43 research outputs found
Color Dispersion as an Indicator of Stellar Population Complexity: Insights from the Pixel Color-Magnitude Diagrams of 32 Bright Galaxies in Abell 1139 and Abell 2589
We investigate the properties of bright galaxies of various morphological types in Abell 1139 and Abell 2589, using pixel color-magnitude diagram (pCMD) analysis. The sample contains 32 galaxies brighter than M-r = -21.3 mag with spectroscopic redshifts, which are deeply imaged in the g and r bands using the MegaCam mounted on the Canada-France-Hawaii Telescope. After masking contaminants with two-step procedures, we examine how the detailed properties in the pCMDs depend on galaxy morphology and infrared color. The mean g - r color as a function of surface brightness (mu(r)) in the pCMD of a galaxy shows good performance in distinguishing between early- and late-type galaxies, but it is not perfect because of the similarity between elliptical galaxies and bulge-dominated spiral galaxies. On the other hand, the g - r color dispersion as a function of mu(r) works better. We find that the best set of parameters for galaxy classification is a combination of the minimum color dispersion at mu(r) <= 21.2 mag arcsec(-2) and the maximum color dispersion at 20.0 <= mu(r) <= 21.0 mag arcsec(-2); the latter reflects the complexity of stellar populations at the disk component in a typical spiral galaxy. Finally, the color dispersion measurements of an elliptical galaxy appear to be correlated with the Wide-field Infrared Survey Explorer infrared color ([4.6]-[12]). This indicates that the complexity of stellar populations in an elliptical galaxy is related to its recent star formation activities. From this observational evidence, we infer that gas-rich minor mergers or gas interactions may have usually occurred during the recent growth of massive elliptical galaxies
Age-Divided Mean Stellar Populations from Full Spectrum Fitting as the Simplified Star Formation and Chemical Evolution History of a Galaxy: Methodology and Reliability
We introduce a practical methodology for investigating the star formation and
chemical evolution history of a galaxy: age-divided mean stellar populations
(ADPs) from full spectrum fitting. In this method, the mass-weighted mean
stellar populations and mass fractions (f_mass) of young and old stellar
components in a galaxy are separately estimated, which are divided with an age
cut (selected to be 10^9.5 yr ~ 3.2 Gyr in this paper). To examine the
statistical reliability of ADPs, we generate 10,000 artificial galaxy spectra,
each of which consists of five random simple stellar population components.
Using the Penalized PiXel-Fitting (pPXF) package, we conduct full spectrum
fitting to the artificial spectra with noise as a function of wavelength,
imitating the real noise of Sydney-Australian Astronomical Observatory
Multi-object Integral field spectrograph (SAMI) galaxies. As a result, the
\Delta (= output - input) of age and metallicity appears to significantly
depend on not only signal-to-noise ratio (S/N), but also luminosity fractions
(f_lum) of young and old components. At given S/N and f_lum, \Delta of young
components tends to be larger than \Delta of old components; e.g.,
\sigma(\Delta [M/H]) ~ 0.40 versus 0.23 at S/N = 30 and f_lum = 50 per cent.
The age-metallicity degeneracy appears to be insignificant, but \Delta
log(age/yr) shows an obvious correlation with \Delta f_mass for young stellar
components (R ~ 0.6). The impact of dust attenuation and emission lines appears
to be mostly insignificant. We discuss how this methodology can be applied to
spectroscopic studies of the formation histories of galaxies, with a few
examples of SAMI galaxies.Comment: 26 pages, 24 figures, accepted for publication in MNRA
The Connection between Star-Forming Galaxies, AGN Host Galaxies and Early-Type Galaxies in the SDSS
We present a study of the connection between star-forming galaxies, AGN host
galaxies, and normal early-type galaxies in the Sloan Digital Sky Survey
(SDSS). Using the SDSS DR5 and DR4plus data, we select our early-type galaxy
sample in the color versus color-gradient space, and we classify the spectral
types of the selected early-type galaxies into normal, star-forming, Seyfert,
and LINER classes, using several spectral line flux ratios. We investigate the
slope in the fundamental space for each class of early-type galaxies and find
that there are obvious differences in the slopes of the fundamental planes
(FPs) among the different classes of early-type galaxies, in the sense that the
slopes for Seyferts and star-forming galaxies are flatter than those for normal
galaxies and LINERs. This may be the first identification of the systematic
variation of the FP slope among the subclasses of early-type galaxies. The
difference in the FP slope might be caused by the difference in the degree of
nonhomology among different classes or by the difference of gas contents in
their merging progenitors. One possible scenario is that the AGN host galaxies
and star-forming galaxies are formed by gas-rich merging and that they may
evolve into normal early-type galaxies after finishing their star formation or
AGN activities.Comment: 5 pages with emulateapj, 2 figures, accepted for publication in the
Astrophysical Journal Letter