Lick Indices Research Articles

The hyperplane of early-type galaxies: using stellar population properties to increase the precision and accuracy of the fundamental plane as a distance indicator

ABSTRACT We use deep spectroscopy from the SAMI (Sydney-AAO Multi-object Integral) Galaxy Survey to explore the precision of the fundamental plane (FP) of early-type galaxies as a distance indicator for future single-fibre spectroscopy surveys. We study the optimal trade-off between sample size and signal-to-noise ratio (SNR), and investigate which additional observables can be used to construct hyperplanes with smaller intrinsic scatter than the FP. We add increasing levels of random noise (parametrized as effective exposure time) to the SAMI spectra to study the effect of increasing measurement uncertainties on the FP- and hyperplane-inferred distances. We find that, using direct-fit methods, the values of the FP and hyperplane best-fitting coefficients depend on the spectral SNR, and reach asymptotic values for a mean $\langle \mathrm{ SNR} \rangle =40\, \mathrm{\mathring{\rm A}}^{-1}$. As additional variables for the FP we consider three stellar-population observables: light-weighted age, stellar mass-to-light ratio, and a novel combination of Lick indices ($I_\mathrm{age}$). For an $\langle \mathrm{ SNR} \rangle =45~\mathrm{\mathring{\rm A}}^{-1}$ (equivalent to 1-h exposure on a 4-m telescope), all three hyperplanes outperform the FP as distance indicators. Being an empirical spectral index, $I_\mathrm{age}$ avoids the model-dependent uncertainties and bias underlying age and mass-to-light ratio measurements, yet yields a 10 per cent reduction of the median distance uncertainty compared to the FP. We also find that, as a by-product, the $I_\mathrm{age}$ hyperplane removes most of the reported environment bias of the FP. After accounting for the different SNR, these conclusions also apply to a 50 times larger sample from SDSS-III (Sloan Digital Sky Survey). However, in this case, only $\mathrm{ age}$ removes the environment bias.

New Observational H(z) Data from Full-spectrum Fitting of Cosmic Chronometers in the LEGA-C Survey

In this work, we perform a full-spectrum fitting of 350 massive and passive galaxies selected as cosmic chronometers from the LEGA-C ESO public survey to derive their stellar ages, metallicities, and star formation histories. We extensively test our results by assessing their dependence on the possible contribution of dust, calibration of noise and signal, and use of photometric data in addition to spectral information; we also identify indicators of the correct convergence of the results, including the shape of the posterior distributions, the analysis of specific spectral features, and the correct reproduction of the observed spectrum. We derive a clear age–redshift trend compatible with the aging in a standard cosmological model showing a clear downsizing pattern, with more massive galaxies being formed at higher redshift (z f ∼ 2.5) with respect to less massive ones (z f ∼ 2). From these data, we measure the differential aging of this population of cosmic chronometers to derive a new measurement of the Hubble parameter, obtaining . This analysis allows us to compare for the first time the differential ages of cosmic chronometers measured on the same sample with two completely different methods, the full-spectrum fit (this work) and the analysis of Lick indices, known to correlate with the age and metallicity of the stellar populations. Albeit an understood offset in the absolute ages, the differential ages have proven to be extremely compatible between the two methods, despite the very different data, assumptions, and models considered, demonstrating the robustness of the method.

Stellar population analysis of MaNGA early-type galaxies: IMF dependence and systematic effects

ABSTRACT We study systematics associated with estimating simple stellar population (SSP) parameters – age, metallicity [M/H], α-enhancement [α/Fe], and initial mass function (IMF) shape – and associated M*/L gradients, of elliptical slow rotators (E-SRs), fast rotators (E-FRs), and S0s from stacked spectra of galaxies in the MaNGA survey. These systematics arise from (i) how one normalizes the spectra when stacking; (ii) having to subtract emission before estimating absorption line strengths; (iii) the decision to fit the whole spectrum or just a few absorption lines; (iv) SSP model differences (e.g. isochrones, enrichment, IMF). The MILES+Padova SSP models, fit to the Hβ, 〈Fe〉, TiO2SDSS, and [MgFe] Lick indices in the stacks, indicate that out to the half-light radius Re: (a) ages are younger and [α/Fe] values are lower in the central regions but the opposite is true of [M/H]; (b) the IMF is more bottom-heavy in the center, but is close to Kroupa beyond about Re/2; (c) this makes M*/L about 2 × larger in the central regions than beyond Re/2. While the models of Conroy et al. return similar [M/H] and [α/Fe] profiles, the age and (hence) M*/L profiles can differ significantly even for solar abundances and a Kroupa IMF; different responses to non-solar abundances and IMF parametrization further compound these differences. There are clear (model independent) differences between E-SRs, E-FRs, and S0s: younger ages and less enhanced [α/Fe] values suggest that E-FRs and S0s are not SSPs, but relaxing this assumption is unlikely to change their inferred M*/L gradients significantly.

