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We have analyzed the distribution of early-type galaxies (ETGs) in the effective surface intensity vs. effective radius (Ie−Re) plane and in the total luminosity vs. central stellar velocity dispersion (L−σ) diagram, with the aim of studying the physical variables that allow the transformation of one space-parameter into the other. We find that the classical Faber–Jackson relation L=L0σα, in which the parameters L0 and α are confined in a small range of possible values, is incompatible with the distribution observed in the Ie−Re plane. The two distributions become mutually consistent only if luminosity is not considered a pure proxy of mass but a variable tightly dependent on the past history of mass assembling and star formation and on the present evolutionary state of the stellar content of a galaxy. The solution comes by considering the L=L0′σβ law proposed by D’Onofrio et al. in 2020, in which both L0′ and β can vary considerably from galaxy to galaxy. We will also show that the data of the Illustris numerical simulation prove the physical foundation of the L=L0′σβ law and confirm the prediction of the Zone of Exclusion (ZoE) originating from the intersection of the virial law with the L=L0′σβ relation. The ZoE is the region in the Ie−Re and Re−Ms diagrams avoided by real galaxies, and the border of which marks the condition of ‘full’ virial equilibrium with no recent significant merger events and no undergoing star formation.

We investigate the variation of the fraction of galaxies with suppressed star formation (MK < −21.m5) and early-type galaxies (fracE) of the “red sequence” along the projected radius in six galaxy clusters:Coma (A1656), A1139, and A1314 in the Leo supercluster region (z ≈ 0.037) and A2040, A2052, A2107 in the Hercules supercluster region (z ≈ 0.036). According to SDSS (DR10) data, fracE is the highest in the central regions of galaxy clusters and it is, on the average, equal to 0.62 ± 0.03, whereas in the 2-3R/R200c interval and beyond the Rsp ≈ 0.95 ± 0.04 R200m radius that we inferred from the observed profile fracE is minimal and equal to 0.25 ± 0.02. This value coincides with the estimate fracE = 0.24 ± 0.01 that we inferred for field galaxies located between the Hercules and Leo superclusters at the same redshifts. We show that the fraction of galaxies with suppressed star formation decreases continuously with cluster radius from 0.87 ± 0.02 in central regions down to 0.43 ± 0.03 in the 2-3 R/R200c interval and beyond Rsp, but remains, on the average, higher than 26% than the corresponding fraction for field objects. This decrease is especially conspicuous in the galaxy mass interval log M* [M⊙] = 9.5-10. We found that galaxies with ongoing star formation have average clustercentric distances 1.5-2.5 R/R200c and that their radial-velocity dispersions are higher than those of galaxies with suppressed star formation. [ABSTRACT FROM AUTHOR]

We utilize the hydrodynamic and N-body code GIZMO coupled with our newly developed subgrid Population III (Pop III) Legacy model, designed specifically for cosmological volume simulations, to study the baseline metal enrichment from Pop III star formation at z > 7. In this idealized numerical experiment, we only consider Pop III star formation. We find that our model Pop III star formation rate density (SFRD), which peaks at ~ 10-3 M ⊙ y r-1 Mpc-1 near z~10, agrees well with previous numerical studies and is consistent with the observed estimates for Pop II SFRDs. The mean Pop III metallicity rises smoothly from z = 25 to 7, but does not reach the critical metallicity value, Zcrit = 10-4 Z⊙, required for the Pop III to Pop II transition in star formation mode until z≃7. This suggests that, while individual haloes can suppress in situ Pop III star formation, the external enrichment is insufficient to globally terminate Pop III star formation. The maximum enrichment from Pop III star formation in star-forming dark matter haloes is Z~10-2 Z⊙, whereas the minimum found in externally enriched haloes is Z > 10-7 Z⊙. Finally, mock observations of our simulated IGM enriched with Pop III metals produce equivalent widths similar to observations of an extremely metalpoor damped Lyman alpha system at z = 7.04, which is thought to be enriched by Pop III star formation only. [ABSTRACT FROM AUTHOR]

To investigate the effects the cluster environment has on late-type galaxies (LTGs), we studied HI perturbation signatures for all Abell 1367 LTGs with HI detections. We used new Very Large Array H I observations combined with AGES single-dish blind survey data. Our study indicates that the asymmetry between the high- and low-velocity wings of the characteristic double-horn-integrated H I spectrum as measured by the asymmetry parameter, Aflux, can be a useful diagnostic for ongoing and/or recent HI stripping. 26 per cent of A1367 LTGs have an Aflux ratio, more asymmetrical than 3 times the 1σ spread in the Aflux ratio distribution of an undisturbed sample of isolated galaxies (2 per cent) and samples from other denser environments (10percent-20percent). Over half of the A1367 LTGs, which are members of groups or pairs, have an Aflux ratio larger than twice the 1a spread found in the isolated sample. This suggests intergroup/pair interactions could be making a significant contribution to the LTGs displaying such Aflux ratios. The study also demonstrates that the definition of the H I offset from the optical centre of LTGs is resolution dependent, suggesting that unresolved AGES HI offsets that are significantly larger than the pointing uncertainties (>2σ), reflect interactions which have asymmetrically displaced, significant masses of lower density H I, while having minimal impact on the location of the highest density H I in resolved maps. The distribution of Aflux from a comparable sample of Virgo galaxies provides a clear indication that the frequency of H I profile perturbations is lower than in A1367. [ABSTRACT FROM AUTHOR]

We present the first results of a new spectroscopic survey of the cluster Abell 85 targeting 1466 candidate cluster members within the central ~1 deg² of the cluster and having magnitudes mr < 20.5 using the VIsible MultiObject Spectrograph on the VLT and the Hydra spectrograh on WIYN. A total of 520 galaxies are confirmed as either relaxed cluster members or part of an infalling population. A significant fraction are low mass; the median stellar mass of the sample is 109.6.6⊙, and 25 per cent have stellar masses below 109⊙ (i.e. 133 dwarf galaxies). We also identify seven active galactic nuclei (AGN), four of which reside in dwarf host galaxies. We probe the evolution of star formation rates, based on Ha emission and continuum modelling, as a function of both mass and environment. We find that more starforming galaxies are observed at larger clustercentric distances, while infalling galaxies show evidence for recently enhanced star-forming activity. Main-sequence galaxies, defined by their continuum star formation rates, show different evolutionary behaviour based on their mass. At the low-mass end, the galaxies have had their star formation recently quenched, while more massive galaxies show no significant change. The time-scales probed here favour fast quenching mechanisms, such as ram-pressure stripping. Galaxies within the green valley, defined similarly, do not show evidence of quenching. Instead, the low-mass galaxies maintain their levels of star-forming activity, while the more massive galaxies have experienced a recent burst. [ABSTRACT FROM AUTHOR]

