We present an overview of the HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds project, which is a Herschel Space Observatory open time key program. We ...describe in detail the data processing, particularly for the PACS data, which required some custom steps because of the large angular extent of a single observational unit and overall the large amount of data to be processed as an ensemble. We report total global fluxes for the LMC and SMC and demonstrate their agreement with measurements by prior missions. We describe the point source extraction processing and the criteria used to establish a catalog for each waveband for the HERITAGE program. The 250 mu m band is the most sensitive and the source catalogs for this band have ~25,000 objects for the LMC and ~5500 objects for the SMC.
Aims. We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim ...is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies. Methods. We used Herschel observations and atomic and molecular gas masses to estimate ϵ(250 μm), the disc-averaged dust emissivity at 250 μm, and from this, the absorption cross section per H atom σ(250 μm) and per dust mass κ(250 μm). The emissivity ϵ(250 μm) requires one assumption, which is the CO-to-H2 conversion factor, and the dust temperature is additionally required for σ(250 μm); yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required for κ(250 μm). Results. We find ϵ(250 μm) = 0.82 ± 0.07 MJy sr−1 (1020 H cm−2)−1 for galaxies with 4 < F(250 μm)/F(500 μm) < 5. This depends only weakly on the adopted CO-to-H2 conversion factor. The value is almost the same as that for the Milky Way at the same colour ratio. Instead, for F(250 μm)/F(500 μm) > 6, ϵ(250 μm) is lower than predicted by its dependence on the heating conditions. The reduction suggests a variation in dust emission properties for spirals of earlier type, higher metallicity, and with a higher fraction of molecular gas. When the standard emission properties of Galactic cirrus are used for these galaxies, their dust masses might be underestimated by up to a factor of two. Values for σ(250 μm) and κ(250 μm) at the Milky Way metallicity are also close to those of the cirrus. Mild trends of the absorption cross sections with metallicity are found, although the results depend on the assumptions made.
Aims. In this work, we aim to provide a consistent analysis of the dust properties from metal-poor to metal-rich environments by linking them to fundamental galactic parameters. Methods. We consider ...two samples of galaxies: the Dwarf Galaxy Survey (DGS) and the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel (KINGFISH), totalling 109 galaxies, spanning almost 2 dex in metallicity. We collect infrared (IR) to submillimetre (submm) data for both samples and present the complete data set for the DGS sample. We model the observed spectral energy distributions (SED) with a physically-motivated dust model to access the dust properties: dust mass, total-IR luminosity, polycyclic aromatic hydrocarbon (PAH) mass fraction, dust temperature distribution, and dust-to-stellar mass ratio. Results. Using a different SED model (modified black body), different dust composition (amorphous carbon in lieu of graphite), or a different wavelength coverage at submm wavelengths results in differences in the dust mass estimate of a factor two to three, showing that this parameter is subject to non-negligible systematic modelling uncertainties. We find half as much dust with the amorphous carbon dust composition. For eight galaxies in our sample, we find a rather small excess at 500 μm (≤1.5σ). We find that the dust SED of low-metallicity galaxies is broader and peaks at shorter wavelengths compared to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The PAH mass fraction and dust temperature distribution are found to be driven mostly by the specific star formation rate, sSFR, with secondary effects from metallicity. The correlations between metallicity and dust mass or total-IR luminosity are direct consequences of the stellar mass-metallicity relation. The dust-to-stellar mass ratios of metal-rich sources follow the well-studied trend of decreasing ratio for decreasing sSFR. The relation is more complex for low-metallicity galaxies with high sSFR, and depends on the chemical evolutionary stage of the source (i.e. gas-to-dust mass ratio). Dust growth processes in the ISM play a key role in the dust mass build-up with respect to the stellar content at high sSFR and low metallicity. Conclusions. We conclude that the evolution of the dust properties from metal-poor to metal-rich galaxies derives from a complex interplay between star formation activity, stellar mass, and metallicity.
Local metal-poor galaxies stand as ideal laboratories for probing the properties of the interstellar medium (ISM) in chemically unevolved conditions. Detailed studies of this primitive ISM can help ...gain insights into the physics of the first primordial galaxies that may be responsible for the reionization. Quantifying the ISM porosity to ionizing photons in nearby galaxies may improve our understanding of the mechanisms leading to Lyman continuum photon leakage from galaxies. The wealth of infrared (IR) tracers available in local galaxies and arising from different ISM phases allows us to constrain complex models in order to estimate physical quantities.
Abstract
We present the results of high spatial resolution HCO
+
(1−0) and HCN(1−0) observations of the N55 south region (N55-S) in the Large Magellanic Cloud (LMC), obtained with the Atacama Large ...Millimeter/submillimeter Array (ALMA). N55-S is a relatively less extreme star-forming region of the LMC characterized by a low radiation field. We carried out a detailed analysis of the molecular emission to investigate the relation between dense molecular clumps and star formation in the quiescent environment of N55-S. We detect 10 molecular clumps with significant HCO
+
(1−0) emission and 8 with significant HCN(1−0) emission, and estimate the molecular clump masses by virial and local thermodynamic equilibrium analysis. All identified young stellar objects (YSOs) in N55-S are found to be near the HCO
+
and HCN emission peaks showing the association of these clumps with recent star formation. The molecular clumps that have associated YSOs show relatively larger line widths and masses than those without YSOs. We compare the clump properties of N55-S with those of other giant molecular clouds (GMCs) in the LMC and find that N55-S clumps possess similar size but relatively lower line width and larger HCN/HCO
+
(1−0) flux ratio. These results can be attributed to the low radiation field in N55-S resulted by relatively low star formation activity compared to other active star-forming regions like 30 Doradus-10 and N159. The dense gas fraction of N55-S is ∼0.025, lower compared to other GMCs of the LMC supporting the low star formation efficiency of this region.