Toward a Better Understanding of Cosmic Chronometers: Stellar Population Properties of Passive Galaxies at Intermediate Redshift

Abstract We take advantage of the publicly available LEGA-C spectroscopic survey to measure the stellar population properties of 140 individual massive and passive galaxies at z ∼ 0.7. We develop and publicly release PyLick, a flexible Python code to measure UV to near-IR spectral indices. With PyLick we study the H/K ratio as a new diagnostic based on the pseudo-Lick Ca ii H and K indices and find that a cut in H/K < 1.1 can be used jointly with other criteria to select (or verify the purity of) samples of passive galaxies. By combining photometric and spectroscopic criteria, we select a reliable sample of passively evolving galaxies. We constrain single-burst stellar ages, metallicities [Z/H], and [α/Fe] with an optimized set of Lick indices, exploring in detail the robustness of our measurement against different combinations. Even without imposing cosmological priors, the derived ages follow a clear trend compatible with the expected cosmological aging of the universe. We observe no significant redshift evolution for the metal abundance with respect to the values derived at z = 0, with median [Z/H] = 0.08 ± 0.18 and [α/Fe] = 0.13 ± 0.11. Finally, we analyze the relations between log age, [Z/H], [α/Fe], and the stellar velocity dispersion, finding slopes of (0.5 ± 0.1), (0.3 ± 0.2), and (0.2 ± 0.1), respectively; the small scatter of <0.2 dex points to rather homogeneous and short star formation histories. Overall, these results confirm and extend low-redshift findings of a mass-downsizing evolution. This work further strengthens the possibility of selecting pure samples of passive galaxies to be exploited reliably as cosmic chronometers to place independent cosmological constraints.

Toward a Better Understanding of Cosmic Chronometers: A New Measurement of H(z) at z ∼ 0.7

Abstract We analyze the stellar ages obtained from a combination of Lick indices in Borghi et al. for 140 massive and passive galaxies selected in the LEGA-C survey at 0.6 < z < 0.9. From their median age–redshift relation, we derive a new direct measurement of H(z) without any cosmological model assumption using the cosmic chronometer approach. We thoroughly study the main systematics involved in this analysis: the choice of the Lick indices combination, the binning method, the assumed stellar population model, and the adopted star formation history; these effects are included in the total error budget. We obtain H(z = 0.75) = 98.8 ± 33.6 km s−1 Mpc−1. In parallel, we also propose a simple framework based on a cosmological model to describe the age–redshift relations in the context of galaxy downsizing. This allows us to derive constraints on the Hubble constant H 0 and the typical galaxy formation time. This new H(z) measurement, whose accuracy is currently limited by the scarcity of the sample analyzed, paves the road for the joint study of the stellar populations of individual passive galaxies and the expansion history of the universe in light of future spectroscopic surveys.

