Marcio A. G. Maia

The Milky Way's Circular-velocity Curve between 4 and 14 kpc from APOGEE data

We measure the Milky Ways rotation curve over the Galactocentric range 4 kpc R 14 kpc from the first year of data from the Apache Point Observatory Galactic Evolution Experiment. We model the line-of-sight velocities of 3365 stars in 14 fields with b = 0? between 30? ? l ? 210? out to distances of 10 kpc using an axisymmetric kinematical model that includes a correction for the asymmetric drift of the warm tracer population (? R 35 km s?1). We determine the local value of the circular velocity to be Vc (R 0) = 218 ? 6 km s?1 and find that the rotation curve is approximately flat with a local derivative between ?3.0 km s?1 kpc?1 and 0.4 km s?1 kpc?1. We also measure the Suns position and velocity in the Galactocentric rest frame, finding the distance to the Galactic center to be 8 kpc 99 % confidence. We find an offset between the Suns rotational velocity and the local circular velocity of 26 ? 3 km s?1, which is larger than the locally measured solar motion of 12 km s?1. This larger offset reconciles our value for Vc with recent claims that Vc 240 km s?1. Combining our results with other data, we find that the Milky Ways dark-halo mass within the virial radius is ~8 ? 1011 M ?.

Ameliorating systematic uncertainties in the angular clustering of galaxies: a study using the SDSS-III

We investigate the effects of potential sources of systematic error on the angular and photometric redshift, zphot, distributions of a sample of redshift 0.4 0.5, the magnitude of the corrections we apply is greater than the statistical uncertainty in w(θ). The photometric redshift catalogue we produce will be made publicly available at http://portal.nersc.gov/project/boss/galaxy/photoz/.

The Southern Sky Redshift Survey

We report redshifts, magnitudes, and morphological classifications for 5369 galaxies with mB ≤ 15.5 and for 57 galaxies fainter than this limit, in two regions covering a total of 1.70 sr in the southern celestial hemisphere. The galaxy catalog is drawn primarily from the list of nonstellar objects identified in the Hubble Space Telescope Guide Star Catalog (GSC). The galaxies have positions accurate to ~1 and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes (mSSRS2) from the relation between instrumental GSC magnitudes and the photometry by Lauberts & Valentijn. From a comparison with CCD photometry, we find that our system is homogeneous across the sky and corresponds to magnitudes measured at the isophotal level ~26 mag arcsec-2. The precision of the radial velocities is ~40 km s-1, and the redshift survey is more than 99% complete to the mSSRS2 = 15.5 mag limit. This sample is in the direction opposite that of the CfA2; in combination the two surveys provide an important database for studies of the properties of galaxies and their large-scale distribution in the nearby universe.

The XMM Cluster Survey: optical analysis methodology and the first data release

The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters and trace the evolution of X-ray scaling relations. In this paper we present the first data release from the XMM Cluster Survey (XCS-DR1). This consists of 503 optically confirmed, serendipitously detected, X-ray clusters. Of these clusters, 256 are new to the literature and 357 are new X-ray discoveries. We present 463 clusters with a redshift estimate (0.06 1.0, including a new spectroscopically confirmed cluster at z= 1.01); (ii) 66 clusters with high TX (>5keV); (iii) 130 clusters/groups with low TX (X values in the Sloan Digital Sky Survey (SDSS) Stripe 82 co-add region; (v) 77 clusters with measured TX values in the Dark Energy Survey region; (vi) 40 clusters detected with sufficient counts to permit mass measurements (under the assumption of hydrostatic equilibrium); (vii) 104 clusters that can be used for applications such as the derivation of cosmological parameters and the measurement of cluster scaling relations. The X-ray analysis methodology used to construct and analyse the XCS-DR1 cluster sample has been presented in a companion paper, Lloyd-Davies et al.

