We present a multiwavelength radio study of the nearby galaxy pair Arp 269(NGC 4490/85). High sensitivity to extended structures gained by using themerged interferometric and single- dish maps allowed us to reveal a previouslyundiscovered extension of the radio continuum emission. Its direction issignificantly different from that of the neutral gas tail, suggesting thatdifferent physical processes might be involved in their creation. Thepopulation of radio- emitting electrons is generally young, signifying anongoing, vigorous star formation -- this claim is supported by strong magneticfields (over 20 {\mu}G), similar to the ones found in much larger spiralgalaxies. From the study of the spectral energy distribution, we conclude thatthe electron population in the intergalactic bridge between member galaxiesoriginates from the disc areas, and therefore its age (approximately 3.7--16.9Myr, depending on the model used) reflects the time-scale of the interaction.We have also discovered an angularly near compact steep source -- which is amember of a different galaxy pair -- at a redshift of approximately 0.125.

We present the detection, performed with the Westerbork Synthesis RadioTelescope (WSRT) and the Karl Jansky Very Large Array (VLA), of a fast HI 21-cmoutflow in the ultra-luminous infrared galaxy Mrk 231. The outflow is observedas shallow HI absorption blueshifted ~1300 km/s with respect to the systemicvelocity and located against the inner kpc of the radio source. The outflowinggas has an estimated column density between 5 and 15x10^18 Tspin cm^-2. Wederive the Tspin to lie in the range 400-2000 K and the densities aren_HI~10-100 cm^-3. Our results confirm the multiphase nature of the outflow inMrk231. Although effects of the interaction between the radio plasma and thesurrounding medium cannot be ruled out, the energetics and the lack of a clearkpc-scale jet suggest that the most likely origin of the HI outflow is awide-angle nuclear wind, as earlier proposed to explain the neutral outflowtraced by NaI and molecular gas. Our results suggest that an HI component ispresent in fast outflows regardless of the acceleration mechanism (wind vs jetdriven) and that it must be connected with common properties of thepre-interaction gas. Considering the observed similarity of their columndensities, the HI outflow likely represents the inner part of the broad windidentified on larger scales in NaI. The mass outflow rate of the HI outflowdoes not appear to be as large as the one observed in molecular gas. Thesecharacteristics suggest that the HI may represent a short intermediate phase inthe rapid cooling of the gas. We also obtained deeper continuum images thanpreviously available. At the resolution of ~1arcsec we do not see a kpc-scalejet. Instead, we detect a plateau of emission, likely due to star formation,surrounding the bright nuclear region. We also detect a poorly collimatedbridge which may represent the channel feeding the southern lobe.

In this second paper of a series, we explore the B-V, U-B, and FUV-NUV radialcolor trends from a multi-wavelength sample of 141 dwarf disk galaxies. Likespirals, dwarf galaxies have three types of radial surface brightness profiles:(I) single exponential throughout the observed extent (the minority), (II)down-bending (the majority), and (III) up-bending. We find that colors of (1)Type I dwarfs generally become redder with increasing radius unlike spiralsthat have a blueing trend that flattens beyond ~1.5 disk scale lengths, (2)Type II dwarfs come in six different "flavors," one of which mimics the "U"shape of spirals, and (3) Type III dwarfs have a stretched "S" shape wherecentral colors are flattish, become steeply redder to the surface brightnessbreak, then remain roughly constant beyond, similar to spiral TypeIII colorprofiles, but without the central outward bluing. Faint (-9 > M_B > -14) TypeII dwarfs tend to have continuously red or "U" shaped colors and steeper colorslopes than bright (-14 > M_B > -19) Type II dwarfs, which additionally havecolors that become bluer or remain constant with increasing radius. Sm dwarfsand BCDs tend to have at least some blue and red radial color trend,respectively. Additionally, we determine stellar surface mass density (Sigma)profiles and use them to show that the break in Sigma generally remains in TypeII dwarfs (unlike Type II spirals) but generally disappears in Type III dwarfs(unlike Type III spirals). Moreover, the break in Sigma is strong,intermediate, and weak in faint dwarfs, bright dwarfs, and spirals,respectively, indicating that Sigma may straighten with increasing galaxy mass.Lastly, the average stellar surface mass density at the surface brightnessbreak is roughly 1-2 M_S/pc^2 for Type II dwarfs but higher at 5.9 M_S/pc^2 or27 M_S/pc^2 for Type III BCDs and dIms, respectively.

The Initial Star formation and Lifetimes of Andromeda Satellites (ISLAndS)project uses Hubble Space Telescope imaging to study a representative sample ofsix Andromeda dSph satellite companion galaxies. The main goal of the programis to determine whether the star formation histories (SFHs) of the AndromedadSph satellites demonstrate significant statistical differences from those ofthe Milky Way, which may be attributable to the different properties of theirlocal environments. Our observations reach the oldest main sequence turn-offs,allowing a time resolution at the oldest ages of ~ 1 Gyr, which is comparableto the best achievable resolution in the MW satellites. We find that the sixdSphs present a variety of SFHs that are not strictly correlated withluminosity or present distance from M31. Specifically, we find a significantrange in quenching times (lookback times from 9 to 6 Gyr), but with allquenching times more than ~ 6 Gyr ago. In agreement with observations of MilkyWay companions of similar mass, there is no evidence of complete quenching ofstar formation by the cosmic UV background responsible for reionization, butthe possibility of a degree of quenching at reionization cannot be ruled out.We do not find significant differences between the SFHs of the three members ofthe vast, thin plane of satellites and the three off-plane dSphs. The primarydifference between the SFHs of the ISLAndS dSphs and Milky Way dSph companionsof similar luminosities and host distances is the absence of very latequenching (< 5 Gyr ago) dSphs in the ISLAndS sample. Thus, models that canreproduce satellite populations with and without late quenching satellites willbe of extreme interest.

In this work, we investigate the implications of the Integrated Galaxy-widestellar Initial Mass Function (IGIMF) approach in the framework of thesemi-analytic model GAEA (GAlaxy Evolution and Assembly), which features adetailed treatment of chemical enrichment and stellar feedback. The IGIMFprovides an analytic description of the dependence of the stellar IMF shape onthe rate of star formation in galaxies. We find that our model with a universalIMF predicts a rather flat [$\alpha$/Fe]-stellar mass relation. The modelassuming the IGIMF, instead, is able to reproduce the observed increase of$\alpha$-enhancement with stellar mass, in agreement with previous studies.This is mainly due to the fact that massive galaxies are characterized bylarger star formation rates at high-redshift, leading to stronger$\alpha$-enhancement with respect to low-mass galaxies. At the same time, theIGIMF hypothesis does not affect significantly the trend for shorter starformation timescales for more massive galaxies. We argue that in the IGIMFscenario the [$\alpha$/Fe] ratios are good tracers of the highest starformation events. The final stellar masses and mass-to-light-ratio of our modelmassive galaxies are larger than those estimated from the synthetic photometryassuming a universal IMF, providing a self-consistent interpretation of similarrecent results, based on dynamical analysis of local early type galaxies.