Investigation of the effect of bars on the properties of spiral galaxies: a multivariate statistical study

Subjective classification of spiral galaxies is not sufficient for studying the effect of bars on their physical characteristics. In reality the problem is to comprehend the complex correlations in a multivariate parametric space. Multivariate tools are the best ones for understanding this complex correlation. In this work an objective classification of a large set (26,089) of spiral galaxies was compiled as a value added galaxy catalogue from sdss DR 15 virtual data archive. Initially for dimensionality reduction, Independent Component Analysis is performed to determine a set of Independent Components that are linear combinations of 48 observed features (namely ionized lines, Lick indices, photometric and morphological properties). Subsequently a K-means cluster analysis is carried out on the basis of the 14 best chosen Independent Components to obtain 12 distinct homogeneous groups of spiral galaxies. Amongst these, 3 groups are the oldest ones (1.6 Gyr − 5.9 Gyr), while 5 groups fall in the medium aged category (1.4 Gyr − 1.6 Gyr), 2 groups consist of only unbarred spirals, 1 group is the youngest one and the remaining one is an outlier. In many groups there are clear indication of recurrent bar formation phenomena which is consistent with few previous simulation works. In order to study the robustness of the clusters with respect to the method of clustering, a second method of clustering by Gaussian Mixture Modeling Method (GMMBC) is applied.

Application of Random Forest Regressions on Stellar Parameters of A-type Stars and Feature Extraction* *Supported by the National Science Foundation for Young Scientists of China Grant No. 11800313. and the Joint Research Fund in Astronomy (U2031142) under cooperative agreement between the National Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS). Technology Innovation Center of Agricultural Multi-Dimensional

Measuring the stellar parameters of A-type stars is more difficult than FGK stars because of the sparse features in their spectra and the degeneracy between effective temperature (T eff) and gravity (log g). Modeling the relationship between fundamental stellar parameters and features through machine learning is possible because we can employ the advantage of big data rather than sparse known features. As soon as the model is successfully trained, it can be an efficient approach for predicting T eff and log g for A-type stars especially when there is large uncertainty in the continuum caused by flux calibration or extinction. In this paper, A-type stars are selected from LAMOST DR7 with a signal-to-noise ratio greater than 50 and the T eff ranging within 7000 to 10,000 K. We perform the Random Forest (RF) algorithm, one of the most widely used machine learning algorithms to establish the regression relationship between the flux of all wavelengths and their corresponding stellar parameters (T eff) and (log g) respectively. The trained RF model not only can regress the stellar parameters but also can obtain the rank of the wavelength based on their sensibility to parameters. According to the rankings, we define line indices by merging adjacent wavelengths. The objectively defined line indices in this work are amendments to Lick indices including some weak lines. We use the Support Vector Regression algorithm based on our new defined line indices to measure the temperature and gravity and use some common stars from Simbad to evaluate our result. In addition, the Gaia Hertzsprung-Russell diagram is used for checking the accuracy of T eff and log g.

A study of outer disc stellar populations of face-on star-forming galaxies in SDSS-IV MaNGA: causes of H α deficiency

ABSTRACT Integral field unit spectra of face-on star-forming galaxies from the MaNGA survey are stacked in radial bins so as to reach an S/N high enough to measure emission lines and Lick indices out to 2.5–3Re. Two-thirds of galaxies have stellar populations in the outer discs that are older, more metal poor, and less dusty than in the inner discs. Recent bursts of star formation have occurred more frequently in the outer disc, but extinction-corrected H α equivalent widths are significantly lower at fixed Dn(4000) in these regions. I examine the properties of a subset of galaxies with the most H α-deficient outer discs. These regions contain young stellar populations that must have formed within the last 0.5 Gyr, but have extinction-corrected H α values well below the values predicted for a standard Kroupa initial mass function. The H α-deficient galaxies have flat Dn(4000) and H δA profiles with little radial fluctuation, indicating that star formation has occurred extremely uniformly across the entire disc. The H α line profiles indicate that the ionized gas kinematics is also very regular across the disc. The main clue to the origin of the H α deficiency is that it sets in at the same radius where the dust extinction abruptly decreases, suggesting a mode of star formation deficient in massive stars in quiescent, H i-dominated gas. Finally, I have carried out a search for galaxies with signatures of unusual H α kinematics and find that 15 per cent of the sample exhibits evidence for significant ionized gas that is displaced from the systemic velocity of the disc.

