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The physical properties of galaxies are encoded within their spectral energy distribution and require comparison with models to be extracted. These models must contain a synthetic stellar population and, where infrared data are to be used, also consider prescriptions for energy reprocessing and re-emission by dust. While many such models have been constructed, there are few analyses of the impact of stellar population model choice on derived dust parameters, or vice versa. Here, we apply a simple framework to compare the impact of these choices, combining three commonly used stellar population synthesis models and three dust emission models. We compare fits to the ultraviolet to far-infrared spectral energy distributions of a validation sample of infrared-luminous galaxies. We find that including different physics, such as binary stellar evolution, in the stellar synthesis model can introduce biases and uncertainties in the derived parameters of the dust and stellar emission models, largely due to differences in the far-ultraviolet emission available for reprocessing. This may help to reconcile the discrepancy between the cosmic star formation rate and stellar mass density histories. Notably the inclusion of a dusty stellar birth cloud component in the dust emission model provides more flexibility in accommodating the stellar population model, as its re-emission is highly sensitive to the ultraviolet radiation field spectrum and density. Binary populations favour a longer birth cloud dissipation time-scale than is found when assuming only single star population synthesis. [ABSTRACT FROM AUTHOR]

ABSTRACT This work concerns the physical properties of very faint (= 28 AB mag; Mstars,lim∼ 108 M⊙), ultraviolet-selected (UV-selected) sub- L* BX galaxies at z∼ 2.3. Stellar masses, dust content and dust-corrected star formation rates are constrained using broad-band spectral energy distribution fitting, resulting in a number of insights into the nature of these low-mass systems. First, a correlation between rest-frame UV luminosity and galaxy stellar mass appears to exist in BX galaxies and its presence suggests that many sub- L* galaxies at this redshift may have approximately constant, rather than highly variable, star formation histories. A nearly-linear relation between stellar mass and star formation rate is also found, hinting that the rate at which a sub- L* BX galaxy forms its stars is directly related to the mass of stars that it has already formed. A possible explanation for this phenomenon lies in a scenario in which new gas that falls on to the galaxy's host halo along with accreting dark matter is the main source of fuel for ongoing star formation. The instantaneous efficiency of star formation is low in this scenario, of the order of 1 per cent. Turning to bulk quantities, it is found that the low-mass end of the stellar mass function at z∼ 2.3 is steeper than expected from extrapolations of shallower surveys, resulting in a stellar mass density at z∼ 2.3 that is ∼25 per cent of the present-day value; this value is ∼1.5-2 times higher than that given by extrapolations of most of the shallower surveys, suggesting that the build-up of stellar mass in the Universe has proceeded somewhat more rapidly than previously thought. With spectral energy distribution fitting results in hand, an update to the Keck Deep Fields z∼ 2 UV luminosity function finds a steeper faint-end slope than previously reported, α=− 1.47, though this is not as steep as that found by Reddy & Steidel. Finally, it is also found that sub- L* galaxies at z∼ 2 carry very small amounts of dust compared to their more luminous cousins, so that while only ∼20 per cent of 1700-Å photons escape from a typical M* galaxy, more than half make it out of an M*+3 one. This paucity of dust highlights the fact that sub- L* galaxies are not simple scaled copies of their more luminous cousins. Assuming that absorption by neutral hydrogen is not stronger in sub- L* galaxies than in their more luminous counterparts, it also means that sub- L* galaxies are important contributors to keeping the Universe ionized at z∼ 2. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a detailed investigation of the near-infrared to far-infrared (near-IR to far-IR) spectral energy distribution (SED) of a large sample of Spitzer-observed active galactic nuclei (AGNs). We fitted the spectra of 51 narrow-line Seyfert 1 galaxies (NLS1s) and 64 broad-line Seyfert 1 galaxies (BLS1s) using a three-component model: a clumpy torus, a dusty narrow-line region and hot pure-graphite dust located in the outer part of the broad-line region (BLR). The fitting was performed on star formation (SF) subtracted SEDs using SF templates that take into account the entire range of possible host galaxy properties. We find that the mid-IR intrinsic emission of NLS1s and BLS1s is very similar, regardless of the AGN luminosity, with long-wavelength downturn at around 20-25 μm. We present a detailed model of the hot-dust component that takes into account the distribution of dust temperature within the clouds and their emission-line spectrum. The hot-dust continuum provides a very good fit to the observed near-IR continuum spectrum. Most line emission in this component is dramatically suppressed, except Mg ii λ2798 and He i lines that are still contributing significantly to the total BLR spectrum. We calculate the covering factors (CFs) of all the AGN components and show that the CF of the hot-dust clouds is about 0.15-0.35, similar to the CF of the torus, and is anticorrelated with the source luminosity and the normalized accretion rate. [ABSTRACT FROM AUTHOR]

