We select far-infrared (FIR: 60 m) and far-ultraviolet ( FUV: 530 8) samples of nearby galaxies in order to discuss the biases encountered by monochromatic surveys ( FIR or FUV ). Very different volumes are sampled by each selection, and much care is taken to apply volume corrections to all the analyses. The distributions of the bolometric luminosity of young stars are compared for both samples: they are found to be consistent with each other for galaxies of intermediate luminosities, but some differences are found for high (>5 ; 10 10 L ) luminosities. The shallowness of the IRAS survey prevents us from securing a comparison at low luminosities (<2 ; 10 9 L ). The ratio of the total infrared (TIR) luminosity to the FUV luminosity is found to increase with the bolometric luminosity in a similar way for both samples up to 5 ; 10 10 L . Brighter galaxies are found to have a different behavior according to their selection: the L TIR /L FUV ratio of the FUV-selected galaxies brighter than 5 ; 10 10 L reaches a plateau, whereas L TIR /L FUV continues to increase with the luminosity of bright galaxies selected in FIR. The volume-averaged specific star formation rate (SFR per unit galaxy stellar mass, SSFR) is found to decrease toward massive galaxies within each selection. The mean values of the SSFR are found to be larger than those measured for optical and NIR-selected samples over the whole mass range for the FIR selection, and for masses larger than 10 10 M for the FUV selection. Luminous and massive galaxies selected in FIR appear as active as galaxies with similar characteristics detected at z $ 0:7.
We study the ultraviolet (UV) and optical properties of 38 massive globular clusters (GCs) in the Virgo elliptical, M87, imaged using the STIS and WFPC2 instruments onboard the Hubble Space Telescope. The majority of these GCs appear extremely bright in the far‐UV (FUV) – roughly a magnitude brighter than their Galactic counterparts with similar metallicities. The observed FUV flux is several times larger than predictions of canonical old stellar population models. These canonical models, which assume a fiducial helium enrichment parameter, ΔY/ΔZ= 2, are able to reproduce the observed FUV fluxes only if ages ∼3–5 Gyr larger than the Wilkinson Microwave Anisotropy Probe (WMAP) age of the Universe are invoked, although the same models fit the UV photometry of Galactic and M31 GCs for ages less than the ‘WMAP age’. A similar discrepancy (∼3 Gyr) is found between the mass‐weighted and UV‐luminosity‐weighted ages of the massive Galactic GC ω Cen, whose colour–magnitude diagram (including peculiar features on its well‐populated horizontal branch) can be accurately reproduced by invoking a small super‐He‐rich (ΔY/ΔZ≳ 90) stellar component. By comparison to ω Cen, we propose that the majority of M87 GCs in our sample contain strong signatures of similarly minor super‐He‐rich subcomponents. This hypothesis is supported by simulations which suggest that, based on the UV detection limit of this survey, the number of GCs detected is several times that predicted by canonical models. Although we cannot prove or disprove the extreme helium scenario at the moment, we show that the same phenomenon that causes the extended horizontal branch of ω Cen explains the UV brightness of our sample. If this is indeed due to the extreme helium, this study would be the first to find its signatures in extragalactic objects.
Context. Claims of an X-shaped Galactic bulge were based on the assumption of red clump stars as standard candles in some lines of sight crossing the off-plane bulge. However, some doubts have been cast on whether the two peaks in star counts along the line of sight really represent a double peak in the density distribution, or whether there is something wrong with the assumption of a unique constant absolute magnitude for all of these stars. Aims. With the advent of Gaia-DR2 parallaxes in combination with near-infrared VISTA-VVV data, we are able to check which of the hypotheses is correct. Methods. We calculated the median absolute magnitude M K corresponding to both peaks of putative red clumps in seven lines of sight with the lowest extinction in the interesting coordinates' range. Results. The difference between the absolute magnitude of the bright and the faint peak is ∆M K ≈ 0.4. The selected stars in both peaks cannot be represented by the same red clump giants with constant M K ≈ −1.6. Conclusions. The hypothesis that the bulge contains an X-shape is based on the assumption that the faint and bright peaks of the density distribution towards the bulge are dominated by standard red clump stars. However, we show that both the faint and bright peaks cannot be dominated by standard red clump stars simultaneously.
Neuropeptides and their degrading enzymes, particularly SP and ACE, have a significant role in the pathogenesis of ACD.
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