The chemical compositions of 10 new sub-DLAs and strong Lyman-limit systems at z≲ 1.5

We present chemical abundance measurements from medium-resolution observations of eight subdamped Lyα (sub-DLA) absorber and two strong Lyman-limit systems at   z ≲ 1.5  observed with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan II Clay telescope. These observations were taken as part of an ongoing project to determine abundances in   z _abs≲ 1.5  quasar absorption line systems focusing on sub-DLA systems. These observations increase the sample of Zn measurements in   z _abs≲ 1.5  sub-DLAs by ∼50 per cent. Lines of Mg  i , Mg  ii , Al  ii , Al  iii , Ca  ii , Mn  ii , Fe  ii and Zn  ii were detected and column densities were determined. Zn  ii , a relatively undepleted element and tracer of the gas-phase metallicity is detected in two of these systems, with  [Zn/H]=−0.05 ± 0.12  and  [Zn/H] > +0.86  . The latter one is however a weak system with   N _{H  I} < 18.8  , and therefore may need significant ionization corrections to the abundances. Fe  ii lines were detected in all systems, with an average Fe abundance of  〈[Fe/H]〉=−0.68  , higher than typical Fe abundances for DLA systems at these redshifts. This high mean [Fe/H] could be due to less depletion of Fe on to dust grains, or to higher abundances in these systems. We also discuss the relative abundances in these absorbers. The systems with high metallicity show high ratios of [Mn/Fe] and [Zn/Fe], as seen previously in another sub-DLA. These higher values of [Mn/Fe] could be a result of heavy depletion of Fe on to grains, unmixed gas, or an intrinsically non-solar abundance pattern. Based on cloudy modelling, we do not expect ionization effects to cause this phenomenon.     

The absolute magnitude of field metal-poor horizontal branch stars

Hipparcos satellite parallaxes for 22 metal-poor field horizontal branch stars with V ₀<9 are used to derive their absolute magnitude. The weighted mean value is M_V =+0.69±0.10 for an average metallicity of [Fe/H]=−1.41; a somewhat brighter average magnitude of M_V =+0.60±0.12 for an average metallicity of [Fe/H]=−1.51 is obtained by eliminating HD 17072, which might be on the first ascent of the giant branch rather than on the horizontal branch. The present values agree with the determinations based on proper motions and application of the Baade–Wesselink method to field RR Lyraes; they are 0.1–0.2 mag fainter than those based on calibration of cluster distances obtained by using local subdwarfs and on alternative distance calibrators for the Large Magellanic Cloud (LMC). The possibility that there is a real difference between the luminosity of the horizontal branch for clusters and the field is briefly commented on.     

Harmonizing the RR Lyrae and clump distance scales – stretching the short distance scale to intermediate ranges?

I explore the consequences of making the RR Lyrae and clump giant distance scales consistent in the solar neighbourhood, Galactic bulge and Large Magellanic Cloud (LMC). I employ two major assumptions: (i) that the absolute magnitude–metallicity, M _V (RR)–[Fe/H], relation for RR Lyrae stars is universal, and (ii) that absolute I magnitudes of clump giants, M _I (RC), in Baade's Window are known (e.g. can be inferred from the local Hipparcos -based calibration or theoretical modelling). A comparison between the solar neighbourhood and Baade's Window sets M _V (RR) at [Fe/H]=−1.6 in the range (0.59±0.05, 0.70±0.05), somewhat brighter than the statistical parallax solution. More luminous RR Lyrae stars imply younger globular clusters, which would be in better agreement with the conclusions from the currently favoured stellar evolution and cosmological models. A comparison between Baade's Window and the LMC sets M ^LMC(RC) _I in the range (−0.33±0.09,−0.53±0.09). The distance modulus to the LMC is μ ^LMC∈(18.24±0.08,18.44±0.07). Unlike M ^LMC(RC) _I , this range in μ ^LMC does not depend on the adopted value of the dereddened LMC clump magnitude, I ^LMC(RC)₀. I argue that the currently available information is insufficient to select the correct distance scale with high confidence.     

