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Register a new userStellar population analysis on local infrared-selected galaxies
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To study the stellar population of local infrared galaxies, which contain star-forming galaxies, composite galaxies, LINERs, and Seyfert 2s. We also want to find whether infrared luminosity and spectral class have any effects on their stellar populations. The sample galaxies are selected from the main galaxy sample of SDSS-DR4 and then cross-correlated with the IRAS-PSCz catalog. We fit our spectra (stellar absorption lines and continua) using the spectral synthesis code STARLIGHT on the base of the templates of Simple Stellar Population and the spectra of star clusters.Among the 4 spectral classes, LINERs present the oldest stellar populations, and the other 3 sub-samples all present substantial young and intermediate age populations and very few old populations. The importance of young populations decreases from star-forming, composite, Seyfert 2 to LINER. As to different infrared luminosity bins, ULIGs & LIGs (log($L_{IR}/L_{odot})geq$11) present younger populations than starbursts and normal galaxies. However, the dominant contributors to mass are old populations in all sample galaxies. The fittings by using the spectra of star clusters with different ages and metallicities as templates also give consistent results. The dominated populations in star-forming and composite galaxies are those with metallicity $Z=0.2Z_odot$, while LINERs and Seyfert 2s are more metal-rich. The normal galaxies are more metal-rich than the ULIGs & LIGs and starbursts for the star-forming galaxies within different infrared luminosity bins. Additionally, we also compare some synthesis results with other parameters obtained from the MPA/JHU catalog.
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We want to develop spectral diagnostics of stellar populations in the near-infrared (NIR), for unresolved stellar populations. We created a semi-empirical population model and we compare the model output with the observed spectra of a sample of elliptical and bulge-dominated galaxies that have reliable Lick-indices from literature to test if the correlation between Mg2 and CO 1.62 micron remains valid in galaxies and to calibrate it as an abundance indicator. We find that (i) there are no significant correlations between any NIR feature and the optical Mg2; (ii) the CaI, NaI and CO trace the alpha-enhancement; and (iii) the NIR absorption features are not influenced by the galaxys age.
We present single stellar population (SSP) equivalent ages, metallicities, and abundance ratios for local elliptical galaxies derived from Hbeta, Mgb, and <Fe> absorption line strengths. We use an extension of the Worthey (1994) stellar population models that incorporates non-solar line-strength response functions by Tripicco & Bell (1995), allowing us to correct the models for the enhancements of Mg and other alpha-like elements relative to the Fe-peak elements. SSP-equivalent ages of local ellipticals from Gonzalez (1993) are found to vary widely, 1.5 < t < 18 Gyr, while metallicities [Z/H] and enhancement ratios [E/Fe] are strongly peaked around <[Z/H]>=+0.26 and <[E/Fe]>=+0.20 (in an aperture of radius Re/8). The enhancement ratios are milder than previous estimates, owing to the application of non-solar abundance corrections to both Mgb and <Fe> for the first time. Gradients in stellar populations within galaxies are found to be mild, with SSP-equivalent age decreasing by 25%, metallicity decreasing by <[Z/H]>=0.20 dex, and [E/Fe] remaining nearly constant out to an aperture of radius Re/2 for nearly all systems. Our ages have an overall zeropoint uncertainty of at least 25% due to uncertainties in the stellar evolution prescription, the oxygen abundance, the effect of non-solar abundances on the isochrones, and other unknowns. However, the relative age rankings of stellar populations should be largely unaffected by these errors. In particular, the large spread in ages appears to be real and cannot be explained by contamination of Hbeta by blue stragglers or hot horizontal branch stars, or by fill-in of Hbeta by emission. Correlations between these derived SSP-equivalent parameters and other galaxy observables will be discussed in future papers. (Abridged)
3D spectroscopy produces hundreds of spectra from which maps of the characteristics of stellar populations (age-metallicity) and internal kinematics of galaxies can be derived. We carried on simulations to assess the reliability of inversion methods and to define the requirements for future observations. We quantify the biases and show that to minimize the errors on the kinematics, age and metallicity (in a given observing time) the size of the spatial elements and the spectral dispersion should be chosen to obtain an instrumental velocity dispersion comparable to the physical dispersion.
We identify a population of 640 obscured and 839 unobscured AGNs at redshifts 0.7<z<~3 using multiwavelength observations of the 9 deg^2 NOAO Deep Wide-Field Survey (NDWFS) region in Bootes. We select AGNs on the basis of Spitzer IRAC colors obtained by the IRAC Shallow Survey. Redshifts are obtained from optical spectroscopy or photometric redshift estimators. We classify the IR-selected AGNs as IRAGN 1 (unobscured) and IRAGN 2 (obscured) using a simple criterion based on the observed optical to mid-IR color, with a selection boundary of R-[4.5]=6.1, where R and [4.5] are the Vega magnitudes in the R and IRAC 4.5 micron bands, respectively. We verify this selection using X-ray stacking analyses with data from the Chandra XBootes survey, as well as optical photometry from NDWFS and spectroscopy from MMT/AGES. We show that (1) these sources are indeed AGNs, and (2) the optical/IR color selection separates obscured sources (with average N_H~3x10^22 cm^-2 obtained from X-ray hardness ratios, and optical colors and morphologies typical of galaxies) and unobscured sources (with no X-ray absorption, and quasar colors and morphologies), with a reliability of >~80%. The observed numbers of IRAGNs are comparable to predictions from previous X-ray, optical, and IR luminosity functions, for the given redshifts and IRAC flux limits. We observe a bimodal distribution in R-[4.5] color, suggesting that luminous IR-selected AGNs have either low or significant dust extinction, which may have implications for models of AGN obscuration.
We performed a deep wide-field (6.76 deg^2) near-infrared survey with the VISTA telescope that covers the entire extent of the Carina nebula complex (CNC). The point-source catalog created from these data contains around four million individual objects down to masses of 0.1 M_sun. We present a statistical study of the large-scale spatial distribution and an investigation of the clustering properties of infrared-excesses objects, which are used to trace disk-bearing young stellar objects (YSOs). We find that a (J - H) versus (Ks - [4.5]) color-color diagram is well suited to tracing the population of YSO-candidates (cYSOs) by their infrared excess. We identify 8781 sources with strong infrared excess, which we consider as cYSOs. This sample is used to investigate the spatial distribution of the cYSOs with a nearest-neighbor analysis. The surface density distribution of cYSOs agrees well with the shape of the clouds as seen in our Herschel far-infrared survey. The strong decline in the surface density of excess sources outside the area of the clouds supports the hypothesis that our excess-selected sample consists predominantly of cYSOs with a low level of background contamination. This analysis allows us to identify 14 groups of cYSOs outside the central area. Our results suggest that the total population of cYSOs in the CNC comprises about 164000 objects, with a substantial fraction (~35%) located in the northern, still not well studied parts. Our cluster analysis suggests that roughly half of the cYSOs constitute a non-clustered, dispersed population.
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