F. S. Tabatabaei

HERSCHEL FAR-INFRARED AND SUBMILLIMETER PHOTOMETRY FOR THE KINGFISH SAMPLE OF NEARBY GALAXIES

New far-infrared and submillimeter photometry from the Herschel Space Observatory is presented for 61 nearby galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH) sample. The spatially integrated fluxes are largely consistent with expectations based on Spitzer far-infrared photometry and extrapolations to longer wavelengths using popular dust emission models. Dwarf irregular galaxies are notable exceptions, as already noted by other authors, as their 500 μm emission shows evidence for a submillimeter excess. In addition, the fraction of dust heating attributed to intense radiation fields associated with photodissociation regions is found to be (21 ± 4)% larger when Herschel data are included in the analysis. Dust masses obtained from the dust emission models of Draine & Li are found to be on average nearly a factor of two higher than those based on single-temperature modified blackbodies, as single blackbody curves do not capture the full range of dust temperatures inherent to any galaxy. The discrepancy is largest for galaxies exhibiting the coolest far-infrared colors.

Mapping the cold dust temperatures and masses of nearby KINGFISH galaxies with Herschel

Taking advantage of the unprecedented combination of sensitivity and angular resolution afforded by the Herschel Space Observatory at far-infrared and submillimetre wavelengths, we aim to characterize the physical properties of cold dust within nearby galaxies, as well as the associated uncertainties, namely the robustness of the parameters we derive using different modified blackbody models. For a pilot subsample of the KINGFISH (Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel) key programme, we perform two-temperature fits of the Spitzer and Herschel photometric data (from 24 to 500 μm), with a warm and a cold component, both globally and in each resolution element. We compare the results obtained from different analysis strategies. At global scale, we observe a range of values of the modified blackbody fit parameters β_c (0.8–2.5) and T_c (19.1–25.1 K). We compute maps of our modelling parameters with β_c fixed or treated as a free parameter to test the robustness of the temperature and dust surface density maps we deduce. When the emissivity is fixed, we observe steeper temperature gradients as a function of radius than when it is allowed to vary. When the emissivity is fitted as a free parameter, barred galaxies tend to have uniform fitted emissivities. Gathering the parameters obtained in each resolution element in a T_c–β_c diagram underlines an anticorrelation between the two parameters. It remains difficult to assess whether the dominant effect is the physics of dust grains, noise, or mixing along the line of sight and in the beam. We finally observe in both cases that the dust column density peaks in central regions of galaxies and bar-ends (coinciding with molecular gas density enhancements usually found in these locations). We also quantify how the total dust mass varies with our assumptions about the emissivity index as well as the influence of the wavelength coverage used in the fits. We show that modified blackbody fits using a shallow emissivity (β < 2.0) lead to significantly lower dust masses compared to the β < 2.0 case, with dust masses lower by up to 50 per cent if β_c = 1.5, for instance. The working resolution affects our total dust mass estimates: masses increase from global fits to spatially resolved fits.

The heating of dust by old stellar populations in the bulge of M31

We use new Herschel multi-band imaging of the Andromeda galaxy to analyze how dust heating occurs in the central regions of galaxy spheroids th at are essentially devoid of young stars. We construct a dust temperature map of M31 through fitt ing modified blackbody SEDs to the Herschel data, and find that the temperature within 2 kp c rises strongly from the mean value in the disk of 17± 1 K to∼ 35 K at the centre. UV to near-IR imaging of the central few kpc shows directly the absence of young stellar populations, delineates the radial profile of the stellar density, and demonstrates that even the near- UV dust extinction is optically thin in M31’s bulge. This allows the direct calculation of the ste llar radiation heating in the bulge, U∗(r), as a function of radius. The increasing temperature profil e in the centre matches that expected from the stellar heating, i.e. that the dust heatin g and cooling rates track each other over nearly two orders of magnitude in U∗. The modelled dust heating is in excess of the observed dust temperatures, suggesting that it is more than suffi cient to explain the observed IR emission. Together with the wavelength dependent absorption cross section of the dust, this demonstrates directly that it is the optical, not UV, ra diation that sets the heating rate. This analysis shows that neither young stellar populations nor stellar near-UV radiation are necessary to heat dust to warm temperatures in galaxy spheroids. Rather, it is the high densities of Gyr-old stellar populations that provide a suffi ciently strong diffuse radiation field to heat the dust. To the extent which these results pertain to the ten uous dust found in the centres of early-type galaxies remains yet to be explored.