We introduce the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE (E-MOSAICS) project. E-MOSAICS incorporates models describing the formation, evolution, and disruption of star clusters into the EAGLE galaxy formation simulations, enabling the examination of the co-evolution of star clusters and their host galaxies in a fully cosmological context. A fraction of the star formation rate of dense gas is assumed to yield a cluster population; this fraction and the population's initial properties are governed by the physical properties of the natal gas. The subsequent evolution and disruption of the entire cluster population are followed accounting for two-body relaxation, stellar evolution, and gravitational shocks induced by the local tidal field. This introductory paper presents a detailed description of the model and initial results from a suite of 10 simulations of ~L* galaxies with disc-like morphologies at z = 0. The simulations broadly reproduce key observed characteristics of young star clusters and globular clusters (GCs), without invoking separate formation mechanisms for each population. The simulated GCs are the surviving population of massive clusters formed at early epochs (z ≳1-2), when the characteristic pressures and surface densities of star-forming gas were significantly higher than observed in local galaxies. We examine the influence of the star formation and assembly histories of galaxies on their cluster populations, finding that (at similar present-day mass) earlier-forming galaxies foster a more massive and disruption-resilient cluster population, while galaxies with late mergers are capable of forming massive clusters even at late cosmic epochs. We find that the phenomenological treatment of interstellar gas in EAGLE precludes the accurate modelling of cluster disruption in low-density environments, but infer that simulations incorporating an explicitly modelled cold interstellar gas phase will overcome this shortcoming. [ABSTRACT FROM AUTHOR]

We use a large sample of ∼350 000 galaxies constructed by combining the UKIDSS UDS, VIDEO/CFHT-LS, UltraVISTA/COSMOS and GAMA survey regions to probe the major (1:4 stellar mass ratio) merging histories of massive galaxies (>1010M☉) at 0.005 < z < 3.5. We use a method adapted from that presented in López-Sanjuan et al., using the full photometric redshift probability distributions, tomeasure pair fractions of flux-limited, stellarmass selected galaxy samples using close-pair statistics. The pair fraction is found to weakly evolve as α (1 + z)0.8 with no dependence on stellar mass.We subsequently derive major merger rates for galaxies at >1010M☉ and at a constant number density of n > 10-4 Mpc-3 and find rates a factor of 2-3 smaller than previous works, although this depends strongly on the assumed merger time-scale and likelihood of a close-pair merging. Galaxies undergo approximately 0.5 major mergers at z < 3.5, accruing an additional (1-4) x 1010M☉ in the process. On average, this represents an increase in stellar mass of 20-030 per cent (40-70 per cent) for constant stellar mass (constant number density) samples. Major merger accretion rate densities of ∼2 x 10-4 M☉ yr-1 Mpc-3 are found for number density selected samples, indicating that direct progenitors of local massive (>1011M☉) galaxies have experienced a steady supply of stellar mass via major mergers throughout their evolution. While pair fractions are found to agree with those predicted by the Henriques et al. semi-analytic model, the Illustris hydrodynamical simulation fails to quantitatively reproduce derived merger rates. Furthermore, we find that major mergers become a comparable source of stellar mass growth compared to star formation at z < 1, but is 10-100 times smaller than the star formation rate density at higher redshifts. [ABSTRACT FROM AUTHOR]

We study the variations of the properties of groups of galaxies with dynamical masses of 10 M < M <10 M , represented by two samples: one has redshifts of z < 0.027 and is located in the vicinity of the Coma cluster, the other has z > 0.027, and is located in the regions of the following superclusters of galaxies: Hercules, Leo, Bootes, Ursa Major, and Corona Borealis. Using the archived data of the SDSS and 2MASX catalogs, we determined the concentration of galaxies in the systems by measuring it as the inner density of the group within the distance of the fifth closest galaxy from the center brighter than M = −23 3. We also measured the magnitude gap between the first and the fourth brightest galaxies Δ M located within one half of the selected radius R , the fraction of early-type galaxies, and the ratio of bright dwarf galaxies (Mr = [−18 5,−16 5]) to giant galaxies ( M < −18 5) (DGR) within the radius R . The main aim of the investigation is to find among these characteristics the ones that reflect the evolution of groups of galaxies.We determined that the ratio of bright dwarf galaxies to early-type giant galaxies on the red sequence depends only on the x-ray luminosity: the DGR increases with luminosity. The fraction of early-type galaxies in the considered systems is equal, on average, to 0.65 ± 0.01, and varies significantly for galaxies with σ < 300 kms. Based on the luminosity of the brightest galaxy, the magnitude gap between the first and the fourth brightest galaxies in the groups, and on model computations of these parameters, we selected four fossil group candidates: AWM4, NGC0533, NGC0741, and NGC6098 (where the brightest galaxy is a double).We observe no increase in the number of faint galaxies (the α parameter of the Schechter function is less than 1) in our composite luminosity function (LF) for galaxy systems with z < 0.027 in the M = [−26m,−21 5] range, whereas earlier we obtained α > 1 for the LF of the Hercules and Leo superclusters of galaxies. [ABSTRACT FROM AUTHOR]

Context. Analytical models of chemical evolution, including inflow and outflow of gas, are important tools for studying how the metal content in galaxies evolves as a function of time. Aims. We present new analytical solutions for the evolution of the gas mass, total mass, and metallicity of a galactic system when a decaying exponential infall rate of gas and galactic winds are assumed. We apply our model to characterize a sample of local starforming and passive galaxies from the Sloan Digital Sky Survey data, with the aim of reproducing their observed mass-metallicity relation. Methods. We derived how the two populations of star-forming and passive galaxies di er in their particular distribution of ages, formation timescales, infall masses, and mass loading factors. Results. We find that the local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies; on the other hand, the star-forming galaxies with higher masses generally show older ages and longer typical formation timescales compared than star-forming galaxies with lower masses. The local star-forming galaxies experience stronger galactic winds than the passive galaxy population. Exploring the e ect of assuming di erent initial mass functions in our model, we show that to reproduce the observed mass-metallicity relation, stronger winds are requested if the initial mass function is top-heavy. Finally, our analytical models predict the assumed sample of local galaxies to lie on a tight surface in the 3D space defined by stellar metallicity, star formation rate, and stellar mass, in agreement with the well-known fundamental relation from adopting gas-phase metallicity. Conclusions. By using a new analytical model of chemical evolution, we characterize an ensemble of SDSS galaxies in terms of their infall timescales, infall masses, and mass loading factors. Local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies. Moreover, the local star-forming galaxies show stronger galactic winds than the passive galaxy population. Finally, we find that the fundamental relation between metallicity, mass, and star formation rate for these local galaxies is still valid when adopting the average galaxy stellar metallicity. [ABSTRACT FROM AUTHOR]

Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (MV = -16.60, Mass ∼4 × 108 M☉), located in the Fornax cluster, have been performed with the Very Large Telescope/Multi Unit Spectroscopic Explorer spectrograph in the wavelength region from 4750 to 9350 Å. In this paper, we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galactocentric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of ∼6 Gyr and a metallicity [Fe/H]∼ -0.4, similar to other dEs of similar mass.We find unusually overabundant values of [Ca/Fe]∼+0.1, and underabundant Sodium, with [Na/Fe] values around -0.1, while [Mg/Fe] is overabundant at all radii, increasing from ∼+ 0.1 in the centre to ∼+ 0.2 dex. We notice a significant metallicity and age gradient within this dwarf galaxy. To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1396 is consistent with either a Kroupa-like or a topheavy distribution, while a bottom-heavy IMF is firmly ruled out. An analysis of the abundance ratios, and a comparison with galaxies in the Local Group, shows that the chemical enrichment history of NGC 1396 is similar to the Galactic disc, with an extended SFH. This would be the case if the galaxy originated from a Large Magellanic Cloud-sized dwarf galaxy progenitor, which would lose its gas while falling into the Fornax cluster. [ABSTRACT FROM AUTHOR]

We present the mufasa suite of cosmological hydrodynamic simulations, which employs the gizmo meshless finite mass (MFM) code including H2-based star formation, nine-element chemical evolution, two-phase kinetic outflows following scalings from the Feedback in Realistic Environments zoom simulations, and evolving halo mass-based quenching. Our fiducial (50h-1 Mpc)³ volume is evolved to z = 0 with a quarter billion elements. The predicted galaxy stellar mass functions (GSMFs) reproduces observations from z = 4 → 0 to ... 1.2σ in cosmic variance, providing an unprecedented match to this key diagnostic. The cosmic star formation history and stellar mass growth show general agreement with data, with a strong archaeological downsizing trend such that dwarf galaxies form the majority of their stars after z ~ 1. We run 25 and 12.5 h-1 Mpc volumes to z = 2 with identical feedback prescriptions, the latter resolving all hydrogen-cooling haloes, and the three runs display fair resolution convergence. The specific star formation rates broadly agree with data at z = 0, but are underpredicted at z ~ 2 by a factor of 3, re-emphasizing a longstanding puzzle in galaxy evolution models. We compare runs using MFM and two flavours of smoothed particle hydrodynamics, and show that the GSMF is sensitive to hydrodynamics methodology at the ~ x 2 level, which is sub-dominant to choices for parametrizing feedback. [ABSTRACT FROM AUTHOR]

We present observations and first results from the FIGGS2 survey. FIGGS2 is an extension of the earlier Faint Irregular Galaxies GMRT survey (FIGGS) towards faint luminosity end. The sample consists of 20 galaxies, 15 of which were detected in HI 21 cm line using the Giant Meterwave Radio Telescope (GMRT). The median blue band magnitude of our sample is approximately −11. 6, which is more than one magnitude fainter than earlier FIGGS survey. From our GMRT observations we found that, for many of our sample galaxies, the HI disks are offset from their optical disks. The HI diameters of the FIGGS2 galaxies show a tight correlation with their HI mass. The slope of the correlation is 2.08 ± 0.20 similar to what is found for FIGGS galaxies. We also found that for almost all galaxies, the HI disks are larger than the optical disks which is a common trend for dwarf or spiral galaxies. The mean value of the ratio of HI to optical diameter is about 1.54. [ABSTRACT FROM AUTHOR]

We use semi-analytic models and cosmological merger trees to provide the initial conditions for multimerger numerical hydrodynamic simulations, and exploit these simulations to explore the effect of galaxy interaction and merging on star formation (SF). We compute numerical realizations of 12 merger trees from z = 1.5 to 0. We include the effects of the large hot gaseous halo around all galaxies, following recent observations and predictions of galaxy formation models. We find that including the hot gaseous halo has a number of important effects. First, as expected, the star formation rate on long time-scales is increased due to cooling of the hot halo and refuelling of the cold gas reservoir. Secondly, we find that interactions do not always increase the SF in the long term. This is partially due to the orbiting galaxies transferring gravitational energy to the hot gaseous haloes and raising their temperature. Finally, we find that the relative size of the starburst, when including the hot halo, is much smaller than previous studies showed. Our simulations also show that the order and timing of interactions are important for the evolution of a galaxy. When multiple galaxies interact at the same time, the SF enhancement is less than when galaxies interact in series. All these effects show the importance of including hot gas and cosmologically motivated merger trees in galaxy evolution models. [ABSTRACT FROM AUTHOR]

We explore the structures of protoclusters and their relationship with high-redshift clusters using the Millennium Simulation combined with a semi-analytic model. We find that protoclusters are very extended, with 90 per cent of their mass spread across ~ 3 5 h-1 Mpc comoving at z = 2 (~30 arcmin). The 'main halo', which can manifest as a high-redshift cluster or group, is only a minor feature of the protocluster, containing less than 20 per cent of all protocluster galaxies at z = 2. Furthermore, many protoclusters do not contain a main halo that is massive enough to be identified as a high-redshift cluster. Protoclusters exist in a range of evolutionary states at high redshift, independent of the mass they will evolve to at z = 0. We show that the evolutionary state of a protocluster can be approximated by the mass ratio of the first and second most massive haloes within the protocluster, and the z = 0 mass of a protocluster can be estimated to within 0.2 dex accuracy if both the mass of the main halo and the evolutionary state are known. We also investigate the biases introduced by only observing star-forming protocluster members within small fields. The star formation rate required for line-emitting galaxies to be detected is typically high, which leads to the artificial loss of low-mass galaxies from the protocluster sample. This effect is stronger for observations of the centre of the protocluster, where the quenched galaxy fraction is higher. This loss of low-mass galaxies, relative to the field, distorts the size of the galaxy overdensity, which in turn can contribute to errors in predicting the z = 0 evolved mass. [ABSTRACT FROM AUTHOR]

We use Horizon-AGN, a hydrodynamical cosmological simulation, to explore the role of mergers in the evolution of massive (M* > 1010 MQ) galaxies around the epoch of peak cosmic star formation (1 < z < 4). The fraction of massive galaxies in major mergers (mass ratio R < 4:1) is around 3 per cent, a factor of ~2.5 lower than minor mergers (4:1 < R < 10:1) at these epochs, with no trend with redshift. At z ~ 1, around a third of massive galaxies have undergone a major merger, while all remaining systems have undergone a minor merger. While almost all major mergers at z > 3 are 'blue' (i.e. have significant associated star formation), the proportion of 'red' mergers increases rapidly at z < 2, with most merging systems at z ~ 1.5 producing remnants that are red in rest-frame UV-optical colours. The star formation enhancement during major mergers is mild (~20-40 per cent) which, together with the low incidence of such events, implies that this process is not a significant driver of early stellar mass growth. Mergers (R < 10: 1) host around a quarter of the total star formation budget in this redshift range, with major mergers hosting around two-thirds of this contribution. Notwithstanding their central importance to the standard A cold dark matter paradigm, mergers are minority players in driving star formation at the epochs where the bulk of today's stellar mass was formed. [ABSTRACT FROM AUTHOR]