Most radiative transfer models assume that dust in spiral galaxies is distributed exponentially. In this paper our goal is to verify this assumption by analysing the two-dimensional large-scale ...distribution of dust in galaxies from the DustPedia sample. For this purpose, we have made use of Herschel imaging in five bands, from 100 to 500 μm, in which the cold dust constituent is primarily traced and makes up the bulk of the dust mass in spiral galaxies. For a subsample of 320 disc galaxies, we successfully performed a simultaneous fitting with a single Sérsic model of the Herschel images in all five bands using the multi-band modelling code GALFITM. We report that the Sérsic index n, which characterises the shape of the Sérsic profile, lies systematically below 1 in all Herschel bands and is almost constant with wavelength. The average value at 250 μm is 0.67 ± 0.37 (187 galaxies are fitted with n250 ≤ 0.75, 87 galaxies have 0.75 < n250 ≤ 1.25, and 46 – with n250 > 1.25). Most observed profiles exhibit a depletion in the inner region (at r < 0.3−0.4 of the optical radius r25) and are more or less exponential in the outer part. We also find breaks in the dust emission profiles at longer distances (0.5−0.6) r25 which are associated with the breaks in the optical and near-infrared. We assumed that the observed deficit of dust emission in the inner galaxy region is related to the depression in the radial profile of the HI surface density in the same region because the atomic gas reaches high enough surface densities there to be transformed into molecular gas. If a galaxy has a triggered star formation in the inner region (for example, because of a strong bar instability, which transfers the gas inwards to the centre, or a pseudobulge formation), no depletion or even an excess of dust emission in the centre is observed.
We present a power spectrum analysis of the Herschel-SPIRE observations of the Polaris flare, a high Galactic latitude cirrus cloud midway between the diffuse and molecular phases. The SPIRE images ...of the Polaris flare reveal for the first time the structure of the diffuse interstellar medium down to 0.01 parsec over a 10 square degrees region. These exceptional observations highlight the highly filamentary and clumpy structure of the interstellar medium even in diffuse regions of the map. The power spectrum analysis shows that the structure of the interstellar medium is well described by a single power law with an exponent of -2.7±0.1 at all scales from 30” to 8°. That the power spectrum slope of the dust emission is constant down to the SPIRE angular resolution is an indication that the inertial range of turbulence extends down to the 0.01 pc scale. The power spectrum analysis also allows the identification of a Poissonian component at sub-arcminute scales in agreement with predictions of the cosmic infrared background level at SPIRE wavelengths. Finally, the comparison of the SPIRE and IRAS 100 μm data of the Polaris flare clearly assesses the capability of SPIRE in maping diffuse emission over large areas.
We present new photometric data from our Herschel guaranteed time key programme, the Dwarf Galaxy Survey (DGS), dedicated to the observation of the gas and dust in low-metallicity environments. A ...total of 48 dwarf galaxies were observed with the PACS and SPIRE instruments onboard the Herschel Space Observatory at 70, 100, 160, 250, 350, and 500 mu m. The goal of this paper is to provide reliable far-infrared (FIR) photometry for the DGS sample and to analyse the FIR/submillimetre (submm) behaviour of the DGS galaxies. We focus on a systematic comparison of the derived FIR properties with more metal-rich galaxies and investigate the detection of a potential submm excess. The data reduction method is adapted for each galaxy in order to derive the most reliable photometry from the final maps. To study the variation in the dust properties with metallicity, we also include galaxies from the Herschel KINGFISH sample, which contains more metalrich environments, totalling 109 galaxies.
An Overview of the Dwarf Galaxy Survey Madden, S. C.; Rémy-Ruyer, A.; Galametz, M. ...
Publications of the Astronomical Society of the Pacific,
06/2013, Letnik:
125, Številka:
928
Journal Article
Recenzirano
Odprti dostop
ABSTRACT The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230 hr of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the ...Herschel Space Observatory and draws from this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity ( Z) galaxies, 1/50 Z⊙, and spans four orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 μm with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, CII 158 μm, OI 63 μm, OI 145 μm, OIII 88 μm, NIII 57 μm, and NII 122 and 205 μm have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines ( J = 4-3 to J = 13-12), NII 205 μm, and CI lines at 370 and 609 μm. This paper describes the sample selection and global properties of the galaxies and the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.
Autism spectrum disorders (ASD) are a group of neurodevelopmental conditions that are accompanied by atypical brain connectivity. So far, in vivo evidence for atypical structural brain connectivity ...in ASD has mainly been based on neuroimaging studies of cortical white matter. However, genetic studies suggest that abnormal connectivity in ASD may also affect neural connections within the cortical gray matter. Such intrinsic gray-matter connections are inherently more difficult to describe in vivo but may be inferred from a variety of surface-based geometric features that can be measured using magnetic resonance imaging. Here, we present a neuroimaging study that examines the intrinsic cortico-cortical connectivity of the brain in ASD using measures of “cortical separation distances” to assess the global and local intrinsic “wiring costs” of the cortex (i.e., estimated length of horizontal connections required to wire the cortex within the cortical sheet). In a sample of 68 adults with ASD and matched controls, we observed significantly reduced intrinsic wiring costs of cortex in ASD, both globally and locally. Differences in global and local wiring cost were predominantly observed in fronto-temporal regions and also significantly predicted the severity of social and repetitive symptoms (respectively). Our study confirms that atypical cortico-cortical “connectivity” in ASD is not restricted to the development of white-matter connections but may also affect the intrinsic gray-matter architecture (and connectivity) within the cortical sheet. Thus, the atypical connectivity of the brain in ASD is complex, affecting both gray and white matter, and forms part of the core neural substrates underlying autistic symptoms.
PDF
