Modelling galaxy spectra in presence of interstellar dust – II. From the ultraviolet to the far-infrared
11 Aug 2006-Monthly Notices of the Royal Astronomical Society (Oxford University Press)-Vol. 370, Iss: 3, pp 1454-1478
TL;DR: In this article, the spectral energy distributions (SEDs) of different morphological types of galaxies are derived by using a simple geometrical model for each type of galaxy, based on a robust model of chemical evolution that assumes a suitable prescription for gas infall, initial mass function, star formation rate and stellar ejecta.
Abstract: In this paper, we present spectrophotometric models for galaxies of different morphological type whose spectral energy distributions (SEDs) take into account the effect of dust in absorbing UV-optical light and re-emitting it in the infrared (IR). The models contain three main components: (i) the diffuse interstellar medium (ISM) composed of gas and dust whose emission and extinction properties have already been studied in detail by Piovan et al. (2006), (ii) the large complexes of molecular clouds (MCs) in which new stars are formed and (iii) the stars of any age and chemical composition. The galaxy models stand on a robust model of chemical evolution that assuming a suitable prescription for gas infall, initial mass function, star formation rate and stellar ejecta provides the total amounts of gas and stars present at any age together with their chemical history. The chemical models are taylored in such a way to match the gross properties of galaxies of different morphological type. In order to describe the interaction between stars and ISM in building up the total SED of a galaxy, one has to know the spatial distribution of gas and stars. This is made adopting a simple geometrical model for each type of galaxy. The total gas and star mass provided by the chemical model are distributed over the whole volume by means of suitable density profiles, one for each component and depending on the galaxy type (spheroidal, disk and disk plus bulge). The galaxy is then split in suitable volume elements to each of which the appropriate amounts of stars, MCs and ISM are assigned. Each elemental volume bin is at the same time source of radiation from the stars inside and absorber and emitter of radiation from and to all other volume bins and the ISM in between. They are the elemental seeds to calculate the total SED. Using the results for the properties of the ISM and the Single Stellar Populations (SSPs) presented by Piovan et al. (2006) we derive the SEDs of galaxies of different morphological type. First the technical details of the method are described and the basic relations driving the interaction between the physical components of the galaxy are presented. Second, the main parameters are examined and their effects on the SED of three prototype galaxies (a disk, an elliptical and a starburster) are highlighted. The final part of the paper is devoted to assess the ability of our galaxy models in reproducing the SEDs of a few real galaxies of the Local Universe.
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TL;DR: The GALEV (Galev Evolutionary Evolutionary Models for Galaxies) model as mentioned in this paper describes the evolution of stellar populations in general, of star clusters as well as of galaxies, both in terms of resolved stellar populations and of integrated light properties over cosmological time-scales of ≥13 Gyr.
Abstract: GALEV (GALaxy EVolution) evolutionary synthesis models describe the evolution of stellar populations in general, of star clusters as well as of galaxies, both in terms of resolved stellar populations and of integrated light properties over cosmological time-scales of ≥13 Gyr from the onset of star formation shortly after the big bang until today. For galaxies, GALEV includes a simultaneous treatment of the chemical evolution of the gas and the spectral evolution of the stellar content, allowing for what we call a chemically consistent treatment: we use input physics (stellar evolutionary tracks, stellar yields and model atmospheres) for a large range of metallicities and consistently account for the increasing initial abundances of successive stellar generations. Here we present the latest version of the GALEV evolutionary synthesis models that are now interactively available at http://www.galev.org. We review the currently used input physics, and also give details on how this physics is implemented in practice. We explain how to use the interactive web interface to generate models for user-defined parameters and also give a range of applications that can be studied using GALEV, ranging from star clusters, undisturbed galaxies of various types E–Sd to starburst and dwarf galaxies, both in the local and the high-redshift Universe.
288 citations
TL;DR: In this article, the stellar spectral synthesis code Starburst99, the nebular modeling code MAPPINGS III and a one-dimensional dynamical evolution model of H II regions around massive clusters of young stars were combined to generate improved models of the spectral energy distribution (SED) of starburst galaxies.
