Context
. Dust in late-type galaxies in the local Universe is responsible for absorbing approximately one third of the energy emitted by stars. It is often assumed that dust heating is mainly ...attributable to the absorption of ultraviolet and optical photons emitted by the youngest (≤100 Myr) stars. Consequently, thermal re-emission by dust at far-infrared wavelengths is often linked to the star-formation activity of a galaxy. However, several studies argue that the contribution to dust heating by much older stellar populations might be more significant than previously thought. Advances in radiation transfer simulations finally allow us to actually quantify the heating mechanisms of diffuse dust by the stellar radiation field.
Aims
. As one of the main goals in the DustPedia project, we have developed a framework to construct detailed 3D stellar and dust radiative transfer models for nearby galaxies. In this study, we analyse the contribution of the different stellar populations to the dust heating in four nearby face-on barred galaxies: NGC 1365, M 83, M 95, and M 100. We aim to quantify the fraction directly related to young stellar populations, both globally and on local scales, and to assess the influence of the bar on the heating fraction.
Methods
. From 2D images we derive the 3D distributions of stars and dust. To model the complex geometries, we used
SKIRT
, a state-of-the-art 3D Monte Carlo radiative transfer code designed to self-consistently simulate the absorption, scattering, and thermal re-emission by the dust for arbitrary 3D distributions.
Results
. We derive global attenuation laws for each galaxy and confirm that galaxies of high specific star-formation rate have shallower attenuation curves and weaker UV bumps. On average, 36.5% of the bolometric luminosity is absorbed by dust in our galaxy sample. We report a clear effect of the bar structure on the radial profiles of the dust-heating fraction by the young stellar populations, and the dust temperature. We find that the young stellar populations are the main contributors to the dust heating, donating, on average ∼59% of their luminosity to this purpose throughout the galaxy. This dust-heating fraction drops to ∼53% in the bar region and ∼38% in the bulge region where the old stars are the dominant contributors to the dust heating. We also find a strong link between the heating fraction by the young stellar populations and the specific star-formation rate.
We present the first nonparametric morphological analysis of a set of spiral galaxies from UV to submillimeter (submm) wavelengths. Our study is based on high-quality multi-wavelength imaging for ...nine well-resolved spiral galaxies from the DustPedia database, combined with nonparametric morphology indicators calculated in a consistent way using the
StatMorph
package. We measure the half-light radius, the concentration index, the asymmetry index, the smoothness index, the Gini coefficient, and the
M
20
indicator in various wavebands from UV to submm wavelengths, and in stellar mass, dust mass, and star formation rate maps. We find that the interstellar dust in galaxies is distributed in a more extended, less centrally concentrated, more asymmetric, and more clumpy way than the stars are. This is particularly evident when comparing morphological indicators based on the stellar mass and dust mass maps. This should serve as a warning sign against treating the dust in galaxies as a simple smooth component. We argue that the nonparametric galaxy morphology of galaxies from UV to submm wavelengths is an interesting test for cosmological hydrodynamics simulations.
Interstellar dust in galaxies can be traced either through its extinction effects on the star light or through its thermal emission at infrared wavelengths. Recent radiative transfer studies of ...several nearby edge-on galaxies have found an apparent inconsistency in the dust energy balance: the radiative transfer models that successfully explain the optical extinction underestimate the observed fluxes by an average factor of 3. We investigate the dust energy balance for IC 4225 and NGC 5166, two edge-on spiral galaxies observed by the Herschel Space Observatory in the frame of the H-ATLAS survey. We start from models which were constrained from optical data and extend them to construct the entire spectral energy distribution of our galaxies. These predicted values are subsequently compared to the observed far-infrared fluxes. We find that including a young stellar population in the modelling is necessary as it plays a non-negligible part in the heating of the dust grains. While the modelling approach for both galaxies is nearly identical, we find two very different results. As is often seen in other edge-on spiral galaxies, the far-infrared emission of our radiative transfer model of IC 4225 underestimates the observed fluxes by a factor of about 3. For NGC 5166 on the other hand, we find that both the predicted spectral energy distribution as well as the simulated images match the observations particularly well. We explore possible reasons for this difference and conclude that it is unlikely that one single mechanism is the cause of the dust energy balance problem in spiral galaxies. We discuss the different approaches that can be considered in order to get a conclusive answer on the origin this discrepancy.
Context.
Investigating the dust heating mechanisms in galaxies provides a deeper understanding of how the internal energy balance drives their evolution. Over the last decade radiative transfer ...simulations based on the Monte Carlo method have emphasised the role of the various stellar populations heating the diffuse dust. Beyond the expected heating through ongoing star formation, older stellar populations (≥8 Gyr) and even active galactic nuclei can both contribute energy to the infrared emission of diffuse dust.
Aims.
In this particular study we examine how the radiation of an external heating source, such as the less massive galaxy NGC 5195 in the M 51 interacting system, could affect the heating of the diffuse dust of its parent galaxy NGC 5194, and vice versa. Our goal is to quantify the exchange of energy between the two galaxies by mapping the 3D distribution of their radiation field.
