509 research outputs found
The Ha Luminosity Function and Star Formation Rate at z\sim 0.2
We have measured the Ha+[N II] fluxes of the I-selected Canada-France
Redshift Survey (CFRS) galaxies lying at a redshift z below 0.3, and hence
derived the Ha luminosity function. The magnitude limits of the CFRS mean that
only the galaxies with M(B) > -21 mag were observed at these redshifts. We
obtained a total Ha luminosity density of at least 10^{39.44\pm 0.04}
erg/s/Mpc^{3} at a mean z=0.2 for galaxies with rest-fame EW(Ha+[N II]) > 10
Angs. This is twice the value found in the local universe by Gallego et al.
1995. Our Ha star formation rate, derived from Madau (1997) is higher than the
UV observations at same z, implying a UV dust extinction of about 1 mag. We
found a strong correlation between the Ha luminosity and the absolute magnitude
in the B-band: M(B(AB)) = 46.7 - 1.6 log L(Ha). This work will serve as a basis
of future studies of Ha luminosity distributions measured from
optically-selected spectroscopic surveys of the distant universe, and it will
provide a better understanding of the physical processes responsible for the
observed galaxy evolution.Comment: Accepted for publication in ApJ, 14 pages, LaTeX (macro aas2pp4.sty),
6 figure
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
Studying the Evolution of Multi-Wavelength Emissivities with the Vimos VLT Deep Survey
The VIMOS VLT Deep Survey is a unique I-selected spectroscopic sample to
study galaxies all the way from z=5 to z=0. We recapitulate the first results
about the evolution of the galaxy populations as a function of type,
morphology, environment and luminosity.Comment: 9 pages, 11 figures. To appear in the proceedings of the XLIst
Rencontres de Moriond, XXVIth Astrophysics Moriond Meeting: "From dark halos
to light", Eds. L.Tresse, S. Maurogordato and J. Tran Thanh Van (Editions
Frontieres
Compact Nuclei in Moderately Redshifted Galaxies
The Hubble Space Telescope WFPC2 is being used to obtain high-resolution
images in the V and I bands for several thousand distant galaxies as part of
the Medium Deep Survey (MDS). An important scientific aim of the MDS is to
identify possible AGN candidates from these images in order to measure the
faint end of the AGN luminosity function as well as to study the host galaxies
of AGNs and nuclear starburst systems. We are able to identify candidate
objects based on morphology. Candidates are selected by fitting bulge+disk
models and bulge+disk+point source nuclei models to HST imaged galaxies and
determining the best model fit to the galaxy light profile. We present results
from a sample of MDS galaxies with I less than 21.5 mag that have been searched
for AGN/starburst nuclei in this manner. We identify 84 candidates with
unresolved nuclei in a sample of 825 galaxies. For the expected range of galaxy
redshifts, all normal bulges are resolved. Most of the candidates are found in
galaxies displaying exponential disks with some containing an additional bulge
component. 5% of the hosts are dominated by an r^-1/4 bulge. The V-I color
distribution of the nuclei is consistent with a dominant population of
Seyfert-type nuclei combined with an additional population of starbursts. Our
results suggest that 10% +/- 1% of field galaxies at z less than 0.6 may
contain AGN/starburst nuclei that are 1 to 5 magnitudes fainter than the host
galaxies.Comment: 12 pages AASTeX manuscript, 3 separate Postscript figures, to be
published in ApJ Letter
The VIMOS VLT Deep Survey. The different assembly history of passive and star-forming L_B >= L*_B galaxies in the group environment at z < 1
We use the VIMOS VLT Deep Survey to study the close environment of galaxies
in groups at 0.2 = L*_B galaxies (Me_B =
M_B + 1.1z <= -20) are identified with Me_B <= -18.25 and within a relative
distance 5h^-1 kpc <= rp <= 100h^-1 kpc and relative velocity Delta v <= 500
km/s . The richness N of a group is defined as the number of Me_B <= -18.25
galaxies belonging to that group. We split our principal sample into red,
passive galaxies with NUV - r >= 4.25 and blue, star-forming galaxies with NUV
- r < 4.25. We find that blue galaxies with a close companion are primarily
located in poor groups, while the red ones are in rich groups. The number of
close neighbours per red galaxy increases with N, with n_red being proportional
to 0.11N, while that of blue galaxies does not depend on N and is roughly
constant. In addition, these trends are found to be independent of redshift,
and only the average n_blue evolves, decreasing with cosmic time. Our results
support the following assembly history of L_B >= L*_B galaxies in the group
environment: red, massive galaxies were formed in or accreted by the dark
matter halo of the group at early times (z >= 1), therefore their number of
neighbours provides a fossil record of the stellar mass assembly of groups,
traced by their richness N. On the other hand, blue, less massive galaxies have
recently been accreted by the group potential and are still in their parent
dark matter halo, having the same number of neighbours irrespective of N. As
time goes by, these blue galaxies settle in the group potential and turn red
and/or fainter, thus becoming satellite galaxies in the group. With a toy
quenching model, we estimate an infall rate of field galaxies into the group
environment of R_infall = 0.9 - 1.5 x 10^-4 Mpc^-3 Gyr^-1 at z ~ 0.7.Comment: Astronomy and Astrophysics, in press. 11 pages, 11 figures, 4 tables.