Abstract: We combine the stellar spectral synthesis code Starburst99, the nebular modeling code MAPPINGS III and a one-dimensional dynamical evolution model of H II regions around massive clusters of young stars to generate improved models of the spectral energy distribution (SED) of starburst galaxies. We introduce a compactness parameter, , which characterizes the specific intensity of the radiation field at ionization fronts in H II regions and which controls the shape of the far-infrared (IR) dust reemission, often referred to loosely as the dust temperature. We also investigate the effect of metallicity on the overall SED and in particular, on the strength of the polycyclic aromatic hydrocarbon (PAH) features. We provide templates for the mean emission produced by the young compact H II regions, the older (10-100 Myr) stars and for the wavelength-dependent attenuation produced by a foreground screen of the dust used in our model. We demonstrate that these components may be combined to produce a excellent fit to the observed SEDs of star formation-dominated galaxies which are often used as templates (Arp 220 and NGC 6240). This fit extends from the Lyman limit to wavelengths of about 1 mm. The methods presented in both this paper and in the previous papers of this series allow the extraction of the physical parameters of the starburst region (star formation rates, star formation rate history, mean cluster mass, metallicity, dust attenuation, and pressure) from the analysis of the pan-spectral SED.
252 citations
Max Planck Society1, INAF2, Cornell University3, University of California, Irvine4, University of Padua5, Smithsonian Astrophysical Observatory6, Paris Diderot University7, Tel Aviv University8, University of Sussex9, University College London10, University of Bologna11, Ames Research Center12, University of Edinburgh13, University of British Columbia14, California Institute of Technology15
TL;DR: In this article, the authors combine far-infrared Herschel photometry from the PACS Evolutionary Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time programs with ancillary datasets in the GOODS-N, COSMOS fields, and it is possible to sample the 8-500μm spectral energy distributions (SEDs) of galaxies with at least 7-10 bands.
Abstract: Combining far-infrared Herschel photometry from the PACS Evolutionary Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time programs with ancillary datasets in the GOODS-N, GOODS-S, and COSMOS fields, it is possible to sample the 8–500 μm spectral energy distributions (SEDs) of galaxies with at least 7–10 bands. Extending to the UV, optical, and near-infrared, the number of bands increases up to 43. We reproduce the distribution of galaxies in a carefully selected restframe ten colors space, based on this rich data-set, using a superposition of multivariate Gaussian modes. We use this model to classify galaxies and build median SEDs of each class, which are then fitted with a modified version of the magphys code that combines stellar light, emission from dust heated by stars and a possible warm dust contribution heated by an active galactic nucleus (AGN). The color distribution of galaxies in each of the considered fields can be well described with the combination of 6–9 classes, spanning a large range of far- to near-infrared luminosity ratios, as well as different strength of the AGN contribution to bolometric luminosities. The defined Gaussian grouping is used to identify rare or odd sources. The zoology of outliers includes Herschel-detected ellipticals, very blue z ~ 1 Ly-break galaxies, quiescent spirals, and torus-dominated AGN with star formation. Out of these groups and outliers, a new template library is assembled, consisting of 32 SEDs describing the intrinsic scatter in the restframe UV-to-submm colors of infrared galaxies. This library is tested against L(IR) estimates with and without Herschel data included, and compared to eightother popular methods often adopted in the literature. When implementing Herschel photometry, these approaches produce L(IR) values consistent with each other within a median absolute deviation of 10–20%, the scatter being dominated more by fine tuning of the codes, rather than by the choice of SED templates. Finally, the library is used to classify 24 μm detected sources in PEP GOODS fields on the basis of AGN content, L(60)/L(100) color and L(160)/L(1.6) luminosity ratio. AGN appear to be distributed in the stellar mass (M_∗) vs. star formation rate (SFR) space along with all other galaxies, regardless of the amount of infrared luminosity they are powering, with the tendency to lie on the high SFR side of the “main sequence”. The incidence of warmer star-forming sources grows for objects with higher specific star formation rates (sSFR), and they tend to populate the “off-sequence” region of the M_∗ − SFR − z space.
