We present an optical-infrared photometric study of galaxies in six nearby clusters of galaxies at z=0.041∼0.098 (A1436, A1773, A1809, A2048, A2142, and A2152). Using BV I photometry obtained at the Bohyunsan Optical Astronomical Observatory and JHKS photometry extracted from the 2-Micron All-Sky Survey catalog, we investigate the colors of galaxies in the clusters. Using the (B − V ) versus (I −KS) color-color diagrams in comparison with the simple stellar population model, we estimate the ages and metallicities of bright early-type member galaxies. Early-type galaxies in each cluster show the color-magnitude relation. Ages and metallicities of early-type members show little dependence on their velocity dispersions. Mean ages of early-types in the clusters range from 3 Gyr to 20 Gyr, showing a large dispersion, and mean metallicities range from Z = 0.03 to 0.05 above the solar value, showing a negligible dispersion.
We present optical and near-infrared imaging and long-slit spectroscopy for the blue compact dwarf galaxy (BCD) Mrk 49 in the Virgo Cluster. The surface brightness distribution analysis shows that Mrk 49 consists of an off-centered blue bright compact core of r = 10′′ and a red faint outer exponential envelope. The Hα image and color difference suggest that these two components have different stellar populations: a high surface brightness population of massive young stars and an underlying low surface brightness population of older stars. The redder near-infrared colors of the inner most region suggest that the near-infrared flux of Mrk 49 originates from evolved massive stars associated with the current star-forming activity. The total apparent magnitude is BT = 14.32 mag and the mean effective surface brightness is μeff (B) = 21.56 mag arcsec−2. Long-slit spectroscopy shows that Mrk 49 rotates apparently as a solid body within r = 10′′ in a plane at position angle 55 degrees with an amplitude of about 20 km sec−1. The measured radial velocity of Mrk 49 was derived as 1,535 km sec−1; and the total mass of stars and gases is in the range of 3 to 6 × 109 M⊙. The mass-to-light ratios for the central region of Mrk 49 in I and B band are estimated 1.0 and 0.5, respectively. The upper limit of the dark matter to visible matter ratio seems to be < 5. The oxygen abundance is 12 + log(O/H) = 8.21 ± 0.1 which is about one quarter of the solar value while the relative helium abundance appears to be similar to that of the sun.
The molecular cloud, embedding AFGL 2591, has a “head-and-tail” structure with a total mass of ∼ 1800 M⊙, about half of the mass (∼ 900 M⊙) in the head (size ∼ 1.2 pc in diameter), and another half in the envelope (∼ 3.5 pc in the east-west direction). We found a new cloud in the direction toward north-east from AFGL 2591 (projected distance ∼ 2.4 pc), which is probably associated with the AFGL 2591 cloud. The 12CO spectrum clearly shows a blue-shifted high-velocity wing at around the velocity −20 ∼ −10 km s−1, but it is not clear whether this high-velocity component has a bipolar nature in our observations. The observed CN spectra also show blue-shifted wing component but the existence of the red-shifted component is not clear, either. In some CN and HCN spectra, the highvelocity components appear as a different velocity component, not a broad line-wing component. The dense cores, traced by CN and HCN, exist in the ‘head’ of the AFGL 2591 cloud with an elongated morphology roughly in the north-south direction with a size of about 0.5 pc. The abundance ratio between CN and HCN is found to be about 2 − 3 within the observed region, which may suggest a possibility that this core is being affected by the embedded YSOs or by possible shocks from outside.