We present a hybrid code combining the OpenMP-parallel tree code VINE with an algorithmic chain regularization scheme. The new code, called "rVINE", aims to significantly improve the accuracy of close encounters of massive bodies with supermassive black holes in galaxy-scale numerical simulations. We demonstrate the capabilities of the code by studying two test problems, the sinking of a single massive black hole to the centre of a gas-free galaxy due to dynamical friction and the hardening of a supermassive black hole binary due to close stellar encounters. We show that results obtained with rVINE compare well with NBODY7 for problems with particle numbers that can be simulated with NBODY7. In particular, in both NBODY7 and rVINE we find a clear N-dependence of the binary hardening rate, a low binary eccentricity and moderate eccentricity evolution, as well as the conversion of the galaxy's inner density profile from a cusp to a a core via the ejection of stars at high velocity. The much larger number of particles that can be handled by rVINE will open up exciting opportunities to model stellar dynamics close to SMBHs much more accurately in a realistic galactic context. This will help to remedy the inherent limitations of commonly used tree solvers to follow the correct dynamical evolution of black holes in galaxy scale simulations. [ABSTRACT FROM AUTHOR]

We present an integral-field study of the internal structure, kinematics and stellar population of the almost edge-on, intermediate-luminosity (L*) elliptical galaxy NGC 4697. We build extended two-dimensional (2D) maps of the stellar kinematics and line strengths of the galaxy up to ~0.7 effective radii (Reff) using a mosaic of eight VIMOS (VIsible Multi-Objects Spectrograph, on the Very Large Telescope) integral-field unit pointings. We find clear evidence for a rotation-supported structure along the major axis from the 2D kinematical maps, confirming the previous classification of this system as a 'fast rotator'. We study the correlations between the third and fourth Gauss-Hermite moments of the line-of-sight velocity distribution (LOSVD) h3 and h4 with the rotation parameter (V/σ), and compare our findings to hydrodynamical simulations. We find remarkable similarities to predictions from gas-rich mergers. Based on photometry, we perform a bulge/disc decomposition and study the stellar population properties of the two components. The bulge and the disc show different stellar populations, with the stars in the bulge being older (agebulge = 13.5-1.4+1.4 Gyr, agedisc = 10.5-2.0+1.6 Gyr) and more metal poor ([M/H]bulge = -0.17-0.1+0.12, [M/H]disc =-0.03-0.1+0.02). The evidence of a later-formed, more metal-rich disc embedded in an older, more metal poor bulge, together with the LOSVD structure, supports a mass assembly scenario dominated by gas-rich minor mergers and possibly with a late gas-rich major merger that left a previously rapidly rotating system unchanged. The bulge and the disc do not show signs of different stellar initial mass function (IMF) slopes, and both match well with a Milky Way-like IMF. [ABSTRACT FROM AUTHOR]

The modification of star formation (SF) in galaxy interactions is a complex process, with SF observed to be both enhanced in major mergers and suppressed in minor pair interactions. Such changes likely to arise on short time-scales and be directly related to the galaxy-galaxy interaction time. Here we investigate the link between dynamical phase and direct measures of SF on different time-scales for pair galaxies, targeting numerous star-formation rate (SFR) indicators and comparing to pair separation, individual galaxy mass and pair mass ratio. We split our sample into the higher (primary) and lower (secondary) mass galaxies in each pair and find that SF is indeed enhanced in all primary galaxies but suppressed in secondaries of minor mergers. We find that changes in SF of primaries are consistent in both major and minor mergers, suggesting that SF in the more massive galaxy is agnostic to pair mass ratio. We also find that SF is enhanced/suppressed more strongly for short-duration SFR indicators (e.g. Ha), highlighting recent changes to SF in these galaxies, which are likely to be induced by the interaction. We propose a scenario where the lower mass galaxy has its SF suppressed by gas heating or stripping, while the higher mass galaxy has its SF enhanced, potentially by tidal gas turbulence and shocks. This is consistent with the seemingly contradictory observations for both SF suppression and enhancement in close pairs. [ABSTRACT FROM AUTHOR]

We report new deep observations obtained with the Atacama Large Millimetre Array (ALMA) aimed at investigating the [C II] 158 µm line and continuum emission in three spectroscopically confirmed Lyman break galaxies at 6.8 < z ≤ 7.1, i.e. well within the re-ionization epoch. With star formation rates of SFR ~ 5-15Mʘ yr-1 these systems are much more representative of the high-z galaxy population than other systems targeted in the past by millimetre observations. For the galaxy with the deepest observation we detect [CII] emission at redshift z = 7.107, fully consistent with the Ly α redshift, but spatially offset by 0.7 arcsec (4 kpc) from the optical emission. At the location of the optical emission, tracing both the Ly α line and the far-UV continuum, no [C II] emission is detected in any of the three galaxies, with 3σ upper limits significantly lower than the [C II] emission observed in lower redshift galaxies. These results suggest that molecular clouds in the central parts of primordial galaxies are rapidly disrupted by stellar feedback. As a result, [C II] emission mostly arises from more external accreting/satellite clumps of neutral gas. These findings are in agreement with recent models of galaxy formation. Thermal far-infrared continuum is not detected in any of the three galaxies. However, the upper limits on the infrared-to-UV emission ratio do not exceed those derived in metal- and dust-poor galaxies. [ABSTRACT FROM AUTHOR]

We explore the assembly history of the M31 bulge within a projected major-axis radius of 180 arcsec (~680 pc) by studying its stellar populations in Hubble Space TelescopeWide Field Camera 3 and Advanced Camera for Surveys observations. Colours formed by comparing nearultraviolet versus optical bands are found to become bluer with increasing major-axis radius, which is opposite to that predicted if the sole sources of near-ultraviolet light were old extreme horizontal branch stars with a negative radial gradient in metallicity. Spectral energy distribution fits require a metal-rich intermediate-age stellar population (300 Myr to 1 Gyr old, ~Z) in addition to the dominant old population. The radial gradients in age and metallicity of the old stellar population are consistent with those in previous works. For the intermediate-age population, we find an increase in age with radius and a mass fraction that increases up to 2 per cent at 680 pc away from the centre. We exclude contamination from the M31 disc and/or halo as the main origin for this population. Our results thus suggest that intermediate-age stars exist beyond the central 5 arcsec (19 pc) of M31 and contribute ~1 per cent of the total stellar mass in the bulge. These stars could be related to the secular growth of the M31 bulge. [ABSTRACT FROM AUTHOR]

Massive relic galaxies formed the bulk of their stellar component before z ~ 2 and have remained unaltered since then. Therefore, they represent a unique opportunity to study in great detail the frozen stellar population properties of those galaxies that populated the primitive Universe. We have combined optical to near-infrared line-strength indices in order to infer, out to 1.5 Re, the initial mass function (IMF) of the nearby relic massive galaxy NGC 1277. The IMF of this galaxy is bottom-heavy at all radii, with the fraction of low-mass stars being at least a factor of two larger than that found in the Milky Way. The excess of low-mass stars is present throughout the galaxy, while the velocity dispersion profile shows a strong decrease with radius. This behaviour suggests that local velocity dispersion is not the only driver of the observed IMF variations seen among nearby early-type galaxies. In addition, the excess of low-mass stars shown in NGC 1277 could reflect the effect on the IMF of dramatically different and intense star formation processes at z ~ 2, compared to the less extreme conditions observed in the local Universe. [ABSTRACT FROM AUTHOR]