203 citations
TL;DR: In this paper, the authors investigated the dependence of the total-infrared to UV luminosity ratio method for calculating the UV dust attenuation A(UV) from the age of the underlying stellar populations by using a library of spectral energy distributions for galaxies with different star formation histories.
Abstract: We investigate the dependence of the total-infrared (TIR) to UV luminosity ratio method for calculating the UV dust attenuation A(UV) from the age of the underlying stellar populations by using a library of spectral energy distributions for galaxies with different star formation histories. Our analysis confirms that the TIR/UV vs. A(UV) relation varies significantly with the age of the underlying stellar population: i.e. for the same TIR/UV ratio, systems with low specific star formation rate (SSFR) suffer a lower UV attenuation than starbursts. Using a sample of nearby field and cluster spiral galaxies we show that the use of a standard (i.e. age independent) TIR/UV vs. A(UV) relation leads to a systematic overestimate up to 2 magnitudes of the amount of UV dust attenuation suffered by objects with low SSFR and in particular HI-deficient star forming cluster galaxies. This result points out that the age independent $TIR/UV$ vs. $A(UV)$ relation cannot be used to study the UV properties of large samples of galaxies including low star-forming systems and passive spirals. Therefore we give some simple empirical relations from which the UV attenuation can be estimated taking into account its dependence on the age of the stellar populations, providing a less biased view of UV properties of galaxies.
164 citations
TL;DR: In this paper, the authors use the latest Padova isochrones, with detailed modelling of the Thermally Pulsing AGB phase, to update theoretical colour-M/L relations in the optical and NIR and discuss the consequences for the estimated stellar masses in external galaxies.
Abstract: Colour-M/L (mass-to-light) relations are a popular recipe to derive stellar mass in external galaxies. Stellar mass estimates often rely on near infrared (NIR) photometry, considered an optimal tracer since it is little affected by dust and by the "frosting" effect of recent star formation episodes. However, recent literature has highlighted that theoretical estimates of the NIR M/L ratio strongly depend on the modelling of the Asymptotic Giant Branch (AGB) phase. We use the latest Padova isochrones, with detailed modelling of the Thermally Pulsing AGB phase, to update theoretical colour-M/L relations in the optical and NIR and discuss the consequences for the estimated stellar masses in external galaxies. We also discuss the effect of attenuation by interstellar dust on colour-M/L relations in the statistical case of large galaxy samples.
157 citations
References
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TL;DR: In this article, a targeted SCUBA survey of microjansky radio sources in the flanking fields of the Hubble Deep Field is presented, where the sources were selected from the uniform (8 μJy at 1 σ) 1.4 GHz VLA image of Richards.
Abstract: Direct submillimeter imaging has recently revealed the 850 μm background to be mostly composed of a population of distant ultraluminous infrared galaxies, but identifying the optical/near-infrared (NIR) counterparts to these sources has proved difficult because of the poor submillimeter spatial resolution. However, the proportionality of both centimeter and submillimeter data to the star formation rate suggests that high-resolution radio continuum maps with subarcsecond positional accuracy can be exploited to locate submillimeter sources. In this paper we present results from a targeted SCUBA survey of microjansky radio sources in the flanking fields of the Hubble Deep Field. The sources were selected from the uniform (8 μJy at 1 σ) 1.4 GHz VLA image of Richards. Even with relatively shallow SCUBA observations (a 3 σ detection limit of 6 mJy at 850 μm), we were successful at making submillimeter detections of optical/NIR-faint (I 24 and K 21–22) radio sources, and our counts closely match the bright counts from submillimeter surveys. An important corollary is that a large fraction of the bright (>6 mJy) submillimeter sources in untargeted submillimeter surveys have extremely faint optical/NIR counterparts and hence are inaccessible to optical imaging and spectroscopy. However, redshift estimates can be made from the ratio of the submillimeter flux to the radio flux across the 100 GHz break in the spectral energy distribution. This procedure, which we refer to as millimetric redshift estimation, places the bright submillimeter population at z = 1–3, where it forms the high-redshift tail of the faint radio population. The star formation rate density (SFRD) due to ultraluminous infrared galaxies increases by more than 2 orders of magnitude from z ~ 0 to z ~ 1–3. The SFRD at high-redshift inferred from our >6 mJy submillimeter observations is comparable with that observed in the ultraviolet/optical.
