1,528 research outputs found
The zCOSMOS 10k-sample: the role of galaxy stellar mass in the colour-density relation up to z ~ 1
Aims. With the first ~10 000 spectra of the flux limited zCOSMOS sample (I_(AB) ≤ 22.5) we want to study the evolution of environmental effects
on galaxy properties since z ~ 1.0, and to disentangle the dependence among galaxy colour, stellar mass and local density.
Methods. We use our previously derived 3D local density contrast δ, computed with the 5th nearest neighbour approach, to study the evolution
with z of the environmental effects on galaxy U-B colour, D4000 Å break and [OII]λ3727 equivalent width (EW[OII]). We also analyze the implications
due to the use of different galaxy selections, using luminosity or stellar mass, and we disentangle the relations among colour, stellar mass
and δ studying the colour-density relation in narrow mass bins.
Results. We confirm that within a luminosity-limited sample (M_B ≤ −20.5 − z) the fraction of red (U − B ≥ 1) galaxies depends on δ at least
up to z ~ 1, with red galaxies residing mainly in high densities. This trend becomes weaker for increasing redshifts, and it is mirrored by the
behaviour of the fraction of galaxies with D4000 Å break ≥1.4. We also find that up to z ~ 1 the fraction of galaxies with log(EW[OII]) ≥ 1.15 is
higher for lower δ, and also this dependence weakens for increasing z. Given the triple dependence among galaxy colours, stellar mass and δ, the
colour-δ relation that we find in the luminosity-selected sample can be due to the broad range of stellar masses embedded in the sample. Thus, we
study the colour-δ relation in narrow mass bins within mass complete subsamples, defining red galaxies with a colour threshold roughly parallel
to the red sequence in the colour-mass plane. We find that once mass is fixed the colour-δ relation is globally flat up to z ~ 1 for galaxies with
log(M/M_⊙) ≳ 10.7. This means that for these masses any colour-δ relation found within a luminosity-selected sample is the result of the combined
colour-mass and mass-δ relations. On the contrary, even at fixed mass we observe that within 0.1 ≤ z ≤ 0.5 the fraction of red galaxies with
log(M/M_⊙) ≲ 10.7 depends on δ. For these mass and redshift ranges, environment affects directly also galaxy colours.
Conclusions. We suggest a scenario in which the colour depends primarily on stellar mass, but for an intermediate mass regime (10.2 ≲ log(M/M_⊙) ≲ 10.7) the local density modulates this dependence. These relatively low mass galaxies formed more recently, in an epoch when
more evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer
periods of time
Isolated galaxies in hierarchical galaxy formation models - present-day properties and environmental histories
In this study, we have carried out a detailed, statistical analysis of
isolated model galaxies, taking advantage of publicly available hierarchical
galaxy formation models. To select isolated galaxies, we employ 2D methods
widely used in the observational literature, as well as a more stringent 3D
isolation criterion that uses the full 3D-real space information. In
qualitative agreement with observational results, isolated model galaxies have
larger fractions of late-type, star forming galaxies with respect to randomly
selected samples of galaxies with the same mass distribution. We also find that
the samples of isolated model galaxies typically contain a fraction of less
than 15 per cent of satellite galaxies, that reside at the outskirts of their
parent haloes where the galaxy number density is low. Projection effects cause
a contamination of 2D samples of about 18 per cent, while we estimate a typical
completeness of 65 per cent. Our model isolated samples also include a very
small (few per cent) fraction of bulge dominated galaxies (B/T > 0.8) whose
bulges have been built mainly by minor mergers. Our study demonstrates that
about 65-70 per cent of 2D isolated galaxies that are classified as isolated at
z = 0 have indeed been completely isolated since z = 1 and only 7 per cent have
had more than 3 neighbours within a comoving radius of 1 Mpc. Irrespectively of
the isolation criteria, roughly 45 per cent of isolated galaxies have
experienced at least one merger event in the past (most of the mergers are
minor, with mass ratios between 1:4 and 1:10). The latter point validates the
approximation that isolated galaxies have been mainly influenced by internal
processes.Comment: 15 pages, 13 figures, minor changes in the text, accepted for
publication by MNRA
Reconstructing the galaxy density field with photometric redshifts: II. Environment-dependent galaxy evolution since
Although extensively investigated, the role of the environment in galaxy
formation is still not well understood. In this context, the Galaxy Stellar
Mass Function (GSMF) is a powerful tool to understand how environment relates
to galaxy mass assembly and the quenching of star-formation. In this work, we
make use of the high-precision photometric redshifts of the UltraVISTA Survey
to study the GSMF in different environments up to , on physical
scales from 0.3 to 2 Mpc, down to masses of . We
witness the appearance of environmental signatures for both quiescent and
star-forming galaxies. We find that the shape of the GSMF of quiescent galaxies
is different in high- and low-density environments up to with the
high-mass end () being enhanced in high-density
environments. On the contrary, for star-forming galaxies a difference between
the GSMF in high- and low density environments is present for masses . Star-forming galaxies in this mass range appear to
be more frequent in low-density environments up to . Differences in
the shape of the GSMF are not visible anymore at . Our results, in terms
of general trends in the shape of the GSMF, are in agreement with a scenario in
which galaxies are quenched when they enter hot gas-dominated massive haloes
which are preferentially in high-density environments.Comment: 18 pages, 10 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
A flexible scintillation light apparatus for rare event searches
Compelling experimental evidences of neutrino oscillations and their
implication that neutrinos are massive particles have given neutrinoless double
beta decay a central role in astroparticle physics. In fact, the discovery of
this elusive decay would be a major breakthrough, unveiling that neutrino and
antineutrino are the same particle and that the lepton number is not conserved.
