Showing papers by "Mike Irwin published in 2014"
University of Hertfordshire1, University of Cambridge2, University of Graz3, University of Warwick4, Radboud University Nijmegen5, University College London6, Spanish National Research Council7, Harvard University8, University of Valencia9, Macquarie University10, University of Southampton11, University of Bristol12, University of Exeter13, Imperial College London14, Armagh Observatory15, European Southern Observatory16, University of Manchester17
TL;DR: The VST Photometric HSurvey of the Southern Galactic Plane and Bulge (VPHAS+) as mentioned in this paper is a survey of the southern Milky Way in u,g,r,i and h 1 arcsec angular resolution.
Abstract: The VST Photometric HSurvey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u,g,r,i and Hat �1 arcsec angular resolution. Its footprint spans the Galactic latitude range 5 o < b < +5 o at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes ±10 ◦ bring in much of the Galactic Bulge. This ESO public sur- vey, begun on 28th December 2011, reaches down to �20th magnitude (10�) and will provide single-epoch digital optical photometry for �300 million stars. The observing strategy and data pipelining is described, and an appraisal of the segmented narrow- band Hfilter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u g), (g r), (r i) and (r H�) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u g,g r) and (r H�,r i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VST/OmegaCam combination used by this survey is a per- fect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources.
241 citations
European Southern Observatory1, Uppsala University2, Max Planck Society3, INAF4, Université libre de Bruxelles5, Instituto Politécnico Nacional6, Lund University7, University of Concepción8, Pontifical Catholic University of Chile9, Millennium Institute10, Heidelberg University11, University of Porto12, Complutense University of Madrid13, Vilnius University14, Leibniz Institute for Astrophysics Potsdam15, University of Cambridge16, University of La Laguna17, Spanish National Research Council18, Centre national de la recherche scientifique19, Paris Diderot University20, University of Padua21, University of Bologna22, Indiana University23, Massachusetts Institute of Technology24, University of Catania25, University of Liège26, University of Florence27, Australian National University28, University of Hertfordshire29, University of Edinburgh30, Keele University31, University of Alicante32, European Space Research and Technology Centre33, Royal Observatory of Belgium34, Valparaiso University35
TL;DR: In this article, the Gaia-ESO Public Spectroscopic Survey is using FLAMES at the VLT to obtain high-quality medium-resolution Giraffe spectra for about 10(5) stars and high-resolution UVES spectra of about 5000 stars.
Abstract: Context. The ongoing Gaia-ESO Public Spectroscopic Survey is using FLAMES at the VLT to obtain high-quality medium-resolution Giraffe spectra for about 10(5) stars and high-resolution UVES spectra for about 5000 stars. With UVES, the Survey has already observed 1447 FGK-type stars. Aims. These UVES spectra are analyzed in parallel by several state-of-the-art methodologies. Our aim is to present how these analyses were implemented, to discuss their results, and to describe how a final recommended parameter scale is defined. We also discuss the precision (method-to-method dispersion) and accuracy (biases with respect to the reference values) of the final parameters. These results are part of the Gaia-ESO second internal release and will be part of its first public release of advanced data products. Methods. The final parameter scale is tied to the scale defined by the Gaia benchmark stars, a set of stars with fundamental atmospheric parameters. In addition, a set of open and globular clusters is used to evaluate the physical soundness of the results. Each of the implemented methodologies is judged against the benchmark stars to define weights in three different regions of the parameter space. The final recommended results are the weighted medians of those from the individual methods. Results. The recommended results successfully reproduce the atmospheric parameters of the benchmark stars and the expected T-eff-log g relation of the calibrating clusters. Atmospheric parameters and abundances have been determined for 1301 FGK-type stars observed with UVES. The median of the method-to-method dispersion of the atmospheric parameters is 55K for T-eff, 0.13dex for log g and 0.07 dex for [Fe/H]. Systematic biases are estimated to be between 50-100 K for T-eff, 0.10-0.25 dex for log g and 0.05-0.10 dex for [Fe/H]. Abundances for 24 elements were derived: C, N, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, Nd, and Eu. The typical method-to-method dispersion of the abundances varies between 0.10 and 0.20 dex. Conclusions. The Gaia-ESO sample of high-resolution spectra of FGK-type stars will be among the largest of its kind analyzed in a homogeneous way. The extensive list of elemental abundances derived in these stars will enable significant advances in the areas of stellar evolution and Milky Way formation and evolution.
222 citations
TL;DR: In this article, the path of the Sagittarius (Sgr) stream across the sky in Sloan Digital Sky Survey data is followed using a variety of stellar tracers, including blue horizontal branch stars, main-sequence turn-off stars and red giants.
Abstract: Using a variety of stellar tracers - blue horizontal branch stars, main-sequence turn-off stars and red giants - we follow the path of the Sagittarius (Sgr) stream across the sky in Sloan Digital Sky Survey data. Our study presents new Sgr debris detections, accurate distances and line-of-sight velocities that together help to shed new light on the puzzle of the Sgr tails. For both the leading and the trailing tails, we trace the points of their maximal extent, or apocentric distances, and find that they lie at R-L = 47.8 +/- 0.5 kpc and R-T = 102.5 +/- 2.5 kpc, respectively. The angular difference between the apocentres is 93.degrees 2 +/- 3.degrees 5, which is smaller than predicted for logarithmic haloes. Such differential orbital precession can be made consistent with models of the Milky Way in which the dark matter density falls more quickly with radius. However, currently, no existing Sgr disruption simulation can explain the entirety of the observational data. Based on its position and radial velocity, we show that the unusually large globular cluster NGC 2419 can be associated with the Sgr trailing stream. We measure the precession of the orbital plane of the Sgr debris in the Milky Way potential and show that, surprisingly, Sgr debris in the primary (brighter) tails evolves differently from the secondary (fainter) tails, both in the north and the south.
