1,721,034 research outputs found
The Influence of Mass and Environment on the Evolution of Early-Type Galaxies
No full textWe report on a uniform comparative analysis of the fundamental parameters of early-type galaxies at z~1 down to MB3×1011 Msolar) with a formation redshift smaller than 2, which cannot be due to selection effects.
We report about the changes to the above-mentioned Letter due to an error in the calibration of the galaxy luminosities used by Jørgensen et al. (2006). To correct for this error, the photometry for the two clusters should be offset to brighter luminosities with a factor (1+z). Correcting for this error corresponds to an offset in logL to brighter luminosities with log(1+z), which is 0.26 and 0.28 for RX J0152.7-1357 (z=0.835) and RX J1226.9+3332 (z=0.892), respectively. As a consequence, Figures 1, 2, 3, and 4 are changed as far as the two clusters are concerned, and the correct versions are given here. As can be clearly seen in Figures 1 and 2, the claimed difference in the fundamental plane (FP) and in the M/LB ratio between the clusters and the field environment is not present any more, and the behavior of the z~1 early-type galaxies (ETGs) is remarkably similar in both environments, as claimed earlier by di Serego Alighieri et al. (2005). Therefore, the estimated formation epoch of ETGs does not depend on the environment but only on the galaxy mass (see Fig. 3). Quantitatively, the mean age difference between clusters and the field in each mass bin is smaller than 5% and is well within the standard deviation due to galaxy-to-galaxy variations (Fig. 4). Clearly it is now no longer relevant to study this age difference as a function of galaxy mass, and so Figure 4 is modified accordingly.
Our correct results are therefore in even larger contrast to the most recent incarnation of the hierarchical models of galaxy formation and evolution, which foresee a marked difference in the formation epoch of ETGs with environment (De Lucia et al. 2006)
Early-type galaxies with neutral hydrogen in the Virgo cluster from the ALFALFA survey
No full textWe extend our published work on the neutral hydrogen content of early-type galaxies in the Virgo cluster using the catalogue of detected sources from the ALFALFA survey, by showing the 21cm spectra of all the detected galaxies and discussing a deeper analysis of the ALFALFA datacubes, searching for lower S/N sources. A view of the multiphase interstellar medium of M86 is also presented, by comparing images of the cold, warm and hot phases
A Lyα emitter at z = 6.5 found with slitless spectroscopy
No full textWith respect to the formation of the first stars from primordial material and the sources of reionization, the observations of galaxies at z = 6.5, where Lyα is observable through an atmospheric window in the z' band, are of great interest. Employing slitless spectroscopy with FORS at the VLT, we have found a Lyα-emitting galaxy at z = 6.5 with a SFR(UV) of 70 Msun yr-1. Together with the small sample of currently known Lyα emitters at z = 6.5, this object puts constraints on the global star-formation history and the epoch of reionization
Metal Enrichment in Near-Infrared Luminous Galaxies at z~2: Signatures of Proto-elliptical Galaxies?
