starburst galaxies play a role in the build-up of the 'red sequence'. Our morphological and structural analysis of an evolutionary sample of 335 (post-) starburst galaxies in the Sloan Digital Sky Survey DR7 with starburst ages 0 < tSB < 0.6 Gyr, shows that 45 per cent of galaxies with young starbursts (tSB < 0.1 Gyr) show signatures of an ongoing or past merger. This fraction declines with starburst age, and we find a good agreement between automated and visual classifications. The majority of the oldest (post-) starburst galaxies in our sample (tSB ∼ 0.6 Gyr) have structural properties characteristic of early-type discs and are not as highly concentrated as the fully quenched galaxies commonly found on the 'red sequence' in the present day Universe. This suggests that, if (post-) starburst galaxies are a transition phase between active star-formation and quiescence, they do not attain the structure of presently quenched galaxies within the first 0.6 Gyr after the starburst. [ABSTRACT FROM AUTHOR]

We carry out a direct search for bar-like non-circular flows in intermediate-inclination, gasrich disc galaxies with a range of morphological types and photometric bar classifications from the first data release (DR1) of the Calar Alto Legacy Integral Field Spectroscopy Area (CALIFA) survey. We use the DISKFIT algorithm to apply rotation only and bisymmetric flow models to H a velocity fields for 49/100 CALIFA DR1 systems that meet our selection criteria. We find satisfactory fits for a final sample of 37 systems. DISKFIT is sensitive to the radial or tangential components of a bar-like flow with amplitudes greater than 15 km s-1 across at least two independent radial bins in the fit, or ~2.25 kpc at the characteristic final sample distance of ~75 Mpc. The velocity fields of 25/37 (67.6+6.6-8.5 per cent) galaxies are best characterized by pure rotation, although only 17/25 (68.0+7.7-10.4 per cent) of them have sufficient H a emission near the galaxy centre to afford a search for non-circular flows. We detect non-circular flows in the remaining 12/37 (32.4+8.5-6.6 per cent) galaxies. We conclude that the non-circular flows detected in 11/12 (91.7+2.8-14.9 per cent) systems stem from bars. Galaxies with intermediate (AB) bars are largely undetected, and our detection thresholds therefore represent upper limits to the amplitude of the non-circular flows therein. We find 2/23 (8.7+9.6-2.9 per cent) galaxies that show non-circular motions consistent with a bar-like flow, yet no photometric bar is evident. This suggests that in ~10 per cent of galaxies either the existence of a bar may be missed completely in photometry or other processes may drive bar-like flows and thus secular galaxy evolution. [ABSTRACT FROM AUTHOR]

We present 80 stellar and ionised gas velocity maps from the Calar Alto Legacy Integral Field Area (CALIFA) survey in order to characterise the kinematic orientation of non-interacting galaxies. The study of galaxies in isolation is a key step towards understanding how fast-external processes, such as major mergers, affect kinematic properties in galaxies. We derived the global and individual (projected approaching and receding sides) kinematic position angles (PAs) for both the stellar and ionised gas line-of-sight velocity distributions. When compared to the photometric PA, we find that morpho-kinematic differences are smaller than 22 degrees in 90% of the sample for both stellar and nebular components and that internal kinematic misalignments are generally smaller than 16 degrees. We find a tight relation between the global stellar and ionised gas kinematic PA consistent with circular-flow pattern motions in both components (~90% of the sample has differences smaller than 16 degrees). This relation also holds, generally in barred galaxies across the bar and galaxy disc scales. Our findings suggest that even in the presence of strong bars, both the stellar and the gaseous components tend to follow the gravitational potential of the disc. As a result, kinematic orientation can be used to assess the degree of external distortions in interacting galaxies. [ABSTRACT FROM AUTHOR]