The first detection of cobalt in a damped Lyman alpha system

The study of elemental abundances in damped Lyman alpha systems (DLAs) at high redshift represents one of our best opportunities to probe galaxy formation and chemical evolution at early times. By coupling measurements made in high- z DLAs with our knowledge of abundances determined locally and with nucleosynthetic models, we can start to piece together the star formation histories of these galaxies. Here, we discuss the clues to galactic chemical evolution that may be gleaned from studying the abundance of Co in DLAs. We present high resolution echelle spectra of two quasi-stellar objects (QSOs), Q2206−199 and Q1223+17, both already known to exhibit intervening damped systems. These observations have resulted in the first ever detection of Co at high redshift, associated with the z _abs=1.92 DLA in the sightline towards Q2206−199. We find that the abundance of Co is approximately 1/4 solar and that there is a clear overabundance relative to iron, [Co/Fe]=+0.31±0.05 . From the abundance of Zn, we determine that this is a relatively metal-rich DLA, with a metallicity of approximately 1/3 Z_⊙ . Therefore, this first detection of Co is similar to the marked overabundance relative to Fe seen in Galactic bulge and thick-disc stars.     

The red giant branch tip and bump of the Leo II dwarf spheroidal galaxy

We present V and I photometry of a  9.4 × 9.4 arcmin²  field centred on the dwarf spheroidal galaxy Leo II. The tip of the red giant branch (TRGB) is identified at   I ^TRGB= 17.83 ± 0.03  and adopting  〈[M/H]〉=−1.53 ± 0.2  from the comparison of RGB stars with Galactic templates, we obtain a distance modulus  ( m − M )₀= 21.84 ± 0.13  , corresponding to a distance   D = 233 ± 15 kpc  . Two significant bumps have been detected in the luminosity function of the RGB. The fainter bump (B1, at   V = 21.76 ± 0.05  ) is the RGB bump of the dominant stellar population while the actual nature of the brightest one (B2, at   V = 21.35 ± 0.05  ) cannot be firmly assessed on the basis of the available data; it may be due to the asymptotic giant branch clump of the main population or it may be a secondary RGB bump. The luminosity of the main RGB bump (B1) suggests that the majority of RGB stars in Leo II belong to a population that is ≳4 Gyr younger than the classical Galactic globular clusters. The stars belonging to the He-burning red clump are shown to be significantly more centrally concentrated than RR Lyrae and blue horizontal branch stars, probing the existence of an age/metallicity radial gradient in this remote dwarf spheroidal.     

Analysis and calibration of Ca ii triplet spectroscopy of red giant branch stars from VLT/FLAMES observations

We demonstrate that low-resolution Ca  ii triplet (CaT) spectroscopic estimates of the overall metallicity ([Fe/H]) of individual red giant branch (RGB) stars in two nearby dwarf spheroidal galaxies (dSphs) agree to ±0.1–0.2 dex with detailed high-resolution spectroscopic determinations for the same stars over the range  −2.5 < [Fe/H] < −0.5  . For this study, we used a sample of 129 stars observed in low- and high-resolution modes with VLT/FLAMES in the Sculptor and Fornax dSphs. We also present the data-reduction steps we used in our low-resolution analysis and show that the typical accuracy of our velocity and CaT [Fe/H] measurement is ∼2 km s⁻¹ and 0.1 dex, respectively. We conclude that CaT–[Fe/H] relations calibrated on globular clusters can be applied with confidence to RGB stars in composite stellar populations over the range  −2.5 < [Fe/H] < −0.5  .     

Ages and metallicities of globular clusters in NGC 4472

We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately −1.6≤[Fe/H]≤0 dex. There is evidence of a radial metallicity gradient in the globular cluster system which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters has an age of 14.5±4 Gyr and the metal-rich population is 13.8±6 Gyr old. Monte Carlo simulations indicate that the globular cluster populations present in these data are older than 6 Gyr at the 95 per cent confidence level. We find that within the uncertainties, the globular clusters are old and coeval, implying that the bimodality seen in the broadband colours primarily reflects metallicity and not age differences.     

