We study the emission by dust and stars in the Large and Small Magellanic Clouds, a pair of low-metallicity nearby galaxies, as traced by their spatially resolved spectral energy distributions. This ...project combines Herschel Space Observatory PACS and SPIRE far-infrared photometry with other data at infrared and optical wavelengths (the data were obtained as part of the HERschel Inventory of The Agents of Galaxy Evolution survey; PI: M. Meixner). We build maps of dust, stellar luminosity, and mass of both Magellanic Clouds, and analyze the spatial distribution of dust/stellar luminosity and mass ratios. These ratios vary considerably throughout the galaxies, generally between the range 0.01 < or =, slant L sub(dust)/L sub(*) < or =, slant 0.6 and 10 super(-4) < or =, slant M sub(dust)/M sub(*) < or =, slant 4 x 10 super(-3). We observe that the dust/stellar ratios depend on the interstellar medium environment, such as the distance from currently or previously star-forming regions, and on the intensity of the interstellar radiation field. In addition, we construct star formation rate (SFR) maps, and find that the SFR is correlated with the dust/stellar luminosity and dust temperature in both galaxies, demonstrating the relation between star formation, dust emission, and heating, though these correlations exhibit substantial scatter.
Le rayonnement thermique est une source décisive d’informations pour une science de l’observation comme l’astrophysique. Dominant dans l’infrarouge lointain, il est difficile à mesurer, et nécessite ...le développement de détecteurs innovants et de techniques cryogéniques de pointe. Mise en œuvre à bord de satellite depuis 40 ans, la mesure du rayonnement thermique a permis de nombreuses découvertes liées à la formation stellaire et à l’évolution des galaxies.
The far-infrared (FIR) regime is one of the wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist. None of the medium-term satellite projects like SPICA, ...Millimetron, or the Origins Space Telescope will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO), light hydrides, and especially from water lines would open the door for transformative science. A main theme will be to trace the role of water in proto-planetary discs, to observationally advance our understanding of the planet formation process and, intimately related to that, the pathways to habitable planets and the emergence of life. Furthermore, key observations will zoom into the physics and chemistry of the star-formation process in our own Galaxy, as well as in external galaxies. The FIR provides unique tools to investigate in particular the energetics of heating, cooling, and shocks. The velocity-resolved data in these tracers will reveal the detailed dynamics engrained in these processes in a spatially resolved fashion, and will deliver the perfect synergy with ground-based molecular line data for the colder dense gas.
The Herschel-PACS photometer calibration Balog, Zoltan; Müller, Thomas; Nielbock, Markus ...
Experimental astronomy,
07/2014, Letnik:
37, Številka:
2
Journal Article
Recenzirano
This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the ...photospheric models of five fiducial stellar standards (
α
Boo,
α
Cet,
α
Tau,
β
And,
γ
Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ∼2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum
νF
ν
=
λF
λ
=
const
as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated.
The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and life-cycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc ...resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21 cm, CO, and H alpha observations. We investigate the range of CO-to-Hsub 2 conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on XCO to be 6 x 10sup 20 cmsup -2 Ksup -1 kmsup -1 s in the LMC (Z = 0.5Z) at 15 pc resolution, and 4 x 1021 cmsup -2 Ksup -1 kmsup -1 s in the SMC (Z = 0.2Z) at 45 pc resolution. Our analysis demonstrates that obtaining robust ISM masses remains a non-trivial endeavor even in the local Universe using state-of-the-art maps of thermal dust emission.
