Radio emission during the formation of stellar clusters in M33

We investigate thermal and non-thermal radio continuum associated with the early formation and evolution of Young Stellar Clusters (YSCs) selected by their MIR emission in M33. For the first time in an external galaxy it has been possible to identify radio counterparts to more than 300 star forming regions. We proof the nature of candidate YSCs fully embedded in molecular clouds, by recovering their associated faint radio continuum luminosities. Using the Halpha line to identify free-free radio emission at 5 GHz in the more evolved, partially exposed YSCs, we retrieve information on the relevance of magnetic fields and cosmic rays across the M33 disk at 25 pc spatial scales. A cross-correlation of MIR and radio continuum luminosities is established from bright to very faint YSCs, with MIR-to-radio emission ratio showing a gradual decline towards the outer disk, while the magnetic field is pervasive at all radii. We establish and discuss the tight relation between radio continuum and other star formation indicators, such as Halpha. This relation holds for individual YSCs over four orders of magnitude as well as for molecular clouds hosting YSCs. On average about half of radio emission at 5 GHz in YSCs is non-thermal. For exposed but compact YSCs the non-thermal radio fraction increases with source brightness, while for large HII regions the fraction is lower and shows no clear trend. This has been found for YSCs with and without identified SNRs and underlines the possible role of massive stars in triggering particle acceleration through winds and shocks: these particles diffuse throughout the native molecular cloud prior to cloud dispersal.Comment: 14 pages, 10 figures, accepted for publication in A&

Lack of Interaction between the Dust Grains and the Anomalous Radio Jet in the Nearby Spiral Galaxy NGC 4258

We obtained Spitzer/IRAC 3.6-8 micron images of the nearby spiral galaxy NGC 4258 to study possible interactions between dust and the radio jet. In our analysis we also included high-resolution radio continuum, H-alpha, CO, and X-ray data. Our data reveal that the 8 micron emission, believed to originate largely from PAH molecules and hot dust, is an excellent tracer of the normal spiral structure in NGC 4258, and hence it originates from the galactic plane. We investigated the possibility of dust destruction by the radio jet by calculating correlation coefficients between the 8 micron and radio continuum emissions along the jet in two independent ways, namely (i) from wavelet-transformed maps of the original images at different spatial scales, and (ii) from one-dimensional intensity cuts perpendicular to the projected path of the radio jet on the sky. No definitive sign of a correlation (or anticorrelation) was detected on relevant spatial scales with either approach, implying that any dust destruction must take place at spatial scales that are not resolved by our observations.Comment: Accepted for publication in the Astronomical Journal (11 pages, 10 figures, 1 table

The Resolved Radio--FIR Correlation in Nearby Galaxies with Herschel and Spitzer

We investigate the correlation between the far-infrared (FIR) and radio continuum emission from NGC6946 on spatial scales between 0.9 and 17 kpc. We use the Herschel PACS (70, 100, 160$\mu$m) and SPIRE (250$\mu$m) data from the KINGFISH project. Separating the free-free and synchrotron components of the radio continuum emission, we find that FIR is better correlated with the free-free than the synchrotron emission. Compared to a similar study in M33 and M31, we find that the scale dependence of the synchrotron--FIR correlation in NGC6946 is more similar to M31 than M33. The scale dependence of the synchrotron--FIR correlation can be explained by the turbulent-to-ordered magnetic field ratio or, equivalently, the diffusion length of the cosmic ray electrons in these galaxies.Comment: 4 pages, 3 figures, The Spectral Energy Distribution of Galaxies Proceedings IAU Symposium No. 284, 2011, R.J. Tuffs & C.C.Popescu, ed

How accessibility influences citation counts: The case of citations to the full text articles available from ResearchGate

It is generally believed that the number of citations to an article can positively be correlated to its free online availability. In the present study, we investigated the possible impact of academic social networks on the number of citations. We chose the social web service “ResearchGate” as a case. This website acts both as a social network to connect researchers, and at the same time, as an open access repository to publish post-print version of the accepted manuscripts and final versions of open access articles. We collected the data of 1823 articles published by the authors from four different universities. By analyzing these data, we showed that although different levels of full text availability are observed for the four universities, there is always a significant positive correlation between full text availability and the citation count. Moreover, we showed that both post-print version and publisher’s version (i.e., final published version) of the archived manuscripts receive more citations than non-OA articles, and the difference in the citation counts of post-print manuscripts and publisher’s version articles is nonsignificant

Mapping dust through emission and absorption in nearby galaxies

Dust has long been identified as a barrier to measuring inherent galaxy properties. However, the link between dust and attenuation is not straightforward and depends on both the amount of dust and its distribution. Herschel imaging of nearby galaxies undertaken as part of the KINGFISH project allows us to map the dust as seen in emission with unprecedented sensitivity and similar to 1 kpc resolution. We present here new optical integral field unit spectroscopy for eight of these galaxies that provides complementary 100-200 pc scale maps of the dust attenuation through observation of the reddening in both the Balmer decrement and the stellar continuum. The stellar continuum reddening, which is systematically less than that observed in the Balmer decrement, shows no clear correlation with the dust, suggesting that the distribution of stellar reddening acts as a poor tracer of the overall dust content. The brightest H II regions are observed to be preferentially located in dusty regions, and we do find a correlation between the Balmer line reddening and the dust mass surface density for which we provide an empirical relation. Some of the high-inclination systems in our sample exhibit high extinction, but we also find evidence that unresolved variations in the dust distribution on scales smaller than 500 pc may contribute to the scatter in this relation. We caution against the use of integrated A(V) measures to infer global dust properties