Self-enrichment by asymptotic giant branch stars in globular clusters: comparison between intermediate and high metallicities

We present theoretical evolutionary sequences of intermediate-mass stars  ( M = 3 − 6.5 M_⊙)  with metallicity   Z = 0.004  . Our goal is to test whether the self-enrichment scenario by massive asymptotic giant branch stars may work for the high-metallicity globular clusters, after previous works by the same group showed that the theoretical yields by this class of objects can reproduce the observed trends among the abundances of some elements, namely the O–Al and O–Na anticorrelations, at intermediate metallicities, i.e.  [Fe/H]=−1.3  . We find that the increase in the metallicity favours only a modest decrease of the luminosity and the temperature at the bottom of the envelope for the same core mass, and also the efficiency of the third dredge-up is scarcely altered. On the contrary, differences are found in the yields, due to the different impact that processes with the same efficiency have on the overall abundance of envelopes with different metallicities. We expect the same qualitative patterns as in the intermediate-metallicity case, but the slopes of some of the relationships among the abundances of some elements are different. We compare the sodium–oxygen anticorrelation for clusters of intermediate metallicity ( Z ≈ 10⁻³) and clusters of metallicity large as in these new models. Although the observational data are still too scarce, the models are consistent with the observed trends, provided that only stars of   M ≳ 5 M_⊙  contribute to self-enrichment.     

The star formation histories of two northern LMC fields

Ground-based UBV photometry of two fields in the northern disc of the Large Magellanic Cloud (LMC) is presented. A distance modulus of ( m − M )₀=18.41±0.04 and an extinction of A _V =0.30±0.05 have been calculated for these fields. The measurable star formation history of the LMC began no more than 12 Gyr ago with a strong star‐forming episode with [Fe/H]=−1.63±0.10 that accounted for approximately half (by mass) of the total star formation of the LMC in the first 3 Gyr. The data do not give accurate star formation rates during intermediate ages, but there appears to have been a recent increase in the star formation rate in these fields, beginning approximately 2.5 Gyr ago, with the current metallicity in the region being [Fe/H]=−0.38±0.10. The two fields have had very similar star formation rates until 200 Myr ago, at which point one shows a large increase.     

Magnetically collimated jets with high mass flux

We present HST /WFPC2 observations of UGC 4483, an irregular galaxy in the M81/NGC 2403 complex. Stellar photometry was carried out with HSTphot, and is complete to V ≃26.0 and I ≃24.7. We measure the red giant branch tip at I =23.56±0.10, and calculate a distance modulus of μ ₀=27.53±0.12 (corresponding to a distance of 3.2±0.2 Mpc), placing UGC 4483 within the NGC 2403 subgroup. We were able to measure properties of a previously known young star cluster in UGC 4483, finding integrated magnitudes of V =18.66±0.21 and I =18.54±0.10 for the stellar contribution (integrated light minus H α and [O  iii ] contribution), corresponding to an age of ∼10–15 Myr and an initial mass of ∼10⁴ M_⊙. This is consistent with the properties of the cluster's brightest stars, which were resolved in the data for the first time. Finally, a numerical analysis of the galaxy's stellar content yields a roughly constant star formation rate of 1.3×10⁻³ M_⊙ yr⁻¹ and mean metallicity of [Fe/H]=−1.3 dex from 15 Gyr ago to the present.     

Re-identification of G35.6−0.4 as a supernova remnant

G35.6−0.4 is an extended radio source in the Galactic plane which has previously been identified as either a supernova remnant or an H  ii region. Observations from the Very Large Array Galactic Plane Survey at 1.4 GHz with a resolution of 1 arcmin allow the extent of G35.6−0.4 to be defined for the first time. Comparison with other radio survey observations show that this source has a non-thermal spectral index, with   S ∝ν^{−0.47±0.07}  . G35.6−0.4 does not have obvious associated infrared emission, so it is identified as a Galactic supernova remnant, not an H  ii region. It is  ≈15 × 11 arcmin²  in extent, showing partial limb brightening.     

