Search

Deep optical CCD images of the supernova remnant G 32.8-0.1 were obtained where filamentary and diffuse emission was discovered. The images were acquired in the emission lines of Hα+[ N ii] and [S ii]. Filamentary and diffuse structures are detected in most areas of the remnant, while no significant [O iii] emission is present. The flux-calibrated images suggest that the optical emission originates from shock-heated gas since the [S ii]/Hαratio is greater than 1.2. The Spitzer images at 8 μm and 24 μm show a few filamentary structures to be correlated with the optical filaments, while the radio emission at 1.4 GHz in the same area is found to be very well correlated with the brightest optical filaments. The results from deep long-slit spectra also support the origin of the emission being from shock-heated gas ([S ii]/Hα> 1.5). The absence of [O iii] emission indicates slow shock velocities into the interstellar $``$clouds” (≤100 km s-1), while the [S ii]$\lambda\lambda$6716/6731 ratio indicates electron densities up to ~200 cm-3. The Hαemission is measured to lie between 1.8 to 4.6 $\times$10-17erg s-1cm-2arcsec-2, while from VGPS Hiimages the distance to the SNR is estimated to be between 6 to 8.5 kpc.

Context. We present the results from a study of the X-ray variability and the near-IR to X-ray spectral energy distribution of four low-luminosity, Seyfert 1 galaxies.

Deep optical CCD images of the supernova remnant G 15.1-1.6 were obtained where filamentary and diffuse emission was discovered. The images, taken in the emission lines of H$\alpha+[$$\ion{N}{ii}$], [S ii], and [$\ion{O}{iii}$], reveal filamentary and diffuse structures all around the remnant. The radio emission at 4850 MHz in the same area is found to be strongly correlated with the brightest optical filaments. The IRAS 60 μm emission may also be correlated with the optical emission but to a lesser extent. The flux-calibrated images suggest that the optical emission originates from shock-heated gas ([S ii]/Hα> 0.4), while there is a possible $\ion{H}{ii}$region ([S ii]/Hα~ 0.3) contaminating the supernova remnant's emission to the east. Furthermore, deep long-slit spectra were taken at two bright filaments and also show that the emission originates from shock-heated gas. An [$\ion{O}{iii}$] filamentary structure is also detected farther to the west, but it lies outside the remnant's boundaries and may not be associated to it. The [$\ion{O}{iii}$] flux suggests shock velocities into the interstellar $``$clouds” ~100 km s-1, while the [$\ion{S}{ii}$$]\lambda\lambda\ 6716/6731$ratio indicates electron densities up to ~250 cm-3. Finally, the Hαemission is measured to be between 2 to $7 \times$10-16erg s-1cm-2arcsec-2, while the lower limit to the distance is estimated at 2.2 kpc.

Flux-calibrated CCD images of HB 21 are presented, along with flux calibrated spectra of moderate resolution. The low ionization images reveal filamentary structures in the east, while the emission in the central to west areas may be either filamentary or patchy. The filaments in the east are correlated very well with the radio emission, but a smaller degree of correlation exists for the patchy emission. An area in the west exhibits strong sulfur emission and is probably associated to the remnant. Uncatalogued $\ion{H}{ii}$regions are present in the area of the remnant, mainly in the south. We find that an ellipse extending for $116\arcmin\times122\arcmin$incorporates most of the radio and optical emission. The actual physical extent of the remnant depends on the distance, which is not well determined since it ranges from 0.8 to 1.7 kpc. Deep long-slit spectra were also acquired at a number of locations. The Hαemission is generally weak, typically below 15 $\times$10-17erg s-1cm-2arcsec-2. The Hβemission was not always detected, suggesting substantial attenuation of the light through the interstellar medium. The medium ionization line of [$\ion{O}{iii}$]5007 Å was not detected indicating low shock velocities into the interstellar clouds whose density is estimated to be a few atoms per cm3.

We use the COBE/DIRBE (1.2, 2.2, 60, 100, 140, and 240 μm) maps and the COBE/FIRAS spectra (for the wavelength range 100-1000 μm) to constrain a model for the spatial distribution of the dust, the stars, and the gas in the Milky Way. By assuming exponential axisymmetric distributions for the dust and the stars and by performing the corresponding radiative transfer calculations we closely (given the simple geometry of the model) reproduce the FIR and NIR maps of the Milky Way. Similar distributions for the atomic and molecular hydrogen in the disk are used (with an inner cut-off radius for the atomic hydrogen) to fit the gas data. The star formation rate as a function of the Galactic radius is derived from the FIR emission and is well in agreement with existing estimates from various star formation tracers. The gas surface density is plotted against the star formation rate density and an “intrinsic” Galactic Schmidt law is derived with excellent agreement with the “external” Schmidt law found for spiral galaxies. The Milky Way is found to consume ~$1\%$and ~$10\%$of its gas in the outer and inner regions respectively (for a period of 0.1 Gyr) to make stars. The dust-induced $B-V$color excess observed in various directions and distances (up to ~6.5 kpc) with well-studied Cepheid stars is compared with the model predictions showing a good agreement. The simple assumption of exponential distributions of stars and dust in the Galaxy is found to be quite instructive and adequate in modeling all the available data sets from 0.45 μm (B-band) to 1000 μm.