We present the largest and most homogeneous catalog of Hii regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the CALIFA survey. We describe the procedures used to detect, select, and analyze the spectroscopic properties of these ionized regions. In the current study we focus on characterizing of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojected distribution of Hii regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of αO/H = -0.1 dex/re between 0.3 and 2 disk effective radii (re), and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, the incidence of bars, absolute magnitude, or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significantly shallower gradient, consistent with previous results. The majority of the 94 galaxies with Hii regions detected beyond two disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes. Our result suggests that galaxy disks grow inside-out, with metal enrichment driven by the local star formation history and with a small variation galaxy-by-galaxy. At a certain galactocentric distance, the oxygen abundance seems to be correlated well with the stellar mass density and total stellar mass of the galaxies, independently of other properties of the galaxies. Other processes, such as radial mixing and inflows/outflows seem to have a limited effect on shaping of the radial distribution of oxygen abundances, although they are not ruled out. [ABSTRACT FROM AUTHOR]

Context. Over the past decade, 3D optical spectroscopy has become the preferred tool for understanding the properties of galaxies and is now increasingly used to carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass, ATLAS3D, PINGS, and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS, GLACE, and IMAGES have targeted the most luminous galaxies to study mainly their kinematic properties. The on-going CALIFA survey (z ~ 0.02) is the first of a series of upcoming integral field spectroscopy (IFS) surveys with large samples representative of the entire population of galaxies. Others include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at higher redshift. Given the importance of spatial scales in IFS surveys, the study of the effects of spatial resolution on the recovered parameters becomes important. Aims. We explore the capability of the CALIFA survey and a hypothetical higher redshift survey to reproduce the properties of a sample of objects observed with better spatial resolution at lower redshift. Methods. Using a sample of PINGS galaxies, we simulated observations at different redshifts. We then studied the behaviour of different parameters as the spatial resolution degrades with increasing redshift. Results. We show that at the CALIFA resolution, we are able to measure and map common observables in a galaxy study: the number and distribution of Hii regions (Ha flux structure), the gas metallicity (using the O3N2 method), the gas ionization properties (through the [Nii]/Ha and [O iii]/Hß line ratios), and the age of the underlying stellar population (using the D4000 index). This supports the aim of the survey to characterise the observable properties of galaxies in the Local Universe. Our analysis of simulated IFS data cubes at higher redshifts highlights the importance of the projected spatial scale per spaxel as the most important figure of merit in the design of an integral field survey. [ABSTRACT FROM AUTHOR]

The use of integral field spectroscopy is since recently allowing to measure the emission line fluxes of an increasingly large number of star-forming galaxies, both locally and at high redshift. Many studies have used these fluxes to derive the gas-phase metallicity of the galaxies by applying the so-called strong-line methods. However, the metallicity indicators that these datasets use were empirically calibrated using few direct abundance data points (Te-based measurements). Furthermore, a precise determination of the prediction intervals of these indicators is commonly lacking in these calibrations. Such limitations might lead to systematic errors in determining the gas-phase metallicity, especially at high redshift, which might have a strong impact on our understanding of the chemical evolution of the Universe. The main goal of this study is to review the most widely used empirical oxygen calibrations, O3N2 and N2, by using new direct abundance measurements. We pay special attention to (1) the expected uncertainty of these calibrations as a function of the index value or abundance derived and (2) the presence of possible systematic offsets. This is possible thanks to the analysis of the most ambitious compilation of Te-based Hii regions to date. This new dataset compiles the Te-based abundances of 603 Hii regions extracted from the literature but also includes new measurements from the CALIFA survey. Besides providing new and improved empirical calibrations for the gas abundance, we also present a comparison between our revisited calibrations with a total of 3423 additional CALIFA Hii complexes with abundances derived using the ONS calibration from the literature. The combined analysis of Te-based and ONS abundances allows us to derive their most accurate calibration to date for both the O3N2 and N2 singleratio indicators, in terms of all statistical significance, quality, and coverage of the parameters space. In particular, we infer that these indicators show shallower abundance dependencies and statistically significant offsets compared to others'. The O3N2 and N2 indicators can be empirically applied to derive oxygen abundances calibrations from either direct abundance determinations with random errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a large amount of data), reaching an average precision of 0.08 and 0.09 dex (random) and 0.02 and 0.08 dex (systematic; compared to the direct estimations), respectively. [ABSTRACT FROM AUTHOR]