Intermediate-metallicity, high-velocity stars and Galactic chemical evolution

High signal-to-noise ratio spectra were obtained of 10 high-proper-motion stars having  −1 ≲[Fe/H] < 0  , and a comparable number of disc stars. All but two of the high-proper-motion stars were confirmed to have  [Fe/H] > −1.0  , some approaching solar metallicity, but, even so, earlier measurements overestimated the metallicities and velocities of some of these stars. Models of stellar populations were used to assign membership probabilities to the Galactic components to which the high-velocity stars might belong. Many were found to be more probably thick-disc than halo objects, despite their large space motions, and two might be associated with the inner Galaxy. It may be necessary to reassess contamination of previous halo samples, such as those used to define the metallicity distribution, to account for contamination by high-velocity thick-disc stars, and to consider possible subcomponents of the halo.
The change in [α/Fe] ratios at  [Fe/H]≃−1.0  is often used to constrain the degree and timing of Type Ia supernova nucleosynthesis in Galactic chemical-evolution models. [Ti/Fe] values were measured for eight of the high-velocity stars. Both high- and low-[Ti/Fe] halo stars exist; likewise high- and low-[Ti/Fe] thick-disc stars exist. We conclude that the [Ti/Fe]'break' is not well defined for a given population; nor is there a simple, continuous evolutionary sequence through the break. Implications for the interpretation of the [α/Fe] break in terms of SN Ia time-scales and progenitors are discussed. The range of [Ti/Fe] found for high -velocity (low rotation) thick-disc stars contrasts with that for the low -velocity (high rotation) thick-disc sample studied by Prochaska et al.     

Metallicities and ages of stellar populations at a high Galactic latitude field

We present an analysis of UBVRI data from the selected area SA 141. By applying recalibrated methods of measuring ultraviolet excess (UVX), we approximate abundances and absolute magnitudes for 368 stars over 1.3 deg² out to distances over 10 kpc. With the density distribution constrained from our previous photometric parallax investigations and with sufficient accounting for the metallicity bias in the UVX method, we are able to compare the vertical abundance distribution to those measured in previous studies. We find that the abundance distribution has an underlying uniform component consistent with previous spectroscopic results that posit a monometallic thick disc and halo with abundances of  [Fe/H]=−0.8  and −1.4, respectively. However, there are a number of outlying data points that may indicate contamination by more metal-rich halo streams. The absence of vertical abundance gradients in the Galactic stellar populations and the possible presence of interloping halo streams would be consistent with expectations from merger models of Galaxy formation. We find that our UVX method has limited sensitivity in exploring the metallicity distribution of the distant Galactic halo, owing to the poor constraint on the UBV properties of very metal-poor stars. The derivation of metallicities from broad-band UBV photometry remains fundamentally sound for the exploration of the halo but is in need of both improved calibration and superior data.     

Clues for the origin of the fundamental metallicity relations – I. The hierarchical building up of the structure

We analyse the evolutionary history of galaxies formed in a hierarchical scenario consistent with the concordance Lambda cold dark matter (ΛCDM) model focusing on the study of the relation between their chemical and dynamical properties. Our simulations consistently describe the formation of the structure and its chemical enrichment within a cosmological context. Our results indicate that the luminosity–metallicity and the stellar mass–metallicity (LZR and MZR) relations are naturally generated in a hierarchical scenario. Both relations are found to evolve with redshift. In the case of the MZR, the estimated evolution is weaker than that deduced from observational works by approximately 0.10 dex. We also determine a characteristic stellar mass, M _c≈ 3 × 10¹⁰ M_⊙, which segregates the simulated galaxy population into two distinctive groups and which remains unchanged since z ∼ 3, with a very weak evolution of its metallicity content. The value and role played by M _c is consistent with the characteristic mass estimated from the SDSS galaxy survey by Kauffmann et al. Our findings suggest that systems with stellar masses smaller than M _c are responsible for the evolution of this relation at least from z ≈ 3. Larger systems are stellar dominated and have formed more than 50 per cent of their stars at   z ≥ 2  , showing very weak evolution since this epoch. We also found bimodal metallicity and age distributions from z ∼ 3, which reflects the existence of two different galaxy populations. Although SN feedback may affect the properties of galaxies and help to shape the MZR, it is unlikely that it will significantly modify M _c since, from   z = 3  this stellar mass is found in systems with circular velocities larger than 100 km s⁻¹.     