Inverse stellar population age gradients of post-starburst galaxies at z = 0.8 with LEGA-C

ABSTRACT We use deep, spatially resolved spectroscopy from the Large Early Galaxy Astrophysics Census Survey to study radial variations in the stellar population of 17 spectroscopically selected post-starburst (PSB) galaxies. We use spectral fitting to measure two Lick indices, H δA and Fe 4383 , and find that, on average, PSB galaxies have radially decreasing H δA and increasing Fe 4383 profiles. In contrast, a control sample of quiescent, non-PSB galaxies in the same mass range shows outwardly increasing H δA and decreasing Fe 4383 . The observed gradients are weak (≈−0.2 Å/Re), mainly due to seeing convolution. A two-SSP (simple stellar population) model suggests that intrinsic gradients are as strong as observed in local PSB galaxies (≈−0.8 Å/Re). We interpret these results in terms of inside-out growth (for the bulk of the quiescent population) versus star formation occurring last in the centre (for PSB galaxies). At z ≈ 0.8, central starbursts are often the result of gas-rich mergers, as evidenced by the high fraction of PSB galaxies with disturbed morphologies and tidal features (40 per cent). Our results provide additional evidence for multiple paths to quiescence: a standard path, associated with inside-out disc formation and with gradually decreasing star formation activity, without fundamental structural transformation, and a fast path, associated with centrally concentrated starbursts, leaving an inverse age gradient and smaller half-light radius.

Star formation in outer rings of S0 galaxies

Aims. Even though S0 galaxies are usually thought to be ‘red and dead’, they often demonstrate star formation organised in ring structures. We try to clarify the nature of this phenomenon and the difference between this occurrence and star formation in spiral galaxies. The luminous S0 galaxy with a large ring, UGC 5936, is studied in this work. Methods. We measured gas and star kinematics by applying long-slit spectroscopy along the major axis of UGC 5936, as well as Lick indices for the main body of the galaxy and strong emission-line flux ratios in the ring. After inspecting the gas excitation in the ring using line ratio diagnostic diagrams and having ensured that it is ionised mostly by young stars, we determined the gas oxygen abundance with popular strong-line methods. We also proved the spatial proximity of the south-eastern dwarf satellite to UGC 5936 and measured its gas metallicity. Results. The ionised gas of the ring is excited by young stars and has solar metallicity. Star formation in the ring is rather prolonged and its intensity corresponds to the current HI content of UGC 5936 (to the Kennicutt-Schmidt relation). The whole morphology of the HI distribution implies current accretion of the cold gas from the satellite onto the outer disc of UGC 5936. The accretion being smooth and laminar provides a favourable condition for star formation ignition; this is a consequence of the satellite location and rotation in the plane of the stellar disc of the host galaxy.

Galaxy properties as revealed by MaNGA – III. Kinematic profiles and stellar population gradients in S0s

ABSTRACT This is the third paper of a series where we study the stellar population gradients (SP; ages, metallicities, α-element abundance ratios, and stellar initial mass functions) of early-type galaxies (ETGs) at $z$ ≤ 0.08 from the Mapping Nearby Galaxies at APO Data Release 15 (MaNGA-DR15) survey. In this work, we focus on the S0 population and quantify how the SP varies across the population as well as with galactocentric distance. We do this by measuring Lick indices and comparing them to SP synthesis models. This requires spectra with high signal-to-noise ratio which we achieve by stacking in bins of luminosity (Lr) and central velocity dispersion (σ0). We find that: (1) there is a bimodality in the S0 population: S0s more massive than $3\times 10^{10}\, \mathrm{M}_\odot$ show stronger velocity dispersion and age gradients (age and σr decrease outwards) but little or no metallicity gradient, while the less massive ones present relatively flat age and velocity dispersion profiles, but a significant metallicity gradient (i.e. [M/H] decreases outwards). Above $2\times 10^{11}\, \mathrm{M}_\odot$, the number of S0s drops sharply. These two mass scales are also where global scaling relations of ETGs change slope. (2) S0s have steeper velocity dispersion profiles than fast-rotating elliptical galaxies (E-FRs) of the same luminosity and velocity dispersion. The kinematic profiles and SP gradients of E-FRs are both more similar to those of slow-rotating ellipticals (E-SRs) than to S0s, suggesting that E-FRs are not simply S0s viewed face-on. (3) At fixed σ0, more luminous S0s and E-FRs are younger, more metal rich and less α-enhanced. Evidently for these galaxies, the usual statement that ‘massive galaxies are older’ is not true if σ0 is held fixed.

