Seyfert Galaxies in the Local Universe: Analysis of Spitzer Spectra of a Complete Sample

The Spitzer high resolution spectra of 72 Seyfert galaxies from the 12$\mu$m Galaxy Sample are presented and discussed. The presence of starburst components in these galaxies can be quantified by powerful mid-IR diagnostics tools (i.e. 11.25$\mu$m PAH feature equivalent width and the H$_2$ emission line intensity), as well as the AGN dominance can be measured by specific fine structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The two types of Seyfert galaxies do not show any statistical difference in our diagnostic tools. However, the Seyfert 2's showing hidden Broad Line Regions in spectro-polarimetric observations have on average an higher AGN dominance, a weaker star formation component and a warmer [60 - 25] spectral index than those without broad emission lines.Comment: Proceedings of the Conference "The central kiloparsec. Active Galactic Nuclei and their hosts, 4-6 June 2008, Ierapetra, Crete, Greec

The Earliest Phases Of High-Mass Star Formation, As Seen In Ngc 6334 By Herschel -Hobys

Aims. To constrain models of high-mass star formation, the Herschel-HOBYS key program aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC 6334, one of the best-studied HOBYS molecular cloud complexes

High-J CO line emission from young stellar objects: from ISO to FIRST

we present the CO pure rotational spectrum at high J (Jup14) obtained with the Long Wavelength Spectrometer (LWS) on board of the ISO satellite towards molecular outflows exciting sources in nearby star formation regions. The physical conditions, derived using an LVG model for the line emission, indicate the presence of warm and dense gas, probably shock excited. The model fits show that often the bulk of this CO emission is expected in the spectral range that will be covered by FIRST, indicating the potentiality of this satellite to trace the warm component of gas emission in young stellar objects

Far-infrared line spectra of active galaxies from the Herschel/PACS Spectrometer: the complete database

We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/PACS archive for a sample of 170 local AGN, plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies. Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our database to the full 10-600 $\mu m$ spectral range. The observations are compared to a set of CLOUDY photoionisation models to estimate the above physical quantities through different diagnostic diagrams. We confirm the presence of a stratification of gas density in the emission regions of the galaxies, which increases with the ionisation potential of the emission lines. The new [OIV]25.9$\mu m$/[OIII]88$\mu m$ vs [NeIII]15.6$\mu m$/[NeII]12.8$\mu m$ diagram is proposed as the best diagnostic to separate: $i)$ AGN activity from any kind of star formation; and $ii)$ low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [OIV]25.9$\mu m$/[OIII]88$\mu m$ ratios, which are much higher when compared to the predicted values. Finally, the ([NeIII]15.6$\mu m$ + [NeII]12.8$\mu m$)/([SIV]10.5$\mu m$ + [SIII]18.7$\mu m$) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity. The diagnostic power of mid- to far-infrared spectroscopy shown here for local galaxies will be of crucial importance to study galaxy evolution during the dust-obscured phase at the peak of the star formation and black-hole accretion activity ($1 < z < 4$). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as JWST, ALMA, and SPICA.Comment: Accepted for publication in the ApJ

The Herschel exploitation of local galaxy Andromeda (HELGA) V: Strengthening the case for substantial interstellar grain growth

In this paper we consider the implications of the distributions of dust and metals in the disc of M31. We derive mean radial dust distributions using a dust map created from Herschel images of M31 sampling the entire far-infrared (FIR) peak. Modified blackbodies are fit to approximately 4000 pixels with a varying, as well as a fixed, dust emissivity index (beta). An overall metal distribution is also derived using data collected from the literature. We use a simple analytical model of the evolution of the dust in a galaxy with dust contributed by stellar sources and interstellar grain growth, and fit this model to the radial dust-to-metals distribution across the galaxy. Our analysis shows that the dust-to-gas gradient in M31 is steeper than the metallicity gradient, suggesting interstellar dust growth is (or has been) important in M31. We argue that M31 helps build a case for cosmic dust in galaxies being the result of substantial interstellar grain growth, while the net dust production from stars may be limited. We note, however, that the efficiency of dust production in stars, e.g., in supernovae (SNe) ejecta and/or stellar atmospheres, and grain destruction in the interstellar medium (ISM) may be degenerate in our simple model. We can conclude that interstellar grain growth by accretion is likely at least as important as stellar dust production channels in building the cosmic dust component in M31.Comment: 12 pages, 7 figures. Published in MNRAS 444, 797. This version is updated to match the published versio

Heating of the molecular gas in the massive outflow of the local ultraluminous-infrared and radio-loud galaxy 4C12.50

