Young Stellar Population In NGC Research Articles

High-resolution, 3D radiative transfer modelling

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.

The Young Stellar Population of NGC 4214 as Observed with theHubble Space Telescope. I. Data and Methods

We present the data and methods that we have used to perform a detailed UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using multifilter Hubble Space Telescope WFPC2 and STIS photometry. We explain the process followed to obtain high-quality photometry and astrometry of the stellar and cluster populations of this galaxy. We describe the procedure used to transform magnitudes and colors into physical parameters using spectral energy distributions. The data show the existence of both young and old stellar populations that can be resolved at the distance of NGC 4214 (2.94 Mpc), and we perform a general description of those populations.

The Young Stellar Population of NGC 4214 as Observed with theHubble Space Telescope. II. Results

We present the results of a detailed UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using multifilter Hubble Space Telescope WFPC2 and STIS photometry. The stellar extinction is found to be quite patchy, with some areas having values of E(4405 - 5495) < 0.1 mag and others, associated with star-forming regions, much more heavily obscured, a result that is consistent with previous studies of the nebular extinction. We determined the ratio of blue to red supergiants and found it to be consistent with theoretical models for the metallicity of the Small Magellanic Cloud. The stellar initial mass function (IMF) of the field in the range 20-100 M⊙ is found to be steeper than γ = -2.8 (γ = -2.35 for a Salpeter IMF). A number of massive clusters and associations with ages between a few and 200 Myr are detected, and their properties are discussed.

Evidence for a Young Stellar Population in NGC 5018

Two absorption line indices, Ca II and Hδ/λ4045, measured from high-resolution spectra are used with evolutionary synthesis models to verify the presence of a young stellar population in NGC 5018. The derived age of this population is ~2.8 Gyr with a metallicity roughly solar, and it completely dominates the integrated light of the galaxy near 4000 A.

Evidence for a Young Stellar Population in NGC 5018

Evidence for a Young Stellar Population in NGC 5018