We identify and phase a sample of 107 Cepheids with 10days<P<100days in M81 (NGC 3031) using the Large Binocular Telescope and calibrate their B, V, and I mean magnitudes with archival Hubble Space Telescope (HST) data. The use of a ground-based telescope to identify and phase the Cepheids and HST only for the final calibration reduces the demand on this highly oversubscribed spacecraft by nearly an order of magnitude and yields period-luminosity (PL) relations with dispersions comparable to the best LMC samples. We fit the sample using the OGLE-II LMC PL relations and are unable to find a self-consistent distance for different band combinations or radial locations within M81. We find a distance modulus for M81, relative to the LMC, of {mu}M_81_-{mu}_LMC_=9.39+/-0.14mag, including uncertainties due to the metallicity corrections. This corresponds to a distance to M81 of 3.6+/-0.2Mpc, assuming an LMC distance modulus of 18.41mag.
We present results of CCD imaging in B, V of five late-type galaxies with radial velocities V_0_<350km/s in the Canes Venatici cloud. Based on the photometry of their brightest blue stars we derived the following distances to the galaxies: 9.7Mpc for NGC 4144, 4.5Mpc for NGC 4244, 4.2Mpc for NGC 4395, 2.9Mpc for NGC 4449, and 8.2Mpc for UGC 8331.
We present deep photometry in the B,V and I filters from CTIO/MOSAIC for about 270.000 stars in the Fornax dwarf Spheroidal galaxy, out to a radius of r_ell_~0.8{deg}. By combining the accurately calibrated photometry with the spectroscopic metallicity distributions of individual Red Giant Branch stars we obtain the detailed star formation and chemical evolution history of Fornax. Fornax is dominated by intermediate age (1-10Gyr) stellar populations, but also includes ancient (10-14Gyr), and young (<1Gyr) stars. We show that Fornax displays a radial age gradient, with younger, more metal-rich populations dominating the central region. This confirms results from previous works. Within an elliptical radius of 0.8 degrees, or 1.9kpc from the centre, a total mass in stars of 4.3*10^7^M_{sun}_ was formed, from the earliest times until 250Myr ago. Using the detailed star formation history, age estimates are determined for individual stars on the upper RGB, for which spectroscopic abundances are available, giving an age-metallicity relation of the Fornax dSph from individual stars. This shows that the average metallicity of Fornax went up rapidly from [Fe/H]<-2.5dex to [Fe/H]=-1.5dex between 8-12Gyr ago, after which a more gradual enrichment resulted in a narrow, well-defined sequence which reaches [Fe/H]~-0.8dex, ~3Gyr ago. These ages also allow us to measure the build-up of chemical elements as a function of time, and thus determine detailed timescales for the evolution of individual chemical elements. A rapid decrease in [Mg/Fe] is seen for the stars with [Fe/H]>-1.5dex, with a clear trend in age.
We present the results of a survey for star clusters in M33 using HST WFPC2 archive images. We have found 104 star clusters, including 32 new ones, in the images of 24 fields that were not included in previous studies. Combining these with previous data in the literature, we increase the number of M33 star clusters found in the HST images to 242. We have derived BVI integrated photometry of these star clusters from the CCD images taken with the CFH12k mosaic camera at the CFHT.
Integrated CCD-photometry of the dwarf nearby galaxies in B, V and I (Cousins) bands is presented. The photometry was performed in increasing circular apertures.
We present initial results from a time series BVI survey of two fields in NGC 4258 using the HST ACS. This galaxy was selected because of its accurate maser-based distance, which is anticipated to have a total uncertainty of 3%. The goal of the HST observations is to provide an absolute calibration of the Cepheid distance scale and to measure its dependence on chemical abundance (the so-called metallicity effect). We carried out observations of two fields at different galactocentric distances with a mean abundance difference of 0.5dex. We discovered a total of 281 Cepheids with periods ranging from 4 to 45 days (the duration of our observing window).
We present an analysis of the globular cluster (GC) population of the elliptical galaxy NGC 4261 based on Hubble Space Telescope Wide Field Planetary Camera 2 data in the B, V and I bands. We study the spatial distribution of the GCs in order to probe the anisotropy in the azimuthal distribution of the discrete X-ray sources in the galaxy revealed by Chandra images.
Two relatively faint (B=15.7 and B=18.4mag, respectively), low velocity (+276 and +322km/s) galaxies were imaged with a CCD in the B, V, I bands at the prime focus of the 6m telescope on 16 October 1993. By means of the brightest stars we estimated their distances to be 6.4 and 5.5(+/-2)Mpc, assuming a galactic extinction of 2.7 and 2.9mag, respectively. We note that these isolated irregular dwarfs are located to a high Supergalactic latitude, -63deg, and their low radial velocities may be the result of a retarded expansion along the polar axis of the Local cloud of galaxies.
We examine the radius-luminosity (R-L) relation for blue galaxies in the Team Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan Digital Sky Survey sample and find that the R-L relation has evolved to lower surface brightness since z=1. Based on the detection limits of GOODS, this cannot be explained by incompleteness in low surface brightness galaxies. Number density arguments rule out a pure radius evolution. It can be explained by a radius-dependent decline in B-band luminosity with time.
Low-luminosity radio-loud active galactic nuclei (AGN) are of importance in studies concerning feedback from radio AGN since a dominant fraction of AGN belong to this class. We report high-resolution Very Large Array (VLA) and European VLBI Network (EVN) observations of HI 21cm absorption from a young, compact steep-spectrum radio source, B2 0258+35, nested in the early-type galaxy NGC 1167, which contains a 160kpc HI disc. Our VLA and EVN HI absorption observations, modelling, and comparison with molecular gas data suggest that the cold gas in the centre of NGC 1167 is very turbulent (with a velocity dispersion of ~90km/s) and that this turbulence is induced by the interaction of the jets with the interstellar medium (ISM). Furthermore, the ionised gas in the galaxy shows evidence of shock heating at a few kpc from the radio source. These findings support the results from numerical simulations of radio jets expanding into a clumpy gas disc, which predict that the radio jets in this case percolate through the gas disc and drive shocks into the ISM at distances much larger than their physical extent. These results expand the number of low-luminosity radio sources found to impact the surrounding medium, thereby highlighting the possible relevance of these AGN for feedback.