We have observed S5 2007+777 and 3C 371 in the Band Ibands for 13 and 8 nights, respectively, during various observing runs in 2001, 2002 and 2004. The observations resulted in almost evenly sampled light curves, $6{-}9$h long. We do not detect any flares within the observed light curves, but we do observe small amplitude, significant variations, in both bands, on time scales of hours and days. The average variability amplitude on time scales of minutes/hours is ~2.5% and ~$1{-}1.5$% in the case of S5 2007+777 and 3C 371, respectively. The average amplitudes increase to $\sim 5{-}12$% and $\sim 4{-}6$%, respectively, on time scales of days. We find that the Band Iband variations are highly correlated, on both short and long time scales. During the 2004 observations, which resulted in the longest light curves, we observe two well defined flux-decay and rising trends in the light curves of both objects. When the flux decays, we observe significant delays, with the Bband flux decaying faster than the flux in the Iband. As a result, we also observe significant, flux related spectral variations as well. The flux-spectral relation is rather complicated, with loop-like structures forming during the flux evolution. The presence of spectral variations imply that the observed variability is not caused by geometric effects. On the other hand, our results are fully consistent with the hypothesis that the observed variations are caused by perturbations which affect different regions in the jet of the sources.

Optical CCD imaging and spectroscopic observations of three supernova remnants are presented. Optical emission from G 54.4-0.3 and G 59.8+1.2 is detected for the first time, while the first flux calibrated CCD images of the supernova remnant G 126.2+1.6 were performed in the optical emission lines of H$\alpha+[$$\ion{N}{ii}$], [$\ion{O}{iii}$] and [$\ion{S}{ii}$]. A mixture of filamentary and diffuse structures is observed in G 54.4-0.3 and G 59.8+1.2, mainly in H$\alpha+[$$\ion{N}{ii}$], while the deep optical images of G 126.2+1.6 reveal several new filamentary and diffuse structures inside the extent of the remnant as defined by its known radio emission. In all cases, the radio emission is found to be well correlated with the optical filaments. [$\ion{O}{iii}$] emission was not detected at G 54.4-0.3 and G 59.8+1.2 while in G 126.2+1.6, significant morphological differences between the low and medium ionization images are present suggesting incomplete shock structures. Deep long-slit spectra were taken at different positions of the remnants. Both the flux calibrated images and the long-slit spectra clearly show that the emission originates from shock-heated gas, while some spectra of G 126.2+1.6 are characterized by large [$\ion{O}{iii}$]/Hβratios. This remnant's [$\ion{O}{iii}$] flux suggests shock velocities into the interstellar “clouds” between 100 and 120 km s-1, while the [$\ion{O}{iii}$] absence in the other two remnants indicates slower shock velocities. For all remnants, the [$\ion{S}{ii}$$]\lambda\lambda\ 6716/6731$ratio indicates electron densities below 600 cm-3with particularly low densities for G 54.4-0.3 (below 50 cm-3). Finally, the Hαemission has been measured to be between 3.0 to 15.2 $\times$10-17erg s-1cm-2arcsec-2, 3.2 $\times$10-17erg s-1cm-2arcsec-2and between 6.5 to 16.8 $\times$10-17erg s-1cm-2arcsec-2for G 54.4-0.3, G 59.8+1.2 and G 126.2+1.6, respectively.

We use the radiation transfer simulation of Xilouris et al. ([CITE]) to constrain the quantity of dust in three nearby spiral galaxies (NGC 4013, NGC 5907 and NGC 4565). The predicted visual optical depth from the model is compared with the thermal continuum radiation detected from NGC 4013 and NGC 5907 at $850~{\mu}$m and from NGC 4565 at 1.2 mm. The former is based on SCUBA images of NGC 4013 and NGC 5907, reduced and presented for the first time in this work. The comparison of visual optical depth and $850~\mu$m (1.2 mm) emission yields the emissivity of dust grains in the submillimeter (millimeter) waveband. We infer a value of $1.2 \times 10^{4}$for the emissivity at $850~\mu$m which is a factor 4 higher than the benchmark, semi-empirical model of Draine & Lee ([CITE]). At 1.2 mm our values are a factor 1.5 higher than this model. Our estimates are more closely aligned with recent measurements carried out in the laboratory on amorphouscarbon and silicate particulates. A comparison between the distribution of $850~\mu$m (1.2 mm) surface brightness and the intensity levels in the 12CO(1–0) and 21 cm lines underlines the spatial association between dust detected in the submillimeter/millimeter waveband and molecular gas clouds. We suggest that the relatively high emissivity values that we derive may be attributable to amorphous, fluffy grains situated in denser gas environments.

