564 research outputs found
High-Resolution Spectroscopy from 3050 to 10000 A of the HDF-S QSO J2233-606 with UVES at the ESO VLT
We report on high-resolution observations () of the Hubble
Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle
Spectrograph (UVES). We present spectral data for the wavelength region \AA. The ratio of the final spectrum is about 50 per
resolution element at 4000 \AA, 90 at 5000 \AA, 80 at 6000 \AA, 40 at 8000 \AA.
Redshifts, column densities and Doppler widths of the absorption features have
been determined with Voigt-profile fitting. A total of 621 lines have been
measured. In particular 270 Ly-alpha lines, 41 Ly-beta and 24 systems
containing metal lines have been identified. Together with other data in the
literature, the present spectrum confirms that the evolution of the number
density of Ly-alpha lines with \huno has an upturn at .Comment: 34 pages Latex, with 3 PostScript figures. Astronomical Journal, in
press. A few revised upper limit
Is my ODE a Painleve equation in disguise?
Painleve equations belong to the class y'' + a_1 {y'}^3 + 3 a_2 {y'}^2 + 3
a_3 y' + a_4 = 0, where a_i=a_i(x,y). This class of equations is invariant
under the general point transformation x=Phi(X,Y), y=Psi(X,Y) and it is
therefore very difficult to find out whether two equations in this class are
related. We describe R. Liouville's theory of invariants that can be used to
construct invariant characteristic expressions (syzygies), and in particular
present such a characterization for Painleve equations I-IV.Comment: 8 pages. Based on talks presented at NEEDS 2000, Gokova, Turkey, 29
June - 7 July, 2000, and at the AMS-HKMS joint meeting 13-16 December, 2000.
Submitted to J. Nonlin. Math. Phy
Dependence of Dust Obscuration on Star Formation Rates in Galaxies
Many investigations of star formation rates (SFRs) in galaxies have explored
details of dust obscuration, with a number of recent analyses suggesting that
obscuration appears to increase in systems with high rates of star formation.
To date these analyses have been primarily based on nearby (z < 0.03) or UV
selected samples. Using 1.4 GHz imaging and optical spectroscopic data from the
Phoenix Deep Survey, the SFR-dependent obscuration is explored. The use of a
radio selected sample shows that previous studies exploring SFR-dependent
obscurations have been biased against obscured galaxies. The observed relation
between obscuration and SFR is found to be unsuitable to be used as an
obscuration measure for individual galaxies. Nevertheless, it is shown to be
successful as a first order correction for large samples of galaxies where no
other measure of obscuration is available, out to intermediate redshifts (z ~
0.8).Comment: 9 pages (including 5 encapsulated postscript figures), aastex, uses
emulateapj5.sty. Accepted for publication in Ap
Studying the evolution of large-scale structure with the VIMOS-VLT Deep Survey
The VIMOS-VLT Deep Survey (VVDS) currently offers a unique combination of
depth, angular size and number of measured galaxies among surveys of the
distant Universe: ~ 11,000 spectra over 0.5 deg2 to I_{AB}=24 (VVDS-Deep),
35,000 spectra over ~ 7 deg2 to I_{AB}=22.5 (VVDS-Wide). The current ``First
Epoch'' data from VVDS-Deep already allow investigations of galaxy clustering
and its dependence on galaxy properties to be extended to redshifts ~1.2-1.5,
in addition to measuring accurately evolution in the properties of galaxies up
to z~4. This paper concentrates on the main results obtained so far on galaxy
clustering. Overall, L* galaxies at z~ 1.5 show a correlation length r_0=3.6\pm
0.7. As a consequence, the linear galaxy bias at fixed luminosity rises over
the same range from the value b~1 measured locally, to b=1.5 +/- 0.1. The
interplay of galaxy and structure evolution in producing this observation is
discussed in some detail. Galaxy clustering is found to depend on galaxy
luminosity also at z~ 1, but luminous galaxies at this redshift show a
significantly steeper small-scale correlation function than their z=0
counterparts. Finally, red galaxies remain more clustered than blue galaxies
out to similar redshifts, with a nearly constant relative bias among the two
classes, b_{rel}~1.4, despite the rather dramatic evolution of the
color-density relation over the same redshift range.Comment: 14 pages. Extended, combined version of two invited review papers
presented at: 1) XXVIth Astrophysics Moriond Meeting: "From Dark Halos to
Light", March 2006, proc. edited by L.Tresse, S. Maurogordato and J. Tran
Thanh Van (Editions Frontieres); 2) Vulcano Workshop 2006 "Frontier Objects
in Astrophysics and Particle Physics", May 2006, proc. edited by F.
