The stellar host in star-forming low-mass galaxies: Evidence for two classes

The morphological evolution of star-forming galaxies provides important clues to understand their physical properties, as well as the triggering and quenching mechanisms of star formation. We aim at connecting morphology and star-formation properties of low-mass galaxies (median stellar mass $\sim$ 10$^{8.5}$ M$_{\odot}$) at low redshift ($z<0.36$). We use a sample of medium-band selected star-forming galaxies from the GOODS-North field. H$\alpha$ images for the sample are created combining both spectral energy distribution fits and HST data. Using them, we mask the star forming regions to obtain an unbiased two-dimensional model of the light distribution of the host galaxies. For this purpose we use $\texttt{PHI}$, a new Bayesian photometric decomposition code. We apply it independently to 7 HST bands assuming a S\'ersic surface brightness model. Star-forming galaxy hosts show low S\'ersic index (with median $n$ $\sim$ 0.9), as well as small sizes (median $R_e$ $\sim$ 1.6 kpc), and negligible change of the parameters with wavelength (except for the axis ratio, which grows with wavelength). Using a clustering algorithm, we find two different classes of star-forming galaxies: A more compact, redder, and high-$n$ (class A) and a more extended, bluer and lower-$n$ one (class B). We also find evidence that the first class is more spheroidal-like. In addition, we find that 48% of the analyzed galaxies present negative color gradients (only 5% are positive). The host component of low-mass star-forming galaxies at $z<0.36$ separates into two different classes, similar to what has been found for their higher mass counterparts. The results are consistent with an evolution from class B to class A. Several mechanisms from the literature, like minor and major mergers, and violent disk instability, can explain the physical process behind the likely transition between the classes. [abridged]Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, 11 figure

Astronomical Site Ranking Based on Tropospheric Wind Statistics

We present comprehensive and reliable statistics of high altitude wind speeds and the tropospheric flows at the location of five important astronomical observatories. Statistical analysis exclusively of high altitude winds point to La Palma as the most suitable site for adaptive optics, with a mean value of 22.13 m/s at the 200 mbar pressure level. La Silla is at the bottom of the ranking, with the largest average value 200 mbar wind speed(33.35 m/s). We have found a clear annual periodicity of high altitude winds for the five sites in study. We have also explored the connection of high to low altitude atmospheric winds as a first approach of the linear relationship between the average velocity of the turbulence and high altitude winds (Sarazin & Tokovinin 2001). We may conclude that high and low altitude winds show good linear relationships at the five selected sites. The highest correlation coefficients correspond to Paranal and San Pedro Martir, while La Palma and La Silla show similar high to low altitude wind connection. Mauna Kea shows the smallest degree of correlation, which suggests a weaker linear relationship. Our results support the idea of high altitude winds as a parameter for rank astronomical sites in terms of their suitability for adaptive optics, although we have no evidence for adopting the same linear coefficient at different sites. The final value of this linear coefficient at a particular site could drastically change the interpretation of high altitude wind speeds as a direct parameter for site characterization.Comment: 18 pages, 5 figures. Accepted in MNRA

Molecular gas in low-metallicity starburst galaxies: Scaling relations and the CO-to-H2_2 conversion factor

We study the molecular content and the star formation efficiency of 21 Blue Compact Dwarfs (BCDs). We present CO(1-0) and (2-1) observations, further supplemented with additional CO measurements and multiwavelength ancillary data from the literature. We find the CO luminosity to be correlated with the stellar and HI masses, SFR tracers, the size of the starburst and its metallicity. BCDs appear offset from the Schmidt-Kennicutt (SK) law, showing extremely low ($\lesssim$0.1 Gyr) H2 and H2+HI depletion timescales. The departure from the SK law is smaller when considering H2+HI rather than H2 only, and is larger for BCDs with lower metallicity and higher specific SFR. Thus, the molecular fraction and H2 depletion timescale of BCDs is found to be strongly correlated with metallicity. Using this and assuming that the empirical correlation found between the specific SFR and galaxy-averaged H2 depletion timescale of more metal-rich galaxies extends to lower masses, we derive a metallicity-dependent CO-to-H2 conversion factor $\alpha_{CO, Z} \propto (Z/Z_{\odot})^{-y}$, with $y=1.5(\pm 0.3)$ in qualitative agreement with previous determinations, dust-based measurements, and recent model predictions. Our results suggest that in vigorously star-forming dwarfs the fraction of H2 traced by CO decreases by a factor of about 40 from $Z \sim Z_{\odot}$ to $Z \sim 0.1 Z_{\odot}$, leading to a strong underestimation of the H2 mass in metal-poor systems when a Galactic $\alpha_{CO, MW}$ is considered. Adopting $\alpha_{CO, Z}$ we find that departures from the SK law are partially resolved. Our results suggest that starbursting dwarfs have shorter depletion gas timescales and lower molecular fractions compared to normal late-type disc galaxies even accounting for the molecular gas not traced by CO emission in metal-poor environments, raising additional constraints to model predictions (Abridged).Comment: 18 pages, 14 Figures, 4 Tables: Accepted for publication in A&

Optical Surface Photometry of a Sample of Disk Galaxies. II Structural Components

This work presents the structural decomposition of a sample of 11 disk galaxies, which span a range of different morphological types. The U, B, V, R, and I photometric information given in Paper I (color and color-index images and luminosity, ellipticity, and position-angle profiles) has been used to decide what types of components form the galaxies before carrying out the decomposition. We find and model such components as bulges, disks, bars, lenses and rings.Comment: 14 figures. Accepted for publication in A&