Star formation in outer rings of S0 galaxies

Aims. Although S0 galaxies are often thought to be “red and dead”, they frequently demonstrate star formation organised in ring structures. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. Here we study the moderate-luminosity nearby S0 galaxy, NGC 4513. Methods. By applying long-slit spectroscopy along the major axis of NGC 4513, we measured gas and star kinematics, Lick indices for the main body of the galaxy, and strong emission-line flux ratios in the ring. After inspecting the gas excitation in the ring using the line ratios diagnostic diagrams and showing that it is ionised by young stars, we determined the gas oxygen abundance using popular strong-line calibration methods. We estimated the star formation rate (SFR) in the outer ring using the archival Galaxy Evolution Explorer (GALEX) ultraviolet images of the galaxy. Results. The ionised gas counter-rotates the stars over the whole extension of NGC 4513 suggesting that it is being accreted from outside. The gas metallicity in the ring is slightly subsolar, [O/H] = −0.2 dex, matching the metallicity of the stellar component of the main galactic disc. However the stellar component of the ring is much more massive than can be explained by the current star formation level in the ring. We conclude that the ring of NGC 4513 is probably the result of tidal disruption of a massive gas-rich satellite, or may be the consequence of a long star-formation event provoked by gas accretion from a cosmological filament that started some 3 Gyr ago.

Stellar population properties of individual massive early-type galaxies at 1.4 < z < 2

ABSTRACT We analyse publicly available, individual spectra of four massive ($M\gt 10^{11}\, \mathrm{M}_{\odot }$) early-type galaxies with redshifts in the range 1.4 ≤ z ≤ 2 to determine their stellar content, extending our previous work up to z ∼ 2. The wide wavelength range of the VLT/X-Shooter spectroscopic data in the UV–Optical–NIR arms along with the availability of spectro-photometry allows us to explore different techniques to obtain the stellar population properties, namely through age/metallicity-sensitive spectral indices, full spectral fitting, and broad-band photometric fitting. Moreover, together with the widely used optical Lick indices, we consider further indices in the UV rest frame, and demonstrate that UV indices significantly help the accuracy of the resulting population parameters. We find galaxy ages ranging from 0.2 to 4 Gyr, where the oldest galaxy is found at the lowest redshift, with an excellent agreement between ages determined via indices, full spectral fitting, or broad-band colours. These ages are in perfect agreement with ages of local galaxies at the same velocity dispersion when we assume pure passive evolution. Total metallicities derived from indices show some scatter (between less than half-solar to very high values, [Z/H] ∼ 0.6). We speculate on possible mechanisms explaining these values, but given the sample size and low S/N of the spectra no conclusion can be made. Indices in the UV rest frame generally lead to similar conclusions as optical indices. For the oldest galaxy (4 Gyr), we show that its UV indices can only be explained by stellar population models including a UV contribution from old stellar populations, suggesting that old, UV bright populations start to inhabit mature galaxies of a few Gyr of age. This is the highest redshift (z ∼ 1.4) detection of the UV upturn up to date.

The Data Analysis Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey: Overview

Abstract The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is currently acquiring integral-field spectroscopy for the largest sample of galaxies to date. By 2020, the MaNGA Survey—which is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV)—will have observed a statistically representative sample of 104 galaxies in the local universe (z ≲ 0.15). In addition to a robust data-reduction pipeline (DRP), MaNGA has developed a data-analysis pipeline (DAP) that provides higher-level data products. To accompany the first public release of its code base and data products, we provide an overview of the MaNGA DAP, including its software design, workflow, measurement procedures and algorithms, performance, and output data model. In conjunction with our companion paper (Belfiore et al.), we also assess the DAP output provided for 4718 observations of 4648 unique galaxies in the recent SDSS Data Release 15 (DR15). These analysis products focus on measurements that are close to the data and require minimal model-based assumptions. Namely, we provide stellar kinematics (velocity and velocity dispersion), emission-line properties (kinematics, fluxes, and equivalent widths), and spectral indices (e.g., D4000 and the Lick indices). We find that the DAP provides robust measurements and errors for the vast majority (>99%) of analyzed spectra. We summarize assessments of the precision and accuracy of our measurements as a function of signal-to-noise. We also provide specific guidance to users regarding the limitations of the data. The MaNGA DAP software is publicly available and we encourage community involvement in its development.