Giovannelli & G. Mannocchi, Italian Physical Society (Editrice Compositori,
Bologna
N-dimensional geometries and Einstein equations from systems of PDE's
The aim of the present work is twofold: first, we show how all the
-dimensional Riemannian and Lorentzian metrics can be constructed from a
certain class of systems of second-order PDE's which are in duality to the
Hamilton-Jacobi equation and second we impose the Einstein equations to these
PDE's
A contribution to the selection of emission-line galaxies using narrow-band filters in the optical airglow windows
Emission line galaxies are an invaluable tool for our understanding of the
evolution of galaxies in the Universe. Imaging of deep fields with narrow-band
filters allows not only the selection of these objects, but also to infer the
line flux and the equivalent width of the emission line with some assumptions.
The narrow-band filter technique provides homogeneous samples of galaxies in
small comoving volumes in the sky. We present an analysis of the selection of
emission-line galaxies using narrow-band filters. Different methods of
observation are considered: broad-band -- narrow-band filters and two
broad-band and one narrow-band filters.
We study also the effect of several lines entering simultaneously inside the
filters (this is the case of Halpha). In each case the equations to obtain the
equivalent width and line flux from the photometry are obtained. Candidates to
emission-line objects are selected by their color excess in a magnitude-color
diagram. For different narrow-band filters, we compute the mean colors of stars
and galaxies, showing that, apart from galaxies, some types of stars could be
selected with certain filter sets. We show how to compute the standard
deviation of the colors of the objects even in the usual case when there are
not enough objects to determine the standard deviation from the data. We
present also helpful equations to compute the narrow-band and the broad-band
exposure times in order to obtain minimum dispersion in the ratio of fluxes of
both bands with minimum total exposure time.Comment: Accepted for publication in PASP 48 pages, 10 figures Corrected
typos, fixed references. Updated reference to T
HeII emitters in the VIMOS VLT Deep Survey: PopIII star formation or peculiar stellar populations in galaxies at 2<z<4.6?
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain
the source of the hard ionizing continuum that powers the HeII emission. We
have assembled a sample of 277 galaxies with a high quality spectroscopic
redshift at 2<z<4.6 from the VVDS survey, and we have identified 39 HeII1640A
emitters. We study their spectral properties, measuring the fluxes, equivalent
widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show
HeII in emission, with rest frame equivalent widths EW0~1-7A, equally
distributed between galaxies with Lya in emission or in absorption. We find 11
high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13
high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and
an additional 12 possible HeII emitters. The properties of the individual broad
emitters are in agreement with expectations from a W-R model. On the contrary,
the properties of the narrow emitters are not compatible with such model,
neither with predictions of gravitational cooling radiation produced by gas
accretion. Rather, we find that the EW of the narrow HeII line emitters are in
agreement with expectations for a PopIII star formation, if the episode of star
formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1
only is enough to sustain the observed HeII flux. We conclude that narrow HeII
emitters are either powered by the ionizing flux from a stellar population rare
at z~0 but much more common at z~3, or by PopIII star formation. As proposed by
Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of
pristine gas at the periphery of galaxies from which PopIII may form, even down
to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in
PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value
predicted by Tornatore et al. (2007).Comment: accepted for publication in A&
Star formation rate indicators in the Sloan Digital Sky Survey
The Sloan Digital Sky Survey (SDSS) first data release provides a database of