In the last years, more and more interest has been devoted to analytical solutions, including inflow and outflow, to study the metallicity enrichment in galaxies. In this framework, we assume a star formation rate which follows a linear Schmidt law, and we present new analytical solutions for the evolution of the metallicity (Z) in galaxies. In particular, we take into account environmental effects including primordial and enriched gas infall, outflow, different star formation efficiencies and galactic fountains. The enriched infall is included to take into account galaxy-galaxy interactions. Our main results can be summarized as: (i) when a linear Schmidt law of star formation is assumed, the resulting time evolution of the metallicity Z is the same either for a closed-box model or for an outflow model. (ii) The mass-metallicity relation for galaxies which suffer a chemically enriched infall, originating from another evolved galaxy with no pre-enriched gas, is shifted down in parallel at lower Z values, if compared to the closed box model. (iii) When a galaxy suffers at the same time a primordial infall and a chemically enriched one, the primordial infall always dominates the chemical evolution. (iv) We present new solutions for the metallicity evolution in a galaxy which suffers galactic fountains and an enriched infall from another galaxy at the same time. The analytical solutions presented here can be very important to study the metallicity (oxygen), which is measured in high-redshift objects. These solutions can be very useful: (a) in the context of cosmological semi-analytical models for galaxy formation and evolution, and (b) for the study of compact groups of galaxies. [ABSTRACT FROM AUTHOR]

In a virialized stellar system, the mean-square velocity is a direct tracer of the energy per unit mass of the system. Here, we exploit this to estimate and compare root-mean-square velocities for a large sample of nuclear star clusters and their host (late- or early-type) galaxies. Traditional observables, such as the radial surface brightness and second-order velocity moment profiles, are subject to short-term variations due to individual episodes of matter infall and/or star formation. The total mass, energy and angular momentum, on the other hand, are approximately conserved. Thus, the total energy and angular momentum more directly probe the formation of galaxies and their nuclear star clusters, by offering access to more fundamental properties of the nuclear cluster-galaxy system than traditional observables. We find that there is a strong correlation, in fact a near equality, between the root-mean-square velocity of a nuclear star cluster and that of its host. Thus, the energy per unit mass of a nuclear star cluster is always comparable to that of its host galaxy. We interpret this as evidence that nuclear star clusters do not form independently of their host galaxies, but rather that their formation and subsequent evolution are coupled. We discuss how our results can potentially be used to offer a clear and observationally testable prediction to distinguish between the different nuclear star cluster formation scenarios, and/or quantify their relative contributions. [ABSTRACT FROM AUTHOR]

The star formation histories (SFHs) of dwarf galaxies are thought to be bursty, with large -order of magnitude - changes in the star formation rate on time-scales similar to O-star lifetimes. As a result, the standard interpretations of many galaxy observables (which assume a slowly varying SFH) are often incorrect. Here, we use the SFHs from hydrodynamical simulations to investigate the effects of bursty SFHs on sample selection and interpretation of observables and make predictions to confirm such SFHs in future surveys. First, because dwarf galaxies' star formation rates change rapidly, the mass-to-light ratio is also changing rapidly in both the ionizing continuum and, to a lesser extent, the non-ionizing ultraviolet continuum. Therefore, flux limited surveys are highly biased towards selecting galaxies in the burst phase and very deep observations are required to detect all dwarf galaxies at a given stellar mass. Second, we show that a log10 [vLv (1500 Å)/LHα] > 2.5 implies a very recent quenching of star formation and can be used as evidence of stellar feedback regulating star formation. Third, we show that the ionizing continuum can be significantly higher than when assuming a constant SFH, which can affect the interpretation of nebular emission line equivalent widths and direct ionizing continuum detections. Finally, we show that a star formation rate estimate based on continuum measurements only (and not on nebular tracers such as the hydrogen Balmer lines) will not trace the rapid changes in star formation and will give the false impression of a star-forming main sequence with low dispersion. [ABSTRACT FROM AUTHOR]

The properties of galaxies in the local Universe have been shown to depend upon their environment. Future large-scale photometric surveys such as Dark Energy Survey (DES) and Euclid will be vital to gain insight into the evolution of galaxy properties and the role of environment. Large samples come at the cost of redshift precision and this affects the measurement of environment. We study this by measuring environments using Sloan Digital Sky Survey (SDSS) spectroscopic and photometric redshifts and also simulated photometric redshifts with a range of uncertainties. We consider the Nth nearest neighbour and fixed aperture methods and evaluate the impact of the aperture parameters and the redshift uncertainty. We find that photometric environments have a smaller dynamic range than spectroscopic measurements because uncertain redshifts scatter galaxies from dense environments into less dense environments. At the expected redshift uncertainty of DES, 0.1, there is Spearman rank correlation coefficient of 0.4 between the measurements using the optimal parameters. We examine the galaxy red fraction as a function of mass and environment using photometric redshifts and find that the bivariate dependence is still present in the SDSS photometric measurements. We show that photometric samples with a redshift uncertainty of 0.1 must be approximately 6-16 times larger than spectroscopic samples to detect environment correlations with equivalent fractional errors. [ABSTRACT FROM AUTHOR]

We perform in-depth dynamical modelling of the luminous and dark matter (DM) content of the elliptical galaxy NGC 1407. Our strategy consists of solving the spherical Jeans equations for three independent dynamical tracers: stars, blue globular clusters (GCs) and red GCs in a self-consistent manner. We adopt a maximum-likelihood Markov Chain Monte Carlo fitting technique in the attempt to constrain the inner slope of the DM density profile (the cusp/core problem), and the stellar initial mass function (IMF) of the galaxy. We find the inner logarithmic slope of the DM density profiles to be γ = 0.6 ± 0.4, which is consistent with either a DM cusp (γ = 1) or with a DM core (γ = 0). Our findings are consistent with a Salpeter IMF, and marginally consistent with a Kroupa IMF. We infer tangential orbits for the blue GCs, and radial anisotropy for red GCs and stars. The modelling results are consistent with the virial mass-concentration relation predicted by A cold dark matter (CDM) simulations. The virial mass of NGC 1407 is logMvir = 13.3 ± 0.2M⊙, whereas the stellar mass is logM+ = 11.8 ± 0.1 M⊙. The overall uncertainties on the mass of NGC 1407 are only 5 per cent at the projected stellar effective radius. We attribute the disagreement between our results and previous X-ray results to the gas not being in hydrostatic equilibrium in the central regions of the galaxy. The halo of NGC 1407 is found be DM-dominated, with a dynamical mass-to-light ratio of M/L = 260+174-104 M⊙/L⊙.b. However, this value can be larger up to a factor of 3 depending on the assumed prior on the DM scale radius. [ABSTRACT FROM AUTHOR]