Unsupervised Classification of Galaxies. I. Independent Component Analysis Feature Selection

Subjective classification of galaxies can mislead us in the quest for the formation and evolution of galaxies since this is necessarily limited to a few features. The human mind is unable to comprehend the complex correlations in a manifold parameter space, and multivariate analyses are the best tools for understanding the differences among various kinds of objects. In this series of papers, an objective classification of 362,923 galaxies from the Value Added Galaxy Catalog is carried out with the help of two methods of multivariate analysis. First, Independent Component Analysis is used to determine a set of derived independent components that are linear combinations of 47 observed features (namely, ionized lines, Lick indices, photometric and morphological properties, star formation rates, etc.) of the galaxies. Subsequently, a K-means cluster analysis is applied to the nine independent components to obtain 10 distinct, homogeneous groups. In this first paper, we describe the methods and the main results. It appears that the nine Independent Components represent a complete physical description of galaxies (velocity dispersion, ionization, metallicity, surface brightness, and structure). We find that our 10 groups can be essentially placed into traditional and empirical classes (from color–magnitude and emission-line diagnostic diagrams, early versus late types) despite the classical corresponding features (color, line ratios, and morphology) not being significantly correlated with the nine Independent Components. A more detailed physical interpretation of the groups will be performed in subsequent papers.

Spectroscopy of Globular Clusters in the Spheroidal Dwarf Galaxy IKN

Moderate resolution spectra of four globular clusters in the dwarf spheroidal galaxy IKN obtained with the 6-m telescope of the Special Astrophysical Observatory have been used to determine the radial velocities, ages, and metallicities of the clusters, and also to derive the first approximate estimates of the abundances of Mg, Ca, and C. Cross-correlation with radial-velocity standards, fitting of the observed spectra with model spectra, diagnostic diagrams based on the Lick absorption indices, and comparison of the spectra and absorption indices with those of Galactic globular clusters are applied. The integrated spectrum of the two bright clusters IKN4 and IKN5, which are close to the center of the galaxy in projection on the celestial sphere, yields the heliocentric radial velocity Vh = 38 ± 30 km/s, age T =12.6 ± 2 Gyr, metallicity [Fe/H] = −2.1 ± 0.2 dex, and abundance of α-process elements [α/Fe] ∼ 0.5 dex. The integrated spectrum of the two weaker clusters IKN1 and IKN3, which are far from the center of the galaxy, yielded the radial velocity Vh = −39 ± 50 km/s. Despite the low signal-to-noise ratio in the integrated spectrum for IKN1 and IKN3, all the analysis methods applied indicate that these two objects have approximately the same age and metallicity as IKN4 and IKN5. According to the measured Lick indices \({{\rm{H}}_{\delta {\rm{F}}}}\) and Hβ, the studied globular clusters in IKN have blue horizontal branches.

SDSS-IV MaNGA: Environmental Dependence of the Mgb/ – Relation for Nearby Galaxies

Abstract We use a sample of ∼3000 galaxies from the MaNGA MPL-7 internal data release to study the α abundance distribution within low-redshift galaxies. We use the Lick index ratio Mgb/ as an α abundance indicator to study relationships between the α abundance distribution and galaxy properties such as effective stellar velocity dispersion within 0.3 effective radii (σ *), galaxy environment, and dark matter halo formation time (z f ). We find that (1) all galaxies show a tight correlation between Mgb/ and (2) “old” (Hβ < 3) low-σ * galaxies in high local density environment and inner regions within galaxy groups are enhanced in Mgb/ , while “young” (Hβ > 3) galaxies and high-mass galaxies show no or less environmental dependence; (3) “old” galaxies with high-z f show enhanced Mgb/ over low- and medium-z f ; and (4) Mgb/ gradients are close to zero and show dependence on σ * but no obvious dependence on the environment or z f . Our study indicates that stellar velocity dispersion or galaxy mass is the main parameter driving the Mgb/ enhancement, although environments appear to have modest effects, particularly for low- and medium-mass galaxies.

