A flat faint end of the Fornax cluster galaxy luminosity function

We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population (M_V>-17 mag), based on a wide field imaging study of the central cluster area in V and I band-passes with IMACS/Magellan at Las Campanas Observatory. We create a fiducial sample of ~100 Fornax cluster dwarf ellipticals (dEs) with -16.6<M_V<-8.8 mag in the following three steps: (1) To verify cluster membership, we measured I-band surface brightness fluctuations (SBF) distances to candidate dEs known from previous surveys; (2) We re-assessed morphological classifications for those candidate dEs that are too faint for SBF detection; and (3) We searched for new candidate dEs in the size-luminosity regime close to the resolution limit of previous surveys. The resulting fiducial dE sample follows a well-defined surface brightness - magnitude relation, showing that Fornax dEs are about 40% larger than Local Group dEs. The sample also defines a colour-magnitude relation similar to that of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax has a very flat faint end slope alpha = -1.1 +/- 0.1. We compare the number of dwarfs per unit mass with those in other environments and find that the Fornax cluster fits well into a general trend of a lack of high-mass dwarfs in more massive environments.Comment: 5 pages, 4 figures, to appear in the proceedings of IAU Symposium 244 'Dark galaxies and lost baryons', Cambridge University Press, editors J. I. Davies & M. D. Disne

A census of ultra-compact dwarf galaxies in nearby galaxy clusters

Ultra-compact dwarf galaxies (UCDs) are predominatly found in the cores of nearby galaxy clusters. Besides the Fornax and Virgo cluster, UCDs have also been confirmed in the twice as distant Hydra I and Centaurus clusters. Having (nearly) complete samples of UCDs in some of these clusters allows the study of the bulk properties with respect to the environment they are living in. Moreover, the relation of UCDs to other stellar systems in galaxy clusters, like globular clusters and dwarf ellipticals, can be investigated in detail with the present data sets. The general finding is that UCDs seem to be a heterogenous class of objects. Their spatial distribution within the clusters is in between those of globular clusters and dwarf ellipticals. In the colour-magnitude diagram, blue/metal-poor UCDs coincide with the sequence of nuclear star clusters, whereas red/metal-rich UCDs reach to higher masses and might have originated from the amalgamation of massive star cluster complexes in merger or starburst galaxies.Comment: 6 pages, 3 figures; to appear in "A Universe of Dwarf Galaxies: Observations, Theories, Simulations", held in Lyon, France (June 14-18, 2010), eds. M. Koleva, P. Prugniel & I. Vauglin, EAS Series (Paris: EDP

Bryophytes from the Republic of Equatorial Guinea (West Central Africa) : 3., contribution to the bryoflora of Rio Muni (continental region)

First results of the identification work of the collections made by Patxi Heras on Río Muni, the continental part of Equatorial Guinea, are offered. A list of 155 taxa (85 liverworts and 70 mosses) is included, 90 of them being new records for the country.Se ofrecen los primeros resultados del trabajo de identificación realizado en el material recolectado por Patxi Heras en Río Muni o Región Continental (Guinea Ecuatorial). Se incluye una lista de 155 táxones (85 hepáticas y 70 musgos), de los cuales 90 son novedad para el país

The specific frequencies of ultra-compact dwarf galaxies

We aim at quantifying the specific frequency of UCDs in a range of environments and at relating this to the frequency of globular clusters (GCs) and potential progenitor dwarf galaxies. Are the frequencies of UCDs consistent with being the bright tail of the GC luminosity function (GCLF)? We propose a definition for the specific frequency of UCDs, S_{N,UCD}=N_{UCD}*10^{0.4*(M_{V,host}-M_{V,0})}*c_{w}. The parameter M_{V,0} is the zeropoint of the definition, chosen such that the specific frequency of UCDs is the same as those of globular clusters, S_{N,GC}, if UCDs follow a simple extrapolation of the GCLF. The parameter c_{w} is a correction term for the GCLF width sigma. We apply our definition of S_{N,UCD} to results of spectroscopic UCD searches in the Fornax, Hydra and Centaurus galaxy clusters, two Hickson Compact Groups, and the Local Group. This includes a large database of 180 confirmed UCDs in Fornax. We find that the specific frequencies derived for UCDs match those of GCs very well, to within 10-50%. The ratio {S_{N,UCD}}/{S_{N,GC}} is 1.00 +- 0.44 for the four environments Fornax, Hydra, Centaurus, and Local Group, which have S_{N,GC} values. This good match also holds for individual giant galaxies in Fornax and in the Fornax intracluster-space. The error ranges of the derived UCD specific frequencies in the various environments then imply that not more than 50% of UCDs were formed from dwarf galaxies. We show that such a scenario would require >90% of primordial dwarfs in galaxy cluster centers (<100 kpc) to have been stripped of their stars. We conclude that the number counts of UCDs are fully consistent with them being the bright tail of the GC population. From a statistical point of view there is no need to invoke an additional formation channel.Comment: 11 pages, 6 figures, A&A accepted. Press release http://www.aanda.org/index.php?option=com_content&task=view&id=788&Itemid=27

