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The content and distribution of cool interstellar medium (<30 K) can indicate the evolutionary mechanisms that transform late-type to early-type galaxies (ETGs). To investigate this, ALMA observations of 12CO[2-1] line emission were obtained for five dusty ETGs from a complete sample in low-density environments. Four of the ETGs have massive (∼109 M⊙), extended molecular gas reservoirs with effective radii ∼3–5 kpc. This work provides a kinematic and structural analysis of these observations, to explore possible evolutionary mechanisms. Axisymmetric or bisymmetric kinematic models were fitted to observations of molecular gas discs, to quantify the dominant structures present and highlight additional structures or asymmetries. Integral field unit observations of these ETGs were also examined where available. Two of the ETGs, GAMA64646 and 622305, appear to have undergone tidal disturbance leading to molecular gas discs and/or star-forming inner rings. GAMA272990 may have undergone a merger, leading to an elliptical galaxy with an embedded star-forming molecular gas disc. GAMA622429 has probably undergone a minor merger, indicated by asymmetry in molecular gas distribution and disturbance in optical images. The remaining ETG, GAMA177186, was affected by source confusion from an offset source which could be a high-mass dust- and gas-rich object at high redshift. Overall, it appears that a high proportion of dusty ETGs in low-density environments have massive, extended molecular gas reservoirs, and have undergone some kind of interaction as part of their recent evolution. Secular evolution can then (re-)transform the ETGs from star-forming to passive galaxies. [ABSTRACT FROM AUTHOR]

Following the discovery of SAGE0536AGN (z ∼ 0.14), with the strongest 10-μm silicate emission ever observed for an active galactic nucleus (AGN), we discovered SAGE0534AGN (z ∼ 1.01), a similar AGN but with less extreme silicate emission. Both were originally mistaken as evolved stars in the Magellanic Clouds. Lack of far-infrared emission, and therefore star formation, implies we are seeing the central engine of the AGN without contribution from the host galaxy. They could be a key link in galaxy evolution. We used a dimensionality reduction algorithm, t-distributed stochastic neighbour embedding with multiwavelength data from Gaia EDR3, VISTA survey of the Magellanic Clouds, AllWISE, and the Australian Square Kilometre Array Pathfinder to find these two unusual AGNs are grouped with 16 other objects separated from the rest, suggesting a rare class. Our spectroscopy at South African Astronomical Observatory/ Southern African Large Telescope and literature data confirm at least 14 of these objects are extragalactic (0.13 < z < 1.23), all hosting AGN. Using spectral energy distribution fitter C  igale we find that the majority of dust emission (⁠|$\gt 70 {{\ \rm per\ cent}}$|⁠) in these sources is due to the AGN. Host galaxies appear to be either in or transitioning into the green valley. There is a trend of a thinning torus, increasing X-ray luminosity, and decreasing Eddington ratio as the AGN transition through the green valley, implying that as the accretion supply depletes, the torus depletes and the column density reduces. Also, the near-infrared variability amplitude of these sources correlates with attenuation by the torus, implying the torus plays a role in the variability. [ABSTRACT FROM AUTHOR]

We use data from the GAMA and GALEX surveys to demonstrate that the UV upturn, an unexpected excess of ultraviolet flux from a hot stellar component, seen in the spectra of many early-type galaxies, arises from processes internal to individual galaxies with no measurable influence from the galaxies' larger environment. We first define a clean sample of passive galaxies without a significant contribution to their UV flux from low-level star formation. We confirm that galaxies with the optical colours of red sequence galaxies often have signs of residual star formation, which, without other information, would prevent a convincing demonstration of the presence of UV upturns. However, by including (NUV− u) and WISE (W2–W3) colours, and FUV data where it exists, we can convincingly constrain samples to be composed of non-star-forming objects. Using such a sample, we examine GALEX photometry of low-redshift GAMA galaxies in a range of low-density environments, from groups to the general field, searching for UV upturns. We find a wide range of (NUV− r) colours, entirely consistent with the range seen – and attributed to the UV upturn – in low-redshift red sequence cluster galaxies. The range of colours is independent of group multiplicity or velocity dispersion, with isolated passive galaxies just as likely to have blue UV-to-optical colours, implying significant upturn components, as those in richer groups and in the previous data on clusters. This is supported by equivalent results for (FUV− r) colours which are clear indicators of upturn components. [ABSTRACT FROM AUTHOR]

We explore the constraints that can be placed on the evolutionary time-scales for typical low-redshift galaxies evolving from the blue cloud through the green valley and on to the red sequence. We utilize galaxies from the GAMA survey with 0.1 < z < 0.2 and classify them according to the intrinsic (u * − r *) colours of their stellar populations, as determined by fits to their multiwavelength spectral energy distributions. Using these fits to also determine stellar population ages and star formation time-scales, we argue that our results are consistent with a green valley population dominated by galaxies that are simply decreasing their star formation (running out of gas) over a time-scale of 2–4 Gyr which are seen at a specific epoch in their evolution (approximately 1.6 e-folding times after their peak in star formation). If their fitted star formation histories are extrapolated forward, the green galaxies will further redden over time, until they attain the colours of a passive population. In this picture, no specific quenching event which cuts-off their star formation is required, though it remains possible that the decline in star formation in green galaxies may be expedited by internal or external forces. However, there is no evidence that green galaxies have recently changed their star formation time-scales relative to their previous longer term star formation histories. [ABSTRACT FROM AUTHOR]