We present mid-infrared (MIR) maps for a sample of 18 early-type galaxies observed at 4.5, 6.7 and 15 $\mu {\rm m}$with the ISOCAM instrument on board the ISO satellite with a 6''spatial resolution. We model the Spectral Energy Distribution (SED) of these galaxies using the stellar evolutionary synthesis model PÉGASE and we derive the MIR excess over the stellar component. We then explore the nature of this excess in terms of dust and Polycyclic Aromatic Hydrocarbon molecules (PAHs). We find that out of 18 galaxies, 10 show excess at 6.7 $\mu {\rm m}$(due to the presence of PAH features) and 14 show excess at 15 $\mu {\rm m}$(due to the presence of warm dust). In two galaxies, where a more complete wavelength coverage exists, an excess around 9.7 $\mu {\rm m}$is seen (presumably due to silicate dust emission), while two other galaxies are totally devoid of dust. We also examine the morphology of the galaxies in these wavelengths by plotting the azimuthally averaged radial profiles as well as the MIR color profiles. We find that for the majority of the galaxies the 4.5 $\mu {\rm m}$emission is well described by a de Vaucouleurs profile. The 6.7 $\mu {\rm m}$and 15 $\mu {\rm m}$emission is smoothly distributed throughout the galaxy while only a few galaxies show MIR emission which is more concentrated close to the center. Two dwarf galaxies in our sample show patchy distributions of the MIR emission while two other galaxies show edge-on disks. With color-color diagrams we delineate the regions occupied by late-type and early-type galaxies. Finally we show that the MIR excess found in strong radio galaxies like NGC 4486 (M87) can be explained by synchrotron emission.

We study the morphology of the central region of a sample of Active Galactic Nuclei (AGN) and a “control” sample of normal galaxies using archival observations of the WFPC2 instrument onboard the Hubble Space Telescope(HST). We use the ellipse fitting technique in order to get a good description of the inner “smooth” light distribution of the galaxy. We then divide the observed galaxy image by the artificial image from the fitted ellipses in order to detect morphological signatures in the central region around the nucleus of the galaxy. We perform quantitative comparisons of different subgroups of our sample of galaxies (according to the Hubble type and the nuclear activity of the galaxies) by calculating the average amplitude of the structures that are revealed with the ellipse fitting technique. Our main conclusions are as follows: 1) All AGNs show significant structure in their inner 100 pc and 1 kpc regions whose amplitude is similar in all of them, independent of the Hubble type of the host galaxy. 2) When considering early-type galaxies, non-AGN galaxies show no structure at all, contrary to what we find for AGN. 3) When considering late-type galaxies, both AGN and non-AGN galaxies show significant structure in their central region. Our results are consistent with the hypothesis that all early-type galaxies host a supermassive black hole, but only those that have enough material in the central regions to fuel it show an active nucleus. The situation is more complicated in late-type galaxies. Either not all of them host a central black hole, or, in some of them, the material inside the innermost 100 pc region is not transported to the scales of the central engine for some reason, or the large amount of gas and dust hides the active nucleus from our sight.

We have conducted a search for “dust chimneys” in a sample of 10 highly-inclined spiral galaxies ($i=86-90^{\circ}$) which we had previously observed in the Hαemission line (Rand 1996). We have procured B-band CCD images for this purpose and employed unsharp-masking techniques to accentuate the structure of the dust lane. A scattering+absorption radiation transfer model enabled us to separate 5 galaxies from the sample which are sufficiently inclined ($i>87^{\circ}$) for us to reliably identify and quantify dust clouds residing at over 2 scale-heights above the disk. Three of these galaxies possess numerous curvi-linear chimney structures stretching up to 2 kpc from the midplane and the fraction of total galactic dust contained in such structures is of order 1%. Optical extinction offers a lower limit to the amount of dust contained in the extraplanar layer but, by examining the transparent submm thermal emission from NGC 891, we fix an upper limit of 5%. Our results are consistent with a similar recent study by Howk & Savage (1999) which indicates that about half of quiescent spiral disks possess detectable dust chimneys.
We have compared our optical images with the corresponding Hαemission-line radiation. We do notfind a detailed spatial correspondance between dust chimneys and either sites of recent star-formation or the extraplanar diffuse ionized gas. This is somewhat surprising given that FIR-bright galaxies, such as M 82, are known to entrain dust at the working surface of the starburst-driven outflow (traced in Hα). It is possible a globalcorrelation exists, with disks experiencing overall higher rates of star-formation also possessing the greatest number of chimneys. This may indicate a timescale difference between the two phenomena with the Hαphase lasting $\sim 10^{6}$yr but chimneys requiring $\sim 10^{7}$yr to form.
Additionally, we have investigated the edge-on disk NGC 55 which, being ten times closer than galaxies in our main sample, allows us to examine in greater spatial detail the relationship between chimneys and recent star-formation. Our discussion touches upon high latitude dust and supershells observed in the Milky Way. We rule out quiescentdisks as prolific sources of intergalactic grains and metals but note that the rate at which dust is expelled from the main dust layer is comparable to the rate at which it is produced by disk stars (suggesting that it may be an important regulatory process).