We present a comparison of the molecular gas properties in the outflow vs. in the ambient medium of the local prototype radio-loud and ultraluminous-infrared galaxy 4C12.50 (IRAS13451+1232), using new data from the IRAM Plateau de Bure interferometer and 30m telescope, and the Herschel space telescope. Previous H_2 (0-0) S(1) and S(2) observations with the Spitzer space telescope had indicated that the warm (~400K) molecular gas in 4C12.50 is made up of a 1.4(+-0.2)x10^8 M_sun ambient reservoir and a 5.2(+-1.7)x10^7 M_sun outflow. The new CO(1-0) data cube indicates that the corresponding cold (25K) H_2 gas mass is 1.0(+-0.1)x10^10 M_sun for the ambient medium and <1.3x10^8 M_sun for the outflow, when using a CO-intensity-to-H_2-mass conversion factor alpha of 0.8 M_sun /(K km/s pc^2). The combined mass outflow rate is high, 230-800 M_sun/yr, but the amount of gas that could escape the galaxy is low. A potential inflow of gas from a 3.3(+-0.3)x10^8 M_sun tidal tail could moderate any mass loss. The mass ratio of warm-to-cold molecular gas is >= 30 times higher in the outflow than in the ambient medium, indicating that a non-negligible fraction of the accelerated gas is heated to temperatures at which star formation is inefficient. This conclusion is robust against the use of different alpha factor values, and/or different warm gas tracers (H_2 vs. H_2 plus CO): with the CO-probed gas mass being at least 40 times lower at 400K than at 25K, the total warm-to-cold mass ratio is always lower in the ambient gas than in the entrained gas. Heating of the molecular gas could facilitate the detection of new outflows in distant galaxies by enhancing their emission in intermediate rotational number CO lines.Comment: A&A, in pres

The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey

The dust in nearby galaxies absorbs a fraction of the UV-optical-near-infrared radiation produced by stars. This energy is consequently re-emitted in the infrared. We investigate the portion of the stellar radiation absorbed by spiral galaxies from the HRS by modelling their UV-to-submillimetre spectral energy distributions. Our models provide an attenuated and intrinsic SED from which we find that on average 32 % of all starlight is absorbed by dust. We define the UV heating fraction as the percentage of dust luminosity that comes from absorbed UV photons and find that this is 56 %, on average. This percentage varies with morphological type, with later types having significantly higher UV heating fractions. We find a strong correlation between the UV heating fraction and specific star formation rate and provide a power-law fit. Our models allow us to revisit the IRX-AFUV relations, and derive these quantities directly within a self-consistent framework. We calibrate this relation for different bins of NUV-r colour and provide simple relations to relate these parameters. We investigated the robustness of our method and we conclude that the derived parameters are reliable within the uncertainties which are inherent to the adopted SED model. This calls for a deeper investigation on how well extinction and attenuation can be determined through panchromatic SED modelling.Comment: 14 pages, 7 figures. Accepted for publication in Astronomy & Astrophysic

The selective effect of environment on the atomic and molecular gas-to-dust ratio of nearby galaxies in the Herschel Reference Survey

We combine dust, atomic (HI) and molecular (H$_{2}$) hydrogen mass measurements for 176 galaxies in the Herschel Reference Survey to investigate the effect of environment on the gas-to-dust mass ($M_{\rm gas}/M_{\rm dust}$) ratio of nearby galaxies. We find that, at fixed stellar mass, the average $M_{\rm gas}/M_{\rm dust}$ ratio varies by no more than a factor of $\sim$2 when moving from field to cluster galaxies, with Virgo galaxies being slightly more dust rich (per unit of gas) than isolated systems. Remarkably, once the molecular and atomic hydrogen phases are investigated separately, we find that \hi-deficient galaxies have at the same time lower $M_{\rm HI}/M_{\rm dust}$ ratio but higher $M_{\rm H_{2}}/M_{\rm dust}$ ratio than \hi-normal systems. In other words, they are poorer in atomic but richer in molecular hydrogen if normalized to their dust content. By comparing our findings with the predictions of theoretical models, we show that the opposite behavior observed in the $M_{\rm HI}/M_{\rm dust}$ and $M_{\rm H_{2}}/M_{\rm dust}$ ratios is fully consistent with outside-in stripping of the interstellar medium (ISM), and is simply a consequence of the different distribution of dust, \hi\ and H$_{2}$ across the disk. Our results demonstrate that the small environmental variations in the total $M_{\rm gas}/M_{\rm dust}$ ratio, as well as in the gas-phase metallicity, do not automatically imply that environmental mechanisms are not able to affect the dust and metal content of the ISM in galaxies.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA