3,792 research outputs found
An Invisible Quantum Tripwire
We present here a quantum tripwire, which is a quantum optical interrogation
technique capable of detecting an intrusion with very low probability of the
tripwire being revealed to the intruder. Our scheme combines interaction-free
measurement with the quantum Zeno effect in order to interrogate the presence
of the intruder without interaction. The tripwire exploits a curious nonlinear
behaviour of the quantum Zeno effect we discovered, which occurs in a lossy
system. We also employ a statistical hypothesis testing protocol, allowing us
to calculate a confidence level of interaction-free measurement after a given
number of trials. As a result, our quantum intruder alert system is robust
against photon loss and dephasing under realistic atmospheric conditions and
its design minimizes the probabilities of false positives and false negatives
as well as the probability of becoming visible to the intruder.Comment: Improved based on reviewers comments; 5 figure
Evolution of hierarchical clustering in the CFHTLS-Wide since z~1
We present measurements of higher order clustering of galaxies from the
latest release of the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS)
Wide. We construct a volume-limited sample of galaxies that contains more than
one million galaxies in the redshift range 0.2<z<1 distributed over the four
independent fields of the CFHTLS. We use a counts in cells technique to measure
the variance and the hierarchical moments S_n = /^(n-1)
(3<n<5) as a function of redshift and angular scale.The robustness of our
measurements if thoroughly tested, and the field-to-field scatter is in very
good agreement with analytical predictions. At small scales, corresponding to
the highly non-linear regime, we find a suggestion that the hierarchical
moments increase with redshift. At large scales, corresponding to the weakly
non-linear regime, measurements are fully consistent with perturbation theory
predictions for standard LambdaCDM cosmology with a simple linear bias.Comment: 17 pages, 11 figures, submitted to MNRA
The clustering properties of radio-selected AGN and star-forming galaxies up to redshifts z~3
We present the clustering properties of a complete sample of 968 radio
sources detected at 1.4 GHz by the VLA-COSMOS survey with radio fluxes brighter
than 0.15 mJy. 92% have redshift determinations from the Laigle et al. (2016)
catalogue. Based on their radio-luminosity, these objects have been divided
into two populations of 644 AGN and 247 star-forming galaxies. By fixing the
slope of the auto-correlation function to gamma=2, we find
r_0=11.7^{+1.0}_{-1.1} Mpc for the clustering length of the whole sample, while
r_0=11.2^{+2.5}_{-3.3} Mpc and r_0=7.8^{+1.6}_{-2.1} Mpc (r_0=6.8^{+1.4}_{-1.8}
Mpc if we restrict our analysis to z<0.9) are respectively obtained for AGN and
star-forming galaxies. These values correspond to minimum masses for dark
matter haloes of M_min=10^[13.6^{+0.3}_{-0.6}] M_sun for radio-selected AGN and
M_min=10^[13.1^{+0.4}_{-1.6}] M_sun for radio-emitting star-forming galaxies
(M_min=10^[12.7^{+0.7}_{-2.2}] M_sun for z<0.9). Comparisons with previous
works imply an independence of the clustering properties of the AGN population
with respect to both radio luminosity and redshift. We also investigate the
relationship between dark and luminous matter in both populations. We obtain
/M_halo/M_halo<~10^{-2.4} in the case of
star-forming galaxies. Furthermore, if we restrict to z<~0.9 star-forming
galaxies, we derive /M_halo<~10^{-2.1}, result which clearly indicates the
cosmic process of stellar build-up as one moves towards the more local
universe. Comparisons between the observed space density of radio-selected AGN
and that of dark matter haloes shows that about one in two haloes is associated
with a black hole in its radio-active phase. This suggests that the
radio-active phase is a recurrent phenomenon.Comment: 11 pages, 7 figures, minor changes to match published version on
MNRA
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
The Evolution of the Stellar Mass Functions of Star-Forming and Quiescent Galaxies to z = 4 from the COSMOS/UltraVISTA Survey
We present measurements of the stellar mass functions (SMFs) of star-forming
and quiescent galaxies to z = 4 using a sample of 95 675 galaxies in the
COSMOS/UltraVISTA field. Sources have been selected from the DR1 UltraVISTA
K_{s}-band imaging which covers a unique combination of a wide area (1.62