Gemini/GMOS Spectroscopy of Globular Clusters in the Merger Remnant Galaxy M85

Abstract M85 is a peculiar S0 galaxy in Virgo and a well-known merger remnant. We present the first spectroscopic study of globular clusters (GCs) in M85. We obtain spectra for 21 GC candidates and the nucleus of M85 using the Gemini Multi-Object Spectrograph on the Gemini North 8.1 m telescope. From their radial velocities, 20 of the GCs are found to be members of M85. We find a strong rotation signal of the M85 GC system with a rotation amplitude of 235 km s−1. The rotation axis of the GC system has a position angle of about 161°, which is 51.°5 larger than that of the stellar light. The rotation-corrected radial velocity dispersion of the GC system is estimated to be km s−1. The rotation parameter of the GC system is derived to be , which is one of the largest among known early-type galaxies. The ages and metallicities of the GCs, which show the same trend as the results based on Lick indices, are derived from full spectrum fitting (ULySS). About half of the GCs are an intermediate-age population whose mean age is ∼3.7 ± 1.9 Gyr, having a mean [Fe/H] value of −0.26. The other half are old and metal-poor. These results suggest that M85 experienced a wet merging event about 4 Gyr ago, forming a significant population of star clusters. The strong rotational feature of the GC system can be explained by an off-center major merging.

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)

Context. At low redshift, early-type galaxies often exhibit a rising flux with decreasing wavelength in the 1000–2500 Å range, called “UV upturn”. The origin of this phenomenon is debated, and its evolution with redshift is poorly constrained. The observed GALEX FUV-NUV color can be used to probe the UV upturn approximately to redshift 0.5.Aim. We provide constraints on the existence of the UV upturn up to redshift ~0.4 in the brightest cluster galaxies (BCG) located behind the Virgo cluster, using data from the GUViCS survey.Methods. We estimate the GALEX far-UV (FUV) and near-UV (NUV) observed magnitudes for BCGs from the maxBCG catalog in the GUViCS fields. We increase the number of nonlocal galaxies identified as BCGs with GALEX photometry from a few tens of galaxies to 166 (64 when restricting this sample to relatively small error bars). We also estimate a central color within a 20 arcsec aperture. By using the r-band luminosity from the maxBCG catalog, we can separate blue FUV-NUV due to recent star formation and candidate upturn cases. We use Lick indices to verify their similarity to redshift 0 upturn cases.Results. We clearly detect a population of blue FUV-NUV BCGs in the redshift range 0.10–0.35, vastly improving the existing constraints at these epochs by increasing the number of galaxies studied, and by exploring a redshift range with no previous data (beyond 0.2), spanning one more Gyr in the past. These galaxies bring new constraints that can help distinguish between assumptions concerning the stellar populations causing the UV upturn phenomenon. The existence of a large number of UV upturns around redshift 0.25 favors the existence of a binary channel among the sources proposed in the literature.

LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449

We present intermediate-resolution (R$\sim$1000) spectra in the $\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large Binocular Telescope. We derived Lick indices in the optical and the CaII-triplet index in the near-infrared in order to infer the clusters' stellar population properties. The inferred cluster ages are typically older than $\sim$9 Gyr, although ages are derived with large uncertainties. The clusters exhibit intermediate metallicities, in the range $-1.2\lesssim$[Fe/H]$\lesssim-0.7$, and typically sub-solar [$\alpha/Fe$] ratios, with a peak at $\sim-0.4$. These properties suggest that i) during the first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic winds having possibly contributed to the expulsion of the $\alpha$-elements, and ii) globular clusters in NGC 4449 formed relatively "late", from a medium already enriched in the products of type Ia supernovae. The majority of clusters appear also under-abundant in CN compared to Milky Way halo globular clusters, perhaps because of the lack of a conspicuous N-enriched, second-generation of stars like that observed in Galactic globular clusters. Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside 2.88 kpc to be M($<$2.88 kpc)=$3.15^{+3.16}_{-0.75} \times 10^9~M_\odot$. We also report the serendipitous discovery of a planetary nebula within one of the targeted clusters, a rather rare event.