EU digital communication strategy during the COVID-19 vaccination campaign: Framing, contents and attributed roles at stake

If in recent years the European Union (EU) has had to face complex and multifactorial “poly-crises” (such as Brexit, refugees or the euro), the pandemic caused by COVID-19 has been an unprecedented event on a global scale with important implications at all levels. Indeed, it has reinforced public health issues aimed at protecting the population as nodal elements of the policies implemented by this organization. This research aims to analyze the different organizational communication strategies on Twitter implemented by the main EU institutions during the COVID-19 vaccination campaign, in order to examine the presence of this exceptional milestone. This study has been carried out using an eminently quantitative methodology, based on a content analysis to quantify the different variables and indicators established for the publications of the official profiles of the European Commission, the European Parliament and the European Council. The proposed categories focus on exploring their predominant thematic areas, as well as main purposes/attributed functions. In the light of the results obtained, it is concluded that the vaccination campaign is a milestone with a considerable volume of publications by all profiles. However, among the attributed functions, the distribution of aseptic information has been predominant, which is why it is discussed whether these institutions have sufficiently taken advantage of the possibilities offered by the digital environment of Twitter for the dissemination of the European message

Astronomical site selection: On the use of satellite data for aerosol content monitoring

The main goal of this work is the analysis of new approaches to the study of the properties of astronomical sites. In particular, satellite data measuring aerosols have recently been proposed as a useful technique for site characterization and searching for new sites to host future very large telescopes. Nevertheless, these data need to be critically considered and interpreted in accordance with the spatial resolution and spectroscopic channels used. In this paper we have explored and retrieved measurements from satellites with high spatial and temporal resolutions and concentrated on channels of astronomical interest. The selected datasets are OMI on board the NASA Aura satellite and MODIS on board the NASA Terra and Aqua satellites. A comparison of remote sensing and in situ techniques is discussed. As a result, we find that aerosol data provided by satellites up to now are not reliable enough for aerosol site characterization, and in situ data are required.Comment: LaTeX2e MN v2.2, 16 pages with 13 figures. Accepted for Mon. Not. R. Astron. Soc.(2008

Starburst galaxies in the COSMOS field : clumpy star-formation at redshift 0 < z <0.5

This work has been funded by the Spanish MINECO, Grant ESTALLIDOS, AYA2013-47742-C4-2P and AYA2010-21887-C04-04. J.M.A. acknowledges support from the European Research Council Starting Grant SEDMorph (P.I. V. Wild). R.H.G. acknowledges the FPI grant from MINECO within ESTALLIDOS project.Context. At high redshift, starburst galaxies present irregular morphologies with 10-20% of their star formation occurring in giant clumps. These clumpy galaxies are considered the progenitors of local disk galaxies. To understand the properties of starbursts at intermediate and low redshift, it is fundamental to track their evolution and the possible link with the systems at higher z. Aims. We present an extensive, systematic, and multiband search and analysis of the starburst galaxies at redshift (0 1010. We classify galaxies into three main types, depending on their HST morphology: single knot (Sknot), single star-forming knot plus diffuse light (Sknot+diffuse), and multiple star-forming knots (Mknots/clumpy) galaxy. We found a fraction of Mknots/clumpy galaxy fclumpy = 0.24 considering out total sample of starburst galaxies up to z ∼ 0.5. The individual star-forming knots in our sample follows the same L(Hα) vs. size scaling relation as local giant HII regions. However, they slightly differ from the one provided using samples at high redshift. This result highlights the importance of spatially resolving the star-forming regions for this kind of study. Star-forming clumps in the central regions of Mknots galaxies are more massive, and present higher star formation rates, than those in the outskirts. This trend is less clear when we consider either the mass surface density or surface star formation rate. Sknot galaxies do show properties similar to both dwarf elliptical and irregulars in the surface brightness (μ) versus Mhost diagram in the B-band, and to spheroidals and ellipticals in the μ versus Mhost diagram in the V-band. Conclusions. The properties of our star-forming knots in Sknot+diffuse and Mknots/clumpy galaxies support the predictions of recent numerical simulations claiming that they have been produced by violent disk instabilities. We suggest that the evolution of these knots means that large and massive clumps at the galaxy centers represent the end product of the coalescence of surviving smaller clumps from the outskirts. Our results support this mechanism and make it unlikely that mergers are the reason behind the observed starburst knots. Sknot galaxies might be transitional phases of the Blue Compact Dwarfs (BCD) class, with their properties consistent with spheroidal-like, but blue structures.Publisher PDFPeer reviewe

Has COVID-19 promoted or discouraged a European Public Sphere? Comparative analysis of the Twitter interactions of German, French, Italian and Spanish MEPSs during the pandemic

This comparative research analyses the political discussion through social media of the top list German, French, Italian and Spanish Members of the European Parliament during COVID-19 crisis times. Through content analysis, the article focuses on Twitter behaviours during a pandemic crisis period (March 23 to April 23, 2020). The study that analyses up to 14 (first listed MEPs) Twitter accounts and a total N of 2101 tweets looks at clarifying if the COVID-19 pandemic has promoted or discouraged the growth of a European Public Sphere. The results show that audience involvement depended on certain online conducts of the MEP rather than on his or her constant activity. Those behaviours produced as well that the COVID-19 debate was mostly restricted to the political elite, who neither allow European civil society to take part in the discussion or communicate to the general public with the aim of shaping a European Public Sphere