The metallicity distribution functions of SEGUE G and K dwarfs: constraints for disk chemical evolution and formation

We present the metallicity distribution function (MDF) for 24,270xa0G and 16,847xa0Kxa0dwarfs at distances from 0.2 to 2.3xa0kpc from the Galactic plane, based on spectroscopy from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. This stellar sample is significantly larger in both number and volume than previous spectroscopic analyses, which were limited to the solar vicinity, making it ideal for comparison with local volume-limited samples and Galactic models. For the first time, we have corrected the MDF for the various observational biases introduced by the SEGUE target-selection strategy. SEGUE is particularly notable for its sample of Kxa0dwarfs, which are too faint to examine spectroscopically far from the solar neighborhood. The MDF of both spectral types becomes more metal-poor with increasing |Z|, which reflects the transition from a sample with small [α/Fe] values at small heights to one with enhanced [α/Fe] above 1xa0kpc. Comparison of our SEGUE distributions to those of two different Milky Way models reveals that both are more metal-rich than our observed distributions at all heights above the plane. Our unbiased observations of G and Kxa0dwarfs provide valuable constraints over the |Z|-height range of the Milky Way disk for chemical and dynamical Galaxy evolution models, previously only calibrated to the solar neighborhood, with particular utility for thin- and thick-disk formation models.

Bayesian distances and extinctions for giants observed by Kepler and APOGEE

We present a first determination of distances and extinctions for individual stars in the first release of the APOKASC catalogue, built from the joint efforts of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the Kepler Asteroseismic Science Consortium (KASC). Our method takes into account the spectroscopic constraints derived from the APOGEE Stellar Parameters and Chemical Abundances Pipeline, together with the asteroseismic parameters from KASC. These parameters are then employed to estimate intrinsic stellar properties, including absolute magnitudes, using the Bayesian tool PARAM. We then find the distance and extinction that best fit the observed photometry in SDSS, 2MASS, and WISE passbands. The first 1989 giants targeted by APOKASC are found at typical distances between 0.5 and 5 kpc, with individual uncertainties of just ~1.8 per cent. Our extinction estimates are systematically smaller than provided in the Kepler Input Catalogue and by the Schlegel, Finkbeiner and Davis maps. Distances to individual stars in the NGC 6791 and NGC 6819 star clusters agree to within their credible intervals. Comparison with the APOGEE red clump and SAGA catalogues provide another useful check, exhibiting agreement with our measurements to within a few percent. Overall, present methods seem to provide excellent distance and extinction determinations for the bulk of the APOKASC sample. Approximately one third of the stars present broad or multiple-peaked probability density functions and hence increased uncertainties. Uncertainties are expected to be reduced in future releases of the catalogue, when a larger fraction of the stars will have seismically-determined evolutionary status classifications.

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: the low redshift sample

We report on the small scale (0:5 < r < 40h 1 Mpc) clustering of 78895 massive (M 10 11:3 M ) galaxies at 0:2 < z < 0:4 from the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS), to be released as part of SDSS Data Release 9 (DR9). We describe the sample selection, basic properties of the galaxies, and caveats for working with the data. We calculate the real- and redshift-space two-point correlation functions of these galaxies, fit these measurements using Halo Occupation Distribution (HOD) modeling within dark matter cosmological simulations, and estimate the errors using mock catalogs. These galaxies lie in massive halos, with a mean halo mass of 5:2 10 13 h 1 M , a large scale bias of 2:0, and a satellite fraction of 12 2%. Thus,

The clustering of galaxies in the SDSS-III DR10 baryon oscillation spectroscopic survey: No detectable colour dependence of distance scale or growth rate measurements