We analyse Herschel/SPIRE images of the edge-on spiral galaxy NGC 891 at 250, 350, and 500 μm. Using a 3D radiative transfer model we confirm that the dust has radial fall-off similar to the stellar disk. The dust disk shows a break at about 12 kpc from the centre, where the profile becomes steeper. Beyond this break, emission can be traced up to 90% of the optical disk on the NE side. To the SW, we confirm dust emission associated with the extended, asymmetric HI disk, previously detected by the Infrared Space Observatory (ISO). This emission is marginally consistent with the large diffuse dust disk inferred from radiative transfer fits to optical images. No excess emission is found above the plane beyond that of the thin, unresolved, disk.

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering  ~40 sq. deg in the far UV (FUV, λeff= 1539   Å, Δλ= 442   Å) and  ~120 sq. deg in the near UV (NUV, λeff= 2316   Å, Δλ= 1060   Å). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared – submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early- and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (α~  −1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference.

We examine the properties of the X-ray-detected infrared excess AGN or dust obscured galaxies (DOGs) in the Chandra deep fields (CDFs). We find 26 X-ray-detected sources that obey the 24 μm to R-band flux ratio criterion f24/fR> 1000. These are at a median redshift of 2.3, while their IR luminosities are above 1012L⊙. Their X-ray luminosities are all above a few times 1042erg   s-1in the 2–10 keV band, which unambiguously argues that they host AGN. Nevertheless, their IR spectral energy distributions are split between AGN (Mrk231) and star-forming templates (Arp220). Our primary goal is to examine their individual X-ray spectra in order to assess whether this X-ray-detected DOG population contains heavily obscured or even Compton-thick sources. The X-ray spectroscopy reveals a mixed bag of objects. We find that four out of the 12 sources with adequate photon statistics and hence reliable X-ray spectra show evidence for a hard X-ray spectral index with Γ ~ 1 or harder, which is consistent with a Compton-thick spectrum. In total 12 out of the 26 DOGs show evidence for flat spectral indices. However, owing to the limited photon statistics we cannot distinguish whether they are flat because they are reflection-dominated or because they show moderate amounts of absorption. Seven DOGs show relatively steep spectra Γ > 1.4, indicative of low column densities. All the above suggests a fraction of Compton-thick sources that does not exceed 50%. The average X-ray spectrum of all 26 DOGs is hard (Γ ~ 1.1) or even harder (Γ ~ 0.6) when we exclude the brightest sources. These spectral indices agree with the stacked spectrum of X-ray-undetected sources (Γ ≈ 0.8 in the CDFN). This could suggest (but not necessarily prove) that X-ray undetected DOGs, in a similar way as the X-ray-detected ones presented here, are hosting a moderate fraction of Compton-thick sources.

We present high-resolution large-scale observations of the molecular and atomic gas in the Local Group galaxy M 33. The observations were carried out using the HEterodyne Receiver Array (HERA) at the 30 m IRAM telescope in the CO(2–1) line, achieving a resolution of 12″ × 2.6   km   s-1, enabling individual giant molecular clouds (GMCs) to be resolved. The observed region is 650 square arcminutes mainly along the major axis and out to a radius of 8.5 kpc, and covers entirely the 2′ × 40′ radial strip observed with the HIFI and PACS Spectrometers as part of the HERM33ESHerschel key program. The achieved sensitivity in main-beam temperature is 20–50 mK at 2.6      km   s-1velocity resolution. The CO(2–1) luminosity of the observed region is 1.7 ± 0.1 × 107K   km   s-1pc2and is estimated to be 2.8 ± 0.3 × 107K   km   s-1pc2for the entire galaxy, corresponding to H2masses of 1.9 × 108M⊙and 3.3 × 108M⊙respectively (including He), calculated with N(H2)/ICO(1 − 0)twice the Galactic value due to the half-solar metallicity of M 33. The H i21 cm VLA archive observations were reduced, and the mosaic was imaged and cleaned using the multi-scale task in the CASA software package, yielding a series of datacubes with resolutions ranging from 5″ to 25″. The H i mass within a radius of 8.5 kpc is estimated to be 1.4 × 109M⊙. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9 ± 0.1 kpc whereas theatomic gas surface density is constant at ΣHi= 6 ± 2   M⊙pc-2deprojected to face-on. For an N(H2)/ICO(1 − 0)conversion factor twice that of the Milky Way, the central kiloparsec H2surface density is ΣH2= 8.5 ± 0.2   M⊙pc-2. The star formation rate per unit molecular gas (SF efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to Hαand FIR brightness, is constant with radius. The SFE, with a N(H2)/ICO(1 − 0)factor twice galactic, appears 2–4 times greater than for large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8 kpc from the galaxy center, are presented.