We present Herschel Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (Herschel SPIRE-FTS) observations of Arp 220, a nearby ultra-luminous infrared galaxy. The FTS provides ...continuous spectral coverage from 190 to 670 Delta *mm, a wavelength region that is either very difficult to observe or completely inaccessible from the ground. The spectrum provides a good measurement of the continuum and detection of several molecular and atomic species. We detect luminous CO (J = 4-3 to 13-12) and water rotational transitions with comparable total luminosity ~2 X 108 L ; very high-J transitions of HCN (J = 12-11 to 17-16) in absorption; strong absorption features of rare species such as OH+, H2O+, and HF; and atomic lines of C I and N II. The modeling of the continuum shows that the dust is warm, with T = 66 K, and has an unusually large optical depth, with Delta *tdust ~ 5 at 100 Delta *mm. The total far-infrared luminosity of Arp 220 is L FIR ~ 2 X 1012 L . Non-LTE modeling of the extinction corrected CO rotational transitions shows that the spectral line energy distribution of CO is fit well by two temperature components: cold molecular gas at T ~ 50 K and warm molecular gas at T ~ 1350+280 -- 100 K (the inferred temperatures are much lower if CO line fluxes are not corrected for dust extinction). These two components are not in pressure equilibrium. The mass of the warm gas is 10% of the cold gas, but it dominates the CO luminosity. The ratio of total CO luminosity to the total FIR luminosity is L CO/L FIR ~ 10--4 (the most luminous lines, such as J = 6-5, have L CO, J = 6-5/L FIR ~ 10--5). The temperature of the warm gas is in excellent agreement with the observations of H2 rotational lines. At 1350 K, H2 dominates the cooling (~20 L M --1 ) in the interstellar medium compared to CO (~0.4 L M --1 ). We have ruled out photodissociation regions, X-ray-dominated regions, and cosmic rays as likely sources of excitation of this warm molecular gas, and found that only a non-ionizing source can heat this gas; the mechanical energy from supernovae and stellar winds is able to satisfy the large energy budget of ~20 L M --1 . Analysis of the very high-J lines of HCN strongly indicates that they are solely populated by infrared pumping of photons at 14 Delta *mm. This mechanism requires an intense radiation field with T > 350 K. We detect a massive molecular outflow in Arp 220 from the analysis of strong P Cygni line profiles observed in OH+, H2O+, and H2O. The outflow has a mass 107 M and is bound to the nuclei with velocity 250 km s--1. The large column densities observed for these molecular ions strongly favor the existence of an X-ray luminous AGN (1044 erg s--1) in Arp 220.
We present low- and high-resolution Spitzer/IRS spectra, supplemented by Infrared Array Camera and Multiband Imaging Photometer for Spitzer measurements, of 22 blue compact dwarf (BCD) galaxies. The ...BCD sample spans a wide range in oxygen abundance (12+log(O/H) between 7.4 and 8.3), and hardness of the interstellar radiation field (ISRF). The Infrared Spectrograph (IRS) spectra provide us with a rich set of diagnostics to probe the physics of star and dust formation in very low metallicity environments. We find that metal-poor BCDs have harder ionizing radiation than metal-rich galaxies: O IV emission is {approx}>4 times as common as Fe II emission. They also have a more intense ISRF, as indicated by the 71 to 160 {mu}m luminosity ratio. Two-thirds of the sample (15 BCDs) show polycyclic aromatic hydrocarbon (PAH) features, although the fraction of PAH emission normalized to the total infrared (IR) luminosity is considerably smaller in metal-poor BCDs ({approx}0.5%) than in metal-rich star-forming galaxies ({approx}10%). We find several lines of evidence for a deficit of small PAH carriers at low metallicity, and attribute this to destruction by a hard, intense ISRF, only indirectly linked to metal abundance. Our IRS spectra reveal a variety of H{sub 2} rotational lines, and more than a third of the objects in our sample (eight BCDs) have {approx}>3sigma detections in one or more of the four lowest-order transitions. The warm gas masses in the BCDs range from 10{sup 3} M{sub sun} to 10{sup 8} M{sub sun}, and can be comparable to the neutral hydrogen gas mass; relative to their total IR luminosities, some BCDs contain more H{sub 2} than Spitzer Nearby Galaxy Survey galaxies.
Ample evidence exists regarding supernovae being a major contributor to interstellar dust. In this work, the deepest far-infrared observations of the Crab Nebula are used to revisit the estimation of ...the dust mass present in this supernova remnant. Images in filters between 70 and 500
μ
m taken by the PACS and SPIRE instruments on-board of the Herschel Space Observatory are used. With a novel and automated approach we constructed the spectral energy distribution of the Crab nebula to recover the dust mass. This approach makes use of several image processing techniques (thresholding, morphological processes, contouring, etc..) to objectively separate the nebula from its surrounding background. After subtracting the non-thermal synchrotron component from the integrated fluxes, the spectral energy distribution is found to be best fitted using a single modified blackbody of temperature
T
= 42.06 ± 1.14 K and a dust mass of
M
d
= 0.056 ± 0.037 M
⊙
. Our aim in this paper is to highlight the importance of the photometric methods and spectral energy distribution construction on the accuracy of inference for astrophysical parameters.
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