No full textHUBBLE-SPACE-TELESCOPE FAR-ULTRAVIOLET IMAGING OF M31, M32, AMD NGC-205
No full textHubble Space Telescope Faint Object Camera (FOG) f/48 images of M31, M32, and NGC 205 (held of view 23'' x 23'' with 0''.45 pixel size) are analyzed as observed through the combined UV filters F150W and F130LP. The absolute calibration of the data and the internal disagreement between observed and expected count rates in the UV region lead us to suggest that the filter combination F150W + F130LP suffers from a 5 times degraded UV sensitivity. A corrected efficiency curve is constructed using the UV/optical spectral energy distributions of these three galaxies, which is consistent with all of the data analyzed here. Eighty-one individual stars are detected in M31, 10 stars in M32, and 78 stars in NGC 205. Comparisons with other UV images and optical images indicates that these stars are hot, UV-bright stars, even though our corrected efficiency curve suggests that flux from 1200-2450 Angstrom contributes only 7% of the counts in M32, 19% in M31, and 60% in NGC 205. The morphology of the galaxies in our images is consistent with existing data. The complex nucleus of M31 as seen by Lauer et al. (1993) is confirmed; M32 has a generally smooth appearance and NGC 205 is dominated by a UV-bright, somewhat resolved nucleus. Analysis of these data is done through the new, extensive stellar isochrones of Bertelli et al. (1994) and the population synthesis models of Bressan, Chiosi, and Fagotto (1994). This analysis shows that high-metal stars (Z > 0.05) evolve into UV-bright stars (P-EAGB, H-HB, and AGB-manque stars) that are less luminous and cooler but are significantly longer lived than the P-AGB stars produced by stars with Z < 0.05. Moreover, the proportion of P-EAGB, H-HB, and AGB-manque stars is also a function of age, with order stars of fixed mean metallicity having a higher proportion than younger stars. Hence, with either metallicity or age differences as an interpretation of the line-strength luminosity correlation for ellipticals, the high-metallicity ''tail'' of the stellar content of a galaxy can produce far-UV flux in much greater proportion than its actual proportion of galaxy mass. Separately, the UV-brightest stars in these stellar populations will be the shorter lived P-AGB stars and, hence, more readily observed in imaging observations such as ours. The resulting model of the sources of far-UV flux is inherently composite, with the total UV flux from a stellar population both rapidly increasing and changing its mean spectrum with increasing mean metallicity (or mean age). This model is consistent with five pieces of observational evidence: (1) the correlation of UV-optical color with metallicity documented by Burstein et al. (1988) for early-type galaxies, (2) the low absolute UV flux from M32, (3) the apparent composite nature of UV flux from giant E's and the bulge of M31, as seen by the Hopkins Ultraviolet Telescope (HUT) spectral observations of Ferguson and Davidsen (1993), (4) our FOC observations of P-AGB stars that contribute a minority UV flux in M31, and (5) the possibility that ellipticals might have correlations of either age or metallicity with absolute luminosity (Faber, Gonzalez, and Worthey 1992)
Polarized Extended Lyalpha Emission from a z = 2.3 Radio Galaxy
No full textWe present spatially resolved spectropolarimetric measurements of the 100 kpc scale gaseous environment of the z = 2.34 radio galaxy TXS 0211-122. The polarization level of the narrow Lyalpha emission is low centrally (P < 5%), but rises to P = 16.4% ± 4.6% in the eastern part of the nebula, indicating that the nebula is at least partly powered by the scattering of Lyalpha photons by H I. Not only is this the first detection of polarized Lyalpha around a radio-loud active galaxy, it is also the second detection to date for any kind of Lyalpha nebula. We also detect a pair of diametrically opposed UV continuum sources along the slit, at the outer edges of the Lyalpha nebula, which we suggest may be the limb of a dusty shell, related to the large-scale H I absorbers often associated with high-z radio galaxies
The knotty structure of the HII dwarf galaxy F348
No full text[O III] images and blue spectra of the emission-line dwarf galaxy F348 are presented. In [O III] light, the object contains two knots about 9'' NE of the nucleus and one large extended knot 11'' to the SW. The nuclear region is hundred times less luminous in emission-line light than the knots. Despite the presence of line intensity ratios [O III] λ5007 Å/Hβ > 3 the prior classification as a Seyfert-2 object cannot be upheld. This clinches an earlier suggestion by Veron-Cetty and Veron (1986). In particular, the authors show that the line spectra can be modeled with photoionization models employing stellar input continua. Also, the line luminosities of the extranuclear knots are typical for giant H II regions. There is neither evidence for tidal tails nor for high velocity differences between the knots. In addition, the linear arrangement of the knots does not support interaction. It rather suggests self-propagating star formation. In this picture, the faintness of the nuclear region can be understood by an edge-on view. In addition, the nuclear starburst appears to be fading in contrast to the young extranuclear star formation regions. Within the scheme of Melnick (1987), F348 has to be classified as a multiple-system H II galaxy
The HI content of early-type galaxies from the ALFALFA survey II. The case of low density environments
No full textAims. We present the analysis of the H
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