It would also impact our efforts to establish the absolute neutrino mass scale
and, ultimately, understand elementary particle interaction unification. All
current experimental programs to search for neutrinoless double beta decay are
facing with the technical and financial challenge of increasing the
experimental mass while maintaining incredibly low levels of spurious
background. The new concept described in this paper could be the answer which
combines all the features of an ideal experiment: energy resolution, low cost
mass scalability, isotope choice flexibility and many powerful handles to make
the background negligible. The proposed technology is based on the use of
arrays of silicon detectors cooled to 120 K to optimize the collection of the
scintillation light emitted by ultra-pure crystals. It is shown that with a 54
kg array of natural CaMoO4 scintillation detectors of this type it is possible
to yield a competitive sensitivity on the half-life of the neutrinoless double
beta decay of 100Mo as high as ~10E24 years in only one year of data taking.
The same array made of 40CaMoO4 scintillation detectors (to get rid of the
continuous background coming from the two neutrino double beta decay of 48Ca)
will instead be capable of achieving the remarkable sensitivity of ~10E25 years
on the half-life of 100Mo neutrinoless double beta decay in only one year of
measurement.Comment: 12 pages, 4 figures. Prepared for submission to EPJ
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model. II. The colour-density relation up to z=1.5
[Abridged] We perform on galaxy mock catalogues the same colour-density
analysis made by Cucciati et al. (2006) on a 5 Mpc/h scale using the VVDS-Deep
survey, and compare the results from mocks with observed data. We use mocks
with the same flux limits (I=24) as the VVDS (CMOCKS), built using the semi-
analytic model by De Lucia & Blaizot (2007) applied to the Millennium
Simulation. From CMOCKS, we extracted samples of galaxies mimicking the VVDS
observational strategy (OMOCKS). We computed the B-band Luminosity Function LF
and the colour-density relation (CDR) in the mocks. We find that the LF in
mocks roughly agrees with the observed LF, but at z<0.8 the faint-end slope of
the model LF is steeper than the VVDS one. Computing the LF for early and late
type galaxies, we show that mocks have an excess of faint early-type and of
bright late-type galaxies with respect to data. We find that the CDR in OMOCKS
is in excellent agreement with the one in CMOCKS. At z~0.7, the CDR in mocks
agrees with the VVDS one (red galaxies reside mainly in high densities). Yet,
the strength of the CDR in mocks does not vary within 0.2<z<1.5, while the
observed relation flattens with increasing z and possibly inverts at z=1.3. We
argue that the lack of evolution in the CDR in mocks is not due only to
inaccurate prescriptions for satellite galaxies, but that also the treatment of
central galaxies has to be revised. The reversal of the CDR can be explained by
wet mergers between young galaxies, producing a starburst event. This should be
seen on group scales. A residual of this is found in observations at z=1.5 on
larger scales, but not in the mocks, suggesting that the treatment of physical
processes affecting satellites and central galaxies in models should be
revised.Comment: 15 pages, 12 figures, accepted for publication in A&
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
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
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&
Measuring galaxy environment with the synergy of future photometric and spectroscopic surveys
We exploit the synergy between low-resolution spectroscopy and photometric redshifts to study environmental effects on galaxy evolution in slitless spectroscopic surveys from space. As a test case, we consider the future Euclid Deep survey (∼40 deg2), which combines a slitless spectroscopic survey limited at Hα flux ≥5 × 10−17 erg cm−2 s−1 and a photometric survey limited in H band (H ≤ 26). We use Euclid-like galaxy mock catalogues, in which we anchor the photometric redshifts to the 3D galaxy distribution of the available spectroscopic redshifts. We then estimate the local density contrast by counting objects in cylindrical cells with radius from 1 to 10 h−1Mpc, over the redshift range 0.9 < z < 1.8. We compare this density field with the one computed in a mock catalogue with the same depth as the Euclid Deep survey (H = 26) but without redshift measurement errors. We find that our method successfully separates high- from low-density environments (the last from the first quintile of the density distribution), with higher efficiency at low redshift and large cells: the fraction of low-density regions mistaken by high-density peaks is <1 per cent for all scales and redshifts explored, but for scales of 1 h−1Mpc for which is a few per cent. These results show that we can efficiently study environment in photometric samples if spectroscopic information is available for a smaller sample of objects that sparsely samples the same volume. We demonstrate that these studies are possible in the Euclid Deep survey, i.e. in a redshift range in which environmental effects are different from those observed in the local Universe, hence providing new constraints for galaxy evolution models
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