The Ultra luminous infrared galaxy (ULIRG) Mrk 231 reveals up to seven rotational lines of water (H2O) in emission, including a very high-lying (Eupper= 640 K) line detected at a 4σlevel, within the Herschel/SPIRE wavelength range (190 < λ(μm) < 640), whereas PACS observations show one H2O line at 78 μm in absorption, as found for other H2O lines previously detected by ISO. The absorption/emission dichotomy is caused by the pumping of the rotational levels by far-infrared radiation emitted by dust, and subsequent relaxation through lines at longer wavelengths, which allows us to estimate both the column density of H2O and the general characteristics of the underlying far-infrared continuum source. Radiative transfer models including excitation through both absorption of far-infrared radiation emitted by dust and collisions are used to calculate the equilibrium level populations of H2O and the corresponding line fluxes. The highest-lying H2O lines detected in emission, with levels at 300–640 K above the ground state, indicate that the source of far-infrared radiation responsible for the pumping is compact (radius = 110–180 pc) and warm (Tdust= 85–95 K), accounting for at least 45% of the bolometric luminosity. The high column density, N(H2O) ~ 5×1017cm-2, found in this nuclear component, is most probably the consequence of shocks/cosmic rays, an XDR chemistry, and/or an “undepleted chemistry” where grain mantles are evaporated. A more extended region, presumably the inner region of the 1-kpc disk observed in other molecular species, could contribute to the flux observed in low-lying H2O lines through dense hot cores, and/or shocks. The H2O 78 μm line observed with PACS shows hints of a blue-shifted wing seen in absorption, possibly indicating the occurrence of H2O in the prominent outflow detected in OH (Fischer et al. 2010, A&A, 518, L41). Additional PACS/HIFI observations of H2O lines are required to constrain the kinematics of the nuclear component, as well as the distribution of H2O relative to the warm dust.

Context. Over the past few years several studies have provided estimates of the SFR (star-formation rate) or the total infrared luminosity from just one infrared band. However these relations are generally derived for entire galaxies, which are known to contain a large scale diffuse emission that is not necessarily related to the latest star-formation episode.Aims. We provide new relations to estimate the SFR from resolved star-forming regions at 100 μm and 160 μm.Methods. We select individual star-forming regions in the nearby (840 kpc) galaxy M 33. We estimate the SFR combining the emission in Hαand at 24 μm to calibrate the emission at 100 μm and 160 μm as SFR estimators, as mapped with PACS/Herschel. The data are obtained in the framework of the HERM33ES open time key program.Results. There is less emission in the HII regions at 160 μm than at 100 μm. Over a dynamic range of almost 2 dex in ΣSFRwe find that the 100 μm emission is a nearly linear estimator of the SFR, whereas that at 160 μm is slightly superlinear.Conclusions. The behaviour of individual star-forming regions is surprisingly similar to that of entire galaxies. At high ΣSFR, star formation drives the dust temperature, whereas uncertainties and variations in radiation-transfer and dust-heated processes dominate at low ΣSFR. Detailed modelling of both galaxies and individual star forming regions will be needed to interpret similarities and differences between the two and assess the fraction of diffuse emission in galaxies.

We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk 231. In total 25 lines are detected, including CO J= 5–4 through J= 13–12, 7 rotational lines of H2O, 3 of OH+and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J= 8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J= 8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk 231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk 231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J= 8. X-rays from the accreting supermassive black hole in Mrk 231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk 231. The extraordinary luminosity of the OH+and H2O+lines reveals the signature of X-ray driven excitation and chemistry in this region.

Context. Within the framework of the HERM33ES key program, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M 33, exploiting the high resolution and sensitivity of Herschel. Aims. We use PACS and SPIRE maps at 100, 160, 250, 350, and 500 μm wavelength, to study the variation of the spectral energy distributions (SEDs) with galacto-centric distance. Methods. Detailed SED modeling is performed using azimuthally averaged fluxes in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance. Simple isothermal and two-component grey body models, with fixed dust emissivity index, are fitted to the SEDs between 24 μm and 500 μm using also MIPS/Spitzerdata, to derive first estimates of the dust physical conditions. Results. The far-infrared and submillimeter maps reveal the branched, knotted spiral structure of M 33. An underlying diffuse disk is seen in all SPIRE maps (250–500 μm). Two component fits to the SEDs agree better than isothermal models with the observed, total and radially averaged flux densities. The two component model, with βfixed at 1.5, best fits the global and the radial SEDs. The cold dust component clearly dominates; the relative mass of the warm component is less than 0.3% for all the fits. The temperature of the warm component is not well constrained and is found to be about 60 K ±10 K. The temperature of the cold component drops significantly from ~24 K in the inner 2 kpc radius to 13 K beyond 6 kpc radial distance, for the best fitting model. The gas-to-dust ratio for β= 1.5, averaged over the galaxy, is higher than the solar value by a factor of 1.5 and is roughly in agreement with the subsolar metallicity of M 33.