We study the clustering of galaxies, as a function of their colour, from Data Release Ten (DR10) of the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillation Spectroscopic Survey. DR10 contains 540 505 galaxies with 0.43 < z < 0.7; from these we select 122 967 for a ‘Blue’ sample and 131 969 for a ‘Red’ sample based on k + e corrected (to z =0.55) r − i colours and i-band magnitudes. The samples are chosen such that both contain more than 100 000 galaxies, have similar redshift distributions and maximize the difference in clustering amplitude. The Red sample has a 40 per cent larger bias than the Blue (bRed/bBlue = 1.39 ± 0.04), implying that the Red galaxies occupy dark matter haloes with an average mass that is 0.5 log10 M⊙ greater. Spherically averaged measurements of the correlation function, ξ0, and the power spectrum are used to locate the position of the baryon acoustic oscillation (BAO) feature of both samples. Using ξ0, we obtain distance scales, relative to the distance of our reference Λ cold dark matter cosmology, of 1.010 ± 0.027 for the Red sample and 1.005 ± 0.031 for the Blue. After applying reconstruction, these measurements improve to 1.013 ± 0.020 for the Red sample and 1.008 ± 0.026 for the Blue. For each sample, measurements of ξ0 and the second multipole moment, ξ2, of the anisotropic correlation function are used to determine the rate of structure growth, parametrized by fσ8. We find fσ8,Red = 0.511 ± 0.083, fσ8, Blue = 0.509 ± 0.085 and fσ8, Cross = 0.423 ± 0.061 (from the cross-correlation between the Red and Blue samples). We use the covariance between the bias and growth measurements obtained from each sample and their cross-correlation to produce an optimally combined measurement of fσ8, comb = 0.443 ± 0.055. This result compares favourably to that of the full 0.43 < z < 0.7 sample (fσ8, full = 0.422 ± 0.051) despite the fact that, in total, we use less than half of the number of galaxies analysed in the full sample measurement. In no instance do we detect significant differences in distance scale or structure growth measurements obtained from the Blue and Red samples. Our results are consistent with theoretical predictions and our tests on mock samples, which predict that any colour-dependent systematic uncertainty on the measured BAO position is less than 0.5 per cent.

Do Observed Metallicity Gradients of Early-Type Galaxies Support a Hybrid Formation Scenario?*

We measure radial gradients of the Mg2 index in 15 E-E/S0 and 14 S0 galaxies. Our homogeneous data set covers a large range of internal stellar velocity dispersions (2.0 < log ? < 2.5) and Mg2 gradients [?Mg2/? log up to -0.14 mag dex-1]. We find for the first time a noticeable lower boundary in the relation between Mg2 gradient and ? along the full range of ?, which may be populated by galaxies predominantly formed by monolithic collapse. At high ?, galaxies showing flatter gradients could represent objects that suffered either important merging episodes or later gas accretion. These processes contribute to the flattening of the metallicity gradients, and their increasing importance could define the distribution of the objects above the boundary expected by the classical monolithic process. This result is in marked contrast to previous works, which found a correlation between ?Mg2/? log and ? confined to the low-mass galaxies, suggesting that only galaxies below some limiting ? were formed by collapse, whereas the massive ones were formed by mergers. We show observational evidence that a hybrid scenario could also arise among massive galaxies. Finally, we estimate ?[Z/H] from Mg2 and H? measurements and single stellar population models. The conclusions remain the same, indicating that the results cannot be ascribed to age effects on Mg2.

LINE STRENGTHS OF EARLY-TYPE GALAXIES*

In this paper we present measurements of velocity dispersions and Lick indices for 509 galaxies in the local universe, based on high signal-to-noise, long-slit spectra obtained with the 1.52 m ESO telescope at La Silla. The conversion of our measurements into the Lick/IDS system was carried out following the general prescription of Worthey & Ottaviani in 1997. Comparisons of our measurements with those of other authors show, in general, good agreement. We also examine the dependence between these indices (e.g., H?, Mg2, Fe5270, and NaD) and the central velocity dispersion (?0), and we find that they are consistent with those previously reported in the literature. Benefiting from the relatively large size of the sample, we are able to investigate the dependence of these relations on morphology and environment, here represented by the local galaxy density. We find that for metallic lines these relations show no significant dependence on environment or morphology, except in the case of NaD, which shows distinct behavior for E and S0. On the other hand, the H?-log ?0 shows a significant difference as a function of the local density of galaxies, which we interpret as being caused by the truncation of star formation in high-density environments. Comparing our results with those obtained by other authors, we find a few discrepancies, adding to the ongoing debate about the nature of these relations. Finally, we report that the scatter of the Mg indices versus ?0 relations correlates with H?, suggesting that age may contribute to the scatter. Furthermore, this scatter shows no significant dependence on morphology or environment. Our results are consistent with the currently popular downsizing model, where low-mass galaxies have an extended star-formation history, except for those located in high-density regions.