ABSTRACT The accretion efficiency for individual black holes is very difficult to determine accurately. There are many factors that can influence each step of the calculation, such as the dust and host galaxy contribution to the observed luminosity, the black hole mass and more importantly the uncertainties on the bolometric luminosity measurement. Ideally, we would measure the active galactic nuclei (AGNs) emission at every wavelength, remove the host galaxy and dust, reconstruct the AGN spectral energy distribution and integrate them to determine the intrinsic emission and the accretion rate. In reality, this is not possible due to observational limitations and our own galaxy line-of-sight obscuration. We have then to infer the bolometric luminosity from spectral measurements made in discontinuous wavebands and at different epochs. In this paper, we tackle this issue by exploring different methods to determine the bolometric luminosity. We first explore the trend of accretion efficiency with black hole mass (ε ∝ M∼0.5) found in recent work by Davis & Laor and discuss why this is most likely an artefact of the parameter space covered by their Palomar-Green quasar sample. We then target small samples of AGNs at different redshifts, luminosities and black hole masses to investigate the possible methods to calculate the accretion efficiency. For these sources we are able to determine the mass accretion rate and, with some assumptions, the accretion efficiency distributions. Even though we select the sources for which we are able to determine the parameters more accurately, there are still factors affecting the measurements that are hard to constrain. We suggest methods to overcome these problems based on contemporaneous multiwavelength data measurements and specifically targeted observations for AGNs in different black hole mass ranges. [ABSTRACT FROM AUTHOR]

ABSTRACT We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground-based optical and near-infrared data to understand how dust heating in the nearby face-on spiral galaxies M81, M83 and NGC 2403 is affected by the starlight from all stars and by the radiation from star-forming regions. We find that 70/160 m surface brightness ratios tend to be more strongly influenced by star-forming regions. However, the 250/350 m and 350/500 m surface brightness ratios are more strongly affected by the light from the total stellar populations, suggesting that the dust emission at >250 m originates predominantly from a component that is colder than the dust seen at <160 m and that is relatively unaffected by star formation activity. We conclude by discussing the implications of this for modelling the spectral energy distributions of both nearby and more distant galaxies and for using far-infrared dust emission to trace star formation. [ABSTRACT FROM AUTHOR]

ABSTRACT Interstellar dust grains are responsible for modifying the spectral energy distribution (SED) of galaxies, both absorbing starlight at ultraviolet and optical wavelengths and converting this energy into thermal emission in the infrared (IR). The detailed description of these phenomena is of fundamental importance in order to compare the predictions of theoretical models of galaxy formation and evolution with the most recent observations in the IR region. In this paper we compare the results of grasil, a code explicitly solving for the equation of radiative transfer in a dusty medium, with the predictions of a variety of IR template libraries, both analytically and observationally determined. We employ star formation history samples extracted from the semi-analytical galaxy formation model morgana to create libraries of synthetic SEDs from the near- to the far-IR. We consider model predictions at different redshift ranges to explore any possible influence in the shape and normalization of the SEDs due to the expected evolution of the galaxy properties. We compute the total absorbed starlight predicted by grasil at optical wavelengths to statistically compare the synthetic SEDs with the selected IR templates. We show that synthetic SEDs at a given total IR luminosity are predicted to be systematically different at different redshifts and for different properties of the underlying model galaxy. However, we determine spectral regions where the agreement between the results of radiative transfer and IR templates is good in a statistical sense (i.e. in terms of the luminosity functions). Moreover, we highlight some potentially relevant discrepancies between the different approaches, both in the region dominated by polycyclic aromatic hydrocarbon emission and at submm wavelengths. These results determine potentially critical issues in the IR luminosity functions as predicted by semi-analytical models coupled with different IR flux estimators. [ABSTRACT FROM AUTHOR]