Improved photometry of SDSS crowded field images: Structure and dark matter content in the dwarf spheroidal galaxy Leo I

We explore how well crowded field point-source photometry can be accomplished with SDSS data: We present a photometric pipeline based on DoPhot, and tuned for analyzing crowded-field images from the SDSS. Using Monte Carlo simulations we show that the completeness of source extraction is above 80% to i < 21 (AB) and a stellar surface density of about 200 sq.amin. Hence, a specialized data pipeline can efficiently be used for e.g. nearby resolved galaxies in SDSS images, where the standard SDSS photometric package Photo, when applied in normal survey mode, gives poor results. We apply our pipeline to an area of about 3.55sq.deg. around the dwarf spheroidal galaxy (dSph) Leo I, and construct a high S/N star-count map of Leo I via an optimized filter in color-magnitude space (g,r,i). Although the radial surface-density profile of the dwarf deviates from the best fit empirical King model towards outer radii, we find no evidence for tidal debris out to a stellar surface-density of 4*10^(-3) of the central value. We determine the total luminosity of Leo I, and model its mass using the spherical and isotropic Jeans equation. Assuming that 'mass follows light' we constrain a lower limit of the total mass of the dSph to be (1.7+/-0.2)*10^7 Msol. Contrary, if the mass in Leo I is dominated by a constant density dark-matter (DM) halo, then the mass within the central 12' is (2+/-0.6)*10^8 Msol. This leads to a mass-to-light ratio of >>6 (Ic_sol), and possibly >75 if the DM halo dominates the mass and extends further out than 12'. In summary, our results show that Leo I is a symmetric, relaxed and bound system; this supports the idea that Leo I is a dark-matter dominated system.Comment: 13 pages, 11 figures; accepted for publication in A

The Remarkable Central Structure of the Barred Galaxy NGC 1415

A remarkable structure is observed in the innermost regions of the barred galaxy NGC 1415 : a small stellar bar, bright circumnuclear ionized gas seen in Halpha, two bright ionized gas sources, seen in Halpha, just beyond the ends of the small bar and a boxy distribution of optical continuum. We have developed a mass distribution model consisting in disk, a bulge, and a bar to approximate t he observed central morphology and its surface brightness. In order to reproduce the observed optical brightness distribution a two-component bar was used, with one component to model the elongated isophotes of the bar and the second component to model the boxy-shaped isophotes. We interpret the circumnuclear ionized gas as forming a circumnuclear ring and the two bright sources as a nuclear and/or circumnuclear outflow slightly out of the plane of the disk.Comment: 19 pages, 29 figures. To be published in February 2000, ApJ, 52

Dynamical modelling of the elliptical galaxy NGC 2974

In this paper we analyse the relations between a previously described oblate Jaffe model for an ellipsoidal galaxy and the observed quantities for NGC 2974, and obtain the length and velocity scales for a relevant elliptical galaxy model. We then derive the finite total mass of the model from these scales, and finally find a good fit of an isotropic oblate Jaffe model by using the Gauss-Hermite fit parameters and the observed ellipticity of the galaxy NGC 2974. The model is also used to predict the total luminous mass of NGC 2974, assuming that the influence of dark matter in this galaxy on the image, ellipticity and Gauss-Hermite fit parameters of this galaxy is negligible within the central region, of radius $0.5R_{\rm e}.$Comment: 7 figure

A Spitzer/IRAC Census of the Asymptotic Giant Branch Populations in Local Group Dwarfs. I. WLM

We present Spitzer/IRAC observations at 3.6 and 4.5 microns along with optical data from the Local Group Galaxies Survey to investigate the evolved stellar population of the Local Group dwarf irregular galaxy WLM. These observations provide a nearly complete census of the asymptotic giant branch (AGB) stars. We find 39% of the infrared-detected AGB stars are not detected in the optical data, even though our 50% completeness limit is three magnitudes fainter than the red giant branch tip. An additional 4% of the infrared-detected AGBs are misidentified in the optical, presumably due to reddening by circumstellar dust. We also compare our results with those of a narrow-band optical carbon star survey of WLM, and find the latter study sensitive to only 18% of the total AGB population. We detect objects with infrared fluxes consistent with them being mass-losing AGB stars, and derive a present day total mass-loss rate from the AGB stars of 0.7-2.4 x 10^(-3) solar masses per year. The distribution of mass-loss rates and bolometric luminosities of AGBs and red supergiants are very similar to those in the LMC and SMC and the empirical maximum mass-loss rate observed in the LMC and SMC is in excellent agreement with our WLM data.Comment: Accepted by ApJ, 34 pages, 13 figures, version with high-resolution figures available at: http://webusers.astro.umn.edu/~djackson

Serum-Nutrient Starvation Induces Cell Death Mediated by Bax and Puma That Is Counteracted by p21 and Unmasked by Bcl-xL Inhibition

