Dwarf elliptical galaxies in Centaurus A group: stellar populations in AM 1339-445 and AM 1343-452

We study the red giant populations of two dE galaxies, AM 1339-445 and AM 1343-452, with the aim of investigating the number and luminosity of any upper asymptotic giant branch (AGB) stars present. The galaxies are members of the Centaurus A group (D~3.8 Mpc) and are classified as outlying (R~350 kpc) satellites of Cen A. The analysis is based on near-IR photometry for individual red giant stars, derived from images obtained with ISAAC on the VLT. The photometry, along with optical data derived from WFPC2 images retrieved from the HST science archive, enable us to investigate the stellar populations of the dEs in the vicinity of the red giant branch (RGB) tip. In both systems we find stars above the RGB tip, which we interpret as intermediate-age upper-AGB stars. The presence of such stars is indicative of extended star formation in these dEs similar to that seen in many, but not all, dEs in the Local Group. For AM 1339-445, the brightest of the upper-AGB stars have Mbol~-4.5 while those in AM 1343-452 have Mbol~-4.8 mag. These luminosities suggest ages of approximately 6.5+/-1 and 4+/-1 Gyr as estimates for the epoch of the last episode of significant star formation in these systems. In both cases the number of upper-AGB stars suggests that ~15% of the total stellar population is in the form of intermediate-age stars, considerably less than is the case for outlying dE satellites of the Milky Way such as Fornax and LeoI.Comment: 18 pages, 19 figures, A&A accepted; high resolution version available from: http://www.eso.org/~mrejkuba/CenA_dEs_I.pd

The Nature of the Density Clump in the Fornax Dwarf Spheroidal Galaxy

We have imaged the recently discovered stellar overdensity located approximately one core radius from the center of the Fornax dwarf spheroidal galaxy using the Magellan Clay 6.5m telescope with the Magellan Instant Camera (MagIC). Superb seeing conditions allowed us to probe the stellar populations of this overdensity and of a control field within Fornax to a limiting magnitude of R=26. The color-magnitude diagram of the overdensity field is virtually identical to that of the control field with the exception of the presence of a population arising from a very short (less than 300 Myr in duration) burst of star formation 1.4 Gyr ago. Coleman et al. have argued that this overdensity might be related to a shell structure in Fornax that was created when Fornax captured a smaller galaxy. Our results are consistent with this model, but we argue that the metallicity of this young component favors a scenario in which the gas was part of Fornax itself.Comment: 24 pages including 8 figures and 3 tables. Accepted by Astronomical Journa

Feedback and the Formation of Dwarf Galaxy Stellar Halos

Stellar population studies show that low mass galaxies in all environments exhibit stellar halos that are older and more spherically distributed than the main body of the galaxy. In some cases, there is a significant intermediate age component that extends beyond the young disk. We examine a suite of Smoothed Particle Hydrodynamic (SPH) simulations and find that elevated early star formation activity combined with supernova feedback can produce an extended stellar distribution that resembles these halos for model galaxies ranging from $v_{200}$ = 15 km s$^{-1}$ to 35 km s$^{-1}$, without the need for accretion of subhalos.Comment: 15 pages, 15 figures, accepted MNRA

The distance to the Fornax Dwarf Spheroidal Galaxy

A large multicolour, wide-field photometric database of the Fornax dwarf spheroidal galaxy has been analysed using three different methods to provide revised distance estimates based on stellar populations in different age intervals. The distance to Fornax was obtained from the Tip of the Red Giant Branch measured by a new method, and using the luminosity of Horizontal Branch stars and Red Clump stars correc ted for stellar population effects. Assuming a reddening $E(B-V)=0.02$, the following distance moduli were derived: $(m-M)_0=20.71 \pm 0.07$ based on the Tip of the Red Giant Branch, $(m-M)_0=20.72 \pm 0.06$ from the level of the Horizontal Branch, and $(m-M)_0=20.73 \pm 0.09$ using the Red Clump method. The weighted mean distance modulus to Fornax is $(m-M)_0=20.72 \pm 0.04$. All these measurements agree within the errors, and are fully consistent with previous determinations and with the distance measurements obtained in a companion paper from near-infrared colour-magnitude diagrams.Comment: Accepted for publication on Monthly Notices of the Royal Astronomical Societ