Aims. Within the framework of the HERM33ESkey program, using the high resolution and sensitivity of the Herschelphotometric data, we study the compact emission in the Local Group spiral galaxy M 33 to investigate the nature of the compact SPIRE emission sources. We extracted a catalogue of sources at 250 μm in order to investigate the nature of this compact emission. Taking advantage of the unprecedented Herschelresolution at these wavelengths, we also focus on a more precise study of some striking Hαshells in the northern part of the galaxy.Methods. We present a catalogue of 159 compact emission sources in M 33 identified by SExtractor in the 250 μm SPIRE band that is the one that provides the best spatial resolution. We also measured fluxes at 24 μm and Hαfor those 159 extracted sources. The morphological study of the shells also benefits from a multiwavelength approach including Hα, far-ultraviolet from GALEX, and infrared from both SpitzerIRAC 8 μm and MIPS 24 μm in order to make comparisons.Results. For the 159 compact sources selected at 250 μm, we find a very strong Pearson correlation coefficient with the MIPS 24 μm emission (r24= 0.94) and a rather strong correlation with the Hαemission, although with more scatter (rHα= 0.83). The morphological study of the Hαshells shows a displacement between far-ultraviolet, Hα, and the SPIRE bands. The cool dust emission from SPIRE clearly delineates the Hαshell structures.Conclusions. The very strong link between the 250 μm compact emission and the 24 μm and Hαemissions, by recovering the star formation rate from standard recipes for H IIregions, allows us to provide star formation rate calibrations based on the 250 μm compact emission alone. The different locations of the Hαand far-ultraviolet emissions with respect to the SPIRE cool dust emission leads to a dynamical age of a few Myr for the Hαshells and the associated cool dust.

We present an analysis of the first space-based far-IR-submm observations of M 33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M 33 is a first step towards young low-metallicity galaxies where the submm may be able to provide an alternative to CO mapping to measure their H2content. In this Letter, we measure the dust emission cross-section σusing SPIRE and recent CO and H iobservations; a variation in σis present from a near-solar neighborhood cross-section to about half-solar with the maximum being south of the nucleus. Calculating the total H column density from the measured dust temperature and cross-section, and then subtracting the H icolumn, yields a morphology similar to that observed in CO. The H2/H imass ratio decreases from about unity to well below 10% and is about 15% averaged over the optical disk. The single most important observation to reduce the potentially large systematic errors is to complete the CO mapping of M 33.

We use the science demonstration phase data of the HerschelVirgo Cluster Survey to search for dust emission of early-type dwarf galaxies in the central regions of the Virgo cluster as an alternative way of identifying the interstellar medium. We present the first possible far-infrared detection of cluster early-type dwarf galaxies: VCC 781 and VCC 951 are detected at the 10σlevel in the SPIRE 250 μm image. Both detected galaxies have dust masses of the order of 105$M_\odot$and average dust temperatures ≈20 K. The detection rate (less than 1%) is quite high compared to the 1.7% detection rate for Hiemission, considering that dwarfs in the central regions are more Hideficient. We conclude that the removal of interstellar dust from dwarf galaxies resulting from ram pressure stripping, harassment, or tidal effects must be as efficient as the removal of interstellar gas.

We present infrared colours (in the 25–500 μm spectral range) and UV to radio continuum spectral energy distributions of a sample of 51 nearby galaxies observed with SPIRE on Herschel. The observed sample includes all morphological classes, from quiescent ellipticals to active starbursts. Active galaxies have warmer colour temperatures than normal spirals. In ellipticals hosting a radio galaxy, the far-infrared (FIR) emission is dominated by the synchrotron nuclear emission. The colour temperature of the cold dust is higher in quiescent E-S0a than in star-forming systems probably because of the different nature of their dust heating sources (evolved stellar populations, X-ray, fast electrons) and dust grain properties. In contrast to the colour temperature of the warm dust, the f350/f500 index sensitive to the cold dust decreases with star formation and increases with metallicity, suggesting an overabundance of cold dust or an emissivity parameter β< 2 in low metallicity, active systems.