Gas-rich minor mergers contribute significantly to the gas reservoir of early-type galaxies (ETGs) at low redshift, yet the star formation efficiency (SFE; the star formation rate divided by the molecular gas mass) appears to be strongly suppressed following some of these events, in contrast to the more well-known merger-driven starbursts. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of six ETGs, which have each recently undergone a gas-rich minor merger, as evidenced by their disturbed stellar morphologies. These galaxies were selected because they exhibit extremely low SFEs. We use the resolving power of ALMA to study the morphology and kinematics of the molecular gas. The majority of our galaxies exhibit spatial and kinematical irregularities, such as detached gas clouds, warps, and other asymmetries. These asymmetries support the interpretation that the suppression of the SFE is caused by dynamical effects stabilizing the gas against gravitational collapse. Through kinematic modelling we derive high velocity dispersions and Toomre Q stability parameters for the gas, but caution that such measurements in edge-on galaxies suffer from degeneracies. We estimate merger ages to be about 100 Myr based on the observed disturbances in the gas distribution. Furthermore, we determine that these galaxies lie, on average, two orders of magnitude below the Kennicutt-Schmidt relation for star-forming galaxies as well as below the relation for relaxed ETGs. We discuss potential dynamical processes responsible for this strong suppression of star formation surface density at fixed molecular gas surface density. [ABSTRACT FROM AUTHOR]

One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the Galaxy And Mass Assembly and VIsible MultiObject Spectrograph Public Extragalactic Redshift surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies.We identify potentially rapidly transitioning post-starburst (PSB) galaxies and slower transitioning green-valley galaxies. Over the last 8Gyr, the quiescent population has grown more slowly in number density at high masses (M* > 1011M☉) than at intermediate masses (M* > 1010.6M☉). There is evolution in both the PSB and green-valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times.At intermediatemasses (M* > 1010.6M☉), we find a green-valley transition time-scale of 2.6 Gyr. Alternatively, at z ~ 0.7, the entire growth rate could be explained by fast-quenching PSB galaxies, with a visibility time-scale of 0.5 Gyr. At lower redshift, the number density of PSBs is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at z < 1. However, at high masses (M* > 1011M☉), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high-mass PSB and green-valley galaxies are transitioning from star forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation. [ABSTRACT FROM AUTHOR]

The merging history of galaxies can be traced with studies of dynamically close pairs. These consist of a massive primary galaxy and a less massive secondary (or satellite) galaxy. The study of the stellar populations of secondary (lower mass) galaxies in close pairs provides a way to understand galaxy growth by mergers. Here we focus on systems involving at least one massive galaxy - with stellar mass above 1011M☉ in the highly complete Galaxy and Mass Assembly (GAMA) survey. Our working sample comprises 2692 satellite galaxy spectra (0.1 ≤ z ≤ 0.3). These spectra are combined into high S/N stacks, and binned according to both an 'internal' parameter, the stellar mass of the satellite galaxy (i.e. the secondary), and an 'external' parameter, selecting either the mass of the primary in the pair, or the mass of the corresponding dark matter halo. We find significant variations in the age of the populations with respect to environment. At fixed mass, satellites around the most massive galaxies are older and possibly more metal-rich, with age differences ~1-2 Gyr within the subset of lower mass satellites (~1010 M☉). These variations are similar when stacking with respect to the halo mass of the group where the pair is embedded. The population trends in the lower mass satellites are consistent with the old stellar ages found in the outer regions of massive galaxies. [ABSTRACT FROM AUTHOR]

We present two large, nearby (0.013 ≤ z ≤ 0.06) samples of early-type galaxies (ETGs): a visually classified sample of 220 ETGs, created using source-matched data from the Galaxy and Mass Assembly (GAMA) data base with far-infrared/submm detections from Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS); and a visually classified sample of 551 ETGs which are undetected with H-ATLAS. Active galactic nuclei are removed from our samples using optical emission-line diagnostics. These samples are scrutinized to determine characteristics of submm detected versus undetected ETGs. We find similarities in the stellar mass distributions of the two ETG samples but testing other properties uncovers significant differences. The submm detected sample is shown to have lower concentration and Sérsic indices than those in the undetected sample – a result which may be linked to the presence of dust in the former. Optical and ultraviolet–optical colours are also shown to be much bluer, indicating that the dust is linked with recent star formation. The intrinsic effective radii are on average 1.5 times larger for the submm detected ETGs. Surface densities and groups data from the GAMA data base are examined for the two samples, leading to the conclusion that dusty ETGs inhabit sparser environments than non-dusty ETGs in the nearby Universe, although environments of the brightest ETGs are shown to differ the least. Modified Planck functions are fit to the H-ATLAS detected Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) fluxes for ETGs with submm flux densities of at least 3σ in the 350 μm SPIRE band, giving a resultant mean cold dust temperature of Td = 22.1 K, with a range of 9–30 K. The corresponding mean dust mass is 1.8 × 107 M⊙, with a range of (0.08–35.0) × 107 M⊙. The dust masses calculated from these fits, normalized by stellar mass, are shown to increase with decreasing stellar mass and bluer colours. Based on visual classifications of elliptical and lenticular, we find similar dust properties for these two early-type morphologies. We conclude that there is a population of elliptical galaxies which exhibit larger dust masses, lower Sérsic index and bluer colours than the more well-known, massive, red population of ellipticals. [ABSTRACT FROM AUTHOR]

