The Local Group Census: planetary nebulae in Sextans B

Five planetary nebulae (PNe) have been discovered in the nearby dwarf irregular galaxy. Emission line images were obtained using the Wide Field Camera of the 2.5m Isaac Newton Telescope (INT) at La Palma (Spain). The candidate PNe were identified by their point-like appearance and relatively strong [OIII] emission-line fluxes. They are located within a galactocentric distance of 2.8 arcmin, corresponding to 1.1 kpc at the distance of Sextans B. Luminosities are in the range 1800--5600Lsolar. Sextans B is one of the smallest dwarf irregular galaxies with a PN population. The number of PNe detected suggest an enhanced star formation rate between 1 and 5 Gyr ago.Comment: 7 pages, 2 figure

The population of planetary nebulae and HII regions in M81. A study of radial metallicity gradients and chemical evolution

We analyze the chemical abundances of planetary nebulae and HII regions in the M81 disk for insight on galactic evolution, and compare it with that of other galaxies, including the Milky Way. We acquired Hectospec/MMT spectra of 39 PNe and 20 HII regions, with 33 spectra viable for temperature and abundance analysis. Our PN observations represent the first PN spectra in M81 ever published, while several HII region spectra have been published before, although without a direct electron temperature determination. We determine elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon in PNe and HII regions, and determine their averages and radial gradients. The average O/H ratio of PNe compared to that of the HII regions indicates a general oxygen enrichment in M81 in the last ~10 Gyr. The PN metallicity gradient in the disk of M81 is -0.055+-0.02 dex/kpc. Neon and sulfur in PNe have a radial distribution similar to that of oxygen, with similar gradient slopes. If we combine our HII sample with the one in the literature we find a possible mild evolution of the gradient slope, with results consistent with gradient steepening with time. Additional spectroscopy is needed to confirm this trend. There are no Type I PNe in our M81 sample, consistently with the observation of only the brightest bins of the PNLF, the galaxy metallicity, and the evolution of post-AGB shells. Both the young and the old populations of M81 disclose shallow but detectable negative radial metallicity gradient, which could be slightly steeper for the young population, thus not excluding a mild gradients steepening with the time since galaxy formation. During its evolution M81 has been producing oxygen; its total oxygen enrichment exceeds that of other nearby galaxies.Comment: A&A, in pres

Inflammatory status and cartilage regenerative potential of synovial fibroblasts from patients with osteoarthritis and chondropathy.

OBJECTIVES: To evaluate the inflammatory status and the cartilage regenerative potential of pathological synovial fibroblasts from patients with osteoarthritis (OA) compared with non-inflamed synovium (NS)-derived cells from patients with chondropathy. METHODS: The inflammatory cell phenotype was investigated based on the constitutive and inducible surface expression and secretion of various effector molecules using flow cytometry or ELISA assays. The capacity of cells to produce cartilage-like extracellular matrix was assessed using acid Alcian blue staining and type II collagen immunostaining after treatment with transforming growth factor beta1 (TGF-beta1). RESULTS: OA and NS fibroblasts consistently expressed CD29, CD44, CD49e, CD54, CD90 and CD106. Expression of high-affinity receptors for IL-4, IL-15, CXCL8 and CXCL12 was also detected but only intracellularly. All types of fibroblasts spontaneously released abundant amounts of CXCL12, CCL2, IL-6 and tissue inhibitor of metalloproteinase 1, while the production of IL-11, TGF-beta1, matrix metalloproteinase 1 (MMP-1) and MMP-9 was detected at moderate levels. Several other secreted factors remained undetectable. No statistically significant differences were noted between the two groups of fibroblasts. Treatment with the proinflammatory cytokine tumour necrosis factor alpha (TNF-alpha) up-regulated the same set of surface and secreted molecules, including CD54, CD106, membrane IL-15, CCL2 and CCL5. Under TGF-beta1 treatment and adipogenic culture conditions, both OA and NS fibroblasts displayed chondrogenic and adipocytic activities that were reduced in OA compared with NS cells. CONCLUSIONS: OA synovial fibroblasts did not display a distinct activated inflammatory phenotype compared with NS cells. However, they did differ in their reduced ability to produce cartilage-like matrix. This difference may be an additional important factor contributing to OA pathogenesis

Discovery in IC10 of the farthest known symbiotic star

We report the discovery of the first known symbiotic star in IC10, a starburst galaxy belonging to the Local Group, at a distance of ~750kpc. The symbiotic star was identified during a survey of emission-line objects. It shines at V = 24.62+-0.04, V - R_C = 2.77+-0.05 and R_C - I_C = 2.39+-0.02 and suffers from E(B-V) = 0.85+-0.05 reddening. The spectrum of the cool component well matches that of solar neighborhood M8III giants. The observed emission lines belong to Balmer series, [SII], [NII] and [OIII]. They suggest a low electronic density, negligible optical depth effects and 35,000K < T_eff < 90,000K for the ionizing source. The spectrum of the new symbiotic star in IC10 is an almost perfect copy of that of Hen 2-147, a well known Galactic symbiotic star and Mira.Comment: 5 pages including 3 figures. MNRAS Letters accepted. Also available at http://pessoais.ov.ufrj.br/denise

CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy III. Nitrogen isotopic ratios in the outer Galaxy

Nitrogen isotopic ratios are a key tool for tracing Galactic stellar nucleosynthesis. We present the first study of the $^{14}$N/$^{15}$N abundance ratio in the outer regions of the Milky Way (namely, for galactocentric distances, $R_{\rm GC}$, from 12 kpc up to 19 kpc), with the aim to study the stellar nucleosynthesis effects in the global Galactic trend. We analysed IRAM 30m observations towards a sample of 35 sources in the context of the CHEMical complexity in star-forming regions of the OUTer Galaxy (CHEMOUT) project. We derived the $^{14}$N/$^{15}$N ratios from HCN and HNC for 14 and 3 sources, respectively, using the $J$ = 1-0 rotational transition of HN$^{13}$C, H$^{15}$NC, H$^{13}$CN, and HC$^{15}$N. The results found in the outer Galaxy have been combined with previous measurements obtained in the inner Galaxy. We find an overall linear decreasing H$^{13}$CN/HC$^{15}$N ratio with increasing $R_{\rm GC}$. This translates to a parabolic $^{14}$N/$^{15}$N ratio with a peak at 11 kpc. Updated Galactic chemical evolution models have been taken into account and compared with the observations. The parabolic trend of the $^{14}$N/$^{15}$N ratio with $R_{\rm GC}$ can be naturally explained (i) by a model that assumes novae as the main $^{15}$N producers on long timescales ($\ge$1 Gyr) and (ii) by updated stellar yields for low- and intermediate-mass stars.Comment: 19 pages, 8 figures, 6 tables, 4 appendix - Accepted for publication in A&

Metal production in M33: space and time variations

Nearby galaxies are ideal places to study in detail metallicity gradients and their time evolution. We consider chemical abundances of a new sample of \hii\ regions complemented with previous literature data-sets. We compare \hii\ region and PN abundances obtained with a common set of observations taken at MMT. With an updated theoretical model, we follow the time evolution of the baryonic components and chemical abundances in the disk of M33, assuming that the galaxy is accreting gas from an external reservoir. Supported by a uniform sample of nebular spectroscopic observations, we conclude that: {\em i}) the metallicity distribution in M33 is very complex, showing a central depression in metallicity probably due to observational bias; {\em ii}) the metallicity gradient in the disk of M33 has a slope of -0.037$\pm$ 0.009 dex kpc$^{-1}$ in the whole radial range up to $\sim$8 kpc, and -0.044$\pm$ 0.009 dex kpc$^{-1}$ excluding the central kpc; {\em iii}) there is a small evolution of the slope with time from the epoch of PN progenitor formation to the present-time.}Comment: A&A accepted, 15 Pags, 13 Figs, language correctio

The Local Group Census: planetary nebulae in IC 10, Leo A and Sextans A

In the framework of our narrow-band survey of the Local Group galaxies, we present the results of the search for planetary nebulae (PNe) in the dwarf irregular galaxies IC10, LeoA and SextansA. Using the standard on-band/off-band technique, sixteen new candidate PNe have been discovered in the closest starburst galaxy, IC10. The optical size of this galaxy is estimated to be much larger than previously thought, considering the location of the new PNe in an area of 3.6 kpc X 2.7 kpc. We also confirm the results of previous studies for the other two dwarf irregular galaxies, with the detection of one candidate PN in LeoA and another one in SextansA. We review the number of planetary nebulae discovered in the Local Group to date and their behaviour with metallicity. We suggest a possible fall in the observed number of PNe when [Fe/H]$<<$-1.0, which might indicate that below this point the formation rate of PNe is much lower than for stellar populations of near Solar abundances. We also find non-negligible metallicity effects on the [OIII] luminosity of the brightest PN of a galaxy.Comment: 10 pages, 4 figures, A&A accepte

Gas accretion as the origin of chemical abundance gradients in distant galaxies

It has recently been suggested that galaxies in the early Universe can grow through the accretion of cold gas, and that this may have been the main driver of star formation and stellar mass growth. Because the cold gas is essentially primordial, it has a very low abundance of elements heavier than helium (metallicity). As it is funneled to the centre of a galaxy, it will lead the central gas having an overall lower metallicity than gas further from the centre, because the gas further out has been enriched by supernovae and stellar winds, and not diluted by the primordial gas. Here we report chemical abundances across three rotationally-supported star-forming galaxies at z~3, only 2 Gyr after the Big Bang. We find an 'inverse' gradient, with the central, star forming regions having a lower metallicity than less active ones, opposite to what is seen in local galaxies. We conclude that the central gas has been diluted by the accretion of primordial gas, as predicted by 'cold flow' models.Comment: To Appear in Nature Oct 14, 2010; Supplementary Information included her