Minor changes with respect to the first versio
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
Integral field spectroscopy with SINFONI of VVDS galaxies. II. The mass-metallicity relation at 1.2 < z < 1.6
This work aims to provide a first insight into the mass-metallicity (MZ)
relation of star-forming galaxies at redshift z~1.4. To reach this goal, we
present a first set of nine VVDS galaxies observed with the NIR integral-field
spectrograph SINFONI on the VLT. Oxygen abundances are derived from empirical
indicators based on the ratio between strong nebular emission-lines (Halpha,
[NII]6584 and [SII]6717,6731). Stellar masses are deduced from SED fitting with
Charlot & Bruzual (2007) population synthesis models, and star formation rates
are derived from [OII]3727 and Halpha emission-line luminosities. We find a
typical shift of 0.2-0.4 dex towards lower metallicities for the z~1.4
galaxies, compared to the MZ-relation in the local universe as derived from
SDSS data. However, this small sample of eight galaxies does not show any clear
correlation between stellar mass and metallicity, unlike other larger samples
at different redshift (z~0, z~0.7, and z~2). Indeed, our galaxies lie just
under the relation at z~2 and show a small trend for more massive galaxies to
be more metallic (~0.1 logarithmic slope). There are two possible explanations
to account for these observations. First, the most massive galaxies present
higher specific star formation rates when compared to the global VVDS sample
which could explain the particularly low metallicity of these galaxies as
already shown in the SDSS sample. Second, inflow of metal-poor gas due to tidal
interactions could also explain the low metallicity of these galaxies as two of
these three galaxies show clear signatures of merging in their velocity fields.
Finally, we find that the metallicity of 4 galaxies is lower by ~0.2 to 0.4 dex
if we take into account the N/O abundance ratio in their metallicity estimate.Comment: 7 pages, 4 figures, accepted in A&A Comments: Comments: more accurate
results with better stellar mass estimate
Compact Nuclei in Galaxies at Moderate Redshift:II. Their Nature and Implications for the AGN Luminosity Function
This study explores the space density and properties of active galaxies to
z=0.8. We have investigated the frequency and nature of unresolved nuclei in
galaxies at moderate redshift as indicators of nuclear activity such as Active
Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged
galaxies with multi-component models using maximum likelihood estimate
techniques to determine the best model fit. We select those galaxies requiring
an unresolved point-source component in the galaxy nucleus, in addition to a
disk and/or bulge component, to adequately model the galaxy light. We have
searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies
containing compact nuclei. In our survey of 1033 galaxies, the fraction
containing an unresolved nuclear component greater than 5% of the total galaxy
light is 9+/-1% corrected for incompleteness. In this second of two papers in
this series, we discuss the nature of the compact nuclei and their hosts.
We present the upper limit luminosity function (LF) for low-luminosity AGN
(LLAGN) in two redshift bins to z=0.8. Mild number density evolution is
detected for nuclei at -18 -16
and this flatness, combined with the increase in number density, is
inconsistent with pure luminosity evolution. Based on the amount of density
evolution observed for these objects, we find that almost all present-day
spiral galaxies could have hosted a LLAGN at some point in their lives. We also
comment on the likely contribution of these compact nuclei to the soft X-ray
background.Comment: 50 pages, 14 figures, to appear in ApJ, April 199
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
The extended epoch of galaxy formation: age dating of ~3600 galaxies with 2<z<6.5 in the VIMOS Ultra-Deep Survey
We aim at improving constraints on the epoch of galaxy formation by measuring
the ages of 3597 galaxies with spectroscopic redshifts 2<z<6.5 in the VIMOS
Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the
simultaneous fitting with the GOSSIP+ software of observed UV rest-frame
spectra and photometric data from the u-band up to 4.5 microns using composite
stellar population models. We conclude from extensive simulations that at z>2
the joint analysis of spectroscopy and photometry combined with restricted age
possibilities when taking into account the age of the Universe substantially
reduces systematic uncertainties and degeneracies in the age derivation. We
find galaxy ages ranging from very young with a few tens of million years to
substantially evolved with ages up to ~1.5-2 Gyr. The formation redshifts z_f
derived from the measured ages indicate that galaxies may have started forming
stars as early as z_f~15. We produce the formation redshift function (FzF), the
number of galaxies per unit volume formed at a redshift z_f, and compare the
FzF in increasing redshift bins finding a remarkably constant 'universal' FzF.
The FzF is parametrized with (1+z)^\zeta, with \zeta~0.58+/-0.06, indicating a
smooth 2 dex increase from z~15 to z~2. Remarkably this observed increase is of
the same order as the observed rise in the star formation rate density (SFRD).
The ratio of the SFRD with the FzF gives an average SFR per galaxy of
~7-17Msun/yr at z~4-6, in agreement with the measured SFR for galaxies at these
redshifts. From the smooth rise in the FzF we infer that the period of galaxy
formation extends from the highest possible redshifts that we can probe at z~15
down to redshifts z~2. This indicates that galaxy formation is a continuous
process over cosmic time, with a higher number of galaxies forming at the peak
in SFRD at z~2 than at earlier epochs. (Abridged)Comment: Submitted to A&A, 24 page
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