Spatially Resolved Kinematics of an Ultra-Compact Dwarf Galaxy

We present the internal kinematics of UCD3, the brightest known ultra-compact dwarf galaxy (UCD) in the Fornax cluster, making this the first UCD with spatially resolved spectroscopy. Our study is based on seeing-limited observations obtained with the ARGUS Integral Field Unit of the VLT/FLAMES spectrograph under excellent seeing conditions (0.5 - 0.67 arcsec FWHM). The velocity field of UCD3 shows the signature of weak rotation, comparable to that found in massive globular clusters. Its velocity dispersion profile is fully consistent with an isotropic velocity distribution and the assumption that mass follows the light distribution obtained from Hubble Space Telescope imaging. In particular, there is no evidence for the presence of an extended dark matter halo contributing a significant (>~33 per cent within R < 200 pc) mass fraction, nor for a central black hole more massive than ~5 per cent of the UCD's mass. While this result does not exclude a galaxian origin for UCD3, we conclude that its internal kinematics are fully consistent with it being a massive star cluster.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Letter

CT Scan Screening for Lung Cancer: Risk Factors for Nodules and Malignancy in a High-Risk Urban Cohort

Low-dose computed tomography (CT) for lung cancer screening can reduce lung cancer mortality. The National Lung Screening Trial reported a 20% reduction in lung cancer mortality in high-risk smokers. However, CT scanning is extremely sensitive and detects non-calcified nodules (NCNs) in 24-50% of subjects, suggesting an unacceptably high false-positive rate. We hypothesized that by reviewing demographic, clinical and nodule characteristics, we could identify risk factors associated with the presence of nodules on screening CT, and with the probability that a NCN was malignant.We performed a longitudinal lung cancer biomarker discovery trial (NYU LCBC) that included low-dose CT-screening of high-risk individuals over 50 years of age, with more than 20 pack-year smoking histories, living in an urban setting, and with a potential for asbestos exposure. We used case-control studies to identify risk factors associated with the presence of nodules (n=625) versus no nodules (n=557), and lung cancer patients (n=30) versus benign nodules (n=128).The NYU LCBC followed 1182 study subjects prospectively over a 10-year period. We found 52% to have NCNs >4 mm on their baseline screen. Most of the nodules were stable, and 9.7% of solid and 26.2% of sub-solid nodules resolved. We diagnosed 30 lung cancers, 26 stage I. Three patients had synchronous primary lung cancers or multifocal disease. Thus, there were 33 lung cancers: 10 incident, and 23 prevalent. A sub-group of the prevalent group were stable for a prolonged period prior to diagnosis. These were all stage I at diagnosis and 12/13 were adenocarcinomas.NCNs are common among CT-screened high-risk subjects and can often be managed conservatively. Risk factors for malignancy included increasing age, size and number of nodules, reduced FEV1 and FVC, and increased pack-years smoking. A sub-group of screen-detected cancers are slow-growing and may contribute to over-diagnosis and lead-time biases

Compact stellar systems in the Fornax cluster: a UV perspective

In recent years, increasing evidence for chemical complexity and multiple stellar populations in massive globular clusters (GCs) has emerged, including extreme horizontal branches (EHBs) and UV excess. Our goal is to improve our understanding of UV excess in the regime of both massive GCs and ultra-compact dwarf galaxies (UCDs). To this end, we use deep archival GALEX data of the central Fornax cluster to measure NUV and FUV magnitudes of UCDs and massive GCs. We obtain NUV photometry for a sample of 35 compact objects with -13.5<M_V<-10 mag. Of those, 21 objects also have FUV photometry. Roughly half of the sources fall into the UCD luminosity regime (M_V <=-11 mag). We find that seven out of 17 massive Fornax GCs exhibit a NUV excess with respect to expectations from stellar population models, even for models with enhanced Helium abundance. This suggests that not only He-enrichment has contributed to forming the EHB population of these GCs. The GCs extend to stronger UV excess than GCs in M31 and massive GCs in M87, at the 97% confidence level. Most of the UCDs with FUV photometry also show evidence for UV excess, but their UV colours can be matched by isochrones with enhanced Helium abundances and old ages 12-14 Gyrs. We find that Fornax compact objects with X-ray emission detected from Chandra images are almost disjunct in colour from compact objects with GALEX UV detection, with only one X-ray source among the 35 compact objects. However, since this source is one of the three most UV bright GCs, we cannot exclude that the physical processes causing X-ray emission also contribute to some of the observed UV excess.Comment: Research Note, 7 pages, 3 figures, accepted for publication in A&