We present the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the HerschelVirgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 + log(O/H) < 8.3) and star-formation rates ≲10-1$M_{\odot}$yr-1. We measure the spectral energy distribution (SED) from 100 to 500 μm and derive dust temperatures and dust masses. The SEDs are fitted by a cool component of temperature T≲ 20 K, implying dust masses around 105$M_{\odot}$and dust-to-gas ratios ${\mathcal D}$within the range 10-3–10-2. The completion of the full survey will yield a larger set of galaxies, which will provide more stringent constraints on the dust content of star-forming dwarf galaxies.

Context. Within the framework of the HERM33ES key program, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M 33, exploiting the high resolution and sensitivity of Herschel.

We describe the HerschelVirgo Cluster Survey (HeViCS) and the first data obtained as part of the science demonstration phase (SDP). The data cover a central 4×4 sq deg region of the cluster. We use SPIRE and PACS photometry data to produce 100, 160, 250, 350 and 500 μm luminosity functions (LFs) for optically bright galaxies that are selected at 500 μm and detected in all bands. We compare these LFs with those previously derived using IRAS, BLAST and Herschel-ATLAS data. The Virgo cluster LFs do not have the large numbers of faint galaxies or examples of very luminous galaxies seen previously in surveys covering less dense environments.

We present a resolved dust analysis of three of the largest angular size spiral galaxies, NGC 4501 and NGC 4567/8, in the HerschelVirgo Cluster Survey (HeViCS) science demonstration field. Herschelhas unprecedented spatial resolution at far-infrared wavelengths and with the PACS and SPIRE instruments samples both sides of the peak in the far infrared spectral energy distribution (SED). We present maps of dust temperature, dust mass, and gas-to-dust ratio, produced by fitting modified black bodies to the SED for each pixel. We find that the distribution of dust temperature in both systems is in the range ~19–22 K and peaks away from the centres of the galaxies. The distribution of dust mass in both systems is symmetrical and exhibits a single peak coincident with the galaxy centres. This Letter provides a first insight into the future analysis possible with a large sample of resolved galaxies to be observed by Herschel.

We present infrared colours (in the 25–500 μm spectral range) and UV to radio continuum spectral energy distributions of a sample of 51 nearby galaxies observed with SPIRE on Herschel. The observed sample includes all morphological classes, from quiescent ellipticals to active starbursts. Active galaxies have warmer colour temperatures than normal spirals. In ellipticals hosting a radio galaxy, the far-infrared (FIR) emission is dominated by the synchrotron nuclear emission. The colour temperature of the cold dust is higher in quiescent E-S0a than in star-forming systems probably because of the different nature of their dust heating sources (evolved stellar populations, X-ray, fast electrons) and dust grain properties. In contrast to the colour temperature of the warm dust, the f350/f500 index sensitive to the cold dust decreases with star formation and increases with metallicity, suggesting an overabundance of cold dust or an emissivity parameter β< 2 in low metallicity, active systems.

Context. Over the past few years several studies have provided estimates of the SFR (star-formation rate) or the total infrared luminosity from just one infrared band. However these relations are generally derived for entire galaxies, which are known to contain a large scale diffuse emission that is not necessarily related to the latest star-formation episode.

The Ultra luminous infrared galaxy (ULIRG) Mrk 231 reveals up to seven rotational lines of water (H2O) in emission, including a very high-lying (Eupper= 640 K) line detected at a 4σlevel, within the Herschel/SPIRE wavelength range (190 < λ(μm) < 640), whereas PACS observations show one H2O line at 78 μm in absorption, as found for other H2O lines previously detected by ISO. The absorption/emission dichotomy is caused by the pumping of the rotational levels by far-infrared radiation emitted by dust, and subsequent relaxation through lines at longer wavelengths, which allows us to estimate both the column density of H2O and the general characteristics of the underlying far-infrared continuum source. Radiative transfer models including excitation through both absorption of far-infrared radiation emitted by dust and collisions are used to calculate the equilibrium level populations of H2O and the corresponding line fluxes. The highest-lying H2O lines detected in emission, with levels at 300–640 K above the ground state, indicate that the source of far-infrared radiation responsible for the pumping is compact (radius = 110–180 pc) and warm (Tdust= 85–95 K), accounting for at least 45% of the bolometric luminosity. The high column density, N(H2O) ~ 5×1017cm-2, found in this nuclear component, is most probably the consequence of shocks/cosmic rays, an XDR chemistry, and/or an “undepleted chemistry” where grain mantles are evaporated. A more extended region, presumably the inner region of the 1-kpc disk observed in other molecular species, could contribute to the flux observed in low-lying H2O lines through dense hot cores, and/or shocks. The H2O 78 μm line observed with PACS shows hints of a blue-shifted wing seen in absorption, possibly indicating the occurrence of H2O in the prominent outflow detected in OH (Fischer et al. 2010, A&A, 518, L41). Additional PACS/HIFI observations of H2O lines are required to constrain the kinematics of the nuclear component, as well as the distribution of H2O relative to the warm dust.

