92,805 research outputs found
On the dependence between UV luminosity and Lyman-alpha equivalent width in high redshift galaxies
We show that with the simple assumption of no correlation between the
Ly-alpha equivalent width and the UV luminosity of a galaxy, the observed
distribution of high redshift galaxies in an equivalent width - absolute UV
magnitude plane can be reproduced. We further show that there is no dependence
between Ly-alpha equivalent width and Ly-alpha luminosity in a sample of
Ly-alpha emitters. The test was expanded to Lyman-break galaxies and again no
dependence was found. Simultaneously, we show that a recently proposed lack of
large equivalent width, UV bright galaxies (Ando et al. 2006) can be explained
by a simple observational effect, based on too small survey volumes.Comment: 7 pages, 3 figures, 2 tables, accepted in MNRA
Extra Dimensions in the Early Universe
We investigate the possible occurrence of extra spatial dimensions (D =
3+epsilon) in the early universe. A detailed calculation is presented which
shows that the crucial signal is the apparent inequality of the cosmological
Z-term between matching Lyman alpha (Ly{alpha}) and Lyman beta (Ly{beta})
spectral lines, both emission and absorption, when using the present epoch
(laboratory) wavelengths. We present preliminary upper limits to the value of
epsilon, to be improved by direct, more careful analysis of the spectra. We
take catalogued quasar Ly{alpha} forest data and perform Student's t-test to
determine whether we should reject the null hypothesis (no fractal dimensions).
Finally, a chi^{2} analysis is done for fitting epsilon in the early universe.
The statistical tests and experimental data are all consistent with epsilon = 0
for Z
4. However, it should be emphasized that the non-zero values of epsilon found
for Z > 4 may be due to undiscovered systematic errors in the original data.Comment: 9 pages, 1 figure. To be published in Physics Letters
Abundances in Damped Ly-alpha Galaxies
Damped Ly_alpha galaxies provide a sample of young galaxies where chemical
abundances can be derived throughout the whole universe with an accuracy
comparable to that for the local universe. Despite a large spread in redshift,
HI column density and metallicity, DLA galaxies show a remarkable uniformity in
the elemental ratios rather suggestive of similar chemical evolution if not of
an unique population. These galaxies are characterized by a moderate, if any,
enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn]
about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the
Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution
and possibly two plateaux. In particular, the plateau at low N abundances
([N/H] < -3), is not observed in other atrophysical sites and might be evidence
for primary N production by massive stars.Comment: To appear in the Proceedings of the ESO/Arcetri Workshop on "Chemical
Abundances and Mixing in Stars in the Milky Way and its Satellites", eds., L.
Pasquini and S. Randich (Springer-Verlag Series, "ESO Astrophysics Symposia"
Physical properties of z~4 LBGs: differences between galaxies with and without Ly-alpha emission
We have analysed the physical properties of z~4 Lyman Break Galaxies observed
in the GOODS-S survey, in order to investigate the possible differences between
galaxies where the Ly-alpha is present in emission, and those where the line is
absent or in absorption. The objects have been selected from their optical
color and then spectroscopically confirmed by Vanzella et al. (2005). From the
public spectra we assessed the nature of the Ly-alpha emission and divided the
sample into galaxies with Ly-alpha in emission and objects without Ly-alpha
line (i.e. either absent or in absorption). We have then used the complete
photometry, from U band to mid infrared from the GOODS-MUSIC database, to study
the observational properties of the galaxies, such as UV spectral slopes and
optical to mid-infrared colors, and the possible differences between the two
samples. Finally through standard spectral fitting tecniques we have determined
the physical properties of the galaxies, such as total stellar mass, stellar
ages and so on, and again we have studied the possible differences between the
two samples. Our results indicate that LBG with Ly-alpha in emission are on
average a much younger and less massive population than the LBGs without
Ly-alpha emission. Both populations are forming stars very actively and are
relatively dust free, although those with line emission seem to be even less
dusty on average. We briefly discuss these results in the context of recent
models for the evolution of Lyman break galaxies and Ly-alpha emitters.Comment: Accepted for publication in A&A. Uses aa.cls, 6 pages, 3 figure
Detecting filaments at z=3
We present the detection of a filament of Ly-alpha emitting galaxies in front
of the quasar Q1205-30 at z=3.04 based on deep narrow band imaging and
follow-up spectroscopy obtained at the ESO NTT and VLT. We argue that Ly-alpha
selection of high redshift galaxies with relatively modest amounts of observing
time allows the detection and redshift measurement of galaxies with
sufficiently high space densities that we can start to map out the large scale
structure at z=2-3 directly. Even more interesting is it that a 3D map of the
filaments will provide a new cosmological test for the value of the
cosmological constant, Omega_Lambda.Comment: 7 pages, 4 figures, contribution to the procedings of the conference
``Lighthouses of the Universe'' held in Garching (Germany), August 200
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