deg^2), to a significant depth (K_{s,tot} = 23.4). The SMFs of the combined
population are in good agreement with previous measurements and show that the
stellar mass density of the universe was only 50%, 10% and 1% of its current
value at z ~ 0.75, 2.0, and 3.5, respectively. The quiescent population drives
most of the overall growth, with the stellar mass density of these galaxies
increasing by 2.71^{+0.93}_{-0.22} dex since z = 3.5. At z > 2.5, star-forming
galaxies dominate the total SMF at all stellar masses, although a nonzero
population of quiescent galaxies persists to z = 4. Comparisons of the
K_{s}-selected star-forming galaxy SMFs to UV-selected SMFs at 2.5 < z < 4 show
reasonable agreement and suggests UV-selected samples are representative of the
majority of the stellar mass density at z > 3.5. We estimate the average mass
growth of individual galaxies by selecting galaxies at fixed cumulative number
density. The average galaxy with Log(M_{*}/M_{sun}) = 11.5 at z = 0.3 has grown
in mass by only 0.2 dex (0.3 dex) since z = 2.0(3.5), whereas those with
Log(M_{*}/M_{sun}) = 10.5 have grown by > 1.0 dex since z = 2. At z < 2, the
time derivatives of the mass growth are always larger for lower-mass galaxies,
which demonstrates that the mass growth in galaxies since that redshift is
mass-dependent and primarily bottom-up. Lastly, we examine potential sources of
systematic uncertainties on the SMFs and find that those from photo-z
templates, SPS modeling, and the definition of quiescent galaxies dominate the
total error budget in the SMFs.Comment: 18 pages paper, 12 pages appendix, 23 figures. Accepted for
publication in the Ap
A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images. II. Quantifying morphological k-correction in the COSMOS field at 1<z<2: Ks band vs. I band
We quantify the effects of \emph{morphological k-correction} at by
comparing morphologies measured in the K and I-bands in the COSMOS area.
Ks-band data have indeed the advantage of probing old stellar populations for
, enabling a determination of galaxy morphological types unaffected by
recent star formation. In paper I we presented a new non-parametric method to
quantify morphologies of galaxies on seeing limited images based on support
vector machines. Here we use this method to classify
selected galaxies in the COSMOS area observed with WIRCam at CFHT. The obtained
classification is used to investigate the redshift distributions and number
counts per morphological type up to and to compare to the results
obtained with HST/ACS in the I-band on the same objects from other works. We
associate to every galaxy with and a probability between 0 and
1 of being late-type or early-type. The classification is found to be reliable
up to . The mean probability is . It decreases with redshift
and with size, especially for the early-type population but remains above
. The classification is globally in good agreement with the one
obtained using HST/ACS for . Above , the I-band classification
tends to find less early-type galaxies than the Ks-band one by a factor
1.5 which might be a consequence of morphological k-correction effects.
We argue therefore that studies based on I-band HST/ACS classifications at
could be underestimating the elliptical population. [abridged]Comment: accepted for publication in A&A, updated with referee comments, 12
pages, 10 figure
Large Structures and Galaxy Evolution in COSMOS at z < 1.1
We present the first identification of large-scale structures (LSS) at z in the Cosmic Evolution Survey (COSMOS). The structures are identified
from adaptive smoothing of galaxy counts in the pseudo-3d space
(,z) using the COSMOS photometric redshift catalog. The
technique is tested on a simulation including galaxies distributed in model
clusters and a field galaxy population -- recovering structures on all scales
from 1 to 20\arcmin without {\it a priori} assumptions for the structure size
or density profile. Our procedure makes {\bf no} {\it a priori} selection on
galaxy spectral energy distribution (SED, for example the Red Sequence),
enabling an unbiased investigation of environmental effects on galaxy
evolution. The COSMOS photometric redshift catalog yields a sample of
galaxies with redshift accuracy, at z down to I mag. Using this sample of galaxies,
we identify 42 large-scale structures and clusters. abstract truncated for
astroph 25 line limit -- see preprintComment: 72 pages with 29 pages of figures, for cosmos apj suppl special issu
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