In order to understand the orbital history of Galactic halo objects, such as globular clusters, authors usually assume a static potential for our Galaxy with parameters that appear at the present day. According to the standard paradigm of galaxy formation, galaxies grow through a continuous accretion of fresh gas and a hierarchical merging with smaller galaxies from high redshift to the present day. This implies that the mass and size of disc, bulge, and halo change with time. We investigate the effect of assuming a live Galactic potential on the orbital history of halo objects and its consequences on their internal evolution. We numerically integrate backwards the equations of motion of different test objects located in different Galactocentric distances in both static and time-dependent Galactic potentials in order to see if it is possible to discriminate between them. We show that in a live potential, the birth of the objects, 13 Gyr ago, would have occurred at significantly larger Galactocentric distances, compared to the objects orbiting in a static potential. Based on the direct N-body calculations of star clusters carried out with collisional N-body code, nbody6, we also discuss the consequences of the time-dependence of a Galactic potential on the early- and long-term evolution of star clusters in a simple way, by comparing the evolution of two star clusters embedded in galactic models, which represent the galaxy at present and 12 Gyr ago, respectively. We show that assuming a static potential over a Hubble time for our Galaxy as it is often done, leads to an enhancement of mass-loss, an overestimation of the dissolution rates of globular clusters, an underestimation of the final size of star clusters, and a shallower stellar mass function. [ABSTRACT FROM AUTHOR]

We present the results of a new search for galaxies at redshift z ≃ 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift solutions, and to minimize incompleteness, we confine our search to objects with σ160 < 28.6 (AB mag), consider only image regions with anrms noise σ160 > 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H160 and J140. The result is a survey covering an effective area (after accounting for magnification) of 10.9 arcmin², which yields 12 galaxies at 8.4 < z < 9.5. Within the Abell-2744 cluster and parallel fields, we confirm the three brightest objects reported by Ishigaki et al., but recover only one of the four z > 8.4 sources reported by Zheng et al. In the MACSJ0416.1-240 cluster field, we report five objects, and explain why each of these eluded detection or classification as z ≃ 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z ≃ 9 galaxies from the MACSJ0416.1-240 parallel field. Based on the published magnification maps, we find that only one of these 12 galaxies is likely boosted by more than a factor of 2 by gravitational lensing. Consequently, we are able to perform a fairly straightforward reanalysis of the normalization of the z ≃ 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star formation rate density) from z â€" 8 to 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization. [ABSTRACT FROM AUTHOR]

We analyse the star formation history (SFH) of galaxies as a function of present-day environment, galaxy stellar mass and morphology. The SFH is derived by means of a non-parametric spectrophotometric model applied to individual galaxies at z ~ 0.04-0.1 in the WIde-field Nearby Galaxy-cluster Survey (WINGS) clusters and the Padova Millennium Galaxy and Group Catalogue (PM2GC) field. The field reconstructed evolution of the star formation rate density (SFRD) follows the values observed at each redshift, except at z > 2, where our estimate is ~1.7 x higher than the high-z observed value. The slope of the SFRD decline with time gets progressively steeper going from low-mass to high-mass haloes. The decrease of the SFRD since z = 2 is due to (1) quenching - 50 per cent of the SFRD in the field and 75 per cent in clusters at z > 2 originated in galaxies that are passive today - and (2) the fact that the average SFR of today's star-forming galaxies has decreased with time. We quantify the contribution to the SFRD(z) of galaxies of today's different masses and morphologies. The current morphology correlates with the current star formation activity but is irrelevant for the past stellar history. The average SFH depends on galaxy mass, but galaxies of a given mass have different histories depending on their environment. We conclude that the variation of the SFRD(z) with environment is not driven by different distributions of galaxy masses and morphologies in clusters and field, and must be due to an accelerated formation in high-mass haloes compared to low-mass ones even for galaxies that will end up having the same galaxy mass today. [ABSTRACT FROM AUTHOR]

Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS integral field spectrograph as part of our ongoing campaign targeting the ionized gas physics and kinematics inside star-forming members of compact groups. Here, we report the discovery of H ii regions with abundance and kinematic offsets in the otherwise unremarkable star-forming spiral HCG 91c. The optical emission line analysis of this galaxy reveals that at least three H ii regions harbour an oxygen abundance ~0.15 dex lower than expected from their immediate surroundings and from the abundance gradient present in the inner regions of HCG 91c. The same star-forming regions are also associated with a small kinematic offset in the form of a lag of 5-10 km s-1 with respect to the local circular rotation of the gas. Hi observations of HCG 91 from the Very Large Array and broad-band optical images from Pan-STARRS (Panoramic Survey Telescope And Rapid Response System) suggest that HCG 91c is caught early in its interaction with the other members of HCG 91. We discuss different scenarios to explain the origin of the peculiar star-forming regions detected with WiFeS, and show that evidence points towards infalling and collapsing extraplanar gas clouds at the disc-halo interface, possibly as a consequence of long-range gravitational perturbations of HCG 91c from the other group members. As such, HCG 91c provides evidence that some of the perturbations possibly associated with the early phase of galaxy evolution in compact groups impact the star-forming disc locally, and on sub-kpc scales. [ABSTRACT FROM AUTHOR]

Dwarf galaxies generally follow a mass-metallicity (MZ) relation, where more massive objects retain a larger fraction of heavy elements. Young tidal dwarf galaxies (TDGs), born in the tidal tails produced by interacting gas-rich galaxies, have been thought to not follow the MZ relation, because they inherit the metallicity of the more massive parent galaxies. We present chemical evolution models to investigate if TDGs that formed at very high redshifts, where the metallicity of their parent galaxy was very low, can produce the observed MZ relation. Assuming that galaxy interactions were more frequent in the denser high-redshift universe, TDGs could constitute an important contribution to the dwarf galaxy population. The survey of chemical evolution models of TDGs presented here captures for the first time an initial mass function (IMF) of stars that is dependent on both the star formation rate and the gas metallicity via the integrated galactic IMF theory. As TDGs form in the tidal debris of interacting galaxies, the pre-enrichment of the gas, an underlying pre-existing stellar population, infall, and mass-dependent outflows are considered. The models of young TDGs that are created in strongly pre-enriched tidal arms with a pre-existing stellar population can explain the measured abundance ratios of observed TDGs. The same chemical evolution models for TDGs, that form out of gas with initially very low metallicity, naturally build up the observed MZ relation. The modelled chemical composition of ancient TDGs is therefore consistent with the observed MZ relation of satellite galaxies. [ABSTRACT FROM AUTHOR]

