Search

We present the first systematic study of the molecular gas and star formation efficiency in a sample of ten narrow-line Seyfert 1 galaxies selected to have X-ray Ultra Fast Outflows and, therefore, to potentially show AGN feedback effects. CO observations were obtained with the IRAM 30-m telescope in six galaxies and from the literature for four galaxies. We derived the stellar mass, star formation rate, AGN, and FIR dust luminosities by fitting the multi-band spectral energy distributions with the CIGALE code. Most of the galaxies in our sample lie above the main sequence (MS), and the molecular depletion time is one to two orders of magnitude shorter than the one typically measured in local star-forming galaxies. Moreover, we found a promising correlation between the star formation efficiency and the Eddington ratio, as well as a tentative correlation with the AGN luminosity. The role played by the AGN activity in the regulation of star formation within the host galaxies of our sample remains uncertain (little or no effect? positive feedback?). Nevertheless, we can conclude that quenching by the AGN activity is minor and that star formation will likely stop in a short time due to gas exhaustion by the current starburst episode. [ABSTRACT FROM AUTHOR]

We here study the multiband properties of a kiloparsec-size superbubble in the late-type spiral galaxy NGC 628. The superbubble is the largest of many holes seen in the early release images using James Webb Space Telescope (JWST)/MIRI filters that trace the polycyclic aromatic hydrocarbon (PAH) emissions. The superbubble is located in the interarm region ∼3 kpc from the Galactic Centre in the south-east direction. The shell surrounding the superbubble is detected in H  i , CO, and H α with an expansion velocity of 12 km s−1 and contains as much as 2 × 107 M⊙ of mass in gas that is mostly in molecular form. We find a clear excess of blue, bright stars inside the bubble as compared to the surrounding disc on the Hubble Space Telescope /Advanced Camera for Surveys images. These excess blue, bright stars are part of a stellar population of 105 M⊙ mass that is formed over the last 50 Myr in different star formation episodes, as determined from an analysis of colour–magnitude diagrams using a Bayesian technique. The mechanical power injected by the massive stars of these populations is sufficient to provide the energy necessary for the expansion of the shell gas. Slow and steady, rather than violent, injection of energy is probably the reason for the maintenance of the shell structure over the kiloparsec scale. The expanding shell is currently the site for triggered star formation as inferred from the JWST 21 µm (F2100W filter) and the H α images. [ABSTRACT FROM AUTHOR]

ε Eridani is a nearby, young Sun-like star that hosts a ring of cool debris analogous to the Solar system's Edgeworth-Kuiper belt. Early observations at (sub-)mm wavelengths gave tentative evidence of the presence of inhomogeneities in the ring, which have been ascribed to the effect of a putative low eccentricity planet, orbiting close to the ring. The existence of these structures has been recently challenged by high-resolution interferometric millimetre observations. Here, we present the deepest single-dish image of ε Eridani at millimetre wavelengths, obtained with the Large Millimetre Telescope Alfonso Serrano (LMT). The main goal of these LMT observations is to confirm (or refute) the presence of non-axisymmetric structure in the disc. The dusty ring is detected for the first time along its full projected elliptical shape. The radial extent of the ring is not spatially resolved and shows no evidence, to within the uncertainties, of dust density enhancements. Additional features of the 1.1 mm map are: (i) the presence of significant flux in the gap between the ring and the star, probably providing the first exo-solar evidence of Poynting-Robertson drag, (ii) an unambiguous detection of emission at the stellar position with a flux significantly above that expected from ε Eridani's photosphere, and (iii) the identification of numerous unresolved sources which could correspond to background dusty star-forming galaxies. [ABSTRACT FROM AUTHOR]