A near-infrared study of AGB and red giant stars in the Leo I dSph galaxy

A near-infrared imaging study of the evolved stellar populations in the dwarf spheroidal galaxy Leo I is presented. Based on JHK observations obtained with the WFCAM wide-field array at the UKIRT telescope, we build a near-infrared photometric catalogue of red giant branch (RGB) and asymptotic giant branch (AGB) stars in Leo I over a 13.5 arcmin square area. The V-K colours of RGB stars, obtained by combining the new data with existing optical observations, allow us to derive a distribution of global metallicity [M/H] with average [M/H] = -1.51 (uncorrected) or [M/H] = -1.24 +/- 0.05 (int) +/- 0.15 (syst) after correction for the mean age of Leo I stars. This is consistent with the results from spectroscopy once stellar ages are taken into account. Using a near-infrared two-colour diagram, we discriminate between carbon- and oxygen-rich AGB stars and obtain a clean separation from Milky Way foreground stars. We reveal a concentration of C-type AGB stars relative to the red giant stars in the inner region of the galaxy, which implies a radial gradient in the intermediate-age (1-3 Gyr) stellar populations. The numbers and luminosities of the observed carbon- and oxygen-rich AGB stars are compared with those predicted by evolutionary models including the thermally-pulsing AGB phase, to provide new constraints to the models for low-metallicity stars. We find an excess in the predicted number of C stars fainter than the RGB tip, associated to a paucity of brighter ones. The number of O-rich AGB stars is roughly consistent with the models, yet their predicted luminosity function is extended to brighter luminosity. It appears likely that the adopted evolutionary models overestimate the C star lifetime and underestimate their K-band luminosity.Comment: MNRAS, accepte

A wide-area view of the Phoenix dwarf galaxy from VLT/FORS imaging

We present results from a wide-area photometric survey of the Phoenix dwarf galaxy, one of the rare dwarf irregular/ dwarf spheroidal transition type galaxies (dTs) of the Local Group (LG). These objects offer the opportunity to study the existence of possible evolutionary links between the late- and early- type LG dwarf galaxies, since the properties of dTs suggest that they may be dwarf irregulars in the process of transforming into dwarf spheroidals. Using FORS at the VLT we have acquired VI photometry of Phoenix. The data reach a S/N~10 just below the horizontal branch of the system and consist of a mosaic of images that covers an area of 26' x 26' centered on the coordinates of the optical center of the galaxy. Examination of the colour-magnitude diagram and luminosity function revealed the presence of a bump above the red clump, consistent with being a red giant branch bump. The deep photometry combined with the large area covered allows us to put on a secure ground the determination of the overall structural properties of the galaxy and to derive the spatial distribution of stars in different evolutionary phases and age ranges, from 0.1 Gyr to the oldest stars. The best-fitting profile to the overall stellar population is a Sersic profile of Sersic radius R_S = 1.82'+-0.06' and m=0.83+-0.03. We confirm that the spatial distribution of stars is found to become more and more centrally concentrated the younger the stellar population, as reported in previous studies. This is similar to the stellar population gradients found for close-by Milky Way dwarf spheroidal galaxies. We quantify such spatial variations by analyzing the surface number density profiles of stellar populations in different age ranges; [Abridged]Comment: 21 pages; 11 figures. Accepted for publication in MNRA

STREGA: STRucture and Evolution of the GAlaxy - I : Survey overview and first results

