| 1. |
- Braine, J., et al.
(författare)
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Cool gas and dust in M33: Results from the HERschel M33 Extended Survey (HERM33ES)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L69
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Tidskriftsartikel (refereegranskat)abstract
- We present an analysis of the first space-based far-IR-submm observations of M33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M33 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 H-2 content. In this Letter, we measure the dust emission cross-section sigma using SPIRE and recent CO and HI observations; a variation in s is 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 HI column, yields a morphology similar to that observed in CO. The H-2/HI mass 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 M33.
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| 2. |
- Kramer, C., et al.
(författare)
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PACS and SPIRE photometer maps of M33: First results of the HERschel M33 Extended Survey (HERM33ES)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L67
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Boquien, M., et al.
(författare)
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Measuring star formation with resolved observations: the test case of M 33
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 578
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Tidskriftsartikel (refereegranskat)abstract
- Context. Measuring star formation on a local scale is important to constrain star formation laws. It is not clear yet, however, whether and how the measure of star formation is affected by the spatial scale at which a galaxy is observed. Aims. We wish to understand the impact of the resolution on the determination of the spatially resolved star formation rate (SFR) and other directly associated physical parameters such as the attenuation. Methods. We carried out a multi-scale, pixel-by-pixel study of the nearby galaxy M33. Assembling FUV, H alpha, 8 mu m, 24 mu m, 70 mu m, and 100 mu m maps, we have systematically compared the emission in individual bands with various SFR estimators from a resolution of 33 pc to 2084 pc. Results. There are strong, scale-dependent, discrepancies of up to a factor 3 between monochromatic SFR estimators and H alpha + 24 mu m. The scaling factors between individual IR bands and the SFR show a strong dependence on the spatial scale and on the intensity of star formation. Finally, strong variations of the differential reddening between the nebular emission and the stellar continuum are seen, depending on the specific SFR (sSFR) and on the resolution. At the finest spatial scales, there is little differential reddening at high sSFR. The differential reddening increases with decreasing sSFR. At the coarsest spatial scales the differential reddening is compatible with the canonical value found for starburst galaxies. Conclusions. Our results confirm that monochromatic estimators of the SFR are unreliable at scales smaller than 1 kpc. Furthermore, the extension of local calibrations to high-redshift galaxies presents non-trivial challenges because the properties of these systems may be poorly known.
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| 4. |
- Mookerjea, B., et al.
(författare)
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The Herschel M 33 extended survey (HerM33es): PACS spectroscopy of the star-forming region BCLMP 302
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 532, s. art. no. A152-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The emission line of [CII] at 158 mu m is one of the strongest cooling lines of the interstellar medium (ISM) in galaxies. Aims. Distinguishing the relative contributions of the different ISM phases to [CII] emission is a major objective of the HerM33es program, a Herschel key project to study the ISM in the nearby spiral galaxy M 33. Methods. Using PACS, we have mapped the emission of [CII] 158 mu m, [OI] 63 mu m, and other FIR lines in a 2' x 2' region of the northern spiral arm of M 33, centered on the HII region BCLMP302. At the peak of Ha emission, we observed in addition a velocity-resolved [CII] spectrum using HIFI. We use scatterplots to compare these data with PACS 160 mu m continuum maps, and with maps of CO and HI data, at a common resolution of 12 '' or 50 pc. Maps of Ha and 24 mu m emission observed with Spitzer are used to estimate the SFR. We created maps of the [CII] and [OI] 63 mu m emission and detected [NII] 122 mu m and [NIII] 57 mu m at individual positions. Results. The [CII] line observed with HIFI is significantly broader than that of CO, and slightly blue-shifted. In addition, there is little spatial correlation between [CII] observed with PACS and CO over the mapped region. There is even less spatial correlation between [CII] and the atomic gas traced by HI. Detailed comparison of the observed intensities towards the HII region with models of photo-ionization and photon-dominated regions, confirms that a significant fraction, 20-30%, of the observed [CII] emission stems from the ionized gas and not from the molecular cloud. The gas heating efficiency, using the ratio of [CII] to the TIR as a proxy, varies between 0.07 and 1.5%, with the largest variations found outside the HII region.
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