481 research outputs found
The ESO Slice Project (ESP) galaxy redshift survey: III. The Sample
The ESO Slice Project (ESP) is a galaxy redshift survey extending over about
23 square degrees, in a region near the South Galactic Pole. The survey is ~85%
complete to the limiting magnitude b_J=19.4 and consists of 3342 galaxies with
redshift determination.
The ESP survey is intermediate between shallow, wide angle samples and very
deep, one-dimensional pencil beams; the spanned volume is ~ 5 x 10^4 Mpc^3 at
the sensitivity peak (z ~ 0.1).
In this paper we present the description of the observations and of the data
reduction, the ESP redshift catalogue and the analysis of the quality of the
velocity determinations.Comment: 10 pages, 4 encapsulated figures, uses A&A LATEX; A&A Supplements in
press (June 1998 issue
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
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&
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
The MeerKAT Fornax Survey
We present the science case and observations plan of the MeerKAT Fornax
Survey, an HI and radio continuum survey of the Fornax galaxy cluster to be
carried out with the SKA precursor MeerKAT. Fornax is the second most massive
cluster within 20 Mpc and the largest nearby cluster in the southern
hemisphere. Its low X-ray luminosity makes it representative of the environment
where most galaxies live and where substantial galaxy evolution takes place.
Fornax's ongoing growth makes it an excellent laboratory for studying the
assembly of clusters, the physics of gas accretion and stripping in galaxies
falling in the cluster, and the connection between these processes and the
neutral medium in the cosmic web.
We will observe a region of 12 deg reaching a projected distance of 1.5
Mpc from the cluster centre. This will cover a wide range of environment
density out to the outskirts of the cluster, where gas-rich in-falling groups
are found. We will: study the HI morphology of resolved galaxies down to a
column density of a few times 1e+19 cm at a resolution of 1 kpc; measure
the slope of the HI mass function down to M(HI) 5e+5 M(sun); and attempt to
detect HI in the cosmic web reaching a column density of 1e+18 cm at a
resolution of 10 kpc.Comment: Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA",
Stellenbosch, 25-27 May 201
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