Eta Carinae across the 2003.5 Minimum: Analysis in the visible and near infrared spectral region

We present an analysis of the visible through near infrared spectrum of Eta Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES at the ESO VLT". This is a part of larger effort to present a complete Eta Carinae spectrum, and extends the previously presented analyses with the HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near UV is characterized by the ejecta absorption. At longer wavelengths, stellar wind features from the central source and narrow emission lines from the Weigelt condensations dominate the spectrum. However, narrow absorption lines from the circumstellar shells are present. This paper provides a description of the spectrum between 3060 and 10,430 A, including line identifications of the ejecta absorption spectrum, the emission spectrum from the Weigelt condensations and the P-Cygni stellar wind features. The high spectral resolving power of VLT/UVES enables equivalent width measurements of atomic and molecular absorption lines for elements with no transitions at the shorter wavelengths. However, the ground based seeing and contributions of nebular scattered radiation prevent direct comparison of measured equivalent widths in the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a small overlap in wavelength coverage which allows us to compare and adjust for the difference in scattered radiation entering the instruments' apertures. This paper provides a complete online VLT/UVES spectrum with line identifications and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160 A.Comment: 13 pages, 11 figures + atlas. The paper accepted for the ApJS and is accompanied with an atlas in the online edition pape

Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust

We present $^{12}$CO(1-0) and $^{12}$CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies and marginally detected in another one. CO fluxes correlate with the FIR 250 $\mu$m emission, and the dwarfs follow the same linear relation that holds for more massive spiral galaxies extended to a wider dynamical range. We compare different methods to estimate H2 molecular masses, namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant at stellar masses <~ 10$^9$ M$_{\odot}$, contrary to the atomic hydrogen fraction, M$_{HI}$/M$_*$, which increases inversely with M$_*$. The flattening of the M$_{H_2}$/M$_*$ ratio at low stellar masses does not seem to be related to the effects of the cluster environment because it occurs for both HI-deficient and HI-normal dwarfs. The molecular-to-atomic ratio is more tightly correlated with stellar surface density than metallicity, confirming that the interstellar gas pressure plays a key role in determining the balance between the two gaseous components of the interstellar medium. Virgo dwarfs follow the same linear trend between molecular gas mass and star formation rate as more massive spirals, but gas depletion timescales, $\tau_{dep}$, are not constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo cluster environment is removing the atomic gas and dust components of the dwarfs, but the molecular gas appears to be less affected at the current stage of evolution within the cluster. However, the correlation between HI deficiency and the molecular gas depletion time suggests that the lack of gas replenishment from the outer regions of the disc is lowering the star formation activity.Comment: 19 pages, 11 figures, accepted for publication in Astronomy & Astrophysic

Controlling Internal Pore Sizes in Bicontinuous Polymeric Nanospheres

Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17?kDa and hydrophilic weight fractions of ?0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460?nm. Significantly, altering the block copolymer hydrophilic–hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19?nm

Radio haloes in nearby galaxies modelled with 1D cosmic-ray transport using SPINNAKER

We present radio continuum maps of 12 nearby ($D\leq 27~\rm Mpc$), edge-on ($i\geq 76^{\circ}$), late-type spiral galaxies mostly at $1.4$ and 5 GHz, observed with the Australia Telescope Compact Array, Very Large Array, Westerbork Synthesis Radio Telescope, Effelsberg 100-m and Parkes 64-m telescopes. All galaxies show clear evidence of radio haloes, including the first detection in the Magellanic-type galaxy NGC 55. In 11 galaxies, we find a thin and a thick disc that can be better fitted by exponential rather than Gaussian functions. We fit our SPINNAKER (SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission) 1D cosmic-ray transport models to the vertical model profiles of the non-thermal intensity and to the non-thermal radio spectral index in the halo. We simultaneously fit for the advection speed (or diffusion coefficient) and magnetic field scale height. In the thick disc, the magnetic field scale heights range from 2 to 8 kpc with an average across the sample of $3.0\pm 1.7~\rm kpc$; they show no correlation with either star-formation rate (SFR), SFR surface density ($\Sigma_{\rm SFR}$) or rotation speed ($V_{\rm rot}$). The advection speeds range from 100 to $700~\rm km\,s^{-1}$ and display correlations of $V\propto \rm SFR^{0.36\pm 0.06}$ and $V\propto \Sigma_{\rm SFR}^{0.39\pm 0.09}$; they agree remarkably well with the escape velocities ($0.5\leq V/V_{\rm esc}\leq 2$), which can be explained by cosmic-ray driven winds. Radio haloes show the presence of disc winds in galaxies with $\Sigma_{\rm SFR} > 10^{-3}~\rm M_{\odot}\,yr^{-1}\,kpc^{-2}$ that extend over several kpc and are driven by processes related to the distributed star formation in the disc.Comment: 39 pages, 20 colour figures, 10 tables. Accepted by MNRA