221 citations
University of Hertfordshire1, University of Cambridge2, University of Graz3, Radboud University Nijmegen4, Spanish National Research Council5, University of La Laguna6, Naresuan University7, University College London8, University of Warwick9, Harvard University10, University of Valencia11, University of Manchester12, University of Exeter13, University of Southampton14, Cornell University15, Australian Astronomical Observatory16, Macquarie University17, Catholic University of the North18, University of Guadalajara19, Max Planck Society20, Imperial College London21, Armagh Observatory22
TL;DR: In this article, the authors present the first quality-controlled and globally calibrated source catalogue derived from the Northern Galactic Plane (IPHAS) survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint.
Abstract: The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800 deg2 imaging survey covering Galactic latitudes |b| < 5° and longitudes l = 30°–215° in the r, i, and Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec pixel−1) and to a mean 5σ depth of 21.2 (r), 20.0 (i), and 20.3 (Hα) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (root mean square) and recommend a series of quality criteria to select accurate data from the catalogue. Finally, we demonstrate the ability of the catalogue's unique (r − Hα, r − i) diagram to (i) characterize stellar populations and extinction regimes towards different Galactic sightlines and (ii) select and quantify Hα emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys.
175 citations
TL;DR: An overview of the 4MOST systems: optomechanical, control, data management and operations concepts; and initial performance estimates are provided.
Abstract: The 4MOST([1]) instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the ESO VISTA telescope designed to perform a massive (initially >25x10(6) spectra in 5 years) combined all-sky public survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of galaxies, X-ray AGN/galaxy evolution to z similar to 5, Galactic X-ray sources and resolving the Galactic edge; Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of similar to 1600 targets at R similar to 5,000 from 390-900nm and similar to 800 targets at R>18,000 in three channels between similar to 395-675nm (channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of similar to 4.1 degrees2. The initial 5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: opto-mechanical, control, data management and operations concepts; and initial performance estimates.
137 citations
TL;DR: In this article, the discovery of a new Galactic companion found in data from the ESO VST ATLAS survey, and followed up with deep imaging on the 4m William Herschel Telescope.
Abstract: We announce the discovery of a new Galactic companion found in data from the ESO VST ATLAS survey, and followed up with deep imaging on the 4-m William Herschel Telescope. The satellite is located in the constellation of Crater (the Cup) at a distance of ∼170 kpc. Its half-light radius is rh = 30 pc and its luminosity is MV = −5.5. The bulk of its stellar population is old and metal poor. We would probably have classified the newly discovered satellite as an extended globular cluster were it not for the presence of a handful of blue loop stars and a sparsely populated red clump. The existence of the core helium burning population implies that star formation occurred in Crater perhaps as recently as 400 Myr ago. No globular cluster has ever accomplished the feat of prolonging its star formation by several Gyr. Therefore, if our hypothesis that the blue bright stars in Crater are blue loop giants is correct, the new satellite should be classified as a dwarf galaxy with unusual properties. Note that only 10°to the north of Crater, two ultrafaint galaxies Leo IV and Leo V orbit the Galaxy at approximately the same distance. This hints that all three satellites may once have been closely associated before falling together into the Milky Way halo.
134 citations
University of Edinburgh1, Australian National University2, Heidelberg University3, Herzberg Institute of Astrophysics4, University of Cambridge5, University of Leicester6, University of Massachusetts Amherst7, Max Planck Society8, University of Sydney9, Dalhousie University10, University of Victoria11
TL;DR: In this paper, a detailed kinematic analysis of the outer halo globular cluster system of the Andromeda galaxy (M31) is presented, based on a set of new spectroscopic observations for 78 clusters lying at projected distances between Rproj � 20-140 kpc from the M31 center.
Abstract: We present a detailed kinematic analysis of the outer halo globular cluster system of the Andromeda galaxy (M31). Our basis for this is a set of new spectroscopic observations for 78 clusters lying at projected distances between Rproj � 20-140 kpc from the M31 centre. These are largely drawn from the recent PAndAS globular cluster catalogue; 63 of our targets have no previous velocity data. Via a Bayesian maximum likelihood analysis we find that globular clusters with Rproj > 30 kpc exhibit coherent rotation around the minor optical axis of M31, in the same direction as more centrallylocated globular clusters, but with a smaller amplitude of 86±17 km s −1 . There is also evidence that the velocity dispersion of the outer halo globular cluster system decreases as a function of projected distance from the M31 centre, and that this relation can be well described by a power law of index � 0.5. The velocity dispersion profile of the outer halo globular clusters is quite similar to that of the halo stars, at least out to the radius up to which there is available information on the stellar kinematics. We detect and discuss various velocity correlations amongst subgroups of globular clusters that lie on stellar debris streams in the M31 halo. Many of these subgroups are dynamically cold, exhibiting internal velocity dispersions consistent with zero. Simple Monte Carlo experiments imply that such configurations are unlikely to form by chance, adding weight to the notion that a significant fraction of the outer halo globular clusters in M31 have been accreted alongside their parent dwarf galaxies. We also estimate the M31 mass within 200 kpc via the Tracer Mass Estimator (TME), finding (1.2 1.6) ± 0.2 × 10 12 M⊙. This quantity is subject to additional systematic effects due to various limitations of the data, and assumptions built in into the TME. Finally, we discuss our results in the context of formation scenarios for the M31 halo.
109 citations
TL;DR: In this paper, the authors report the discovery of 59 globular clusters (GCs) and two candidate GCs in a search of the halo of M31, primarily via visual inspection of CHFT/MegaCam imagery from the Pan-Andromeda Archaeological Survey (PAndAS).