The cyclin-dependent kinase inhibitor p21 (p21WAF1/Cip1) is a multifunctional protein known to promote cell cycle arrest and survival in response to p53-dependent and p53 independent stimuli. We herein investigated whether and how it might contribute to the survival of cancer cells that are in low-nutrient conditions during tumour growth, by culturing isogenic human colorectal cancer cell lines (HCT116) and breast cancer cell lines in a medium deprived in amino acids and serum. We show that such starvation enhances, independently from p53, the expression of p21 and that of the pro-apoptotic BH3-only protein Puma. Under these conditions, p21 prevents Puma and its downstream effector Bax from triggering the mitochondrial apoptotic pathway. This anti-apoptotic effect is exerted from the cytosol but it is unrelated to the ability of p21 to interfere with the effector caspase 3. The survival function of p21 is, however, overcome by RNA interference mediated Bcl-xL depletion, or by the pharmacological inhibitor ABT-737. Thus, an insufficient supply in nutrients may not have an overt effect on cancer cell viability due to p21 induction, but it primes these cells to die, and sensitizes them to the deleterious effects of Bcl-xL inhibitors regardless of their p53 status

Evidence for alternative electron sinks to photosynthetic carbon assimilation in the high mountain plant species Ranunculus glacialis

International audienceThe high mountain plant species Ranunculus glacialis has a low antioxidative scavenging capacity and a low activity of thermal dissipation of excess light energy despite its growth under conditions of frequent light and cold stress. In order to examine whether this species is protected from over-reduction by matching photosystem II (PSII) electron transport (ETR) and carbon assimilation, both were analysed simultaneously at various temperatures and light intensities using infrared gas absorption coupled with chlorophyll fluorescence. ETR exceeded electron consumption by carbon assimilation at higher light intensities and at all temperatures tested, necessitating alternative electron sinks. As photorespiration might consume the majority of excess electrons, photorespiration was inhibited by either high internal leaf CO2 molar ratio (C-i), low oxygen partial pressure (0.5% oxygen), or both. At 0.5% oxygen ETR was significantly lower than at 21% oxygen. At 21% oxygen, however, ETR still exceeded carbon assimilation at high C-i, suggesting that excess electrons are transferred to another oxygen consuming reaction when photorespiration is blocked. Nevertheless, photorespiration does contribute to electron consumption. While the activity of the water -water cycle to electron consumption is not known in leaves of R. glacialis, indirect evidence such as the high sensitivity to oxidative stress and the low initial NADP-malate dehydrogenase (NADP-MDH) activity suggests only a minor contribution as an alternative electron sink. Alternatively, the plastid terminal oxidase (PTOX) may transfer excess electrons to oxygen. This enzyme is highly abundant in R. glacialis leaves and exceeds the PTOX content of every other plant species so far examined, including those of transgenic tomato leaves overexpressing the PTOX protein. Finally, PTOX contents strongly declined during deacclimation of R. glacialis plants, suggesting their important role in photoprotection. Ranunculus glacialis is the first reported plant species with such a high PTOX protein content

SN 1998A: Explosion of a Blue Supergiant

We present spectroscopic and photometric observations of the peculiar Type II supernova (SN) 1998A. The light curves and spectra closely resemble those of SN 1987A, suggesting that the SN 1998A progenitor exploded when it was a compact blue supergiant. However, the comparison with SN 1987A also highlights some important differences: SN 1998A is more luminous and the spectra show bluer continua and larger expansion velocities at all epochs. These observational properties indicate that the explosion of SN 1998A is more energetic than SN 1987A and more typical of SNe II. Comparing the observational data to simulations, we deduce that the progenitor of SN 1998A was a massive star (~ 25 Mo) with a small pre-supernova radius (< 6 x 10^{12} cm). The Ba II lines, unusually strong in SN 1987A and some faint II--P events, are almost normal in the case of SN 1998A, indicating that the temperature plays a key role in determining their strength.Comment: 15 pages, 16 figures, accepted for publication in MNRA

The Local Group Census: searching for PNe in IC 1613, WLM and GR8

In the framework of the Local Group Census (LGC), a survey of the Local Group (LG) galaxies above Dec=$-30^\circ$, which is aimed at surveying their populations with strong emission lines, we have searched for planetary nebulae (PNe) in the low-metallicity dwarf irregular galaxies IC1613, WLM, GR8. Two new candidate PNe have been found in IC1613, one in WLM and none in GR8. The observations presented in this paper, together with the previous results from the LGC, represent the first step in the study of the PN population in low-metallicity, dwarf irregular galaxies of the Local Group. They will be followed by deep spectroscopy to confirm their nature and to study their physical-chemical properties. We used the observed number of PNe in each LG galaxy to estimate a lower limit to the mass of the intermediate-age population which was compared to the Star Formation Rate (SFR) of LG dwarf galaxies. These results are in agreement with those from accurate star formation history (SFH) analysis for these small galaxy systems.Comment: 10 pages, 6 figures, MNRAS accepte

Problems involving pp-Laplacian type equations and measures

summary:In this paper I discuss two questions on $p$-Laplacian type operators: I characterize sets that are removable for Hölder continuous solutions and then discuss the problem of existence and uniqueness of solutions to $-\div (|\nabla u|^{p-2}\nabla u)=\mu$ with zero boundary values; here $\mu$ is a Radon measure. The joining link between the problems is the use of equations involving measures