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TOPIC: Fornax

Blobrana

L

Posts: 131433

Date: Jul 5 16:20 2007

Fornax Dwarf Spheroidal Galaxy	Permalink

Title: The distance to the Fornax Dwarf Spheroidal Galaxy Authors: L. Rizzi, E.V. Held, I. Saviane, R.B. Tully, M. Gullieuszik A large multicolour, wide-field photometric database of the Fornax dwarf spheroidal galaxy has been analysed using three different methods to provide revised distance estimates based on stellar populations in different age intervals. The distance to Fornax was obtained from the Tip of the Red Giant Branch measured by a new method, and using the luminosity of Horizontal Branch stars and Red Clump stars corrected for stellar population effects. Assuming a reddening E(B-V)=0.02, the following distance moduli were derived: (m-M)_0=20.71 ± 0.07 based on the Tip of the Red Giant Branch, (m-M)_0=20.72 ± 0.06 from the level of the Horizontal Branch, and (m-M)_0=20.73 ± 0.09 using the Red Clump method. The weighted mean distance modulus to Fornax is (m-M)_0=20.72 ± 0.04. All these measurements agree within the errors, and are fully consistent with previous determinations and with the distance measurements obtained in a companion paper from near-infrared colour-magnitude diagrams. Read more (184kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Dec 28 22:55 2006

Dwarf Spheroidal Galaxies	Permalink

Title: Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. V: Final Measurement for Fornax Authors: Slawomir Piatek, Carlton Pryor, Paul Bristow, Edward W. Olszewski, Hugh C. Harris, Mario Mateo, Dante Minniti, Christopher G. Tinney The measured proper motion of Fornax, expressed in the equatorial coordinate system, is (µ_{\alpha},µ_{\delta})=(47.6 ± 4.6,-36.0\pm 4.1) mas century^{-1}. This proper motion is a weighted mean of four independent measurements for three distinct fields. Each measurement uses a quasi-stellar object as a reference point. Removing the contribution of the motion of the Sun and of the Local Standard of Rest to the measured proper motion produces a Galactic rest-frame proper motion of (µ_{\alpha}^{\mbox{\tiny{Grf}}}, µ_{\delta}^{\mbox{\tiny{Grf}}}) = (24.4 ± 4.6,-14.3 ± 4.1) mas century^{-1}. The implied space velocity with respect to the Galactic centre has a radial component of V_{r}=-31.8 ± 1.7 km s^{-1} and a tangential component of V_{t}=196 ±29 km s^{-1}. Integrating the motion of Fornax in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 118 (66, 137) kpc and 152 (144, 242) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.13 (0.11, 0.38), and the orbital period is 3.2 (2.5, 4.6) Gyr. The orbit is retrograde and inclined by 101^{\circ} (94^{\circ}, 107^{\circ}) to the Galactic plane. Fornax could be a member of a proposed ''stream'' of galaxies and globular clusters, however the membership of another proposed galaxy in the stream, Sculptor, has been previously ruled out. Fornax is in the Kroupa-Theis-Boily plane that contains eleven of the Galactic satellite galaxies, but its orbit will take it out of that plane. Read more (858kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Aug 18 11:50 2006

Fornax Dwarf Galaxy	Permalink

Title: The DART imaging and CaT survey of the Fornax Dwarf Spheroidal Galaxy Authors: G. Battaglia, E. Tolstoy, A. Helmi, M.J. Irwin, B. Letarte, P. Jablonka, V. Hill, K.A. Venn, M.D. Shetrone, N. Arimoto, F. Primas, A. Kaufer, P. Francois, T. Szeifert, T. Abel, K. Sadakane As part of the DART project we have used the ESO/2.2m Wide Field Imager in conjunction with the VLT/FLAMES GIRAFFE spectrograph to study the detailed properties of the resolved stellar population of the Fornax dwarf spheroidal galaxy out to and beyond its tidal radius. We re-derived the structural parameters of the Fornax dwarf spheroidal using our wide field imaging covering the galaxy out to its tidal radius, and analysed the spatial distribution of the Fornax stars of different ages as selected from Colour-Magnitude Diagram analysis. We have obtained accurate velocities and metallicities from spectra in the CaII triplet wavelength region for 562 Red Giant Branch stars which have velocities consistent with membership in Fornax dwarf spheroidal. We have found evidence for the presence of at least three distinct stellar components: a young population (few 100 Myr old) concentrated in the centre of the galaxy, visible as a Main Sequence in the Colour-Magnitude Diagram; an intermediate age population (2-8 Gyr old); and an ancient population (> 10Gyr),which are distinguishable from each other kinematically, from the metallicity distribution and in the spatial distribution of stars found in the Colour-Magnitude Diagram. From our spectroscopic analysis we find that the "metal rich'' stars (Fe/H > -1.3) show a less extended and more concentrated spatial distribution, and display a colder kinematics than the ''metal poor'' stars (Fe/H<-1.3). There is tentative evidence that the ancient stellar population in the centre of Fornax does not exhibit equilibrium kinematics. This could be a sign of a relatively recent accretion of external material. Read more (963kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jun 8 10:54 2006