Abstract: We report the discovery of 59 globular clusters (GCs) and two candidate GCs in a search of the halo of M31, primarily via visual inspection of CHFT/MegaCam imagery from the Pan-Andromeda Archaeological Survey (PAndAS). The superior quality of these data also allow us to check the classification of remote objects in the Revised Bologna Catalogue (RBC), plus a subset of GC candidates drawn from SDSS imaging. We identify three additional new GCs from the RBC, and confirm the GC nature of 11 SDSS objects (8 of which appear independently in our remote halo catalogue); the remaining 188 candidates across both lists are either foreground stars or background galaxies. Our new catalogue represents the first uniform census of GCs across the M31 halo - we find clusters to the limit of the PAndAS survey area at projected radii of up to R_proj ~ 150 kpc. Tests using artificial clusters reveal that detection incompleteness cuts in at luminosities below M_V = -6.0; our 50% completeness limit is M_V ~ -4.1. We construct a uniform set of PAndAS photometric measurements for all known GCs outside R_proj = 25$ kpc, and any new GCs within this radius. With these data we update results from Huxor et al. (2011), investigating the luminosity function (LF), colours and effective radii of M31 GCs with a particular focus on the remote halo. We find that the GCLF is clearly bimodal in the outer halo (R_proj > 30 kpc), with the secondary peak at M_V ~ -5.5. We argue that the GCs in this peak have most likely been accreted along with their host dwarf galaxies. Notwithstanding, we also find, as in previous surveys, a substantial number of GCs with above-average luminosity in the outer M31 halo - a population with no clear counterpart in the Milky Way.
107 citations
Franche Comté Électronique Mécanique Thermique et Optique Sciences et Technologies1, University of California, Los Angeles2, Max Planck Society3, University of Massachusetts Amherst4, University of Cambridge5, University of Sydney6, Herzberg Institute of Astrophysics7, Institut d'Astrophysique de Paris8, Dalhousie University9, University of Edinburgh10, Texas Tech University11, Australian National University12, University of Leicester13
TL;DR: In this article, the authors reveal the highly structured nature of the Milky Way stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars.
Abstract: We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ∼5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ∼17 kpc. With a surface brightness of Σ {sub V} ∼ 32-32.5 mag arcsec{sup –2}, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion thatmore » is lower than 7.1 km s{sup –1} at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.« less
102 citations
Max Planck Society1, Dalhousie University2, University of California, Los Angeles3, University of Sydney4, Spanish National Research Council5, Graduate University for Advanced Studies6, Subaru7, University of Edinburgh8, Heidelberg University9, Herzberg Institute of Astrophysics10, University of Leicester11
TL;DR: In this article, the authors investigate the claim that all dwarf spheroidal galaxies reside within halos that share a common, universal mass profile as has been derived for dSphs of the galaxy.
Abstract: We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile cannot be found to fit all of the observations well. Further, the best-fit dark matter density profile measured solely for the Milky Way dSphs is marginally discrepant with that of the Andromeda dSphs (at just beyond the 1? level), where a profile with lower maximum circular velocity, and hence mass, is preferred. The agreement is significantly better when three extreme Andromeda outliers, And XIX, XXI, and XXV, all of which have large half-light radii ( 600 pc) and low-velocity dispersions (? v < 5 km s?1), are omitted from the sample. We argue that the unusual properties of these outliers are likely caused by tidal interactions with the host galaxy.
93 citations
INAF1, European Southern Observatory2, University of Cambridge3, Australian National University4, Paris Diderot University5, University of Hertfordshire6, Lund University7, University of Edinburgh8, Keele University9, University of Alicante10, European Space Research and Technology Centre11, Max Planck Society12, Spanish National Research Council13, University of La Laguna14, Royal Observatory of Belgium15, Uppsala University16, University of Catania17, Instituto Politécnico Nacional18, University of Nice Sophia Antipolis19, Université libre de Bruxelles20
TL;DR: In this article, the authors describe the methods and software used for the data reduction, the derivation of the radial velocities, and the quality control of the FLAMES-UVES spectra.
Abstract: The Gaia-ESO Survey is a large public spectroscopic survey that aims to derive radial velocities and fundamental parameters of about 10(5) Milky Way stars in the field and in clusters. Observations are carried out with the multi-object optical spectrograph FLAMES, using simultaneously the medium-resolution (R similar to 20 000) GIRAFFE spectrograph and the high-resolution (R similar to 47 000) UVES spectrograph. In this paper we describe the methods and the software used for the data reduction, the derivation of the radial velocities, and the quality control of the FLAMES-UVES spectra. Data reduction has been performed using a workflow specifically developed for this project. This workflow runs the ESO public pipeline optimizing the data reduction for the Gaia-ESO Survey, automatically performs sky subtraction, barycentric correction and normalisation, and calculates radial velocities and a first guess of the rotational velocities. The quality control is performed using the output parameters from the ESO pipeline, by a visual inspection of the spectra and by the analysis of the signal-to-noise ratio of the spectra. Using the observations of the first 18 months, specifically targets observed multiple times at different epochs, stars observed with both GIRAFFE and UVES, and observations of radial velocity standards, we estimated the precision and the accuracy of the radial velocities. The statistical error on the radial velocities is sigma similar to 0.4 km s(-1) and is mainly due to uncertainties in the zero point of the wavelength calibration. However, we found a systematic bias with respect to the GIRAFFE spectra (similar to 0.9 km s(-1)) and to the radial velocities of the standard stars (similar to 0.5 km s(-1)) retrieved from the literature. This bias will be corrected in the future data releases, when a common zero point for all the set-ups and instruments used for the survey is be established.
University of Padua1, INAF2, University of Hertfordshire3, University of Cambridge4, University of Graz5, University of Barcelona6, Royal Observatory of Belgium7, Spanish National Research Council8, European Southern Observatory9, University of Bologna10, Indiana University11, Massachusetts Institute of Technology12, National and Kapodistrian University of Athens13, Vilnius University14, University of Concepción15, Lund University16, University of Nice Sophia Antipolis17, Pontifical Catholic University of Chile18, Millennium Institute19
TL;DR: In this article, the authors used BVI and ri photometry and comparison with theoretical isochrones to derive the age of NGC 6705, which is a young and massive open cluster located towards the inner region of the Milky Way.