Towards the absolute planes: a new calibration of the bolometric corrections and temperature scales for Population II giants

We present new determinations of bolometric corrections and effective temperature scales as a function of infrared optical colours, using a large data base of photometric observations of about 6500 Population II giants in Galactic globular clusters (GGCs), covering a wide range in metallicity (−2.0 < [Fe/H] < 0.0).   New relations for BC _K versus ( V  −  K ) , ( J  −  K ) and BC _V versus ( B  −  V ), ( V  −  I ), ( V  −  J ), and new calibrations for T _eff, using both an empirical relation and model atmospheres, are provided.   Moreover, an empirical relation to derive the R parameter of the infrared flux method as a function of the stellar temperature is also presented.     

Intermediate-age Galactic open clusters: fundamental parameters of NGC 2627

Charge-coupled device (CCD) photometry in the Johnson V , Kron–Cousins I and Washington CMT ₁ systems is presented in the field of the poorly known open cluster NGC 2627. Four independent Washington abundance indices yield a mean cluster metallicity of  [Fe/H]=−0.12 ± 0.08  , which is compatible with the existence of a radial gradient in the Galactic disc. The resultant colour–magnitude diagrams indicate that the cluster is an intermediate-age object of 1.4 Gyr. Based on the best fits of the Geneva group's isochrones to the ( V , V − I ) and  ( T ₁, C − T ₁)  diagrams, we estimate   E ( V − I ) = 0.25 ± 0.05  and   V − M_V = 11.80 ± 0.25  for  log  t = 9.15  , and   E ( C − T ₁) = 0.23 ± 0.07  and   T ₁− M _{T 1}= 11.85 ± 0.25  for  log  t = 9.10  , respectively, assuming solar metal content. The derived reddening value   E ( C − T ₁)  implies   E ( B − V ) = 0.12 ± 0.07  and a distance from the Sun of  2.0 ± 0.4 kpc  . Using the WEBDA data base and the available literature, we re-examined the overall properties of all the open clusters with ages between 0.6 and 2.5 Gyr. We identified peaks of cluster formation at 0.7–0.8, 1.0–1.1, 1.6–1.7 and 2.0–2.1 Gyr, separated by relative quiescent epochs of ∼0.2–0.3 Gyr. We also estimated a radial abundance gradient of  −0.08 ± 0.02  , which is consistent with the most recent determinations for the Galactic disc, but no clear evidence for a gradient perpendicular to the Galactic plane is found.     

The Sagittarius Dwarf Galaxy Survey (SDGS) – II. The stellar content and constraints on the star formation history

A detailed study of the star formation history of the Sagittarius dwarf spheroidal galaxy is performed through the analysis of data from the Sagittarius Dwarf Galaxy Survey (SDGS). Accurate statistical decontamination of the SDGS colour–magnitude diagrams (CMDs) allows us to obtain many useful constraints on the age and metal content of the Sgr stellar populations in three different regions of the galaxy.
A coarse metallicity distribution of Sgr stars is derived, ranging from [Fe/H]∼−2.0 to [Fe/H]∼−0.7, the upper limit being somewhat higher in the central region of the galaxy. A qualitative global fit to all the observed CMD features is attempted, and a general scheme for the star formation history of the Sgr dSph is derived. According to this scheme, star formation began at a very early time from a low metal content interstellar medium and lasted for several  Gyr, coupled with progressive chemical enrichment. The star formation rate (SFR) had a peak from 8 to 10  Gyr ago, when the mean metallicity was in the range −1.3≤[Fe/H]≤−0.7. After that maximum, the SFR rapidly decreased and a very low rate of star formation took place until ∼1–0.5  Gyr ago.     