We produce an atlas of homogeneously reduced and calibrated low-resolution IRS spectra of the nuclear regions of nearby early-type galaxies (ETGs, i.e. Es and S0s), in order to build a reference sample in the mid-infrared window. From the Spitzer Heritage Archive we extract ETGs in the Revised Shapley–Ames Catalog of Bright Galaxies having an IRS SL and/or LL spectrum. We recover 91 spectra out of 363 galaxies classified as ETGs in the catalogue: 56 E (E0–E6), 8 mixed E/S0+S0/E and 27 S0 (both normal and barred – SB0) plus mixed types SB0/Sa+SB0/SBa. For each galaxy, we provide the fully reduced and calibrated spectrum and the intensity of nebular and molecular emission lines as well as of the polycyclic aromatic hydrocarbons (PAHs) after a template spectrum of a passively evolving ETG has been subtracted. Spectra are classified into five mid-infrared classes, ranging from active galactic nuclei (class-4) and star-forming nuclei (class-3), to transition class-2 (with PAHs) and class-1 (no-PAHs), to passively evolving nuclei (class-0).A demographic study of mid-infrared spectra shows that Es are significantly more passive than S0s: 46$^{+11}_{-10}$ per cent of Es and 20$^{+11}_{-7}$ per cent of S0s have a spectrum of class-0. Emission lines are revealed in 64$^{+12}_{-6}$ per cent of ETGs. The H2S(1) line is found with similar rate in Es (34$^{+10}_{-8}$ per cent) and in S0s (51$^{+15}_{-12}$ per cent). PAHs are detected in 47$^{+8}_{-7}$ per cent of ETGs, but only 9$^{+4}_{-3}$ per cent have PAH ratios typical of star-forming galaxies.Several indicators, such as peculiar morphologies and kinematics, the irregular shape of dust-lanes, and radio and X-ray properties, suggest that mid-infrared spectral classes are associated with phases of accretion/feedback phenomena occurring in the nuclei of ETGs. [ABSTRACT FROM AUTHOR]

We describe radio observations at 244 and of a sample of 20 luminous and ultra-luminous IRAS galaxies. These are a subset of a sample of 31 objects that have well-measured radio spectra up to at least . The radio spectra of these objects below show a great variety of forms and are rarely a simple power-law extrapolation of the synchrotron spectra at higher frequencies. Most objects of this class have spectral turn-overs or bends in their radio spectra. We interpret these spectra in terms of free–free absorption in the starburst environment. Several objects show radio spectra with two components having free–free turn-overs at different frequencies (including Arp 220 and Arp 299), indicating that synchrotron emission originates from regions with very different emission measures. In these sources, using a simple model for the supernova rate, we estimate the time for which synchrotron emission is subject to strong free–free absorption by ionized gas and compare this to expected H ii region lifetimes. We find that the ionized gas lifetimes are an order of magnitude larger than the plausible lifetimes for individual H ii regions. We discuss the implications of this result and argue that those sources which have a significant radio component with strong free–free absorption are those in which the star formation rate is still increasing with time. We note that if ionization losses are important, the resulting curvature of the radio spectrum would much reduce the often observed deficit in fluxes above . [ABSTRACT FROM AUTHOR]

In this paper we analyze the evolution of actively star-forming galaxies in the mid-infrared (MIR). This spectral region, characterized by continuum emission by hot dust and by the presence of strong emission features generally ascribed to polycyclic aromatic hydrocarbon (PAH) molecules, is the most strongly affected by the heating processes associated with star formation and/or active galactic nuclei (AGNs). Following the detailed observational characterization of galaxies in the MIR by the Infrared Space Observatory ( ISO), we have updated the modelling of this spectral region in our spectrophotometric model grasil. In the diffuse component we have updated the treatment of PAHs according to the model by Li & Draine. As for the dense phase of the interstellar medium associated with the star-forming regions, the molecular clouds, we strongly decrease the abundance of PAHs as compared to that in the cirrus, based on the observational evidence of the lack or weakness of PAH bands close to the newly formed stars, possibly due to the destruction of the molecules in strong ultraviolet fields. The robustness of the model is checked by fitting near-infrared to radio broad-band spectra and the corresponding detailed MIR spectra of a large sample of galaxies, at once. With this model, we have analyzed the larger sample of actively star-forming galaxies by Dale et al. We show that the observed trends of galaxies in the ISO– IRAS–radio colour–colour plots can be interpreted in terms of the different evolutionary phases of star formation activity, and the consequent different dominance in the spectral energy distribution of the diffuse or dense phase of the ISM. We find that the observed colours indicate a surprising homogeneity of the starburst phenomenon, allowing only a limited variation of the most important physical parameters, such as the optical depth of the molecular clouds, the time-scale of the escape of young stars from their for mation sites, and the gas consumption time-scale. In this paper we do not attempt to reproduce the far-infrared coolest region in the colour–colour plots, as we concentrate on models meant to reproduce active star-forming galaxies, but we discuss possible requirements of a more complex modelling for the coldest objects. [ABSTRACT FROM AUTHOR]