Browsing by Author "Jablonka, P"

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    On-axis spatially resolved spectroscopy of low redshift quasar host galaxies
    (2002) Courbin, F; Letawe, G; Magain, P; Wisotzki, L; Jablonka, P; Jahnke, DK; Kuhlbrodt, B; Alloin, D; Meylan, G; Minniti, D; Burud, I
    We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the "MCS deconvolution algorithm". The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE 1503+0228 at z = 0.135 (M-B = -23.0), it provides us with the spectrum of the host galaxy between 3600 Angstrom and 8500 Angstrom (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE 1503+0228 are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 400 away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r < 1 kpc) = (2.0 +/- 0.3) x 10(10) M-. within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r < 10 kpc) = (1.9 +/- 0.3) x 10(11) M-., with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE 1503+0228 is a normal spiral galaxy.
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    Resolved stellar populations of super-metal-rich star clusters in the bulge of M 31
    (2000) Jablonka, P; Courbin, F; Meylan, G; Sarajedini, A; Bridges, TJ; Magain, P
    We have applied the MCS image deconvolution algorithm (Magain et al. 1998) to HST/WFPC2 V, I data of three M 31 bulge globular clusters (G170, G177, and G198) and control fields near each cluster. All three clusters are clearly detected, with an increase in stellar density with decreasing radius from the cluster centers: this is the first time that stars have been resolved in bulge clusters in the inner regions of another galaxy. From the RGB slopes of the clusters and the difference in I magnitude between the HE and the top of the RGB, we conclude that these three clusters all have roughly solar metallicity, in agreement with earlier integrated-light spectroscopic measurements. Our data support a picture whereby the M 31 bulge clusters and field stars were born from the same metal-rich, gas, early in the galaxy formation.
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    The stellar content of the bulge of M31
    (2003) Stephens, AW; Frogel, JA; DePoy, DL; Freedman, W; Gallart, C; Jablonka, P; Renzini, A; Rich, RM; Davies, R
    We analyze the stellar populations present in M31 by using nine sets of adjacent Hubble Space Telescope NICMOS camera 1 and 2 fields with galactocentric distances ranging from 2' to 20'. These infrared observations provide some of the highest spatial resolution measurements of M31 to date; our data place tight constraints on the maximum luminosities of stars in the bulge of M31. The tip of the red giant branch is clearly visible at M-bol similar to -3.8, and the tip of the asymptotic giant branch (AGB) extends to M-bol similar to -5. This AGB peak luminosity is significantly fainter than previously claimed; through direct comparisons and simulations we show that previous measurements were affected by image blending. We do observe field-to-field variations in the luminosity functions, but simulations show that these differences can be produced by blending in the higher surface brightness fields. We conclude that the red giant branch of the bulge of M31 is not measurably different from that of the bulge of the Milky Way. We also find an unusually high number of bright bluish stars (7.3 arcmin(-2)), which appear to be Galactic foreground stars.