334 citations
TL;DR: In this paper, the authors describe how huge amounts of data produced by sky surveys from the ground and in space will eventually merge into a multi-wavelength virtual sky, and in many cases, astronomers will make more efficient "observations" through their computer terminal accessing databases rather than at a telescope.
Abstract: Considerable changes are under way in the practice of observational astronomy due to the improvements of panoramic detectors, the increasing archiving capacity of computers and the acceleration of communication networks. The huge amounts of data produced by sky surveys from the ground and in space will eventually merge into a multiwavelength virtual sky, and in many cases, astronomers will make more efficient “observations” through their computer terminal accessing databases rather than at a telescope.
325 citations
TL;DR: In this article, total flux density, peak flux densities, and spatial extents at 12, 25, 60, and 100 microns are presented for the 330 sources in the IRAS Bright Galaxy Sample.
Abstract: Total flux densities, peak flux densities, and spatial extents at 12, 25, 60, and 100 microns are presented for the 330 sources in the IRAS Bright Galaxy Sample. The flux density ratios S sub nu (60 microns)/S sub nu (100 microns) and S sub nu (12 microns)/S sub n (25 microns) are found to correlate with both the infrared luminosity and the ratio of IR to visible flux. The relation between these two flux density ratios is shown to follow that found previously, with different slopes appearing for the warmer and colder galaxies in the sample. The results suggest that single photon heating of small grains (often the dominant source of 12 and 25 micron radiation from galaxies) significantly affects the emission of some galaxies at 60 microns, and that optical depth effects may alter the emergent radiation at 12 and 25 microns.
323 citations
TL;DR: In this article, a catalog of the IRAS observations of 85 galaxies listed in the Second Reference Catalogue ofBright Galaxies with blue-light isophotal diameters greater than 8' is presented.
Abstract: A catalog is presented of the IRAS observations of 85 galaxies listed in the Second Reference Catalogue of
Bright Galaxies with blue-light isophotal diameters greater than 8'. “Total” flux densities at 12, 25, 60, and 100 µm, obtained from spatial maps constructed from co-added IRAS detector data, are reported. Infrared brightness profiles of the detected galaxies and infrared surface brightness contour maps of the galaxies for which structural features were resolved are displayed in an atlas. A far-infrared classification scheme based on the degree of central concentration and spatial structure of the 60 µm emission of the best-resolved galaxies is proposed. The 60 µm and blue-light isophotal diameters of the largest galaxies are compared.
322 citations
TL;DR: In this article, the authors presented the second in a series of papers presenting results from the SCUBA Local Universe Galaxy Survey (LUSGMS) and provided 450 micron data for the galaxies.
Abstract: This is the second in a series of papers presenting results from the SCUBA Local Universe Galaxy Survey. In our first paper we provided 850 micron flux densities for 104 galaxies selected from the IRAS Bright Galaxy Sample and we found that the 60, 100 micron (IRAS) and 850 micron (SCUBA) fluxes could be adequately fitted by emission from dust at a single temperature. In this paper we present 450 micron data for the galaxies. With the new data, the spectral energy distributions of the galaxies can no longer be fitted with an isothermal dust model - two temperature components are now required. Using our 450 micron data and fluxes from the literature, we find that the 450/850 micron flux ratio for the galaxies is remarkably constant and this holds from objects in which the star formation rate is similar to our own Galaxy, to ultraluminous infrared galaxies (ULIRGS) such as Arp 220. The only possible explanation for this is if the dust emissivity index for all of the galaxies is ~2 and the cold dust component has a similar temperature in all galaxies (20-21 K). The dust masses estimated using the new temperatures are higher by a factor ~2 than those determined previously using a single temperature. This brings the gas-to-dust ratios of the IRAS galaxies into agreement with those of the Milky Way and other spiral galaxies which have been intensively studied in the submm.
320 citations