A near-infrared and optical photometric study of the Sculptor dwarf spheroidal galaxy: implications for the metallicity spread

The Sculptor dwarf spheroidal galaxy has a giant branch with a significant spread in colour, symptomatic of an intrinsic age–metallicity spread. We present here a detailed study of the Sculptor giant branch and horizontal branch (HB) morphology, combining new near-infrared photometry from the Cambridge Infrared Survey Instrument (CIRSI), with optical data from the European Southern Observatory Wide Field Imager. For a Sculptor-like old and generally metal-poor system, the position of red giant branch (RGB) and asymptotic giant branch (AGB) stars on the colour–magnitude diagram (CMD) is mainly metallicity dependent. The advantage of using optical–near-infrared colours is that the position of the RGB locus is much more sensitive to metallicity than with optical colours alone. In contrast the HB morphology is strongly dependent on both metallicity and age. Therefore a detailed study of both the RGB in optical–near-infrared colours and the HB can help break the age–metallicity degeneracy. Our measured photometric width of the Sculptor giant branch corresponds to a range in metallicity of 0.75 dex. We detect the RGB and AGB bumps in both the near-infrared and the optical luminosity functions, and derive from them a mean metallicity of  [M/H]=−1.3 ± 0.1  . From isochrone fitting we derive a mean metallicity of  [Fe/H]=−1.42  with a dispersion of 0.2 dex. These photometric estimators are for the first time consistent with individual metallicity measurements derived from spectroscopic observations. No spatial gradient is detected in the RGB morphology within a radius of 13 arcmin, twice the core radius. On the other hand, a significant gradient is observed in the HB morphology index, confirming the 'second parameter problem' present in this galaxy. These observations are consistent with an early extended period of star formation continuing in time for a few Gyr.     

Metallicity measurements using atomic lines in M and K dwarf stars

We report the first survey of chemical abundances in M and K dwarf stars using atomic absorption lines in high-resolution spectra. We have measured Fe and Ti abundances in 35 M and K dwarf stars using equivalent widths measured from  λ/Δλ≈ 33 000  spectra. Our analysis takes advantage of recent improvements in model atmospheres of low-temperature dwarf stars. The stars have temperatures between 3300 and 4700 K, with most cooler than 4100 K. They cover an iron abundance range of  −2.44 < [Fe/H] < +0.16  . Our measurements show [Ti/Fe] decreasing with increasing [Fe/H], a trend similar to that measured for warmer stars, where abundance analysis techniques have been tested more thoroughly. This study is a step towards the observational calibration of procedures to estimate the metallicity of low-mass dwarf stars using photometric and low-resolution spectral indices.     

Pulsational MV versus [Fe/H] relation(s) for globular cluster RR Lyrae variables

We use the results from recent computations of updated non-linear convective pulsating models to constrain the distance modulus of Galactic globular clusters through the observed periods of first-overtone (RR _c ) pulsators. The resulting relation between the mean absolute magnitude of RR Lyrae stars 〈 M _V (RR)〉 and the heavy element content [Fe/H] appears well in the range of several previous empirical calibrations, but with a non-linear dependence on [Fe/H] so that the slope of the relation increases when moving towards larger metallicities. On this ground, our results suggest that metal-poor ([Fe/H]<−1.5) and metal-rich ([Fe/H]>−1.5) variables follow two different linear 〈 M _V (RR)〉−[Fe/H] relations. Application to RR Lyrae stars in the metal-poor globular clusters of the Large Magellanic Cloud (LMC) provides an LMC distance modulus of the order of 18.6 mag, thus supporting the 'long' distance scale. The comparison with recent predictions based on updated stellar evolution theory is briefly presented and discussed.