Fornax Cluster	Permalink

Title: First results from SAPAC: towards a 3D-picture of the Fornax cluster core Authors: Laura P. Dunn, Helmut Jerjen A sophisticated SBF analysis package has been developed, designed to measure distances of early-type galaxies by means of surface brightness fluctuations of unresolved stars. This suite of programs called SAPAC is made readily available to the astronomical community for extensive testing with the long-term goal to provide the necessary tools for systematic distance surveys of early-type galaxies using modern optical/NIR telescopes equipped with wide-field cameras. We discuss the technical and scientific concepts of SAPAC and demonstrate its capabilities by analysing deep B and R-band CCD images of 10 dwarf elliptical (dE) galaxy candidates in the Fornax cluster obtained with FORS1 at the VLT. All candidates are confirmed as cluster members. We then turn our attention to the innermost region of the Fornax cluster. A total of 29 early-type galaxies closer than three cluster core radii (2 degrees) from the central galaxy NGC1399 have radial velocities and SBF distances. Their Hubble diagram exhibits a pronounced S-shaped infall pattern suggesting a picture that Fornax is still in the process of formation during the present epoch through a general collapse and possible accretion of distinct groups of galaxies. The associated collapse time is 2.9(+1.6, -0.9)Gyr. After cleansing our galaxy sample from a few kinematical outliers the true distance of the Fornax cluster core is determined at 20.13+-0.40 Mpc ((m-M)_0=31.51+-0.04mag). Applying a bootstrap resampling technique on the distance distribution with individual distance errors taken into account further reveals a small intrinsic cluster depth of sigma_int=0.74(+0.52,-0.74)Mpc in best agreement with the cluster's linear extension in the sky: sigma_R.A=sigma_DEC~=0.5Mpc. (Abridged) Read more (486kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Aug 4 16:04 2005

Fornax	Permalink

The Hubble Space Telescope has spied a menagerie of galaxies. Located within the same tiny region of space, these numerous galaxies display an assortment of unique characteristics. Some are big; some are small. A few are relatively nearby, but most are far away. Hundreds of these faint galaxies have never been seen before until their light was captured by Hubble. Expand Position (2000): R.A. 3h 32m 38s Dec. -27° 56' 53" This image represents a typical view of our distant universe. In taking this picture, Hubble is looking down a long corridor of galaxies stretching billions of light-years distant in space, corresponding to looking billions of years back in time. The field shown in this picture covers 3.5 arcminutes across, a relatively small patch of sky, in the constellation Fornax, yet it is richly populated with a variety of galaxy types. A handful of large fully formed galaxies are scattered throughout the image. These galaxies are easy to see because they are relatively close to us. Several of the galaxies are spirals with flat disks that are oriented edge-on or face-on to our line of sight, or somewhere in between. Elliptical galaxies and more exotic galaxies with bars or tidal tails are also visible. Many galaxies that appear small in this image are simply farther away. These visibly smaller galaxies are so distant that their light has taken billions of years to reach us. We are seeing these galaxies, therefore, when they were much younger than the larger, nearby galaxies in the image. One red galaxy to the lower left of the bright central star is acting as a lens to a large galaxy directly behind it. Light from the farther galaxy is bent around the nearby galaxy's nucleus to form a distorted arc. Sprinkled among the thousands of galaxies in this image are at least a dozen foreground stars that reside in our Milky Way Galaxy. The brightest of these foreground stars is the red object in the centre of the image. The stars are easily discernable from galaxies because of their diffraction spikes, long cross-hair-like features that look like they are emanating from the centres of the stars. Diffraction spikes are an image artefact caused by starlight travelling through the telescope's optical system. This image is a composite of multiple exposures of a single field taken by the Advanced Camera for Surveys. The image, taken in September 2003, was a bonus picture, taken when one of the other Hubble cameras was snapping photos for a science program. This image took nearly 40 hours to complete and is one of the longest exposures ever taken by Hubble. __________________

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