Abstract: Context. Chemically inhomogeneous populations are observed in most globular clusters, but not in open clusters. Cluster mass seems to play a key role in the existence of multiple populations. Aims. Studying the chemical homogeneity of the most massive open clusters is needed to better understand the mechanism of their formation and determine the mass limit under which clusters cannot host multiple populations. Here we studied NGC 6705, which is a young and massive open cluster located towards the inner region of the Milky Way. This cluster is located inside the solar circle. This makes it an important tracer of the inner disk abundance gradient. Methods. This study makes use of BVI and ri photometry and comparisons with theoretical isochrones to derive the age of NGC 6705. We study the density profile of the cluster and the mass function to infer the cluster mass. Based on abundances of the chemical elements distributed in the first internal data release of the Gaia-ESO Survey, we study elemental ratios and the chemical homogeneity of the red clump stars. Radial velocities enable us to study the rotation and internal kinematics of the cluster. Results. The estimated ages range from 250 to 316 Myr, depending on the adopted stellar model. Luminosity profiles and mass functions show strong signs of mass segregation. We derive the mass of the cluster from its luminosity function and from the kinematics, finding values between 3700 M-circle dot and 11 000 M-circle dot. After selecting the cluster members from their radial velocities, we obtain a metallicity of [Fe/H] = 0.10 +/- 0.06 based on 21 candidate members. Moreover, NGC 6705 shows no sign of the typical correlations or anti-correlations between Al, Mg, Si, and Na, which are expected in multiple populations. This is consistent with our cluster mass estimate, which is lower than the required mass limit proposed in the literature to develop multiple populations.
TL;DR: WEAVE as mentioned in this paper is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multiobject (MOS) fibres, 20 integral field units, or a single large IFU for each observation.
Abstract: We present an overview of and status report on the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT). WEAVE principally targets optical ground-based follow up of upcoming ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single spectrograph, with a pair of 8k(spectral) x 6k (spatial) pixel cameras, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project is now in the final design and early procurement phase, with commissioning at the telescope expected in 2017.
TL;DR: In this article, the authors used BVI and ri photometry and comparison with theoretical isochrones to derive the age of NGC6705, a young and massive open cluster located towards the inner region of the Milky Way.
Abstract: Chemically inhomogeneous populations are observed in most globular clusters, but not in open clusters. Cluster mass seems to play a key role in the existence of multiple populations.
Studying the chemical homogeneity of the most massive open clusters is necessary to better understand the mechanism of their formation and determine the mass limit under which clusters cannot host multiple populations. Here we studied NGC6705, that is a young and massive open cluster located towards the inner region of the Milky Way. This cluster is located inside the solar circle. This makes it an important tracer of the inner disk abundance gradient. This study makes use of BVI and ri photometry and comparisons with theoretical isochrones to derive the age of NGC6705. We study the density profile of the cluster and the mass function to infer the cluster mass. Based on abundances of the chemical elements distributed in the first internal data release of the Gaia-ESO Survey, we study elemental ratios and the chemical homogeneity of the red clump stars. Radial velocities enable us to study the rotation and internal kinematics of the cluster.
The estimated ages range from 250 to 316Myr, depending on the adopted stellar model. Luminosity profiles and mass functions show strong signs of mass segregation. We derive the mass of the cluster from its luminosity function and from the kinematics, finding values between 3700 M$_{\odot}$ and 11 000 M$_{\odot}$. After selecting the cluster members from their radial velocities, we obtain a metallicity of [Fe/H]=0.10$\pm$0.06 based on 21 candidate members. Moreover, NGC6705 shows no sign of the typical correlations or anti-correlations between Al, Mg, Si, and Na, that are expected in multiple populations. This is consistent with our cluster mass estimate, which is lower than the required mass limit proposed in literature to develop multiple populations.
TL;DR: WEAVE as mentioned in this paper is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multiobject (MOS) fibres, 20 integral field units, or a single large IFU for each observation.
Abstract: We present an overview of and status report on the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT). WEAVE principally targets optical ground-based follow up of upcoming ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single spectrograph, with a pair of 8k(spectral) x 6k (spatial) pixel cameras, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project is now in the final design and early procurement phase, with commissioning at the telescope expected in 2017.
TL;DR: In the rest frame of the Local Group (LG), the total momentum of the Milky Way (MW) and Andromeda (M31) should balance to zero as discussed by the authors, which is consistent with other properties such as the maximum rotational velocities, total stellar content, and numbers of globular clusters and dwarf satellites.
Abstract: In the rest frame of the Local Group (LG), the total momentum of the Milky Way (MW) and Andromeda (M31) should balance to zero. We use this fact to constrain new solutions for the solar motion with respect to the LG centre-of-mass, the total mass of the LG, and the individual masses of M31 and the MW. Using the set of remote LG galaxies at $>350$ kpc from the MW and M31, we find that the solar motion has amplitude $V_{\odot}=299\pm 15 {\rm ~km~s^{-1}}$ in a direction pointing toward galactic longitude $l_{\odot}=98.4^{\circ}\pm 3.6^{\circ}$ and galactic latitude $b_{\odot}=-5.9^{\circ}\pm 3.0^{\circ}$. The velocities of M31 and the MW in this rest frame give a direct measurement of their mass ratio, for which we find $\log_{10} (M_{\rm M31}/M_{\rm MW})=0.36 \pm 0.29$. We combine these measurements with the virial theorem to estimate the total mass within the LG as $M_{\rm LG}=(2.5\pm 0.4)\times 10^{12}~{\rm M}_{\odot}$.
Our value for $M_{\rm LG}$ is consistent with the sum of literature values for $M_{\rm MW}$ and $M_{\rm M31}$. This suggests that the mass of the LG is almost entirely located within the two largest galaxies rather than being dispersed on larger scales or in a background medium. The outskirts of the LG are seemingly rather empty. Combining our measurement for $M_{\rm LG}$ and the mass ratio, we estimate the individual masses of the MW and M31 to be $M_{\rm MW}=(0.8\pm 0.5)\times 10^{12}~{\rm M}_{\odot}$ and $M_{\rm M31}=(1.7\pm 0.3)\times 10^{12}~{\rm M}_{\odot}$, respectively. Our analysis favours M31 being more massive than the MW by a factor of $\sim$2.3, and the uncertainties allow only a small probability (9.8%) that the MW is more massive. This is consistent with other properties such as the maximum rotational velocities, total stellar content, and numbers of globular clusters and dwarf satellites, which all suggest that $M_{\rm M31}/M_{\rm MW}>1$.
University of Guadalajara1, Australian Astronomical Observatory2, Macquarie University3, Spanish National Research Council4, University of La Laguna5, European Southern Observatory6, University College London7, University of Hertfordshire8, University of Graz9, Radboud University Nijmegen10, Harvard University11, University of Cambridge12, Universidad de Sonora13, University of Bristol14
TL;DR: In this article, the first results of the search for new, extended planetary nebulae (PNe) based on careful, systematic, visual scrutiny of the imaging data from the Isaac Newton Telescope Photometric Hα Survey of the Northern Galactic plane (IPHAS) are presented.
Abstract: We present the first results of our search for new, extended planetary nebulae (PNe) based on careful, systematic, visual scrutiny of the imaging data from the Isaac Newton Telescope Photometric Hα Survey of the Northern Galactic plane (IPHAS). The newly uncovered PNe will help to improve the census of this important population of Galactic objects that serve as key windows into the late-stage evolution of low- to intermediate-mass stars. They will also facilitate study of the faint end of the ensemble Galactic PN luminosity function. The sensitivity and coverage of IPHAS allows PNe to be found in regions of greater extinction in the Galactic plane and/or those PNe in a more advanced evolutionary state and at larger distances compared to the general Galactic PN population. Using a set of newly revised optical diagnostic diagrams in combination with access to a powerful, new, multiwavelength imaging data base, we have identified 159 true, likely and possible PNe for this first catalogue release. The ability of IPHAS to unveil PNe at low Galactic latitudes and towards the Galactic Anticentre, compared to previous surveys, makes this survey an ideal tool to contribute to the improvement of our knowledge of the whole Galactic PN population.
TL;DR: In this paper, deep photometry of the Carina dwarf spheroidal galaxy in the B and V filters from CTIO/MOSAIC out to and beyond the tidal radius of rell ≈ 0.48 degrees is presented.
Abstract: We present deep photometry of the Carina dwarf spheroidal galaxy in the B and V filters from CTIO/MOSAIC out to and beyond the tidal radius of rell ≈ 0.48 degrees. The accurately calibrated photometry is combined with spectroscopic metallicity distributions of red giant branch (RGB) stars to determine the detailed star formation and chemical evolution history of Carina. The star formation history (SFH) confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail as a function of radius from the centre. Two main episodes of star formation occurred at old (>8 Gyr) and intermediate (2−8 Gyr) ages, both enriching stars starting from low metallicities ([Fe/H] < − 2 dex). By dividing the SFH into two components, we determine that 60 ± 9 percent of the total number of stars formed within the intermediate-age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07 ± 0.08 × 106 M⊙ was formed, giving Carina a stellar mass-to-light ratio of 1.8 ± 0.8. By combining the detailed SFH with spectroscopic observations of RGB stars, we determined the detailed age-metallicity relation of each episode and the timescale of α-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation during ≈6 Gyr with steadily declining α-element abundances and a possible α-element "knee" visible at [Fe/H] ≈ − 2.5 dex. The intermediate-age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in α-element abundances with a slope much steeper than observed in the old episode, starting from [Fe/H] = −1.8 dex and [Mg/Fe] ≈ 0.4 dex and declining to Mg-poor values ([Mg/Fe] ≤ − 0.5 dex). This clearly indicates that the two episodes of star formation formed from gas with different abundance patterns, which is inconsistent with simple evolution in an isolated system.
TL;DR: In this paper, the authors exploit data from the Pan-Andromeda Archaeological Survey (PAndAS) to study the extended structures of M31's dwarf elliptical companions, NGC 147 and NGC 185.
Abstract: © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. We exploit data from the Pan-Andromeda Archaeological Survey (PAndAS) to study the extended structures of M31's dwarf elliptical companions, NGC 147 and NGC 185. Our wide-field, homogeneous photometry allows us to construct deep colour-magnitude diagrams which reach down to ~3 mag below the red giant branch (RGB) tip. We trace the stellar components of the galaxies to surface brightness of μg~ 32 mag arcsec-2and show that they have much larger extents (~5 kpc radii) than previously recognized. While NGC 185 retains a regular shape in its peripheral regions, NGC 147 exhibits pronounced isophotal twisting due to the emergence of symmetric tidal tails. We fit single Sersic models to composite surface brightness profiles constructed from diffuse light and star counts and find that NGC 147 has an effective radius almost three times that of NGC 185. In both cases, the effective radii that we calculate are larger by a factor of ~2 compared to most literature values.We also calculate revised total magnitudes of Mg= -15.36 ± 0.04 for NGC 185 and Mg= -16.36 ± 0.04 for NGC 147. Using photometric metallicities computed for RGB stars, we find NGC 185 to exhibit a metallicity gradient of [Fe/H]~-0.15 dex kpc-1over the radial range 0.125-0.5 deg. On the other hand, NGC 147 exhibits almost no metallicity gradient, ~-0.02 dex kpc-1from 0.2 to 0.6 deg. The differences in the structure and stellar populations in the outskirts of these systems suggest that tidal influences have played an important role in governing the evolution of NGC 147.
TL;DR: In this article, the authors used Z and J-band images from the VISTA telescope to construct the spatially resolved J vs. Z-J colour-magnitude diagrams (CMDs).