Improving upon the standard evolutionary population synthesis technique, we present spec-trophotometric models of galaxies with morphology going from spherical structures to discs, properly accounting for the effect of dust in the interstellar medium (ISM). The models contain three main physical components: the diffuse ISM made of gas and dust, the complexes of molecular clouds where active star formation occurs, and stars of any age and chemical composition. These models are based on robust evolutionary chemical description providing the total amount of gas and stars present at any age, and matching the properties of galaxies of different morphological types. We have considered the results obtained by Piovan et al. for the properties of the ISM, and those by Cassara et al. for the spectral energy distribution (SED) of single stellar populations, both in presence of dust, to model the integral SEDs of galaxies of different morphological types, going from pure bulges to discs passing through a number of composite systems with different combinations of the two components. The first part of the paper is devoted to recall the technical details of the method and the basic relations driving the interaction between the physical components of the galaxy. Then, the main parameters are examined and their effects on the SED of three prototype galaxies are highlighted. The theoretical SEDs nicely match the observational ones both for nearby galaxies and those at high redshift. [ABSTRACT FROM AUTHOR]

We have studied the occurrence frequency of the current star formation in the outer stellar rings of early-type disk galaxies based on a representative sample of nearby galaxies from the ARRAKIS catalog. We show that regular rings reveal current star formation with a young stellar population age of less than 200 Myr in about half the cases, while in the pseudorings (open rings), which are only found in spiral galaxies, current star formation is present almost always. [ABSTRACT FROM AUTHOR]

Interstellar dust plays decisive roles in the conversion of neutral to molecular hydrogen (H2), the thermodynamical evolution of interstellar medium (ISM), and the modification of spectral energy distributions (SEDs) of galaxies. These important roles of dust have not been selfconsistently included in previous numerical simulations of galaxy formation and evolution. We have therefore developed a new model by which one can investigate whether and how galaxy formation and evolution can be influenced by dust-related physical processes such as photoelectric heating, H2 formation on dust, and stellar radiation pressure on dust in detail. A novel point of the model is that different dust species in a galaxy are represented by 'live dust' particles (i.e. not test particles). Therefore, dust particles in a galaxy not only interact gravitationally with all four components of the galaxy (i.e. dark matter, stars, gas, and dust) but also are grown and destroyed through physical processes of ISM. First, we describe a way to include dust-related physical processes in N-body+hydrodynamical simulations of galaxy evolution in detail. Then, we show some preliminary results of dust-regulated galaxy evolution. The preliminary results suggest that the evolution of dust distributions driven by radiation pressure of stars is very important for the evolution of star formation rates, chemical abundances, H2 fractions, and gas distributions in galaxies. [ABSTRACT FROM AUTHOR]

In order to understand the forming mechanism of the radial abun- dance gradient of the Galactic disk and the evolution of cold gas, we have con- structed a chemical evolution model of the Galactic disk, in which the star for- mation law concerned with molecular hydrogens is adopted, and the evolution of mass surface density is calculated for the molecular and atomic hydrogens separately, then the model predictions and the observed radial distributions of some physical quantities are compared. The result indicates that the model prediction is sensitive to the adopted infall timescale, the model which adopts the star formation law concerned with the molecular hydrogens can agree well with the major observed properties of the Galactic disk, especially can obtain naturally the radial oxygen abundance gradient of the Galactic disk, and the radial surface density profile of cold gas. The assumption of instantaneous or non-instantaneous recycling approximation has a small effect on the evolution of cold gas, especially in the case of rather low gas density. [ABSTRACT FROM AUTHOR]

Giant Low Surface Brightness (GLSB) galaxies are amongst the most massive spiral galaxies that we know of in our Universe. Although they fall in the class of late type spiral galaxies, their properties are far more extreme. They have very faint stellar disks that are extremely rich in neutral hydrogen gas but low in star formation and hence low in surface brightness. They often have bright bulges that are similar to those found in early type galaxies. The bulges can host low luminosity Active Galactic Nuclei (AGN) that have relatively low mass black holes. GLSB galaxies are usually isolated systems and are rarely found to be interacting with other galaxies. In fact many GLSB galaxies are found under dense regions close to the edges of voids. These galaxies have very massive dark matter halos that also contribute to their stability and lack of evolution. In this paper we briefly review the properties of this unique class of galaxies and conclude that both their isolation and their massive dark matter halos have led to the low star formation rates and the slower rate of evolution in these galaxies. [ABSTRACT FROM AUTHOR]

In this paper we present the stellar population synthesis results for a sample of 75 bulges in isolated spiral Sb-Sc galaxies, using the spectroscopic data from the Sloan Digital Sky Survey and the STARLIGHT code. We find that both pseudo-bulges and classical bulges in our sample are predominantly composed of old stellar populations, with mean mass-weighted stellar age around 10 Gyr. While the stellar population of pseudo-bulges is, in general, younger than that of classical bulges, the difference is not significant, which indicates that it is hard to distinguish pseudo-bulges from classical bulges, at least for these isolated galaxies, only based on their stellar populations. Pseudo-bulges have star formation activities with relatively longer timescale than classical bulges, indicating that secular evolution is more important in this kind of systems. Our results also show that pseudo-bulges have a lower stellar velocity dispersion than their classical counterparts, which suggests that classical bulges are more dispersion-supported than pseudo-bulges. [ABSTRACT FROM AUTHOR]

We present a catalog of 520 most isolated nearby galaxies with angular velocities V < 3500 km/s, covering the entire sky. This population of 'space orphans' makes up 4.8% among 10 900 galaxies with measured radial velocities. We describe the isolation criterion used to select our sample, called the 'Local Orphan Galaxies'(LOG), and discuss their basic optical and HI properties. A half of the LOG catalog is occupied by the Sdm, Im and Ir morphological type galaxies without a bulge. The median ratio M/ M in the LOG galaxies exceeds 1. The distribution of the catalog galaxies on the sky looks uniform with some signatures of a weak clustering on the scale of about 0.5 Mpc. The LOG galaxies are located in the regions where the mean local density of matter is approximately 50 times lower than the mean global density. We indicate a number of LOG galaxies with distorted structures, which may be the consequence of interaction of isolated galaxies with massive dark objects. [ABSTRACT FROM AUTHOR]

We have analyzed the distribution of early-type galaxies (ETGs) in the effective surface intensity vs. effective radius ( I e − R e ) plane and in the total luminosity vs. central stellar velocity dispersion ( L − σ ) diagram, with the aim of studying the physical variables that allow the transformation of one space-parameter into the other. We find that the classical Faber–Jackson relation L = L 0 σ α , in which the parameters L 0 and α are confined in a small range of possible values, is incompatible with the distribution observed in the I e − R e plane. The two distributions become mutually consistent only if luminosity is not considered a pure proxy of mass but a variable tightly dependent on the past history of mass assembling and star formation and on the present evolutionary state of the stellar content of a galaxy. The solution comes by considering the L = L 0 ′ σ β law proposed by D'Onofrio et al. in 2020, in which both L 0 ′ and β can vary considerably from galaxy to galaxy. We will also show that the data of the Illustris numerical simulation prove the physical foundation of the L = L 0 ′ σ β law and confirm the prediction of the Zone of Exclusion (ZoE) originating from the intersection of the virial law with the L = L 0 ′ σ β relation. The ZoE is the region in the I e − R e and R e − M s diagrams avoided by real galaxies, and the border of which marks the condition of 'full' virial equilibrium with no recent significant merger events and no undergoing star formation. [ABSTRACT FROM AUTHOR]