Passive early-type galaxies (ETGs) provide an ideal laboratory for studying the interplay between dust formation around evolved stars and its subsequent destruction in a hot gas. Using Spitzer-IRS and Herscheldata we compare the dust production rate in the envelopes of evolved AGB stars with a constraint on the total dust mass. Early-type galaxies which appear to be truly passively evolving are not detected by Herschel. We thus derive a distance independent upper limit to the dust grain survival time in the hostile environment of ETGs of <46±25 Myr for amorphous silicate grains. This implies that ETGs which aredetected at far-infrared wavelengths have acquired a cool dusty medium via interaction. Given likely time-scales for ram-pressure stripping, this also implies that only galaxies with dust in a cool (atomic) medium can release dust into the intra-cluster medium.

By combining Herschel-SPIRE observations obtained as part of the HerschelVirgo Cluster Survey with 21 cm Hidata from the literature, we investigate the role of the cluster environment on the dust content of Virgo spiral galaxies. We show for the first time that the extent of the dust disk is significantly reduced in Hi-deficient galaxies, following remarkably well the observed “truncation” of the Hidisk. The ratio of the submillimetre-to-optical diameter correlates with the Hi-deficiency, suggesting that the cluster environment is able to strip dust as well as gas. These results provide important insights not only into the evolution of cluster galaxies but also into the metal enrichment of the intra-cluster medium.

The origin of the far-infrared emission from the nearby radio galaxy M 87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We present HerschelPACS and SPIRE observations of M 87, taken as part of the science demonstration phase observations of the HerschelVirgo Cluster Survey. We compare these data with a synchrotron model based on mid-infrared, far-infrared, submm and radio data from the literature to investigate the origin of the far-infrared emission. Both the integrated SED and the Herschelsurface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M 87, which is not unexpected in the harsh X-ray environment of this radio galaxy sitting at the core of the Virgo cluster.

Aims. Within the framework of the HERM33ESkey program, using the high resolution and sensitivity of the Herschelphotometric data, we study the compact emission in the Local Group spiral galaxy M 33 to investigate the nature of the compact SPIRE emission sources. We extracted a catalogue of sources at 250 μm in order to investigate the nature of this compact emission. Taking advantage of the unprecedented Herschelresolution at these wavelengths, we also focus on a more precise study of some striking Hαshells in the northern part of the galaxy.

We present the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the HerschelVirgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 + log(O/H) < 8.3) and star-formation rates ≲10-1$M_{\odot}$yr-1. We measure the spectral energy distribution (SED) from 100 to 500 μm and derive dust temperatures and dust masses. The SEDs are fitted by a cool component of temperature T≲ 20 K, implying dust masses around 105$M_{\odot}$and dust-to-gas ratios ${\mathcal D}$within the range 10-3–10-2. The completion of the full survey will yield a larger set of galaxies, which will provide more stringent constraints on the dust content of star-forming dwarf galaxies.

We present an analysis of the first space-based far-IR-submm observations of M 33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M 33 is a first step towards young low-metallicity galaxies where the submm may be able to provide an alternative to CO mapping to measure their H2content. In this Letter, we measure the dust emission cross-section σusing SPIRE and recent CO and H iobservations; a variation in σis present from a near-solar neighborhood cross-section to about half-solar with the maximum being south of the nucleus. Calculating the total H column density from the measured dust temperature and cross-section, and then subtracting the H icolumn, yields a morphology similar to that observed in CO. The H2/H imass ratio decreases from about unity to well below 10% and is about 15% averaged over the optical disk. The single most important observation to reduce the potentially large systematic errors is to complete the CO mapping of M 33.

We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk 231. In total 25 lines are detected, including CO J= 5–4 through J= 13–12, 7 rotational lines of H2O, 3 of OH+and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J= 8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J= 8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk 231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk 231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J= 8. X-rays from the accreting supermassive black hole in Mrk 231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk 231. The extraordinary luminosity of the OH+and H2O+lines reveals the signature of X-ray driven excitation and chemistry in this region.

We use the science demonstration phase data of the HerschelVirgo Cluster Survey to search for dust emission of early-type dwarf galaxies in the central regions of the Virgo cluster as an alternative way of identifying the interstellar medium. We present the first possible far-infrared detection of cluster early-type dwarf galaxies: VCC 781 and VCC 951 are detected at the 10σlevel in the SPIRE 250 μm image. Both detected galaxies have dust masses of the order of 105$M_\odot$and average dust temperatures ≈20 K. The detection rate (less than 1%) is quite high compared to the 1.7% detection rate for Hiemission, considering that dwarfs in the central regions are more Hideficient. We conclude that the removal of interstellar dust from dwarf galaxies resulting from ram pressure stripping, harassment, or tidal effects must be as efficient as the removal of interstellar gas.