Abstract: Context. Outskirts of large galaxies contain important information about galaxy formation and assembly. Resolved star count studies can probe the extremely low surface brightness of the outer halos. Aims. NGC 253 is a nearly edge-on disk galaxy in the Sculptor group where we resolved the halo stars from ground-based images, with the aim of studying its stellar population content, the structure and the overall extent of the halo. Methods. We use Z and J-band images from the VIRCAM camera mounted on the VISTA telescope to construct the spatially resolved J vs. Z-J colour-magnitude diagrams (CMDs). The very deep photometry and the wide area covered allows us to trace the red giant branch (RGB) and asymptotic giant branch (AGB) stars that belong to the halo of NGC 253 out to 50 kpc along the galaxy minor axis. Results. We confirm the existence of an extra planar stellar component of the disk, with a very prominent southern shelf and a symmetrical feature on the north side. The only additional visible sub-structure is an overdensity in the north-west part of the halo 28 kpc distant from the plane and extending over 20 kpc parallel with the disk. We measure the transition from the disk to the halo at a radial distance of about 25 kpc with a clear break in the number density profile. The isodensity contours show that the inner halo is a flattened structure that blends with a more extended, di use, rounder outer halo. Such external structure can be traced to the very edge of our image out to 50 kpc from the disk plane. The number density profile of the stars in the stellar halo follows a power law with index 1:6, as function of radius. The CMD shows a very homogeneous stellar population across the field; by comparing with isochrones we conclude that the RGB stars are 8 Gyr old or more, while the AGB stars trace a population of about 2 10 8 M formed from 0:5 to a few Gyr ago. Surprisingly, part of this latter population appears scattered over a wide area. We explore several ideas to explain the origin of this relatively young component in the inner halo of NGC 253.
TL;DR: In this paper, deep optical photometry from the DECam imager on the 4m Blanco telescope of over 12 deg$^2$ around the Carina dwarf spheroidal, with complete coverage out to 1 degree and partial coverage extending out to 2.6 degrees.
Abstract: We present deep optical photometry from the DECam imager on the 4m Blanco telescope of over 12 deg$^2$ around the Carina dwarf spheroidal, with complete coverage out to 1 degree and partial coverage extending out to 2.6 degrees. Using a Poisson-based matched filter analysis to identify stars from each of the three main stellar populations, old, intermediate, and young, we confirm the previously identified radial age gradient, distance, tidal radius, stellar radial profiles, relative stellar population sizes, ellipticity, and position angle. We find an angular offset between the three main elliptical populations of Carina, and find only tentative evidence for tidal debris, suggesting that past tidal interactions could not have significantly influenced the Carina dwarf. We detect stars in the vicinity of, but distinct to, the Carina dwarf, and measure their distance to be 46$\pm$2 kpc. We determine this population to be part of the halo of the Large Magellanic Cloud at an angular radius of over 20 degrees. Due to overlap in colour-magnitude space with Magellanic stars, previously detected tidal features in the old population of Carina are likely weaker than previously thought.
University of California, Santa Cruz1, University of Washington2, University of Minnesota3, University of La Laguna4, Spanish National Research Council5, Raytheon6, Herzberg Institute of Astrophysics7, University of Edinburgh8, University of Maryland, College Park9, INAF10, University of Tasmania11, Space Telescope Science Institute12, University of Cambridge13, Max Planck Society14, Centre national de la recherche scientifique15, ETH Zurich16, University of Zurich17, University of Victoria18
TL;DR: In this article, the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites were compared using the Advanced Camera for Surveys on board the Hubble Space Telescope, yielding color-magnitude diagrams that extend at least 1?mag below the oldest main-sequence turnoff.
Abstract: We present the first comparison between the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites. Using the Advanced Camera for Surveys on board the Hubble Space Telescope, we obtained deep optical imaging of Andromeda II (And II; MV = ?12.0; log(M /M ?) ~ 6.7) and Andromeda XVI (And XVI; MV = ?7.5; log(M /M ?) ~ 4.9) yielding color-magnitude diagrams that extend at least 1?mag below the oldest main-sequence turnoff, and are similar in quality to those available for the MW companions. And II and And XVI show strikingly similar SFHs: both formed 50%-70% of their total stellar mass between 12.5 and 5?Gyr ago (z ~ 5-0.5) and both were abruptly quenched ~5?Gyr ago (z ~ 0.5). The predominance of intermediate age populations in And XVI makes it qualitatively different from faint companions of the MW and clearly not a pre-reionization fossil. Neither And II nor And XVI appears to have a clear analog among MW companions, and the degree of similarity in the SFHs of And II and And XVI is not seen among comparably faint-luminous pairs of MW satellites. These findings provide hints that satellite galaxy evolution may vary substantially among hosts of similar stellar mass. Although comparably deep observations of more M31 satellites are needed to further explore this hypothesis, our results underline the need for caution when interpreting satellite galaxies of an individual system in a broader cosmological context.
University College London1, Fermilab2, University of Cambridge3, Institut de Ciències de l'Espai4, Institut d'Astrophysique de Paris5, University of Illinois at Urbana–Champaign6, University of Michigan7, University of São Paulo8, Max Planck Society9, Autonomous University of Barcelona10, Space Telescope Science Institute11, University of Pennsylvania12, Argonne National Laboratory13, Carnegie Learning14, Institute of Cosmology and Gravitation, University of Portsmouth15, Australian National University16, Stanford University17, University of Queensland18, Texas A&M University19, Ludwig Maximilian University of Munich20, Swinburne University of Technology21, Ohio State University22, University of the Western Cape23, Lawrence Berkeley National Laboratory24, Australian Astronomical Observatory25, Catalan Institution for Research and Advanced Studies26, Complutense University of Madrid27, SLAC National Accelerator Laboratory28, National Center for Supercomputing Applications29, University of Manchester30
TL;DR: In this article, the combination of optical data from the Science Verification phase of the DES with near-infrared (NIR) data from VISTA Hemisphere Survey (VHS) is presented.
