550 research outputs found
The VIMOS-VLT Deep Survey: Dependence of Galaxy Clustering on Luminosity
We have investigated the dependence of galaxy clustering on their intrinsic luminosities at z ~ 1, using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS). We have measured the projected two-point correlation function of galaxies, w_p(r_p), for a set of volume-limited samples at an effective redshift =0.9 and median absolute magnitude -19.6< M_B < -21.3. We find that the clustering strength is rising around M_B^*, apparently with a sharper turn than observed at low redshifts. The slope of the correlation function is observed to steepen significantly from \gamma=1.6^{+0.1}_{-0.1} to \gamma=2.4^{+0.4}_{-0.2}. This is due to a significant change in the shape of w_p(r_p), increasingly deviating from a power-law for the most luminous samples, with a strong upturn at small (< 1-2 h^{-1} Mpc) scales. This trend, not observed locally, also results in a strong scale dependence of the relative bias, b/b* and possibly imply a significant change in the way luminous galaxies trace dark-matter halos at z ~ 1 with respect to z ~ 0
The Dwarf Irregular Galaxy UGC 7636 Exposed: Stripping At Work In The Virgo Cluster
We present the results of optical spectroscopy of a newly discovered H II
region residing in the H I gas cloud located between the dwarf irregular galaxy
UGC 7636 and the giant elliptical galaxy NGC 4472 in the Virgo Cluster. By
comparing UGC 7636 with dwarf irregular galaxies in the field, we show that the
H I cloud must have originated from UGC 7636 because (1) the oxygen abundance
of the cloud agrees with that expected for a galaxy with the blue luminosity of
UGC 7636, and (2) M_{H I}/L_B for UGC 7636 becomes consistent with the measured
oxygen abundance of the cloud if the H I mass of the cloud is added back into
UGC 7636. It is likely that tides from NGC 4472 first loosened the H I gas,
after which ram-pressure stripping removed the gas from UGC 7636.Comment: 12 pages, 2 eps figures (AASTeX 5.0); accepted for publication in ApJ
Letter
The VIMOS-VLT Deep Survey: Dependence of galaxy clustering on stellar mass
We have investigated the dependence of galaxy clustering on their stellar
mass at z~1, using the data from the VIMOS-VLT Deep Survey (VVDS). We have
measured the projected two-point correlation function of galaxies, wp(rp) for a
set of stellar mass selected samples at an effective redshift =0.85. We have
control and quantify all effects on galaxy clustering due to the incompleteness
of our low mass samples. We find that more massive galaxies are more clustered.
When compared to similar results at z~0.1 in the SDSS, we observed no evolution
of the projected correlation function for massive galaxies. These objects
present a stronger linear bias at z~1 with respect to low mass galaxies. As
expected, massive objects at high redshift are found in the highest pics of the
dark matter density field.Comment: 4 pages, 2 figures, 43rd Rencontres de Moriond - March 15-22, 2008 -
La Thuile (Val d'Aosta, Italy
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
Spitzer bright, UltraVISTA faint sources in COSMOS: the contribution to the overall population of massive galaxies at z=3-7
We have analysed a sample of 574 Spitzer 4.5 micron-selected galaxies with
[4.5]24 (AB) over the UltraVISTA ultra-deep COSMOS field. Our
aim is to investigate whether these mid-IR bright, near-IR faint sources
contribute significantly to the overall population of massive galaxies at
redshifts z>=3. By performing a spectral energy distribution (SED) analysis
using up to 30 photometric bands, we have determined that the redshift
distribution of our sample peaks at redshifts z~2.5-3.0, and ~32% of the
galaxies lie at z>=3. We have studied the contribution of these sources to the
galaxy stellar mass function (GSMF) at high redshifts. We found that the
[4.5]24 galaxies produce a negligible change to the GSMF
previously determined for Ks_auto<24 sources at 3=<z<4, but their contribution
is more important at 4=~50% of the galaxies with stellar
masses Mst>~6 x 10^10 Msun. We also constrained the GSMF at the highest-mass
end (Mst>~2 x 10^11 Msun) at z>=5. From their presence at 5=<z<6, and virtual
absence at higher redshifts, we can pinpoint quite precisely the moment of
appearance of the first most massive galaxies as taking place in the ~0.2 Gyr
of elapsed time between z~6 and z~5. Alternatively, if very massive galaxies
existed earlier in cosmic time, they should have been significantly
dust-obscured to lie beyond the detection limits of current, large-area, deep
near-IR surveys.Comment: 18 pages, 15 figures, 4 tables. Updated to match version in press at
the Ap
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&
The Evolution of the Optical and Near-Infrared Galaxy Luminosity Functions and Luminosity Densities to z~2
Using Hubble Space Telescope and ground-based U through K- band photometry
from the Great Observatories Origins Deep Survey (GOODS), we measure the
evolution of the luminosity function and luminosity density in the rest-frame
optical (UBR) to z ~ 2, bridging the poorly explored ``redshift desert''
between z~1 and z~2. We also use deep near-infrared observations to measure the
evolution in the rest-frame J-band to z~1. Compared to local measurements from
the SDSS, we find a brightening of the characteristic magnitude, (M*), by ~2.1,
\~0.8 and ~0.7 mag between z=0.1 and z=1.9, in U, B, and R bands, respectively.
The evolution of M* in the J-band is in the opposite sense, showing a dimming
between redshifts z=0.4 and z=0.9. This is consistent with a scenario in which
the mean star formation rate in galaxies was higher in the past, while the mean
stellar mass was lower, in qualitative agreement with hierarchical galaxy
formation models. We find that the shape of the luminosity function is strongly
dependent on spectral type and that there is strong evolution with redshift in
the relative contribution from the different spectral types to the luminosity
density.
We find good agreement in the luminosity function derived from an R-selected
and a K-selected sample at z~1, suggesting that optically selected surveys of
similar depth (R < 24) are not missing a significant fraction of objects at
this redshift relative to a near-infrared-selected sample. We compare the
rest-frame B-band luminosity functions from z~0--2 with the predictions of a
semi-analytic hierarchical model of galaxy formation, and find qualitatively
good agreement. In particular, the model predicts at least as many optically
luminous galaxies at z~1--2 as are implied by our observations.Comment: 43 pages; 15 Figures; 5 Tables, Accepted for publication in Ap.
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