One of the complexities in modelling integrated spectra of stellar populations is the effect of interacting binary stars besides Type Ia supernovae (SNeIa). These include common envelope systems, cataclysmic variables, novae, and are usually ignored in models predicting the chemistry and spectral absorption line strengths in galaxies. In this paper, predictions of chemical yields from populations of single and binary stars are incorporated into a galactic chemical evolution model to explore the significance of the effects of these other binary yields. Effects on spectral line strengths from different progenitor channels of SNeIa are also explored. Small systematic effects are found when the yields from binaries, other than SNeIa, are included, for a given star formation history. These effects are, at present, within the observational uncertainties on the line strengths. More serious differences can arise in considering different types of SNIa models, their rates and contributions. [ABSTRACT FROM AUTHOR]

Stellar population characteristics are presented for a sample of low-luminosity early-type galaxies (LLEs) in order to compare them with their more luminous counterparts. Long-slit spectra of a sample of 10 LLEs were taken with the ESO New Technology Telescope, selected for their low luminosities. Line strengths were measured on the Lick standard system. Lick indices for these LLEs were correlated with velocity dispersion (σ), alongside published data for a variety of Hubble types. The LLEs were found to fall below an extrapolation of the correlation for luminous ellipticals and were consistent with the locations of spiral bulges in plots of line strengths versus σ. Luminosity weighted average ages, metallicities and abundance ratios were estimated from fitting of 19 Lick indices to predictions from simple stellar population models. The LLEs appear younger than luminous ellipticals and of comparable ages to spiral bulges. These LLEs show a bimodal metallicity distribution, consisting of a low-metallicity group (possibly misclassified dwarf spheroidal galaxies) and a high-metallicity group (similar to spiral bulges). Finally, they have low α-element to iron peak abundance ratios indicative of slow, extended star formation. [ABSTRACT FROM AUTHOR]

Massive haloes of hot plasma exist around some, but not all elliptical galaxies. There is evidence that this is related to the age of the galaxy. In this paper, new X-ray observations are presented for three early-type galaxies that show evidence of youth, in order to investigate their X-ray components and properties. NGC 5363 and NGC 2865 were found to have X-ray emission dominated by purely discrete stellar sources. Limits are set on the mass distribution in one of the galaxies observed with XMM–Newton, NGC 4382, which contains significant hot gas. We detect the X-ray emission in NGC 4382 out to . The mass-to-light ratio is consistent with a stellar origin in the inner regions but rises steadily to values indicative of some dark matter by . These results are set in context with other data drawn from the literature, for galaxies with ages estimated from dynamical or spectroscopic indicators. Ages obtained from optical spectroscopy represent central luminosity-weighted stellar ages. We examine the X-ray evolution with age, normalized by B- and K-band luminosities. Low values of and are found for all galaxies with ages between 1 and 4 Gyr. Luminous X-ray emission only appears in older galaxies. This suggests that the interstellar medium is removed and then it takes several gigayears for hot gas haloes to build up, following a merger. A possible mechanism for gas expulsion might be associated with feedback from an active nucleus triggered during a merger. [ABSTRACT FROM AUTHOR]

We present line-strengths and kinematics from the central regions of 32 galaxies with Hubble types ranging from E to Sbc. Spectral indices, based on the Lick system, are measured in the optical and near-infrared (NIR). The 24 indices measured, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy, and allow estimation of enhancements in specific light elements (particularly C and Mg). The large range of Hubble types observed allows direct comparison of line-strengths in the centres of early-type galaxies (E and S0) with those in spiral bulges, free from systematic differences that have plagued comparisons of results from different studies. Our sample includes field and Virgo cluster galaxies. For early-type galaxies our data are consistent with previously reported trends of Mg[sub 2] and Mgb with velocity dispersion. In spiral bulges we find trends in all indices with velocity dispersion. We estimate luminosity-weighted ages, metallicities and heavy-element abundance ratios (enhancements) from optical indices. These show that bulges are less enhanced in light (α-capture) elements and have lower average age than early-type galaxies. Trends involving age and metallicity also differ sharply between early and late types. An anticorrelation exists between age and metallicity in early types, while, in bulges, metallicity is correlated with velocity dispersion. We consider the implications of these findings for models of the formation of these galaxies. We find that primordial collapse models of galaxy formation are ruled out by our observations, while several predictions of hierarchical clustering (merger) models are confirmed. [ABSTRACT FROM AUTHOR]