Abstract
We present new WFC3/UVIS observations of UGC 4483, the closest example of a metal-poor blue compact dwarf galaxy, with a metallicity of
Z
≃ 1/15
Z
⊙
and located at a distance of
D
≃ 3.4 ...Mpc. The extremely high quality of our new data allows us to clearly resolve the multiple stellar evolutionary phases populating the color–magnitude diagram (CMD), to reach more than 4 mag deeper than the tip of the red giant branch, and to detect for the first time core He-burning stars with masses ≲2
M
⊙
, populating the red clump and possibly the horizontal branch (HB) of the galaxy. By applying the synthetic CMD method to our observations, we determine an average star formation rate over the whole Hubble time of at least
(
7.01
±
0.44
)
×
10
−
4
M
⊙
yr
−
1
, corresponding to a total astrated stellar mass of
(
9.60
±
0.61
)
×
10
6
M
⊙
, 87% of which went into stars at epochs earlier than 1 Gyr ago. With our star formation history recovery method we find the best fit with a distance modulus of DM = 27.45 ± 0.10, slightly lower than previous estimates. Finally, we find strong evidence of an old (≳10 Gyr) stellar population in UGC 4483 thanks to the detection of an HB phase and the identification of six candidate RR Lyrae variable stars.
Abstract
We carry out a comparative analysis of the metallicities from the stellar, neutral-gas, and ionized-gas components in the metal-rich spiral galaxy M83. We analyze spectroscopic observations ...taken with the Hubble Space Telescope, the Large Binocular Telescope, and the Very Large Telescope. We detect a clear depletion of the H
i
gas, as observed from the H
i
column densities in the nuclear region of this spiral galaxy. We find column densities of log
N
(H
i
) cm
−2
< 20.0 at galactocentric distances of <0.18 kpc, in contrast to column densities of log
N
(H
i
) cm
−2
∼ 21.0 in the galactic disk, a trend observed in other nearby spiral galaxies. We measure a metallicity gradient of −0.03 ± 0.01 dex kpc
−1
for the ionized gas, comparable to the metallicity gradient of a local benchmark of 49 nearby star-forming galaxies of −0.026 ± 0.002 dex kpc
−1
. Our cospatial metallicity comparison of the multiphase gas and stellar populations shows excellent agreement outside of the nucleus of the galaxy, hinting at a scenario where the mixing of newly synthesized metals from the most massive stars in the star clusters takes longer than their lifetimes (∼10 Myr). Finally, our work shows that caution must be taken when studying the metallicity gradient of the neutral-gas component in star-forming galaxies, since this can be strongly biased, as these environments can be dominated by molecular gas. In these regions the typical metallicity tracers can provide inaccurate abundances, as they may trace both the neutral- and molecular-gas components.
The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to ...those seen at high z (z > 6). The prime high-level science product of CLASSY is accurately coadded UV spectra, ranging from ∼1000 to 2000 Å, derived from a combination of archival and new data obtained with HST's Cosmic Origins Spectrograph (COS). This paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via C iii nebular emission. Despite changes in spectral resolution of up to ∼25% between individual data sets (due to changes in the COS line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of S/N < 20.
Alginate (ALG) and chitosan (CS) have been extensively used for biomedical applications; however, data relative to immune responses exerted by them are scarce. We synthesized a submicron vesicle ...system (SV) displaying a CS shell over an ALG core. Intravenous injection of these promising carriers could be a possible route of delivery; therefore, we evaluated their impact on human peripheral blood mononuclear cells (PBMCs). By this ex vivo approach, we established how SV chemical-physical characteristics affected the immune cells in terms of cellular uptake, viability, and state of activation. By flow cytometry, we demonstrated that SVs were internalized by PBMCs with differential trends. No substantial necrotic and apoptotic signals were recorded, and SVs weakly affected activation status of PBMCs (concerning the markers CD69, CD25, CD80, and the cytokines TNF-α and IL-6), showing high immune biocompatibility and low immunomodulating properties. Our findings gain particular value toward the biomedical applications of SVs and make these polymer-based structures more attractive for translation into clinical uses.
Only about 19 Galactic and 25 extragalactic bonafide luminous blue variables (LBVs) are known to date. This incomplete census prevents our understanding of this crucial phase of massive star ...evolution which leads to the formation of heavy binary black holes via the classical channel. With large samples of LBVs one could better determine the duration and maximum stellar luminosity which characterize this phase. We search for candidate LBVs (cLBVs) in a new galaxy, NGC 7793. For this purpose, we combine high spatial resolution images from two Hubble Space Telescope (HST) programs with optical spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). By combining PSF-fitting photometry measured on F547M, F657N, and F814W images, with restrictions on point-like appearance (at HST resolution) and Ha luminosity, we find 100 potential cLBVs, 36 of which fall in the MUSE fields. Five of the latter 36 sources are promising cLBVs which have M-V <= -7 and a combination of: H alpha with a P-Cygni profile; no O Ilambda 6300 emission; weak or no O IIIlambda 5007 emission; large N II/H alpha relative to HII regions; and S IIlambda 6716/S IIlambda 6731 similar to 1. It is not clear if these five cLBVs are isolated from O-type stars, which would favour the binary formation scenario of LBVs. Our study, which approximately covers one fourth of the optical disc of NGC 7793, demonstrates how by combining the above HST surveys with multi-object spectroscopy from 8-m class telescopes, one can efficiently find large samples of cLBVs in nearby galaxies.
Versatile methods are here presented for the assembling of magnetic nanoparticles in controlled super-structures with different final aspect ratios. The first step of the procedure is based on the ...destabilization, and consequently clustering, of a dextran-coated nanoparticles suspension, altering the colloidal stability of the initial building blocks. Subsequently, a second polysaccharide shell, based on chitosan, is grafted to the super-structure surface, for stopping the aggregation of the nanoparticles and enhancing the stability of the resulting assembly. For achieving a finer control of the process, spherical magnetic clusters (SMC) are prepared through a microfluidic aided clustering, investigating the contribution of flow rates and injection scheme geometry to the nanoparticle assembly. Besides, the use of static magnetic fields applied during the first step results in the preparation of micrometric elongated magnetic super-structures (EMS), tuning the average aspect ratio up to a value of 13±4.
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