Methods.
We used
SKIRT
, a state-of-the-art 3D Monte Carlo radiative transfer code, to construct the 3D model of the radiation field of M 51, following the methodology defined in the DustPedia framework. In the interest of modelling, the assumed centre-to-centre distance separation between the two galaxies is ∼10 kpc.
Results.
Our model is able to reproduce the global spectral energy distribution of the system, and it matches the resolved optical and infrared images fairly well. In total, 40.7% of the intrinsic stellar radiation of the combined system is absorbed by dust. Furthermore, we quantify the contribution of the various dust heating sources in the system, and find that the young stellar population of NGC 5194 is the predominant dust-heating agent, with a global heating fraction of 71.2%. Another 23% is provided by the older stellar population of the same galaxy, while the remaining 5.8% has its origin in NGC 5195. Locally, we find that the regions of NGC 5194 closer to NGC 5195 are significantly affected by the radiation field of the latter, with the absorbed energy fraction rising up to 38%. The contribution of NGC 5195 remains under the percentage level in the outskirts of the disc of NGC 5194. This is the first time that the heating of the diffuse dust by a companion galaxy is quantified in a nearby interacting system.
Summary
Comparing companies can be useful for various purposes. Despite the widespread use of industry classification systems as a peer selection standard, these have been criticized for various ...reasons. Financial statements, however, offer a promising alternative to such classification systems. They are standardized, widely available, and offer deep insights into the nature of the company. In this paper, we present a graph distance metric for financial statements using the earth mover's distance. When using the distance metric on real‐world tasks such as peer identification and industry classification, it shows promising results in terms of accuracy and computational efficiency.
Galaxies are generally considered as the basic building blocks of the Universe. Besides stars, galaxies also contain a supermassive black hole, a dark matter halo, and a multi-phase interstellar ...medium that consists of molecules, atoms, ions, and dust grains. A global picture of the structure, dynamics, formation, and evolution of galaxies requires observations of all these different components, and hence a multi-wavelength approach. We describe the main contributions of the UGent astronomy group to extragalactic astronomy over the last years. We focus on two broad and slightly overlapping fields in which our team has been active: galaxy kinematics and dynamics, and the study of the interstellar medium in galaxies. Possibilities for collaboration with the Indian astronomical community in the frame of the BINA network are highlighted.
Evidence is mounting that a significant fraction of the early-type galaxy population contains substantial reservoirs of cold interstellar gas and dust. We investigate the gas and dust in NGC 5485, an ...early-type galaxy with a prominent minor-axis dust lane. Using new Herschel PACS and SPIRE imaging data, we detect 3.8 × 106 M⊙ of cool interstellar dust in NGC 5485, which is in stark contrast with the non-detection of the galaxy in sensitive H i and CO observations from the ATLAS3D consortium. The resulting gas-to-dust ratio upper limit is M
gas/M
d < 14.5, almost an order of magnitude lower than the canonical value for the Milky Way. We scrutinize the reliability of the dust, atomic gas and molecular gas mass estimates, but these do not show systematic uncertainties that can explain the extreme gas-to-dust ratio. Also a warm or hot ionized gas medium does not offer an explanation. A possible scenario could be that NGC 5485 merged with an SMC-type metal-poor galaxy with a substantial CO-dark molecular gas component and that the bulk of atomic gas was lost during the interaction, but it remains to be investigated whether such a scenario is possible.
Abstract
The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys ...reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming ‘main sequence’ and a separate region of ‘passive’ or ‘red-and-dead’ galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red star-forming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations – they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population.
VALES Couto, Guilherme S.; Hughes, Thomas M.; Boquien, Médéric ...
Astronomy and astrophysics (Berlin),
10/2021, Letnik:
654
Journal Article
Recenzirano
We characterize the ionized gas outflows in 15 low-redshift star-forming galaxies, a Valparaíso ALMA/APEX Line Emission Survey (VALES) subsample, using MUSE integral field spectroscopy and GAMA ...photometric broadband data. We measure the emission-line spectra by fitting a double-component profile, with the second and broader component related to the outflowing gas. This interpretation is in agreement with the correlation between the observed star-formation rate (SFR) surface density (Σ
SFR
) and the second-component velocity dispersion (
σ
2nd
), expected when tracing the feedback component. By modeling the broadband spectra with spectral energy distribution fitting and obtaining the star-formation histories of the sample, we observe a small decrease in SFR between 100 and 10 Myr in galaxies when the outflow H
α
luminosity contribution is increased, indicating that the feedback somewhat inhibits the star formation within these timescales. The observed emission-line ratios are best reproduced by photoionization models when compared to shock ionization, indicating that radiation from the young stellar population is dominant and seems to be a consequence of a continuous star-formation activity instead of a “bursty” event. The outflow properties, such as the mass outflow rate (∼0.1
M
⊙
yr
−1
), the outflow kinetic power (∼5.2 × 10
−4
%
L
bol
), and the mass loading factor (∼0.12), point toward a scenario where the measured feedback is not strong and has a low impact on the evolution of galaxies in general.
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