Gas deficiency in cluster spirals is well known and ram-pressure stripping is considered the main gas removal mechanism. In some compact groups too gas deficiency is reported. However, gas deficiency in loose groups is not yet well established. Lower dispersion of the member velocities and the lower density of the intragroup medium in small loose groups favour tidal stripping as the main gas removal process in them. Recent releases of data from the H i Parkes All-Sky Survey (HIPASS) and catalogues of nearby loose groups with associated diffuse X-ray emission have allowed us to test this notion. In this paper, we address the following questions: (i) do galaxies in groups with diffuse X-ray emission statistically have lower gas content compared to the ones in groups without diffuse X-ray emission? (ii) does H i deficiency vary with the X-ray luminosity, LX, of the loose group in a systematic way? We find that (i) galaxies in groups with diffuse X-ray emission, on average, are H i deficient, and have lost more gas compared to those in groups without X-ray emission; the latter are found not to have significant H i deficiency; (ii) no systematic dependence of the H i deficiency with LX is found. Ram-pressure-assisted tidal stripping and evaporation by thermal conduction are the two possible mechanisms to account for this excess gas loss. [ABSTRACT FROM AUTHOR]

We have used Visible MultiObject Spectrograph Integral-Field Unit observations centred on a radio galaxy atto search for Lyα emitters within a comoving volume of. We find 14 Lyα emitters with flux, yielding a comoving space density of. We fit a Schechter luminosity function that agrees well with previous studies both at similar redshiftand higher redshift. We therefore find no evidence for evolution in the properties of Lyα emitters between, although our sample is small. By summing the star-formation rates of the individual Lyα emitters we find a total cosmic star-formation rate density of. Integrating over the luminosity function for the combined Lyα surveys atand accounting for the difference in obscuration between the Lyα line and the ultraviolet-continuum yields an estimate of, in line with previous multi-colour and narrow-band surveys of high-redshift star-forming galaxies.The detection of high-redshift emission-line galaxies in our volumetric search shows that the unique capabilities of wide-field integral-field spectroscopy are well suited to searching for high-redshift galaxies in a relatively unbiased manner. [ABSTRACT FROM AUTHOR]

We investigate the structural, kinematical and spectrophotometric properties of‘E+A’ galaxies– those with strong Balmer absorption lines but no significant[O ii] emission– using numerical simulations combined with stellar population synthesis codes. We particularly focus on the two-dimensional (2D) distributions of line-of-sight velocity, velocity dispersion, colour and line index in E+A galaxies formed via the interaction and merging of two gas-rich spirals. Our numerical simulations demonstrate that E+A elliptical galaxies formed by major galaxy merging have positive radial colour gradients and negative radial Hδ gradients by virtue of their central post-starburst populations. Furthermore, we show that the projected kinematical and spectroscopic properties of the simulated E+A galaxies can be remarkably different for different major merger models. For example, the simulated E+A ellipticals with kinematically decoupled cores clearly show regions of strong Hδ absorption which are very flattened, with differences in rotation and velocity dispersion between the old and young stars. E+A ellipticals are highly likely to show more rapid rotation and a smaller central velocity dispersion in young stars than in old ones. E+A galaxies formed from the strong tidal interaction between gas-rich spirals have discy morphologies with thick discs and are highly likely to be morphologically classified as barred S0 galaxies. We also provide specific predictions on the structural, kinematical and spectrophotometric properties of young globular cluster systems in E+A galaxies. Based on these results, we discuss the importance of spatially resolved, integral field unit spectroscopy on large (8–10 m) ground-based telescopes in confirming the formation of kinematically distinct cores in elliptical galaxies produced via dissipative merging and determining the most probable physical mechanism(s) for E+A formation with discy and spheroidal morphologies. [ABSTRACT FROM AUTHOR]

We compute population synthesis models for the variation of Hα absorption indices (and), as a function of age and metallicity in old stellar systems. The models are based on the STELIB spectral library of Le Borgne et al., and defined at a resolution of 3 Å full width at half-maximum. Errors in the age and metallicity responses are derived by bootstrap resampling the input measurements on the stellar library. The indices are found to be highly sensitive to age variation, with only moderate response to metallicity. For galaxies uncontaminated by nebular emission, ourindex is more powerful in breaking the age–metallicity degeneracy than Hβ or. Using a sample of red cluster galaxies from Nelan et al., carefully selected to exclude objects with emission, we find a steep decline ofwith velocity dispersion (slope). The slope can be translated to constraints on age and metallicity scaling relations, incorporating measurement errors and also the model errors determined from the bootstrap method. If theslope is due only to age, we obtain Age∝σ0.95±0.12. Becausedepends quite weakly on[Fe/H], a metallicity interpretation would requireor steeper. Theslope is consistent with the combined age and metallicity scaling relations reported by Nelan et al. from classical Lick indices. The relations obtained by Thomas et al. significantly underpredict the observed slope. The discrepancy could arise from differences in the sample selection. In particular, our sample probes a lower mass range, is not explicitly selected on morphological criteria, and excludes objects significantly bluer than the red sequence. We discuss in detail the impact of emission contamination on the results, and conclude that this effect is unlikely to yield the observed behaviour in the Hα–σ relations. Indeed, similar results are obtained using, despite its different sensitivity to Hα and[N ii] emission lines. The steep age–mass relation supports a‘downsizing’ formation scenario: fainter red-sequence galaxies became quiescent at lower redshifts,. This picture accords with recent observations of truncated red sequences in clusters at. [ABSTRACT FROM AUTHOR]

We analyse near-infraredHubble Space Telescope(HST)/Near-Infrared Camera and Multi-Object SpectrometerF110W(J) andF160W(H) band photometry of a sample of 27i′-drop candidategalaxies in the central region of theHST/Advanced Camera for SurveysUltra Deep Field. The infrared colours of the 20 objects not affected by near neighbours are consistent with a high-redshift interpretation. This suggests that the low-redshift contamination of thisi′-drop sample is smaller than that observed at brighter magnitudes, where values of 10–40 per cent have been reported. TheJ– Hcolours are consistent with a slope flat in, as would be expected for an unreddened starburst. However, there is evidence for a marginally bluer spectral slope, which is perhaps indicative of an extremely young starburst (∼10 Myr old) or a top heavy initial mass function and little dust. The low levels of contamination, median photometric redshift ofand blue spectral slope, inferred using the near-infrared data, support the validity of the assumptions in our earlier work in estimating the star formation rates, and that the majority of thei-drop candidates galaxies lie at. [ABSTRACT FROM AUTHOR]