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Register a new userSpectral Energy Distributions and Masses of 304 M31 Old Star Clusters
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This paper presents CCD multicolor photometry for 304 old star clusters in the nearby spiral galaxy M31. Of which photometry of 55 star clusters is first obtained. The observations were carried out as a part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March, using 15 intermediate-band filters covering 3000--10000 AA. Detailed comparisons show that our photometry is in agreement with previous measurements. Based on the ages and metallicities from Caldwell et al. and the photometric measurements here, we estimated the clusters masses by comparing their multicolor photometry with stellar population synthesis models. The results show that the sample clusters have masses between $sim 3times10^4 M_odot$ and $sim 10^7 M_odot$ with the peak of $sim 4times10^5 M_odot$. The masses here are in good agreement with those in previous studies. Combined with the masses of young star clusters of M31 from Wang et al., we find that the peak of mass of old clusters is ten times that of young clusters.
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We present photometry of 104 M31 globular clusters (GCs) and GC candidates in 15 intermediate-band filters of the Beijing-Arizona-Taiwan-Connecticut (BATC) photometric system. The GCs and GC candidates were selected from the Revised Bologna Catalog (v.3.5). We obtain the cluster ages by comparing the photometric data with up-to-date theoretical synthesis models. The photometric data used are {sl GALEX} far- and near-ultraviolet and 2MASS near-infrared $JHK_{rm s}$ magnitudes, combined with optical photometry. The ages of our sample clusters cover a large range, although most clusters are younger than 10 Gyr. Combined with the ages obtained in our series of previous papers focusing on the M31 GC system, we present the full M31 GC age distribution. The M31 GC system contains populations of young and intermediate-age GCs, as well as the `usual complement of well-known old GCs, i.e., GCs of similar age as the majority of the Galactic GCs. In addition, young GCs (and GC candidates) are distributed nearly uniformly in radial distance from the center of M31, while most old GCs (and GC candidates) are more strongly concentrated.
This paper supplements Jiang et al. (2003), who studied 172 M31 globular clusters (GCs) and globular cluster candidates from Battistini et al. (1987) on the basis of integrated photometric measurements in the Beijing-Arizona-Taiwan-Connecticut (BATC) photometric system. Here, we present multicolor photometric CCD data (in the BATC system) for the remaining 39 M31 GCs and candidates. In addition, the ages of 35 GCs are constrained by comparing our accurate photometry with updated theoretical stellar synthesis models. We use photometric measurements from GALEX in the far- and near-ultraviolet and 2MASS infrared $JHK_s$ data, in combination with optical photometry. Except for two clusters, the ages of the other sample GCs are all older than 1 Gyr. Their age distribution shows that most sample clusters are younger than 6 Gyr, with a peak at ~3 Gyr, although the `usual complement of well-known old GCs (i.e., GCs of similar age as the majority of the Galactic GCs) is present as well.
We analyze our accurate kinematical data for the old clusters in the inner regions of M31. These velocities are based on high S/N Hectospec data (Caldwell et al 2010). The data are well suited for analysis of M31s inner regions because we took particular care to correct for contamination by unresolved field stars from the disk and bulge in the fibers. The metal poor clusters show kinematics which are compatible with a pressure-supported spheroid. The kinematics of metal-rich clusters, however, argue for a disk population. In particular the innermost region (inside 2 kpc) shows the kinematics of the x2 family of bar periodic orbits, arguing for the existence of an inner Lindblad resonance in M31.
The shape of the OB-star spectral energy distribution is a critical component in many diagnostics of the ISM and galaxy properties. We use single-star HII regions from the LMC to quantitatively examine the ionizing SEDs from widely available CoStar, TLUSTY, and WM-basic atmosphere grids. We evaluate the stellar atmosphere models by matching the emission-line spectra that they predict from CLOUDY photoionization simulations with those observed from the nebulae. The atmosphere models are able to reproduce the observed optical nebular line ratios, except at the highest energy transitions > 40 eV, assuming that the gas distribution is non-uniform. Overall we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rate of ionizing photons produced by the model SEDs is consistent with the rate derived from the Halpha luminosity for standard, log(g) = 4.0 models adopted from the atmosphere grids. However, there is a systematic offset between the rate of ionizing photons from different atmosphere models that is correlated with the relative hardness of the SEDs. In general WM-basic and TLUSTY atmosphere models predict similar effective temperatures, while CoStar predicts effective temperatures that are cooler by a few thousand degrees. We compare our effective temperatures, which depend on the nebular ionization balance, to conventional photospheric-based calibrations from the literature. We suggest that in the future, spectral type to effective temperature calibrations can be constructed from nebular data.
We introduce ProSpect, a generative galaxy spectral energy distribution (SED) package that encapsulates the best practices for SED methodologies in a number of astrophysical domains. ProSpect comes with two popular families of stellar population libraries (BC03 and EMILES), and a large variety of methods to construct star formation and metallicity histories. It models dust through the use of a Charlot & Fall attenuation model, with re-emission using Dale far-infrared templates. It also has the ability to model AGN through the inclusion of a simple AGN and hot torus model. Finally, it makes use of MAPPINGS-III photoionisation tables to produce line emission features. We test the generative and inversion utility of ProSpect through application to the Shark galaxy formation semi-analytic code, and informed by these results produce fits to the final ultraviolet to far-infrared photometric catalogues produces by the Galaxy and Mass Assembly Survey (GAMA). As part of the testing of ProSpect, we also produce a range of simple photometric stellar mass approximations covering a range of filters for both observed frame and rest frame photometry.
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