PACS and SPIRE photometer maps of M33: First results of the HERschel M33 Extended Survey (HERM33ES)

Context. Within the framework of the HERM33ES key program, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M33, exploiting the high resolution and sensitivity of Herschel. Aims. We use PACS and SPIRE maps at 100, 160, 250, 350, and 500 mu m 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 mu m and 500 mu m using also MIPS/Spitzer data, to derive first estimates of the dust physical conditions. Results. The far-infrared and submillimeter maps reveal the branched, knotted spiral structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500 mu m). 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 beta fixed 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 similar to 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 beta = 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 M33.

High-resolution radio continuum survey of M33 II. Thermal and nonthermal emission

Context. Constraints on the origin and propagation of cosmic rays can be achieved by studying the variation in the spectral index of the synchrotron emission across external galaxies. Aims. We determine the variation in the nonthermal radio spectral index in the nearby spiral galaxy M 33 at a linear resolution of 360 pc. Methods. We separated the thermal and nonthermal components of the radio continuum emission without the assumption of a constant nonthermal spectral index. Using the Spitzer FIR data at 70 and 160 µm and a standard dust model, we dereddened the Hα emission. The extinction corrected Hα emission serves as a template for the thermal free-free radio emission. Subtracting this free-free emission from the observed 3.6 cm and 20 cm emission (Effelsberg and the VLA), we obtained the nonthermal maps. A constant electron temperature used to obtain the thermal radio intensity seems appropriate for M 33, which, unlike the Milky Way, has a shallow metallicity gradient. Results. For the first time, we derive the distribution of the nonthermal spectral index across a galaxy, M 33. We detect strong nonthermal emission from the spiral arms and starforming regions. Wavelet analysis shows that at 3.6 cm the nonthermal emission is dominated by contributions from starforming regions, while it is smoothly distributed at 20 cm. For the whole galaxy, we obtain thermal fractions of 51% and 18% at 3.6 cm and 20 cm, respectively. The thermal emission is slightly stronger in the southern than in the northern half of the galaxy. We find a clear radial gradient of mean extinction in the galactic plane. Conclusions. The nonthermal spectral index map indicates that the relativistic electrons suffer energy loss when diffusing from their origin in starforming regions towards interarm regions and the outer parts of the galaxy. We also conclude that the radio emission is mostly nonthermal at R > 5 kpc in M 33.

[C II] 158 μm EMISSION AS A STAR FORMATION TRACER

The [CII] 157.74

Calibration of the total infrared luminosity of nearby galaxies from Spitzer and Herschel bands

\mu

Mapping Dust through Emission and Absorption in Nearby Galaxies

m transition is the dominant coolant of the neutral interstellar gas, and has great potential as a star formation rate (SFR) tracer. Using the Herschel KINGFISH sample of 46 nearby galaxies, we investigate the relation of [CII] surface brightness and luminosity with SFR. We conclude that [CII] can be used for measurements of SFR on both global and kiloparsec scales in normal star-forming galaxies in the absence of strong active galactic nuclei (AGN). The uncertainty of the

A detailed study of the radio-FIR correlation in NGC 6946 with Herschel-PACS/SPIRE from KINGFISH

\Sigma_{\rm [CII]}-\Sigma_{\rm SFR}

Dust and gas power spectrum in M 33 (HERM33ES)

calibration is