Abstract: We present the combination of optical data from the Science Verification phase of the Dark Energy Survey (DES) with near-infrared (NIR) data from the European Southern Observatory VISTA Hemisphere Survey (VHS). The deep optical detections from DES are used to extract fluxes and associated errors from the shallower VHS data. Joint seven-band (grizYJK) photometric catalogues are produced in a single 3 sq-deg dedicated camera field centred at 02h26m-04d36m where the availability of ancillary multiwavelength photometry and spectroscopy allows us to test the data quality. Dual photometry increases the number of DES galaxies with measured VHS fluxes by a factor of ~4.5 relative to a simple catalogue level matching and results in a ~1.5 mag increase in the 80 per cent completeness limit of the NIR data. Almost 70 per cent of DES sources have useful NIR flux measurements in this initial catalogue. Photometric redshifts are estimated for a subset of galaxies with spectroscopic redshifts and initial results, although currently limited by small number statistics, indicate that the VHS data can help reduce the photometric redshift scatter at both z 1. We present example DES+VHS colour selection criteria for high-redshift luminous red galaxies (LRGs) at z ~ 0.7 as well as luminous quasars. Using spectroscopic observations in this field we show that the additional VHS fluxes enable a cleaner selection of both populations with <10 per cent contamination from galactic stars in the case of spectroscopically confirmed quasars and <0.5 per cent contamination from galactic stars in the case of spectroscopically confirmed LRGs. The combined DES+VHS data set, which will eventually cover almost 5000 sq-deg, will therefore enable a range of new science and be ideally suited for target selection for future wide-field spectroscopic surveys.
TL;DR: Kirkpatrick et al. as mentioned in this paper used the statistical properties of the WISE multi-frame measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources.
Abstract: A method is defined for identifying late T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the WISE multi-frame measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space we use a control sample of isolated non-moving non-variable point sources from the SDSS, and identify a sample of 158 WISE W2-only candidates down to a signal-to-noise limit of 8. For signal-to-noise ranges >10 and 8-10 respectively, �45% and �90% of our sample fall outside the selection criteria published by the WISE team (Kirkpatrick et al. 2012), due mainly to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (�1.3 and �1.8 arcsec yr 1 ). Both objects show a mid-infrared/near-infrared excess of �1-1.5 magnitudes, and are K band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disk) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late T and Y dwarfs may have a higher thick-disk/halo population fraction than earlier objects.
TL;DR: In this paper, deep photometry of the Carina dwarf Spheroidal galaxy in the B,V filters from CTIO/MOSAIC, out to and beyond the tidal radius is presented.
Abstract: We present deep photometry of the Carina dwarf Spheroidal galaxy in the B,V filters from CTIO/MOSAIC, out to and beyond the tidal radius. The accurately calibrated photometry is combined with spectroscopic metallicity distributions of Red Giant Branch stars to determine the detailed star formation and chemical evolution history. The star formation history confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail, as a function radius from the centre. Two main episodes of star formation occurred at old (>8 Gyr) and intermediate (2-8 Gyr) ages, both enriching stars starting from low metallicities ([Fe/H]<-2 dex). By dividing the SFH into two components, we determine that 60pm9 percent of the total number of stars formed within the intermediate age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07pm0.08 x10^6 M_sun was formed, giving Carina a stellar mass-to-light ratio of 1.8pm0.8. Combining the detailed star formation history with spectroscopic observations of RGB stars, we are able to determine the detailed age-metallicity relation of each episode and the timescale of alpha-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation over 6 Gyr with steadily declining alpha-element abundances and a possible alpha-element knee at [Fe/H]~ -2.5 dex. The intermediate age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in alpha-element abundances with a slope much steeper than observed in the old episode, starting from [Fe/H]=-1.8 dex and [Mg/Fe]~0.4 dex and declining to Mg-poor values ([Mg/Fe]<-0.5 dex). This indicates clearly that both episodes of star formation formed from gas with different abundance patterns, inconsistent with simple evolution in an isolated system.
TL;DR: In this paper, the stellar population and spatial properties of a diffuse substructure in the outer halo of M31 were analyzed using Pan-Andromeda Archaeological Survey photometry of red giant branch stars.
Abstract: We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo of M31. The South-West Cloud lies at a projected distance of ~100 kpc from the centre of M31, and extends for at least ~50 kpc in projection. We use Pan-Andromeda Archaeological Survey photometry of red giant branch stars to determine a distance to the South-West Cloud of 793 +/- 45 kpc. The metallicity of the cloud is found to be [Fe/H] = -1.3 +/- 0.1. This is consistent with the coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities determined using an independent technique of [Fe/H] = -1.35 +/- 0.15. We measure a brightness for the Cloud of M_V = -12.1 mag; this is ~75 per cent of the luminosity implied by the luminosity-metallicity relation. Under the assumption that the South-West Cloud is the visible remnant of an accreted dwarf satellite, this suggests that the progenitor object was amongst M31's brightest dwarf galaxies prior to disruption.
TL;DR: In this article, the authors quantify the structures in the stellar disk of the barred Sc galaxy NGC 253 located in the Sculptor group, at 3.47 Mpc distance.
Abstract: Context. The presence of a bar affects the distribution and dynamics of a stellar disk at all scales, from a fraction of a kpc in the inner central region to tens of kpc at the disk’s edge. The quantitative study of the disk response to a bar can be hampered by the presence of dust, which is common in late type spirals.Aims. We want to quantify the structures in the stellar disk of the barred Sc galaxy NGC 253 located in the Sculptor group, at 3.47 Mpc distance.Methods. We use J and K s band images acquired with the VISTA telescope as part of the Science Verification. The wide field of view and the high angular resolution of this survey facility allow the mapping of the large and small scale structure of the stellar disk in NGC 253. We use unsharp masking and two dimensional modelling of the smooth light distribution in the disk to identify and measure the sub-structures induced by the bar in the stellar disk of NGC 253. We build azimuthally-averaged profiles in the J and K s bands to measure the radial surface brightness profile of the central bulge, bar and disk.Results. Moving outward from the galaxy center, we find a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring with 2.9 kpc radius, and spiral arms in the outer disk. From the K s image we obtain a new measure of the de-projected length of the bar of 2.5 kpc. The bar’s strength, as derived from the curvature of the dust lanes in the J -K s image, is typical of weak bars with Δα = 25 degree/kpc. From the de-projected length of the bar, we establish the co-rotation radius (R CR = 3 kpc) and bar pattern speed (Ωb = 61.3 km s-1 kpc-1 ), which provides the connection between the high frequency structures in the disk and the orbital resonances induced by the bar. The nuclear ring is located at the Inner Lindblad resonance. The second ring (at 2.9 kpc) does not have a resonant origin, but it could be a merger remnant or a transient structure formed during an intermediate stage of the bar formation. The inferred bar pattern speed places the Outer Lindblad resonance within the optical disk at 4.9 kpc, in the same radial range as the peak in the HI surface density. The disk of NGC 253 has a down-bending profile with a break at R ~ 9.3 kpc, which corresponds to about 3 times the scale length of the inner disk. We discuss the evidence for a threshold in star formation efficiency as a possible explanation for the steep gradient in the surface brightness profile at large radii.Conclusions. The near-infrared photometry unveils the dynamical response of the NGC 253 stellar disk to its central bar. The formation of the bar may be related to the merger event that determined the truncation of stars and gas at large radii and the perturbation of the disk’s outer edge.