STREGA (STRucture and Evolution of the GAlaxy) is a guaranteed time survey being performed at the VST (the ESO Very Large Telescope Survey Telescope) to map about 150 square degrees in the Galactic halo, in order to constrain the mechanisms of galactic formation and evolution. The survey is built as a 5 yr project, organized in two parts: a core programme to explore the surrounding regions of selected stellar systems and a second complementary part to map the southern portion of the Fornax orbit and extend the observations of the core programme. The adopted stellar tracers are mainly variable stars (RR Lyraes and long-period variables) and main-sequence turn-off stars for which observations in the g, r, i bands are obtained. We present an overview of the survey and some preliminary results for three observing runs that have been completed. For the region centred on ω Cen (37 deg^2), covering about three tidal radii, we also discuss the detected stellar density radial profile and angular distribution, leading to the identification of extratidal cluster stars. We also conclude that the cluster tidal radius is about 1.2 deg, in agreement with values in the literature based on the Wilson model.Peer reviewedFinal Accepted Versio

How a Diverse Research Ecosystem Has Generated New Rehabilitation Technologies: Review of NIDILRR’s Rehabilitation Engineering Research Centers

Over 50 million United States citizens (1 in 6 people in the US) have a developmental, acquired, or degenerative disability. The average US citizen can expect to live 20% of his or her life with a disability. Rehabilitation technologies play a major role in improving the quality of life for people with a disability, yet widespread and highly challenging needs remain. Within the US, a major effort aimed at the creation and evaluation of rehabilitation technology has been the Rehabilitation Engineering Research Centers (RERCs) sponsored by the National Institute on Disability, Independent Living, and Rehabilitation Research. As envisioned at their conception by a panel of the National Academy of Science in 1970, these centers were intended to take a “total approach to rehabilitation”, combining medicine, engineering, and related science, to improve the quality of life of individuals with a disability. Here, we review the scope, achievements, and ongoing projects of an unbiased sample of 19 currently active or recently terminated RERCs. Specifically, for each center, we briefly explain the needs it targets, summarize key historical advances, identify emerging innovations, and consider future directions. Our assessment from this review is that the RERC program indeed involves a multidisciplinary approach, with 36 professional fields involved, although 70% of research and development staff are in engineering fields, 23% in clinical fields, and only 7% in basic science fields; significantly, 11% of the professional staff have a disability related to their research. We observe that the RERC program has substantially diversified the scope of its work since the 1970’s, addressing more types of disabilities using more technologies, and, in particular, often now focusing on information technologies. RERC work also now often views users as integrated into an interdependent society through technologies that both people with and without disabilities co-use (such as the internet, wireless communication, and architecture). In addition, RERC research has evolved to view users as able at improving outcomes through learning, exercise, and plasticity (rather than being static), which can be optimally timed. We provide examples of rehabilitation technology innovation produced by the RERCs that illustrate this increasingly diversifying scope and evolving perspective. We conclude by discussing growth opportunities and possible future directions of the RERC program

A close look at the Centaurus A group of galaxies II. Intermediate-age populations in early-type dwarfs

Aims. We investigate the resolved stellar content of early-type dwarf galaxies in the Centaurus A group, to estimate their intermediate-age population fractions. Methods. We use near-infrared photometric data taken with the VLT/ISAAC instrument, togethe

Inclusive Search for Anomalous Production of High-pT Like-Sign Lepton Pairs in Proton-Antiproton Collisions at sqrt{s}=1.8 TeV

We report on a search for anomalous production of events with at least two charged, isolated, like-sign leptons with pT > 11 GeV/c using a 107 pb^-1 sample of 1.8 TeV ppbar collisions collected by the CDF detector. We define a signal region containing low background from Standard Model processes. To avoid bias, we fix the final cuts before examining the event yield in the signal region using control regions to test the Monte Carlo predictions. We observe no events in the signal region, consistent with an expectation of 0.63^(+0.84)_(-0.07) events. We present 95% confidence level limits on new physics processes in both a signature-based context as well as within a representative minimal supergravity (tanbeta = 3) model.Comment: 15 pages, 4 figures. Minor textual changes, cosmetic improvements to figures and updated and expanded reference