106000 unique galaxies in the main galaxy sample with measured spectra. A
sample of star-forming (SF) galaxies are identified from among the 3079 of
these having 1.4 GHz luminosities from FIRST, by using optical spectral
diagnostics. Using 1.4 GHz luminosities as a reference star formation rate
(SFR) estimator insensitive to obscuration effects, the SFRs derived from the
measured SDSS Halpha, [OII] and u-band luminosities, as well as far-infrared
luminosities from IRAS, are compared. It is established that straightforward
corrections for obscuration and aperture effects reliably bring the SDSS
emission line and photometric SFR estimates into agreement with those at 1.4
GHz, although considerable scatter (~60%) remains in the relations. It thus
appears feasible to perform detailed investigations of star formation for large
and varied samples of SF galaxies through the available spectroscopic and
photometric measurements from the SDSS. We provide herein exact prescriptions
for determining the SFR for SDSS galaxies. The expected strong correlation
between [OII] and Halpha line fluxes for SF galaxies is seen, but with a median
line flux ratio F_[OII]/F_Halpha=0.23, about a factor of two smaller than that
found in the sample of Kennicutt (1992). This correlation, used in deriving the
[OII] SFRs, is consistent with the luminosity-dependent relation found by
Jansen et al. (2001). The median obscuration for the SDSS SF systems is found
to be A_Halpha=1.2 mag, while for the radio detected sample the median
obscuration is notably higher, 1.6 mag, and with a broader distribution.Comment: Accepted for publication in ApJ, 40 pages, 26 figure
The Star Formation Rate Density and Dust Attenuation Evolution over 12 Gyr with the VVDS Surveys
[Abridged] We investigate the global galaxy evolution over 12 Gyr
(0.05<z<4.5), from the star formation rate density (SFRD), combining the VVDS
Deep (17.5<=I<=24.0) and Ultra-Deep (23.00<=i<=24.75) surveys. We obtain a
single homogeneous spectroscopic redshift sample, totalizing about 11000
galaxies. We estimate the rest-frame FUV luminosity function (LF) and
luminosity density (LD), extract the dust attenuation of the FUV radiation
using SED fitting, and derive the dust-corrected SFRD. We find a constant and
flat faint-end slope alpha in the FUV LF at z1.7, we set alpha
steepening with (1+z). The absolute magnitude M*_FUV brightens in the entire
range 02 it is on average brighter than in the literature,
while phi* is smaller. Our total LD shows a peak at z=2, present also when
considering all sources of uncertainty. The SFRD history peaks as well at z=2.
It rises by a factor of 6 during 2 Gyr (from z=4.5 to z=2), and then decreases
by a factor of 12 during 10 Gyr down to z=0.05. This peak is mainly produced by
a similar peak within the population of galaxies with -21.5<=M_FUV<=-19.5 mag.
As times goes by, the total SFRD is dominated by fainter and fainter galaxies.
The presence of a clear peak at z=2 and a fast rise at z>2 of the SFRD is
compelling for models of galaxy formation. The mean dust attenuation A_FUV of
the global galaxy population rises by 1 mag during 2 Gyr from z=4.5 to z=2,
reaches its maximum at z=1 (A_FUV=2.2 mag), and then decreases by 1.1 mag
during 7 Gyr down to z=0. The dust attenuation maximum is reached 2 Gyr after
the SFRD peak, implying a contribution from the intermediate-mass stars to the
dust production at z<2.Comment: 23 pages, 15 figures, accepted for publication in A&
Invariants of pseudogroup actions: Homological methods and Finiteness theorem
We study the equivalence problem of submanifolds with respect to a transitive
pseudogroup action. The corresponding differential invariants are determined
via formal theory and lead to the notions of k-variants and k-covariants, even
in the case of non-integrable pseudogroup. Their calculation is based on the
cohomological machinery: We introduce a complex for covariants, define their
cohomology and prove the finiteness theorem. This implies the well-known
Lie-Tresse theorem about differential invariants. We also generalize this
theorem to the case of pseudogroup action on differential equations.Comment: v2: some remarks and references addee
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