University of California, Santa Cruz1, University of Washington2, University of Minnesota3, Spanish National Research Council4, University of La Laguna5, Raytheon6, Herzberg Institute of Astrophysics7, University of Edinburgh8, University of Maryland, College Park9, INAF10, University of Tasmania11, Space Telescope Science Institute12, University of Cambridge13, Max Planck Society14, Centre national de la recherche scientifique15, ETH Zurich16, University of Zurich17, University of Victoria18
TL;DR: In this article, the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites were compared using the Advanced Camera for Surveys aboard the Hubble Space Telescope, yielding color-magnitude diagrams that extend at least 1 magnitude below the oldest main sequence turnoff.
Abstract: We present the first comparison between the lifetime star formation histories (SFHs) of M31 and Milky Way (MW) satellites. Using the Advanced Camera for Surveys aboard the Hubble Space Telescope, we obtained deep optical imaging of Andromeda II (M$_{V} = -$12.0; log(M$_{\star}$/M$_{\odot}$) $\sim$ 6.7) and Andromeda XVI (M$_{V} = -$7.5; log(M$_{\star}$/M$_{\odot}$) $\sim$ 4.9) yielding color-magnitude diagrams that extend at least 1 magnitude below the oldest main sequence turnoff, and are similar in quality to those available for the MW companions. And II and And XVI show strikingly similar SFHs: both formed 50-70% of their total stellar mass between 12.5 and 5 Gyr ago (z$\sim$5-0.5) and both were abruptly quenched $\sim$ 5 Gyr ago (z$\sim$0.5). The predominance of intermediate age populations in And XVI makes it qualitatively different from faint companions of the MW and clearly not a pre-reionization fossil. Neither And II nor And XVI appears to have a clear analog among MW companions, and the degree of similarity in the SFHs of And II and And XVI is not seen among comparably faint-luminous pairs of MW satellites. These findings provide hints that satellite galaxy evolution may vary substantially among hosts of similar stellar mass. Although comparably deep observations of more M31 satellites are needed to further explore this hypothesis, our results underline the need for caution when interpreting satellite galaxies of an individual system in a broader cosmological context.
TL;DR: In this paper, a Bayesian approach was used to model the spectra using the newly constructed reference spectral library and literature-driven priors, and the efficiency of the algorithm for SNe type I is higher than 80% for magnitudes G 618, dropping to approximately 60% at magnitude G=19.
Abstract: We present an algorithm for classifying the nearby transient objects detected by the Gaia satellite. The algorithm will use the low-resolution spectra from the blue and red spectrophotometers on board of the satellite. Taking a Bayesian approach we model the spectra using the newly constructed reference spectral library and literature-driven priors. We find that for magnitudes brighter than 19 in Gaia G magnitude, around 75% of the transients will be robustly classified. The efficiency of the algorithm for SNe type I is higher than 80% for magnitudes G 618, dropping to approximately 60% at magnitude G=19. For SNe type II, the efficiency varies from 75 to 60% for G 618, falling to 50% at G=19. The purity of our classifier is around 95% for SNe type I for all magnitudes. For SNe type II it is over 90% for objects withG 619. GS-TEC also estimates the redshifts with errors of z 6 0.01 and epochs with uncertainties t ’ 13 and 32 days for type SNe I and SNe II respectively. GS-TEC has been designed to be used on partially calibrated Gaia data. However, the concept could be extended to other kinds of low resolution spectra classification for ongoing surveys.
TL;DR: In this article, the spatial distribution of the asymptotic giant branch (AGB) population in IC 1613 and its metallicity was studied using WFCAM on UKIRT.
Abstract: A member of the Local Group, IC 1613 is a gas rich irregular dwarf galaxy that appears to have formed stars continuously over the last 10 Gyr and is relatively independent of external influences from other galaxies. This paper aims to study the spatial distribution of the asymptotic giant branch (AGB) population in IC 1613 and its metallicity. Using WFCAM on UKIRT, high quality JHK photometry of an area of 0.8 deg^2 centered on IC 1613 was obtained. The data have been used to isolate the C- and M-type components of the AGB population and using their number ratio, C/M, a global mean metallicity has been derived. The metallicity and the TRGB magnitude have been studied as a function of distance from the galactic centre and as a function of azimuthal angle. The tip of the RGB (TRGB) has been found at K_0 = 18.25 +/- 0.15 mag. The colour separation between the C- and M-type components of the AGB population has been located at (J-K) = 1.15 +/- 0.05 mag, giving a global C/M ratio of 0.52 +/- 0.04 and from this an iron abundance of [Fe/H] = -1.26 +/- 0.07 dex has been calculated. The AGB population has been detected out to a radial distance of 4.5 kpc in the de-projected plane of the galaxy. The measured TRGB is consistent with previous measurements and no significant variation is detected in the TRGB or in metallicity either with galactocentric distance or azimuthal angle.