Hot Interstellar Gas and Stellar Energy Feedback in the Antennae Galaxies

We have analyzed Chandra archival observations of the Antennae galaxies to study the distribution and physical properties of its hot interstellar gas. Eleven distinct diffuse X-ray emission regions are selected according to their underlying interstellar structures and star formation activity. The X-ray spectra of these regions are used to determine their thermal energy contents and cooling timescales. Young star clusters in these regions are also identified and their photometric measurements are compared to evolutionary stellar population synthesis models to assess their masses and ages. The cluster properties are then used to determine the stellar wind and supernova energies injected into the ISM. Comparisons between the thermal energy in the hot ISM and the expected stellar energy input show that young star clusters are sufficient to power the X-ray-emitting gas in some, but not all, active star formation regions. Super-star clusters, with masses >= 1x10^5 M_sol, heat the ISM, but the yield of hot interstellar gas is not directly proportional to the cluster mass. Finally, there exist diffuse X-ray emission regions which do not show active star formation or massive young star clusters. These regions may be powered by field stars or low-mass clusters formed within the last ~100 Myr.Comment: 36 pages, 6 figures, 8 tables, 2 appendices, to appear in the Astrophysical Journal, April 20 issu

Waiting in the Wings: Reflected X-ray Emission from the Homunculus Nebula

We report the first detection of X-ray emission associated with the Homunculus Nebula which surrounds the supermassive star Eta Carinae. The emission is characterized by a temperature in excess of 100 MK, and is consistent with scattering of the time-delayed X-ray flux associated with the star. The nebular emission is bright in the northwestern lobe and near the central regions of the Homunculus, and fainter in the southeastern lobe. We also report the detection of an unusually broad Fe K fluorescent line, which may indicate fluorescent scattering off the wind of a companion star or some other high velocity outflow. The X-ray Homunculus is the nearest member of the small class of Galactic X-ray reflection nebulae, and the only one in which both the emitting and reflecting sources are distinguishable.Comment: 17 pages, 5 figures, accepted by Ap

The dependence of oxygen and nitrogen abundances on stellar mass from the CALIFA survey

We analysed the optical spectra of HII regions extracted from a sample of 350 galaxies of the CALIFA survey. We calculated total O/H abundances and, for the first time, N/O ratios using the semi-empirical routine HII-CHI-mistry, which, according to P\'erez-Montero (2014), is consistent with the direct method and reduces the uncertainty in the O/H derivation using [NII] lines owing to the dispersion in the O/H-N/O relation. Then we performed linear fittings to the abundances as a function of the de-projected galactocentric distances. The analysis of the radial distribution both for O/H and N/O in the non-interacting galaxies reveals that both average slopes are negative, but a non-negligible fraction of objects have a flat or even a positive gradient (at least 10\% for O/H and 4\% for N/O). The slopes normalised to the effective radius appear to have a slight dependence on the total stellar mass and the morphological type, as late low-mass objects tend to have flatter slopes. No clear relation is found, however, to explain the presence of inverted gradients in this sample, and there is no dependence between the average slopes and the presence of a bar. The relation between the resulting O/H and N/O linear fittings at the effective radius is much tighter (correlation coefficient $\rho_s$ = 0.80) than between O/H and N/O slopes ($\rho_s$ = 0.39) or for O/H and N/O in the individual \hii\ regions ($\rho_s$ = 0.37). These O/H and N/O values at the effective radius also correlate very tightly (less than 0.03 dex of dispersion) with total luminosity and stellar mass. The relation with other integrated properties, such as star formation rate, colour, or morphology, can be understood only in light of the found relation with mass.Comment: Accepted for publication in A&A. 20 pages, 19 figure

Evidence for Expanding Superbubbles in a Galaxy at z=0.7443

The intervening z=0.7443 Mg II absorption system in the spectrum of MC 1331+170 shows an unusual series of line pairs, each with velocity separations of 30 km/s. These lines could be explained as the shells of expanding superbubbles residing in the outer regions of an edge-on spiral galaxy visible in the optical image of the MC 1331+170 field. The color and brightness of this galaxy make it the most likely candidate z=0.7443 absorber, though two other galaxies in the quasar field could also be contributing to the Mg II absorption profile. Kinematic models of absorption from compact groups and galaxy pairs produce profiles largely inconsistent with the observed Mg II spectrum. Superbubbles would naturally generate more regular structures such as those observed. Photoionization models of the superbubble shell are consistent with the observed profile for many realistic physical conditions. In a pure superbubble model, the large velocity spread of the Mg II absorption system is inconsistent with the expected spread of a quiescent, rotating disk. This requires unusual kinematics within the host galaxy, perhaps due to a recent interaction.Comment: Five Figures; Two Tables; 12 Pages using emulateapj.sty; Submitted to Ap